Surface modification of titanium with gold nanoparticles and interaction with prototype protein

Aseptic loosening is a leading cause of joint replacement failure. Modifying titanium surfaces with chemically bound functional proteins, such as bone morphogenetic protein (BMP), can efficiently strengthen the interface between prosthesis and bone. A prototype system was developed by using gold nanoparticles (AuNPs) to bridge lysozyme and titanium.;For reference, lysozyme-conjugated gold nanoparticles (Lys-AuNPs) were made in solution via the following pathways, (i) gold compound, HAuC14, was reduced in the presence of lysozyme to form Lys-AuNPs or (ii) citrate-capped AuNPs were functionalized with mercaptopropionic acid (MPA) to produce carboxylic acid (COOH) terminated AuNPs, and then mixed with lysozyme in solution. The two reference systems were characterized with transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-vis), circular dichroism spectroscopy (CD), and enzymatic assays with M. lysodeikticus. Next, AuNPs were made on the surface of 99.5% titanium foil discs (1.1 cm diameter) through electroless deposition using HAuCl4. Deposition parameters were modified to create two groups of discs (each with n=26) with different average diameters of AuNPs. Scanning electron microscopy (SEM) was used to characterize the size and coverage of AuNPs. Some discs also underwent treatment with MPA or mercaptoundecanoic acid (MUA) in order to functionalize the AuNPs with COOH. All discs were treated with lysozyme solution and the adsorbed amount and activity of the lysozyme on the discs were examined with Micro BCA assays and enzymatic assays.;Lysozyme and AuNPs can be conjugated in solution as shown by TEM and UVvis. CD results showed a significant change in the secondary structure of the lysozyme when directly conjugated to AuNPs; however, only a slight change in secondary structure was observed for the lysozyme with COOH functionalized AuNPs. Enzymatic assays showed that lysozyme directly bound to AuNPs had significantly less activity than pure lysozyme while the lysozyme with COOH functionilized AuNPs showed the same activity as pure lysozyme. For the AuNPs on the titanium discs, SEM showed that the two groups had significantly different average AuNP diameters with 24.4 +/-10.3 nm and 66.5 +1- 34.7 nm (p<0.05). Both groups had similar surface coverages (p>0.05) at around 12 %. Bioactive lysozyme was immobilized onto the discs and the assay results showed that discs with the larger AuNPs functionalized with COOH had higher adsorption and activity of lysozyme than plain AuNPs and titanium controls.;A wet-chemical technique may be used to bind lysozyme to titanium via gold nanoparticles. Additionally, it was possible to control the size of the AuNPs on titanium which provides a potential platform for further functionalization with molecules such as MPA or MUA. This technique holds great promise for binding more functional molecules (like BMP) to surgical implants, hence creating "smart" implants that react to their local environment.