The optimal SAM surface functional group for producing a biomimetic HA coating on Ti

Abstract

Commercial interest is growing in biomimetic methods that employ self assembled mono-layers (SAMs) to produce biocompatible HA coatings on Ti-based orthopedic implants. Recently, separate studies have considered HA formation for various SAM surface functional groups. However, these have often neglected to verify crystallinity of the HA coating, which is essential for optimal bioactivity. Furthermore, differing experimental and analytical methods make performance comparisons difficult. This article investigates and evaluates HA formation for four of the most promising surface functional groups: --OH, --SO(3)H, --PO(4)H(2) and --COOH. All of them successfully formed a HA coating at Ca/P ratios between 1.49 and 1.62. However, only the --SO(3)H and --COOH end groups produced a predominantly crystalline HA. Furthermore, the --COOH end group yielded the thickest layer and possessed crystalline characteristics very similar to that of the human bone. The --COOH end group appears to provide the optimal SAM surface interface for nucleation and growth of biomimetic crystalline HA. Intriguingly, this finding may lend support to explanations elsewhere of why human bone sialoprotein is such a potent nucleator of HA and is attributed to the protein's glutamic acid-rich sequences.

Functional Hybrid Materials with Polymer Nanoparticles as Templates

“…[86] In previous studies of self-assembled monolayers (SAMs) with several anionic functional groups on Ti wafers, it was shown that ÀCOOH and ÀPO 4 H 2 functional groups can nucleate HAP. [88] Thus, the use of carboxylated and phosphonated functionalized polymer particles templates seems to be a practical way to synthesize hybrid colloids with highly crystalline HAP.…”

Chemical analyses of hydroxyapatite formation on SAM surfaces modified with COOH, NH2, CH3, and OH functions

“…Liu et al 8) reported that HA formation was successfully achieved with -PO4H2 and -COOH, but not with -OH and -CH=CH2. Notably, the -COOH end group appeared to provide the optimal SAM surface for nucleation and growth of biomimetic crystalline HA 8) . This finding reinforced the notion that human bone sialoprotein is a potent nucleator of HA and is linked to the protein's glutamic acid-rich sequences.…”

“…Many researchers have used simulated body fluid (SBF) solutions in their investigations of apatite formation on functionalized surfaces 4,[7][8][9][10][11] , but the reproducibility of data posed a problem. Moreover, in most investigations, SBF solutions were adapted to simulate clinical use, such as hydroxyapatite coating on titanium surface.…”

“…Our next focus was to conduct a basic research on chemical analysis, where surface plasmon resonance (SPR) analysis -in addition to SEM, XRD, ESCA-was used for real-time observation of the early initial deposition of calcium phosphate. In view of this focus on chemical analysis, a simple CaP supersaturated solution was used in this study as opposed to an SBF containing Ca 2+ , PO4 3− , and OH − ions with other trace elements, which was frequently used in experiments on biomimetic hydroxyapatite formation 4,[7][8][9][10][11] . …”

Thin carbonate apatite layer biomimetically-coated on SAM-Ti substrate surfaces

“…In the biomimetic process like the one used in the present study, introduction of negatively charged functional groups is crucial to the surface of substrates in inducing heterogeneous apatite nucleation. and SO 3 H 5),6), 18) have been reported to show ability to nucleate apatite. In the present study, sulfonated SAMs were used primarily because the conversion of vinyl end groups into sulfonated ones was easily carried out by simply exposing SAMs to SO 3 gas 5),6) and sulfate groups in proteoglycans have been demonstrated to be deeply associated with initial bone mineralization.…”