Photocrosslinkable Hydrogel Research Articles

A photo-crosslinkable cartilage-derived extracellular matrix bioink for auricular cartilage tissue engineering

Three-dimensional (3D) bioprinting of patient-specific auricular cartilage constructs could aid in the reconstruction process of traumatically injured or congenitally deformed ear cartilage. To achieve this, a hydrogel-based bioink is required that recapitulates the complex cartilage microenvironment. Tissue-derived decellularized extracellular matrix (dECM)-based hydrogels have been used as bioinks for cell-based 3D bioprinting because they contain tissue-specific ECM components that play a vital role in cell adhesion, growth, and differentiation. In this study, porcine auricular cartilage tissues were isolated and decellularized, and the decellularized cartilage tissues were characterized by histology, biochemical assay, and proteomics. This cartilage-derived dECM (cdECM) was subsequently processed into a photo-crosslinkable hydrogel using methacrylation (cdECMMA) and mixed with chondrocytes to create a printable bioink. The rheological properties, printability, and in vitro biological properties of the cdECMMA bioink were examined. The results showed cdECM was obtained with complete removal of cellular components while preserving major ECM proteins. After methacrylation, the cdECMMA bioinks were printed in anatomical ear shape and exhibited adequate mechanical properties and structural integrity. Specifically, auricular chondrocytes in the printed cdECMMA hydrogel constructs maintained their viability and proliferation capacity and eventually produced cartilage ECM components, including collagen and glycosaminoglycans (GAGs). The potential of cell-based bioprinting using this cartilage-specific dECMMA bioink is demonstrated as an alternative option for auricular cartilage reconstruction.

Regenerative Potential of Mandibular Condyle Cartilage and Bone Cells Compared to Costal Cartilage Cells When Seeded in Novel Gelatin Based Hydrogels.

The field of temporomandibular joint (TMJ) condyle regeneration is hampered by a limited understanding of the phenotype and regeneration potential of cells in mandibular condyle cartilage. It has been shown that chondrocytes derived from hyaline and costal cartilage exhibit a greater chondro-regenerative potential in vitro than those from mandibular condylar cartilage. However, our recent in vivo studies suggest that mandibular condyle cartilage cells do have the potential for cartilage regeneration in osteochondral defects, but that bone regeneration is inadequate. The objective of this study was to determine the regeneration potential of cartilage and bone cells from goat mandibular condyles in two different photocrosslinkable hydrogel systems, PGH and methacrylated gelatin, compared to the well-studied costal chondrocytes. PGH is composed of methacrylated poly(ethylene glycol), gelatin, and heparin. Histology, biochemistry and unconfined compression testing was performed after 4 weeks of culture. For bone derived cells, histology showed that PGH inhibited mineralization, while gelatin supported it. For chondrocytes, costal chondrocytes had robust glycosaminoglycan (GAG) deposition in both PGH and gelatin, and compression properties on par with native condylar cartilage in gelatin. However, they showed signs of hypertrophy in gelatin but not PGH. Conversely, mandibular condyle cartilage chondrocytes only had high GAG deposition in gelatin but not in PGH. These appeared to remain dormant in PGH. These results show that mandibular condyle cartilage cells do have innate regeneration potential but that they are more sensitive to hydrogel material than costal cartilage cells.

Visible-light-induced hyaluronate hydrogel for soft tissue fillers

Hyaluronic acid (HA) is widely used as a filler owing to its excellent biocompatibility and biodegradability. However, commercial HA-based filler products have some limitations and can cause side effects due to the presence of residual chemical crosslinking agents. In this study, tyramine (Tyr) was introduced into HA to impart photocrosslinking ability to HA, and a photocrosslinked hydrogel was formed using a less toxic vitamin B2 derivative as a photoinitiator. For injection, an injectable filler was prepared by converting the photocrosslinked hydrogel to a microgel form. The crosslinking of the tyramine-modified HA (HA-Tyr) hydrogel, which can be applied as a soft tissue filler, increased with an increase in the irradiation time, and the crosslinked hydrogel showed excellent mechanical strength, elastic recovery rate, and injectability. It also showed non-cytotoxicity and cell proliferation behavior in fibroblasts. Therefore, injectable HA hydrogels have great potential as an alternative to conventional commercial dermal fillers.

Photocrosslinked natural hydrogel composed of hyaluronic acid and gelatin enhances cartilage regeneration of decellularized trachea matrix

Repair of long segmental trachea defects is always a great challenge in the clinic. The key to solving this problem is to develop an ideal trachea substitute with biological function. Using of a decellularized trachea matrix based on laser micropore technique (LDTM) demonstrated the possibility of preparing ideal trachea substitutes with tubular shape and satisfactory cartilage regeneration for tissue-engineered trachea regeneration. However, as a result of the very low cell adhesion of LDTM, an overly high concentration of seeding cell is required, which greatly restricts its clinical translation. To address this issue, the current study proposed a novel strategy using a photocrosslinked natural hydrogel (PNH) carrier to enhance cell retention efficiency and improve tracheal cartilage regeneration. Our results demonstrated that PNH underwent a rapid liquid-solid phase conversion under ultraviolet light. Moreover, the photo-generated aldehyde groups in PNH could rapidly react with inherent amino groups on LDTM surfaces to form imine bonds, which efficiently immobilized the cell-PNH composite to the surfaces of LDTM and/or maintained the composite in the LDTM micropores. Therefore, PNH significantly enhanced cell-seeding efficiency and achieved both stable cell retention and homogenous cell distribution throughout the LDTM. Moreover, PNH exhibited excellent biocompatibility and low cytotoxicity, and provided a natural three-dimensional biomimetic microenvironment to efficiently promote chondrocyte survival and proliferation, extracellular matrix production, and cartilage regeneration. Most importantly, at a relatively low cell-seeding concentration, homogeneous tubular cartilage was successfully regenerated with an accurate tracheal shape, sufficient mechanical strength, good elasticity, typical lacuna structure, and cartilage-specific extracellular matrix deposition. Our findings establish a versatile and efficient cell-seeding strategy for regeneration of various tissue and provide a satisfactory trachea substitute for repair and functional reconstruction of long segmental tracheal defects.

Biomimetic Nanoengineered Scaffold for Enhanced Full-Thickness Cutaneous Wound Healing

Wound healing is a complex process which is based on the coordinated signaling molecules and dynamic interactions between the engineered scaffold and newly formed tissue. So far, most of the engineered scaffolds used for the healing of full-thickness skin wound do not mimic the natural extracellular matrix (ECM) complexity and therefore are not able to provide an appropriate niche for endogenous tissue regeneration. To address this gap and to accelerate the wound healing process, we present biomimetic bilayer scaffolds compositing of gelatin nanofibers (GFS) and photocrosslinkable composite hydrogels loaded with epidermal growth factors (EGF). The nanofibers operate as the dermis layer and EFG-loaded composite hydrogels acted as the epidermis matrix for the full-thickness wound healing application. The hydrogels are composed of gelatin metacryloyl (GelMA) modified with silicate nanoplatelets (Laponite). To overcome the challenges of transdermal delivery of EGF including short half-life and lack of efficient formulation precise, controlled delivery was attained by immobilization of EGF on Laponite. It is shown that the addition of 1wt% silicate nanoplatelet increases the compressive modulus of the hydrogels by 170%. In vitro wound closure analysis also demonstrated improved adhesion of the scaffolds to the native tissue by 3.5 folds. Moreover, the tunable hemostatic ability of the scaffolds due to the negatively charged nanoplatelets is shown. In an established excisional full-thickness wound model, an enhanced wound closure (up to 93.1 ± 1.54%) after 14 days relative to controls (GFS and saline-treated groups) is demonstrated. The engineered adhesive and hemostatic scaffolds with sustained release of the growth factors have the potential to stimulate complete skin regeneration for full-thickness wound healing.

Photo-activated platelet-rich plasma (PRP)-based patient-specific bio-ink for cartilage tissue engineering

Nowadays, scientists focus on the development of tissue-specific and personalized bio-ink that can be used in 3D bioprinting technologies. Platelet-rich plasma (PRP) is a person-specific source that is used as a therapeutic adjunct for the treatment of cartilage damage because it offers a cocktail of growth factors that are necessary for wound healing and tissue regeneration. However, PRP treatments in the clinic are not satisfactory and require upgrading, especially the point of maintaining bioactivity. In this study, we presented PRP as a photo-activated and photo-crosslinkable bio-ink in terms of tissue-specific structures for the first time. We achieved long-term and constant rate growth factor release and bioactivity protection of PRP with satisfactory mechanical characteristics. Photo-crosslinked PRP hydrogel was enabled by the addition of microwave-induced methacrylated gelatin (Gel-MA), which is connected to platelets in PRP via integrin receptors in its structure and chemically cross-linked upon UV irradiation (300–500 nm). Photo-activation of PRP was realized by a polychromatic light source in the near-infrared region (PAC, 600–1200 nm). Our results showed that Gel-MA/PRP hydrogels with the desired mechanical properties (low degradation rate and high mechanical strength) released growth factors at a constant rate for the long-term by the periodic PAC application. In vitro cell culture studies (viability, proliferation, morphology, histology, immunochemistry, biochemistry, gene expression analyses) proved that proliferation and differentiation of the ATDC5 cells increased in the periodically light-applied Gel-MA/PRP hydrogel without any external chemical agents.

Visible Light-Induced 3D Bioprinting Technologies and Corresponding Bioink Materials for Tissue Engineering: A Review

Three-dimensional (3D) bioprinting based on traditional 3D printing is an emerging technology that is used to precisely assemble biocompatible materials and cells or bioactive factors into advanced tissue engineering solutions. Similar technology, particularly photo-cured bioprinting strategies, plays an important role in the field of tissue engineering research. The successful implementation of 3D bioprinting is based on the properties of photopolymerized materials. Photocrosslinkable hydrogel is an attractive biomaterial that is polymerized rapidly and enables process control in space and time. Photopolymerization is frequently initiated by ultraviolet (UV) or visible light. However, UV light may cause cell damage and thereby, affect cell viability. Thus, visible light is considered to be more biocompatible than UV light for bioprinting. In this review, we provide an overview of photo curing-based bioprinting technologies, and describe a visible light crosslinkable bioink, including its crosslinking mechanisms, types of visible light initiator, and biomedical applications. We also discuss existing challenges and prospects of visible light-induced 3D bioprinting devices and hydrogels in biomedical areas.

Decellularized dermal matrix-based photo-crosslinking hydrogels as a platform for delivery of adipose derived stem cells to accelerate cutaneous wound healing

The development of an effective delivery vehicle that gives rise to a microenvironment that promotes skin regeneration remains a challenge in the field of stem cell-based therapeutic strategy for skin tissue engineering. Here, we fabricated a photo-crosslinkable hydrogel based on a decellularized dermal matrix (DDM) combined with o-nitrobenzene-modified hyaluronic acid (HA-NB). The HA-NB/DDM hydrogels can be crosslinked in situ under UV ultraviolet light irradiation and adhere strongly to the surrounding skin tissue. Results showed that nude mice treated with the HA-NB/DDM hydrogel loaded with adipose-derived stem cells (ASCs) accelerated wound healing compared with those treated with the hydrogel or ASCs alone and untreated control animals. Neo-epidermal formation and angiogenesis was better in wounds treated with ASC-loaded hydrogels. Further, epidermal–dermal junctions with healthy epidermal protrusions and dermal projections were observed in wounds treated with the ASC-loaded HA-NB/DDM hydrogels. Collagen deposits resembling the natural collagen structure and arrangement were observed in wounds treated with the ASC-loaded HA-NB/DDM hydrogel. Further, ASC-loaded HA-NB/DDM hydrogels can achieve satisfactory therapeutic effects in wounds with irregular defects. Hence, the developed HA-NB/DDM hydrogel can serve as a stem-cell delivery platform that undergoes rapid in situ gelation and strong adhesion with the surrounding tissue and accelerate wound healing.

FLASH: Fluorescently LAbelled Sensitive Hydrogel to monitor bioscaffolds degradation during neocartilage generation

Regenerative therapies based on photocrosslinkable hydrogels and stem cells are of growing interest in the field of cartilage repair. Cell-mediated degradation is critical for the successful clinical translation of implanted hydrogels. However, characterising cell-mediated degradation, while simultaneously monitoring the deposition of a distinct new matrix, remains a major challenge.In this study we generated a Fluorescently LAbelled Sensitive Hydrogel (FLASH) to correlate the degradation of a hydrogel bioscaffold with neocartilage formation. Gelatine Methacryloyl (GelMA) was covalently bound to the FITC fluorophore to generate FLASH and bioscaffolds were produced by casting different concentrations of FLASH GelMA, with and without human adipose-derived stem cells (hADSCs) undergoing chondrogenesis. The loss of fluorescence from FLASH bioscaffolds was correlated with changes in mechanical properties, expression of chondrogenic markers and accumulation of a cartilaginous extracellular matrix. The ability of the system to be used as a sensor to monitor bioscaffold degradability during chondrogenesis was evaluated in vitro, in a human ex vivo model of cartilage repair and in a full chondral defect in vivo rabbit model. This study represents a step towards the generation of a high throughput monitoring system to evaluate de novo cartilage formation in tissue engineering therapies.

Reconfigurable Microphysiological Systems for Modeling Innervation and Multitissue Interactions.

Tissue-engineered models continue to experience challenges in delivering structural specificity, nutrient delivery, and heterogenous cellular components, especially for organ-systems that require functional inputs/outputs and have high metabolic requirements, such as the heart. While soft lithography has provided a means to recapitulate complex architectures in the dish, it is plagued with a number of prohibitive shortcomings. Here, concepts from microfluidics, tissue engineering, and layer-by-layer fabrication are applied to develop reconfigurable, inexpensive microphysiological systems that facilitate discrete, 3D cell compartmentalization, and improved nutrient transport. This fabrication technique includes the use of the meniscus pinning effect, photocrosslinkable hydrogels, and a commercially available laser engraver to cut flow paths. The approach is low cost and robust in capabilities to design complex, multilayered systems with the inclusion of instrumentation for real-time manipulation or measures of cell function. In a demonstration of the technology, the hierarchal 3D microenvironment of the cardiac sympathetic nervous system is replicated. Beat rate and neurite ingrowth are assessed on-chip and quantification demonstrates that sympathetic-cardiac coculture increases spontaneous beat rate, while drug-induced increases in beating lead to greater sympathetic innervation. Importantly, these methods may be applied to other organ-systems and have promise for future applications in drug screening, discovery, and personal medicine.

Effect of altering photocrosslinking conditions on the physical properties of alginate gels and the survival of photoencapsulated cells

Research on biocompatible photocrosslinked organic chemical polymers for applications in biomedicine and tissue engineering has achieved satisfactory results, such as repairing or augmenting tissues. Photocrosslinked alginate gel is one of those polymers. However, there is little information in the literature regarding the preparation of photocrosslinked alginate hydrogels with high cell activity and appropriate mechanical properties by using suitable photoinitiator concentrations and reasonable ultraviolet (UV) exposure times. In this work, photocrosslinked alginate hydrogels formed with different concentrations of photoinitiator or UV exposure times were characterized by testing their mechanical properties and the viability of photoencapsulated osteoblast-like cells. To explore the degree of photocrosslinking of methacrylated alginate, the 1H NMR spectra of the gels were recorded with an NMR spectrometer, and the results showed that methacrylated alginate did not photocrosslink completely at low photoinitiator concentrations or for short UV exposure times. It was also revealed that the swelling behaviour, degradation profiles and elastic moduli of the hydrogel are tuneable by varying the photoinitiator concentration or UV exposure time. In addition, the viability and proliferation of the cells photoencapsulated in the gels gradually decreased with increasing photoinitiator concentration or UV exposure time. However, when the photoinitiator concentration and UV exposure time were controlled within a reasonable range, the cells in the gels maintained their high activity. In summary, the results indicated that the performance of the hydrogels could be tailored by adjusting the concentrations of photoinitiator or UV exposure time. This research may be used to further optimize cell photoencapsulation and photopolymerization strategies of photocrosslinked alginate gels or other biophotopolymers in tissue engineering and biomedicine and provides a theoretical basis for related research and future applications.

Naturally Derived Photoinitiators for Dental and Biomaterials Applications

AbstractBiocompatibility of materials used in dental and biomaterials applications is very important and depends on the components of these materials. Photopolymerized materials for dental and biomaterials applications have been progressively used since the 1970s. One of the crucial components in these materials is the photoinitiator (PI) that initiates the polymerization reaction. Synthetic PIs are the most commonly used types, but owing to their drawbacks such as cytotoxicity, insolubility in water, and high cost, research on naturally derived (bio-sourced) PIs is growing, to find an alternative to these synthetic types, especially in the growing field of three-dimensional (3D) printing and bioprinting of biomaterials for tissue engineering applications. Naturally derived PIs are biocompatible, highly water-soluble, and abundant. Naturally derived PIs have been used to prepare experimental dentine bonding agents, dentine primers, photo-crosslinked hydrogels for tissue engineering applications, antibacterial coatings, guided tissue regeneration membranes, and 3D printed biomaterials. An electronic search was done using MEDLINE/PubMed and Scopus databases using the keywords naturally derived, bio-sourced, PIs, dental, biomaterials, 3D printing, and 3D bioprinting, to review potential naturally derived PIs for dental and biomaterials applications. There are a variety of naturally derived PIs with various colors and absorption spectra to choose from, according to the intended application. Most of naturally derived PIs can be used with modern conventional dental light curing units, making them applicable for experimental studies for potential dental and biomaterials applications. Due to their biocompatibility and availability it is expected that in the upcoming years, research on naturally derived PIs and their dental and biomaterials applications will increase especially in the growing field of 3D bioprinting in which cell viability is essential; thus this review was done.

Direct 3D bioprinting of cardiac micro-tissues mimicking native myocardium

The heart possesses a complex three-dimensional (3D) laminar myofiber organization; however, because engineering physiologically relevant 3D tissues remains a technical challenge, the effects of cardiomyocyte alignment on excitation-contraction coupling, shortening and force development have not been systematically studied. Cellular shape and orientations in 3D can be controlled by engineering scaffold microstructures and encapsulating cells near these geometric cues. Here, we show that a novel method of cell encapsulation in 3D methacrylated gelatin (GelMA) scaffolds patterned via Microscale Continuous Optical Printing (μCOP) can rapidly micropattern neonatal mouse ventricular cardiomyocytes (NMVCMs) in photocrosslinkable hydrogels. Encapsulated cardiomyocytes preferentially align with the engineered microarchitecture and can display morphology and myofibril alignment phenotypic of myocardium in vivo. Utilizing the μCOP system, an asymmetric, multi-material, cantilever-based scaffold was directly printed, so that the force produced by the microtissue was transmitted onto a single deformable pillar. Aligned 3D encapsulated NMVCM scaffolds produced nearly 2 times the force compared to aligned 2D seeded samples. To further highlight the flexibility of μCOP, NMVCMs were encapsulated in several patterns to compare the effects of varying degrees of alignment on tissue displacement and synchronicity. Well aligned myofiber cultured patterns generated 4–10 times the contractile force of less anisotropically patterned constructs. Finally, normalized fluo-4 fluorescence of NMVCM-encapsulated structures showed characteristic calcium transient waveforms that increased in magnitude and rate of decline during treatment with 100 nM isoproterenol. This novel instrumented 3D cardiac microtissue serves as a physiologically relevant in vitro model system with great potential for use in cardiac disease modeling and drug screening.

Spatiotemporally Controlled Photoresponsive Hydrogels: Design and Predictive Modeling from Processing through Application.

Photoresponsive hydrogels (PRHs) are soft materials whose mechanical and chemical properties can be tuned spatially and temporally with relative ease. Both photo-crosslinkable and photodegradable hydrogels find utility in a range of biomedical applications that require tissue-like properties or programmable responses. Progress in engineering with PRHs is facilitated by the development of theoretical tools that enable optimization of their photochemistry, polymer matrices, nanofillers, and architecture. This review brings together models and design principles that enable key applications of PRHs in tissue engineering, drug delivery, and soft robotics, and highlights ongoing challenges in both modeling and application.

Synthesis of photocrosslinkable hydrogels for engineering three-dimensional vascular-like constructs by surface tension-driven assembly.

Surface tension-driven assembly is a simple routine used in modular tissue engineering to create three-dimensional (3D) biomimetic tissues with desired structural and biological characteristics. A major bottleneck for this technology is the lack of suitable hydrogel materials to meet the requirements of the assembly process and tissue regeneration. Identifying specific requirements and synthesizing novel hydrogels will provide a versatile platform for generating additional biomimetic functional tissues using this approach. In this paper, we present a novel composite hydrogel system based on methacrylated gelatin and γ-polyglutamic acid by UV copolymerization as the building block for fabricating vascular-like tissue via surface tension-driven assembly. The resulting composite hydrogels exhibited the improved mechanical properties and hydrophilicity, which greatly facilitate the assembly process. Subsequent cell encapsulation experiment proved that the hydrogel could provide 3D support for cellular spreading and migration. Furthermore, based on the composite microgel building blocks, cylindrical vascular-like construct with a perfusable microchannel was generated by the needle-assisted sequential assembly. In order to construct a biomimetic vascular tissue, the endothelial cells and smooth muscle cells were encapsulated in the microgels assembly with a spatial arrangement to build a heterogeneous double-layer tubular structure and the cells could readily elongate and migrate in the hollow concentric construct over 3days. These data suggest that this composite hydrogel is an attractive candidate for surface tension-driven assembly purposes, making the hydrogel potentially applicable in the fabrication of biomimetic vascularized tissues.

Hybrid Bioprinting of Chondrogenically Induced Human Mesenchymal Stem Cell Spheroids.

To date, the treatment of articular cartilage lesions remains challenging. A promising strategy for the development of new regenerative therapies is hybrid bioprinting, combining the principles of developmental biology, biomaterial science, and 3D bioprinting. In this approach, scaffold-free cartilage microtissues with small diameters are used as building blocks, combined with a photo-crosslinkable hydrogel and subsequently bioprinted. Spheroids of human bone marrow-derived mesenchymal stem cells (hBM-MSC) are created using a high-throughput microwell system and chondrogenic differentiation is induced during 42 days by applying chondrogenic culture medium and low oxygen tension (5%). Stable and homogeneous cartilage spheroids with a mean diameter of 116 ± 2.80 μm, which is compatible with bioprinting, were created after 14 days of culture and a glycosaminoglycans (GAG)- and collagen II-positive extracellular matrix (ECM) was observed. Spheroids were able to assemble at random into a macrotissue, driven by developmental biology tissue fusion processes, and after 72 h of culture, a compact macrotissue was formed. In a directed assembly approach, spheroids were assembled with high spatial control using the bio-ink based extrusion bioprinting approach. Therefore, 14-day spheroids were combined with a photo-crosslinkable methacrylamide-modified gelatin (gelMA) as viscous printing medium to ensure shape fidelity of the printed construct. The photo-initiators Irgacure 2959 and Li-TPO-L were evaluated by assessing their effect on bio-ink properties and the chondrogenic phenotype. The encapsulation in gelMA resulted in further chondrogenic maturation observed by an increased production of GAG and a reduction of collagen I. Moreover, the use of Li-TPO-L lead to constructs with lower stiffness which induced a decrease of collagen I and an increase in GAG and collagen II production. After 3D bioprinting, spheroids remained viable and the cartilage phenotype was maintained. Our findings demonstrate that hBM-MSC spheroids are able to differentiate into cartilage microtissues and display a geometry compatible with 3D bioprinting. Furthermore, for hybrid bioprinting of these spheroids, gelMA is a promising material as it exhibits favorable properties in terms of printability and it supports the viability and chondrogenic phenotype of hBM-MSC microtissues. Moreover, it was shown that a lower hydrogel stiffness enhances further chondrogenic maturation after bioprinting.

Research Progress of Photocrosslinked Hydrogel in Tissue Engineering

Research Progress of Photocrosslinked Hydrogel in Tissue Engineering

Free-form co-axial bioprinting of a gelatin methacryloyl bio-ink by direct in situ photo-crosslinking during extrusion

3D bioprinting is an emerging technology for arranging cells and biomaterials in 3D, with the goal to develop functional substitutes for damaged tissue. Photo-crosslinkable hydrogels are promising materials for formulating printable bio-inks. However, owing to conflicting constraints around printability and cell survival, achieving good shape fidelity is a challenge. The typical approach to ‘post-crosslink’ a 3D bioprinted structure necessitates highly viscous bio-inks. Meanwhile ‘pre-crosslinking’ can result in the extrusion of overly gelated bio-inks, which increases shear-stresses experienced by encapsulated cells. Neither of these strategies are amenable to creating free-standing structures, or structures with overhangs, without using secondary support materials. Here, for the first time, an on board light exposure strategy is demonstrated which enables rapid (<1s) and direct crosslinking of the bio-ink as it is being extruded from the nozzle, and without the use of transparent tubing to stabilize the filament. The utilization of this technique on a manually operated device is described, allowing for free-form additive sculpting of bio-ink structures in 3D. Finally, a co-axial freeform extrusion system is demonstrated, allowing for encapsulation of a very soft, or entirely liquid, core within the rapidly photocrosslinked shell filament.

A facile way to synthesize a photocrosslinkable methacrylated chitosan hydrogel for biomedical applications

In this study, we introduced a novel and modified method to synthesize photocrosslinkable chitosan hydrogel. Three methacrylated samples under two concentrations of methacrylic anhydride and using EDC/NHS as a crosslinker were prepared. Methacrylated chitosan obtained under controlled conditions and using EDC/NHS had significant coupling efficiency and capacity of gel formation compared to other samples. Diluted culture media provided a favorable solubility condition for methacrylated chitosan and could be tolerated by cells during gelation time. The hydrogels included interconnected pores ranging 100–300 µm and swelling ratios of 40–400%. The results opened the new aspects for developing novel biomaterials in cell-based therapies.

Fabrication of Photocurable Hyaluronic Acid Coated Microneedle Sensor for Glucose Monitoring

Introduction Microneedle (MN) has been developed to diagnose and detect the biomarkers which are related to various diseases such as diabetes mellitus (DB) and caner. The biomarkers could be extracted from interstitial fluid (ISF) in the human body by using MN with a minimally-invasive and pain-free manner. In particular, glucose sensing has widely been investigated due to increase of DB patients who suffered inconvenience of frequent monitoring of glucose levels. MN-based sensors targeting ISF glucose monitoring was introduced and showed the possibility to replace the existing blood-based glucose sensing technologies [1-3]. We hypothesized that the coating of a MN surface with swellable material such as hydrogel could increase detection sensitivity and time for stabilization. Thus, we developed a swellable hydrogel coated MN sensor which could extract the glucose from ISF with swelling for a short time. Methacrylated hyaluronic acid (MeHA), photo-crosslinkable hydrogel, was utilized to absorb ISF containing biomarkers for electrochemical reaction with the metallized surface of a MN. Cyclic voltammetry (CV) with a model redox species, ferricyanide, were performed to characterize the MeHA-coated MN sensors for the detection of glucose. Experimental Methods To fabricate the MeHA coated MN sensor, 3×3 SU-8 MN array was transfer molded on the 1 cm × 2 cm of the glass wafer. The female PDMS mold which was patterned MN shapes were filled with SU-8 in a vacuum condition and the mold was gently transferred on the glass wafer. After UV curing, the MN electrode was prepared by the Ti-gold sputtering. MeHA was synthesized by modifying from the hydroxyl groups to the methyl group in basic condition. Dimethylformamide, methacrylic anhydride, and sodium chloride were mixed in the 2% of hyaluronic acid solution while a solution was controlled in basic condition. The precursor was washed three times by ethanol and was freeze-dried to obtain the MeHA sponges. Then, the MeHA sponges were dissolved into the deionized water which was contained 0.05% of the photoinitiator for preparing the MeHA solution. The MeHA solution was poured on the surface of gold-sputtered SU-8 MN arrays and the swellable MN sensor was fabricated after drying. Before measuring the glucose, potassium ferricyanide (K3[Fe(CN)6]) which was the standard redox solution to conduct CV was used as an alternative of the biomarker. The MeHA coated MN electrode was used as a working electrode and a Pt mesh electrode was used as a counter electrode. The MN sensor was immersed into the potassium ferricyanide solution and the CV was conducted while the concentration chose 10 mM, 10 μM, and 1 μM to confirm sensitivity and detection limit of the three-electrode system with MeHA coated MN sensor. Results and Discussion The 3×3 array of SU-8 MNs fabricated on a glass wafer had the height of 640 μm and the aspect ratio of 1.6. The MeHA was successfully synthesized and the MeHA film had a swelling ratio of 450% after 10 sec swelling in the phosphate buffered saline. By using the three-electrode system including the MeHA uniform coated MN electrode, in vitro sensing tests were performed with various concentrations of potassium ferricyanide. As the results of the CV analysis, when the concentration of potassium ferricyanide was 10 mM, the anodic and cathodic peak currents of the measured I-V curve were 135 and 144 μA, respectively. Although the peaks were observed from the CV plots, it was hard to measure the exact value of peak currents when the concentration of potassium ferricyanide, 10 μM, and 1 μM. Nevertheless, the current peaks of 10 μM was slightly higher than the peaks of the 1 μM sample. Since the peak current was increased in proportion to the level of potassium ferricyanide, it was concluded that the MeHA coated MN sensor system could be used to measure the biomarker. These results also support that the biomarkers could be extracted from the ISF by the swelling behavior of the MeHA coated on the surface of MNs. Summary The MeHA coated MN sensor was fabricated with simple molding techniques and various photocurable materials such as SU-8 2010 and MeHA. The ferricyanide could be extracted by using the swelling behavior of the MeHA. As the results of in vitro test, the various concentration of potassium ferricyanide solution was measured with the three-electrode system including MeHA coated MN sensor and the detection limit was observed at least 1 μM. Reference 1. Sharma, Sanjiv, et al. "A pilot study in humans of microneedle sensor arrays for continuous glucose monitoring." (2018).2. Caliò, A., et al. "Polymeric microneedles based enzymatic electrodes for electrochemical biosensing of glucose and lactic acid." Sensors and Actuators B: Chemical 236 (2016): 343-349.3. Ribet, Federico, Göran Stemme, and Niclas Roxhed. "Real-time intradermal continuous glucose monitoring using a minimally invasive microneedle-based system." Biomedical microdevices 20.4 (2018): 101.