Photo-crosslinkable Resin Research Articles

Degradable 4D-printed hydration-driven actuators from a single family of amphiphilic star-shaped copolymers

Actuators are largely used in biomedical applications in the presence of sensitive live cells or biomolecules, which makes actuators triggered by water uptake highly appealing. Dual-material printing and hydration driven expansion is a method of choice to produce such actuators, but mostly rely of non-degradable polymers or on the combination of polymers of different nature that may lead to interface incompatibilities. To overcome this challenge, we report here on two photocrosslinkable resins based on a single family of degradable hydrophilic or hydrophobic star-shaped poly(ethylene glycol)-poly(lactide) copolymers. The two materials are first printed individually and characterized to ensure that their properties enable the printing of dual material objects by stereolithographic digital-light processing. Dual-materials actuators are then printed by sequential switching of the hydrophobic and hydrophilic resin baths. Objects of simple and complex shapes are easily obtained and exhibit rapid actuation (<60 s) upon hydration. The swelling-induced shape changes are accurately reproduced by numerical modeling of the printed geometries using the obtained material swelling properties. This set of results offers new perspectives to develop 4D-printed temporary medical devices.

Unleashing the potential of waste: A supercharged high-performance 3D printing resin from discarded polylactic acid

In additive manufacturing/3D printing, the limitation no longer lies in people’s imagination but in the materials that one can print with. While the additive manufacturing process can virtually create any geometry, available applications are often limited by factors like parts’ mechanical strength, glass transition temperature, and heat deflection temperature. These factors are especially critical for polymer-based printing. Here we introduce a simple formulation derived from the aminolysis of polylactic acid (PLA) plastic waste, namely the N-lactoyl ethanolamine (N-LEA). The N-LEA is next reacted with excess methacrylic anhydride, forming a photo-crosslinkable resin for MSLA 3D printing. The resulting 3D printed part has a set of impressive properties that is unrivaled amongst engineering grade 3D printing resins on the market and research literature. The 3D printed part has an ultrahigh tensile strength of 131.7 MPa, glass transition at ∼190 °C, and heat deflection temperature at 162.6 °C. This work demonstrates a true upcycling approach for turning PLA waste into a value-added product in a simple and efficient manner while also expanding the high-performance material portfolio available for photocuring additive manufacturing.

Bioactive photocrosslinkable resin solely based on refined decellularized small intestine submucosa for vat photopolymerization of in vitro tissue mimics

Three-dimensionally (3D) printed tissue mimics are unique in vitro platforms for studying human pathophysiology in a more physiologically relevant manner compared to oversimplified 2D cell cultures and complex animal models. However, their 3D printing requires an availability of materials that at the same time show a high level of biomimicry and also have a suitable viscosity profile and crosslinking kinetics for the desired printing technique. We developed a new biomimetic material for vat photopolymerization by solubilizing and functionalizing porcine small intestine submucosa (dSIS) into photocrosslinkable dSIS methacryloyl (dSIS-MA) and by subsequently formulating it into a bioactive 3D printing resin. The concentration of 1.5 wt% of dSIS-MA yielded desired viscosity and photocrosslinking kinetics, and the 3D printing of the resin resulted in fully transparent and highly swelling dSIS-MA hydrogels with a stiffness resembling native intestinal tissue. The new dSIS-MA resin was successfully 3D printed into acellular intestine-mimicking scaffolds that desirably guided the seeded human intestinal cells to grow along the 3D villi mimics. Human small intestinal organoid-derived undifferentiated primary cells grew to confluency on the dSIS-MA hydrogels and formed continuous tight junctions, thereby demonstrating the suitability of the 3D printing material for growing intestinal epithelium mimics. Furthermore, a small fraction of the human primary intestinal cells produced mucin 5AC, demonstrating early differentiation of these cells on the dSIS-MA hydrogels. The excellent cell compatibility of the dSIS-MA material combined with its high printability and biomimicry indicated that this new resin can be a great help in modelling and reproducing native tissue architectures where enhanced physiological relevancy is desired.

Projection printing of scaffolds with shape recovery capacity and simultaneously improved stiffness and toughness using an ultra-fast-curing poly(propylene fumarate)/hyperbranched additive resin

Projection micro-stereolithography (PμSL) is an effective technique to rapidly fabricate porous scaffolds with complex structures of photo-crosslinkable polymer resins, which normally contain a reactive diluent and a photo-initiator. In previous reports on 3D printing of poly(propylene fumarate) (PPF) scaffolds, diethyl fumarate (DEF) was unavoidably used as a reactive diluent in the PPF resin. Here we present a photo-crosslinkable resin composed of PPF and hyperbranched polyester acrylate (HPA), which has multiple carbon-carbon double bonds to participate in photo-crosslinking as a reactive diluent, and PμSL 3D fabrication of tissue-engineering scaffolds using this resin. The structure and viscoelastic behavior of uncrosslinked PPF/HPA, and the gel fraction, thermal and mechanical properties of photo-crosslinked PPF/HPA samples have been investigated, in comparison with those of PPF/DEF. Blending HPA with PPF was found to decrease the viscosity of PPF and to expedite the photo-crosslinking process, both of which are important in formation of PPF networks. In addition, HPA can effectively enhance the stiffness and toughness of the fabricated network simultaneously. In PμSL 3D fabrication, the cure depth (C d ) experiments proved that the PPF/HPA resin had an extremely low critical energy (E c ) of 2.1 mJ/cm 2 , leading to ultra-fast curing when exposed to ultraviolet (UV) light. Our rapid prototyping characteristics are evident under the premise of ensuring high precision. For the PPF/HPA resin, the exposure time per layer was only 0.1–2 s, which at least doubled the printing speed compared with the other 3D fabrication techniques. At high printing resolution of 50 µm, an ultra-fast printing speed of 18 cm/h was achieved by using the PPF/HPA resin, while the value for the PPF/DEF resin was only 3.6 cm/h. Benefited from the better crosslinked networks, the fabricated PPF/HPA scaffolds exhibited a lower shrinkage, higher stiffness and toughness, and better recovery capacity than their PPF/DEF counterparts, indicating their 4D printing characteristics.

Selective Fluorination of the Surface of Polymeric Materials after Stereolithography 3D Printing.

With the microfluidics community embracing 3D resin printing as a rapid fabrication method, controlling surface chemistry has emerged as a new challenge. Fluorination of 3D-printed surfaces is highly desirable in many applications due to chemical inertness, low friction coefficients, antifouling properties, and the potential for selective hydrophobic patterning. Despite sporadic reports, silanization methods have not been optimized for covalent bonding with polymeric resins. As a case study, we tested the silanization of a commercially available (meth)acrylate-based resin (BV-007A) with a fluoroalkyl trichlorosilane. Interestingly, plasma oxidation was unnecessary for silanization of this resin and indeed was ineffective. Solvent-based deposition in a fluorinated oil (FC-40) generated significantly higher contact angles than deposition in ethanol or gas-phase deposition, yielding hydrophobic surfaces with contact angle >110° under optimized conditions. Attenuated total reflectance-Fourier transform infrared spectroscopy indicated that the increase in the contact angle correlated with consumption of a carbonyl moiety, suggesting covalent bonding of silane without plasma oxidation. Consistent with a covalent bond, silanization was resistant to mechanical damage and hydrolysis in methanol and was stable over long-term storage. When tested on a suite of photocrosslinkable resins, this silanization protocol generated highly hydrophobic surfaces (contact angle > 110°) on three resins and moderate hydrophobicity (90-100°) on the remainder. Selective patterning of hydrophobic regions in an open 3D-printed microchannel was possible in combination with simple masking techniques. Thus, this facile fluorination strategy is expected to be applicable for resin-printed materials in a variety of contexts including micropatterning and multiphase microfluidics.

Synthesis of an UV-Curable Divinyl-Fumarate Poly-ε-Caprolactone for Stereolithography Applications.

The limited number of commercially available photocrosslinkable resins for stereolithography has often been considered the main limitation of this technique. In this manuscript, a photocrosslinkable poly-ε-caprolactone (PCL) has been synthesized by a two-step method starting from ring opening polymerization (ROP) of ε-caprolactone. Hydroxyethyl vinyl ether (HEVE) has been used both as the initiator of ROP and as photo-curable functional group to obtain a vinyl poly-ε-caprolactone (VPCL). The following reaction of VPCL with fumaryl chloride (FuCl) results in a divinyl-fumarate polycaprolactone (VPCLF). Moreover, a catalyst based on Al, instead of the most popular Tin(II) 2-ethylhexanoate, has been employed to reduce the cytotoxicity of the material. VPCLF has been successfully used, in combination with N-vinyl-pyrrolidone (NVP), to fabricate 3D porous scaffolds by micro-stereolithography (μ-SL) with mathematically defined architectures.

Optimization of Photocrosslinkable Resin Components and 3D Printing Process Parameters

The role of 3D printing in the biomedical field is growing. In this context, photocrosslink-based 3Dprinting procedures for resorbable polymers stand out. Despite much work, more studies are needed on photocuring stereochemistry, new resin additives, new polymers and resin components. As par tof these studies it is vital to present the logic used to optimize the amount of each resin constituent and how that effects printing process parameters.The present manuscript aims to analyze the effects the poly(propylene fumarate) (PPF) resin components and their effect on 3D printing process parameters. Diethyl fumarate (DEF),bisacylphosphine oxide (BAPO), Irgacure 784, 2-hydroxy-4-methoxybenzophenone (HMB) and,for the first time, in biomedical 3D printing, ethyl acetate (EA), were the resin components under investigation in this study. Regarding printing process parameters, Exposure Time, Voxel Depth,and Overcuring Depth were the parameters studied. Taguchi Design of Experiments was used tosearch for the effect of varying these resin constituent concentrations and 3D printing parameters onthe curing behavior of 3D printable PPF resins.Our results indicate that resins with higher polymer cross-link density, especially those with a higher content of PPF, are able to be printed at higher voxel depth and with greater success (i.e.,high yield). High voxel depth, as long as it does not sacrifice required resolution, is desirable as it speeds printing. Nevertheless, the overall process is governed by the correct setup of the voxeldepth in relation to overcuring depth. In regards to resin biocompatibility, it was observed that EAis more effective than DEF, the material we had previously relied on. Our preliminary in vitrocytotoxicity tests indicate that the use of EA does not reduce scaffold biocompatibility as measured by standard cytotoxicity testing (i.e., ISO 10993-5). We demonstrate a workpath for resin constituent concentration optimization through thin film tests and photocrosslinkable process optimization.

A drug eluting poly(trimethylene carbonate)/poly(lactic acid)-reinforced nanocomposite for the functional delivery of osteogenic molecules.

BackgroundPoly(trimethylene carbonate) (PTMC) has wide biomedical applications in the field of tissue engineering, due to its biocompatibility and biodegradability features. Its common manufacturing involves photofabrication, such as stereolithography (SLA), which allows the fabrication of complex and controlled structures. Despite the great potential of SLA-fabricated scaffolds, very few examples of PTMC-based drug delivery systems fabricated using photo-fabrication can be found ascribed to light-triggered therapeutics instability, degradation, side reaction, binding to the macromers, etc. These concerns severely restrict the development of SLA-fabricated PTMC structures for drug delivery purposes.MethodsIn this context, we propose here, as a proof of concept, to load a drug model (dexamethasone) into electrospun fibers of poly(lactic acid), and then to integrate these bioactive fibers into the photo-crosslinkable resin of PTMC to produce hybrid films. The hybrid films’ properties and drug release profile were characterized; its biological activity was investigated via bone marrow mesenchymal stem cells culture and differentiation assays.ResultsThe polymer/polymer hybrids exhibit improved properties compared with PTMC-only films, in terms of mechanical performance and drug protection from UV denaturation. We further validated that the dexamethasone preserved its biological activity even after photoreaction within the PTMC/poly(lactic acid) hybrid structures by investigating bone marrow mesenchymal stem cells proliferation and osteogenic differentiation.ConclusionThis study demonstrates the potential of polymer–polymer scaffolds to simultaneously reinforce the mechanical properties of soft matrices and to load sensitive drugs in scaffolds that can be fabricated via additive manufacturing.

Surface functionalization of acrylic based photocrosslinkable resin for 3D printing applications

The limited number of resins, available for stereolithography applications, is one of the key drivers in research applied to rapid prototyping. In this work an acrylic photocrosslinkable resin based on methyl methacrylate (MMA), butyl methacrylate (BMA) and poly(ethylene glycol) dimethacrylate (PEGDA) was developed with different composition and characterized in terms of mechanical, thermal and biological behaviour. Two different systems have been developed using different amount of reagent. The influence of every components have been evaluated on the final characteristic of the resin in order to optimize the final composition for applications in bone tissue engineering. The crosslinked materials showed good mechanical properties and thermal stabilities and moreover cytotoxicity test confirms good biocompatibility with no cytotoxic effect on cells metabolism. Moreover two different treatments have been proposed, using fetal bovine serum (FBS) and methanol (MeOH), in order to improve cell recognition of the surfaces. Samples threatened with MeOH allow cell adhesion and survival, promoting spreading, elongation and fusion of C2C12 muscle myoblast cells.

蛍光センサを用いた培養環境の酸素分布モニタリング

This paper reports the measurement of oxygen distribution inside spheroid using fluorescence microbead sensor. Measurement of oxygen distribution inside the tissue such as spheroid is one of the most important issues for creating high-quality tissue and organ. Fluorescence measurement is suitable since the non-contact measurement is possible. This sensor consists of hydrophilic and biocompatible photo-crosslinkable resin, polyethylene glycol diacrylate, oxygen-sensitive fluorescence indicators, Ru(bpy)3]Cl2 and STELLA. Ratio measurement of fluorescence microbead sensor using two indicators for absolute and robust measurement of oxygen against photo-bleaching. The fluorescence microbead sensor was calibrated with oxygen and inserted into the spheroid. A demonstration of measurement of the time-course variation of oxygen concentration inside the spheroid was performed.

Preparation of a designed poly(trimethylene carbonate) microvascular network by stereolithography.

Designed flexible and elastic network structures are prepared by stereolithography using a photo-crosslinkable resin based on a poly(trimethylene carbonate) (PTMC) macromer with a molecular weight of 3150 g/mol. Physical properties and the compatibility with human umbilical vein endothelial cells (HUVECs) are evaluated. The hydrophobic networks are found to be flexible and elastic, with an E modulus of 7.9 ± 0.1 MPa, a tensile strength of 3.5 ± 0.1 MPa and an elongation at break of 76.7 ± 0.7%. HUVECs attach and proliferate well on the surfaces of the built structures. A three-dimensional microvascular network is designed to serve as a perfusable scaffold for tissue engineering. In the design, 5 generations of open channels each branch into 4 smaller channels yielding a microvascular region with a high density of capillaries. The overall cross-sectional area through which medium or blood can be perfused remains constant. These structures would ensure efficient nourishment of cells in a large volume of tissue. Built by stereolithography using the PTMC resin, the smallest channels of these structures have square cross-sectional areas, with inner widths of approximately 224 μm and wall thicknesses of approximately 152 μm. The channels are open, allowing water to perfuse the scaffold at 0.279 ± 0.006 mL/s at 80 mmHg and 0.335 ± 0.009 mL/s at 120 mmHg.

Improved Laser Manipulation for On-chip Fabricated Microstructures Based on Solution Replacement and Its Application in Single Cell Analysis

In this paper, we present the fabrication and assembly of microstructures inside a microfluidic device based on a photocrosslinkable resin and optical tweezers. We also report a method of solution replacement inside the microfluidic channel in order to improve the manipulation performance and apply the assembled microstructures for single cell cultivation. By the illumination of patterned ultraviolet (UV) through a microscope, microstructures of arbitrary shape were fabricated by the photocrosslinkable resin inside a microfluidic channel. Based on the microfluidic channel with both glass and polydimethylsiloxane (PDMS) surfaces, immovable and movable microstructures were fabricated and manipulated. The microstructures were fabricated at the desired places and manipulated by the optical tweezers. A rotational microstructure including a microgear and a rotation axis was assembled and rotated in demonstrating this technique. The improved laser manipulation of microstructures was achieved based on the on-chip solution replacement method. The manipulation speed of the microstructures increased when the viscosity of the solvent decreased. The movement efficiency of the fabricated microstructures inside the lower viscosity solvent was evaluated and compared with those microstructures inside the former high viscosity solvent. A novel cell cage was fabricated and the cultivation of a single yeast cell ( w303) was demonstrated in the cell cage, inside the microfluidic device.

Fabrication of Microstructures Embedding Controllable Particles inside Dielectrophoretic Microfluidic Devices

This paper presents a method of particle manipulation by dielectrophoresis (DEP) and immobilization using photo-crosslinkable resin inside microfluidic devices. High speed particle manipulation, including patterning and concentration control by DEP was demonstrated. Immovable and movable microstructures embedding particles were fabricated on-chip. Several microelectrodes were fabricated using Indium Tin Oxides (ITO) and Cr/Au. The two kinds of DEP responses of yeast cells (W303) and other particles were experimentally confirmed. Based on negative DEP phenomenon, cell traps generated by microelectrodes were demonstrated. Position control, transportation and patterning of cells were performed with cell traps. The on-chip fabrication of arbitrary shapes of microstructures based on Poly(ethylene glycol) diacrylate (PEGDA) was reported. With cell patterning by DEP and immobilization using on-chip fabrication, microstructures embedding line patterned cells were fabricated inside microfluidic channels. A novel m...

Ethanol production by repeated-batch simultaneous saccharification and fermentation (SSF) of alkali-treated rice straw using immobilized Saccharomyces cerevisiae cells

Repeated-batch simultaneous saccharification and fermentation (SSF) of alkali-treated rice straw using immobilized yeast was developed to produce ethanol. Saccharomyces cerevisiae cells were immobilized by entrapping in photocrosslinkable resin beads, and we evaluated the possibility of its reuse and ethanol production ability. In batch SSF of 20% (w/w) rice straw, the ethanol yields based on the glucan content of the immobilized cells were slightly low (76.9% of the theoretical yield) compared to free cells (85.2% of the theoretical yield). In repeated-batch SSF of 20% (w/w) rice straw, stable ethanol production of approx. 38gL−1 and an ethanol yield of 84.7% were obtained. The immobilizing carrier could be reused without disintegration or any negative effect on ethanol production ability.

Photoprocessible Hydrogel Microsensor for Local Environment Measurement on a Microfluidic Chip

On-chip environment measurement is an important technique for control ambient conditions of cells and monitoring cell activities. However, integration of many sensors in the chip has difficulties such as position and interconnection of sensors. We developed hydrogel microsensors made of photocrosslinkable resin impregnating with indicators for on-chip measurement. This sensor can be used for both area measurement and 3-D sensing by shaping the hydrogel by UV ray patterning. This sensor requires no interconnections since environmental information is detected as optical information such as brightness and color. The YCrCb color space was suitable than the HSV color space in terms of the linearity of the color calibration (H: hue, S: saturation, V: values (brightness). Y : brightness, Cr: color difference of red, Cb: color difference of blue). In this paper, we demonstrated measurement of pH distribution in the microchannel using a color indicator and measurement of oxygen consumption of brown fat cell (BFC) using a fluorescent oxygen indicator. On pH measurement, we used YCrCb color space because Cr and Cb represented monotone variation and robust against brightness fluctuation. The hydrogel was patterned by photolithography into the stripe shape and modified with the indicator. Color change was detected by a color charge-coupled device (CCD). On oxygen measurement, we formed the hydrogel impregnating with the fluorescent indicator into microsphere. Fluorescence change was detected by the spectrophotometer. We succeeded in measuring local pH distribution and oxygen consumption of BFC inside the microfluidic chip.

Optical Adhesion Control of Hydrogel Microtools for On-Demand Immobilization and Measurement of Cells on a Microfluidic Chip

Optical adhesion control of hydrogel microtools, made of hydrophilic photo-crosslinkable resin, was developed for on-demand immobilization and measurement of cells on a microfluidic chip. The hydrogel microtool was manipulated by optical tweezers and modified by spiropyran chromospheres, which was a photochromic polymer. We developed on-demand control of uni/bidirectional adhesiveness of the microtool by control of electrolyte concentration in a solution. Photo illumination controls the adhesiveness of the microtools. In case of unidirectional control of adhesiveness, the microtools adhere to glass, other microtools and cells by illumination of ultraviolet (UV) light. Spiropyran chromospheres were used for bidirectional control of adhesiveness to cell. In case of bidirectional control of adhesiveness, the microtools adhere to cells by UV illumination. On the other hand, the microtool detaches from the adhered cells by visible (VIS) light illumination. Electrolyte concentration in the solution controlled these adhesiveness controls. Adherence of the microtool was enough to keep its position on a microfluidic chip. We applied these immobilization methods to measure the local conditions around cells by modifying the microtool with a pH indicator, bromothymol blue (BTB). Local measurements of the ambient pH value of yeast cells were performed by immobilizing the cell on the surface of the pH sensing microtool. Moreover, culture monitoring of a single yeast cell was demonstrated by immobilization to the microtool.

2A2-A01 オンチップ細胞計測に関する研究 : その1:マイクロ流体チップ内での単一ウイルス操作

We developed manipulation of single virus using optical tweezers and dielectrophoretic force in a microfluidic chip. We used a microfluidic chip made of poly (dimethylsiloxane) (PDMS). The chip has independent virus chamber and cell chamber to make quantitative analysis of the functions of influenza virus before and after infection to a cell. Dielectrophoretic force integrated inside virus chamber concentrates the virus. Concentrated viruses flow to the part for sample selection. The virus was transported to the cell chamber using optical tweezers. After virus transport, these chambers were isolated by photocrosslinkable resin. In this paper, we demonstrated concentration of influenza virus, manipulation of the single virus to transport the cell chamber, contact to a target cell in the chip and isolation of chambers in the microfluidic chip.

Fermentative lactic acid production with a metabolically engineered yeast immobilized in photo-crosslinkable resins

In this study, the immobilization technique involving photo-crosslinkable resin gels was used for lactic acid production. Saccharomyces cerevisiae OC-2T T165R , a metabolically engineered yeast that produces optically pure l(+)-lactic acid, was immobilized in hydrophilic photo-crosslinked resin gels as a biocatalyst. Three resin gels, TEP 1, TEP 2 and TEP 3, were examined and all of them showed high performance as to lactic acid production. Resin gel TEP 1, which exhibited the highest productivity among the resin gels was used for 15 consecutive batch fermentations without decreases in productivity and mechanical deformation, indicating that it was a suitable carrier for long-term lactic acid fermentation. Moreover, the use of the immobilization technique can improve the productivity of the metabolically engineered yeast in the fermentation with or without extraction, showing promise for using the immobilized engineered yeast for lactic acid production.

Characteristics of phenol degradation by immobilized activated sludge

The effects of various factors involved in phenol degradation through an immobilized activated sludge with a photo-crosslinked resin were investigated. The immobilized activated sludge showed a higher relative activity of phenol degradation across a broader range of pH than free activated sludge. A higher rate of phenol degradation was observed when the bead size was smaller. The phenol degradation in the free activated sludge was inhibited at the 3000 mg/L of phenol, while that in the immobilized activated sludge was maintained at the same concentration for 28 h without any inhibition. The degradation rates of phenol were not directly proportional to the increasing amount of immobilized bead dosage, but the phenol degradation was completed in a shorter time than that for the free activated sludge. For the repeated reaction of immobilized activated sludge, the relative activity is increased up to eight times after seven repeated initial cycles. Continued treatment of immobilized activated sludge showed more than 95% of phenol removal efficiency under a loading rate of 5.59 kg-phenol/(m 3 d), which is twice as large as the loading rate for the free activated sludge.

Functional gel-microbead manipulated by optical tweezers for local environment measurement in microchip

A novel on-chip environment measurement with functional gel-microtool was developed. Environment measurement gel-microtool was fabricated by connecting the gel-microbeads impregnated with indicators in a microchip. In this artcle, Bromothymol blue (BTB) and Bromocresol green (BCG) were employed as pH indicators. BTB and BCG have the different indicator range. Rhodamine B is temperature sensitive fluorescent dye and is used for temperature measurement. Gel-microbead is made by salting-out of hydrophilic photo-crosslinkable resin and is manipulated by optical tweezers. Moreover, gel-microbead is polymerized by UV illumination and connected to other gel-microbead under an electrolyte solution. The connection of gel-microbeads is performed by contact of gel-microbeads under UV illumination. Environment measurement gel-microtool with an arbitrary shape is fabricated by connection of the gel-microtool impregnated with arbitrary indicator. Multiple environments measurement gel-microtool included with several indicators is realized by assembly of the gel-microbeads impregnated with different indicators. Environment measurement is performed by detecting the color and the fluorescence intensity of each gel-microbead. We succeeded in the on-chip fabrication of the environment measurement gel-microtools such as circular pH measurement gel-microtool and wide range pH measurement gel-microtool in a microchip.