Optimized Bone Regeneration in Calvarial Bone Defect Based on Biodegradation-Tailoring Dual-shell Biphasic Bioactive...

Bone defects remain a major clinical challenge due to limited natural healing capacity. Traditional grafting methods often fail to provide sufficient structural support or biological activity. Recent advances in biomaterials have focused on developing synthetic substitutes that mimic natural bone composition and degradation rates. While bioceramics like calcium phosphate (CaP) and calcium silicate (CaSi) are known for their osteoconductive properties, their degradation profiles are fixed, limiting their adaptability to specific healing timelines. Prior research has demonstrated that combining different bioceramics can enhance bone regeneration, but controlling degradation remains a key limitation. This gap motivated the development of a new microsphere design that allows for tunable degradation. No prior work had resolved how to spatially arrange different bioceramic layers to influence both degradation and bone growth. The need for a material that can degrade in sync with new bone formation remains unmet. This paper addresses that need through a novel dual-shell microsphere design.

The study aimed to develop a new type of bioceramic microsphere with a dual-shell structure to control degradation and promote bone regeneration. The researchers sought to address the challenge of synchronizing material degradation with tissue healing. By adjusting the composition and layering of calcium phosphate and calcium silicate, the team aimed to create a material that degrades at a rate matching new bone growth. The study also aimed to evaluate how this design affects mesenchymal stem cell behavior in vitro and bone regeneration in vivo. The motivation was to create a versatile biomaterial that can be tailored for different healing scenarios. The researchers wanted to test whether layering order influences degradation and bone growth outcomes. They also aimed to compare two different microsphere configurations to determine optimal performance. This approach could lead to more predictable and effective bone repair strategies.

The researchers used a co-concentric capillary system to fabricate dual-shell microspheres with alternating layers of calcium phosphate (CaP) and calcium silicate (CaSi). Two configurations were tested: CaP@CaSi@CaP and CaSi@CaP@CaSi. In vitro experiments involved culturing bone marrow mesenchymal stem cells (BMSCs) with microsphere extracts to assess proliferation, alkaline phosphatase (ALP) activity, and mineralization via Alizarin Red staining. In vivo studies used calvarial bone defects in animal models to evaluate bone regeneration and microsphere degradation over time. Micro-computed tomography (μCT) and histological analysis were employed to assess new bone formation and microsphere resorption. The study compared degradation rates and bone growth between the two microsphere types. The researchers also analyzed how layering order influenced degradation kinetics and biological performance. This method allowed for a direct comparison of how material design affects both degradation and regeneration outcomes.

The in vitro results showed that the optimal extract concentration (1/16 of 200 mg/ml) of dual-shell microspheres significantly promoted BMSC proliferation and increased ALP activity and Alizarin Red staining. In vivo, pure CaP microspheres were minimally resorbed after 18 weeks, with limited new bone formation. In contrast, dual-shell microspheres degraded over time, with CaSi layers degrading before CaP layers. The CaSi@CaP@CaSi configuration showed significantly better bone regeneration than the CaP@CaSi@CaP design. μCT and histological evaluations confirmed enhanced new bone growth in the CaSi@CaP@CaSi group. The study demonstrated that layering order directly affects degradation and regeneration outcomes. The dual-shell design allowed for controlled degradation in sync with tissue healing. These findings suggest that tailoring microsphere composition can optimize bone repair processes.

The study concludes that dual-shell bioceramic microspheres with adjustable CaP and CaSi layers offer a promising strategy for tailoring degradation and bone regeneration rates. The in vitro and in vivo results suggest that the CaSi@CaP@CaSi configuration is more effective than the CaP@CaSi@CaP design. The findings indicate that layering order influences both degradation kinetics and biological performance. The researchers propose that this design allows for better synchronization between material resorption and new bone formation. The study supports the idea that biphasic microspheres can be engineered for specific healing timelines. The authors suggest that such a versatile design could be adapted for various bone repair applications. The results align with the hypothesis that material composition and structure directly affect regeneration outcomes. The study highlights the potential of this approach for developing advanced biomaterials with tunable properties.