Photocrosslinkable Hydrogel Research Articles

Self-Standing Photo-Crosslinked Hydrogel Construct: in vitro Microphysiological Vascular Model

Modeling of the human vascular microphysiological system (MPS) has gained attention due to precise prediction of drug response and toxicity during drug screening process. Developing a physiologically equivalent vascular MPS still remains complex as it demands the recapitulation of dynamic structural and biological microenvironment similar to native vasculature. Hence, an ideal MPS would involve developing perfusable 3D in vitro models with multilayered human vascular cells encapsulated in a matrix to regulate the vascular tone resembling the native. Several attempts to model such anatomically accurate physiological and pathological blood vessels often fail to harmonize the essential vascular microenvironment. For instance, conventional microfluidic-based approaches employed for vascular MPS, though offering creation of perfusable channel, do not replicate the vascular hierarchical cellular arrangement due to planar geometry and confluent monolayered cell seeding. Also, recent advances with 3D biofabrication strategies are still limited by fabrication of small-diameter constructs and scalability besides post-processing techniques that indirectly distort the structural integrity of the hydrogel tubular constructs. These existing limitations toward fabricating a relevant vascular MPS demand a facile and mechanically stable construct. Hence, the present study is aimed toward developing a stable viable self-standing perfusable hydrogel construct by a rapid and scalable strategy toward vascular MPS application. The fabricated tubular constructs were found to be structurally stable with end-to-end perfusability exhibiting their potential as self-standing perfusable structures. Also, the construct exhibited nonhemolytic behavior with perfusion of red blood cells inside the luminal channel. The present study evidences creation of a dual-crosslinked stable, viable self-standing hydrogel construct with multilayered homogenous distribution of viable smooth muscle cells throughout the construct, thereby demonstrating its applicability as a promising 3D in vitro vascular microphysiological system.

Synthesis of pH responsive, photocrosslinked gelatin-based hydrogel system for control release of ceftriaxone

Stimuli-responsive or smart nanocarriers are emerging class of materials used for drug delivery and tissue engineering applications. The objective of this study was to develop environment friendly, economic and smart gelatin based hydrogel for controlled delivery of ceftriaxone. Gelatin was modified with furfuryl amine and converted to hydrogel via photo oxidation reaction, initiated with visible light in the presence of crosslinking agent (eosin Y and riboflavin) to enhance the mechanical properties and increase structural integrity of the hydrogel. The conjugated gelatin-furfuryl amine (GFA) was characterized by 1H NMR and FTIR techniques. An antimicrobial drug (ceftriaxone) was encapsulated in hydrogels systems (HG-E and HG-R) and its encapsulation efficiency was found as 88 % and 74 %, respectively. The in-vitro swelling property and release profile of the drug reveals that the behavior of hydrogel was pH dependent for both the hydrogels systems. Antibacterial study performed on HG-R hydrogel system via disc diffusion method revealed a greater zone of inhibition for Staphylococcus aureus. Findings of the presented work revealed the formation of an excellent, smart hydrogel system using Eosin-Y as cross-linker having greater encapsulation efficiency that can potentially be used for drug delivery application of ceftriaxone to enhance its therapeutic effects.

Anti-fatigue, highly resilient photocrosslinkable gellan gum hydrogels reinforced by flexible nanoparticulate polyurethane multi-crosslinkers

In this study, multifunctional polyurethane nanoparticles (MPUNs) were embedded into the methacrylated gellan gum (MGG) to prepare stimuli-responsive hydrogels with improved mechanical properties including remarkable fatigue resistance and excellent self-recoverability. The photocurable MPUNs/MGG nanocomposite hydrogels with different formulations were synthesized through a facile and green solution mixing method. The result obtained from mechanical analysis displayed an excellent improvement in compression strength (120 6 ± 83.7 kPa) and ultimate strain (94.2 ± 2.7%) in the optimized formulation. Furthermore, the optimized formulation could restore approximately its original shape after continuous loading-unloading compression tests over 100 cycles which might result from its favorable crosslinked structure. These reinforced hydrogels exhibited a dual physical and chemical crosslinking mechanism based on the hydrogen bonding formation and photocrosslinking of methacrylate functional groups, respectively. Interestingly, the nanocomposite hydrogels exhibited no significant cytotoxicity to human dermal fibroblast cells which made them suitable as the appropriate biomaterials for the engineering of soft tissues.

Bio-functional strontium-containing photocrosslinked alginate hydrogels for promoting the osteogenic behaviors

In recent years, photocrosslinked alginate hydrogel has been widely studied in bone tissue engineering, owing to its numerous advantages. However, there are still some shortcomings like insufficient mechanical strength and lack of bone induction. To compensate for these deficiencies, in this work, a novel doped strontium (Sr) photocrosslinked methacrylated alginate (Sr-PMA) hydrogel was developed. Photocrosslinked alginate hydrogel fabricated via crosslinking methacrylate-modified alginate under ultraviolet (UV) light was placed into strontium solutions to prepare Sr-PMA gel by chelating reaction. The chemical structures, swelling behaviors, degradation profiles, elastic moduli, Sr2+ ion release and surface morphology of the Sr-PMA hydrogel were characterized, and we found that physical properties of the gels can be tailored by varying concentration of Sr2+ ions. And MC3T3-E1 cell viability, proliferation and mineralization outside the hydrogel were also investigated. Further research on cell survival, multiplication, osteogenic differentiation of the cells encapsulated in Sr-PMA hydrogels were explored. In vitro studies of biological properties revealed that incorporation of Sr2+ into photocrosslinked alginate gels significantly improved osteogenic differentiation capabilities and mineralization via stimulating expression of osteogenesis related genes and proteins of the cells compared to strontium-free photocrosslinked alginate gels. The research demonstrates that the innovative Sr-PMA hydrogels possessing adjustable physical performances, excellent biocompatibility and osteogenic differentiation capabilities could be potentially applied to bone tissue engineering and regenerative medicine. Meanwhile, it also provides a reference for the modification of biological properties of biomaterials.

Dual-crosslinked silk fibroin hydrogels with elasticity and cytocompatibility for the regeneration of articular cartilage

Water-soluble conjugates of silk fibroin (SF) and butyl glycidyl ether (BGE) were synthesized via the ring-opening reaction of BGE of the epoxide group of BGE with the side chains of SF (-COOH, –OH, and –NH2 groups). The degree of substitution of the SF-BGE conjugates was calculated by 1H NMR spectroscopy and amino acid analysis. The color of the SF-BGE solution gradually changed from transparent to pale yellow with the increase in the amount of BGE, and its pH also changed from acidic to a weakly basic one. The photocrosslinking efficiency of the SF-BGE solution according to the polymer concentration, photoinitiator content, and irradiation time were investigated to achieve optimal chemical crosslinking. In addition, the mechanical strength of the photocrosslinked SF-BGE hydrogels was increased by treating with an aqueous ethanol solution to generate a dual-crosslinked structure. The crystalline structure, mechanical strength, crosslinking density, swelling, and biodegradation behavior of the SF-BGE hydrogels were analyzed. Finally, the in vitro cytocompatibility of the SF-BGE hydrogels was evaluated as a preliminary study toward its application in articular cartilage.

BoneMA—synthesis and characterization of a methacrylated bone-derived hydrogel for bioprinting of in-vitro vascularized tissue constructs

It has long been proposed that recapitulating the extracellular matrix (ECM) of native human tissues in the laboratory may enhance the regenerative capacity of engineered scaffolds in-vivo. Organ- and tissue-derived decellularized ECM biomaterials have been widely used for tissue repair, especially due to their intrinsic biochemical cues that can facilitate repair and regeneration. The main purpose of this study was to synthesize a new photocrosslinkable human bone-derived ECM hydrogel for bioprinting of vascularized scaffolds. To that end, we demineralized and decellularized human bone fragments to obtain a bone matrix, which was further processed and functionalized with methacrylate groups to form a photocrosslinkable methacrylate bone ECM hydrogel— bone-derived biomaterial (BoneMA). The mechanical properties of BoneMA were tunable, with the elastic modulus increasing as a function of photocrosslinking time, while still retaining the nanoscale features of the polymer networks. The intrinsic cell-compatibility of the bone matrix ensured the synthesis of a highly cytocompatible hydrogel. The bioprinted BoneMA scaffolds supported vascularization of endothelial cells and within a day led to the formation of interconnected vascular networks. We propose that such a quick vascular network formation was due to the host of pro-angiogenic biomolecules present in the bone ECM matrix. Further, we also demonstrate the bioprintability of BoneMA in microdimensions as injectable ECM-based building blocks for microscale tissue engineering in a minimally invasive manner. We conclude that BoneMA may be a useful hydrogel system for tissue engineering and regenerative medicine.

Sequential drug delivery of vancomycin and rhBMP-2 via pore-closed PLGA microparticles embedded photo-crosslinked chitosan hydrogel for enhanced osteointegration

As generally accepted, inhibiting the bacterial invasion at initial stage and promoting the behavior of related osteogenesis cells afterwards is crucial to achieve favorable osteointegration after dental implantation. In this study, a novel combined structured hydrogel composed of chitosan and pore-closed poly(lactic-co-glycolic acid) microparticles was prepared and characterized. In vitro and in-vivo studies have identified that this biocompatible material can rapidly release vancomycin at initial 2 days and then sustainedly release recombinant human bone morphogenetic protein-2 for about 12 days, thus respectively accomplish antibacterial and osteogenesis functions. This sequential drug release system can be used as a promising coating material to improve the surface conditions of dental implant to enhance the osteointegration after surgery.

Biomimetic injectable hydrogel microspheres with enhanced lubrication and controllable drug release for the treatment of osteoarthritis

The occurrence of osteoarthritis (OA) is highly associated with the reduced lubrication property of the joint, where a progressive and irreversible damage of the articular cartilage and consecutive inflammatory response dominate the mechanism. In this study, bioinspired by the super-lubrication property of cartilage and catecholamine chemistry of mussel, we successfully developed injectable hydrogel microspheres with enhanced lubrication and controllable drug release for OA treatment. Particularly, the lubricating microspheres (GelMA@DMA-MPC) were fabricated by dip coating a self-adhesive polymer (DMA-MPC, synthesized by free radical copolymerization) on superficial surface of photo-crosslinked methacrylate gelatin hydrogel microspheres (GelMA, prepared via microfluidic technology), and encapsulated with an anti-inflammatory drug of diclofenac sodium (DS) to achieve the dual-functional performance. The tribological test and drug release test showed the enhanced lubrication and sustained drug release of the GelMA@DMA-MPC microspheres. In addition, the functionalized microspheres were intra-articularly injected into the rat knee joint with an OA model, and the biological tests including qRT-PCR, immunofluorescence staining assay, X-ray radiography and histological staining assay all revealed that the biocompatible microspheres provided significant therapeutic effect against the development of OA. In summary, the injectable hydrogel microspheres developed herein greatly improved lubrication and achieved sustained local drug release, therefore representing a facile and promising technique for the treatment of OA.

Effect of Divalent Metal Cations on the Conformation, Elastic Behavior, and Controlled Release of a Photocrosslinked Protein Engineered Hydrogel.

We investigate the effect of Zn2+, Cu2+, and Ni2+ coordination on the conformation, mechanical properties, contraction, and small-molecule drug encapsulation and release of a photocrosslinked protein-engineered hydrogel, CEC-D. The treatment of the CEC-D hydrogel with divalent metal (M2+) results in significant conformational changes where a loss in structure is observed with Zn2+, while both Cu2+ and Ni2+ induce a blueshift. The relationship of M2+ to mechanical properties illustrates a trend, while the CEC-D hydrogel in the presence of 2 mM Cu2+ reveals the highest increase in G' to 14.4 ± 0.7 kPa followed by 9.7 ± 0.9 kPa by addition of 2 mM Zn2+, and a decrease to 1.1 ± 0.2 kPa is demonstrated in the presence of 2 mM Ni2+. A similar observation in M2+ responsiveness emerges where CEC-D hydrogels contract into a condensed state of 2.6-fold for Cu2+, 2.4-fold for Zn2+, and 1.6-fold for Ni2+. Furthermore, CEC-D hydrogels coordinated with M2+ demonstrate control over the encapsulation and release of the small molecule curcumin. The trend of release is opposite of the mechanical and contraction properties with a 70.0 ± 5.3% release with Ni2+, 64.2 ± 1.2% release with Zn2+, and 42.3 ± 11.3 release with Cu2+. Taken together, these results indicate that the CEC-D hydrogel tuned by M2+ is a promising drug delivery platform with tunable physicochemical properties.

3D Encapsulation and tethering of functionally engineered extracellular vesicles to hydrogels

Mesenchymal stem cell (MSC) derived extracellular vesicles (EVs) in their naïve and engineered forms have emerged as potential alternatives to stem cell therapy. While they have a defined therapeutic potential, the spatial and temporal control of their activity in vivo remains a challenge. The objective of this study was to devise a methodology to encapsulate EVs in 3D hydrogels for prolonged delivery. To achieve this, we have leveraged the MSC EV interactions with ECM proteins and their derivative peptides. Using osteoinductive functionally engineered EVs (FEEs) derived from MSCs, we show that FEEs bind to mimetic peptides from collagen (DGEA, GFPGER) and fibronectin (RGD). In in vitro experiments, photocrosslinkable alginate hydrogels containing RGD were able to encapsulate, tether and retain the FEEs over a period of 7 days while maintaining the structural integrity and osteoinductive functionality of the EVs. When employed in a calvarial defect model in vivo, alginate-RGD hydrogels containing the FEEs enhanced bone regeneration by a factor of 4 compared to controls lacking FEEs and by a factor of 2 compared to controls lacking the tethering peptide. These results show that EVs can be tethered to biomaterials to promote bone repair and the importance of prolonged delivery in vivo. Results also provide a prelude to the possible use of this technology for controlled delivery of EVs for other regenerative medicine applications. Statement of significanceThe beneficial effects of human MSC (HMSC) therapy are attributable to paracrine effects of the HMSC derived EVs. While EV engineering has the potential to impact several fields of regenerative medicine, targeted delivery of the engineered EVs with spatial and temporal control is necessary to prevent off-target effects and enhance tissue specificity. Here, we have leveraged the interactions of MSC EVs with ECM proteins to develop a tethering system that can be utilized to prolong EV delivery in vivo while maintaining the structural and functional integrity of the EVs. Our work has provided a tunable platform for EV delivery that we envision can be formulated as an injectable material or a bulk hydrogel suitable for regenerative medicine applications.

Free-Standing Photocrosslinked Protein Polymer Hydrogels for Sustained Drug Release.

The fabrication of protein hydrogels consisting of different properties and functional motifs is critical in the development of protein-based materials for biomedical applications. Here, we report the design and characterization of a triblock protein polymer, CEC, composed of two different self-assembling domains derived from elastin protein (E) and coiled-coil protein (C), photopolymerized with a NHS-diazirine (D) crosslinker into a CEC-D hydrogel. The optimal photocrosslinker concentration and exposure time is determined to fabricate a free-standing hydrogel. Upon increasing the concentration of the CEC-D monomer and environmental temperature, the CEC-D hydrogel's conformation decreases in helical content from 58.0% to 44.8% and increases in β-content from 25.9% to 38.1%. These gels experience 55 ± 6% protein erosion from the free-standing gel in 13 days as the gel films gradually decrease in size. The swelling ratio of 12 ± 1% denotes that the gel has a swelling ability comparable to other protein hydrogels. These photocrosslinked CEC-D hydrogels can be employed for drug delivery with high encapsulation and 14 ± 2% release of curcumin into the supernatant in a week long study. Overall, the photocrosslinked CEC-D hydrogels exhibit stability, swelling ability, and sustained release of drug.

Photo-crosslinkable amniotic membrane hydrogel for skin defect healing

The human amniotic membrane (HAM) collagen matrix derived from human placenta can be decellularized (dHAM) to form a natural biocompatible material. dHAM has different bioactive substances and has been used widely in human tissue engineering research. However, dHAM has some disadvantages, e.g., poor mechanical properties, easy degradation and inconvenient operation and use, so it is not conducive to large-area or full-thickness skin defect healing. To overcome these limitations, for the first time, dHAM was grafted with methacrylic anhydride (MA) to form photocrosslinked dHAM methacrylate (dHAMMA); dHAMMA was then blended with methacrylated gelatin (GelMA), followed by the addition of a photosensitizer for photocrosslinking to obtain the fast-forming GelMA-dHAMMA composite hydrogel. Further, GelMA-dHAMMA was found to have the porous structure of a bicomponent polymer network and good physical and chemical properties. In vitro experiments, GelMA-dHAMMA was found to promote fibroblast proliferation and α-smooth muscle actin (α-SMA) expression. In vivo investigations also demonstrated that GelMA-dHAMMA promotes wound collagen deposition and angiogenesis, and accelerates tissue healing. GelMA-dHAMMA inherits the good mechanical properties of GelMA and maintains the biological activity of the amniotic membrane, promoting the reconstruction and regeneration of skin wounds. Thus, GelMA-dHAMMA can serve as a promising biomaterial in skin tissue engineering. Statement of significanceSince the early 20th century, the human amniotic membrane (HAM) has been successfully used for trauma treatment and reconstruction purposes. dHAM has different bioactive substances and has been used widely in human tissue-engineering research. In this work, the dHAM and gelatin were grafted and modified by using methacrylic anhydride (MA) to form photocrosslinked dHAMMA and methacrylated gelatin (GelMA). Then, the dHAMMA and GelMA were blended with a photosensitizer to form the GelMA-dHAMMA composite hydrogel derived from gelatin-dHAM. GelMA-dHAMMA exhibits a bicomponent-network (BCN) interpenetrating structure. dHAM dydrogel has advantages, e.g., good mechanical properties, slow degradation and convenient operation, so it is conducive to large-area or full-thickness skin defect healing.

An open-source technology platform to increase reproducibility and enable high-throughput production of tailorable gelatin methacryloyl (GelMA) - based hydrogels

Gelatin methacryloyl (GelMA)-based hydrogels have become highly studied as modular tissue culture platforms due to the combination of the bioactivity of gelatin and tailorability of photo-crosslinkable hydrogels. However, current production and characterization workflows still rely on manual, time-consuming, and low-throughput processes, ultimately limiting widespread adaption. To address these challenges, an open-source technology platform is engineered and validated for automated high-throughput production of GelMA-based 3D constructs by integrating automated pipetting capabilities for viscous and non-viscous liquids. Firstly, the platform is applied in combination with inexpensive absorbance measurements to systematically optimize the mixing sequence for GelMA-based precursor solutions. This enables a decrease in the relative standard deviation of the prepared mixtures from 63% to 2.5%, demonstrating a significantly improved reproducibility. Next, the applicability and high-throughput capacity are demonstrated by the reproducible generation of GelMA dilution series with 0.5 and 2% (w/v) concentration steps as well as double network hydrogels consisting of 2% (w/v) alginate and 5% (w/v) GelMA. Finally, a simple and user-friendly methodology is described that integrates Design of Experiments approaches to systematically study the combinatorial effects of material and crosslinking parameters and to establish a parameter library for on-demand production of mechanically defined GelMA-based hydrogels. The platform enables reproducible production and offers an open-source and accessible alternative to high-priced liquid-handling robots and bioprinters.

Photocrosslinked poly(γ-glutamic acid) hydrogel for 3D bioprinting

In this study, tyramine-modified poly(γ-glutamic acid) (γ-PGA/Tyr) was synthesized to fabricate a photocrosslinked γ-PGA hydrogel for 3D bioprinting. The Tyr moiety was successfully introduced into γ-PGA at different degrees of substitution (DS) ranging from 13.4 to 53.8%, as determined by 1H NMR spectroscopy. The gelation time of γ-PGA/Tyr conjugate decreased with increasing DS of Tyr in the presence of Ru2+/sodium persulfate initiators. The optimum photoinitiation conditions for the gelation of γ-PGA/Tyr conjugate at the concentration of 12 wt% and DS of 53.8% were found to be Ru2+ concentration of 0.5 mM, and sodium persulfate of 40 mM, resulting in the highest mechanical strength of the γ-PGA/Tyr hydrogel. The crosslinking density, molecular weight between crosslinks, and mesh size of the γ-PGA/Tyr hydrogel calculated using the Flory-Rehner equation agreed with the rheological and mechanical properties of the hydrogel. The cytotoxicity and proliferative ability of γ-PGA/Tyr hydrogels with a DS, 53.8% were found to be excellent through live/dead and WST-1 assay. Finally, a lattice structure of the γ-PGA/Tyr hydrogel (DS, 53.8%) blended with cellulose nanofibrils was successfully fabricated via 3D bioprinting.

Development and characterization of photo-responsive cinnamoly modified alginate

A photo-crosslinkable hydrogel derived from cinnamoyl modified alginate (Alg-CN) was prepared via hydrazide intermediate and employed as an efficient drug carrier using the painkiller drug paracetamol. Methyl ester of the alginic acid was first prepared and converted into the corresponding hydrazide intermediate (Alg-Hyd) and then the cinnamoyl units were incorporated using cinnamoyl chloride. The synthesized derivatives were characterized by spectral and instrumental methods to confirm their suggested chemical structures. The obtained Alg-CN derivatives displayed initiator-free crosslinking capabilities upon the UV exposure for adequate periods of time, which was demonstrated due to the formation of cyclobutane bridges connecting the alginate polysaccharide chains through the [2π+2π] cycloaddition reaction carried out by the CHCH units of the inserted cinnamoyl moieties. The cross-linking of the Alg-CN was monitored by observing the lowering of the UV spectral band related to the cinnamoyl units and then the gelation efficiency along with the swelling degree was investigated over the UV light exposure time. Moreover, the developed hydrogel derivatives present considerable potentials as drug carriers that enable the control of the drug release by varying the degree of hydrogel cross-linking either by cinnamoyl functionalization or UV light exposure time.

A tissue-engineered human trabecular meshwork hydrogel for advanced glaucoma disease modeling

Abnormal human trabecular meshwork (HTM) cell function and extracellular matrix (ECM) remodeling contribute to HTM stiffening in primary open-angle glaucoma (POAG). Most current cellular HTM model systems do not sufficiently replicate the complex native three dimensional (3D) cell-ECM interface, limiting their use for investigating POAG pathology. Tissue-engineered hydrogels are ideally positioned to overcome shortcomings of current models. Here, we report a novel biomimetic HTM hydrogel and test its utility as a POAG disease model. HTM hydrogels were engineered by mixing normal donor-derived HTM cells with collagen type I, elastin-like polypeptide and hyaluronic acid, each containing photoactive functional groups, followed by UV crosslinking. Glaucomatous conditions were induced with dexamethasone (DEX), and effects of the Rho-associated kinase (ROCK) inhibitor Y27632 on cytoskeletal organization and tissue-level function, contingent on HTM cell-ECM interactions, were assessed. DEX exposure increased HTM hydrogel contractility, f-actin and alpha smooth muscle actin abundance and rearrangement, ECM remodeling, and fibronectin deposition - all contributing to HTM hydrogel condensation and stiffening consistent with glaucomatous HTM tissue behavior. Y27632 treatment produced precisely the opposite effects and attenuated the DEX-induced pathologic changes, resulting in HTM hydrogel relaxation and softening. For model validation, confirmed glaucomatous HTM (GTM) cells were encapsulated; GTM hydrogels showed increased contractility, fibronectin deposition, and stiffening vs. normal HTM hydrogels despite reduced GTM cell proliferation. We have developed a biomimetic HTM hydrogel model for detailed investigation of 3D cell-ECM interactions under normal and simulated glaucomatous conditions. Its bidirectional responsiveness to pharmacological challenge and rescue suggests promising potential to serve as screening platform for new POAG treatments with focus on HTM biomechanics.

Biomimetic nanoengineered scaffold for enhanced full-thickness cutaneous wound healing

Wound healing is a complex process 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 wounds do not mimic the natural extracellular matrix (ECM) complexity and therefore are not able to provide an appropriate niche for endogenous tissue regeneration [1]. 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 EGF-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 ± 1.5%) 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-crosslinked gelatin methacrylate hydrogels with mesenchymal stem cell and endothelial cell spheroids as soft tissue substitutes

Photo-crosslinked gelatin methacrylate hydrogels with mesenchymal stem cell and endothelial cell spheroids as soft tissue substitutes

Bidirectional differentiation of BMSCs induced by a biomimetic procallus based on a gelatin-reduced graphene oxide reinforced hydrogel for rapid bone regeneration

Developmental engineering strategy needs the biomimetic composites that can integrate the progenitor cells, biomaterial matrices and bioactive signals to mimic the natural bone healing process for faster healing and reconstruction of segmental bone defects. We prepared the gelatin-reduced graphene oxide (GOG) and constructed the composites that mimicked the procallus by combining the GOG with the photo-crosslinked gelatin hydrogel. The biological effects of the GOG-reinforced composites could induce the bi-differentiation of bone marrow stromal cells (BMSCs) for rapid bone repair. The proper ratio of GOG in the composites regulated the composites' mechanical properties to a suitable range for the adhesion and proliferation of BMSCs. Besides, the GOG-mediated bidirectional differentiation of BMSCs, including osteogenesis and angiogenesis, could be activated through Erk1/2 and AKT pathway. The methyl vanillate (MV) delivered by GOG also contributed to the bioactive signals of the biomimetic procallus through priming the osteogenesis of BMSCs. During the repair of the calvarial defect in vivo, the initial hypoxic condition due to GOG in the composites gradually transformed into a well-vasculature robust situation with the bi-differentiation of BMSCs, which mimicked the process of bone healing resulting in the rapid bone regeneration. As an inorganic constituent, GOG reinforced the organic photo-crosslinked gelatin hydrogel to form a double-phase biomimetic procallus, which provided the porous extracellular matrix microenvironment and bioactive signals for the bi-directional differentiation of BMSCs. These show a promised application of the bio-reduced graphene oxide in biomedicine with a developmental engineering strategy.

Thiol-norbornene gelatin hydrogels: influence of thiolated crosslinker on network properties and high definition 3D printing

Photocrosslinkable gelatin hydrogels are excellent bioinks or biomaterial ink components to serve biofabrication applications. Especially the widely investigated gelatin-methacroyl (gel-MA) hydrogels hold an impressive track record. However, over the past decade, increasing attention is being paid to thiol-ene photo-click chemistry to obtain hydrogel networks benefitting from a faster reactivity (i.e. seconds vs minutes) along with superior biocompatibility and processability. In order to exploit this photo-click chemistry, often an ene-functionality (e.g. norbornene) is introduced onto gelatin followed by crosslinking in the presence of a multifunctional thiol (e.g. dithiothreitol). To date, very limited research has been performed on the influence of the applied thiolated crosslinker on the final hydrogel properties. Therefore, the present work assesses the influence of different thiolated crosslinkers on the crosslinking kinetics, mechanical properties and biological performance of the hydrogels upon encapsulation of primary adipose tissue-derived stem cells which indicated a cell viability exceeding 70%. Furthermore, the different formulations were processed using two-photon polymerization which indicated, in addition to differences in processing window and swelling ratio, a previously unreported phenomenon. At high intensities (i.e. ⩾150 mW), the laser results in cleavage of the gelatin backbone even in the absence of distinct photo-cleavable functionalities. This can have potential to introduce channels or softer regions in gels to result in zones characterized by different degradation speeds or the formation of blood vessels. Consequently, the present study can be used to provide guidance towards tailoring the thiol-ene system towards the desired applications.