Abstract
The osteocyte network, through the numerous dendritic processes of osteocytes, is responsible for sensing mechanical loading and orchestrates adaptive bone remodelling by communicating with both the osteoclasts and the osteoblasts. The osteocyte network in the vicinity of implant surfaces provides insight into the bone healing process around metallic implants. Here, we investigate whether osteocytes are able to make an intimate contact with topologically modified, but micrometre smooth (S a < 0.5 µm) implant surfaces, and if sub-micron topography alters the composition of the interfacial tissue. Screw shaped, commercially pure (cp-Ti) titanium implants with (i) machined (S a = ~0.2 µm), and (ii) two-step acid-etched (HF/HNO3 and H2SO4/HCl; S a = ~0.5 µm) surfaces were inserted in Sprague Dawley rat tibia and followed for 28 days. Both surfaces showed similar bone area, while the bone-implant contact was 73 % higher for the acid-etched surface. By resin cast etching, osteocytes were observed to maintain a direct intimate contact with the acid-etched surface. Although well mineralised, the interfacial tissue showed lower Ca/P and apatite-to-collagen ratios at the acid-etched surface, while mineral crystallinity and the carbonate-to-phosphate ratios were comparable for both implant surfaces. The interfacial tissue composition may therefore vary with changes in implant surface topography, independently of the amount of bone formed. Implant surfaces that influence bone to have higher amounts of organic matrix without affecting the crystallinity or the carbonate content of the mineral phase presumably result in a more resilient interfacial tissue, better able to resist crack development during functional loading than densely mineralised bone.
Highlights
The osteocyte network is responsible for sensing mechanical loading and orchestrates adaptive bone remodelling by communicating with both the osteoclasts and the osteoblasts [1]
Based on the Sa values, both implant surfaces are considered smooth in accordance with Albrektsson and Wennerberg [12]
Threads located in cortical bone were generally completely filled with high amounts of remodelled, lamellar bone at four weeks of healing (Fig. 2)
Summary
The osteocyte network is responsible for sensing mechanical loading and orchestrates adaptive bone remodelling by communicating with both the osteoclasts and the osteoblasts [1]. Osteocytes may sense mechanical loading in several ways [3], the dendritic processes are indicated to be of considerable importance [4]. Osteocytes in the vicinity of implant surfaces provide insight into the bone healing process around metallic implants [5]. Topographical features such as undercuts on the submicron scale present a three dimensional structure with which the extracellular matrix of newly formed bone can establish mechanical interlocking [6], strongly influencing the bone-bonding ability of implant surfaces. Modification of implant surface topography is frequently carried out by the use of acids such as HCl, H2SO4, HNO3, and HF [8]
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