Osteoblast response to phospholipid modified titanium surface

Abstract

The objective of this study was to evaluate the effect of different phospholipid coatings on osteoblast responses in vitro. Commercially available phospholipids [phosphatidylcholine (PC), phosphatidyl-serine (PS) and phosphatidylinositol (PI)] were converted to their Ca–PL–PO₄ and were coated on commercially pure titanium (Ti) grade 2 disks. Using uncoated Ti surfaces as controls, cell responses to phospholipid-coated surfaces were evaluated using the American Type Culture Collection (Manassas, VA, USA) CRL-1486 human embryonic palatal mesenchyme cells (HEPM), an osteoblast precursor cell line, over a 14-day period. Total protein synthesis and alkaline phosphatase specific activity at 0, 7, and 14 days were measured. It was observed that Ti surfaces coated with PS exhibited enhanced protein synthesis and alkaline phosphatase specific activity compared to other phospholipids and uncoated surfaces. These results indicate the possible usefulness of PS-coated Ti surfaces for inducing enhanced bone formation and are very encouraging for bone and dental implantology.

Introduction

Titanium (Ti) is the implant material of choice for use in dental and orthopedic applications. The stable oxide that formed readily on Ti surfaces was reported to attribute to its excellent biocompatibility [1]. However, it was also reported that bone response to implant surfaces was dependent on the chemical and physical properties of Ti surfaces, thereby affecting implant success [2]. As such, attention has been focused on the surface preparation of the Ti implant.

Several techniques such as plasma spraying, laser deposition, ion beam dynamic mixing, ion beam deposition, magnetic sputtering, hot isostatic pressing, electrophoretic deposition, sol–gel, ion implantation, NaOH treatment, and electrochemical methods have been employed to deposit hydroxyapatite (HA) or calcium phosphate coatings on Ti surfaces [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18]. Among the different processes described, plasma spraying of HA and Ti has been the most common method for modifying implant surfaces. However, numerous problems with the plasma-sprayed coatings have also been cited, including variation in bond strength between the coatings and the metallic substrates, non-uniformity in coating density as a result of the process, poor adhesion between the coatings and metallic substrates, and microcracks on the coating surface [19], [20], [21], [22]. However, these problems do not reflect shortcomings inherent in the rationale for HA coating, but rather in the plasma spray and other technologies currently used to apply the coatings.

Recently, an alternative implant surface modification using phospholipids coatings have been suggested. It has been reported that various kind of calcium deposition processes involve the use of phospholipids [23], [24], [25], [26], [27]. It has also been reported that a complex between calcium-inorganic phosphate and the phospholipid was essential for inducing the deposition of calcium phosphate [28]. Despite numerous chemical and structural characterizations, cellular responses to these phospholipids-coated implants anodized surfaces have yet to be evaluated. As such, the effect of different phospholipid coatings on in vitro osteoblast responses was evaluated in this study.