Patent Application
20250101642
This document relates to devices and methods for making and using shape memory polymer yarns. For example, this document relates to devices and methods for programming a deformed shape memory polymer yarn to return to an original shape and/or exert a force under certain conditions.
Shape memory polymer (SMP) yarns are specialized fibers made from SMPs that can change shape in response to external stimuli. SMP yarns can be deformed into a temporary shape. When occupying the temporary shape, SMP yarns can return to their original shape when triggered by an appropriate stimulus. Examples of stimuli include heating the yarn to a particular temperature, applying light to the yarn, or applying an electrical signal to the yarn. This ability to return to an original shape can make SMP yarns useful in various applications (e.g., smart textiles, medical devices, and adaptive clothing), where dynamic shape-changing properties provide functionality, comfort, or aesthetics.
The present document relates to shape memory polymer (SMP) yarns. Methods of making and using such yarns are also described herein. For example, this document relates to devices and methods for programming a deformed shape memory polymer yarn to return to an original shape and/or exert a force under certain conditions.
In one aspect, the present document relates to a yarn including a plurality of monofilaments, wherein at least one monofilament comprises a shape memory polymer, and wherein the yarn is configured to generate a predetermined force (e.g., a predetermined compressive force), generate a predetermined strain, or generate a combination of force and strain. In some embodiments, the yarn is torque unbalanced (or torque imbalanced). In other embodiments, the yarn is torque balanced.
In some embodiments, the yarn includes two, three, four, five, six, seven, eight, nine, ten, or more monofilaments.
In some embodiments, the at least one monofilament is characterized as having a first stored configuration. In some embodiments, the first stored configuration includes a non-linear shape (e.g., a curvilinear shape, a loop, etc.) formed by treating the at least one monofilament to a temperature between a glass transition temperature (Tg) and a melting temperature (Tm) of the shape memory polymer. In some embodiments, the first stored configuration includes a linear shape formed by treating the at least one monofilament to a temperature between a glass transition temperature (Tg) and a melting temperature (Tm) of the shape memory polymer.
In some embodiments, the at least one monofilament is characterized as having a second stored configuration that is different than the first stored configuration. In some embodiments, the at least one monofilament is configured to be actuated between the first and second stored configurations upon exposure to a stimulus (e.g., a change in temperature, such as an actuation temperature or a transformation temperature between Tg and Tm of the shape memory polymer).
In some embodiments, the yarn is characterized as having a first stored configuration. In some embodiments, the first stored configuration includes a non-linear shape (e.g., a curvilinear shape, a loop, etc.) formed by treating the yarn to a temperature between a glass transition temperature (Tg) and a melting temperature (Tm) of the shape memory polymer. In some embodiments, the first stored configuration includes a linear shape formed by treating the yarn to a temperature between a glass transition temperature (Tg) and a melting temperature (Tm) of the shape memory polymer. In some embodiments, the yarn is characterized as having a second stored configuration that is different than the first stored configuration. In some embodiments, the yarn is configured to be actuated between the first and second stored configurations upon exposure to a stimulus (e.g., any described herein).
In some embodiments, at least one of the plurality of monofilaments is annealed (e.g., at an annealing temperature between Tg and Tm of the shape memory polymer).
In some embodiments, the yarn is annealed (e.g., at an annealing temperature between Tg and Tm of the shape memory polymer).
In some embodiments, at least one of the plurality of monofilaments is extruded, spun (e.g., by way of melt spinning, drying spinning, wet spinning, electrospinning, etc.), hot drawn (e.g., at a temperature between Tg and Tm of the shape memory polymer), cold drawn (e.g., at a temperature below Tg of the shape memory polymer), printed (e.g., 3D printed), and the like, as well as combinations thereof.
In some embodiments, the shape memory polymer includes poly (lactic acid) (PLA), poly (urethane), nylon, a copolymer of any of these, and/or a linear and/or branched polymer form of any of these. In some embodiments, the shape memory polymer includes any polymer described herein.
In some embodiments, the at least one monofilament is continuous along a predetermined length of the yarn (e.g., a predetermined length that is at least 50%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or more of a total length of the yarn).
In some embodiments, the plurality of monofilaments is not entangled along a predetermined length of the yarn (e.g., a predetermined length that is at least 50%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or more of a total length of the yarn).
In some embodiments, the yarn is characterized by a twist factor τ of about 10 to 150.
In another aspect, the present document includes a textile having any yarn described herein. In some embodiments, the textile includes a knit, woven, and/or braided textile. In some embodiments, the textile includes a garment (e.g., a compression garment, an athletic garment, a body shapewear, a shoe, a sensory clothing, and the like), a suture, a stent, a graft (e.g., a tissue graft), a scaffold, a bandage, or a joint support.
In another aspect, the present document includes methods of making, using, or forming a yarn. In some embodiments, the method includes spinning a plurality of monofilaments to provide an initial yarn configured to generate a predetermined force (e.g., a predetermined compressive force), wherein at least one monofilament includes a shape memory polymer.
In some embodiments, said spinning includes increasing a twist factor of the initial yarn, the torque balanced yarn, or the torque imbalanced yarn (e.g., increasing a twist factor τ to about 10 to 150 or higher). In some embodiments, said increasing the twist factor provides an increase in strain of the initial yarn, the torque balanced yarn, or the torque imbalanced yarn (e.g., as compared to a yarn lacking the increased twist factor). In some embodiments, said increasing the twist factor provides an increase in strain of the initial yarn, the torque balanced yarn, or the torque imbalanced yarn (e.g., as compared to a yarn lacking the increased twist factor).
In some embodiments, the method further includes: plying the initial yarn to provide a torque balanced yarn or a torque imbalanced yarn.
In some embodiments, the method further includes: annealing the initial yarn, the torque balanced yarn, or the torque imbalanced yarn (e.g., at an annealing temperature between Tg and Tm of the shape memory polymer).
In some embodiments, the method further includes: programming at least a first stored configuration in the initial yarn, the torque balanced yarn, or the torque imbalanced yarn (e.g., using any process herein).
In some embodiments, the method further includes (e.g., before said spinning): thermally and/or mechanically and/or chemically processing the plurality of monofilaments (e.g., by annealing, cold drawing, hot drawing, crosslinking, or combinations thereof).
In some embodiments, the method further includes (e.g., before or after said spinning): thermally and/or mechanically and/or chemically processing the initial yarn, the torque balanced yarn, or the torque imbalanced yarn (e.g., by annealing, cold drawing, hot drawing, crosslinking, or combinations thereof).
In some embodiments, the method further includes: knitting the yarn to form a textile, wherein the textile is configured to apply said predetermined force upon exposure to a stimulus.
In some embodiments, the initial yarn, the torque balanced yarn, or the torque imbalanced yarn includes any yarn described herein. In some embodiments, the textile includes any textile described herein. Additional details follow.
As used herein, the term “about” means +/−10% of any recited value. As used herein, this term modifies any recited value, range of values, or endpoints of one or more ranges.
As used herein, the terms “top,” “bottom,” “upper,” “lower,” “above,” and “below” are used to provide a relative relationship between structures. The use of these terms does not indicate or require that a particular structure must be located at a particular location in the apparatus.
Other features and advantages of the present document will be apparent from the following detailed description, the figures, and the claims.
The following drawings illustrate certain embodiments of the features and advantages of this document. These embodiments are not intended to limit the scope of the appended claims in any manner. Like reference symbols in the drawings indicate like elements.
The present document relates to yarns formed from shape memory polymers (SMPs). In general, SMP yarns are materials that can be deformed from an original shape and actuated to return from the deformed shape to the original shape. This feature of SMP yarns can make these materials useful in many applications where it is beneficial for a material to change shape on command. For example, a process can involve controlling certain conditions to actuate an SMP yarn, thus controlling the yarn to change shape.
In some embodiments, an SMP yarn is composed of few filaments (e.g., less than 100). In some embodiments, the filament is a monofilament, and the yarn includes a plurality of monofilaments. Unless otherwise specified, the terms “filament” and “monofilament” are used interchangeably. In some examples, the SMP yarn comprises two, three, four, five, six, seven, eight, nine, ten, or more monofilaments.
In few filament yarns, the ratio of the filament diameter to the yarn diameter can be high (e.g., a ratio of 1:2 or higher, such as, e.g., from about 1:2 to 1:20, as well as ranges therebetween). Without wishing to be limited by mechanism or theory, this ratio can contribute to unique stress and strain behavior, as compared to yarns of infinite filaments. In some non-limiting embodiments, the yarn includes a plurality of filaments, in which each filament is independent (e.g., not entangled), continuous (e.g., not stapled fibers), and few in quantity (e.g., more than one and less than about 100 filaments).
In some embodiments, a yarn is formed by taking a finite number of monofilaments and spinning and/or braiding them together. These monofilaments, in some examples, can be under torsion within a yarn when the monofilaments are spun and/or braided together. For example, a plurality of monofilaments can be bundled together into a yarn, each individual microfilament being under torsion. In some embodiments, the yarn as a whole is not necessarily under torsion even when each individual monofilament is under torsion. That is, each of the monofilaments can extend substantially parallel to other monofilaments of the yarn, with each monofilament being under torsion about a longitudinal axis of the monofilament. The polymer filaments can be used as-is from the manufacturer or can be further processed (e.g., extruded, drawn to a smaller diameter, annealed, and the like, as well as combinations thereof). Optionally, the monofilament may also undergo thermal processing prior to being incorporated into a yarn structure to improve the shape memory performance.
The monofilaments and yarns can be formed from any useful SMP (e.g., any described herein). Generally, the SMP material can be characterized by high strains. However, in use, the SMP material itself can often be limited by the type of force it can generate. For example, and without limitation, the magnitude and directionality of applied force can be difficult to control. Accordingly, in some aspect, the present document describes the potential to expand the design space for shape memory polymers by allowing for greater strains without compromising the force generated. The yarn and textile structure may also increase the percentage of the force and/or strain recovered by the shape memory polymer. In some embodiments, a polymer that generates higher forces but does not have the desired strain characteristics could be spun into a yarn structure to obtain more strain without compromising the force. Compositions and methods for providing such structures are described herein.
The yarns herein can have any useful structure. For instance, the yarn structures can be torque balanced or torque imbalanced. In some embodiments, torque balance can be achieved by plying a yarn with a similar imbalanced twist. In some embodiments, torque imbalance can be achieved by applying strain to the yarn, but this is not always the case. Applying strain to the yarn might not create a torque imbalance in some embodiments.
Yarns with the same geometry can, in some examples, create stable torque balanced yarns or energetic torque imbalanced yarns, but this is not always the case. In some embodiments, the insertion of twist of the plurality of monofilaments can impose a mixture of bending and torsional strains into the plurality of monofilaments. As a structure, this can result in a torque imbalance that can cause a yarn to untwist if both ends are not fixed. However, with both ends constrained, slack may cause kinking or pig tailing of the yarn. In some examples, torque balancing may include thermal processing a yarn after spinning to shape-set the plurality of monofilaments in their twisted structures and remove any residual stresses from the imposed manufacturing strains. These shape-set, or in this case twist-set yarn, may continue to maintain structure upon slack. In some embodiments, a single yarn may be plied together by twisting together two or more torque imbalanced single yarns in an opposite direction of an initial twist or an initial coil.
Torque imbalance may be implemented in any useful manner. As described herein, twists or torsion can be applied to filaments or yarns to impose bending and torsional strains, which in turn creates a torsional imbalance. Once the torsional imbalance reaches a threshold, coils may form in yarn in a certain coil direction, and/or twists in a certain twist direction. In some examples, a yarn may not be torque balanced to remain an energetic torque imbalanced yarn, such as to provide additional actuation or customization of yarn performance.
Yarn structures can be manufactured and optimized for force and/or strain application. For example, and without limitation, the effect of yarn structure on the actuation of the SMP can be investigated. Both semi-crystalline (e.g., PLA) and amorphous (e.g., acrylonitrile butadiene styrene, ABS) SMPs can be employed. In some embodiments, a yarn structure can include one or more characteristics that increases the force recovery ratio (e.g., the ratio between the programming force and the actuating force) of the SMP when actuated. Non-limiting variables to modify yarn structure include one or more of the following: filament diameter, filament length, filament cross-section, ply, twist, manufacturing temperature, and composite yarn structures. Mechanical properties can be evaluated in any useful manner, e.g., by dynamic mechanical analysis and tensile testing. Chemical morphology can be evaluated in any useful manner, e.g., by differential scanning calorimetry. A design of experiments (DOE) can be used to identify which one or more variables to achieving desired yarn performance.
The yarn can include a certain ply parameter. A single filament may compose the yarn. In some embodiments, a single ply (e.g., group of monofilaments) yarn can be employed. In some embodiments a two-, three-, or more ply yarns can be used. In some embodiments, plied yarns can be twisted to create a cabled yarn. For example, the cable can include a set of yarns and each yarn can include a group of plied monofilaments. The yarns can be twisted together to create the cable. The number of twists per inch when plying filaments together can influence the properties of textile.
Yarn can be provided by spinning, bundling, and/or braiding (e.g., a plurality of filaments). For example, monofilaments can be bundled together to create a yarn. Each monofilament in the yarn, in some cases, can be under torsion even in cases when the yarn as a whole is not twisted and/or under torsion. Without wishing to be limited by mechanism or theory, spinning and/or braiding can alter the mechanical properties of the original material filament by pre-stressing and constraining the materials in a helical geometry. The design parameters for a continuous filament yarn (e.g., the number of bundled filaments, the applied twist per unit length, and/or the applied torque to the yarn) can be used to tune the flexural rigidity, breaking strength, and/or strain elongation of the yarn.
The monofilament and/or the yarn may undergo one or more shape memory programming processes. Any useful programming process can be employed. In some embodiments, the process may include applying stress to a monofilament or a yarn and affixing that stress by thermal treatment at a temperature between a glass transition temperature (Tg) and a melting temperature (Tm) of the SMP. In some embodiments the stress can be affixed at a temperature lower than Tg or greater than Tm. A skilled artisan would understand how to determine Tg and Tm depending on the type, molecular weight, crystallinity, or other properties of the SMP. Optionally, the yarn structure may undergo an annealing process to release any manufacturing stresses (e.g., at an annealing temperature between Tg and Tm).
In some embodiments, the programming process can be applied to the yarn including an SMP. The process can include: heating the yarn above Tg (e.g., to a programming temperature that is 1° C., 2° C., 3° C., 4° C., 5° C., 6° C., 7° C., 8° C., 9° C., 10° C., 11° C., 12° C., 13° C., 14° C., 15° C., or more above Tg). Once above the Tg, a force or strain is applied to the yarn. The applied force can be any stress, strain, or other constraint that deforms the yarn from its original configuration or its permanent configuration. Programming force or strain can be any useful amount (e.g., about 5%, 10%, 15%, 20%, 25%, 30%, or more of the force at 10% strain for the programming temperature). The yarn can then cool below the transition temperature while maintaining the force. Once the yarn is below the transition temperature, the force can be removed. The temporary configuration (e.g., elongated, stretched, bent, shaped, etc.) of the yarn can be set, thereby providing a yarn having a first stored configuration. The yarn can now be actuated by re-heating the yarn above the transition temperature to access another configuration (e.g., an initial configuration, a permanent configuration, a second stored configuration that is different than the first stored configuration, etc.). In some examples, the yarn can have more than two stored configurations. For example, the yarn can include three stored configurations, four stored configurations, or more than four stored configurations. Heating without constraint can cause the yarn to recover displacement. Heating a constrained yarn can cause the yarn to generate force. For example, and without limitation, it was observed that a non-limiting SMP yarn generated additional force upon cooling after heating under constraint. This behavior can be useful for numerous applications, e.g., medical compression applications. For example, and without limitation, the initial force and displacement generated by heating the polymer could be used to fit the garment to the body; and the additional force generated upon cooling could apply the compression necessary to facilitate improved circulation. Such processes can be applied to monofilaments, as well as yarns. Furthermore, such processes can be employed to program a plurality of stored configurations.
Without wishing to be limited by mechanism or theory, it was also observed that increasing the twist in the yarn structure can increase the amount of strain that the material can undergo without significantly compromising the amount of force generated. This behavior may also be useful for compression applications. Other structures such as braids can be created from the filaments and yarns herein. The SMP monofilament and SMP yarns may be made of one material or composed of different materials.
These yarns can be incorporated into textile structures to create unique textile actuations. For example, and without limitation, the pattern employed within the textile can be optimized to provide desired direction and magnitude of the force being applied upon actuation. In some embodiments, a knitted textile can be configured to deform in three dimensions (e.g., optionally as a function of the specific properties of the yarn used, the techniques applied to construct the yarn, and the combination of knit stitches throughout the knitted textile). For example, the use of weft and warp knitting techniques can influence the stretch and bi-stretch of resulting knitted textile. Weft knitting can be typically characterized as very elastic with high shrinkage, with comparatively low tensile strength and a resulting thin knitted material. In comparison, warp knitting can be typically characterized as having lower elasticity and shrinkage, with comparatively higher tensile strength, and a resulting course knitted material. Non-limiting weft knit stitch patterns include, e.g., rib stitch, garter stitch, stockinet stitch, linen stitch, reverse ridge stitch, and cables.
In some embodiments, a netted textile can be employed. For example, and without limitation, netting can result in a material that has elasticity, ability to deform along three dimensions, and can be influenced based on the specific properties of the yarn used, the techniques applied to construct the yarn, and the combination of knit stitches throughout the knitted material. Non-limiting netted materials can be produced by a Ceylon stitch, nalbinding stitches (e.g. York, Oslo, Mammen, Finnish stitches), Diamond Loop stitch, or other stitch patterns.
In some embodiments, a design of a textile can incorporate shape memory materials that result in different forces and displacements when actuated. Non-limiting variables that affect actuation include one or more of the following: yarn twist, ply, and diameter; relative loop dimensions; relative loop geometry; stitch size; and knitting pattern. The forces and displacements can be evaluated in any useful manner, e.g., through digital image correlation, tensile testing, and measuring the compression around a cylinder.
Any useful processes can be employed to provide filaments, yarns, and textiles. For example, filaments and yarns can be produced by spinning, extruding, melt processing, drawing, thermal processing, annealing, twisting, and the like, as well as combination thereof. In turn, filaments and yarns can be incorporated into knitted, woven, braided, knotted, and/or other textile structures. Non-limiting examples of textiles can include a garment (e.g., a compression garment, an athletic garment, a body shapewear, a shoe, a sock, a stocking, a sensory clothing, and the like), a suture, a stent, a graft (e.g., a tissue graft), a scaffold, a bandage, or a joint support, as well as portions or sections of any of these.
Compression stockings are currently used to prevent or treat diseases such as venous ulcers, deep vein thrombosis, or edema. These stockings are typically made of passive textiles stretched by the user and are frequently difficult to don and doff, resulting in ineffective treatment or patient non-compliance. Through smart materials, there are increased opportunities for the textile itself to change dimension or modulate the amount of generated force. Incorporating smart materials into textiles for compression stockings can make more accessible and more effective treatments. In some embodiments, a compression garment can be formed from any filament, yarn, or textile described herein.
Non-limiting filaments, yarns, textiles, and processes are described in PCT Pub. Nos. WO 2022/056545, WO 2021/113864, WO 2021/050944, and WO 2019/108794, as well as U.S. Pat. App. Pub. No. 2021/0301432 and U.S. Pat. No. 11,280,031, each of which is incorporated herein by reference in its entirety.
Any useful shape memory polymers (SMPs) can be employed within monofilaments, yarns, and textiles. In some embodiments, SMPs can include any polymer capable of storing one, two, three, or more stored configurations. A stored configuration can be programmed by exposing an original configuration to stress or strain. In some embodiments, such exposure occurs at certain temperature ranges (e.g., at a temperature between Tg and Tm) that facilitate affixing the stored configuration as latent strain energy. Such stored configurations can include linear and non-linear shapes (e.g., in two or three dimensions), in which exposure to a stimulus allows for transition or actuation between the stored configuration and the original configuration or between two or more different stored configurations. Non-limiting stimulus can include changes in temperature, electric field, magnetic field, light, solvent exposure, pH, humidity, and the like. Response to such stimulus can include, e.g., changes in shape, volume, conductivity, optical properties, or some other characteristic.
An SMP can be characterized by one or more of the following: a stress recovery ratio of Factuation/Fprogramming, where Factuation represents stress or strain during or after actuation and Fprogramming represents force during or after programming; a shape fixity ratio of ε/εload, where ε represents strain after the programming force or strain is removed and εload represents the strain with the applied programming force or strain; a shape recovery ratio which may be defined as εactuation/εprogramming where εprogramming is the strain after programming and εactuation is the strain during or after actuation; a deformation strain of greater than about 100%, 200%, 300%, 400%, 500%, 600%, 700%, 800%, or more; a Young's modulus of about 0.01 to 15 GPa at a temperature that is below the transformation temperature; a Young's modulus of about 0.01 to 500 MPa at a temperature that is above the transformation temperature; a deformation stress from about 0.1 to 500 MPa; a recovery stress from about 0.1 to 5 MPa; an actuation temperature from about −70° C. to 100° C.; and the like. For any ratios, percentage amounts can be determined by multiplying by 100. Deformation strain can, in some examples, be much smaller than 100% such as smaller than about 10%, 1%, or 0.1%.
Non-limiting examples of SMPs include, e.g., poly (lactic acid) (PLA), poly (urethane), poly (amide) (e.g., nylon), poly (acrylic acid) (PAA), poly (alkyl methacrylate) such as, e.g., poly (methyl methacrylate) (PMMA), poly (caprolactone) (PCL), poly (propylene carbonate) (PPC), poly (esteramide) (PEA), poly (ethylene terephthalate) (PET), poly (ethyleneoxide) (PEO), poly (styrene) (PS), poly (butadiene), poly (norbornene), poly (ether ether ketone) (PEEK), poly (vinyl alcohol) (PVA), a copolymer of any of these, a crosslinked form of any of these, a blend of any of these, and/or a linear and/or branched polymer form of any of these. SMPs include thermoplastic and/or thermoset polymers (e.g., including homopolymers or copolymers, such as block copolymers). SMPs can include composites, in which one or more polymers (e.g., any herein) can be combined with another material (e.g., particles, including nanoparticles or microparticles; granules; powders; nanomaterials, such as nanoparticles and/or nanotubes, including carbon nanotubes; and the like). The monofilament or yarn can include one or more SMPs.
Any useful SMP can be selected and evaluated. In some embodiments, non-limiting considerations for a compression garment can include one or more of the following characteristics: a specific transition temperature (e.g., between about 20° C. and 40° C.); a capacity to apply the correct amount of compression (e.g., from about 20 mmHg when unactuated or from about 40 to 80 mmHg when actuated); a useful form factor (e.g., monofilament, roving, etc.); washability; moisture/sweat resistance; a capacity for reversible actuation; and an ability to transition between multiple shapes.
Polylactide (PLA) is a sustainable, biocompatible polymer, making it a suitable, non-limiting material candidate for biomedical applications. In some examples, PLA can be referred to as a “filament.” PLA also exhibits shape memory and can be programmed to change its shape when activated by heat. PLA filaments have the potential to be spun into yarns and knit into structures, such as stents or compression garments. Leveraging and optimizing the shape memory capability of PLA in textiles may result in new and more effective medical treatments. Described herein are experiments to evaluate the effect of different manufacturing and programming methods on the shape memory response of PLA.
Programming a shape-memory filament such as PLA refers to the process of deforming the filament from its original (e.g., permanent) shape into a new (e.g., temporary) shape. The programmed material can remain in the temporary, deformed shape until the material is triggered to return to its permanent form. Shape-memory filaments such as PLA can be made of specialized polymers or alloys that can change shape in response to external stimuli such as heat, light, or an electrical signal. Programming can work by heating a filament and deforming the filament when heated, and subsequently cooling the filament to fix the deformed shape. The filament can be triggered to return to its original shape, such as by reheating the filament. Thus, the filament can be deformed and “programmed” to return to its original shape.
PLA is a semicrystalline polymer and will undergo crystallization when heated above the glass transition temperature or stretched. Because of this change in microstructure, the shape memory response of PLA can be affected by the shape programming process.
PLA monofilaments that are not annealed are about 11% crystalline. When heated above the glass transition temperature (Tg), the PLA will crystallize until it is about 35% crystalline. Annealing the PLA can induce crystallization and thus can minimize its occurrence during the shape-setting process.
Referring now to
Referring now to
Step 32 involves cooling the extruded PLA below Tm to set a permanent shape. In some examples, the PLA is cooled to more than a threshold temperature below Tm. Optionally, step 33 involves the filament being annealed to induce crystallization. Annealing can include wrapping the filament around a shape (e.g., a 7-inch diameter hollow cylinder) and heating the filament to a temperature that is between Tg and Tm (e.g., between 60° C. and 165° C., such as about 100° C.) for any useful time period (e.g., for 5, 10, 15, or more minutes) to induce crystallization. This crystallization can be beneficial, because crystallization makes PLA stiffer and stronger as compared with examples where PLA is not annealed to induce crystallization. Crystallization also improves an ability of PLA to prevent gas leakage.
In some examples, annealing PLA can provide one or more benefits other than crystallization. For example, annealing can increase a heat deflection temperature of PLA and improve an ability of PLA to withstand higher temperatures without deforming. Annealing can also improve dimensional stability by decreasing a risk of warping. In some cases, annealing improves tensile strength and impact resistance of PLA. Brittleness can be reduced through annealing, improving performance in applications where flexibility and durability are important. Annealing can also help to retain biodegradability of PLA.
Without wishing to be limited by mechanism, annealing can improve crystallization and may improve the shape programming process. In some examples, 31-33 can be avoided if the filament is purchased or manufactured separately. That is, it is possible to perform steps 34-37 using an annealed or a non-annealed filament that is purchased or manufactured separately. In some embodiments, step 33 can be conducted for a purchased or separately manufactured filament to anneal the purchased or separately manufactured filament before performing steps 34-37.
Steps 34-37 provides processes to affix a stored configuration. In general, these steps involve applying a force or strain to the filament (or yarn) and then exposing the filament (or yarn) to a temperature that can be between Tg and Tm. It is not required to expose the filament to a temperature between Tg and Tm. In some cases, the filament can be exposed to a temperature that is lower than Tg or greater than Tm. As seen in step 34, force can be applied to the filament to form a temporary shape when the temperature of the filament is below Tm. this shape can be a curvilinear shape as illustrated in
Depending on the temporary shape, differing strains or forces can be applied in any useful manner. In some embodiments, stress and/or strain can be imposed on the material by wrapping the filament around a form (e.g., provided as pegboard pegs in
In step 35, the temporary shape is affixed by heating the material to a suitable programming temperature corresponding to the material and its properties. In some examples, this temperature is within a range from Tg to Tm, but this is not required. The temperature can be below Tg or greater than Tm. In some embodiments, the filament can be heated while being wrapped around a form (e.g., provided as a pegboard in
In step 36, the shaped filaments are cooled below a transition temperature (e.g., Tg) and then removed from the form. Here, the loops maintain the temporary loop shape without the pegboard. In step 36, the filament is set in its temporary shape and “programmed” to return to its original shape shown in steps 31-33. The temporary shape shown in step 36 is secure and does not depend on any pegs (e.g., the pegs of steps 34-35) to hold the temporary shape. In some examples, the filament will remain in the temporary shape under normal temperature conditions under Tg. The filament is programmed to return to its original shape when heated to a certain temperature, as demonstrated in step 37.
In step 37, the shaped filaments can be actuated by heating to a transition temperature. In some examples, the transition temperature is between Tg and Tm (e.g., between 60° C. and 165° C., such as about 80° C.). The shaped filament returns to the permanent shape (e.g., here, a non-limiting straight shape) when actuated. Actual temperatures for annealing, affixing the stored configuration, cooling the shaped filament, setting the shaped filament, and actuating the shaped filament can be optimized and determined by a skilled artisan. Furthermore, processes and description herein for a filament can be extended to form a yarn.
Referring now to
Monofilament PLA was employed to provide a knit structure. As seen in
Described herein are experiments to evaluate the effect of yarn geometry on the stress memory performance of few filament PLA yarns. Three different PLAs were selected for manufacturing the few filament yarns: Indorama, Hatchbox, and Polymaker. In general, filament PLA yarns can be programmed to return to an original length when actuated after being altered to a temporary length. This can be beneficial in several applications which involve changing the length of one or more elongated members under certain conditions.
Referring now to
Referring now to
PLA yarns can be shape programmed in any useful manner. Referring now to
For example, steps 82, 84, 86, and 88 involve programming a filament PLA yarn and step 90 involves actuating a filament yarn. In step 82, a process involves heating the filament PLA yarn above Tg without applying force. As seen in
In step 86, the process includes cooling the polymer below Tg while maintaining the programming force. As seen in
Yarns having varying geometries can be manufactured. As seen in
τ=T√C
where T is yarn twist determined by turns per cm [tpcm] and C is yarn count or a linear density of the yarn [g/km]. The twist factor, τ, relates yarns of similar geometries that differ by a scale factor. Non-limiting examples 102 of yarns with similar twist factors are provided in
Stress-temperature-strain profiles for few filament yarns were determined for PLA from Indorama (
Overall, yarn structure can affect the shape memory performance of the yarns. In some non-limiting embodiments, increasing the twist can increase the strain without compromising the magnitude of the stress generated by the yarn during actuation. This pattern appears to be material independent because Indorama, Hatchbox, and Polymaker PLA display a similar trend.
Described herein are experiments to evaluate the yarn structure characteristics for producing a shape memory polymer yarn with performance characteristics favorable for medical compression applications.
Shape memory materials are materials that can recall a remembered shape when actuated by a stimulus such as heat. Incorporating these materials into textile structures can create active textiles that change their geometry in response to their environment. These textiles have the potential to make compression garments more comfortable and effective. One non- limiting goal includes evaluating the effect of yarn and textile structures on shape memory performance and demonstrating the effectiveness of the structures though a proof-of-concept prototype.
Successfully accomplishing this will open up the design space for advanced textiles not only for space exploration, but also for other medical and commercial applications. For instance, spaceflight poses many challenges to the human body, one of which is the effect of extended exposure to microgravity. Exposure to microgravity can cause cardiovascular deconditioning and upon returning to Earth blood may fail to return from the lower limbs. This can lead to orthostatic intolerance in about 20% of astronauts for short duration spaceflights (4-18 days) and in about 80% of astronauts for long duration spaceflights (4-6 months). The symptoms of orthostatic intolerance are a safety hazard to the astronauts because symptoms such as dizziness and confusion may interfere with normal operational tasks or an unassisted emergency egress.
One of the strategies for mitigating orthostatic intolerance is a compression garment that applies 40-80 mmHg of pressure to the lower body. Anti-gravity suits (AGS) are an inflatable compression garment that is currently in use. This compression garment can be pressurized to 0.5-1.5 psi (26-78 mmHg) during re-entry and landing. Although this design has the advantage of variable pressure, the AGS can depressurize when disconnected from the gas supply in the cabin, is uncomfortable, and it increases oxygen consumption and heart rate when walking. A different solution is the Kentavr worn by cosmonauts which is a set of elastic lower body compression garments consisting of two gaiters and a pair of shorts. The Kentavr provides 30 mmHg of compression on the covered areas, which can mitigate the effects of orthostatic intolerance. A gradient compression garment (GCG) composed of thigh high stockings and shorts that applies 55 mmHg of compression at the ankles and 6 mmHg at the thighs may prevent symptoms of orthostatic intolerance. Although the GCG has the advantage of increased mobility compared to the AGS and better coverage compared to the Kentavr, it may be uncomfortable if worn for an extended amount of time and the amount of compression is not adjustable.
Shape memory materials (SMM) present the opportunity for the design of active textiles. An active textile can include a textile that is made from a SMM filament and provides contraction or other 3D shape changes in response to a stimulus such as heat. While current compression garments rely on heavy, pneumatic infrastructure, SMM-based compression garments are intrinsically active and can therefore provide a lightweight and effective alternative to state-of-the-art systems. A coiled SMA cartridge actuator integrated into a cylindrical cuff designed for extravehicular activity in space demonstrated the potential to apply 29.6 kPa (222 mmHg) of pressure. Knitted shape memory alloy (SMA) actuators have also been demonstrated as a viable option for a variable compression garment. An advantage of the knitted textile design over the coiled cartridge is that the knitted structures exhibit a three-dimensional response when actuated, whereas the coiled cartridge or simple wire only exhibits a one-dimensional response. SMAs can exhibit a moderate strain recovery, and large strains can be achieved if this material is manufactured into a knit structure. The evaluation of a knit actuator design predicts that it could be possible for the garment to exert a lower compression when donned (19 mmHg at the ankle), and then exert a higher compression when actuated (52 mmHg at the ankle).
The design space for compression garments can be further expanded by evaluating the performance of shape memory polymers (SMP) in yarn and textile structures. SMPs are less expensive than SMAs, more lightweight, recover larger strains (up to 400%), and have a wide range of actuation temperatures (−70° C. to 70° C.), but can exert lower forces than SMAs. Developing appropriate yarn and knitted textile structures could amplify forces produced by SMPs. Amplifying the forces produced by SMPs could provide useful compression garment fabrication, therefore opening up the design space to lighter materials, other temperature ranges for actuation, and lower costs. In some embodiments, structural changes to the yarn and knit textile have the potential to increase the compression range.
Described herein are structures that can leverage the properties of shape memory materials, especially shape memory polymers. The capability of shape memory polymers can be expanded by incorporating these, and other novel materials, into yarns and knitted structures. In turn, yarns and knitted textiles composed of SMP can guide the design of devices including compression garments and actuators. Integration of active textiles into these and other applications may result in mass and volume reduction of systems and devices.
As discussed herein, PLA is a sustainable, biocompatible polymer that exhibits shape memory. A non-limiting shape programming process for knitted loops is shown in
Referring now to
As seen in
In addition, PLA filaments have the potential to be spun into yarns and knit into structures including textiles for compression garments. When the PLA monofilament is incorporated into a knit structure, the shape recovery caused multidirectional actuation, as shown in
SMPs are more lightweight than SMAs, less expensive, have a broad temperature range for actuation, and can be spun into yarns, which make this category of materials an attractive candidate for improved compression garments. Through incorporating shape memory polymers into compression garments, the garment itself may apply the appropriate amount of compression when actuated by heat. Fabricating a compression garment out of shape memory polymer has the potential to be more comfortable and more safe than bulkier pneumatic solutions that may restrict movement or deflate.
Such garments may provide solutions for medical compression garments to treat illness such as deep vein thrombosis, venous ulcers, and varicose veins. Compression stockings treat and prevent DVT but are frequently difficult to don and doff which can result in an ineffective treatment or patient non-compliance. Through smart materials (e.g., any described herein), there are increased opportunities for the textile itself to expand or contract. Incorporating SMP into textiles for compression therapies can make them more accessible and more effective. Such textiles may also provide insights for other medical devices (e.g., orthopedic implants) and consumer goods, such as load distribution in backpacks.
Whilst the invention has been disclosed in particular embodiments, it will be understood by those skilled in the art that certain substitutions, alterations and/or omissions may be made to the embodiments without departing from the spirit of the invention. Accordingly, the foregoing description is meant to be exemplary only, and should not limit the scope of the invention. All references (including those listed above), scientific articles, patent publications, and any other documents cited herein are hereby incorporated by reference for the substance of their disclosure.
This application claims the benefit of U.S. Provisional Application No. 63/540,533, filed Sep. 26, 2023, the entire contents of which is incorporated herein by reference.
This invention was made with government support under 2237827 awarded by the National Science Foundation. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63540533 | Sep 2023 | US |
