Scaffolds For Repair Research Articles

Investigating the Biological Efficacy of Albumin-Enriched Platelet-Rich Fibrin (Alb-PRF): A Study on Cytokine Dynamics and Osteoblast Behavior

The development of effective biomaterials for tissue regeneration has led to the exploration of blood derivatives such as leucocyte- and platelet-rich fibrin (L-PRF). A novel variant, Albumin-Enriched Platelet-Rich Fibrin (Alb-PRF), has been introduced to improve structural stability and bioactivity, making it a promising candidate for bone regeneration. This study aimed to evaluate Alb-PRF’s capacity for cytokine and growth factor release, along with its effects on the proliferation, differentiation, and mineralization of human osteoblasts in vitro. Alb-PRF membranes were analyzed using histological, scanning electron microscopy, and fluorescence microscopy techniques. Cytokine and growth factor release was quantified over seven days, and osteoinductive potential was evaluated with MG-63 osteoblast-like cells. Structural analysis showed Alb-PRF as a biphasic, highly cellularized material that releases lower levels of inflammatory cytokines and higher concentrations of platelet-derived growth factor (PDGF) and vascular endothelial growth factor (VEGF) compared to L-PRF. Alb-PRF exhibited higher early alkaline phosphatase activity and in vitro mineralization (p < 0.05) and significantly increased the OPG/RANKL mRNA ratio (p < 0.05). These results indicate that Alb-PRF has promising potential as a scaffold for bone repair, warranting further in vivo and clinical assessments to confirm its suitability for clinical applications.

3D printed collagen scaffold for heart valve repair

Three-dimensional (3D) bioprinting has emerged as a promising approach for the development of functional tissues and organs, including the heart valves. In this study, we investigated the interaction of 3D printed collagen scaffolds with H9c2(2–1) and NIH/3T3 cells to improve heart-valve repair strategies. Type I collagen was extracted from rat tails, characterized using SDS-PAGE and Raman spectroscopy, and used as a biomaterial ink for 3D printing. The rheological properties were evaluated. The FRESH technique was used to support the printed construct. In vitro assessments were performed to determine the cell viability and distribution within the scaffold. These results demonstrated the successful extraction and characterization of Type I collagen, which exhibited suitable rheological properties for 3D bioprinting. The printed collagen scaffolds supported the growth and distribution of H9c2(2–1) and NIH/3T3 cells, indicating their potential application in heart valve repair. This study highlights the importance of collagen as a biomaterial in 3D bioprinting and provides insights into the development of advanced strategies for heart valve repair.

Biomimetic Mineralized Organic–Inorganic Hybrid Scaffolds From Microfluidic 3D Printing for Bone Repair

AbstractBone defect is a common clinical orthopedic disease. The trend in this field is to develop tissue engineering scaffolds with appropriately designed components and structures for bone repair. Herein, inspired by the organic and inorganic components of bone matrix and the natural biomineralization mechanism, a MgSiO3@Fe3O4 nanoparticle composite polycaprolactone (PCL) hybrid mineralized scaffold for bone repair is developed by microfluidic 3D printing. The incorporation of MgSiO3@Fe3O4 within the PCL scaffold can effectively improve the bioactivity. In addition, a biomimetic mineralized layer is prepared on the surface of the scaffold, which endowed it with unique microstructural characteristics, enhanced cell adhesion and osteogenic activity, and thus improved the bone repair performance. Owing to these advantages, both in vivo and in vitro experiments have demonstrated that the designed scaffold has outstanding biocompatibility and bone repair performance. These features indicate that the organic–inorganic biomineralized hybrid scaffold can be a potential bone graft substitute for clinical bone repair.

A strategy for introducing biopotency-enhanced chirality coating on bio-magnesium

Biomedical magnesium alloys (Mg) are often considered potential metallic materials for bone repair scaffolds due to their excellent biomechanical properties, biocompatibility, and biodegradability. However, their rapid degradation behavior is insufficient to support the rapid growth and repair of living tissues. The new surface modification methods to slow down the degradation rate of Mg scaffolds and promote the rapid growth of living tissues is urgent. Here, we developed a chiral-enhanced composite functional coating on the surface of biomedical magnesium. Specifically, a chiral supramolecular hydrogel with graphene oxide (GO) was used to simulate the chiral environment of biological systems, enhancing the adsorption of osteogenic growth factors. Additionally, the silane layers cleverly crosslink traditional silane chains with supramolecular chiral fibers through a hydrogen bond network, which allows the bonding strength (critical loads) of the composite coating to be maintained between 245–275 mN and retains structural integrity when soaked in SBF for 7 days. It was found that both MC3T3-E1 cells growth and BMP-2 adhesion were significantly enhanced by GO-added left-handed chiral coatings, which exhibit superior bone growth-promoting effects. In summary, incorporating chiral features into functional coatings represents a transformative approach in the design and application of bone defect repair materials.

Tuning the stiffness and stretchability of micro-scale-structured polymer membrane simultaneously by integrating mechanical modeling and spatiotemporal controllable photolithograph

Micro-scale structural polymer membranes with desired mechanical properties, such as modulus and stretchability, have extensive applications in repair scaffolds, stretchable electronic devices, etc., yet how to achieve the simultaneous tunability of high modulus (MPa-level) and excellent resilience in micron-scale polymer membrane remains challenge. In this work, based on the material-structure integrated design aided by mechanical modeling and photolithograph, a micro-scale-structured solid-state lithography polyurethane-urea (UVSLPU) membrane has been fabricated, achieving a wide range of controllability on elastic modulus of 25-55 MPa and stretchability of 2.7-7.6 by simultaneously controlling the exposure time and area. Based on the physical mechanism of solid-state lithography, a novel visco-hyperelastic constitutive model is developed to facilitate the quantitative tunning of the mechanical property of UVSLPU. According to the microstructure analysis, the model decomposes the free energy of UVSLPU into three components, including crosslinked network, free chains as well as dangling chains, and describes the influence of exposure time on their nonlinear evolutions through increasing chain density and reducing the number of Kuhn monomers per chain. The proposed model is validated through uniaxial tensile tests conducted at different strain rates and exposure conditions, and reveals the significant contribution of crosslinks and free chains in enhancing the modulus over exposure time. Then, by integrating constitutive modeling and spatiotemporal controllable photolithograph, the design and manufacture for the micro-scale-structured UVSLPU membrane achieving increasing stiffness without losing the stretchability is realized by precisely controlling the exposure area. This work offers a novel and efficient approach for the design and manufacture of micro-scale-structured membranes with desired mechanical properties.

Incorporation of small extracellular vesicles in PEG/HA-Bio-Oss hydrogel composite scaffold for bone regeneration

Stem cell derived small extracellular vesicles (sEVs) have emerged as promising nanomaterials for the repair of bone defects. However, low retention of sEVs affects their therapeutic effects. Clinically used natural substitute inorganic bovine bone mineral (Bio-Oss) bone powder lacks high compactibility and efficient osteo-inductivity that limit its clinical application in repairing large bone defects. In this study, a poly ethylene glycol/hyaluronic acid (PEG/HA) hydrogel was used to stabilize Bio-Oss and incorporate rat bone marrow stem cell-derived sEVs (rBMSCs-sEVs) to engineer a PEG/HA-Bio-Oss (PEG/HA-Bio) composite scaffold. Encapsulation and sustained release of sEVs in hydrogel scaffold can enhance the retention of sEVs in targeted area, achieving long-lasting repair effect. Meanwhile, synergistic administration of sEVs and Bio-Oss in cranial defect can improve therapeutic effects. The PEG/HA-Bio composite scaffold showed good mechanical properties and biocompatibility, supporting the growth of rBMSCs. Furthermore, sEVs enhancedin vitrocell proliferation and osteogenic differentiation of rBMSCs. Implantation of sEVs/PEG/HA-Bio in rat cranial defect model promotedin vivobone regeneration, suggesting the great potential of sEVs/PEG/HA-Bio composite scaffold for bone repair and regeneration. Overall, this work provides a strategy of combining hydrogel composite scaffold systems and stem cell-derived sEVs for the application of tissue engineering repair.

Synergistic effects of calcium and zinc on bio-functionalized 3D Ti cancellous bone scaffold with enhanced osseointegration capacity in rabbit model

The present research aims to develop a Ca-Zn ion-incorporated surface functionalized 3D Ti cancellous bone scaffold for bone defect repair. The scaffold is designed to mimic human cancellous bone architecture through selective laser melting-based additive manufacturing. The chemical-based surface modification approach employed here created a Ca and Zn ions incorporated nano-porous surface layer with enhanced surface roughness and hydrophilicity. The modified biomimetic scaffold improved corrosion resistance behaviour with ICORR and ECORR values of 0.174 and 0.0097 respectively. It is learned that incorporating Zn as ZnO over the scaffold has antibacterial activity against Staphylococcus aureus and Escherichia coli. The cellular response of MG-63 to the modified scaffold was evaluated through in-vitro studies which focus on the cytocompatible properties. The intra-osseous biomimetic Ti-Na-Ca:Zn 3D scaffold revealed significant improvement in the osseointegration capabilities in terms of bone mineral density (BMD) and bone volume/total volume (BV/TV) in the rabbit model. The osseointegration potential at the Ti-Na-Ca:Zn interface was evidenced by histological analysis and micro-CT imaging. In addition to this, the remarkable upregulation of osteogenic genes such as OCN, COL1A1, OPN, ALP, RUNX2, and OSX evidences the dynamics of the osseointegration process at each surgical period. This Ca and Zn surface functionalised porous architecture of the 3D Ti cancellous bone scaffold similar to bone with enhanced biological response and bone integration can potentially allow implant customisation by utilizing additive manufacturing technology with improved clinical outcomes.

Laser powder bed fusion printed poly-ether-ether-ketone/bioactive glass composite scaffolds with dual-scale pores for enhanced osseointegration and bone ingrowth

Although poly-ether-ether-ketone (PEEK) implants hold significant medical promise, their bioinert nature presents challenges in osseointegration and bone ingrowth within clinical contexts. To mitigate these challenges, the present study introduces Diamond PEEK/bioactive glass (BG) composite scaffolds, characterized by macro/micro dual-porous structures, precisely fabricated via laser powder bed fusion (LPBF) technology. The findings indicate that an increase in BG content within these scaffolds significantly augments their hydrophilicity and hydroxyapatite formation capacities. Stress-strain curve analysis demonstrates reliable load-bearing stability across all scaffold types. In vitro assessments confirmed the non-cytotoxicity of PEEK/BG samples and demonstrated improved osteogenic differentiation and mineralization with increased BG incorporation. Further, in vivo experiments illustrated that the Diamond porous structure of these scaffolds facilitated bone growth, an effect notably amplified with higher BG content. Particularly in groups with 15 wt% and 25 wt% BG scaffolds, new bone formation was observed not only within the macropores of the Diamond structure but also within the micropores inside the scaffold rod, suggesting an almost seamless fusion with the new bone. This demonstrates the scaffolds’ effective osteointegration and bone ingrowth properties. This study conclusively established the effectiveness of Diamond-structured PEEK/BG composite scaffolds, fabricated via LPBF, in bone repair. It highlights the crucial role of BG in enhancing osteogenic potential through interaction with the macro/micro pores of the scaffold. Statement of significanceThis study addresses the bioinert nature of PEEK implants by developing Diamond-structured PEEK/bioactive glass (BG) composite scaffolds by laser powder bed fusion. The dual-porous macro/microstructure enhances hydrophilicity and hydroxyapatite formation, vital for bone regeneration. By adjusting the BG content, we controlled the melt viscosity and sintering rate, leading to the formation of beneficial microscale pores. These pores resolve the issue of ineffective bioactive fillers in previous LPBF-fabricated scaffolds, enhancing the osteogenic potential of BG and inducing superior bone ingrowth and osseointegration. In vitro and in vivo analyses show enhanced osteogenic differentiation, mineralization, and bone growth, underscoring the clinical potential of these scaffolds for bone repair.

Mesenchymal stem cells derived extracellular vesicles modified PLGA electrospinning nanofibrous scaffolds for corneal and retinal repair

Tissue self-renewal is crucial for ocular diseases such as corneal damage and retinal holes. In this study, a novel Poly (lactic-co-glycolic acid) (PLGA) electrospinning nanofibrous scaffold (PLGAENS), loaded with mesenchymal stem cells-derived extracellular vesicles (MSC-EVs), was developed to accelerate the healing of the cornea and retina. In-vitro experiments confirmed the supportive properties of PLGAENS, demonstrating its ability to promote cellular proliferation, migration, and extension. In the rat corneal alkali burn model and rabbit retinal hole model, MSC-EVs modified PLGAENS (PLGAMSC-EVs) accelerated the restoration of the corneal epithelium and stroma, as well as the closure of retinal holes. Additionally, miR-21-5p was identified as being enriched in MSC-EVs. Mechanistically, miR-21-5p suppressed scar formation by targeting the programmed cell death protein 4 (PDCD4) gene, reducing fibrosis and the expression of collagen-related genes, which helped maintain corneal transparency and retinal integrity. Overall, these findings underscored the potential of PLGAMSC-EVs in promoting ocular wound healing and suggested a promising new therapeutic strategy for the clinical treatment of corneal damage and retinal holes.

Vat photopolymerization of ultra-porous bioactive glass foams

The introduction of additive manufacturing technologies in the field of biomaterials science has opened new horizons for regenerative medicine. In this work, we pushed the potential of vat polymerization to the limit for fabricating ultra-porous bioactive SiO2-CaO-MgO-P2O5-CaF2-Na2O glass scaffolds with bone-like architectural characteristics. The tomographic reconstruction of an open-cell foam was used as input file to the printing system and reliably reproduced in all its exquisite details, as assessed by morphological analyses of sintered scaffolds (thickness of single struts 35 μm, exceptionally high porosity around 94 vol%, most pores with size from 500 to 900 μm). Immersion studies in simulated body fluid (SBF) revealed the apatite-forming ability (i.e., in vitro bioactivity) of the scaffolds, the surface of which started being coated by calcium phosphate after just 3 days from the beginning of the experiments. Taken together, these results show great promise for application of such scaffolds in bone defect repair.

Harnessing potential of microwave-assisted ultrafast synthesis of reduced graphene oxide/Mn3O4 bioactive nanocomposite hydrogel for bone tissue engineering

The development of functional materials with the potential for bone tissue regeneration along with rapid synthesis and cost-effective approach has been challenging. In this regard, hydrogels have been explored as a potent candidate to behave as a 3D scaffold for bone repair. However, poor mechanical attributes impeded their clinical translation. Enthralling demonstration of the potential of carbon-based nanocomposites in bone tissue engineering has been constantly encouraging the fabrication of advanced nanocomposites. Here, we investigated the fabrication of reduced graphene/manganese (II, III) oxide (RGO/Mn3O4) nanocomposites by taking advantage of the microwave-assisted synthesis approach for cost effective, and ultrafast synthesis. Mn3O4 nanoparticles with uniform distribution in RGO sheets and ∼ 1.7 nm size was fabricated using the approach. Further, fine-tuning of the structural interaction and mechanical behavior of the GelMA-based hydrogels upon reinforcement with RGO/Mn3O4 nanocomposites was investigated as a function of different concentrations of the nanocomposites where upto 50 % increment in the compressive stress was observed compared to native GelMA hydrogel. The ability of these hydrogels was further investigated for their osteogenic behaviour on MC3T3-E1 preosteoblast cells where constant cell proliferation for up to 10 days was witnessed for the hybrid hydrogel with the highest concentration of the nanofillers.

Cartilage Repair: Promise of Adhesive Orthopedic Hydrogels.

Cartilage repair remains a major challenge in human orthopedic medicine, necessitating the application of innovative strategies to overcome existing technical and clinical limitations. Adhesive hydrogels have emerged as promising candidates for cartilage repair promotion and tissue engineering, offering key advantages such as enhanced tissue integration and therapeutic potential. This comprehensive review navigates the landscape of adhesive hydrogels in cartilage repair, discussing identified challenges, shortcomings of current treatment options, and unique advantages of adhesive hydrogel products and scaffolds. While emphasizing the critical need for in situ lateral integration with surrounding tissues, we dissect current limitations and outline future perspectives for hydrogel scaffolds in cartilage repair. Moreover, we examine the clinical translation pathway and regulatory considerations specific to adhesive hydrogels. Overall, this review synthesizes the existing insights and knowledge gaps and highlights directions for future research regarding adhesive hydrogel-based devices in advancing cartilage tissue engineering.

Biodegradable Piezoelectric-Conductive Integrated Hydrogel Scaffold for Repair of Osteochondral Defects.

Osteochondral injury is a prevalent condition for which no specific treatment is currently available. This study presents a piezoelectric-conductive scaffold composed of a piezoelectric cartilage-decellularized extracellular matrix (dECM) and piezoelectric-conductive modified gelatin (Gel-PC). The piezoelectricity of the scaffold is achieved through the modification of diphenylalanine (FF) assembly on the pore surface, while the conductive properties of scaffold are achieved by the incorporating poly(3,4-ethylenedioxythiophene). In vitro experiments demonstrate that bone marrow mesenchymal stem cells (BMSCs) undergo biphasic division during differentiation. In vivo studies using a Parma pig model of osteochondral defects demonstrate that the piezoelectric-conductive scaffold exhibits superior reparative efficacy. Notably, the generation of electrical stimulation is linked to joint movement. During joint activity, mechanical forces compress the scaffold, leading to deformation and the subsequent generation of an electric potential difference. The positive charges accumulated on the upper layer of the scaffold attract BMSCs, promoting their migration to the upper layer and chondrogenic differentiation. Meanwhile, the negative charges in the lower layer induce the osteogenic differentiation of BMSCs. Overall, this piezoelectric-conducive scaffold provides a promising platform for the effective repair of osteochondral defects.

Microsphere-Composite Hydrogel for Recruiting Stem Cells and Promoting Osteogenic Differentiation.

By recruiting stem cells into scaffolds and differentiating them into osteoblasts, stem cells can be mobilized to directly repair bone defects, which avoids a series of disadvantages of exogenous stem cell implantation. In this study, a microsphere-composite hydrogel for the recruitment and osteogenic differentiation of stem cells was constructed. Methacrylic anhydride modified gelatin (GelMA) and heparin (HepMA), as well as nanohydroxyapatite (nHAP), were used to prepare microspheres followed by adsorbing platelet-derived growth factor BB (PDGF-BB) whose loading efficiency was 53.7 ± 2.2%. Then the microspheres were compounded to the GelMA hydrogel encapsulated with simvastatin (SIM) to obtain microsphere-composite hydrogel GHnH-P@GS. GHnH-P@GS hydrogel could slowly release SIM and PDGF-BB, and the extents of release within 7 days were 44.1 ± 2.0% and 32.8 ± 1.1%. The synergistic effect of small molecule drugs and growth factors not only induced the recruitment of rabbit bone marrow-derived mesenchymal stem cells, but also promoted the osteogenic differentiation of stem cells, which was confirmed by experiments of cell migration, alkaline phosphatase, and alizarin red staining. Collectively, the microsphere-composite hydrogel GHnH-P@GS has a certain reference significance for the design of scaffolds for alveolar bone repair and regeneration.

In vitro studies of biodegradable Zn-0.8Li-0.4 Mg alloy for uterine stent application

Uterine stent implantation is an effective treatment for human intrauterine adhesion. Current clinical interventions, such as Cu-IUD or polymer balloons, have limitations including inflammatory responses and the need for a second operation. Thus, investigating a biodegradable scaffold for uterine repair is crucial. We studied the degradation behavior of the Zn-0.8Li-0.4 Mg alloy in the uterine microenvironment and its compatibility with endometrial epithelial cells. The formation of Li₂CO3 was observed in Zn-0.8Li-0.4 Mg alloy. The in vitro degradation rates of Zn-0.8Li-0.4 Mg alloy were 1.29 × 10-2 mm/year in SUF. The Zn2+ concentration in the extract solution for the Zn-0.8Li-0.4 Mg alloy was 12.94 ± 1.80 mg/L, significantly lower than that of Zn, which was 16.73 ± 2.93 mg/L. Additionally, the Li+ concentration in the Zn-0.8Li-0.4 Mg alloy was 1.35 ± 0.34 mg/L. The alloy exhibited good compatibility with HEECs cultured in a 50 % leaching solution and culture on the surface of the Zn-0.8Li-0.4 Mg alloy, suggesting its potential for intrauterine applications.

Highly aligned electroactive ultrafine fibers promote the differentiation of mesenchymal stem cells into Schwann-like cells for nerve regeneration

This study investigates the efficacy of a novel tissue-engineered scaffold for nerve repair and functional reconstruction following injury. Utilizing stable jet electrospinning, we fabricated aligned ultrafine fibers from dopamine and poly(L-lactic acid) (PLLA), further developing a biomimetic, oriented, and electroactive scaffold comprising poly(pyrrole) (PPy), polydopamine (PDA), and PLLA through dual in situ polymerizations. The scaffold demonstrated enhanced cell adhesion and reactive oxygen species (ROS) scavenging capabilities and promoted the differentiation of mesenchymal stem cells (MSCs) into Schwann-like cells, essential for nerve regeneration. In vivo assessments revealed significant peripheral nerve regeneration in 10 mm sciatic nerve defects in rats, with observations made 12 weeks post-transplantation. This included facilitated myelination and increased muscle density on the injured side, leading to improved motor function recovery. Our results suggest that the aligned PPy/PDA/PLLA fibrous scaffold offers a promising approach for promoting the differentiation of MSCs into Schwann-like cells conducive to nerve regeneration and represents a significant advancement in nerve repair technologies. This study provides a foundational basis for future research into tissue-engineered solutions for nerve damage, potentially impacting clinical strategies for nerve reconstruction.

Diffusion‐induced phase separation 3D printed scaffolds for dynamic tissue repair (3/2024)

Diffusion‐induced phase separation 3D printed scaffolds for dynamic tissue repair (3/2024)

Regenerated Fat Induced by a Decellularized Adipose Matrix Can Survive Long-term In Vivo

Decellularized adipose matrix (DAM) is considered to be the most potential biological scaffold for soft tissue repair and reconstruction, as it is able to induce the regeneration of adipose tissue in situ in adulthood. But how does this adipose tissue regeneration happen and develop in vivo? Is it the same as the original autologous one? Temporary existence or long-term survival? These are the key questions that will determine the future applications of DAM. In this study, we investigated the composition, structure and biomechanical properties of DAM before implanting it into the subcutaneous back of immunodeficient mice. The entire regeneration process in vivo was closely monitored histologically from 3 days to 1 year after implantation, including fat regeneration, vascular growth, inflammatory responses, and matrix degradation and remodeling. Transcriptome sequencing was used to analyze the difference in gene expression between regenerated fat and autologous fat at different periods. The results showed that the DAM-induced regenerated fat first appeared at 1w and remained stable over 6m, indicating remarkable similarity to autologous fat at the later stages of implantation. And about (18.3 ± 29.3) % of the regenerated adipocytes were still viable after one year. The process of adipogenesis was enhanced by the decrease in inflammatory infiltration and proceeded in parallel with angiogenesis. Statement of significance: The decellularized adipose matrix (DAM) is the only biological scaffold that can spontaneously generate adipocytes in vivo without the need to add exogenous cells. However, in the previous studies, the longest DAM-related animal experiments were about 3 months. The different stages and characteristics of DAM implantation cannot be fully captured. Comprehensive preclinical researches on the initiation, characteristics, and long-term outcomes of DAM-induced adipose tissue regeneration in adulthood is crucial.In this study, we closely observed various aspects of the entire process in vivo from 3 days to 1 year after implantation including fat regeneration, vascular growth, inflammatory reactions as well as matrix degradation and remodeling. The thorough research will contribute to the understanding of stability and dynamic remodeling of DAM regeneration models.

Application and progress of bionic scaffolds in nerve repair: a narrative review

Nerve injury can result in severe damage and potentially permanent disability, imposing substantial physical, psychological, and economic burdens on affected individuals and their families. Despite advances in surgical repair techniques, the functional recovery of nerves remains suboptimal. The current therapeutic approaches for nerve injury exhibit limited efficacy in restoring function, underscoring the imperative for the development of innovative treatment modalities. In recent years, bionics has emerged as a promising field in medicine, particularly in the treatment and rehabilitation of nerve injuries. We review the advances in the application of bionic technology within the realm of nerve injury treatment, encompassing bionic nerve scaffolds, nerve regeneration materials, and nerve modulation techniques. We delve into how these technologies may facilitate the repair and functional restoration of nerve tissues, as well as the challenges they encounter in clinical translation and their prospective directions for future development. Furthermore, we explore the convergence of bionic technology with existing therapeutic strategies and discuss the potential for interdisciplinary collaboration to catalyze innovation in nerve injury treatment. The integration of bionics with conventional methods may offer a synergistic approach, enhancing the efficacy of nerve repair and rehabilitation processes.

Impact of Annealing Chemistry on the Properties and Performance of Microporous Annealed Particle Hydrogels.

Microporous annealed particle (MAP) hydrogels are a promising class of in situ-forming scaffolds for tissue repair and regeneration. While an expansive toolkit of annealing chemistries has been described, the effects of different annealing chemistries on MAP hydrogel properties and performance have not been studied. In this study, we address this gap through a controlled head-to-head comparison of poly(ethylene glycol) (PEG)-based MAP hydrogels that were annealed using tetrazine-norbornene and thiol-norbornene click chemistry. Characterization of material properties revealed that tetrazine click annealing significantly increases MAP hydrogel shear storage modulus and results in slower in vitro degradation kinetics when microgels with a higher cross-link density are used. However, these effects are muted when the MAP hydrogels are fabricated from microgels with a lower cross-link density. In contrast, in vivo testing in murine critical-sized calvarial defects revealed that these differences in physicochemical properties do not translate to differences in bone volume or calvarial defect healing when growth-factor-loaded MAP hydrogel scaffolds are implanted into mouse calvarial defects. Nonetheless, the impact of tetrazine click annealing could be important in other applications and should be investigated further.