The ongoing biomedical nanotechnology has intrigued increasingly intense interests in cerium oxide nanoparticles, ceria nanoparticles or nano-ceria (CeO₂-NPs). Their remarkable vacancy-oxygen defect (VO) facilitates the redox process and catalytic activity. The verification has illustrated that CeO₂-NPs, a nanozyme based on inorganic nanoparticles, can achieve the anti-inflammatory effect, cancer resistance, and angiogenesis. Also, they can well complement other materials in tissue engineering (TE). Pertinent to the properties of CeO₂-NPs and the pragmatic biosynthesis methods, this review will emphasize the recent application of CeO₂-NPs to orthopedic biomedicine, in particular, the bone tissue engineering (BTE). The presentation, assessment, and outlook of the orthopedic potential and shortcomings of CeO₂-NPs in this review expect to provide reference values for the future research and development of therapeutic agents based on CeO₂-NPs.

Traffic accidents, falls, and many other events may cause traumatic spinal cord injuries (SCIs), resulting in nerve cells and extracellular matrix loss in the spinal cord, along with blood loss, inflammation, oxidative stress (OS), and others. The continuous development of neural tissue engineering has attracted increasing attention on the application of fibrin hydrogels in repairing SCIs. Except for excellent biocompatibility, flexibility, and plasticity, fibrin, a component of extracellular matrix (ECM), can be equipped with cells, ECM protein, and various growth factors to promote damage repair. This review will focus on the advantages and disadvantages of fibrin hydrogels from different sources, as well as the various modifications for internal topographical guidance during the polymerization. From the perspective of further improvement of cell function before and after the delivery of stem cell, cytokine, and drug, this review will also evaluate the application of fibrin hydrogels as a carrier to the therapy of nerve repair and regeneration, to mirror the recent development tendency and challenge.

The materials used in bone tissue engineering (BTE) have been advancing with each passing day. With the continuous development of nanomedicine, gold nanoparticles (GNPs), which are easy to be synthesized and functionalized, have attracted increasing attention. Recent years have witnessed this amazing material, i.e., GNPs characterized with large surface area to volume ratio, biocompatibility, medical imaging property, hypotoxicity, translocation into the cells, high reactivity, and other properties, perform distinct functions in BTE. However, the low stability of GNPs in the biotic environment makes them in the requirements of modification or recombination before being used. After being combined with the advantages of other materials, the structures of GNPs have exhibited great potential in stem cells, scaffolds, delivery systems, medical imaging, and other aspects. This review will focus on the advances in the application of GNPs after modification or recombination with other materials to BTE.

At present, the healing of osteopathy, especially the healing of cartilage, has been proven to be difficult. Commonly used treatment methods are autogenous bone grafts and allogeneic bone grafts, but grafts cannot fully meet the clinical treatment requirements due to problems related to the source, price, immunity, and other concerns. Thus, the combination of biomaterials and tissue engineering technology has become a new direction in research. Among studies on tissue engineering bone and cartilage materials, hydrogels that show biological activity, absorbability after degradability, plasticity, and easy preparation have become the focus. Hydrogels are used as extracellular matrix mimics. Although various materials are able to form hydrogels, hyaluronic acid and its derivatives are prominently used. Hyaluronic acid hydrogels have many advantages, such as promoting cell adhesion and proliferation and wound healing. They also demonstrate sufficient biological activity for stimulating a microenvironment for cell survival. However, their disadvantages require further modification and include a poor degradation rate and insufficient mechanical performance. In this paper, hyaluronic acid-based hydrogels, their modifications, applications, and mechanisms, as well as new techniques for processing hyaluronic acid hydrogels in bone and cartilage tissue engineering, are briefly reviewed, and their future prospects and directions for future work are discussed.

Chitosan (CS) has been extensively studied as a natural polymer, in the field of wound repair, due to its useful properties, which include a lack of toxicity and stimulation, excellent biological affinity, degradability, and promotion of collagen deposition. However, inferior mechanical strength and moderate antibacterial properties are the drawbacks restricting its further clinical application. Many researchers have adopted the use of nanotechnology, in particular metallic nanoparticles (MNPs), in order to improve the mechanical strength and specific antibacterial properties of chitosan composites, with promising results. Furthermore, chitosan naturally functions as a reducing agent for MNPs, which can also reduce cytotoxicity. Thus, CS, in combination with MNPs, exhibits antibacterial activity, excellent mechanical strength, and anti‐inflammatory properties, and it has great potential to accelerate the process of wound healing. This review discusses the current use of CS and MNPs in wound healing and emphasises the synergy and the advantages for various applications in wound healing.

Background: Spinal cord injury (SCI) is a serious injury with high mortality and disability rates, and there is no effective treatment at present. It has been reported that some treatments, such as drug intervention and stem cell transplantation have positive effects in promoting neurological recovery. Although those treatments are effective for nerve regeneration, many drawbacks, such as low stem cell survival rates and side effects caused by systemic medication, have limited their development. In recent years, injectable hydrogel materials have been widely used in tissue engineering due to their good biocompatibility, biodegradability, controllable properties, and low invasiveness. The treatment strategy of injectable hydrogels combined with stem cells or drugs has made some progress in SCI repair, showing the potential to overcome the drawbacks of traditional drugs and stem cell therapy. Methods: In this study, a novel injectable electroactive hydrogel (NGP) based on sodium hyaluronate oxide (SAO) and polyaniline-grafted gelatine (NH₂-Gel-PANI) was developed as a material in which to load neural stem cells (NSCs) and donepezil (DPL) to facilitate nerve regeneration after SCI. To evaluate the potential of the prepared NGP hydrogel in SCI repair applications, the surface morphology, self-repairing properties, electrical conductivity and cytocompatibility of the resulting hydrogel were analysed. Meanwhile, we evaluated the neural repair ability of NGP hydrogels loaded with DPL and NSCs using a rat model of spinal cord injury. Results: The NGP hydrogel has a suitable pore size, good biocompatibility, excellent conductivity, and injectable and self-repairing properties, and its degradation rate matches the repair cycle of spinal cord injury. In addition, DPL could be released continuously and slowly from the NGP hydrogel; thus, the NGP hydrogel could serve as an excellent carrier for drugs and cells. The results of in vitro cell experiments showed that the NGP hydrogel had good cytocompatibility and could significantly promote the neuronal differentiation and axon growth of NSCs, and loading the hydrogel with DPL could significantly enhance this effect. More importantly, the NGP hydrogel loaded with DPL showed a significant inhibitory effect on astrocytic differentiation of NSCs in vitro. Animal experiments showed that the combination of NGP hydrogel, DPL, and NSCs had the best therapeutic effect on the recovery of motor function and nerve conduction function in rats. NGP hydrogel loaded with NSCs and DPL not only significantly increased the myelin sheath area, number of new neurons and axon area but also minimized the area of the cystic cavity and glial scar and promoted neural circuit reconstruction. Conclusions: The DPL- and NSC-laden electroactive hydrogel developed in this study is an ideal biomaterial for the treatment of traumatic spinal cord injury.