# Regulation of calcium delivery and pore structure via osteoinductive microspheres of HA/CS/PGCL for orbital bone regeneration

## TL;DR

This study develops a new composite material for orbital bone repair that improves healing by regulating calcium release and pore structure.

## Contribution

The novel HA/CS/PGCL composite microspheres enable sequential calcium ion release and spatial pore regulation for enhanced bone regeneration.

## Key findings

- HA/CS/PGCL microspheres achieved a new bone volume ratio of 78.72% in vivo after 10 weeks.
- MC3T3-E1 cell proliferation and alkaline phosphatase activity were significantly higher on HA/CS/PGCL surfaces.
- Histological analysis confirmed ordered collagen arrangement and dense new bone formation.

## Abstract

Repairing orbital bone defects remains a complex challenge in craniofacial surgery. Existing bone repair materials are plagued by issues such as intricate preparation processes and inadequate consideration of the spatiotemporal characteristics of bone healing. This study aimed to enhance the osteoinductive activity of poly (glycolide-co-caprolactone) (PGCL)-based materials through bicomponent modification, thereby providing a basis for the design of clinical bone repair materials. Hydroxyapatite/calcium sulfate/PGCL (HA/CS/PGCL) composite microspheres were fabricated via electrostatically assisted spray evaporation (ESASE). Their physicochemical properties and in vitro/in vivo osteogenic efficacy were evaluated using degradation-mineralization assays, MC3T3-E1 cell differentiation assessments and a rabbit orbital bone defect model. Innovatively, CS mesocrystal pore structure regulation was introduced to synergize with HA, achieving multidimensional optimization of surface hydrophilicity, sequential calcium ion release and mechanical properties. Results showed that in vitro mineralization formed native-like hydroxyapatite structures within 14 days. On HA/CS/PGCL surfaces, the proliferation activity of MC3T3-E1 cells reached 1.8 times that of the PGCL group after 7 days, with a 1.6-fold increase in alkaline phosphatase activity. In vivo, the composite microspheres achieved a new bone volume ratio (BV/TV) of 78.72% at 10 weeks, resulting in complete closure of the bone defect. Their trabecular structural parameters (trabecular thickness, Tb.Th; trabecular number, Tb.N) outperformed those of the single-component groups. Histological staining confirmed their ability to induce ordered collagen arrangement and the formation of dense new bone. In conclusion, the HA/CS synergistic modification strategy achieved the sequential release of calcium ions during bone repair and spatial regulation of the microsphere surface pore structure. The superior performance of HA/CS/PGCL microspheres in repairing complex bone defects lays an experimental foundation for clinical translation. Further research into the interactions between ion release and cell signaling is warranted.