Long-term in vitro degradation and in vivo evaluation of resorbable bioceramics

Bone Tissue Engineering and Nanotechnology: A Promising Combination for Bone Regeneration

Large bone defects are the leading contributor to disability worldwide, affecting approximately 1.71 billion people. Conventional bone graft treatments show several disadvantages that negatively impact their therapeutic outcomes and limit their clinical practice. Therefore, much effort has been made to devise new and more effective approaches. In this context, bone tissue engineering (BTE), involving the use of biomaterials which are able to mimic the natural architecture of bone, has emerged as a key strategy for the regeneration of large defects. However, although different types of biomaterials for bone regeneration have been developed and investigated, to date, none of them has been able to completely fulfill the requirements of an ideal implantable material. In this context, in recent years, the field of nanotechnology and the application of nanomaterials to regenerative medicine have gained significant attention from researchers. Nanotechnology has revolutionized the BTE field due to the possibility of generating nanoengineered particles that are able to overcome the current limitations in regenerative strategies, including reduced cell proliferation and differentiation, the inadequate mechanical strength of biomaterials, and poor production of extrinsic factors which are necessary for efficient osteogenesis. In this review, we report on the latest in vitro and in vivo studies on the impact of nanotechnology in the field of BTE, focusing on the effects of nanoparticles on the properties of cells and the use of biomaterials for bone regeneration.

Mineralized Collagen/Polylactic Acid Composite Scaffolds for Load-Bearing Bone Regeneration in a Developmental Model

Repairing load-bearing bone defects in children remains a big clinical challenge. Mineralized collagen (MC) can effectively simulate natural bone composition and hierarchical structure and has a good biocompatibility and bone conductivity. Polylactic acid (PLA) is regarded as a gold material because of its mechanical properties and degradability. In this study, we prepare MC/PLA composite scaffolds via in situ mineralization and freeze-drying. Cell, characterization, and animal experiments compare and evaluate the biomimetic properties and repair effects of the MC/PLA scaffolds. Phalloidin and DAPI staining results show that the MC/PLA scaffolds are not cytotoxic. CCK-8 and scratch experiments prove that the scaffolds are superior to MC and hydroxyapatite (HA)/PLA scaffolds in promoting cell proliferation and migration. The surface and interior of the MC/PLA scaffolds exhibit rich interconnected pore structures with a porosity of ≥70%. The XRD patterns are typical HA waveforms. X-ray, micro-CT, and H&E staining reveal that the defect boundary disappears, new bone tissue grows into MC/PLA scaffolds in a large area, and the scaffolds are degraded after six months of implantation. The MC/PLA composite scaffold has a pore structure and composition similar to cancellous bone, with a good biocompatibility and bone regeneration ability.

Multifunctional Hydroxyapatite Composites for Orthopedic Applications: A Review

Being a bioactive material, hydroxyapatite (HAp) is regarded as one of the most attractive ceramic biomaterials for bone and hard-tissue replacement and regeneration. Despite its substantial biocompatibility, osteoconductivity, and compositional similarity to that of bone, the employment of HAp is still limited in orthopedic applications due to its poor mechanical (low fracture toughness and bending strength) and antibacterial properties. These significant challenges lead to the notion of developing novel HAp-based composites via different fabrication routes. HAp, when efficaciously combined with functionally graded materials and antibacterial agents, like Ag, ZnO, Co, etc., form composites that render remarkable crack resistance and toughening, as well as enhance its bactericidal efficacy. The addition of different materials and a fabrication method, like 3D printing, greatly influence the porosity of the structure and, in turn, control cell adhesion, thereby enabling biological fixation of the material. This article encompasses an elaborate discussion on different multifunctional HAp composites developed for orthopedic applications with particular emphasis on the incorporation of functionally graded materials and antibacterial agents. The influence of 3D printing on the fabrication of HAp-based scaffolds, and the different in vitro and in vivo studies conducted on these, have all been included here. Furthermore, the present review not only provides insights and broad understanding by elucidating recent advancements toward 4D printing but also directs the reader to future research directions in design and application of HAp-based composite coatings and scaffolds.

iTRAQ-based proteomic analysis reveals potential osteogenesis-promoted role of ATM in strontium-incorporated titanium implant

The present study aims to reveal the osteogenic roles played by DNA damage response biomarkers through implementing isobaric tags for relative and absolute quantitation (iTRAQ) technique. First, sandblasted large-grit double acid-etched (SLA) titanium implant and strontium-incorporated (SLA-Sr) titanium implant were used for inserting in the tibiae of rats. iTRAQ technique was used to detect protein expression changes and identify differentially expressed proteins (DEPs). In total, 19,343 peptides and 4280 proteins were screened out. Among them, 91 and 138 DEPs were identified in the SLA-Sr group after implantation for 3 and 7 days, respectively. Ataxia-telangiectasia mutated (ATM) protein up-regulated on the 3rd day showed a trend of further up-regulation on the 7th day. Moreover, functional enrichment analyses were also conducted to explore the biological function of DEPs during the initial stage of osseointegration in vivo, which revealed that the biological functions of the DEPs on the 7th day were mainly related to "mismatch repair" and "mitotic G1 DNA damage checkpoint." Analysis of the Reactome signaling pathway showed that ATM was associated with TP53's regulation and activation. Finally, DNA damage repair related genes were selected for validation at mRNA and protein expression levels. Real-time reverse transcription-polymerase chain reaction and immunohistochemistry validation results demonstrated that mRNA expression level of ATM was higher in SLA-Sr group. In conclusion, SLA-Sr titanium implant could initiate DNA damage repair by activating expression levels of ATM. This study was striving to reveal new faces of better osseointegration and shedding light on the biological function and underlying mechanisms of this important procedure.

Transformation from calcium sulfate to calcium phosphate in biological environment

The formation of a nano-apatite surface layer is frequently considered a measure of bioactivity, especially for non-phosphate bioceramics. In the present study, strontium-doped calcium sulfate, (Ca,Sr)SO₄, was used to verify the feasibility of this measure. The (Ca,Sr)SO₄ specimen was prepared by mixing 10% SrSO₄ by weight with 90% CaSO₄·½H₂O powder by weight. A solid solution of (Ca,7.6%Sr)SO₄ was then produced by heating the powder mixture at 1100 °C for 1 h. The resulting (Ca,Sr)SO₄ specimen was readily degradable in phosphate solution. A newly formed surface layer in the form of flakes was formed within one day of specimen immersion in phosphate solution. Structural and microstructure-compositional analyses indicated that the flakes were composed of octacalcium phosphate (OCP) crystals. An amorphous interface containing OCP nanocrystals was found between the newly formed surface layer and the remaining (Ca,Sr)SO₄ specimen. The specimen was also implanted into a rat distal femur bone defect. In addition to new bone, fibrous tissue and inflammatory cells were found to interlace the (Ca,Sr)SO₄ specimen. The present study indicated that a more comprehensive evaluation is needed to assess the bioactivity of non-phosphate bioceramics. The newly formed surface layer on the (Ca,Sr)SO₄ specimen after soaking in phosphate solution for 28 days.