Structure and biocompatibility of an injectable bone regeneration composite

Advancements and Applications of Injectable Hydrogel Composites in Biomedical Research and Therapy

Injectable hydrogels have gained popularity for their controlled release, targeted delivery, and enhanced mechanical properties. They hold promise in cardiac regeneration, joint diseases, postoperative analgesia, and ocular disorder treatment. Hydrogels enriched with nano-hydroxyapatite show potential in bone regeneration, addressing challenges of bone defects, osteoporosis, and tumor-associated regeneration. In wound management and cancer therapy, they enable controlled release, accelerated wound closure, and targeted drug delivery. Injectable hydrogels also find applications in ischemic brain injury, tissue regeneration, cardiovascular diseases, and personalized cancer immunotherapy. This manuscript highlights the versatility and potential of injectable hydrogel nanocomposites in biomedical research. Moreover, it includes a perspective section that explores future prospects, emphasizes interdisciplinary collaboration, and underscores the promising future potential of injectable hydrogel nanocomposites in biomedical research and applications.

Risedronate-Loaded Macroporous Gel Foam Enriched with Nanohydroxyapatite: Preparation, Characterization, and Osteogenic Activity Evaluation Using Saos-2 Cells

The application of minimally invasive surgical techniques in the field of orthopedic surgery has created a growing need for new injectable synthetic materials that can be used for bone grafting. In this work, novel injectable thermosensitive foam was developed by mixing nHAP powder with a thermosensitive polymer with foaming power (Pluronic F-127) and loaded with a water-soluble bisphosphonate drug (risedronate) to promote osteogenesis. The foam was able to retain the porous structure after injection and set through temperature change of PF-127 solution to form gel inside the body. The effect of different formulation parameters on the gelation time, porosity, foamability, injectability, and in vitro degradation in addition to drug release from the prepared foams were analyzed using a full factorial design. The addition of a co-polymer like methylcellulose or sodium alginate into the foam was also studied. Results showed that the prepared optimized thermosensitive foam was able to gel within 1 min at 37°C, and sustain the release of drug for 72 h. The optimized formulation was further tested for any interactions using DSC and IR, and revealed no interactions between the drug and the used excipients in the prepared foam. Furthermore, the ability of the pre-set foam to support osteoblastic-like Saos-2-cell proliferation and differentiation was assessed, and revealed superior function on promoting cellular proliferation as confirmed by fluorescence microscope compared to the plain drug solution. The activity of the foam treated cells was also assessed by measuring the alkaline phosphatase activity and calcium deposition, and confirmed that the cellular activity was greatly enhanced in foam treated cells compared to those treated with the plain drug solution only. The obtained results show that the prepared risedronate-loaded thermosensitive foam would represent a step forward in the design of new materials for minimally invasive bone regeneration.

Drug-Loadable Calcium Alginate Hydrogel System for Use in Oral Bone Tissue Repair

This study developed a drug-loadable hydrogel system with high plasticity and favorable biological properties to enhance oral bone tissue regeneration. Hydrogels of different calcium alginate concentrations were prepared. Their swelling ratio, degradation time, and bovine serum albumin (BSA) release rate were measured. Human periodontal ligament cells (hPDLCs) and bone marrow stromal cells (BMSCs) were cultured with both calcium alginate hydrogels and polylactic acid (PLA), and then we examined the proliferation of cells. Inflammatory-related factor gene expressions of hPDLCs and osteogenesis-related gene expressions of BMSCs were observed. Materials were implanted into the subcutaneous tissue of rabbits to determine the biosecurity properties of the materials. The materials were also implanted in mandibular bone defects and then scanned using micro-CT. The calcium alginate hydrogels caused less inflammation than the PLA. The number of mineralized nodules and the expression of osteoblast-related genes were significantly higher in the hydrogel group compared with the control group. When the materials were implanted in subcutaneous tissue, materials showed favorable biocompatibility. The calcium alginate hydrogels had superior osteoinductive bone ability to the PLA. The drug-loadable calcium alginate hydrogel system is a potential bone defect reparation material for clinical dental application.

Biodegradable, phosphate-containing, dual-gelling macromers for cellular delivery in bone tissue engineering

Injectable, biodegradable, dual-gelling macromer solutions were used to encapsulate mesenchymal stem cells (MSCs) within stable hydrogels when elevated to physiologic temperature. Pendant phosphate groups were incorporated in the N-isopropyl acrylamide-based macromers to improve biointegration and facilitate hydrogel degradation. The MSCs were shown to survive the encapsulation process, and live cells were detected within the hydrogels for up to 28 days in vitro. Cell-laden hydrogels were shown to undergo significant mineralization in osteogenic medium. Cell-laden and acellular hydrogels were implanted into a critical-size rat cranial defect for 4 and 12 weeks. Both cell-laden and acellular hydrogels were shown to degrade in vivo and help to facilitate bone growth into the defect. Improved bone bridging of the defect was seen with the incorporation of cells, as well as with higher phosphate content of the macromer. Furthermore, direct bone-to-hydrogel contact was observed in the majority of implants, which is not commonly seen in this model. The ability of these macromers to deliver stem cells while forming in situ and subsequently degrade while facilitating bone ingrowth into the defect makes this class of macromers a promising material for craniofacial bone tissue engineering.

Integration of a novel injectable nano calcium sulfate/alginate scaffold and BMP2 gene-modified mesenchymal stem cells for bone regeneration

The repair of craniofacial bone defects is surgically challenging due to the complex anatomical structure of the craniofacial skeleton. Current strategies for bone tissue engineering using a preformed scaffold have not resulted in the expected clinical regeneration due to difficulty in seeding cells into the deep internal space of scaffold, and the inability to inject them in minimally invasive surgeries. In this study, we used the osteoconductive and mechanical properties of nano-scale calcium sulfate (nCS) and the biocompatibility of alginate to develop the injectable nCS/alginate (nCS/A) paste, and characterized the effect of this nCS/A paste loaded with bone morphogenetic protein 2 (BMP2) gene-modified rat mesenchymal stem cells (MSCs) on bone and blood vessel growth. Our results showed that the nCS/A paste was injectable under small injection forces. The mechanical properties of the nCS/A paste were increased with an increased proportion of alginate. MSCs maintained their viability after the injection, and MSCs and BMP2 gene-modified MSCs in the injectable pastes remained viable, osteodifferentiated, and yielded high alkaline phosphatase activity. By testing the ability of this injectable paste and BMP2-gene-modified MSCs for the repair of critical-sized calvarial bone defects in a rat model, we found that BMP2-gene-modified MSCs in nCS/A (nCS/A+M/B2) showed robust osteogenic activity, which resulted in consistent bone bridging of the bone defects. The vessel density in nCS/A+M/B2 was significantly higher than that in the groups of blank control, nCS/A alone, and nCS/A mixed with MSCs (nCS/A+M). These results indicate that BMP2 promotes MSCs-mediated bone formation and vascularization in nCS/A paste. Overall, the results demonstrated that the combination of injectable nCS/A paste and BMP2-gene-modified MSCs is a new and effective strategy for the repair of bone defects.

Synthesis and application of nanostructured calcium phosphate ceramics for bone regeneration

In the past two decades, nanotechnology has entered the field of regenerative medicine, resulting in the development of a novel generation of instructive, nanostructured biomaterials that are able to orchestrate cellular behavior by presenting specific morphological and biological cues. Using nanotechnology, materials containing nanosized features (e.g., pores, patterns, textures, grain sizes) can be obtained that exhibit properties that are considerably altered compared with micron-structured materials. Inspired by the hierarchical nanostructure of bone, the application of nanostructured materials for bone regeneration is gaining increasing interest in the field of biomaterials research. Because crystallographic and chemical studies have shown that synthetic hydroxyapatite closely resembles the inorganic phase found in bone and teeth, synthesis and applications of nanostructured calcium phosphate ceramics have been reviewed. Synthesis techniques for the preparation of calcium phosphate nanoparticles include precipitation, sol-gel, and hydrothermal processes, whereas four main biomedical applications of nanostructured calcium phosphate ceramics in bone regeneration have been addressed in more detail, that is, (1) polymer/calcium phosphate nanocomposites, (2) nanostructured monophasic calcium phosphate bone fillers, (3) nanostructured precursor phases for calcium phosphate cements, and (4) nanostructured calcium phosphate coatings.

Repair of rat calvarial bone defects by controlled release of rhBMP-2 from an injectable bone regeneration composite

The objective of the present study was to enhance the regeneration ability of an injectable bone regeneration composite (IBRC) by the controlled release of recombinant human bone morphogenetic protein-2 (rhBMP-2). The IBRC comprised nano-hydroxyapatite/collagen (nHAC) particles in an alginate hydrogel carrier. First, bovine serum albumin (BSA) as a model protein was released from IBRC to evaluate its release rules. The results suggested that IBRC is a good controlled release carrier for BSA in the range 5-75 µg/ml. In the in vitro study the rhBMP-2 released from IBRC was determined by an enzyme-linked immunosorbent assay specific for rhBMP-2. The bioactivity of the released rhBMP-2 was evaluated through differentiated function of marrow mesenchymal stem cells (MSCs), as measured by alkaline phosphatase activity. The results of an in vitro study confirmed that rhBMP-2 released continuously for 21 days, and its bioactivity was well preserved during this period. The bone formation ability was assessed using a rat calvarial defect model of critical size. Micro-computed tomography (micro-CT) and histological analysis demonstrated that the IBRC had good bone formation ability, which was promoted through rhBMP-2 released from IBRC/rhBMP-2. In vitro and in vivo studies suggested that the present system is a potential bone critical defect repair material for clinical applications.