Nanostructure of bioactive glass affects bone cell attachment via protein restructuring upon adsorption

Ukrit Thamma,Matthias M Falk,Tia J Kowal,Himanshu Jain

doi:10.1038/s41598-021-85050-7

Abstract

The nanostructure of engineered bioscaffolds has a profound impact on cell response, yet its understanding remains incomplete as cells interact with a highly complex interfacial layer rather than the material itself. For bioactive glass scaffolds, this layer comprises of silica gel, hydroxyapatite (HA)/carbonated hydroxyapatite (CHA), and absorbed proteins—all in varying micro/nano structure, composition, and concentration. Here, we examined the response of MC3T3-E1 pre-osteoblast cells to 30 mol% CaO–70 mol% SiO2 porous bioactive glass monoliths that differed only in nanopore size (6–44 nm) yet resulted in the formation of HA/CHA layers with significantly different microstructures. We report that cell response, as quantified by cell attachment and morphology, does not correlate with nanopore size, nor HA/CHO layer micro/nano morphology, or absorbed protein amount (bovine serum albumin, BSA), but with BSA’s secondary conformation as indicated by its β-sheet/α-helix ratio. Our results suggest that the β-sheet structure in BSA interacts electrostatically with the HA/CHA interfacial layer and activates the RGD sequence of absorbed adhesion proteins, such as fibronectin and vitronectin, thus significantly enhancing the attachment of cells. These findings provide new insight into the interaction of cells with the scaffolds’ interfacial layer, which is vital for the continued development of engineered tissue scaffolds.

Highlights

The nanostructure of engineered bioscaffolds has a profound impact on cell response, yet its understanding remains incomplete as cells interact with a highly complex interfacial layer rather than the material itself
In order to explain the differences in cell attachment and adhesion on different HA/carbonated hydroxyapatite (CHA) microstructures, it is advantageous to understand how the amount and structure/conformation of adsorbed proteins is affected by HA/CHA microstructures, which, in our case, are determined by the nanopore size of the 30 mol% CaO–70 mol% SiO2 (30C70S) bioactive glass substrate
To begin answering the fundamental question of what cells perceive when attaching to the surface of bioactive glasses, we fabricated and tested sol-gel-derived nanoporous monoliths with four different nanopore sizes

Summary

Introduction

The nanostructure of engineered bioscaffolds has a profound impact on cell response, yet its understanding remains incomplete as cells interact with a highly complex interfacial layer rather than the material itself. Our results suggest that the β-sheet structure in BSA interacts electrostatically with the HA/CHA interfacial layer and activates the RGD sequence of absorbed adhesion proteins, such as fibronectin and vitronectin, significantly enhancing the attachment of cells. It is well established that the nanoscale structure of an engineered tissue scaffold significantly affects its performance, but its mechanistic understanding remains incomplete[1,2,3,4,5] This is especially the case with multicomponent materials such as bioactive glasses, where the nanoscale structure may show variations of local chemistry even if the average composition and physical morphology appear to be homogeneous. Very little is known about how exactly the micro/nano structure of a bioactive glass affects the formation of HA/CHA and/or the structure of absorbed proteins

Methods

Results

Discussion

Conclusion