The influence of surface microroughness and hydrophilicity of titanium on the up-regulation of TGFβ/BMP signalling in osteoblasts.

doi:10.1016/j.biomaterials.2010.09.025

Biomaterials

Volume 32, Issue 3, January 2011, Pages 665-671

https://doi.org/10.1016/j.biomaterials.2010.09.025 Get rights and content

Abstract

The topography of titanium implants has been identified as an important factor affecting the osseointegration of surgically placed dental implants. Further modification to produce a hydrophilic microrough titanium implant surface has been shown to increase osseointegration compared with microrough topology alone. This study aimed to determine possible molecular mechanisms to explain this clinical observation by examining differences in the whole genome mRNA expression profile of primary human osteoblasts in response to sand-blasted acid-etched (SLA) and hydrophilic SLA (modSLA) titanium surfaces. A decrease in osteoblast proliferation associated with the titanium surfaces (modSLA > SLA > control) correlated with an increase in expression of the osteogenic differentiation markers BSPII and osteocalcin. Pathway analysis demonstrated that a number of genes associated with the TGFβ‑BMP signalling cascade (BMP2, BMP6, SP1, CREBBP, RBL2, TBS3, ACVR1 and ZFYVE16) were significantly differentially up-regulated with culture on the modSLA surface. BMP2 was shown to have the largest fold change increase in expression which was subsequently confirmed at the protein level by ELISA. Several other genes associated with the functionally important mechanisms relevant to bone healing, such as Wnt signalling (CTNNA1, FBX4, FZD6), angiogenesis (KDR), osteoclastogenesis (HSF2, MCL1) and proteolysis (HEXB, TPP1), were also differentially regulated. These results suggest that chemical (hydrophilic) modification of the SLA surface may result in more successful osseointegration through BMP signalling.

Introduction

Titanium has been the material of choice for implants, both in dentistry and orthopaedic medicine, due to its high corrosion and wear resistance, high strength, durability, low density, and most importantly biocompatibility. Clinical success using dental implants when placed in healthy patients and in favourable anatomical positions is well documented [1], [2]. However with increased clinical usage, due to a greater acceptance and popularity of implants, there is a demand and a need to provide successful long term implant treatment for patients with reduced bone quality and quantity.

Consequently, titanium implants are continually being modified to enhance their osteogenic capabilities. The topography of titanium implants has been identified as one of the most influential factors in governing the reaction of tissues to the surgically placed implants, and in particular, the degree of osseointegration that is achieved. A microrough implant surface such as the commercially available sand-blasted, large grit, acid-etched (SLA), has been extensively studied both in vitro and in vivo. It has been shown to promote osteoblast differentiation, increased production of osteogenic factors, cytokines and growth factors and increase bone to implant contact (for review [3]).

The original SLA surface has subsequently been chemically modified by rinsing under N₂ protection and storage in an isotonic NaCl solution, again protected by N₂. This chemically modified surface (modSLA) maintains the topography of the original surface, but exhibits increased hydrophilicity (for review [4]). It has been shown that the modSLA surface induces greater bone to implant contact, osteoblast differentiation, growth factor production, and osteogenic gene expression than the original SLA surface [5], [6], [7], [8], [9], [10].

The precise molecular mechanism(s) of why and how chemical surface modification and increased hydrophilicity impacts on tissues is not well understood. To ensure optimal osseointegration and thus provide successful long term implant treatment for patients with reduced bone quality and quantity, it is important that the effects of an implant on the surrounding tissues, at both the cellular and molecular level, are determined. Understanding these underlying processes will ultimately allow the establishment of implant surfaces that will achieve optimal osseointegration even in compromised clinical scenarios. The aim of the present study was to investigate the in vitro effect of a chemically modified microrough implant surface (modSLA) on osteoblast function and gene expression.

Section snippets

Titanium

This study utilized discs (15 mm in diameter and 1 mm in thickness) of grade II commercially pure titanium as supplied by Institut Straumann (Basel, Switzerland). The SLA surface modification was obtained by blasting the surface with 250–500 μm corundum grit and acid etching with hot solution of hydrochloric/sulfuric acids (Sa = 1.8 μm). The modSLA surface was obtained by rinsing the SLA disks under N₂ protection and storage in an isotonic saline solution at pH 4–6. Glass cover slips (CS)

Osteoblast function

At the 60 min time point, there was significantly higher attachment of osteoblasts to both the SLA and modSLA surfaces compared to the control surface; however, there was no statistically significant difference in attachment between the SLA and modSLA surfaces (Fig. 1). Over a 7 day period, there was a progressive and significant (p < 0.001) increase in osteoblast cell numbers on all three surfaces with the highest levels of proliferation seen on the control surface (Fig. 2). Compared to the

Discussion

In addition to topographical changes, chemical modification of titanium has become a focus of attempts to positively influence the process of osseointegration. A chemically modified titanium surface which exhibits increased hydrophilicity (modSLA) has been shown both in vitro [6], [7], [8], [10] and in vivo [5], [9] to have superior osteogenic properties compared with the original SLA surface. The osteoblast functional data in this study are consistent with previously reported findings

Conclusions

This study showed that titanium surface modification, and in particular, chemical modification leading to increased hydrophilicity, results in increased osteogenic differentiation by primary alveolar bone derived osteoblasts. Whole genome analysis identified an over-representation of genes associated with TGFβ/BMP signalling among the list of genes that were significantly up-regulated by chemical modification of the titanium surface. The identification of this pathway, as well as other genes

Acknowledgements

The authors would like to thank Institut Straumann, Basel, Switzerland, for providing the experimental titanium discs for the study. The microarray research was conducted at the Australian Research Council’s Special Research Centre for Functional and Applied Genomics (Institute for Molecular Bioscience) Microarray Facility within the University of Queensland.

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The influence of surface microroughness and hydrophilicity of titanium on the up-regulation of TGFβ/BMP signalling in osteoblasts.

Abstract

Introduction

Section snippets

Titanium

Osteoblast function

Discussion

Conclusions

Acknowledgements

Dent Mater

Biomaterials

Biomaterials

Bone

Exp Cell Res

J Biol Chem

J Biol Chem

Gene

Dev Biol

Exp Cell Res

Mol Cell Endocrinol

J Biol Chem

Arch Biochem Biophys

J Biol Chem

A systematic review of the incidence of biological and technical complications in implant dentistry reported in prospective longitudinal studies of at least 5 years

J Clin Perio

A prospective 15-year follow-up study of mandibular fixed prostheses supported by osseointegrated implants. Clinical results and marginal bone loss

Clin Oral Implants Res

Effects of titanium surface topography on bone integration: a systematic review

Clin Oral Implants Res

Potential of chemically modified hydrophilic surface characteristics to support tissue integration of titanium dental implants

J Biomed Mater Res B Appl Biomater

Enhanced bone apposition to a chemically modified SLA titanium surface

J Dent Res