Hierarchical Surface Texturing of Hydroxyapatite Ceramics: Influence on the Adhesive Bonding Strength of Polymeric Polycaprolactone.

Jonas Biggemann,Paula Heik,Philipp Müller,Patrizia Hoffmann,David Köllner,Jung Heon Lee,Tobias Fey,Swantje Simon

doi:10.3390/jfb11040073

Abstract

The tailored manipulation of ceramic surfaces gained recent interest to optimize the performance and lifetime of composite materials used as implants. In this work, a hierarchical surface texturing of hydroxyapatite (HAp) ceramics was developed to improve the poor adhesive bonding strength in hydroxyapatite and polycaprolactone (HAp/PCL) composites. Four different types of periodic surface morphologies (grooves, cylindric pits, linear waves and Gaussian hills) were realized by a ceramic micro-transfer molding technique in the submillimeter range. A subsequent surface roughening and functionalization on a micron to nanometer scale was obtained by two different etchings with hydrochloric and tartaric acid. An ensuing silane coupling with 3-aminopropyltriethoxysilane (APTES) enhanced the chemical adhesion between the HAp surface and PCL on the nanometer scale by the formation of dipole–dipole interactions and covalent bonds. The adhesive bonding strengths of the individual and combined surface texturings were investigated by performing single-lap compressive shear tests. All individual texturing types (macro, micro and nano) showed significantly improved HAp/PCL interface strengths compared to the non-textured HAp reference, based on an enhanced mechanical, physical and chemical adhesion. The independent effect mechanisms allow the deliberately hierarchical combination of all texturing types without negative influences. The hierarchical surface-textured HAp showed a 6.5 times higher adhesive bonding strength (7.7 ± 1.5 MPa) than the non-textured reference, proving that surface texturing is an attractive method to optimize the component adhesion in composites for potential medical implants.

Highlights

A great variety of material properties are predominantly influenced by their surface characteristics such as the surface topography, morphology, roughness, energy, specific surface area, chemistry and wettability [1,2,3,4,5,6]
We have shown that the developed hierarchical surface texturing approach can be used to tailor the surface area and morphology in order to improve the interface strength in bonding applications
Hydroxyapatite ceramics with a hierarchical surface texturing were fabricated in order to improve the adhesive bonding strength in ceramic–polymer composites (HAp/PCL) used as potential implants

Summary

Introduction

A great variety of material properties are predominantly influenced by their surface characteristics such as the surface topography, morphology, roughness, energy, specific surface area, chemistry and wettability [1,2,3,4,5,6]. The surface represents the interface between living tissue and artificial implant and governs the cascade of biological events after implantation [4,6] This includes the initial adsorption of proteins and the subsequent attachment, proliferation and differentiation of cells on the implant [2,5,7,8]. The surface, in addition, strongly affects the mechanical strength and wear resistance. Based on their inherent brittle nature, the strength of ceramics is highly sensitive to the existence of surface flaws (cracks, pores, scratches) and even in their absence failure may occur initiated from the microscopic roughness of large grains [11,12]. Commercial full-ceramic ZrO2 or Al2O3 artificial hip and knee implants are typically polished (Ra < 10 nm) to avoid surface defects and to achieve a high strength and a low-friction surface [13,14]

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Results

Conclusion