Time-Course Evaluation of the In Vivo Resorption Process of Calcium Phosphates/Poly(lactide-co-glycolide) Composites...

Area of Science:

• Biomaterials Science
• Orthopedic Research
• Tissue Engineering

Background:

• Development of calcium phosphate and polymer composites for artificial bone applications is ongoing.
• Understanding the in vivo absorption mechanisms of these bioresorbable materials is crucial for clinical success.

Purpose of the Study:

• To clarify the in vivo absorption mechanisms of calcium phosphate-polymer composites used in artificial bones and bone grafts.
• To evaluate the degradation rates and cellular interactions of different composite formulations.

Main Methods:

• Preparation of composites using β-tricalcium phosphate (β-TCP) or unsintered hydroxyapatite (uHA) with poly-dl-lactide-co-glycolide (PDLGA) or poly-l-lactide-co-glycolide (PLGA).
• In vivo implantation of composites in rabbit femur for up to 48 weeks.
• Continuous evaluation using positron emission tomography/X-ray computed tomography (PET/CT) and histological analysis to assess sample changes and cellular accumulation.

Main Results:

• The primary absorption mechanism identified was phagocytosis by macrophages.
• Composites containing β-TCP (β-TCP(40)) showed a faster disappearance rate compared to those with a high concentration of uHA (uHA(40)).
• Composites with a lower proportion of uHA (uHA(10)) exhibited reduced aggregation and a disappearance rate similar to β-TCP(40).

Conclusions:

• Phagocytosis by macrophages is the dominant resorption pathway for these bioresorbable materials.
• The resorption period is influenced by the type of polymer and the proportion of calcium phosphate used.
• Optimizing the composition of bioresorbable materials is essential to match degradation rates with the healing capacity of damaged bone areas.