Patent Application
20230170116
The present invention relates to a method of fabricating a programmable and/or reprogrammable magnetic soft device having a Young's modulus of less than 500 MPa in one or more parts of the device. The invention further relates to an untethered programmable and/or reprogrammable, in particular 3D, magnetic soft device having a part with Young's modulus of less than 500 MP, to a method of encoding a programmable and/or reprogrammable magnetic soft device, and to a use of a programmable and/or reprogrammable magnetic soft device.
Shape-changing active matter that can be actuated via external stimuli, such as light, temperature, humidity, pH, and acoustic, electrical and magnetic fields, holds great importance for future applications in minimally invasive medicine, implantable and wearable pieces of equipment, soft robotics, and micromachines. Magnetically responsive soft matter with programmable shape deformation is particularly promising for fast, reversible, and complex morphing of flexible structures for untethered devices.
Shape-programmable magnetic soft matter, composed of magnetic micro/nanoparticles embedded in soft polymers, is promising for the development of untethered (wireless) devices or robots with complex deformation and locomotion capabilities that can operate at small scales.
Magnetic fields generate torque on magnetic soft materials until the magnetization direction of all domains are aligned with the applied field direction. Therefore, creating a spatial distribution of magnetization directions in a magnetic soft material enables programmable shape-deformation under magnetic fields. Current three-dimensional (3D), discrete magnetic programming approaches rely on arranging physical orientation of ferromagnetic particles or alignment of superparamagnetic particles in polymer matrices during curing, which prevents reprogramming once fabricated.
It is an object of the present invention to make available a device by means of which the drawbacks of the prior art are overcome. It is yet a further object of the present invention to make available a device which can be used for a plurality of applications and uses.
This object is satisfied by a method of fabricating a programmable and/or reprogrammable magnetic soft device having a Young's modulus of less than 500 MPa in a part of the device, the method comprising the steps of:
In this connection it should be noted that temperatures close to the Curie temperature(Tc) could be used for partial magnetization. i.e. if the sample was already demagnetized it can be magnetized to half strength of the full magnetization of the material of the magnetic elements by only heating to below the Curie temperature.
In this connection a temperature close to or above the Curie temperature of said magnetic elements is selected in the range of less than 25% below the Curie temperature and to a temperature 25% above the Curie temperature, in particular to a temperature in the range of less than 10% below the Curie temperature and to a temperature 10% above the Curie temperature, most preferably to a temperature in the range of less than 5% below the Curie temperature and to a temperature 5% above the Curie temperature. Such ranges of temperatures permit a partial magnetization of the respective material, since one can achieve a partial magnetization of 25% to 100% of its max magnetization strength for a demagnetized material already at these temperatures.
The Curie temperature of e.g. Cobalt lies at 1126° C., whereas for CrO2 the Curie temperature lies at 120° C. Depending on whether the material should be partially magnetized one can heat to within 25% of the Curie temperature, i.e. to 250° C. below the Curie temperature to 250° C. above the Curie temperature for Cobalt. Having regard to CrO2 this partial magnetization state is already achievable at 110° C. of the material of the magnetic elements, in particular in the range of 110° to 115° C. which is between 5 and 10% below the Curie temperature for CrO2.
Preferably the step of heating is carried out to a temperature below the melting point of the composite respectively of the base material, preferably to a temperature 5° below the melting point of the composite respectively of the base material.
Thus, the present invention makes use of heat-assisted magnetic programming of soft materials by heating the magnetic elements present in the device to above the Curie temperature of the ferromagnetic particles and thereby being able to reorient their magnetic domains with external magnetic fields during cooling. By means of e.g. sequential heat-assisted magnetization over a magnetic soft body, shape-changing instructions in 3D can be encoded discretely and reprogrammed on demand.
Thus, the present invention makes available a versatile strategy for encoding reprogrammable shape-changing instructions into soft materials by encoding the three-dimensional magnetization profile of planar and three-dimensional structures.
The programming approach is based on heating the magnetic soft materials of the composite above the Curie temperature of the ferromagnetic particles and reorienting their magnetic domains by applying an external magnetic field during cooling.
Using heat-assisted magnetic programming, a plethora of flexible structures can be built, including a “dragonfly”, a “stickman”, magnetic leaves on a non-magnetic tree branches, and microscale “petals”, demonstrating discrete, three-dimensional, and reprogrammable magnetization of three-dimensional structures at a high spatiotemporal resolution (currently of approximately 38 μm).
Using the reprogrammable magnetization capability of the presented approach, the reconfigurable mechanical behavior of an auxetic metamaterial structure, tunable locomotion patterns of a surface walking soft robot, and adaptive grasping behavior of a soft gripper can be shown as will be discussed in the following.
Heat-assisted magnetic programming further enables high-throughput magnetic encoding via contact transfer of distributed magnetization profile from a master, which can go up to 10 samples per minute using a single master. Heat-assisted magnetic programming strategy described here establishes a rich design space and one-shot mass-manufacturing capability for development of multi-scale and reprogrammable soft systems and robots with unprecedented shape-morphing capabilities.
Making available a device that is programmable as well as reprogrammable provides magnetic devices which can be programmed to carry out specific tasks and who can be reprogrammed in the event it is found that fine tuning of parts of the device are required in order to make the device function in an improved or different manner. This was previously not possible, since the devices of the prior art were not reprogrammable.
In this connection it should be noted that a magnetic soft device is a device comprising one or more parts which have a Young's modulus of less than 500 MPa, some parts may have a Young's modulus of less than 100 MPa and some parts may even have a Young's modulus of less than 10 MPa.
In this connection it should also be noted that the average Young's modulus of the magnetic soft device or of parts of the device may be less than 500 MPa, in particular of less than 100 MPa.
This means that the device is generally more flexible than e.g., a device made purely of metal or a rigid plastic such as polyamide (PA), polytetrafluoroethylene (PTFE) and high density polyethylene (HDPE).
In this connection it should be noted that the magnetic elements can be at least one of particles, rods, cubes, wires, disks, spheroids, whiskers, irregular particles, Janus particles, and combinations of the foregoing.
The step of heating may be carried out before, after and/or during the step of shaping the composite. In this way the method can be adapted in correspondence to the materials and the different methods of producing composite materials as required.
The step of shaping and the step of heating may be carried out simultaneously. In this way the production time of the devices can be reduced effectively.
The applied magnetic field during the heating and/or cooling step may be below the coercive magnetic field of the magnetic element at its room temperature state. In this way one prevents magnetization of the undesired regions.
In this connection it should be noted that the applied magnetic field is selected to be within the range of 1 to 99.9% of the coercive magnetic field of the magnetic element at its room temperature state, in particular within the range of 5 to 50% of the coercive magnetic field of the magnetic element at its room temperature state. It should further be noted in this connection that the applied magnetic field could be at least 1 mT.
The step of shaping the composite may comprise at least one of the following steps; molding the composite in one mold of pre-defined shape and size, molding one or more parts of the composite in one or more molds of same shape and size, molding the composite in one or more molds of differing shapes and sizes, photolithographing the composite, photolithographing one or more parts of the composite, stereo lithographing the composite, stereo lithographing one or more parts of the composite, 3D printing the composite, 3D printing one or more parts of the composite, combining parts of the composite, cutting sections of material from the composite, cutting sections of material from parts of the composite and combinations of the foregoing.
In this connection it should be noted that various parts of the device can be manufactured separate from one another and then one can bond the different parts one to another. For example, one could mold the device in eight separate parts and then bond these eight parts to one another. In such cases ail eight parts could be magnetized separate from one another. Moreover, some of the parts may be made of non-magnetic materials into which no magnetic elements are introduced, harder or softer materials (in terms of young's modulus), the parts may be made of materials into which different types of magnetic elements are incorporated, the parts may comprise electrically conductive and/or non-conductive materials, piezoelectric materials, magnetocaloric materials, magnetostrictive materials, photovoltaic materials, optoelectronic materials, photomechanical materials, thermoelectric materials, biological materials with and without cultured cells and the parts may comprise combinations of the foregoing.
These parts can be integrated into the device during the molding or printing stage, or separately fabricated parts can be assembled by bonding after their respective manufacture.
In this connection it is feasible to form parts of the composite with a higher density of magnetic elements so that different parts of the composite have different magnitudes of magnetization in addition to different orientations of magnetization.
The melting temperature of the base material may be higher than the maximum temperature applied to the magnetic composite during the heating step. In this way one avoids a melting of the device on programming or reprogramming the device. For example, the melting temperature of the base material is at least 5° C., preferably at least 10° C. and most preferably at least 20° C. higher than the maximum temperature applied to the magnetic composite during the heating step.
The steps of heating and cooling the composite may be carried out a plurality of times sequentially for different regions of the composite. In this way one device can be scanned over its various regions by the same heating device and magnetic field generating device in order to impart a specific magnetization profile to each region. Preferably each region is only scanned once during the sequential scanning of the plurality of regions.
In this connection it should be noted that if a magnetic master is used then during the method of fabricating a programmable and/or reprogrammable magnetic soft device the steps of heating the composite and cooling of the composite can be carried out only once and these steps are carried out in so to say one-shot. Magnetic masters can be configured to generate arbitrary magnetization fields in neighboring sections and placed nearby the sample to be magnetized. Then heating all sections of the sample will allow magnetization. The magnetic master should possess a Curie temperature above the temperature reached in the step of heating in this process.
In this manner programmable and/or reprogrammable magnetic soft devices having a size selected in the range of 1 μm to 1 m, in particular of 20 μm to 30 cm can be produced. Such devices can be used as miniature cargo delivery devices such as drug delivery devices, or for the transport of parcels using e.g. drones or the like.
The step of magnetization may be carried out for each step of cooling for each region of the composite so that each region is provided with its own magnetization direction. In this way one device can be scanned over its various regions by the same heating device and magnetic field generating device in order to impart a specific magnetization profile to each region.
The step of heating the composite may be carried out with a tunable light source, such as a collimated laser. Tunable light sources provide pre-defined heating capabilities which can be configured to reliably and repeatedly work with the magnetic elements present in the composite forming the device. The step of heating the composite may also be carried out with ultrasound, radio frequency electric/electromagnetic radiation, and alternating magnetic fields.
The step of heating the composite may be carried out with one of a convection oven, a hot-plate and a heat-gun. Such apparatus can be reliably used to regionally or completely heat the device during programming and reprogramming of the device.
The steps of heating and cooling the composite may be carried out a single time globally for different regions of the composite, in particular wherein the step of magnetization may be carried out for a single time during cooling for each region of the composite by using a magnetic master configured to generate desired magnetization profile so that each region is provided with its own magnetization direction.
In this connection it should be noted that the step of local and sequential heating, apart from use of a laser, can also be done using a contact-based apparatus, such as a soldering iron tip or other heating devices.
The step of applying the magnetic field may be carried out with a magnetic field having a magnitude selected in the range of 1 mT to 10 T. Such magnetic field strengths enable the programming and reprogramming of the respective regions in an efficient manner.
In this connection it should be noted that the maximum applicable magnetic field depends on the coercive field of the chosen magnetic material.
In accordance with a further aspect the present invention relates to an untethered programmable and/or reprogrammable 3D magnetic soft device having one or more parts with Young's modulus of less than 500 MPa, the programmable and/or reprogrammable 3D magnetic soft device comprising a body formed of a composite material, the composite material comprising a base material and magnetic elements distributed within said base material, wherein the body has an arbitrary magnetization profile, with different regions of the body having different magnetization profiles, wherein the information encoded into the programmable and/or reprogrammable 3D magnetic soft device comprises shape changing instructions for changing a shape of at least some of the regions of the body relative to one another on application of an external field.
The advantages achievable with such a device are the provision of programmable as well as reprogrammable magnetic devices which can be programmed to carry out specific tasks and who can be reprogrammed in the event it is found that fine tuning of parts of the device are required in order to make the device function in an improved or different manner. This was previously not possible, since the device were not reprogrammable.
The base material may be selected from the group of members consisting of elastomers, thermoplastic elastomers, rubbers, duroplastics, thermoplastics, e.g., polydimethylsiloxane, aliphatic aromatic copolyester or modified polyester, or modified copolyester, polyurethane elastomer, silicone rubber, natural rubber, latex, styrene ethylene butylene styrene, butyl rubber, fluorosilicone rubber, polyester, nylon, thermoplastic polyurethane; biodegradable synthetic material, e.g., polyglycolide polylactides, poly(caprolactone), poly(dioxanone), poly(ethylene glycol)diacrylate, poly(N-isopropylacrylamide); biomaterial, e.g., gelatine, chitosan, alginate, agarose, hyaluronic acid derivatives, fibrin glue, elastin, cellulose, methylcellulose, fibronectin, collagen, silk; hydrogel; ionic gel; liquid crystal polymer, elastomer or gel; shape memory polymer; photoresist polymer, e.g., SU-8; biological protein, e.g., squid ring teeth protein; fabric material; non-magnetic metal; silicon; silica, glass; wood; carbon fibre; and derivates and combinations of the foregoing. Such materials can be used to provide a soft device in comparison to a rigid device.
The magnetic elements may be selected from the group of members consisting of chromium dioxide (CrO2), samarium-cobalt (SmCo), neodymium-Iron-Boron (NdFeB), cobalt (Co), ferrite, permalloy (NiFe), carbon steel, tungsten steel, Alnico, iron, stainless steel, nickel (Ni), iron platinum (FePt), iron oxide (Fe2O3), barium ferrite, magnetite; combinations, alloys or composites of the foregoing. Such materials can be programmed and reprogrammed by heating to or above their Curie temperature.
In accordance with a further aspect the present invention relates to a method of encoding a programmable and/or reprogrammable magnetic soft device as discussed herein, the method comprising the steps of:
The magnetic elements, such as particles, only realign themselves after the Curie temperature point has been achieved. Once the Curie temperature point has been reached and the magnetic elements have realigned themselves an external magnetic field can be used to realign, i.e. program the magnetic elements, i.e. particles, in order to have the desired new alignment, i.e. programming of the magnetic domains.
The magnetic field may also be applied during the step of heating, but in any event has to be applied during the step of cooling in order to be a able to re-orient the magnetic domains of the magnetic elements.
The steps of heating and cooling the composite may be carried out sequentially by sequentially focusing a tunable light source, i.e. a collimated laser, onto regions of said composite and cooling said regions optionally before moving on to further regions of said composite. In this way each region of the device can be programmed with its own magnetization profile.
The steps of heating and cooling the composite may be carried out globally by using a convection oven of said composite and cooling the composite with a magnetic master placed adjacent to the said composite. Such an assembly can be effectively used for batch processing of identical types of devices.
The step of reprogramming can also be achieved by using a magnetic master, e.g. comprising a jig and a magnetic field generating device, or simply a magnetic field generating device providing a magnetic field of pre-defined orientation and magnitude, and globally heating everything in one-shot. Magnetic masters can be configured to generate arbitrary magnetization fields in neighboring sections and placed nearby the sample to be magnetized. Then heating the all sections of the sample will allow magnetization. The magnetic master should possess a Curie temperature above the applied heating in this process.
The step of applying the magnetic field may be carried out with a magnetic field having a magnitude selected in the range of 1 mT to 10 T, in particular in the range of 15 mT to 3 T, in particular for each cooling cycle to orient each region of the composite with its own magnetic magnetization profile.
This magnetization profile may differ from or be the same as a magnetization profile of other regions of the composite. In this way one can program different parts of the device with different magnetization profiles in such a way that each part of the device can carry out one or more specific movement types.
According to a further aspect the present invention relates to a use of a programmable and/or reprogrammable magnetic soft device manufactured and/or to an untethered programmable and/or reprogrammable 3D magnetic soft device as at least one of a reconfigurable gripper, a programmable and/or reprogrammable acoustic wave guide, a programmable and/or reprogrammable electronic circuit, a programmable and/or reprogrammable antenna, programmable and/or reprogrammable mechanical metamaterials, programmable and/or reprogrammable wearable pieces of equipment, adaptive medical robots and combinations of the foregoing.
The present invention will be described in detail with reference to the following drawings. There is shown:
The legs 16, wings 18 and tail 19 can be formed of the same composite 12 as the body 14 or of further composites 12, differing in their material composition and/or material properties, such as hardness, stiffness, magnetization profile etc. Parts or regions of the body 14 may comprise material without magnetic elements embedded therein. The respective composite 12 having a magnetization profile which is non-zero comprises a base material and magnetic elements distributed within said base material.
The body 14, the legs 16, the wings 18, the tail 19 and any further shapes or sections 20 (see e.g.
In this connection it should be noted that the base material used to form the various parts, i.e. the body 14, the legs 16, the wings 18, the tail 19, the sections 20, the fingers 34 etc., of the programmable and/or reprogrammable 3D magnetic soft device 10 may be selected from the group of members consisting of elastomers, thermoplastic elastomers, rubbers, duroplastics, thermoplastics, e.g., polydimethylsiloxane, aliphatic aromatic copolyester or modified polyester, or modified copolyester, polyurethane elastomer, silicone rubber, natural rubber, latex, styrene ethylene butylene styrene, butyl rubber, fluorosilicone rubber, polyester, nylon, thermoplastic polyurethane; biodegradable synthetic material, e.g., polyglycolide polylactides, poly(caprolactone), poly(dioxanone), polyethylene glycol)diacrylate, poly(N-isopropylacrylamide); biomaterial, e.g., gelatine, chitosan, alginate, agarose, hyaluronic acid derivatives, fibrin glue, elastin, cellulose, methylcellulose, fibronectin, collagen, silk; hydrogel; ionic gel; liquid crystal polymer, elastomer or gel; shape memory polymer; photoresist polymer, e.g., SU-8; biological protein, e.g., squid ring teeth protein; fabric material; non-magnetic metal; silicon; silica; glass; wood; carbon fibre; and derivates and combinations of the foregoing.
In this connection it should be noted that the magnetic elements used in the various parts, i.e. the body 14, the legs 16, the wings 18, the tail 19, the sections 20, and the fingers 34 etc., of the programmable and/or reprogrammable 3D magnetic soft device 10 may be selected from the group of members consisting of chromium dioxide, samarium-cobalt, neodymium-Iron-Boron, cobalt, ferrite, permalloy, carbon steel, tungsten steel, Alnico, iron, stainless steel, nickel, iron platinum, iron oxide, barium ferrite, magnetite; combinations, alloys or composites of the foregoing.
In this connection it should further be noted that the magnetic elements may be present in the form of particles, rods, wires, disks, spheroids, whiskers, irregular particles, Janus particles, and combinations of the foregoing.
In the example of
In this connection it should be noted that the step of heating may be carried out before, after and/or during the step of shaping the composite.
In this connection it should further be noted that the step of shaping and the step of heating may be carried out simultaneously.
In this connection it should further be noted that the magnetic field applied during the heating and/or cooling step is below the coercive magnetic field of the magnetic element at its room temperature state, i.e. generally speaking between 25 to 99% below the coercive magnetic field of the magnetic element. For e.g. CrO2 the magnetic field applied during the heating and/or cooling step may be between 50 to 95% below the coercive magnetic field of the magnetic element.
The step of shaping the composite 12 may comprise at least one of the following steps; molding the composite 12 in one mold of pre-defined shape and size, molding one or more parts of the composite 12 in one or more molds of same shape and size, molding the composite 12 in one or more molds of differing shapes and sizes, 3D printing the composite 12, 3D printing one or more parts of the composite 12, combining parts of the composite 12, cutting sections of material from the composite 12, cutting sections of material from parts of the composite 12 and combinations of the foregoing.
The melting temperature of the base material may be higher than the maximum temperature applied to the magnetic composite 12 during the heating step in order to prevent a phase change of the base material.
The steps of heating and cooling the composite 12 may be carried out a plurality of times sequentially for different regions 22 of the composite 12. Alternatively, the steps of heating and cooling the composite 12 may be carried out once for the complete 3D magnetic soft device 10.
The step of magnetization may be carried out for each step of cooling for each region 22 of the composite 12 so that each region 22 is provided with its own magnetization direction. Alternatively, the step of magnetization of the composite 12 may be carried out once for the complete 3D magnetic soft device 10, if. e.g. a Jig 26 (see
As indicated in
In this connection it should be noted that an average diameter respectively width of each region 22 can be selected in the range of 1 μm to 100 mm, in particular in the range of 20 μm to 50 mm, in dependence on the heating device and e.g. its optical components used to bring about a heating of the specific region 22.
The step of applying the magnetic field may be carried out with a magnetic field having a magnitude selected in the range of 1 mT to 10 T. In the example of
Once the regions 22 are locally heated to close to and preferably above the Curie temperature of the particles via the laser 24, the magnetic elements, e.g. the particles, lose their permanent magnetization and their magnetization direction is reoriented by applying the external magnetic field during the step of cooling.
Magnetization and related fabrication capabilities of the heat-assisted magnetic programming strategy presented herein are compared with those of existing magnetic programming approaches for soft materials in the literature. Magnetization dimension indicates the degree of freedom available for magnetization, where 3D refers to the capability to magnetize in arbitrary direction. In continuous magnetization, neighboring sections cannot have sharp changes in magnetization, whereas discrete magnetization enable independent magnetization of adjacent sections. In reprogrammability, limited refers to reprogramming in directions designated during fabrication and technically challenging approaches at small scale. Actuated structure refers to the dimension of soft systems demonstrated in different approaches. In magnetic programming and fabrication, coupled refers to magnetic programming during the fabrication process and decoupled indicates magnetic programming afterwards the fabrication. In mass production, limited refers to restricted high-throughput production capability compared to lithography and roll to roll compatible methods.
The devices 10 shown in the foregoing disclose devices 10 of programmable magnetic soft matter, in which magnetic micro/nanoparticles are embedded in soft polymers. Such devices 10 are promising for the development of untethered (wireless) devices or robots with complex deformation and locomotion capabilities that can operate at small scales. Magnetic fields generate torque on magnetic soft materials until the magnetization direction of all domains are aligned with the applied field direction. Therefore, creating a spatial distribution of magnetization directions in a magnetic soft material enables programmable shape-deformation under magnetic fields. Current three-dimensional (3D), discrete magnetic programming approaches rely on arranging physical orientation of ferromagnetic particles or alignment of superparamagnetic particles in polymer matrices during curing, which prevents reprogramming once fabricated. In this work, we use heat-assisted magnetic programming of soft materials by heating above the Curie temperature of the ferromagnetic particles and reorienting their magnetic domains with external magnetic fields during cooling (
The presented magnetic soft elastomers are composed of chromium dioxide (CrO2) microparticles with an average diameter of 10 μm embedded in a polydimethylsiloxane (PDMS) elastomer, CrO2 is a ferromagnetic material (
The CrO2/PDMS magnetic soft elastomer composite sheets are prepared by curing the CrO2 particles and PDMS mixture in molds of different thicknesses, resulting in magneto-elastic films in a range of 25-200 μm thickness (
In this connection it should be noted that the devices 10 can have device thicknesses of at least some of their parts selected in the range of 25-200 μm thickness. It is also possible that the devices 10 can have device thicknesses of at least some of their parts selected in the range of 10 μm to 10 mm thickness.
A collimated near-infrared (NIR) laser with tunable power is used for heating the magnetic soft elastomers locally and precisely with controlled temperature, heating-cooling duration, and heated spot size (
Such high magnetization efficiencies indicate almost complete reorientation of magnetic domains in the desired direction, while minimizing undesired magnetization in other directions. The same materials can be then demagnetized locally or fully by heating again above the Curie temperature of CrO2 particles in the absence of a magnetic field (
To illustrate heat-assisted magnetic programming of CrO2 particle-embedded soft materials, planar magnetic soft elastomer films cut into shapes of a body with a tail and wings and a six-legged body (
Upon application of a magnetic field of 60 mT perpendicular to the plane, magnetic torques on components with different magnetization directions try to align them in the direction of the external field, resulting in 3D deformations of the structures (
In
While a ring structure with 4-segmented alternating magnetization profile generates a vertically rising profile upon magnetic actuation (
In-situ, i.e. in the lab, magnetic reprogramming of the soft systems is crucial for their optimization, multifunctional operation, and adaptation to dynamic environments. Heat-assisted magnetization strategy allows facile magnetic reprogramming of soft structures on demand.
In
In
To further highlight the importance of facile reprogramming, a 4-legged flexible robot with a specific magnetization direction assigned for each leg (
Heat-assisted magnetization can also be extended for programming complex 3D structures. In
Sequential programming of all magnetic leaves in the same direction results in actuation of all leaves synchronously in the same direction (
As an example, an adaptive soft gripper composed of 4 fingers made out of magnetic soft elastomers (
Microscale robots and machines hold significant potential for manipulation of the microscopic world with applications ranging from bioengineering to minimally invasive medicine. Magnetically programmed shape deformations can enable a new class of microsystems with advanced locomotion and manipulation capabilities. The heat-assisted magnetization approach presented herein can be scaled down to magnetically program microstructures with a spatial resolution of 38 μm (
One route for down-scaling is, focusing the NIR laser beam size below 200 μm by using a microscope objective (
Other than laser-based sequential heating and magnetization, magnetic programming can be also realized by generating the desired magnetic pattern (master) in close proximity to the magnetic soft elastomers (slave) and heating the system globally (
Heat-assisted magnetic programming strategy introduced here is inherently decoupled from the fabrication method of the magnetic soft elastomers and enables a non-invasive, i.e. non-surgical and non-destructive, means for reprogramming shape-deformations encoded into the material at high spatial resolutions. Facile and non-invasive magnetic reprogramming can enable rapid and data-based optimization of performance and behavior of soft systems, such as mechanical and optical soft metamaterials and kirigami-enabled structures. Resolution and speed of heat-assisted magnetic programming can be further scaled down using well-established magneto-optical recording techniques used in the data storage industry. Moreover, heat-assisted magnetic contact transfer shown in
Other magnetic particles, with engineered Curie temperatures low enough to sustain operation temperature of polymers, as well as other polymers or gels with softer material properties, can be employed for enhanced material performance. In the present description the focus is on a laser 24 for heating the soft magnetic elastomers, remote and selective heating can be also achieved by remote power transfer to thin receiver coils attached on the elastomers. Application of AC magnetic fields can be also used for global heating along with spatially patterned DC magnetic fields for programming the magnetic soft elastomers. Remote magnetic programming and reprogramming can enable adaptive operation of soft untethered systems in closed and confined dynamic environments. Magnetically responsive multi-scale soft systems with reprogrammable complex shape-transformation capabilities will inspire diverse applications in medical robots, wearable health monitoring pieces of equipment, and bio-inspired microrobots.
In order to prepare the composite, the following can be done:
Preparation of the composite 12 formed by magnetic elastomers:
CrO2 powder (Sigma-Aldrich, St. Louis, Mo.) was heated for 3 h at 300° C. in an oven. 22 g of baked CrO2 particles were dispersed in 250 mL of sodium bisulfite (NaHSO3) solution (from https://www.sigmaaldrich.com/catalog/product/sigald/243973?lang=de®ion=DE) in deionized (DI) water (50 g/L, Sigma-Aldrich, St. Louis, Mo.) and kept at 65° C. for 16 h while agitated occasionally. Then, the particles were washed 5 times with 1 L DI water and filtered by using a test sieve with a mesh size of 20 μm. The remaining CrO2 particles were, left in a fume hood for two days to remove any remaining water. The resulting film was scraped and crushed using a pestle and mortar to obtain final dried and stabilized CrO2 particles.
CrO2/PDMS magnetic soft elastomer composites were prepared by adding the dried and stabilized CrO2 particles into the siloxane base (Dow Corning, Midland, Mich.) at 1:2 (CrO2:Siloxane base) mass ratio and shear mixing with a Pasteur pipette for 5 min. Next, the crosslinking agent was added into the pre-polymer mixture at a crosslinking agent to mixture mass ratio of 1:10 and further shear mixed for 5 min. Then, the mixture was cast into molds composed of two tapes of desired thicknesses (25 μm to 200 μm) adhered on a flat glass substrate and cured for 4 h at 90° C. A UV laser system (LPKF ProtoLaser U3, Garbsen, Germany) was used to cut the desired geometries out of the magnetic elastomer films. Thickness of the magnetic elastomer films was measured with an optical profilometer (VK-X250, Keyence, Osaka, Japan). Elastic modulus (E) and strain of the magnetic elastomers were experimentally characterized by uniaxial tensile testing of non-heated and heated dog-bone-shaped samples at a strain rate of 0.005 s−1 (Instron 5942, Instron, Norwood, Mass.).
Once the magnetic soft devices 10 have been formed, one can start with the heat-assisted magnetic (re)programming.
Local heating of CrO2 elastomer films, i.e. of the regions 22 of the device 10, was achieved by using a power-adjustable fiber-coupled NIR laser with a collimator (808 nm, 133-457 mW, Edmund Optics, Barrington, N.J.). The temperature and the heated spot size on the magnetic elastomer films were measured using an infrared thermal camera (ETS320, Wilsonville, Oreg.) at 7 cm distance. Heating and cooling times of the magnetic soft elastomers were measured by heating the samples for 100 s. Samples were placed on an automated stage (Axidraw v3, Evil Mad Scientist, Sunnyvale, Calif.) and NdFeB magnet (20 mm diameter and 20 mm thickness, Supermagnete, Gottmadingen, Germany) that can be rotated 360° were placed underneath the magnetic soft elastomer during heating and cooling to align the magnetization direction of the CrO2 particles (
Applied magnetic field magnitude and direction were continuously monitored by using a 3D magnetic hall sensor (TLE493D-W2B6, Infineon Technologies, Munich, Germany) and adjusted according to the desired magnetization direction.
Magnetization of the magnetic soft elastomers was measured with a vibrating sample magnetometer (VSM; MicroSense, Lowell, Mass.). Circular samples with 1 mm diameter were placed on a sample holder and hysteresis loop of CrO2 obtained at external fields ranging from 1.5 T to −1.5 T (
In order to design the devices 10 and then compare the designs to the model developed computational modeling of shape deformations was performed. For this purpose, a finite element analysis is employed for predictive modeling of the shape changes under magnetic actuation (
COMSOL structural mechanics module (COMSOL, Burlington, Mass.) is linked to a custom MATLAB script (MathWorks, Natick, Mass.) via “LiveLink”. Sample geometries are divided into smaller sub-sections with pre-defined magnetization profiles and MATLAB script is used for calculation of magnetic forces and torques, while mechanical deformations are solved in COMSOL.
After every iteration, magnetic forces and torques were recalculated according to the updated magnetization direction vector for each subsection until a quasi-static equilibrium state in 3D is reached. For all simulations, experimentally measured E of 200 kPa and magnetization of 9.8 kA/m were employed. Density of the magnetic soft elastomer was calculated as 3.89 g/cm3 and Poisson's ratio is assumed 0.49.
In order to magnetically actuated the devices 10 formed a cylindrical NdFeB magnet 44 (60 mm diameter and 10 mm thick. Supermagnete, Gottmadingen, Germany) was used. The magnet 44 was guided towards the devices 10 arranged on the platform 46 in the vertical or horizontal direction for magnetic actuation (
Once a device 10 had been programmed, Magnetic (re)programming at the micron scale can be carried out. For magnetic (re)programming at the micron scale, three different approaches were employed: focused laser heating, photomask-enabled micropatterned laser heating, and contact magnetic transfer via global heating. Focused laser heating was achieved by placing a microscope objective (20×, NA 0.5, Carl Zeiss, Oberkochen, Germany) in the laser 24 beam path and decreasing the beam size below 200 microns.
For photomask-enabled micropatterned laser heating, a photomask containing microscale patterns (
For contact transfer of magnetic profiles, polyurethane NdFeB magnetic composites of different shapes were utilized. First, an SU-8 positive template of desired geometries on a silicon wafer was fabricated by photolithography and wet chemical development. For positive template fabrication, SU-8 100 (Microchem Inc., Newton, Mass.) was disposed on a silicon wafer, spin-coated at 2500 rpm for 45 s, pre-baked on a hot plate at 95° C. for 30 min, and cooled down to room temperature. Next, the photoresist coated wafer is loaded into a mask aligner (MJB4 Mask Aligner, SUSS MicroTec, Garching, Germany) with a photomask containing desired patterns to be fabricated and exposed to a UV light (365 nm, 13 mW/cm2) for 15 s. Then, photoresist-coated wafers was baked for 10 min at 95° C., cooled down to room temperature, and immersed in a chemical developer (mr-600, micro resist technology, Berlin, Germany) with slight agitation for approximately 10 minutes and later rinsed in IPA for about 2 minutes. Last, the microfabricated template was baked on a hotplate for 30 min. at 100° C. Then, silicone rubber (Mold Max 20, Smooth-On, Macungie, Pa.) was poured over the positive template, cured at room temperature for 4 h, and peeled off, resulting in a negative template. Afterwards, polyurethane pre-polymer (Smooth-Cast 310/1, Smooth-On, Macungie, Pa.) mixed with NdFeB powder (MQFP-15-7, Magnequench, Toronto, Canada) at 1:1 mass ratio was molded into the negative template and cured for 4 h at room temperature and peeled off.
Prepared polyurethane NdFeB magnets were pre-magnetized and magnetic fields generated by polyurethane NdFeB magnets were smaller than the coercivity of the magnetic soft elastomers. While modular polyurethane magnets were manually arranged in desired configurations, the ones with complex shapes were used as monolithic units. Finally, for contact magnetic transfer, the magnetic soft elastomers were placed on top of polyurethane NdFeB magnets and placed into an oven for 5 min. at 150° C. and cooled down to room temperature while in contact.
In this way a method of encoding a programmable and/or reprogrammable magnetic soft device 10 is made available, the method comprising the steps of:
The steps of heating and cooling the composite may be carried out sequentially by sequentially focusing the tunable laser 24 onto regions of said composite and cooling said regions optionally before moving on to further regions of said composite, alternatively they may be carried out only once using e.g. a master as described in the foregoing.
The step of applying the magnetic field may be carried out with a magnetic field having a magnitude selected in the range of 1 mT to 10 T, in particular for each cooling cycle to orient each region of the composite 12 with its own magnetic magnetization profile. Design of the magnetic soft structures 10 takes both the geometry and the magnetization profile into consideration for controlled shape changing. Intuitive designs can be used for simple shape changes under external magnetic fields, but more demanding and complex deformations require a predictive model. For this reason, a predictive model utilizing COMSOL and a custom MATLAB script to solve for the quasi static state of the magnetic soft structures was developed.
The predictive model is based on the following assumptions: Magnetic soft structures 10 are subjected to magnetic forces (f), magnetic torques (τ), and gravitational forces (mg), which creates stresses on the soft body 10 which deforms to minimize the total magnetic and elastic potential energy. Moreover, direction of magnetic forces and tor ques changes along with the magnetization direction during deformation, creating a distributed heterogeneous response to the external magnetic fields over the structure. To capture this heterogeneous response, each sample geometry is divided into smaller subsections labeled by ‘i’ with the pre-defined dimensions of dx, dy, dz and magnetic moment of mi (
where fτ
Validation of the model is performed by using a beam structure with dimension of 10 mm length×1 mm width×0.17 mm thickness. Beam is magnetized along its long axis and fixed at 1.25 mm from one end. Then, magnetic fields in the range of 0 to 56 mT applied vertical to the magnetization direction of the beam. Both experimental and simulation results are obtained for the same conditions (
| Number | Date | Country | Kind |
|---|---|---|---|
| 20171719.6 | Apr 2020 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/060313 | 4/21/2021 | WO |
