3D printing technology and its combination with nanotechnology in bone tissue engineering

With the graying of the world's population, the morbidity of age-related chronic degenerative bone diseases, such as osteoporosis and osteoarthritis, is increasing yearly, leading to an increased risk of bone defects, while current treatment methods face many problems, such as shortage of grafts and an incomplete repair. Therefore, bone tissue engineering offers an alternative solution for regenerating and repairing bone tissues by constructing bioactive scaffolds with porous structures that provide mechanical support to damaged bone tissue while promoting angiogenesis and cell adhesion, proliferation, and activity. 3D printing technology has become the primary scaffold manufacturing method due to its ability to precisely control the internal pore structure and complex spatial shape of bone scaffolds. In contrast, the fast development of nanotechnology has provided more possibilities for the internal structure and biological function of scaffolds. This review focuses on the application of 3D printing technology in bone tissue engineering and nanotechnology in the field of bone tissue regeneration and repair, and explores the prospects for the integration of the two technologies.

Dual-functional 3D-printed porous bioactive scaffold enhanced bone repair by promoting osteogenesis and angiogenesis

The treatment of bone defects is a difficult problem in orthopedics. The excessive destruction of local bone tissue at defect sites destroys blood supply and renders bone regeneration insufficient, which further leads to delayed union or even nonunion. To solve this problem, in this study, we incorporated icariin into alginate/mineralized collagen (AMC) hydrogel and then placed the drug-loaded hydrogel into the pores of a 3D-printed porous titanium alloy (AMCI/PTi) scaffold to prepare a bioactive scaffold with the dual functions of promoting angiogenesis and bone regeneration. The experimental results showed that the ACMI/PTi scaffold had suitable mechanical properties, sustained drug release function, and excellent biocompatibility. The released icariin and mineralized collagen (MC) synergistically promoted angiogenesis and osteogenic differentiation in vitro. After implantation into a rabbit radius defect, the composite scaffold showed a satisfactory effect in promoting bone repair. Therefore, this composite dual-functional scaffold could meet the requirements of bone defect treatment and provide a promising strategy for the repair of large segmental bone defects in clinic.

Decellularized liver ECM-based 3D scaffolds: Compositional, physical, chemical, rheological, thermal, mechanical, and in vitro biological evaluations

The extracellular matrix (ECM) is involved in many critical cellular interactions through its biological macromolecules. In this study, a macroporous 3D scaffold originating from decellularized bovine liver ECM (dL-ECM), with defined compositional, physical, chemical, rheological, thermal, mechanical, and in vitro biological properties was developed. First, protocols were determined that effectively remove cells and DNA while ECM retains biological macromolecules collagen, elastin, sGAGs in tissue. Rheological analysis revealed the elastic properties of pepsin-digested dL-ECM. Then, dL-ECM hydrogel was neutralized, molded, formed into macroporous (~100-200 μm) scaffolds in aqueous medium at 37 °C, and lyophilized. The scaffolds had water retention ability, and were mechanically stable for at least 14 days in the culture medium. The findings also showed that increasing the dL-ECM concentration from 10 mg/mL to 20 mg/mL resulted in a significant increase in the mechanical strength of the scaffolds. The hemolysis test revealed high in vitro hemocompatibility of the dL-ECM scaffolds. Studies investigating the viability and proliferation status of human adipose stem cells seeded over a 2-week culture period have demonstrated the suitability of dL-ECM scaffolds as a cell substrate. Prospective studies may reveal the extent to which 3D dL-ECM sponges have the potential to create a biomimetic environment for cells.

The recent advances in scaffolds for integrated periodontal regeneration

The periodontium is an integrated, functional unit of multiple tissues surrounding and supporting the tooth, including but not limited to cementum (CM), periodontal ligament (PDL) and alveolar bone (AB). Periodontal tissues can be destructed by chronic periodontal disease, which can lead to tooth loss. In support of the treatment for periodontally diseased tooth, various biomaterials have been applied starting as a contact inhibition membrane in the guided tissue regeneration (GTR) that is the current gold standard in dental clinic. Recently, various biomaterials have been prepared in a form of tissue engineering scaffold to facilitate the regeneration of damaged periodontal tissues. From a physical substrate to support healing of a single type of periodontal tissue to multi-phase/bioactive scaffold system to guide an integrated regeneration of periodontium, technologies for scaffold fabrication have emerged in last years. This review covers the recent advancements in development of scaffolds designed for periodontal tissue regeneration and their efficacy tested in vitro and in vivo. Pros and Cons of different biomaterials and design parameters implemented for periodontal tissue regeneration are also discussed, including future perspectives.

Bioactive gel self-assembled from phosphorylate biomimetic peptide: A potential scaffold for enhanced osteogenesis

Bone morphogenetic protein-2 biomimetic peptide (BMPBP) is a potent osteoinductive cytokine and plays a critical role during bone regeneration. Efforts to prepare hydrogels with surface modification or physical absorption of bioactive molecules do not provide sufficient bioactivity to meet the requirements of clinical application. The goal of this study was to form a three-dimensional hydrogel comprised of BMP-2 core sequence oligopeptide, phosphoserine, a synthetic cell adhesion peptide (RGDS), and polyaspartic acid to synergistically promote osteogenesis. Experiments performed in vitro revealed that the peptide gel was conducive to adhesion and proliferation of rat marrow mesenchymal stem cells (rMSCs). In addition, RT-PCR analysis indicated that rMSCs allowed better expression of osteogenesis-related genes such as BMP-2, runt-related transcription factor 2 (RUNX2), alkaline phosphatase (ALP), osteocalcin (OCN), and osteopontin (OPN). Use of the rat cranial bone defects model with micro-CT 3D reconstruction showed that bone regeneration patterns occurred from one side edge toward the center of the area implanted with the prepared biomimetic peptide hydrogels, demonstrating significantly accelerated bone regeneration. This work will provide a basis to explore the further application potential of this bioactive scaffold.