Additive Manufacturing and Surface Modification of Biomaterials using Selfassembled Monolayers - Biointerfaces: Where Material Meets Biology - page 43

d n 3 r 4 n g | 0

Figure 2.7 Schematic representation of the binding mechanism of phosphonic acid

SAMs to a metal surface.

form a metal phosphonate bond when adsorbed to a metal oxide surface (Ti-
O-P). Adsorption of long-chain alkyl phosphonic acid SAMs on metal oxides
has been reported to offer densely packed and well-ordered SAMs. 71-74
Various surfaces including silicon, titanium, cobalt-chromium, Nitinol
and gold have been functionalised using phosphonic acid monolayers for
biomedical applications. 72-75 Tosatti et al. studied the assembly of phos-
phate monolayers on rough and smooth titanium and titanium oxide coated
glass surfaces. 76 The structure and order of phosphonic acid based mono-
layers on silicon was studied by Dubey et al. 77 Their studies concluded that
alkyl organophosphate monolayers can be assembled on titanium surfaces.
Bhure et al. investigated the stability of phosphonic acid monolayers on
Co-Cr surfaces and showed that the monolayers were highly stable when
the surfaces were exposed to atmospheric conditions. 78 Kaufmann et al.
explored the in-vitro stability of phosphonic acid monolayers on an
electropolished Co-Cr surface and showed that the monolayers gradually
desorbed over the course of 28 days in Tris buffer solution. 73
Mani et al. 52 have reported the use of phosphonic acid SAMs to immo-
bilise flufenamic acid on gold and titanium surfaces and later immobilised
paclitaxel, an anti-cancer drug, on a cobalt-chromium metal surface. The
later study showed a sustainable release of paclitaxel from the monolayers.
Torres et al. reported the use of phosphonic acid monolayers to deliver an
antibacterial drug from the surface of biomedical implants to prevent bac-
terial infections. 79 Schwartz et al. demonstrated the functionalisation of a
protein (RGD peptide) to phosphonate SAMs adsorbed on pure titanium and
Ti6Al4V surfaces for osteoconductive surfaces. 80 The versatility of phos-
phonic acid monolayers to form densely packed, well-ordered and highly
stable SAMs on metal oxide surfaces makes them ideal for these biomedical
applications.

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2.3.2.3 Formation of Self-assembled Monolayers
Deposition of monolayers on substrates offer one of the highest quality
routes for preparing chemically and structurally well-defined surfaces. 81