Self-assembled peptide-polymer hydrogels as a 3D nanofiber substrate for biomimetic hydroxyapatite mineralization

Abstract

Event Abstract Back to Event Self-assembled peptide-polymer hydrogels as a 3D nanofiber substrate for biomimetic hydroxyapatite mineralization Elham Radvar1, C Remzi Becer1 and Helena S. Azevedo1 1 Institute of Bioengineering, Queen Mary University of London, School of Engineering and Materials Science, United Kingdom Introduction: Hard tissues in vertebrates, such as bones, are produced by controlled biomineralization of an organic matrix that regulates the growth of the inorganic phase. In bone, the fundamental subunit is a collagen fibril, formed by self-assembly of single tropocollagen molecules (triple helix), where hydroxyapatite nanocrystals grow with their crystallographic c-axes aligned with the fibril long axes. Molecular self-assembly offers the possibility to recreate the same degree of nanoscale order in synthetic biomaterials and promote epitaxial mineralization mediated by an organic matrix. The self-assembly between a negatively charged polymer and a peptide amphiphile (PA) of opposite charge was shown to result in the formation of sacs and membranes[1]. Inspired by this seminal work, here we investigate the use of the negatively charged synthetic polymer polystyrene sulfonate (PSS) with a positively charged PA to form self-assembling matrices and their ability to direct hydroxyapatite mineralization. Materials and Methods: PSS (1 MDa, Fig 1-A) was commercially available from Sigma. C15H31CONH-V3A3K3-CONH2 PA (Fig 1-A) was synthesized by solid phase and purified as described elsewhere[2]. PSS/PA hydrogels were obtained by self-assembly combining aqueous solutions of PSS (2% w/v) and PA (2% w/v). Mineralization studies were performed by incubating the PSS/PA hydrogels in a simulated body fluid (SBF[3]) solution at 37°C for several days. Then, the gels were washed with distilled water and prepared for surface analysis by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Results and Discussion: Conversely to previous work reporting the self-assembly between PAs and oppositely charged polysaccharides, combining an aqueous PSS solution with a positively charged PA resulted in the formation of a self-supporting gel (Fig 1-B) exhibiting a random nanofibrilar network (Fig 1-C). PSS has been shown to direct the nucleation and growth of calcium carbonate mineral by binding to calcium ions[4]. Thus, we hypothesize that these nanofiber PSS/PA gels could be used as a 3D matrix to drive the nucleation of hydroxyapatite and create a mineralized matrix resembling the structure of natural bone. The formation of hydroxyapatite mineral on the surface of hydrogels after 14 days of incubation in SBF was confirmed by SEM (Fig 1-D, E) and EDS (Fig 1-F) analysis which show a typical morphology of hydroxyapatite crystals and the presence of calcium and phosphorus, respectively. Conclusions: While further studies are necessary to characterize the formed mineral, these self-assembled PSS/PA gels present an interesting approach to develop new biomaterials for bone regeneration considering the potential for further functionalization of the peptide segment with bioactive sequences. I would like to acknowledge the help of Dr. Daniela Ferreira and Sofia Ribeiro in peptide synthesis and SBF preparation, respectively. This work is supported by School of Engineering and Materials Science (SEMS)