Biomimetic Hydrogel Scaffolds Research Articles

Biomimetic cascade-released hydrogel scaffolds from microfluidics for efficient T cell recruitment and expansion

Adoptive T-cell immunotherapy has shown powerful therapeutic effects in cancer treatment. Attempts to implement T cell therapy have tended to focus on providing T cells with specific targeting and sufficient activation to enhance their tumor killing ability. Although biomaterial-based scaffolds can provide necessary molecular cues for T cell activation, efficient stimulation necessitates more attention on the reconstruction of natural T cell activation processes. Here, we present a novel biomimetic scaffold with cascade-released capacity for T-cell recruitment and activation. Core-shell structured hydrogel scaffolds are fabricated by single-step microfluidic electrospray, and chemokines and stimulatory antibodies are compartmentalized in the shell and core, respectively. Benefiting from the heterogeneity in the microstructure and swelling degree of the core and shell hydrogels, chemokine peptides are robustly released to recruit tumor-reactive T cells, and stimulatory antibodies are continuously released to support T cell proliferation. Such biomimetic recruitment and activation processes contribute to the formation of T cell clusters, which enhances their proliferation and infiltration in tumor tissues. Owing to the high expression of cytotoxic receptor and chemokine receptor, the activated T cells exhibit potent antitumor activity in vitro and in vivo. These features demonstrate that the cascade-released hydrogel scaffolds are promising for the local recruitment and activation of tumor-reactive T cells.

Trilayered biomimetic hydrogel scaffolds with dual-differential microenvironment for articular osteochondral defect repair

Commonly, articular osteochondral tissue exists significant differences in physiological architecture, mechanical function, and biological microenvironment. However, the development of biomimetic scaffolds incorporating upper cartilage, middle tidemark-like, and lower subchondral bone layers for precise articular osteochondral repair remains elusive. This study proposed here a novel strategy to construct the trilayered biomimetic hydrogel scaffolds with dual-differential microenvironment of both mechanical and biological factors. The cartilage-specific microenvironment was achieved through the grafting of kartogenin (KGN) into gelatin via p-hydroxyphenylpropionic acid (HPA)-based enzyme crosslinking reaction as the upper cartilage layer. The bone-specific microenvironment was achieved through the grafting of atorvastatin (AT) into gelatin via dual-crosslinked network of both HP-based enzyme crosslinking and glycidyl methacrylate (GMA)-based photo-crosslinking reactions as the lower subchondral bone layer. The introduction of tidemark-like middle layer is conducive to the formation of well-defined cartilage-bone integrated architecture. The in vitro experiments demonstrated the significant mechanical difference of three layers, successful grafting of drugs, good cytocompatibility and tissue-specific induced function. The results of in vivo experiments also confirmed the mechanical difference of the trilayered bionic scaffold and the ability of inducing osteogenesis and chondrogenesis. Furthermore, the articular osteochondral defects were successfully repaired using the trilayered biomimetic hydrogel scaffolds by the activation of endogenous recovery, which offers a promising alternative for future clinical treatment.

Kuragel: A biomimetic hydrogel scaffold designed to promote corneal regeneration

Cornea-related injuries are the most common cause of blindness worldwide. Transplantation remains the primary approach for addressing corneal blindness, though the demand for donor corneas outmatches the supply by millions. Tissue adhesives employed to seal corneal wounds have shown inefficient healing and incomplete vision restoration. We have developed a biodegradable hydrogel- Kuragel, with the ability to promote corneal regeneration. Functionalized gelatin and hyaluronic acid form photo-crosslinkable hydrogel with transparency and compressive modulus similar to healthy human cornea. Kuragel composition was tuned to achieve sufficient adhesive strength for sutureless integration to host tissue, with minimal swelling post-administration. Studies in the New Zealand rabbit mechanical injury model affecting corneal epithelium and stroma demonstrate that Kuragel efficiently promotes re-epithelialization within 1month of administration, while stroma and sub-basal nerve plexus regenerate within 3months. We propose Kuragel as a regenerative treatment for patients suffering from corneal defects including thinning, by restoration of transparency and thickness.

3D printing sequentially strengthening high-strength natural polymer hydrogel bilayer scaffold for cornea regeneration.

3D printing of high-strength natural polymer biodegradable hydrogel scaffolds simultaneously resembling the biomechanics of corneal tissue and facilitating tissue regeneration remains a huge challenge due to the inherent brittleness of natural polymer hydrogels and the demanding requirements of printing. Herein, concentrated aqueous solutions of gelatin and carbohydrazide-modified alginate (Gel/Alg-CDH) are blended to form a natural polymer hydrogel ink, where the hydrazides in Alg-CDH are found to form strong hydrogen bonds with the gelatin. The hydrogen-bonding-strengthened Gel/Alg-CDH hydrogel demonstrates an appropriate thickened viscosity and shear thinning for extrusion printing. The strong hydrogen bonds contribute to remarkably increased mechanical properties of Gel/Alg-CDH hydrogel with a maximum elongation of over 400%. In addition, sequentially Ca2+-physical crosslinking and then moderately chemical crosslinking significantly enhance the mechanical properties of Gel/Alg-CDH hydrogels that ultimately exhibit an intriguing J-shaped stress-strain curve (tensile strength of 1.068 MPa and the toughness of 677.6 kJ/m2). The dually crosslinked Gel-Alg-CDH-Ca2+-EDC hydrogels demonstrate a high transparency, physiological swelling stability and rapid enzymatic degradability, as well as suturability. The growth factor and drug-loaded biomimetic bilayer hydrogel scaffold are customized via a multi-nozzle printing system. This bioactive bilayer hydrogel scaffold considerably promotes regeneration of corneal epithelium and stroma and inhibits cornea scarring in rabbit cornea keratoplasty.

Bioactive and biomimetic 3D scaffolds for bone tissue engineering using graphitic carbon nitride as a sustainable visible light photoinitiator

Graphitic carbon nitride (g-C3N4) is explored as a novel sustainable visible light photoinitiator for the preparation of biomimetic 3D hydrogel scaffolds comprising gelatin methacrylamide (GelMA) and dopamine methacrylamide for use in tissue engineering. The initiator efficiency was assessed by comparing the swelling behavior and the stability of photopolymerized hydrogels prepared with GelMA of different degrees of functionalization and different comonomer compositions. Bioactive composite hydrogels with a 50 wt% nanohydroxyapatite (nHAp) content, to closely mimic the actual bone composition, were successfully obtained by the introduction of nHAp in the prepolymer solutions followed by photopolymerization. The composite hydrogels demonstrated enhanced mechanical properties and excellent stability in PBS verifying the preparation of robust 3D scaffolds for use in cancellous or pre-calcified bone tissue engineering applications. The in vitro cell response of the composite scaffolds exhibited high cell viability and enhanced differentiation of pre-osteoblasts to mature osteoblasts, demonstrating their osteogenic potential. This work establishes, for the first time, the excellent properties of g-C3N4 as a sustainable, visible light initiator, fully satisfying the principles of green chemistry, for the preparation of robust and biologically relevant hydrogels, and proposes a new approach to overcome the main challenges of conventional photoinitiators in cell scaffold fabrication, such as photobleaching, high cost and non-scalable synthesis employing toxic organic precursors and solvents.

Biomimetic Conductive Hydrogel Scaffolds with Anisotropy and Electrical Stimulation for In Vivo Skeletal Muscle Reconstruction.

The nature of the hydrogel scaffold mimicking extracellular matrix plays a crucial role in tissue engineering like skeletal muscle repair. Herein, an anisotropic and conductive hydrogel scaffold is fabricated using gelatin methacryloyl (GelMA) as the matrix hydrogel and silver nanowire (AgNW) as the conductive dopant, through a directional freezing technique for muscle defect repair. The scaffold has an anisotropic structure composed of a directional longitudinal section and a honeycomb cross-section, with high mechanical strength of 10.5kPa and excellent conductivity of 0.26 S m-1 . These properties are similar to native muscle extracellular matrix (ECM) and allow for cell orientation under the guidance of contact cues and electrical stimulation synergistically. In vitro experiments show that the scaffold's oriented structure combined with electrical stimulation results in enhanced myotube formation, with a length of up to 863µm and an orientation rate of 81%. Furthermore, the electrically stimulated scaffold displays a promoted muscle reconstruction ability when transplanted into rats with muscle defects, achieving a muscle mass and strength restoration ratio of 95% and 99%, respectively, compared to normal levels. These findings suggest that the scaffold has great potential in muscle repair applications.

Biomimetic hydrogel scaffolds embedded with porous microtubes as perfusion channels

Despite the remarkable progress in biofabrication, the vascularization of large-sized tissue scaffolds remains a great challenge for tissue engineering. The lack of effective capillary vessels in the scaffold can result in cellular necrosis due to the lack of oxygen and nutrients. Integrating capillary vessels in scaffolds is critical to maintaining cellular metabolic functions and the ultimate success of engineering large-scale tissues and organs. This paper demonstrates a novel hybrid biofabrication method that combines coaxial electrospinning and extrusion-based bioprinting to fabricate microtube-embedded hydrogel scaffolds. The porous microtubes mimicked the capillary morphology and were embedded between layers of 3D printed sodium alginate scaffold to function as a microchannel diffusion system. The dye diffusion test showed that the microtubes enhanced the mass transport within the scaffold.

A hyaluronic acid/silk fibroin/poly-dopamine-coated biomimetic hydrogel scaffold with incorporated neurotrophin-3 for spinal cord injury repair

Bio-factor stimulation is essential for axonal regeneration in the central nervous system. Thus, persistent and efficient factor delivery in the local microenvironment is an ideal strategy for spinal cord injury repair. We developed a biomimetic hydrogel scaffold to load biofactors in situ and release them in a controlled way as a promising therapeutic modality. Hyaluronic acid and silk fibroin were cross-linked as the basement of the scaffolds, and poly-dopamine coating was used to further increase the loading of factors and endow the hydrogel scaffolds with ideal physical and chemical properties and proper biocompatibility. Notably, neurotrophin-3 release from the hydrogel scaffolds was prolonged to 28 days. A spinal cord injury model was constructed for hydrogel scaffold transplantation. After eight weeks, significant NF200-positive nerve fibers were observed extending across the glial scar to the center of the injured area. Due to the release of neurotrophin-3, spinal cord regeneration was enhanced, and the cavity area of the injury graft site and inflammation associated with CD68 positive cells were reduced, which led to a significant improvement in hind limb motor function. The results show that the hyaluronic acid/silk fibroin/poly-dopamine-coated biomimetic hydrogel scaffold achieved locally slow release of neurotrophin-3, thus facilitating the regeneration of injured spinal cord. Statement of significanceHydrogels have received great attention in spinal cord regeneration. Current research has focused on more efficient and controlled release of bio-factors. Here, we adopted a mussel-inspired strategy to functionalize the hyaluronic acid/silk fibroin hydrogel scaffold to increase the load of neurotrophin-3 and extend the release time. The hydrogel scaffolds have ideal physiochemical properties, proper release rate, and biocompatibility. Owing to the continuous neurotrophin-3 release from implanted scaffolds, cavity formation is reduced, inflammation alleviated, and spinal cord regeneration enhanced, indicating great potential for bio-factor delivery in soft tissue regeneration applications.

Enhanced Proliferation of Human Mesenchymal Stem Cells by Self-Assembled Peptide Hydrogel Modified with Heparin Mimetic Peptide

The development of three-dimensional (3D) microenvironments that mimic the role of native extracellular matrix (ECM) components is very crucial. Self-assembling peptide (SAP) hydrogels have been utilized as scaffolds for encapsulation, 3D culture, proliferation, and differentiation of cells and also for repairing defects in cartilage tissue. SAPs can be biofunctionalized with short peptide epitopes to form biomimetic scaffolds. Herein, KLD (KLDLKLDLKLDL) SAP was functionalized with a short bioactive motif, EGDK, to fabricate KLD-HM (KLDLKLDLKLDL-EGDK) SAP hydrogel and self-assembled. In this study, it was aimed to investigate the effect of developed KLD-HM SAP hydrogels on the viability and proliferation of human mesenchymal stem cells (hMSCs). For ensuring the stability of SAPs, the rheological properties and degradation profile of produced SAP hydrogels were assessed. After the encapsulation of hMSCs in SAP hydrogels, MTT assay and Live and Dead staining assay were conducted. We showed that these biomimetic peptide hydrogel scaffolds provided a proper microenvironment for encapsulated hMSCs and the developed SAP hydrogels promoted the adhesion, viability, and proliferation of hMSCs. Our results suggest that designed bioactive SAP hydrogel scaffolds might be useful for promoting the regeneration of cartilage tissue.

Remote control of the recruitment and capture of endogenous stem cells by ultrasound for in situ repair of bone defects.

Stem cell-based tissue engineering has provided a promising platform for repairing of bone defects. However, the use of exogenous bone marrow mesenchymal stem cells (BMSCs) still faces many challenges such as limited sources and potential risks. It is important to develop new approach to effectively recruit endogenous BMSCs and capture them for in situ bone regeneration. Here, we designed an acoustically responsive scaffold (ARS) and embedded it into SDF-1/BMP-2 loaded hydrogel to obtain biomimetic hydrogel scaffold complexes (BSC). The SDF-1/BMP-2 cytokines can be released on demand from the BSC implanted into the defected bone via pulsed ultrasound (p-US) irradiation at optimized acoustic parameters, recruiting the endogenous BMSCs to the bone defected or BSC site. Accompanied by the daily p-US irradiation for 14 days, the alginate hydrogel was degraded, resulting in the exposure of ARS to these recruited host stem cells. Then another set of sinusoidal continuous wave ultrasound (s-US) irradiation was applied to excite the ARS intrinsic resonance, forming highly localized acoustic field around its surface and generating enhanced acoustic trapping force, by which these recruited endogenous stem cells would be captured on the scaffold, greatly promoting them to adhesively grow for in situ bone tissue regeneration. Our study provides a novel and effective strategy for in situ bone defect repairing through acoustically manipulating endogenous BMSCs.

Biomimetic Hydrogel Scaffolds with Copper Peptide-Functionalized RADA16 Nanofiber Improve Wound Healing in Diabetes.

Wound healing in diabetes is retarded by the dysfunctional local microenvironment. Although there are many studies using hydrogels as substitutes for natural extracellular matrices (ECMs), hydrogels that can mimic both the structure and functions of natural ECM remain a challenge. Self-assembling peptide RADA16 nanofiber has distinct advantages to provide a biomimetic extracellular matrix nanofiber structure. However, it still lacks biological cues to promote angiogenesis that is of vital significance for diabetic wound healing. With a customized copper peptide glycyl-histidyl-lysine (GHK) functionalized RADA16, an integrated approach using functionalized RADA16 nanofiber to chelate copper ion, is innovatively proposed in this present study. The acquired composite hydrogel holds the biomimetic nanofiber architecture, and exhibits promoting angiogenesis by both enhancing adhesion and proliferation of endothelial cells (EC) in vitro and neovascularization in vivo. It shows that the functionalized nanofiber scaffolds significantly accelerated wound closure, collagen deposition, and tissue remodeling both in healthy and diabetic mice. Furthermore, immunohistochemical analysis give evidence that an upregulated expression of eNOS and CD31 in the copper peptide-functionalized RADA16 treated group. It can be envisioned that this scaffold can serve as a promising dressing for diabetic wound healing.

Biomimetic porous hydrogel scaffolds enabled vascular ingrowth and osteogenic differentiation for vascularized tissue-engineered bone regeneration

The construction of vascularized tissue-engineered bone (VTEB) has been a promising alternative for bone defect repair but remains a remarkable challenge. To date, there have been very limited breakthroughs in VTEB regeneration based on hydrogel scaffolds due to nutrient exchange obstacle caused by a dense hydrogel network, as well as the lack of an osteogenic microenvironment and vascularized pipeline. Here, we developed a novel strategy to prepare porous hydrogel scaffolds with bone biomimetic microenvironments to promote vascular ingrowth and osteogenic differentiation for VTEB regeneration. Based on the phase-separation void-formation technology, porous hydrogel scaffolds with satisfactory mass transport capability were conveniently prepared using gelatin methacryloyl (GelMA) and poly (ethylene oxide) (PEO) emulsified two-phase aqueous solutions. By further combining the osteogenic ingredient, decalcified bone matrix (DBM) particles, and poly (lactic-co-glycolic acid)-encapsulated angiogenic vascular endothelial growth factor (PLGA/VEGF) microspheres, the porous hydrogel scaffolds with biomimetic osteogenic/angiogenic microenvironments were successfully constructed. Moreover, the osteogenic/angiogenic designs based on the DBM particles, porous structure, and VEGF-released microspheres efficiently enhanced the survival, spreading, migration, and osteogenic differentiation of BMSCs in the hydrogels in vitro, and significantly prompted bone regeneration of BMSC-laden hydrogels in vivo. More importantly, in situ bone defects in a rabbit skull model were successfully repaired with VTEB regenerated by BMSC-laden biomimetic porous hydrogels. This study developed a novel bone-biomimetic porous hydrogel scaffold, which provided promising strategies for ectopic VTEB regeneration and in situ bone defect repair.

Mimicking Extracellular Matrix via Engineered Nanostructured Biomaterials for Neural Repair.

Extracellular matrix (ECM) consists of proteins, proteoglycans, and different soluble molecules. ECM provides structural support to mammalian cells. ECM is responsible for important cell functions, as well as assembling cells into various tissues and organs, regulating growth and cell-cell interaction. Recent studies have shown the potential of nanostructured biomaterials to mimic native ECM. Developing tailor-made biomaterials that mimic the complex nanoscale mesh of local ECM is not a trivial endeavor: bio-inspired biomaterials are designed to supply a healthy ECM-like structure, capable of filling the lesion cavity, favoring transplanted cell engraftment, providing physical support to endogenous neurogenesis and also tuning the inflammatory response to protect spared neurons. The strategies used to manufacture biomimetic hydrogel scaffold represent particularly important prospects of novel therapies for CNS regeneration. During this review, we describe with details the most promising regulatory pathways from ECM involved in the CNS injury and regeneration and we draw a line to the biomimetic potential of engineered nanostructured biomaterials aimed at mimicking extracellular matrix constructs and favoring the release of pro-regenerative agents. Lastly, a brief overview of their application in clinical trials is provided.

Adipose-Derived Stromal Cells Seeded in Pullulan-Collagen Hydrogels Improve Healing in Murine Burns.

Burn scars and scar contractures cause significant morbidity for patients. Recently, cell-based therapies have been proposed as an option for improving healing and reducing scarring after burn injury, through their known proangiogenic and immunomodulatory paracrine effects. Our laboratory has developed a pullulan-collagen hydrogel that, when seeded with mesenchymal stem cells (MSCs), improves cell viability and augments their proangiogenic capacity in vivo. Concurrently, recent research suggests that prospective isolation of cell subpopulations with desirable transcriptional profiles can be used to further improve cell-based therapies. In this study, we examined whether adipose-derived stem cell (ASC)-seeded hydrogels could improve wound healing following thermal injury using a murine contact burn model. Partial thickness contact burns were created on the dorsum of mice. On days 5 and 10 following injury, burns were debrided and received either ASC hydrogel, ASC injection alone, hydrogel alone, or no treatment. On days 10 and 25, burns were harvested for histologic and molecular analysis. This experiment was repeated using CD26+/CD55+ FACS-enriched ASCs to further evaluate the regenerative potential of ASCs in wound healing. ASC hydrogel-treated burns demonstrated accelerated time to reepithelialization, greater vascularity, and increased expression of the proangiogenic genes MCP-1, VEGF, and SDF-1 at both the mRNA and protein level. Expression of the profibrotic gene Timp1 and proinflammatory gene Tnfa was downregulated in ASC hydrogel-treated burns. ASC hydrogel-treated burns exhibited reduced scar area compared to hydrogel-treated and control wounds, with equivalent scar density. CD26+/CD55+ ASC hydrogel treatment resulted in accelerated healing, increased dermal appendage count, and improved scar quality with a more reticular collagen pattern. Here we find that ASC hydrogel therapy is effective for treating burns, with demonstrated proangiogenic, fibromodulatory, and immunomodulatory effects. Enrichment for CD26+/CD55+ ASCs has additive benefits for tissue architecture and collagen remodeling postburn injury. Research is ongoing to further facilitate clinical translation of this promising therapeutic approach. Impact statement Burns remain a significant public health burden. Stem cell therapy has gained attention as a promising approach for treating burns. We have developed a pullulan-collagen biomimetic hydrogel scaffold that can be seeded with adipose-derived stem cells (ASCs). We assessed the delivery and activity of our scaffold in a murine contact burn model. Our results suggest that localized delivery of ASC hydrogel treatment is a promising approach for the treatment of burn wounds, with the potential for rapid clinical translation. We believe our work will have broad implications for both hydrogel therapeutics and regenerative medicine and will be of interest to the general scientific community.

Biomimetic Hydrogels Loaded with Nanofibers Mediate Sustained Release of pDNA and Promote In Situ Bone Regeneration.

Polymer hydrogels are generally insufficient biomechanics, strong resistance to cell adhesion, and weak bioactivity which limits their application in bone tissue engineering considerably. In order to develop a bone tissue engineering material with both good mechanical properties, osteogenic and angiogenic activity. Nanofibers carrying DNA plasmid (pNF) are introduced to gelatin methacryloyl (GelMA) and thiolated chitosan (TCS) system for preparing a novel GelMA/TCS/pNF composite hydrogel with dual network structure. By characterization of the compressive measurements, the resulting composite scaffold shows greatly enhanced mechanical strength (0.53MPa) and is not damaged after 20 cycles of compression. And the fabricated composite scaffold displays sustained release of bone morphogenetic protein-2 that can induce osteogenic differentiation and angiopoietin-1 that promotes vascularization. The cell experiment shows that this system can significantly promote MC3T3-E1 cell attachment, proliferation, as well as osteogenic-related and angiogenic-related genes expression of MC3T3-E1 cells. Moreover, the in vivo results show that the composite scaffold with activated gene fibers can significantly promote osteogenesis and vascularization leading to favorable capacity of bone regeneration, meaning that the resulting biomimetic composite hydrogel scaffolds are excellent candidates for bone repair materials.

Effect of microfracture combined with biomimetic hydrogel scaffold on rotator cuff tendon-to-bone healing in rabbits

To assess the effect of microfracture and biomimetic hydrogel scaffold on tendon-to-bone healing in a rabbit rotator cuff tear model. Gelatin and methacrylic anhydride were used to synthesize gelatin methacryloyl (GelMA). Then the GelMA were treated with ultraviolet rays and vacuum freeze-drying method to obtain a biomimetic hydrogel scaffold. The morphology of the scaffold was observed by gross observation and scanning electron microscope. Degradation of the scaffold was determined at different time points. Twenty-four adult New Zealand rabbits, weighting 2.8-3.5 kg and male or female, were surgically created the bilateral acute rotator cuff tear models. One shoulder was treated with microfractures on the footprint and transosseous suture (control group, n=24). The other shoulder was treated with the same way, except for putting the scaffold on the footprint before transosseous suture (experimental group, n=24). The general conditions of rabbits were observed postoperatively. Tendon-to-bone healing was evaluated by gross observation, Micro-CT, HE staining, and bio-mechanical testing at 4 and 8 weeks after operation. The scaffold was white and has a porous structure with pore size of 31.7-89.9 μm, which degraded slowly in PBS solution. The degradation rate was about 95% at 18 days. All the rabbits survived to the completion of the experiment. Micro-CT showed that there was no obvious defect and re-tear at the tendon-to-bone interface in both groups. No difference was found in bone mineral density (BMD), tissue mineral density (TMD), and bone volume/total volume (BV/TV) between the two groups at 4 and 8 weeks postoperatively ( P>0.05). HE staining showed that the fibrous scar tissue was the main component at the tendon-to-bone interface in the control group at 4 and 8 weeks postoperatively; the disorderly arranged mineralized cartilage and fibrocartilage formation were observed at the tendon-to-bone interface in the experimental group at 4 weeks, and the orderly arranged cartilage formation was observed at 8 weeks. Besides, the tendon maturation scores of the experimental group were significantly higher than those of the control group at 4 and 8 weeks ( P<0.05). There was no significant difference in the ultimate load to failure and stiffness between the two groups at 4 weeks ( P>0.05); the ultimate load to failure at 8 weeks was significantly higher in the experiment group than in the control group ( t=4.162, P=0.009), and no significant difference was found in stiffness between the two groups at 8 weeks ( t=2.286, P=0.071). Compared with microfracture alone, microfracture combined with biomimetic hydrogel scaffold can enhance tendon-to-bone healing and improve the ultimate load to failure in rabbits.

Fabrication of micro-porous hyaluronic acid hydrogels through salt leaching

Development of physiologically relevant culture platforms for studying cell behavior has been of particular interest in tissue engineering as well as in development of in vitro disease models. Hyaluronic acid is a glycosaminoglycan found in the extracellular matrix, derivatives of which are commonly used to create three-dimensional biomimetic hydrogel scaffolds for the study of cell behavior in vitro. Herein, we report the fabrication of micro-porous hyaluronic acid hydrogels using a simple salt leaching technique. Porogens, specifically, salt particles of different sizes (i.e., <63 µm, 63–106 µm, 106–250 µm in diameter), were utilized to obtain a range of porous structures. The microstructure of the hydrogels was characterized through scanning electron microscopy, and rheological and swelling studies were performed to further evaluate morphological and mechanical properties. Analysis of these studies indicated that an increase in pore area corresponded to a larger porogen size, whereas porogen size had no significant effect on storage modulus or water absorption. However, porous hydrogels exhibited a greater degree of swelling and reduced storage modulus compared to nonporous hydrogels. In particular, the largest particle size of 106–250 µm resulted in a swelling ratio of 44.6 ± 2.28 and storage modulus of 54 ± 4.97 Pa versus a swelling ratio of 24.3 ± 2.30 and storage modulus of 402 ± 209 Pa noted for nonporous hyaluronic acid hydrogels, respectively. No significant difference in degradation of hydrogels was observed at later time points; however, hydrogels with the largest pore area degraded to a greater extent initially. Assessment of cellular compatibility showed no evidence of cytotoxicity for all hydrogel conditions tested. Such a system, incorporating micron-level porosity, could provide a useful tool for studying cell–matrix interactions in a physiologically relevant setting.

Delivery of MSCs with a Hybrid β-Sheet Peptide Hydrogel Consisting IGF-1C Domain and D-Form Peptide for Acute Kidney Injury Therapy.

PurposeBy providing a stem cell microenvironment with particular bioactive constituents in vivo, synthetic biomaterials have been progressively successful in stem cell-based tissue regeneration by enhancing the engraftment and survival of transplanted cells. Designs with bioactive motifs to influence cell behavior and with D-form amino acids to modulate scaffold stability may be critical for the development and optimization of self-assembling biomimetic hydrogel scaffolds for stem cell therapy.Materials and MethodsIn this study, we linked naphthalene (Nap) covalently to a short D-form peptide (Nap-DFDFG) and the C domain of insulin-like growth factor-1 (IGF-1C) as a functional hydrogel-based scaffolds, and we hypothesized that this hydrogel could enhance the therapeutic efficiency of human placenta-derived mesenchymal stem cells (hP-MSCs) in a murine acute kidney injury (AKI) model.ResultsThe self-assembling peptide was constrained into a classical β-sheet structure and showed hydrogel properties. Our results revealed that this hydrogel exhibited increased affinity for IGF-1 receptor. Furthermore, cotransplantation of the β-IGF-1C hydrogel and hP-MSCs contributed to endogenous regeneration post-injury and boosted angiogenesis in a murine AKI model, leading to recovery of renal function.ConclusionThis hydrogel could provide a favorable niche for hP-MSCs and thereby rescue renal function in an AKI model by promoting cell survival and angiogenesis. In conclusion, by covalently linking the desired functional groups to D-form peptides to create functional hydrogels, self-assembling β-sheet peptide hydrogels may serve as a promising platform for tissue-engineering and stem cell therapy.

Integration of flexible polyimide arrays into soft extracellular matrix-based hydrogel materials for a tissue-engineered electronic nerve interface (TEENI)

BackgroundBiomimetic hydrogels used in tissue engineering can improve tissue regeneration and enable targeted cellular behavior; there is growing interest in combining hydrogels with microelectronics to create new neural interface platforms to help patient populations. However, effective processes must be developed to integrate flexible but relatively stiff (e.g., 1−10 GPa) microelectronic arrays within soft (e.g., 1−10 kPa) hydrogels. New methodHere, a novel method for integrating polyimide microelectrode arrays within a biomimetic hydrogel scaffold is demonstrated for use as a tissue-engineered electronic nerve interface (TEENI). Tygon tubing and a series of 3D printed molds were used to facilitate hydrogel fabrication and device assembly. Comparison with existing methodsOther comparable regenerative peripheral nerve interface technologies do not utilize the flexible microelectrode array design nor the hydrogel scaffold described here. These methods typically use stiff electrode arrays that are affixed to a similarly stiff implantable tube serving as the nerve guidance conduit. ResultsOur results indicate that there is a substantial mechanical mismatch between the flexible microelectronic arrays and the soft hydrogel. However, using the methods described here, there is consistent fabrication of these regenerative peripheral nerve interfaces suitable for implantation. ConclusionsThe assembly process that was developed resulted in repeatable and consistent integration of microelectrode arrays within a soft tissue-engineered hydrogel. As reported elsewhere, these devices have been successfully implanted in a rat sciatic nerve model and yielded neural recordings. This process can be adapted for other applications and hydrogels in which flexible electronic materials are combined with soft regenerative scaffolds.

3D-bioprinted functional and biomimetic hydrogel scaffolds incorporated with nanosilicates to promote bone healing in rat calvarial defect model.

Three-dimensional (3D) bioprinting is an extremely convenient biofabrication technique for creating biomimetic tissue-engineered bone constructs and has promising applications in regenerative medicine. However, existing bioinks have shown low mechanical strength, poor osteoinductive ability, and lacking a suitable microenvironment for laden cells. Nanosilicate (nSi) has shown to be a promising biomaterial, due to its unique properties such as excellent biocompatibility, degrade into nontoxic products, and with osteoinductive properties, which has been used in bone bioprinting. However, the long term bone healing effects and associating risks, if any, of using nSi in tissue engineering bone scaffolds in vivo are unclear and require a more thorough assessment prior to practical use. Hence, a functional and biomimetic nanocomposite bioink composed of rat bone marrow mesenchymal stem cells (rBMSCs), nSi, gelatin and alginate for the 3D bioprinting of tissue-engineered bone constructs is firstly demonstrated, mimicking the structure of extracellular matrix, to create a conducive microenvironment for encapsulated cells. It is shown that the addition of nSi significantly increases the printability and mechanical strength of fabricated human-scale tissue or organ structures (up to 15mm height) and induces osteogenic differentiation of the encapsulated rBMSCs in the absence of in vitro osteoinductive factors. A systematic in vivo research of the biomimetic nanocomposite bioink scaffolds is further demonstrated in a rat critical-size (8mm) bone defect-repair model. The in vivo results demonstrate that the 3D bioprinted nanocomposite scaffolds can significantly promote the bone healing of the rat calvarial defects compared to other scaffolds without nSi or cells, and show rarely side effects on the recipients. Given the above advantageous properties, the 3D bioprinted nanocomposite scaffolds can greatly accelerate the bone healing in critical bone defects, thus providing a clinical potential candidate for orthopedic applications.