Poly-ε-caprolactone Coated and Functionalized Porous Titanium and Magnesium Implants for Enhancing Angiogenesis in Critically Sized Bone Defects

TLDR

Biocompatible, angiogenesis‑supporting implants are preferred for healing critically sized bone defects. The study aimed to enhance vascular ingrowth into porous titanium and magnesium implants by incorporating VEGF and HMGB1 and to develop an in vitro angiogenesis assay to reduce animal use. The authors compared pure porous titanium and PCL‑coated porous titanium implants using live‑cell imaging of GFP‑labeled osteoblasts, while also incorporating VEGF and HMGB1 into the coatings to assess angiogenic potential. PCL‑coated porous titanium implants supported osteoblast proliferation comparable to other polymers and titanium controls, but the added VEGF and HMGB1 did not improve angiogenesis, and magnesium implants caused cytotoxic pH changes leading to cell death.

Abstract

For healing of critically sized bone defects, biocompatible and angiogenesis supporting implants are favorable. Murine osteoblasts showed equal proliferation behavior on the polymers poly-ε-caprolactone (PCL) and poly-(3-hydroxybutyrate)/poly-(4-hydroxybutyrate) (P(3HB)/P(4HB)). As vitality was significantly better for PCL, it was chosen as a suitable coating material for further experiments. Titanium implants with 600 µm pore size were evaluated and found to be a good implant material for bone, as primary osteoblasts showed a vitality and proliferation onto the implants comparable to well bottom (WB). Pure porous titanium implants and PCL coated porous titanium implants were compared using Live Cell Imaging (LCI) with Green fluorescent protein (GFP)-osteoblasts. Cell count and cell covered area did not differ between the implants after seven days. To improve ingrowth of blood vessels into porous implants, proangiogenic factors like Vascular Endothelial Growth Factor (VEGF) and High Mobility Group Box 1 (HMGB1) were incorporated into PCL coated, porous titanium and magnesium implants. An angiogenesis assay was performed to establish an in vitro method for evaluating the impact of metallic implants on angiogenesis to reduce and refine animal experiments in future. Incorporated concentrations of proangiogenic factors were probably too low, as they did not lead to any effect. Magnesium implants did not yield evaluable results, as they led to pH increase and subsequent cell death.