Polycaprolactone-Coated 3D Printed Tricalcium Phosphate Scaffolds for Bone Tissue Engineering: In Vitro Alendronate Release Behavior and Local Delivery Effect on In Vivo Osteogenesis

The aim of this work was to evaluate the effect of in vitro alendronate (AD) release behavior through polycaprolactone (PCL) coating on in vivo bone formation using PCL-coated 3D printed interconnected porous tricalcium phosphate (TCP) scaffolds. Higher AD and Ca2+ ion release was observed at lower pH (5.0) than that at higher pH (7.4). AD and Ca2+ release, surface morphology, and phase analysis after release indicated a matrix degradation dominated AD release caused by TCP dissolution. PCL coating showed its effectiveness for controlled and sustained AD release. Six different scaffold compositions, namely, (i) TCP (bare TCP), (ii) TCP + AD (AD-coated TCP), (iii) TCP + PCL (PCL-coated TCP), (iv) TCP + PCL + AD, (v) TCP + AD + PCL, and (vi) TCP + AD + PCL + AD were tested in the distal femoral defect of Sprague Dawley rats for 6 and 10 weeks. An excellent bone formation inside the micro and macro pores of the scaffolds was observed from histomorphology. Histomorphometric analysis revealed maximum new bone formation in TCP + AD + PCL scaffolds after 6 weeks. No adverse effect of PCL on bioactivity of TCP and in vivo bone formation was observed. All scaffolds with AD showed higher bone formation and reduced TRAP (tartrate resistant acid phosphatase) positive cells activity compared to bare TCP and TCP coated with only PCL. Bare TCP scaffolds showed the highest TRAP positive cells activity followed by TCP + PCL scaffolds, whereas TCP + AD scaffolds showed the lowest TRAP activity. A higher TRAP positive cells activity was observed in TCP + AD + PCL compared to TCP + AD scaffolds after 6 weeks. Our results show that in vivo local AD delivery from PCL-coated 3DP TCP scaffolds could further induce increased early bone formation.