3D printing, also knows as Additive Manufacturing (AM), was first commercialized in 1986, and has been growing at breakneck speed since 2009 when Stratasys’ key patent expired. Currently the 3D printing machines coming on the market can be broadly classified into three categories from the material state point of view: plastic filament printers, powder (or pellet) printers, film printers and liquid photopolymer printers.
Much of the work in our laboratory revolves around the crystalline gels. We have succeeded in developing them with high toughness, high flexibility, particularly with many functions as shape memory, energy storage, freshness-retaining, water-absorbing, etc. These crystalline gels are synthesized by light-induced radical polymerization that involves light-reactive monomer having the property of curing with light of a sufficient energy to drive the reaction from liquid to solid. Note that the light-induced polymerized 3D printing uses the same principle. To open up the possibilities for broader application of our crystalline functional gels, we are interested in making them available for 3D printing. In this paper, we share the results of our latest research on the 3D printing of crystalline gels on light-induced 3D printers.
Phase change materials (PCMs) are considered one of the most reliable latent heat storage and thermoregulation materials. In this paper, a vinyl monomer is used to provide energy storage capacity and synthesize gel with phase change property. The side chain of copolymer form crystal microcell to storage/release energy through phase change. The crosslinking structure of the copolymer can protect the crystalline micro-area maintaining the phase change stable in service and improving the mechanical strength. By selecting different monomers and adjusting their ratios, we design the chemical structure and the crystallinity of gels, which in further affect their properties, such as strength, flexibility, thermal absorb/release transition temperature, transparency and the water content. Using the light-induced polymerization 3D printing techniques, we synthesize the energy storage gel and shape it on a 3D printer at the same time. By optimizing the 3D printing conditions, including layer thickness, curing time and light source, etc., the 3D printing objects are obtained.
In our group, highly transparent shape memory gels were successfully synthesized for the first time in the world. These
gels have the high strength of 3MPs modulus even with the water content of 40wt% water and high transparency. We
consider that these highly transparent and high strength gels can be applied to the optical devices such as intraocular-lenses
and optical fibers. In previous research by our group, attempts were made to manufacture the gel intraocular-lenses using
highly transparent shape memory gels. However, it was too difficult to print the intraocular-lens finely enough. Here, we
focus on a 3D printer, which can produce objects of irregular shape. 3D printers generally we fused deposition modeling
(FDM), a stereo lithography apparatus (SLA) and selective laser sintering (SLS). Because highly transparent shape memory
gels are gelled by light irradiation, we used 3D printer with stereo lithography apparatus (SLA). In this study, we found
the refractive index of highly transparent shape memory gels depend on monomer concentration, and does not depend on
the cross-linker or initiator concentration. Furthermore, the cross-linker and initiator concentration can change the gelation
progression rate. As a result, we have developed highly transparent shape memory gels, which can have a range of
refractive indexes, and we defined the optimal conditions that can be modeling in the 3D printer by changing the cross-linker
and initiator concentration. With these discoveries we were able to produce a gel intraocular-lens replica.
In the past decade, several high-strength gels have been developed, especially from Japan. These gels are expected to use
as a kind of new engineering materials in the fields of industry and medical as substitutes to polyester fibers, which are
materials of artificial blood vessels. We consider if various gel materials including such high-strength gels are 3D-printable,
many new soft and wet systems will be developed since the most intricate shape gels can be printed regardless
of the quite softness and brittleness of gels. Recently we have tried to develop an optical 3D gel printer to realize the
free-form formation of gel materials. We named this apparatus Easy Realizer of Soft and Wet Industrial Materials
(SWIM-ER). The SWIM-ER will be applied to print bespoke artificial organs, including artificial blood vessels, which
will be possibly used for both surgery trainings and actual surgery. The SWIM-ER can print one of the world strongest
gels, called Double-Network (DN) gels, by using UV irradiation through an optical fiber. Now we also are developing
another type of 3D gel printer for foods, named E-Chef. We believe these new 3D gel printers will broaden the
applications of soft-matter gels.
Gels, soft and wet materials, have unique properties such as material permeability, biocompatibility and low friction, which are hardly found in hard and dry materials. These superior characteristics of hydrogels promise to expand the medical applications. In recent years, the optical 3D gel printer named SWIM-ER (Soft and Wet Industrial – Easy Realizer) was developed by our team in order to fabricate tough gels with free form. We are aiming to create artificial blood vessel of the gel material by 3D gel printer. Artificial blood vessel is expected to be used for vascular surgery practice. The artificial blood vessel made by 3D gel printer can be create to free form on the basis of the biological data of the patient. Therefore, we believe it is possible to contribute to increasing the success rate and safety of vascular surgery by creating artificial blood vessel with 3D gel printer. The modeling method of SWIM-ER is as follow. Pregel solution is polymerized by one-point UV irradiation with optical fiber. The irradiation area is controlled by computer program, so that exact 3D free forming is realized. In this study, synthesis conditions are re-examined in order to improve the degree of freedom of fabrication. The dimensional accuracy in height direction is improved by increasing the cross linker concentration. We examined the relationship of resolution to the pitch and UV irradiation time in order to improve the modeling accuracy.
Shape Memory Gel (SMG) is one of the most interesting unique soft and wet materials. The elastic modulus of the SMG
is changed by the kinds of solvent ( S-switch SMG). Here we have an idea that these properties are possibly applied to
develop a novel gel-switch chemical semiconductor, named “Gel-con(ductor)”. The Gel-con will be made from the
combination of the different kinds of the S-switch gel membranes and is used to rectify the flux of the solvent in
chemical circuits, where the solvent molecules behave as electron and hole.
The shape memory hydrogels were synthesized and studied the physical properties. The gels were made by a hydrophilic monomer named N, N-dimethyl acrylamide (DMAAm) and a hydrophobic monomer named stearyl acrylate (SA). The water-swollen hydrogels show well transparency and shape memory property while gels absorb large water content. The properties were characterized by varying the cross-link concentration, whereas the concentration of other chemical components was remained constant. In this study, the DMAAm and the SA ratio was 3:1 to make one mole solution. It is observed that the swelling ratio slightly depends on the cross-link concentration at certain amount. However, mechanical properties strongly depend on the cross-link concentration. Thermal properties were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC spactra of dried samples exhibits complex crystalline nature, while swollen samples show homogeneous crystallinity. A well thermal stability is observed regard less of cross-link concentration.
Recently we successfully developed novel transparent shape memory gels. The SMG memorize their original shapes during the gelation process. In the room temperature, the SMG are elastic and show plasticity (yielding) under deformation. However when heated above about 50˚C, the SMG induce hard-to-soft transition and go back to their original shapes automatically. We focus on new soft and wet systems made of the SMG by 3-D printing technology.
The 3D printing technology, causing much attention from the beginning of 2013, will be possibly an alternative method
to fabricate the biological soft tissues. Recently our group of Yamagata University has developed the world-first 3D Gel
Printer to fabricate the complicated gel-materials with high-strength and biocompatibility. However, there are no 3D
scanners that collect the data from the internal structure of complicated gel objects such as eye lens. It means that a new
system for scanning the internal structure is needed now. In this study, firstly, we have tried to investigate the gel
network of synthetic and biological gel with scanning microscopic light scattering (SMILS). We calculated the
Young’s modulus of synthetic gels with the SMILS and with the tensile test, and precisely compared the results between
them. The temperature dependences of the inside structure and the transparency are observed in the pig crystalline lens.
The quantitative analysis indicates the importance of the internal structure of real object. Secondary, we show the new
system named Gel-scanner that can provide the 2-dimentional data of the internal structure. From examining our findings,
the scanning of internal structure will enable us to expect physical properties of the real object. We convince that the gelscanner
will play major role in the various fields.
Eyeball plays a quite important role in acquiring the vision. Vitreous body occupies the largest part of the eyeball and consists of biological, elastic, transparent, gel materials. In the present medical examination, the non-destructive examination method of the vitreous body has not been well established. Here, we focus on an application of dynamic light scattering to this topic. We tried to apply our lab-made apparatus, scanning microscopic light scattering (SMILS), which was specially designed for observing the nanometer-scale network structure in gel materials. In order to examine the vitreous body using SMILS method, a commercial apparatus, nano Partica (Horiba Co. Ltd.) was also customized. We analyzed vitreous body using both the SMILS and the customized nano Partica. We successfully examined the vitreous bodies of healthy pigs in non-destructive way.
In recent years, aging is progressing in Japan. Elderly people can't swallow the food well. So, the need of soft food is increasing greatly with the aging of the population. There are so few satisfying foods for the elderly to enjoy a meal. An equipment of printing soft food gives the elderly a big dream and is promising. In this study, we aim at developing a 3D edible gel printer in order to make soft food for the elderly. We made a prototype of the 3D edible gel printer. The printer consists of syringe pump and dispenser. The syringe pump extrudes the solution. The dispenser allows to model threedimensional objects. We use agar solution as the ink to carry out the printing. Agar’s gelation deeply depends on temperature. Therefore temperature control of the solution is important to mold optimal shapes because the physical crosslinking network of agar’s solution is instable. We succeeded in making the gels and plate-shape gel using the 3D edible gel printer. Further more, in order to increase the gelation speed agar’s solution, we changed the dispenser and the printing test is being done now. 4 kinds of soft food prepared from agar and gelatin were printed by the 3D edible gel printer. The compression tests of the printed soft food samples were done and their hardness is measured because the hardness is one of very important factors which influence the food texture greatly. In the future, the viscosity of the agar solution or other food ink should be adjusted to suitable for printing.
The frictional behavior of the four kinds of high functional gels, which are double network (DN) gels, particle-double network gels (P-DN), shape memory gels (SMG), LA-shape memory gels (LA-SMG) and was studied. The velocity dependence looks similar for both the DN gels and the SMG, however the details of the dependence are different. The coefficient of the DN gels is smaller than that of the SMGs. The coefficient decreases as the normal force increases. This normal force dependence was observed for the DN gels previously, however for the first time for the SMGs. The velocity dependence looks similar for both the DN gels and the SMG, however the details of the dependence are different. The coefficient of the DN gels is smaller than that of the SMGs. The difference of the dependences is possibly related to the different softness by the temperature change of the gels. The temperature dependence of the coefficient of friction in LA-SMG was observed. Increase of the perpendicular load and the surface softness were influenced by coefficient of friction increase. In addition, the frictional coefficient of P-DN that different particle size was measured for the first time. The difference of the friction behavior of LA-SMG by the particle size was clear. Therefore, we show frictional coefficient of various high functional gels.
In 2003, the most effective but simple way was proposed to synthesize double network gels, whose compression fracture stress reached about 30MPa, while that of common gels were several tens kPa. Our group has focused on PAMPSPDMAAm DN gel, because it possibly has both biocompatibility and permeability, which are good for developing artificial articular cartilage and artificial blood vessel. It is also possibly used for rapid additive manufacturing with 3D gel printer. Here, we develop a novel apparatus of the ball on disk method to observe the surface friction of the DN gels. We hope to apply this apparatus for various studies about the tribological behavior of the gels, especially about the effect of external electric field on the gel friction.
Several synthesis methods have been devised to improve the mechanical strength of gels extraordinarily after 2001. It was a trigger to use gels as a new industrial materials, since gels had been considered difficult for industrial materials because of their weakness. In a recent study, we had designed transparency shape memory gels for the first time. Shape memory gels are one of the gels with characteristic networks, and have a shape memory function by copolymerizing an acrylic monomer with a hydrophobic long alkyl side group. It is well known that the mechanical properties such as Young’s modulus and friction coefficient of shape memory gels depend on temperature. In this study, we tried to change the frictional properties of shape memory gels by laser surface texturing. Two types of processed surface were prepared. The hexagonal close packed pattern and the square close packed pattern of dimples were formed on the surface of gel sheets with CO2 laser. The intensity of laser was optimized to avoid cutting gels. The friction coefficients of unprocessed gels and two types of processed gels were measured by ball-on-disk method. Measurement partner material was sodalime glass ball. The measurement results of processed gels showed clear differences from unprocessed gels. The friction coefficients of processed gels were larger than unprocessed gels. However, these results specifically showed the velocity dependence. It indicates that surface texturing enable to control the friction coefficient of polymer gels by surface pattern and velocity.
Gels are a new material having three-dimensional network structures of macromolecules. They possess excellent
properties as swellability, high permeability and biocompatibility, and have been applied in various fields of daily life,
food, medicine, architecture, and chemistry. In this study, we tried to prepare new multi-functional and high-strength
gels by using Meso-Decoration (Meso-Deco), one new method of structure design at intermediate mesoscale.
High-performance rigid-rod aromatic polymorphic crystals, and the functional groups of thermoreversible Diels-Alder
reaction were introduced into soft gels as crosslinkable pendent chains. The functionalization and strengthening of gels
can be realized by meso-decorating the gels’ structure using high-performance polymorphic crystals and
thermoreversible pendent chains. New gels with good mechanical properties, novel optical properties and thermal
properties are expected to be developed.
Gels are soft and wet materials that differ from hard and dry materials like metals, plastics and ceramics. These have some unique characteristic such as low frictional properties, high water content and materials permeability. A decade earlier, DN gels having a mechanical strength of 30MPa of the maximum breaking stress in compression was developed and it is a prospective material as the biomaterial of the human body. Indeed it frictional coefficient and mechanical strength are comparable to our cartilages. In this study, we focus on the dynamic frictional interface of hydrogels and aim to develop a new apparatus with a polarization microscope for observation. The dynamical interface is observed by the friction of gel and glass with hudroxypropylcellulose (HPC) polymer solution sandwiching. At the beginning, we rubbed hydrogel and glass with HPC solution sandwiching on stage of polarization microscope. Second step, we designed a new system which combined microscope with friction measuring machine. The comparison between direct observation with this instrument and measurement of friction coefficient will become a foothold to elucidate distinctive frictional phenomena that can be seen in soft and wet materials.
Gels have unique properties such as low frictional properties, permeability and biocompatibility due to their high water content. When the gels are developed as industrial materials, we need to establish a method of quantitative analysis derived from the internal structure and the mechanical properties of these gels. However, the static inhomogeneities in gels prevent us to observe the structure of gels by scattering method. To solve this problem, we have developed scanning microscopic light scattering (SMILS) originally. In this study, firstly, the internal structure of the dry-synthesis gels are precisely examined experimentally by the scattering microscopic light scattering and theoretically by the tensile test. By comparing the two quantities, the dense network structure makes the mechanical properties of gels smaller than theoretical estimation. Secondary, we show the new system named Visual-SMILS that can provide the 2-dimentional data of the distribution. Based on our findings, the strength of the gels can be controlled and expected. We believe the Visual-SMILS system will promote research significantly in the field of gels.
In the present study, we characterize internal structure of shape memory gel with Scanning Microscopic Light Scattering (SMILS), which is typically a dynamic light scattering system developed in our laboratory. It is specialized for analyzing the microscopic structure of gels having scanning as well as multi-angle facility. Transparent shape memory gel is prepared by solvent free technique using two monomers. The ratio of N,N-dimethyl acrylamide (DMAAm) and Stearyl acrylate (SA) is 3:1 in molar ratio. The mesh size of internal network structure of shape memory gel is determined by the SMILS and it is found in several nm in size. The diffusion coefficient is calculated and the critical temperature is observed where gel is changed its phase.
The polyelectrolyte of high-strength gels was made to improve the mechanical properties in our previous study. In the field of electronic devices, the demand of polymer electrodes, which have high conductivity, high flexibility and transparence, is increasing. In this study, we attempt to make a transparent polymer electrode by laminating polymer thin film and silver nanowire (AgNW). High transparenct poly(methyl methacrylate) (PMMA) film, which is produced by using solvent cast method is used. AgNW is prepared by reacting Silver chloride (AgCl) with Silver nitrate (AgNO3) based on previous study. The AgNWs taking on different shapes were obtained. Fibrous AgNWs are formed by using high molecular weight polyvinylpyrrolidone (PVP). These results showed a possibility of developing the polymer electrode with high conductivity, high flexibility and transparence.
In the past decade, several high-strength gels have been developed. These gels are expected to use as a kind of new engineering materials in the fields of industry and medical as substitutes to polyester fibers, which are materials of artificial blood vessels. The gels have both low surface friction and well permeability due to a large amount of water absorbed in the gels, which are superiority of the gels compering to the polyester fibers. It is, however, difficult for gels to be forked structure or cavity structure by using cutting or mold. Consequently, it is necessary to develop the additive manufacturing device to synthesize and mode freely gels at the same time. Here we try to develop an optical 3D gel printer that enables gels to be shaped precisely and freely. For the free forming of high-strength gels, the 1st gels are ground to particles and mixed with 2nd pregel solution, and the mixed solution is gelled by the irradiation of UV laser beam through an optical fiber. The use of the optical fiber makes one-point UV irradiation possible. Since the optical fiber is controlled by 3D-CAD, the precise and free molding in XYZ directions is easily realized. We successfully synthesized tough gels using the gel printer.
Gels are a new material having three-dimensional network structures of macromolecules. They possess excellent properties as swellability, high permeability and biocompatibility, and have been applied in various fields of daily life, food, medicine, architecture, and chemistry. In this study, we tried to prepare new multi-functional and high-strength gels by using Meso-Decoration (Meso-Deco), one new method of structure design at intermediate mesoscale. High-performance rigid-rod aromatic polymorphic crystals, and the functional groups of thermoreversible Diels-Alder reaction were introduced into soft gels as crosslinkable pendent chains. The functionalization and strengthening of gels can be realized by meso-decorating the gels’ structure using high-performance polymorphic crystals and thermoreversible pendent chains. New gels with good mechanical properties, novel optical properties and thermal properties are expected to be developed.
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