Photocurable 3D-Printed PMBG/TCP Scaffold Coordinated with PTH (1-34) Bidirectionally Regulates Bone Homeostasis to Accelerate Bone Regeneration

Recent Strategies and Advances in Hydrogel-Based Delivery Platforms for Bone Regeneration

Bioactive molecules have shown great promise for effectively regulating various bone formation processes, rendering them attractive therapeutics for bone regeneration. However, the widespread application of bioactive molecules is limited by their low accumulation and short half-lives in vivo. Hydrogels have emerged as ideal carriers to address these challenges, offering the potential to prolong retention times at lesion sites, extend half-lives in vivo and mitigate side effects, avoid burst release, and promote adsorption under physiological conditions. This review systematically summarizes the recent advances in the development of bioactive molecule-loaded hydrogels for bone regeneration, encompassing applications in cranial defect repair, femoral defect repair, periodontal bone regeneration, and bone regeneration with underlying diseases. Additionally, this review discusses the current strategies aimed at improving the release profiles of bioactive molecules through stimuli-responsive delivery, carrier-assisted delivery, and sequential delivery. Finally, this review elucidates the existing challenges and future directions of hydrogel encapsulated bioactive molecules in the field of bone regeneration.

Carbonate Apatite Honeycomb Scaffold-Based Drug Delivery System for Repairing Osteoporotic Bone Defects

Osteoporotic bone defects are difficult to repair in elderly patients. This study aimed to repair osteoporotic bone defects using a combination of bone tissue engineering (BTE) and drug delivery systems (DDS). Herein, honeycomb granules (HCGs) composed of carbonate apatite microspheres were fabricated as BTE scaffolds. Each HCG possesses hexagonal macropores and abundant interconnected micropores between the microspheres. Owing to these multiscale interconnected pores, HCGs can readily contain antibodies against sclerostin (Scl), which causes imbalances in bone homeostasis. Anti-Scl antibody-loaded HCGs (Scl-Ab-HCGs) regulate the release of Scl-Abs in response to the pH of the osteoporotic environment. In ovariectomized rabbit osteoporotic femurs, HCG monotherapy forms new bone with less osteocyte damage (fewer empty bone lacunae) and fewer osteoclasts than osteoporotic bone; however, it is insufficient to prevent receptor activator of nuclear factor-kappa B ligand (RANKL) overexpression. Consequently, HCG monotherapy restores bone quantity better than no treatment but not to normal levels. In contrast, new bone tissue formed by Scl-Ab-HCG-based DDS predominantly expresses osteocalcin rather than RANKL, similar to normal bone, and shows a similar osteocyte apoptosis level, bone quantity, and osteoclast number as normal bone. Thus, Scl-Ab-HCG-based DDS is a promising approach for osteoporotic bone defect repair.

Combining "waste utilization" and "tissue to tissue" strategies to accelerate vascularization for bone repair

Background

A pivotal determinant for the success of tissue regeneration lies in the establishment of sufficient vasculature. Utilizing autologous tissue grafts from donors offers the dual advantage of mitigating the risk of disease transmission and circumventing the necessity for post-transplant immunosuppression, rendering it an exemplary vascularization strategy. Among the various potential autologous donors, adipose tissue emerges as a particularly auspicious source, being both widely available and compositionally rich. Notably, adipose-derived microvascular fragments (ad-MVFs) are a promising candidate for vascularization. ad-MVFs can be isolated from adipose tissue in a short period of time and show high vascularized capacity. In this study, we extracted ad-MVFs from adipose tissue and utilized their strong angiogenic ability to accelerate bone repair by promoting vascularization.

Methods

ad-MVFs were extracted from the rat epididymis using enzymatic hydrolysis. To preserve the integrity of the blood vessels, gelatin methacryloyl (GelMA) hydrogel was chosen as the carrier for ad-MVFs in three-dimensional (3D) culture. The ad-MVFs were cultured directly on the well plates for two-dimensional (2D) culture as a control. The morphology of ad-MVFs was observed under both 2D and 3D cultures, and the release levels of vascular endothelial growth factor (VEGF) and bone morphogenetic protein 2 (BMP-2) were assessed under both culture conditions. In vitro studies investigated the impact of ad-MVFs/GelMA hydrogel on the toxicity, osteoblastic activity, and mineralization of rat bone marrow mesenchymal stem cells (rBMSCs), along with the examination of osteogenic gene and protein expression. In vivo experiments involved implanting the ad-MVFs/GelMA hydrogel into critical-size skull defects in rats, and its osteogenic ability was evaluated through radiographic and histological methods.

Results

ad-MVFs were successfully isolated from rat adipose tissue. When cultured under 2D conditions, ad-MVFs exhibited a gradual disintegration and loss of their original vascular morphology. Compared with 2D culture, ad-MVFs can not only maintain the original vascular morphology, but also connect into a network in hydrogel under 3D culture condition. Moreover, the release levels of VEGF and BMP-2 were significantly higher than those in 2D culture. Moreover, the ad-MVFs/GelMA hydrogel exhibited superior osteoinductive activity. After implanting into the skull defect of rats, the ad-MVFs/GelMA hydrogel showed obvious effects for angiogenesis and osteogenesis.

The translational potential of this article

The utilization of autologous adipose tissue as a donor presents a more direct route toward clinical translation. Anticipated future clinical applications envision the transformation of discarded adipose tissue into a valuable resource for personalized tissue repair, thereby realizing a paradigm shift in the utilization of this abundant biological material.

Calcium Orthophosphate (CaPO4) Containing Composites for Biomedical Applications: Formulations, Properties, and Applications

The goal of this review is to present a wide range of hybrid formulations and composites containing calcium orthophosphates (abbreviated as CaPO4) that are suitable for use in biomedical applications and currently on the market. The bioactive, biocompatible, and osteoconductive properties of various CaPO4-based formulations make them valuable in the rapidly developing field of biomedical research, both in vitro and in vivo. Due to the brittleness of CaPO4, it is essential to combine the desired osteologic properties of ceramic CaPO4 with those of other compounds to create novel, multifunctional bone graft biomaterials. Consequently, this analysis offers a thorough overview of the hybrid formulations and CaPO4-based composites that are currently known. To do this, a comprehensive search of the literature on the subject was carried out in all significant databases to extract pertinent papers. There have been many formulations found with different material compositions, production methods, structural and bioactive features, and in vitro and in vivo properties. When these formulations contain additional biofunctional ingredients, such as drugs, proteins, enzymes, or antibacterial agents, they offer improved biomedical applications. Moreover, a lot of these formulations allow cell loading and promote the development of smart formulations based on CaPO4. This evaluation also discusses basic problems and scientific difficulties that call for more investigation and advancements. It also indicates perspectives for the future.

Advances in 3D Printing of Highly Bioadaptive Bone Tissue Engineering Scaffolds

The number of patients with bone defects caused by trauma, bone tumors, and osteoporosis has increased considerably. The repair of irregular, recurring, and large bone defects poses a great challenge to clinicians. Bone tissue engineering is emerging as an appropriate strategy to replace autologous bone grafting in the repair of critically sized bone defects. However, the suitability of bone tissue engineering scaffolds in terms of structure, mechanics, degradation, and the microenvironment is inadequate. Three-dimensional (3D) printing is an advanced additive-manufacturing technology widely used for bone repair. 3D printing constructs personalized structurally adapted scaffolds based on 3D models reconstructed from CT images. The contradiction between the mechanics and degradation is resolved by altering the stacking structure. The local microenvironment of the implant is improved by designing an internal pore structure and a spatiotemporal factor release system. Therefore, there has been a boom in the 3D printing of personalized bone repair scaffolds. In this review, successful research on the preparation of highly bioadaptive bone tissue engineering scaffolds using 3D printing is presented. The mechanisms of structural, mechanical, degradation, and microenvironmental adaptations of bone prostheses and their interactions were elucidated to provide a feasible strategy for constructing highly bioadaptive bone tissue engineering scaffolds.