Suppression of apoptosis by enhanced protein adsorption on polymer/hydroxyapatite composite scaffolds

Abstract

Bone tissue engineering is a promising alternative to bone grafting. Scaffolds play a critical role in tissue engineering. Composite scaffolds made of biodegradable polymers and bone mineral-like inorganic compounds have been reported to be advantageous over plain polymer scaffolds by our group and others. In this study, we compared cellular and molecular events during the early periods of osteoblastic cell culture on poly(l-lactic acid)/hydroxyapatite (PLLA/HAP) composite scaffolds with those on plain PLLA scaffolds, and showed that PLLA/HAP scaffolds improved cell survival over plain PLLA scaffolds. Most cells (MC3T3-E1) on PLLA/HAP scaffolds survived the early culture. In contrast, about 50% of the cells initially adhered to the plain PLLA scaffolds were detached within the first 12 h and showed characteristics of apoptotic cell death, which was confirmed by TUNEL staining and caspase-3 activation. To investigate the mechanisms, we examined the adsorption of serum protein and adhesion molecules to the scaffolds. The PLLA/HAP scaffold adsorbed more than 1.4 times of total serum protein and much greater amounts of serum fibronectin and vitronectin than pure PLLA scaffolds. Similarly, significantly larger amounts of individual adhesion proteins and peptides (fibronectin, vitronectin, RGD, and KRSR) were adsorbed on the PLLA/HAP scaffolds than on the PLLA scaffolds, which resulted in higher cell density on the PLLA/ HAP scaffolds. Furthermore, β1 and β3 integrins and phosphorylation of Fak and Akt proteins in the cells on the PLLA/HAP scaffolds were significantly more abundent than those on PLLA scaffolds, which suggest that enhanced adsorption of serum adhesion proteins to PLLA/HAP scaffolds protect the cells from apoptosis possibly through the integrin-Fak-Akt pathway. These results demonstrate that biomimetic composite scaffolds are advantageous for bone tissue engineering.

Physical properties and cellular responses to crosslinkable poly(propylene fumarate)/hydroxyapatite nanocomposites

“…These features have been reported from protein adsorption measurements on the surface of other substrates or polymer/calcium phosphate nanocomposites using human serum or FBS in many previous efforts [10,14,42,47,48]. Recently, Woo et al [49] showed more amount of adsorbed specific serum proteins such albumin, fibronectin, and vitronectin as well as higher DNA content of MC3T3-E1 cells cultured on poly(L-lactic acid)(PLLA)/HA composite scaffolds than on PLLA scaffolds only. Our results were consistent with previous studies and demonstrate that increased protein adsorption on PPF/HA nanocomposites leads to increased initial cell attachment.…”

Biomimetic materials for tissue engineering

“…Although the salt-leaching technique has limitations in generating highly porous and wellconnected pore structures, they also consistently demonstrated the improved osteoconductivity over the PLGA scaffolds. Our recent data indicate that HAP in the composite scaffolds significantly improves the protein adsorption capacity, suppresses apoptotic cell death, and provides a more favorable microenvironment for bone tissue regeneration [108].…”

“…The nano-HAP/polymer composite scaffolds not only improved the mechanical properties, but also significantly enhanced protein absorption over micro-sized HAP/polymer scaffolds [109]. The enhanced protein adsorption improves cell adhesion and function [99,108].…”

Calcium orthophosphate-based biocomposites and hybrid biomaterials

“…The combination of high pressures and temperatures was found to decrease porosity and guarantee a close apposition of a polymer to the particles, thereby improving the compressive strength [228] and fracture energy [260] of the biocomposites. The PLLA/HA biocomposites scaffolds were found to improve cell survival over plain PLLA scaffolds [261].…”