Patent Application
20240025768
Environmental remediation after oil spills is an ongoing concern, in part due to the long-lasting nature of clean-ups after catastrophes such as the British Petroleum oil spill in the Gulf of Mexico, among many other high-profile occurrences. However, despite the publicity and public outrage that has occurred after such events, there are still few viable options to allow for the salvaging or reclamation of the spilled oil and the cleaning of the local environments. In fact, the Environmental Protection Agency often is required to maintain a permanent presence after waterway spills due, at least in part, to the persistent presence of surface oil slick, even if larger oil residues have been cleaned. Just as importantly, human contact with the current cleaning methods, including dispersants, often leads to concerning long-term complications including altered blood and liver enzymes as well as concerning outcomes for various levels of life in the surrounding regions.
Shape memory polymer (SMP) foams have been touted as offering a variety of different fields access to low-density, stimuli-responsive materials capable of changing their respective industries, and may be of great interest to oil remediation strategies moving forward. Many different species of SMPs have been developed and examined as porous media, including polyurethanes, polyureas, polyesters, polyethers (derived from epoxides as well as those from other sources), polyamides, polycarbonates, and many others. Foams have been produced from many of these materials, with a huge range of morphologies, pore/cell sizes, strut thicknesses and geometries, densities, and physical properties. However, in fields such as biomedical engineering, these materials have been limited by their final material properties compared with the design criteria of the application. For example, aromatic polyurethanes have been linked with hydrolytic degradation in instances where biostability is required (breast implant coatings). Conversely, certain species of aliphatic polyurethanes have been linked with oxidative degradation, which may limit their translational potential. Additionally, polyurethane foams, among others, often rely on a two-step synthetic approach, where the pre-polymer step may require as long as 48 h before the foaming may proceed, after which additional thermal treatments and post processing is needed, making the process a week or more from start to finish, a distinct disadvantage for many applications.
Epoxy-thiol resins have seen use in a variety of different uses, ranging from biomedical devices to aerospace, adhesives, and coatings. Traditional epoxy resins typically make use of amine hardeners or utilize other nucleophiles to facilitate rapid ring opening of the epoxides. The use of thiols has been more recently explored as part of the thiol-epoxy “click” reaction, which has been explored for a range of applications including self-assembly reactions, thermoset resins, and even vitrimer materials. In particular, the use of difunctional epoxide monomers has been explored for these purposes, with commodity materials providing a wide array of possible combinations for production of polymers, including bisphenol A derivatives. Importantly, this reaction has been utilized to yield materials within hours of mixing the components, which, while still too slow for conventional foaming, has been utilized to produce porous scaffolds through the incorporation of different particulates and salts.
As discussed herein, thiol-epoxy “click” reactions are performed using different epoxides in conjunction with a multifunctional, commercially available Pentaerythritoltetra (3-mercaptopropionate) (PETMP) in the presence of the super organobase DBU. Rheology, spectroscopy, and physical experimentation are used to demonstrate rapid foam blowing within seconds of mixing the reactants. The resulting materials are characterized for thermomechanical behaviors, degradability, shape memory properties, and even potential for scavenging oil in aquatic environments through the use of a model study. These materials, and their post-foaming functionalized equivalents, demonstrated potential for environmental remediation, biomedical engineering applications, and beyond.
Furthermore, porous media is used in a variety of applications including environmental remediation and medicine. Recently, porous tissue scaffolds have grown to become one of the most important types of implantable material classes in clinical use. In general, porosity allows for cellular infiltration that leads to healing, while simultaneously allowing for the diffusion of waste and nutrients needed to promote vascularization and healing. Compared with non-porous implants, the biological response to such materials is moderated with improved healing rates, reduced fibrous capsule formation, and a reduced inflammatory load at the implant site. Simply by introducing or tailoring pores in foams, the biocompatibility of materials may be enhanced.
Previous work with polymer foam biomaterials has focused on polyurethanes (PUs), polyethers, polyesters, and polycarbonates, where PUs have perhaps been the most widely utilized clinically. PUs have been proposed for applications ranging from aneurysm occlusive devices to breast implant coatings, one of the most well-known applications. The limitations of PUs in breast implants, and to some extent other applications, has been suspicions of toxic degradation products, namely the formation of toluene diamine during hydrolysis. While the conditions required to cleave the aromatic urethane linkages are unlikely to occur in vivo (the in vitro testing conditions utilized to achieve the oligomeric and monomeric degradation products were wildly exaggerated compared with those found in the body), the concern surrounding these products was sufficient to limit PUs foam utility in breast implant coatings to this day. This is despite the limited negative outcomes reported by patients or the adverse events reported by clinicians, and the benefits achieved by introducing porous media rather than merely texturing the implant's surface (which did not achieve nearly the same biocompatibility benefits as the foams). There is a need for alternative foam chemistries that can be utilized for soft and hard void implant devices which do not suffer from the potential to produce carcinogenic or toxic degradation products.
Furthermore, poly(β-hydroxythioether) are a newer class of material suitable for foaming that have several distinct advantages compared with other biomaterials. While poly(thioketals) and poly(sulfides) have become noted in literature for biomedical potential, poly β-hydroxythioethers) remain fairly unexplored despite their positive attributes, including being produced through the simple thio-epoxy “click” reaction that is highly efficient, robust, bio-orthogonal, and even stereoselective in some cases. The starting reagents for poly(β-hydroxythioether), epoxides and thiols, are generally less reactive and more biotolerable compared with the diisocyanates commonly leveraged for PU synthesis. Another crucial benefit is the thiol and epoxy monomers overall display minimal health risks, especially when compared with diisocyanates. Finally, the degradation products of these materials are not linked with carcinogenic or otherwise-concerning outcomes as some PU formulations/devices have been, including the hydrolytic decomposition of TDI-derived PUs that form the carcinogenic toluene diamine. This combination of factors means that the thermoset network required for crosslinked foams may form rapidly (displaying a high rate of gelation) and robustly without requiring elevated temperatures or prolonged curing times, and the synthetic process does not present the same level of risk as diisocyanate exposure will to manufacturing personnel. Furthermore, such materials are known to be SMPs displaying high strain recoveries and thus are for replacing PUs in some tissue engineering applications.
A novel series of poly(β-hydroxythioether) foams for implantable biomaterials in described herein. In some embodiments, two bi-functional epoxide monomers are used to tune the physical properties of the porous scaffolds, requiring the transition to salt-leached foaming as opposed to gas-blown foaming Additionally, the physical and chemical properties of the resulting foams are characterized with regards to the materials' suitability in biomedical applications. Importantly, shape memory responsiveness, hydrolytic stability, and cytocompatibility are demonstrated. To our knowledge, this is the first instance of poly(β-hydroxythioether) foams demonstrated for biomedical materials, and this disclosure demonstrates, among other things, their clinical translational potential.
Oil spills are incredibly harmful to all forms of life that come into contact with them. As found in the Gulf of Mexico, oil spills can have negative impacts of all levels of wildlife. These impacts include organ/tissue mutations and greatly increased rates of death in infants and adults of all species. For this reason alone, there is a distinct need to improve environmental cleanup after oil spills. However, compounding this problem is the limitation that many chemical dispersants and agents that could aid in spill cleanup are also associated with long-term complications to human health including altered blood and liver enzymes. In large, open waterways, cleanup efforts primarily are focused on efficient methods that may be used in conjunction with skimmers and centrifugation techniques. While sorbent materials are not easily compatible with these techniques, closed interior waterways have different design requirements due to the complications of relatively shallow environments combined with complex geometries of the banks. This often leads to residual oil slick that may never fully be removed.
A variety of methods have been used or proposed to clean up oil spills. Standard approaches have included polyethylene or polypropylene sorbent sheeting, where the sheets float on the water surface and absorb oil skim that otherwise cannot be scavenged, the use of booms to push oil slick into enclosed areas, and chemical dispersants to disperse oil into the water. However, these methods may be slow, require significant manpower, are only capable of scavenging only a small amount of oil slick, or may result in significant introduction of oil into the aquatic environment. Several design criteria are considered for the design of oil sorbents, including sorption efficiency, porosity, cost, biodegradability, and selectivity of oil over water for sorption.
To this end, a number of studies have focused on improving oil sorption using different media, (m) where porous media in particular is of growing interest as alternative options to the more standard petrochemical sheets such as polyethylene or polypropylene. It has been found that the use of poly(β-hydroxythioether) (PBHTE) low density foams are effective as an oil sorbent, finding good selectivity of the materials in biphasic oil/water mixtures. However, the role of environmental conditions and the ultimate comparison of these materials with other state-of-the-art solutions was not fully realized.
The PBHTEs are especially of interest for these applications due to the unique combination of synthetic factors and resultant material properties. The epoxy-thiol reaction that results in PBHTEs is a highly efficient “click” reaction, with yields higher than 99% possible while also allowing for stereoselective control as part of biotolerable reagent mixtures. Super organobases such as 1,8-Diazabicyclol[5.4.0]undec-7-ene (DBU) could be leveraged to rapidly gel and physically blow PBHTE foams within seconds of mixing, allowing for rapid formulation from start to finish. This is a decided advantage when compared with other porous media, including polyurethane foams, which often utilize two-step premixes that may take days to prepare. PBHTE foams also demonstrate a wide range of densities and representative oil sorption, so the best foam for an oil spill, or other oil clean up situation can be chosen. These foams are less dense than materials like the petroleum polymer sheets and can even have a higher sorption rate. Though on the other side, poly(tetrafluoroethylene), poly(methyl meth-acrylate), nonwoven poly(propylene), and poly(ethylene)nonwoven materials that are denser than PBHTE foams and have a higher sorption, though the ease of reaction and producing PBTHE foams is still relevant.
The wide range of densities on PBHTE foams is comparable to poly(dimethyl siloxane) foams where the only true difference is the better sorption of the silicon-based PDMS foams. One significant feature of PBTHE foams is that as the densities change so does the sorption. A significant increase in sorption can be found when the when these foams go below 0.8 g×cm−3, which keeps PBTHE foams comparable to top performing PS foams, graphene foams, denser grafted PU foams, and less dense PET-PU foams. The major benefit to using PBTHE foams is the tunability based on density that allows for optimal sorption rate foams for different scenarios.
Accordingly, there is a need for oil sorption performance foams, such as PBHTE foams. In this disclosure, materials were characterized for physical characteristics including pore size, thermal properties, and density prior to examination for oil sorption. The role of temperature and time were examined to understand the kinetic behavior of oil sorption and the potential of these materials for interior waterway remediation. Ultimately, the determined performances were compared with other porous materials to assemble an oil sorption vs density design chart, which may be used for design of sorbent devices and other applications, where oil can be recovered and recycled.
Poly(β-hydroxythioether) are a newer class of material suitable for foaming that have several distinct advantages compared with other biomaterials. Notably, β-hydroxythioether are synthesized as part of a thio-epoxy “click” reaction that is highly efficient, robust, bio-orthogonal, and even stereoselective in some cases. This combination of factors means that the thermoset network required for crosslinked foams, which in shape memory (4D) materials reduces the expansion force to negligible values, may form rapidly and robustly without requiring elevated temperatures or prolonged curing times, and the synthetic process does not present the same level of risk as diisocyanate exposure will to manufacturing personnel.
Here, a novel series of poly(β-hydroxythioether) foams as proposed implantable biomaterials are described. Two bi-functional epoxide monomers are used to tune the physical properties of the porous scaffolds, requiring the transition to salt-leached foaming as opposed to gas-blown foaming, and the physical and chemical properties of the resulting foams are characterized. Importantly, shape memory responsiveness, hydrolytic stability, and cytocompatibility are demonstrated, being important criteria for clinical translational potential.
Certain exemplary aspects of the invention are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be explicitly set forth below.
To address the aforementioned issues, in an embodiment of the present invention a method of reclaiming oil is provided. The method includes administering a shape memory polymer foam to absorb an amount of oil. The method further includes collecting the shape memory polymer foam with the absorbed oil. The method further includes treating the shape memory polymer foam to collect the absorbed oil. The shape memory polymer foam used in the method includes a reaction product of a reaction of an epoxide and a thiol monomer in the presence of an organobase.
In a related embodiment, the shape memory polymer foam includes pores having an average pore size of between 400 μm and 1100 μm.
In a related embodiment, the shape memory polymer foam includes at least a first shape memory polymer foam, a second shape memory polymer foam, and a third shape memory polymer foam, and wherein each of the first shape memory polymer foam, the second shape memory polymer foam, and the third shape memory polymer foam comprise different, discrete average pore sizes.
In a related embodiment, the first shape memory polymer foam having an average pore size of about 400 μm.
In a related embodiment, the second shape memory polymer foam includes an average pore size of about 800 μm.
In a related embodiment, the second shape memory polymer foam includes an average pore size of about 1100 μm.
In a related embodiment, the third shape memory polymer foam includes an average pore size of about 800 μm.
In a related embodiment, the shape memory polymer foam is administered to the amount of oil for at least 24 hours.
Also disclosed herein is a shape memory polymer foam including a reaction product of a reaction of an epoxide and a thiol monomer in the presence of an organobase.
In a related embodiment, the epoxide is selected from a group consisting of bisphenol A diglycidyl ether (BADGE), BADGE derivatives, neopentyl monomer (NEO), NEO derivatives, N epoxide, Isophorone di(oxiran-2-methyl carbamate) (IDPI) epoxide, IDPI epoxide derivatives, and combinations thereof.
In a related embodiment, the shape memory polymer foam is compressible to a compressed state, which the shape memory polymer foam retains until the shape memory polymer foam is heated.
In a related embodiment, the shape memory polymer foam has a glass transition at approximately 51.5° C. when dry.
In a related embodiment, the shape memory polymer foam has a glass transition at approximately 25° C. when wet.
In a related embodiment, the shape memory polymer foam is a product of a reaction of pentaerythritoltetra(3-mercaptopropionate) and bisphenol A diglycidyl ether in the presence of 1,8-diazabicyclol[5.4.0]undec-7-ene.
One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
To address the aforementioned issues, aspects of the present invention include shape memory polymer (SMP) foam including a reaction product of a reaction of an epoxide and a thiol monomer in the presence of an organobase, as shown in
The epoxide used in the reaction to form the SMP foam may be any epoxide configured to form an SMP foam when reacted with a thiol monomer in the presence of an organobase catalyst. In some examples, the epoxide used in the reaction is selected from a group consisting of bisphenol A diglycidyl ether (BADGE), BADGE derivatives, neopentyl monomer (NEO), NEO derivatives, N epoxide, Isophorone di(oxiran-2-methyl carbamate) (IDPI) epoxide, IDPI epoxide derivatives, and combinations thereof.
The thiol monomer used in the reaction to form the SMP foam may be any thiol monomer configured to form an SMP foam when reacted with an epoxide in the presence of an organobase catalyst. In some examples, the thiol monomer used in the reaction is selected from a group consisting of pentaerythritoltetra(3 -mercaptopropionate).
Stoichiometric amounts of each of the epoxide and the thiol monomer may be reacted to form the SMP foam according to an embodiment of the invention. The reaction is encouraged if performed in the presence of an organobase. The epoxide and the thiol monomer may be combined in a container, such as a beaker, in the presence of an organobase and mixed. Alternatively or in addition, the reaction may occur in the presence of acetone, which may aid in dissolving reactants and to serve as a physical blowing agent for foam creation.
In another embodiment, a method of making an SMP foam is described. The method includes reacting an epoxide with a thiol monomer in the presence of an organobase, a salt, and, optionally, acetone to form a shape memory polymer foam-salt composite. The shape memory polymer foam-salt composite may include a salt template formed from the salt used in the reaction previously described. The salt template may be removed by washing, for example by a water extraction, resulting in porous scaffolds of SMP foam. In some examples, the formed SMP foam includes β-hydroxythioether as a product of the above-described reaction.
Applications of the SMP foams described herein are myriad, with examples including cleaning environments that have been contaminated with oil, salvaging oil from environments into which oil has seeped or spilled, harvesting crude oil, or even medical applications.
At least because the SMP foams may be safe for treatment of humans, such as through implantation, in some examples, the SMP foams described herein may be used to medically treat a patient. The method may include administering an amount of the SMP foam into the patient's bloodstream followed by stabilizing the patient's blood flow. In these examples, the SMP foam may include poly(β-hydroxythioether). In some examples, the poly(β-hydroxythioether) used in the SMP foams is formed by the reactions described herein between an epoxide and one or more thiol monomers in the presence of an organobase catalyst. Specifically, in an embodiment, the SMP foam used in medically treating a patient includes a poly(β-hydroxythioether) formed from a reaction between BADGE and PETMP in the presence of an organobase such as DBU.
Alternatively or in addition, the SMP foams described herein may be used in harvesting crude oil. Such methods may include administering the SMP foam described herein to absorb an amount of crude oil, collecting the SMP foam with the absorbed crude oil included therein, and subsequently treating the SMP foam to extract the crude oil absorbed in the SMP foam. In these examples, the SMP foam may include poly(β-hydroxythioether). In some examples, the poly(β-hydroxythioether) used in the SMP foams is formed by the reactions described herein between an epoxide and one or more thiol monomers in the presence of an organobase catalyst. Specifically, in an embodiment, the SMP foam used in medically treating a patient includes a poly(β-hydroxythioether) formed from a reaction between BADGE and PETMP in the presence of an organobase such as DBU.
Alternatively or in addition, the SMP foams described herein may be used in breast implants. For example, a breast implant may include a housing and an SMP foam as described herein may be encased in the housing. At least because the SMP foams may be acceptable material for implantation into a human body, it is possible to implant the SMP foams described herein in the breast of a human.
General: Chemicals were purchased and used without purification from VWR®, a subsidiary of Avantor®, having its corporate headquarters in Radnor, PA, USA. Spectroscopic analysis was conducted on a NMR spectra (400 MHz for 1H and 125 MHz for 13C) were recorded on a Bruker® 400 spectrometer and processed using MestReNova® v9.0.1 (from Mestrelab® Research, having a place of business in S.L., Santiago de Compostela, Spain). Chemical shifts were referenced to residual solvent peaks at δ=7.26 ppm (1H) and δ=77.16 ppm (13C) for CDCl3. Fourier transform infrared spectroscopy (FT-IR) was performed in attenuated total reflectance (ATR) mode on a Bruker® infrared spectrometer (Bruker®, having a place of business in Billerica, MA, USA) using 50 scans with background subtraction and a resolution of 2 cm−1. Rheology was conducted on a TA Instruments DH3® rheometer (TA Instruments Inc®, having a place of business in Delaware, USA) fitted with a Peltier parallel plate system (40 mm stainless steel plate with 0° surface, TA Instruments®, having a place of business in New Castle, Delaware, USA) and adjusted to a gap of 500 μm for all studies. Dynamic mechanical analysis (DMA) was conducted using a TA Instruments® DMA 800 (TA Instruments Inc®, having a place of business in Delaware, USA).
Synthesis of Isophorone di(oxiran-2-methyl carbamate) (IPDI Epoxide): Isophorone diisocyanate (IPDI) was added to a round bottom flask equipped with a stir bar, along with a stoichiometric amount of glycidol and 20 mL of dry acetone. The reaction vessel was sealed and heated to 50° C. for 24 h, over which time the viscosity of the mixture dramatically increased until the stir bar could no longer move. The crude product was taken up in ethyl acetate after removing residual acetone, and washed once with 0.1 M HCl and once with brine. The collected product was a clear high viscosity liquid at room temperature (Yield=81%) ESI MS: 370.45 (theoretical), 388.48 (mass+NH4) 1H NMR (CDCl3): (
Synthesis of 3,3-bis(hexadecylthio)propan-1-ol: Propargyl alcohol was added to a dry vial containing a stir bar, after which a stoichiometric amount of hexadecanethiol, and Irgacure 819 (1% wt), were added. The vial was heated while stirring to 80° C. and held isothermal for 24 h. During the isothermal treatment, the vial was irradiated with 365 to 420 nm (50 W) and was a yellowish liquid. Upon cooling, the product was a yellowish waxy solid, which was precipitated into cold methanol and collected as a white solid (Yield=92%) 1H NMR (CDCl3): (
Film Synthesis: Stoichiometric amounts of the epoxide monomer and PETMP were mixed in a vial along with 5 wt % acetone until a homogeneous solution was achieved, and the solution was then cooled to 0° C. To this solution, DBU was added and the solution was poured onto a flat, smooth silicone sheet. The film was allowed to warm to ambient temperature over a 24 h period, after which the film was heated for an additional 24 h period at 120° C.
Foam Synthesis: Polymer foam was produced by adding the epoxide monomer, PETMP, the surfactant, acetone (for dissolving reactants and to serve as a physical blowing agent), and the organobase catalyst into a single container. For the BADGE foam synthesis, BADGE monomer was added to a beaker and dissolved in 2 mL of acetone. Stoichiometric amounts of PETMP and 2 g of Silslab 2790 were added to the same beaker and mixed until all reagents were dissolved into a homogenous, low viscosity solution. To a second beaker, 0.260 g DBU and 2 mL were added and mixed. While stirring the beaker containing BADGE, the DBU solution was added as a single unit as quickly as possible, and the mixture was stirred for an additional 20 s before being placed on a room temperature surface. At this time, the foam rose and solidified over a 30 s period. The reaction was carried to completion by incubating the foam in a 120° C. oven for 12 h afterwards. Following this, the foam was removed, cut into cubes and rectangular prisms, and washed with an alternating organic solvent and water washes using a modified protocol previously described, substituting acetone for isopropyl alcohol. After washing, foams were dried overnight and then used for subsequent characterizations.
Data relating to the premixes for the foams are shown in
Rheological Characterization: Stoichiometric amounts of PETMP and the corresponding epoxide were first mixed together and then added to the parallel plate geometry on the rheometer (500 μm) at room temperature, at which time the samples were subjected to uniaxial rotation and oscillatory shears. Subsequent testing of the reaction kinetics was done including 0.1 wt % DBU.
Foaming kinetics were studied using the foam mixture composition, including surfactants and solvent, with the gap set to 700 μm specifically for this test only in a customized testing array allowing for videography from below. A kinetic sweep (timed flow) was performed, with a constant oscillatory rotation of 1% at 1 Hz conducted. At 100 s, a 0.1 wt % solution of DBU on the reactive components (0.5 mL volume total in acetone) was added at a rate of 10 mL×min−1. The foaming was recorded both optically and by the rheometer.
Micro CT and Microscopy Imaging: The 400, 900, and 1400 μm foam samples (representative achievable pore sizes) were cut using a hot wire cutter into cubes (1 cm3) and were then scanned by a TriFoil Imaging eXplore CT 120 Small Animal X-ray CT Scanner (Northridge Tri-Modality Imaging, Inc. Chatsworth, CA, U.S.A.) with a 120 kV/5 kW capability and 24.7×24.7×24.7 μm3 voxel size. The scan data was processed via Amira version 2020.2. (Thermo FisherScientific). The reconstructed foam cube images were first isosurface rendered using volren yellow, with color then inverted followed by histogram thresholding at different intensity values (4850, 6000, 7200) in order to show the inner structure as the membranes are removed.
Compressive and Tensile Thermomechanical Testing: A TA Instruments DMA 800® in compression mode was used for analyzing mechanical properties of the SMP foams. 1 cm3 foams were centered in the test platens, and the sample was first equilibrated at 25° C. for 1 min, after which the sample was compressed at 5 mm×min−1 to failure as defined by the instrument, specifically the static force or yield point of the sample. Elastic moduli, ultimate stress and strain, toughness, and strain at failure (corresponding to the aforementioned definition) were calculated from the corresponding stress-strain curves.
Thermal properties of foams were characterized using the same instrument, with samples incubated at 25° C. followed by a 2° C.×min−1 ramp to 220° C. During heating, samples were compressed with a 5 mN force, with a 10 Hz oscillatory load applied over the course of the test. Representative thermomechanical analysis of the porous, thermoset SMP foams was conducted.
Thermal Analysis: Thermal transitions of foams were examined using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). DSC was used to determine the Tg using a TA Instruments Q200 equipped with TA Refrigerated Cooling System 90 (TA Instruments, New Castle, DE). DSC samples (approximately 5 mg) were sealed in a Hermetic Tzero pan cooled to −100° C. before being heated to 180° C. at 10° C.×min−1. The half-height transition of the DSC thermogram was determined as the Tg from TA Analysis software (TA Instruments, New Castle, DE, U.S.A.). A TA Instruments SDT Q600 (TA Instruments, New Castle, DE, U.S.A.)was used to determine the thermal decomposition temperature (TD), characterized as the point of 5% mass loss. Samples isothermally equilibrated at 120° C. for 30 min before being heated to 500° C. at 10° C.×min−1, after which the heating rate was increased to 20° C.×min−1 until 1000° C. was reached.
Degradation: Cubes (˜2 cm3) were cut using a hot wire cutter and weighed in milligrams. Each cube was then immersed in 10 mL of either 35% H2O2 or 1.0 M NaOH, respectively. At discrete timepoints, samples were removed from the degradation solutions, blotted dry, and weighed. At the same time, the used degradation solution was replaced with fresh solution, and the samples were again immersed and incubated.
These conditions, as well as the 37° C. incubation temperature and 1 Hz solution perturbation, were selected to both address possible translation of these materials towards biological applications as well as using the aggressive conditions as the most likely problematic to be experienced.
Oil Reclamation and Surface Functionalization: Cubes (˜1 cm3) were cut using a hot wire cutter and immersed in acetone at 37° C. for 24 h, after which they were immersed in isophorone diisocyanate solution (50 wt %) for another 24 h at 50° C. Samples were washed in clean acetone, sponged dry, and then immersed immediately in either 20 mL hexadecanethiol (with 1 wt % DBU) or 20 mL of 2,3-di(hexadecanethioether) propyl alcohol.
Referring to
The reaction of the epoxide moiety with the thiol nucleophile on the PETMP molecule, qualitatively, took place rapidly, and was denoted by an increase in vessel temperature as well as gas formation in solution. Spectroscopically, crosslinking was noted by the broadening of most peaks, as well as the formation of peaks at 2.36 and 2.14 ppm (shown in
Additionally, the formation of the peak at 3.15 indicates the formation of disulfide bonds, which are likely a side product of an organobase-catalyzed epoxy ring opening. It was hypothesized that the disulfide formation is likely 5% byproduct for in-air reactions.
FT-IR ATR was further conducted to analyze both the resultant film and foam materials (
The carbonyl peak, a characteristic peak found in many different foams, appeared at 1731 (±1) cm−1 for the BADGE and N Epoxide materials, while the IPDI Epoxide carbonyl peak was found at 1698 cm−1. The BADGE and N Epoxide materials possess a carbonyl peak solely because of the PETMP monomer, and thus the peak is narrow and sharp as characteristic of aliphatic esters. Furthermore, the in-chain ester linkage has no hydrogen bonding, and therefore will appear at a higher wavenumber. By comparison, the IPDI Epoxide materials possess three different carbonyl linkages: PETMP esters, and both a primary and secondary carbamate. Previous work with aliphatic polyurethanes has indicated that the hydrogen bonding of urethane linkages (carbamates) will shift the carbonyl stretch to lower wavenumbers as found here. Additionally, a very slight shoulder is found at 1647 cm−1, associated with bidentate ureas (both amines participating in hydrogen bonding with another carbonyl) and possibly indicating slight impurities in the final material. The lack of peaks in the 2500 to 2700 cm−1 region indicates that the thiols are consumed during synthesis. Peaks at 772 cm−1 (IPDI Epoxide), 800 cm−1 (N Epoxide) and 827 cm−1 (BADGE) are indicative of the thioether linkage.
In fact, differences between the materials will be primarily due to incomplete extraction of surfactants and residual solvents, as the foaming reaction is purely physical, with the thiol-epoxy “click” reaction being sufficiently exothermic to evaporate the acetone as the polymer network forms. These bubble nucleation sites will then form the pores within the foam, with gaseous diffusion enabled by the presence of the surfactant. While this is similar to the more traditional polyurethane two-step foaming method, the synthesis of foams was conducted over a 5 min period, where the epoxide and thiol monomers were added in a single pot along with a surfactant, acetone as a blowing agent, and the organobase DBU. Stoichiometric balances were maintained, while acetone and DBU concentrations were varied, resulting in different foam pore sizes and distributions. During the foaming process itself, the best results were obtained by mixing all components together at room temperature and allowing the reaction to proceed spontaneously (over the course of approximately 1 min).
The behavior of the materials during and prior to the foaming process were characterized using rheology, with the mixtures displaying Newtonian fluid behavior prior to the addition of the DBU catalyst (as evidenced by the data shown in
The BADGE monomer was found to result in the most rapid reactions, although all systems reacted within minutes to form a gelled material. This is further supported by images collected during the parallel plate shear test, which displayed the rapid foaming after addition of the DBU, and are shown in
The resulting thermoset networks were found to have highgel fractions (˜91% and above) similar to other porous materials such as poly(HIPES) materials, but with ultralow densities which are of interest for many biomaterials and pore sizes tunable from approximately 400 to 2000 μm (smallest short axis to largest long axis, respectively) with consistent pore geometry as noted by the consistent anisotropy ratio of 1.8-1.9 (Table 1). The connectivity of these ultralow densities is of importance, as well, since a continuous pathway is needed to achieve transportation of waste and nutrients throughout biomaterials once implanted, or to ensure that the maximum amount of solvent/oil may be scavenged without decreasing the efficiency due to inaccessible void space.
The resultant pores were found to be partially opened as a result of the foaming process itself, and no additional processing was required as determined by microscopic imaging (
Mechanical compression of the samples was conducted using a DMA (Table 1 and
αThermal sweeps (DSC) were conducted at 10° C. × min−1, n = 3; DMA analysis of film bars in tension were conducted in tension at 1 Hz, preloadforce of 0.01N, heated from 20 to 200° C. at10° C. × min−1 at ambient atmosphere, n = 3; DMA analysis of foams in compression were treated inthe same manner, n = 3; thermal degradation samples were heated at 10° C. × min−1, n = 3; compression testing of porous cylinders (1 cm in diameter, 4 mm thickness) were tested in compression at ambient conditions for mechanical properties, 5 mm × min−1 to yield, n = 7.bα, DSC half height transition used to determine Tg;
βdata collected for films in tension;
γdata collected for foams in compression;
ΔDisplayed multiple peaks; ε, compressive yielding during DMA compression, but not catastrophic failure. (n = 7).
Referring to
IPDI Epoxide foams displayed the interesting dual-peak tan δ behaviors, indicating the possibility of multi-shape recovery behaviors. The plasticized behavior of the materials displayed a single peak that is both reduced in magnitude and the temperature at which the event occurs. This type of relaxation is not unusual for polymers, where the thermosolvation of the chains causes plasticization.
The foamed materials display the typical soft behavior expected for such physical material foams, with peak moduli values in the 10 to 100 MPa region for compressed samples even when glassy, and moduli values in the 1-10 kPa region above the Tg. Interestingly, the IPDI Epoxide materials display a more relaxed lossy behavior relative to the other compositions, indicating that at elevated temperatures these may be incredibly soft materials more similar to the less rigid aliphatic polyurethanes.
Shape Memory Response
Referring to
Polyurethane-based SMP foams have demonstrated a range of strain recoveries, ranging from complete recovery (coupled with a thermo-solvation swelling effect) to less than 10% strain. The residual presence of alcohols in aliphatic polyurethane systems has been hypothesized to induce excess tackiness and reduce strain, and therefore volumetric, recovery. Representative compressive stress-strain plots of a variety of foams, compressed at 5 mm×min−1 to yield using the DMA at room temperature and ambient atmosphere is shown in
Furthermore,
The shape memory response of the foams in DI H2O was a thermo-solvated plasticization-driven strain recovery mechanism. At temperatures below the plasticized Tg, less than 20% recovery was found. Data showing strain recovery of BADGE foam in DI H2O at different temperatures and the strain recovery behaviors for different SMP formulations according to the invention at 37° C. in DI H2O is shown in
The shape memory response of the foam was also examined to determine if pore orientation impacted the response (without solvent-induced swelling) by compressing sections along the foaming axis (z-axis), as well as in the xy plane. The recoverable strain was not impacted, with compression in any dimension providing for approximately 100% strain fixation and 100% strain recovery (with greater than 100% volumetric recovery possible in solvent).
Material Stability
The degradation of foams has been widely reported, especially in biomaterials, with degradable formulations displaying often exaggerated behavior because of the greatly increased surface area-to-volume ratios. Hydrolytic and oxidative mechanisms are the most common degradation schemes in polymers, although other routes to material decomposition are found for different environments. In the poly(β-hydroxythioethers), oxidation will be limited compared with more traditional amine-epoxide or amine-alcohol systems that yield labile linkages of higher amines and ethers, respectively. The thioether, compared to these, will oxidize with limited chain scission. It is important to note, however, that the selected species of polythiols and polyepoxides used will therefore have enormous impact on the biostability of the system, as is demonstrated here. The consideration of this material stability is crucial due to possible long-term immersion of the SMP foams in a hydrolytic environment, with possible contaminants or other factors contributing to degradation.
Mechanistically, all of the foams contain thioether linkages, which will oxidize, thereby scavenging hydroxyl radical concentrations. In the BADGE and N Epoxide foams, reduces the subsequent chain cleavage which results from the corresponding oxidation-reduction reactions of the ether and tertiary amine linkages, respectively. In the IPDI Epoxide foams, oxidation of the urethanes linkages was previously revealed in similar conditions to be highly unfavored and slow.
Hydrolytically, the IPDI Epoxide materials displayed the most rapid degradation of any examined composition. Within 18 h of immersion in 1 M NaOH at ° C., only 5% of mass is remaining. This may be due to the plasticization-type interactions which are possible around urethane and urea linkages in polyurethanes, allowing for greater interactions between the polymers and the hydrolytically labile polyester linkages. The N epoxide materials, while more hydrolytically stable relative to the aliphatic foams, still displayed rapid gravimetric changes in this environment. By comparison, BADGE foams displayed swelling in line with the uptake of solvent, but no noticeable mass loss was found. Importantly, this test was limited by the combinatorial effects of mass loss and chain cleavage as well as thermosolvated swelling, which makes initial or slow degradation processes difficult to isolate. Further analysis, using sacrificial samples, will be necessary to fully characterize environmental stability compared with slow gravimetric changes..
Post-Foaming Modifications
Based upon the material stability studies, and assuming an environmental application, the BADGE foams were selected for post-foaming modifications as the most likely translational candidate with regards to oil remediation and collection after spills. This application, which ideally encompasses a combination of shape recovery in lipophilic or hydrophilic solvents preferably to water or alcohols as well as a high upper swelling limit, would see materials deployed in aqueous environments similar to polyethylene sheeting after an oil spill. The foams would then be used to collect residual and surface oil, thereby cleaning the local environment more rapidly, using a technique with scalable potential. However, the residual alcohol groups would be likely a limitation for the collection of large amounts of oil, and post-foaming functionalizations would likely be needed. At least one technique to achieve such modifications includes the use of designer nanoparticles. A reaction formula showing the reaction of post-foaming functionalization of a BADGE SMP foam is shown in
Reclamation of oil was first examined using the original SMP foams, immersed in a 1:1 volumetric amount of hydraulic oil and water at room temperature. The mass of the compress, shape set foam was determined at 6 h after immersion, and the majority species of the taken up material was determined volumetrically as well. Based on materials stability and mechanical properties (specifically the final brittleness), N Epoxide was excluded from this study. IPDI Epoxide materials were found to take up primarily water, with approximate 3× mass H2O taken by the material, a trend which was repeated at 30° C. and ultimately resulted in expansion of the material. Interestingly, the IPDI-derived materials floated primarily in the water layer for the duration of the studies.
Importantly, the average volumetric recovery of the samples was low. It was hypothesized that part of mechanism for this would be the residual alcohols formed from the epoxide ring opening, leaving a number of alcohol moieties which would initially reduce the lipophilicity but also could be leveraged to enhance it with subsequent functionalization. IPDI was selected as a common, readily available, and reactive surface modifier, and SMP foam cubes were incubated in a 80 wt % solution of IPDI and tetrahydrofuran (THF) over night, followed by a 5 min wash in THF. The residual isocyanate groups on the foam surface, confirmed by FT-IR (
As stated, the functionalization was monitored by FT-IR, with the BADGE SMP foams displaying characteristics bands for the thioether, alcohol groups and carbonyl groups. After immersion in the isocyanate solution, the characteristic isocyanate band was found at 2286 to 2229 cm−1, and the subsequent shift from 1727 to 1721 cm−1 indicated the formation of the urethane linkage, denoted that tethering of the IPDI molecules onto the surface of the foams. Further treatment using hexadecanethiol demonstrated the formation of a new peak at 1646 cm−1, likely due to the altered orientation of the hydrogen bonding in the new thiourethane linkage that is formed by reaction with the surface isocyanate groups. Importantly, the isocyanate peak was consumed after 24 h in the second solution.
Morphologically and regarding material performance, post foaming did not alter the properties or behaviors of the SMPs significantly. Shape recovery was found to be retained at approximately 100% strain, and the recovery rate was not impacted during cursory inspection. Additional work is needed to characterize the extent to which surface modification may impact such properties, as well as thermomechanical behaviors.
Collection of Oil
The foams described herein, such as poly(β-thioether), can be used to collect oil from the environment. The naturally occurring oil often needs to be harvested from spaces where existing technologies are ineffective, destructive, or harmful to the environment. At least due to the rapid foaming, tunable expansion, scavenging properties of hydrophobic liquids, and potential for subsequent functionalization after foaming at least to change the hydrophobicity of the foams, the foams described herein may be used to collect oil or other natural resources in a safe, effective, and healthy way by absorbing oil to which it is exposed, particularly because the poly(β-thioether) is capable of tunable expansion and scavenging properties to absorb hydrophobic liquids, such as oil and/or crude oil. The foam, having absorbed oil therein, may be collected and subsequently treated to harvest the oil from the foam. This method of harvesting may replace otherwise hazardous procedures such as fracking, and has the benefit of avoiding the detrimental environmental effects. Moreover, the high porosity of the shape memory polymer foams described herein lead to vast surface area upon which the crude oil can be absorbed. A qualitative example of oil collection is shown in
Blood Flow Stability and Breast Implant Applications
The foams described herein, such as poly(β-thioether), have myriad applications, several of which include medical applications. Particularly, at least due to the rapid foaming, tunable expansion, scavenging properties of hydrophobic liquids, and potential for subsequent functionalization after foaming at least to change the hydrophobicity of the foams, the foams described herein may be used to stabilize blood flow. For example, medical patients that have suffered a stroke or aneurysm occlusion often have hydrophobic material in their blood that must be removed to restore stability of the patient's blood flow, or expanding the diameter of blood vessels to allow for the stabilization of blood flow beyond obstructions in the blood vessels.
Furthermore, the foams described herein, such as poly(β-thioether), may be used in breast implant applications. For example, a housing material acceptable to be implanted in a human breast, for cosmetic or medical purposes, may encase the foams described herein and may be particularly sized per the need or desire of the patient at least because the foaming is a tunable expansion.
3-D Printing
The foams described herein may be formed from a 3-D printer. The epoxide and thiol monomers in the presence of an organobase. Particularly, the shape memory polymer foams described herein may be formed by reacting pentaerythritoltetra(3-mercaptopropionate) and bisphenol A diglycidyl ether in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene to form a filament. The filament may be printed using a 3-D printer to form desired structures.
Oil Remediation and Cost Analysis
The BADGE foams were then studied alongside the IPDI foams for potential in scavenging surface oil slicks after spills. Modern techniques that have been utilized for this problem have focused on polyethylene sheeting, however a number of smaller, less economically-viable solutions have been explored with differing effects. Polymeric foams have emerged on the forefront of possible technologies used to combat oil spills, and to aid in the remediation of otherwise tainted environments. For example, polyHIPEs of polystyrene, a surfactant and SiO2 microparticles have been demonstrated to be utilized in producing highly porous materials (0.186 to 0.036 g cm−3 reported), but the oil recovery never exceeded the mass of the composite material, even when using ideal organic solvents. Similarly, polypropylene foams containing polytetrafluoroethylene nanoparticles produced through extrusion and subsequent super critical carbon dioxide resulted in approximately 10 μm pores and oil absorptions of nearly 5× the original mass of the polymer (8× for organic solvents), but unfortunately material density and porosity were not reported. Similarly, polypropylene foams containing polytetrafluoroethylene nanoparticles produced through extrusion and subsequent super critical carbon dioxide resulted in approximately 10 μm pores and oil absorptions of nearly 5× the original mass of the polymer (8× for organic solvents), but unfortunately material density and porosity were not reported.
Images of compressed BADGE and IPDI Epoxide foams are shown in
Additional images of compressed foams is shown in
The use of the BADGE foams at 20° C. was found to allow for scavenging up to 5× the foam mass in the compressed foams (SMPs in the temporary, secondary shape which are too far below the Tg to expand), and this was dramatically increased to nearly 25× the mass in the expanded BADGE materials. In the compressed samples, longer exposure times resulted in greater uptake of remedial oil, which was not significantly found in the expanded BADGE samples. Increased temperature resulted in greater uptake, likely due to the greater mobility of the polymer network which would allow for more swelling, even if the majority of the material is still thermally constrained. However, the temperature at which the materials are tested does not seem to influence the uptake of oil as much as the accessible porosity of the material.
Surface functionalization using the hexadecanethiol was found to provide marginal increases in the uptake of oil, while the dihexadecanethiol modification displayed more significant increases. However, as demonstrated by the raw comparisons, the porous nature of the materials themselves seem to be the dominating factor compared with surface functionalizations, as confirmed by cost analysis.
Analysis of the return on scavenged oil was done for 1 kg and 100 kg of material, assessing the efficiency of the methods. The unmodified BADGE foams display the highest efficiency by this analysis, which excludes processing time and worker-time costs; including these costs, which are difficult to accurately calculate, would only further improve the BADGE foam.
The original foam was found to yield approximately 10% of its mass in recovered oil from the oil:water mixture when accounting for the manufacturing cost, while the hexadecanethiol and dihexadecanethiol modified materials were below 8%, regardless of the immersion time or examined temperatures. This is especially insightful, as it means in the case of environmental remediation after a spill, time does not need to be wasted by performing multi-step modifications and processing for the raw material. Rather, the raw material seems best suited for the performance and can be rapidly developed then deployed.
Another important factor to consider here is the water uptake of the materials, as both the oil reclamation and the TGA studies indicated the presence of water in the materials, although this appears to be very low amounts and would be consistent with a hydroxyl-containing porous material. A dried material, while providing a higher efficiency for such testing, would not be a feasible test article for oil reclamation on a large scale due to the impracticalities of maintaining a water-free environment for storage and transportation on the scales necessary for environmental remediation. Additionally, these assessments do not fully encompass the reclamation process involving isolating pure oil and reusing it. These types of studies will be necessary for more application-specific testing. Finally, material degradation with regards to cost analysis and the energy needs for full recycling or decomposition are not included in this evaluation, and will be factors of consideration moving forward to greater scales of production and assessment.
In conclusion, we present the development of low density, high porosity shape memory poly(β-thioether) foams in a rapid reaction of economically-scalable epoxide and thiol monomers in the presence of the organobase DBU. The rapid reaction allows for the production of controlled pore morphology and density in SMP foams, with 5 min required from the addition of monomers to the final material product. The use of a BPA derivative, a tertiary amine-containing epoxide, and an epoxide with two urethane linkages demonstrated the tunability of thermomechanical properties and biostability. The formation of the poly(β-hydroxythioether) network, which produces alcohol groups during the epoxide ring opening, was then leveraged for post-foaming functionalization using first isophorone diisocyanate followed by either hexadecanethiol or a di-hexadecanethiol monomer to compare both the efficiencies and the idealized economics of these materials in oil scavenging using hydraulic motor oil. While the porous materials are suitable for recovering large masses and volumes of oils selectively from oil:water mixtures, ultimately the unmodified BADGE materials demonstrated the most economic route towards oil recovery with regards to both the recoverable oil from polluted environments, and the cost effectiveness of such a method, providing a feasible route to aid in environmental recovery plans globally.
General: Chemicals were purchased and used without purification from TCI® (having a place of business in Tokyo, Japan).
Foam Synthesis: Polymer foam was produced by adding the epoxide monomer, PETMP, acetone and the organobase catalyst into a single container with salt. For the Neopentyl foam synthesis, Neopentyl glycol diglycidyl ether monomer was added to a beaker with stoichiometric amounts of PETMP and mixed until the reagents were homogeneous. A small amount of DBU was added into the beaker containing Neopentyl and mixed for approximately 30 s before being poured into the container containing salt. The mixture was placed on a room temperature surface and allowed to completely settle around the salt particles for. The foam solidified over a 10 min period and was placed in a 120° C. oven for 12 h to carry the reaction to completion. Following the curing process, the foam was removed and cut into cubes and placed in a heated (90° C.) beaker with water. The foams were left in the beaker for 72 h with a magnetic stir bar to keep the water oscillating, replacing the water every 24 h. After washing, the foams were dried at 50° C. overnight using the Across International AT09-UL Vacuum Drying Oven (Across International®, having a place of business in Livingston, NJ) and used for subsequent characterizations.
Rheology Characterization: Stoichiometric amounts of PETMP and the corresponding epoxide were first mixed together and then added to the parallel plate geometry on the rheometer (500 μm) at room temperature, at which time the samples were subjected to uniaxial rotation and oscillatory shears. Subsequent testing of the reaction kinetics was done including 0.1 wt % DBU, added immediately prior to shearing. These kinetic studies were conducted over 5000 s, measuring storage and loss moduli using oscillatory testing at 1 Hz frequency and 1% oscillatory rotation.
Dynamic Mechanical Analysis: The mechanical properties of the foams were analyzed using a TA Instruments DMA 800 in compression mode. 1 cm3 foam cubes were centered in the test platens and equilibrated at 25° C. and 37° C. at which the sample was compressed at 50%×min−1 to failure. Elastic moduli, strain at failure, toughness, and ultimate stress and strain were calculated from the corresponding stress-strain curves. This test was completed both with dry and submerged foams to look at how the plasticization effects the mechanical properties. Thermal properties of the foams were characterized using the same instrument with samples incubated.
Thermal Analysis: Using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), the thermal transitions of foams were analyzed. DSC was used to determine the Tg using a TA Instruments Q200 equipped with TA Refrigerated Cooling System (TA Instruments, New Castle, DE). To obtain the wet Tg, DSC samples (approximately were placed in hot water (approximately 90° C.) for 10 minutes. Samples were taken out and squeezed with a paper towel to remove any excess water. Samples were then sealed in a Hermetic Tzero pan with a small hole poked in the lid before being heated from −90° C. to 200° C. at 10° C.×min−1. Using TA Analysis software (TA Instruments®, having a place of business in New Castle, DE, USA), the half-height transition of the DSC thermogram was determined as the Tg. A TA Instruments SDT Q600 (TA Instruments®, having a place of business in New Castle, DE, USA) was used to determine the thermal decomposition temperature (TD), characterized as the point of 5% mass loss. Samples were isothermally equilibrated at 120° C. for 30 mins to remove any residual moisture before being heated to 500° C. at 30° C.×min−1, followed by rapid heating to 1000° C. at 50° C.×min−1.
Cytocompatibility
Spin coating: The BADGE and Neopentyl mixtures were prepared by adding 10 wt % polymer to dissolve in chloroform and a small amount of the catalyst DBU. The solution was then spun onto 12 mm glass slides for 10 secs at 50 RPM and another 10 secs at 110 RPM using a KW-4A spin coater. Once the slides were spin coated they were placed in an oven at 120° C. for 24 hours to allow the foam to cure.
Indirect Cell Viability Culturing: 3 foam (1 cm3) cubes were immersed in ethanol for 1 hour, followed by a 96 h immersion in Dulbecco's modified Eagle's medium (DMEM) growth media supplemented with 10% fetal bovine serum (FBS) and 1% penicillin-streptomycin solution for a total media volume of 3 mL, with concentration of the extract foams varied across a range of concentrations. MG63 and SAOS2 cell lines were seeded in 96-well plates at 10,000 cells per well and were allowed to adhere for 24 h at 37° C. before being exposed to the solution. Proliferation was determined using a MTT assay after 3 hours of exposure to 50 μL of solution, and absorbance at 570 nm was compared with a control well for normalization.
Cell Culture and Proliferation: Raw 264.7 cells were cultured in Dulbecco's modified eagle'e medium (DMEM) growth media supplemented with 10% fetal bovine serum (FBS) and 1% penicillin-streptomycin solution. Cells were kept in a humidified 37° C. incubator with a 5% CO2 atmosphere before being seeded onto the polymer spin coated slides. To prepare for the cyto-compatibility study, the spin coated slides were immersed in isopropyl alcohol (IPA) for 10 mins, removed and repeated 4-5 times. After the last rinse, IPA was removed from the slides and replaced with 70% ethanol for 15 min, followed by exposure to UV light for 20 min. RAW 264.7 cells were seeded at a density of 10000 cells/mL in the respective growth media. A 3D study was conducted by cutting the foam into a 10 mm disc with a height of 3-4 mm These foam samples were cleaned by soaking in 200 mL of water at 90° C. for 48 hours, changing the water every 12 hours. Next the foams were rinsed with IPA the same way the spin coated slides were. RAW 264.7 cells were seeded at a density of 20000 cell/mL in their respective growth media. Using CellTiter 96 AQueous® one solution cell proliferation assay (MTS), cell viability was determined by absorbance measurements obtained using a Synergy HTX® multi-mode microplate reader from Biotek® at 490 nm. These measurements were taken on day 1, day 3, day 5, and day 7 for the 2D study and days 2, 4, 7, 10, 14, 17, 21, 25, and 30 for the 3D study allowing for the cells to integrate into the porous sample. Invitrogen CellTracker CMAC Blue Dye® (7-amino-4-chloromethylcoumarin) was used to stain cells which were then imaged using a Nikon eclipse Ti inverted fluorescence microscope.
Results and Discussion
The thiol-epoxy “click” reaction was previously found to occur rapidly in the presence of DBU when using the BADGE monomer (bisphenol A (BPA) derivative), yielding gas-blown foams with tunable physical pore morphology. However, the use of the Neopentyl monomer (NEO) noticeably reduced the curing rate of the networks. In fact, the reduction prevented gas blown foam formation from occurring at all (foams would collapse due to the reduced mechanical properties), as noted with the rheological analysis of the BADGE and NEO thermoset networks. The BADGE network is several orders of magnitude greater in both storage and loss moduli, with a distinct difference between the two. This indicates the final materials is glassier than the NEO network, where the loss and storage moduli are approximately the same, indicating a material is close to its phase transition region. These differences in network behaviors ultimately resulted in the need for a different foaming approach, with saltleached scaffold templating selected due to its robustness, low cost, and ease of implementation.
The salt template was washed from the foams with simple water extraction over a 7 day period, resulting in porous scaffolds with pore diameters less than 500 μm repeatedly, providing an alternative method of achieving such pores compared with gas-blown foaming. The removal of salt was confirmed by both SEM (visual inspection) and using TGA (gravimetric inspection) (data shown in
Micro-CT imaging of the foams reveals no significant differences between the BADGE and NEO derived 0-hydroxythioether networks (
The porosity of the resultant foams was characterized through examination of the cross-sectional microCT images. Porosity measurements ranged from ˜90 to greater than 99%, influenced by the distribution of the salt template within the polymer matrix. This indicates that these materials, despite their small pore size, possess highly interconnected pores and should display a high surface area. Additionally, the low density of the materials indicates that such materials could be used for high compressible strain reactions without undergoing catastrophic failure.
The swelling ratio of the original (virgin) materials was found to range from ˜75% to ˜280% after 24 hr in acetone (20 volume excess) at 70° C., per ISO 10993 standards on implantable material preparation. Importantly, this study was also used to probe the extent of the thiol-epoxy click reaction by further drying the samples to study to probe the change in dry weights. This analysis revealed that the gel fractions of the network, or the extent to which the network reacted with all possible components to form infinite molecular weight structures with no solubility. This analysis revealed a high degree of gelation in the material (upon removal of the template), with gel fractions exceeding 99% for most materials. There does not appear to be a significant relationship between the material composition and the resultant porous foams.
For many formulations, the Fox equation (Eq 1) is accepted for predicting the Tg of a system made of two or more discrete components:
where the final Tg of the network is taken from averaging the mass ratios of the mixed components. The linear nature of this relationship here indicates that a high level of control may be achieved with regards to the final thermomechanical properties of the foams through the independent control of foam morphology and composition. For our system, we were able to account for both the formulation of the foams as well as the plasticization in the system using Eq 2:
T
g
=−0.53x+(43.28−18.93A) Eq 2.
where A is a volume ratio of plasticized bonds to non-plasticized bonds within the bulk material, as this is known to be a limitation of the Fox relationship for some materials applications. Using this relationship (limited to the samples tested here) provides an error of ±4% of the Tg (in Kelvin). Future work exploring this relationship will focus on expanding the utility of this relationship as well as determining the role of moisture within the system, as we are currently limited to using A as a Boolean operator representing either fully plasticized or no water-induced plasticization (0), unlike other studies that have been able to account for moisture content as a volume fraction of a single polymer composition using the Fox relationship or using time-water master curves.
Mechanical compression testing was performed using the DMA with both moisture and thermal environmental controls. Plasticized and non-plasticized samples, as well as two temperatures, were used to examine the three formulations of foams in order to determine the impact on network behavior as well as to probe the suitability of such formulations for biomedical applications using a previously described immersion experiment. Specifically, the cylindrical samples were studied in compression at 25° C. and 37° C., as well as with dry and saturated samples. In this manner, the role of solvation and thermal transitions could be decoupled and possibly leveraged for device applications.
Examining the compressive mechanical properties (data shown in
In cyclic compression, similar sample geometries were examined for repeated compression to 40% strain under in vitro conditions. Similar to the trend displayed with monotonic compressive testing, the higher Tg, glassier polymers (high BADGE content) display lower numbers of cycles prior to failure of the cycle, with 100% BADGE foams displaying a lack of recovery after 200 cycles that eventually limited testing. The BADGE foams seemed to undergo microstructural failure, likely a result of their glassy nature coupled with stress concentrations developed at the vertices of the cubic pores. More elastomeric materials are able to withstand significantly more cycles prior to “failure.” Specifically, this indicated that the BADGE foam would fail within 200 compressive cycles as noted by the reduction in the energy absorbed. Importantly, the failure determined here only seems to relate to the loading of a single testing cycle, not of the material entirely. With the application of heat in the absence of a mechanical restraining load, the samples will recovery their original geometries and are suitable for more compressive studies (discussed below). Therefore, for applications needing the BADGE foam, ensuring a constant moisture presence and that the tissue region does not cool below core body temperature are crucial requirements if maintaining the device geometry if a requirement.
Shape memory response as a function of total occupied volume of the foams was examined using foam cubes. All foam formulations displayed greater than 99% strain recovery within 3 minutes upon immersion in 37° C. PBS (
Cytocompatibility Analysis: Cytocompatibility testing was performed on the solution extractions and the foams themselves, providing insights into the clinical utility of these materials by looking at the extractable content, the material surface (2D) and the material morphology (3D). For reactive thermosets, extractable content may contain a wide variety of materials including catalysts, unreacted monomers, oligomeric materials, surfactants and additives, particulates, and even material associated with the vessel in which the extraction is conducted. In the case of these poly(β-hydroxythioether) foams, the oraganobase DBU, food-grade sodium chloride, residual epoxides and thiols, and low molecular weight, soluble oligo(β-hydroxythioether) units will be the primary constituents of the extract. DBU's oral LD50 in a murine model ranges from 215 to 681 mg×kg−1, while Neopentyl was found to be nearly nontoxic orally, with no adverse findings reported for doses exceeding 1000 mg×kg−1 when injected intravenously. Importantly, it is further known to be non-mutagenic. (PubCChem Neopenyl Glycol).
Using MG63 (fibroblasts) and SAOS2 (osteoblasts) cells, extract solutions were studied to determine a concentration vs viability relationship. Cell viability exceeding ˜85% is found for all examined samples, with no dilution resulting in cellular viabilities 100% for Neopentyl materials (data shown in
The increase in cellular viability indicates that the cytocompatibility of the materials, particularly the Neopentyl materials. 2D cell studies, using RAW 264.7 macrophages over a 7-day period, reflected this trend. On flat films, the cells were able to proliferate and demonstrate significant growth without differing from the control (untreated glass slides).
These promising results led to 3D cell culture experiments, conducted over 30 days using the same macrophage line. Excellent cytocompatibility was found in the porous scaffolds (both formulations) and cells were shown to proliferate throughout the material matrix (
The BADGE foams were implanted in murine subcutaneous tissue for a period of 4 and 8 weeks, providing an opportunity to examine the host-material interactions. At four weeks, the foam was encapsulated by a fibrovascular capsule which include macrophages and foreign body giant cells (FBGCs).
Method and Materials
General: Chemicals were purchased and used without purification from VWR. Fourier transform infrared spectroscopy (FT-IR) was performed in attenuated total reflectance (ATR) mode on a Bruker infrared spectrometer (Bruker, Billerica, MA) using 50 scans with background subtraction and a resolution of 2 cm−1. DSC was used to determine the Tg using a TA Instruments Q200 equipped with TA Refrigerated Cooling System 90 (TA Instruments, New Castle, DE). Dynamic mechanical analysis (DMA) was conducted using a TA Instruments DMA 800 (TA Instruments Inc, Delaware, USA). Optical analysis was performed on a Keyence VHX-7000 Digital Light Microscope (Osaka, Japan) with 20-100× lens, the analysis software delivered with the microscope, and ImageJ (U.S. NIH, Bethesda, Maryland, USA).
Foam Synthesis: Polymer foam was produced by adding the bifunctional bisphenol A diglycidyl ether (BADGE) monomer, pentaerythritol tetrakis(3-mercaptopropionate (PETMP), the surfactant, acetone (physical blowing agent), and the organobase catalyst into a single container. Specifically, the BADGE (10.000 g, 0.030 mol) monomer was added to a beaker and dissolved in 2 mL of acetone. Stoichiometric amounts of PETMP (7.178 g, 0.014 mol) and 2 g of Silslab 2790 were added to the same beaker and mixed until all reagents were dissolved into a homogenous, low viscosity solution. To a second beaker, 0.100 g DBU (0.657 mmol) and 2 ml of acetone were added and homogenized using a high speed mixer (3000 rpm) until a single phase forms (approximately 20 s). The mixture was then placed on a room temperature surface (remaining in the container), at which point the foam rose and solidified (within 30 s period). The reaction was carried to completion by isothermal annealing in a 120° C. oven for 12 h, after which the foam was removed and cut into cubes (1 cm3). The cubes were washed with an alternating organic solvent (MeOH) and DI water washes using a modified protocol previously described, substituting acetone for isopropyl alcohol. PBHTE foam synthesis was confirmed using FTIR
Micro CT Imaging: The foam cubes (1 cm3) were scanned by a TriFoil Imaging eXplore CT 120 Small Animal X-Ray CT Scanner(Northridge Tri-Modality Imaging, Inc. Chatsworth, CA, USA) with a 120 kV/ 5 kW capability and 24.7×24.7×24.7 μm3 voxel size, with the scan data processed via Amira version 2020.2 (Thermo Fisher Scientific). The reconstructed foam cube images were used in conjunction with optical microscopy images to obtain average pore sizes (averaging long and short diameters) and anisotropy of pores dimensions.
Optical Imaging: A Keyence digital microscope VHX (Keyence Corporation of America, Itasca, IL, USA) was used to capture digital images of the PBHTE materials at multiple zooms and scaled accordingly using the microscopes software.
Thermal Analysis: Thermal transitions of foams were examined using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). DSC samples (approximately 5 mg) were sealed in a Hermetic Tzero pan cooled to −100° C. before being heated to 180° C. at 10° C.×min−1. The half-height transition of the DSC thermogram was determined as the Tg from TA Analysis software (TA Instruments, New Castle, DE, USA). DMA was conducted by first isothermally equilibrating samples at 0° C. for 10 min before being heated to 200° C. at 2° C.×min−1.
Thermal gravimetric analysis (TGA) of the foams was conducted using TA Instrument SDT Q600 (TA Instruments, New Castle, DE) to find the thermal decomposition temperature (TD). The test conditions were set to ramp the temperature of the sample from room temperature to 120° C. where the temperature was held there for 10 min. This was to ensure no laden water was still in the system to affect the results. Then the sample temperature increased from 120 to 500° C. at 10° C.×min−1. Finally, to ensure total sample decomposition the temperature was ramped up to 1000° C. and held for 10 min. The data collected is at the 5% and 10% thermal decomposition points to analyze thermal stability of the materials.
Shape Memory: Strain fixation and recovery were examined for the polymer cubes at ambient conditions and immersed in water of varying temperatures, respectively. To shape set (fix) the materials, cubes were heated 20° C. above Tg and mechanically compressed to 20% of their original height. The mechanical load was held until the sample had again cooled to room temperature, after which it was removed. Change in strain after removal of the load was used to determine strain fixation (%). The fixed samples were then fully immersed in DI water (heated previously to 25, 30, 35, 40, 45 or 50° C.) Images were collected over the course of the immersion study, and changes in the sample height were used to find the strain recovery (%) as previously reported.
Oil Reclamation and Surface Functionalization: Cubes (˜1 cm3) were cut using a hot wire cutter and immersed in acetone at 37° C. for 24 h, after which they were immersed in isophorone diisocyanate solution (50 wt %) for another 24 h at 50° C. Samples were washed in clean acetone, blotted dry, and then immersed immediately in either 20 mL hexadecanethiol (with 1 wt % DBU) or 20 mL of 2,3-di(hexadecanethioether) propyl alcohol. After 48 h incubation at 50° C., samples were washed with acetone and allowed to dry for 48 h at 50° C. Samples were then immersed in a 1:1 (vol:vol) tube of oil and DI H2O for varying times in both the expanded and compressed states, with samples examined at both 20 and 30° C., modified from the protocol presented by Venosa and Holder. For method efficiency analysis, reagent costs were collected from Merck (costed December 2020) for enough material to produce 1 kg of shape memory polymer (SMP) foam, from which efficiency per method was calculated (excluding manufacturing time and manpower costs).
Results and Discussion:
The use of DBU was initially used to ensure a rapid thermoset network would form during the gas blown foaming process (
The pore sizes produced for such materials ranged from approximately 400 to 1100 μm in three discrete size distributions, and is a suitable range of oil sorption from aquatic environments (
Importantly, the foams display a sufficiently high Tg which may be used to deform them into a temporary, secondary shape for shape memory utilization. In this compressed form, the secondary shape is maintained until it is heated again. Differential scanning calorimetry (DSC) revealed a glass transition at approximately 51.5° C. when dry, with a wet Tg of approximately 25° C. revealed. This plasticized behavior is unusual for non-hydrogen bonding materials, although it is commonly found in polyurethane foams, and in this instance maybe useful to a device design. When analyzing the thermal decomposition pore size has a slight impact on the 5% and 10% degradation temperatures. The best consideration for this is that larger pore size allows for more heat transfer with the super-heated air to allow for more degradation. Though in the end the mass remaining for each sample is approximately similar, meaning there is confirmation of no material difference in the BADGE foams in terms of thermal stability.
The role of temperature in oil scavenging was examined using isothermal, monophasic solutions of oil, with foams incubated statically for 24-h periods and samples taken at discrete time points. The behaviors allowed for determining the role of physical characteristics such as pore size as well as external factors including temperature and time (
Overall, oil sorption with the foams seemed to take place within a few minutes of exposure, with little return typically found over the course of the immersion after the initial 5 min Statistically, samples from 5 min display no difference compared with 24 h of exposure across all temperatures of interest. This stable behavior is likely a result of the porous nature of the materials and is an advantage when compared with other oil scavenging media that require longer uptake or sorption times.
On average, oil sorption was reduced at 0° C. (
Overall, the oil sorption behaviors revealed important relationships between physical properties, such as density (related to pore size) (
The relationship between the maximum, idealized oil sorption and the material density was developed for porous polymer foams and commodity polymers that have been examined for oil sorption (
Conclusions: In conclusion, we demonstrate the use of PBHTE for oil remediation. By making porous SMPs, oil sorption in aqueous environments becomes a viable alternative to contemporary methods including polymer sheets and other porous materials. PBHTE foams demonstrated significant oil sorption obtaining over 1250% when tested in temperatures from 0 to 40° C. Here, environmental conditions were varied as a means of probing oil uptake as a function of temperature. This helps reinforce the viability of these foams being in used in interior waterways, which can vary in temperature depending on location. In the use of oil remediation pore size of the PBHTE was evaluated to determine which pore size would perform the best in oil remediation. When evaluating, the medium pore size range (800 μm) performed the best for its density, in ability to stay in an oil layer, and in terms of sorption of oil obtained. Relative toother materials, our PBHTEs are shown to display both a high sorption efficiency coupled with a low density. For oil sorption devices, these materials display excellent potential and are viable candidates in future devices.
The embodiments of the present invention recited herein are intended to be merely exemplary and those skilled in the art will be able to make numerous variations and modifications to it without departing from the spirit of the present invention. Notwithstanding the above, certain variations and modifications, while producing less than optimal results, may still produce satisfactory results. All such variations and modifications are intended to be within the scope of the present invention as defined by the claims appended hereto.
What is claimed is:
This application is a Continuation-in-part Application that claims the benefit of, and priority to, U.S. patent application Ser. No. 18/262,278, entitled “SHAPE MEMORY POLY(β-HYDROXYTHIOETHER) FOAMS RAPIDLY PRODUCED FROM MULTIFUNCTIONAL EPOXIDES AND THIOLS” filed on Jul. 20, 2023, the disclosure of which is hereby incorporated by reference herein in its entirety. This Application also claims the benefit of, and priority to, International PCT Application No. PCT/US22/13481, entitled “SHAPE MEMORY POLY(β-HYDROXYTHIOETHER) FOAMS RAPIDLY PRODUCED FROM MULTIFUNCTIONAL EPOXIDES AND THIOLS” filed Jan. 24, 2022, the disclosure of which is hereby incorporated by reference herein in its entirety. This Application also claims the benefit of, and priority to, U.S. Provisional Patent Application No. 63/140,487, entitled “SHAPE MEMORY POLY(β-HYDROXYTHIOETHER) FOAMS RAPIDLY PRODUCED FROM MULTIFUNCTIONAL EPOXIDES AND THIOLS” filed on Jan. 22, 2021, the disclosure of which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63140487 | Jan 2021 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 18262278 | Jan 0001 | US |
| Child | 18227542 | US |
