Anne E. Meyer

Effect of cleaning and sterilization on titanium implant surface properties and cellular response

Titanium (Ti) has been widely used as an implant material due to the excellent biocompatibility and corrosion resistance of its oxide surface. Biomaterials must be sterile before implantation, but the effects of sterilization on their surface properties have been less well studied. The effects of cleaning and sterilization on surface characteristics were bio-determined using contaminated and pure Ti substrata first manufactured to present two different surface structures: pretreated titanium (PT, Ra=0.4 μm) (i.e. surfaces that were not modified by sandblasting and/or acid etching); (SLA, Ra=3.4 μm). Previously cultured cells and associated extracellular matrix were removed from all bio-contaminated specimens by cleaning in a sonicator bath with a sequential acetone-isopropanol-ethanol-distilled water protocol. Cleaned specimens were sterilized with autoclave, gamma irradiation, oxygen plasma, or ultraviolet light. X-ray photoelectron spectroscopy (XPS), contact angle measurements, profilometry, and scanning electron microscopy were used to examine surface chemical components, hydrophilicity, roughness, and morphology, respectively. Small organic molecules present on contaminated Ti surfaces were removed with cleaning. XPS analysis confirmed that surface chemistry was altered by both cleaning and sterilization. Cleaning and sterilization affected hydrophobicity and roughness. These modified surface properties affected osteogenic differentiation of human MG63 osteoblast-like cells. Specifically, autoclaved SLA surfaces lost the characteristic increase in osteoblast differentiation seen on starting SLA surfaces, which was correlated with altered surface wettability and roughness. These data indicated that recleaned and resterilized Ti implant surfaces cannot be considered the same as the first surfaces in terms of surface properties and cell responses. Therefore, the reuse of Ti implants after resterilization may not result in the same tissue responses as found with never-before-implanted specimens.

Barnacle settlement and the adhesion of protein and diatom microfouling to xerogel films with varying surface energy and water wettability

Previous work has shown that organosilica-based xerogels have the potential to control biofouling. In this study, modifications of chemistry were investigated with respect to their resistance to marine slimes and to settlement of barnacle cyprids. Adhesion force measurements of bovine serum albumin (BSA)-coated atomic force microscopy (AFM) tips to xerogel surfaces prepared from aminopropylsilyl-, fluorocarbonsilyl-, and hydrocarbonsilyl-containing precursors, indicated that adhesion was significantly less on the xerogel surfaces in comparison to a poly(dimethylsiloxane) elastomer (PDMSE) standard. The strength of adhesion of BSA on the xerogels was highest on surfaces with the highest and the lowest critical surface tensions, γC and surface energies, γS, and duplicated the ‘Baier curve’. The attachment to and removal of cells of the diatom Navicula perminuta from a similar series of xerogel surfaces were examined. Initial attachment of cells was comparable on all of the xerogel surfaces, but the percentage removal of attached cells by hydrodynamic shear stress increased with γC and increased wettability as measured by the static water contact angle, θWs, of the xerogel surfaces. The percentage removal of cells of Navicula was linearly correlated with both properties (R 2 = 0.74 for percentage removal as a function of θWs and R 2 = 0.69 for percentage removal as a function of γC). Several of the aminopropylsilyl-containing xerogels showed significantly greater removal of Navicula compared to a PDMSE standard. Cypris larvae of the barnacle B. amphitrite showed preferred settlement on hydrophilic/higher energy surfaces. Settlement was linearly correlated with θWs (R 2 = 0.84) and γC (R 2 = 0.84). Hydrophilic xerogels should prove useful as coatings for boats in regions where fouling is dominated by microfouling (protein and diatom slimes).

Hybrid Xerogel Films as Novel Coatings for Antifouling and Fouling Release

Hybrid sol-gel-derived xerogel films prepared from 45/55 (mol ratio) n-propyltrimethoxysilane (C3-TMOS)/tetramethylorthosilane (TMOS), 2/98 (mol ratio) bis[3-(trimethoxysilyl)propyl]-ethylenediamine (enTMOS)/tetraethylorthosilane (TEOS), 50/50 (mol ratio) n-octyltriethoxysilane (C8-TEOS)/TMOS, and 50/50 (mol ratio) 3,3,3-trifluoropropyltrimethoxysilane (TFP-TMOS)/TMOS were found to inhibit settlement of zoospores of the marine fouling alga Ulva (syn. Enteromorpha) relative to settlement on acid-washed glass and give greater release of settled zoospores relative to glass upon exposure to pressure from a water jet. The more hydrophobic 50/50 C8-TEOS/TMOS xerogel films had the lowest critical surface tension by comprehensive contact angle analysis and gave significantly greater release of 8-day Ulva sporeling biomass after exposure to turbulent flow generated by a flow channel than the other xerogel surfaces or glass. The 50/50 C8-TEOS/TMOS xerogel was also a fouling release surface for juveniles of the tropical barnacle Balanus amphitrite. X-ray photon electron data indicated that the alkylsilyl residues of the C3-TMOS-, C8-TEOS-, and TFP-TMOS-containing xerogels were located on the surface of the xerogel films (in a vacuum), which contributes to the film hydrophobicity. Similarly, the amine-containing silyl residues of the enTMOS/TEOS films were located at the surface of the xerogel films, which contributes to the more hydrophilic character and increased critical surface tension of these films.

Surface analysis of fouling-resistant marine coatings

Generally applicable techniques for surface analysis are described for prepared coating surfaces, with the recommendation that they be utilized prior to any fouling‐release field trials. The effectiveness of these techniques to predict nontoxic fouling‐release is supported by citation of results from the performance of commercial coatings in both seawater and freshwater environments, and comparison with standard reference materials. It is no longer necessary to rely on assumptions about the types of surfaces that will most easily allow physical release of accumulated biofouling, since the field results now show why analysing the surfaces in advance of their aqueous exposure gives important clues about their likely fouling performance. Written test protocols that do not include this level of surface inspection limit understanding and do not aid it, since ambiguities in fouling results are not otherwise traceable to characterized initial coating qualities.

Silicone Foul Release Coatings: Effect of the Interaction of Oil and Coating Functionalities on the Magnitude of Macrofouling Attachment Strengths

Silicone biofouling release coatings have been shown to be an effective method of combating fouling. Nearly all silicone foul release coatings are augmented with an oil additive to decrease macrofouling attachment strength. This paper addresses the effect of the type of oil that is incorporated into the silicone coating and the type of silicone coating itself (silica vs calcium carbonate filled) on macrofouling adhesion strengths to the coating. It was found that not only are the main effects of oil type and silicone coating type important in determining the magnitude of the attachment strength of the organism, but the interaction term (oil type crossed with coating type) is highly significant for all organisms studied, except oysters at the University of Hawaii test site (Oahu, Hawaii) which has a significance level of f =0.1. Each of the organisms exhibited a unique response to the various silicone fouling release coatings. Thus, in order to predict the effectives of foul release coatings, the composition variables of the coatings and the type of target organisms must be considered.

The Effects of Silicone Fluid Additives and Silicone Elastomer Matrices on Barnacle Adhesion Strength

Barnacle adhesion strength was used to screen seventy-seven polydimethylsiloxane elastomeric coatings for fouling-release properties. The test coatings were designed to investigate the effect on barnacle adhesion strength of silicone fluid additive type, additive location, additive molecular weight, additive loading level, mixtures of additives, coating matrix type and coating fillers. The type of silicone fluid additive was the primary controlling factor in barnacle fouling-release. The type of silicone matrix in which the fluid resided was found to alter the effect on fouling-release. Two PDMS fluids, DMSC15 and DBE224, significantly reduced the adhesion strength of barnacles compared to unmodified elastomers. Optimum fouling-release performance was dependent on the interaction of fluid type and elastomeric matrix.

Structure-Property Relationships of Silicone Biofouling-Release Coatings: Effect of Silicone Network Architecture on Pseudobarnacle Attachment Strengths

Model silicone foul-release coatings with controlled molecular architecture were evaluated to determine the effect of compositional variables such as filler loading and crosslink density on pseudobarnacle attachment strength. Pseudobarnacle adhesion values correlated with filler loadings in both condensation and hydrosilylation-cured silicones. Variation of crosslink density of hydrosilylation-cured silicones had an insignificant effect on attachment strength. X-ray photoelectron spectroscopy (XPS) indicated that the mode of failure upon detachment of the pseudobarnacle was dependent upon the crosslink density; samples with high crosslink density failed cohesively within the silicone.

Degradative effects of conventional steam sterilization on biomaterial surfaces

Prior to implantation trials in animals, the effect of steam sterilization on the surface properties of metallic and coated biomaterials was studied. Pure germanium plates and cast surgical Vitallium discs and subperiosteal implants were treated to present three standard types of biomaterials surfaces prior to steam sterilization, ranging from scrupulously clean, high-energy metals to uniformly low-energy organic layers. Both before and after sterilization, the sample surfaces were characterized by a variety of nondestructive physiochemical techniques. The results indicate that steam sterilization is likely to compromise the properties of otherwise carefully prepared biomedical implants by depositing hydrophobic organic and hygroscopic salt contaminants over the implant surfaces.

Evaluation of the performance enhancement of silicone biofouling‐release coatings by oil incorporation

In response to increased evidence of ecosystem damage by toxic antifouling paints, many researchers have developed nontoxic silicone fouling release coatings. The fouling release capability of these Systems may be improved by adding nonbonding silicone oils to the coating matrix. This idea has been tested by comparing the adhesion strength of hard‐ and soft‐fouling organisms on a cured polydimethylsilicone (PDMS) network to that of the same network containing free polydi‐methyldiphenylsilicone (PDMDPS) oil at five exposure sites in North America and Hawaii. Fouling coverage is discussed, together with the bioadhesion data, to emphasize that although these coatings foul the fouling is easily removed. The partitioning of the incorporated oil upon exposure of the coatings to a simulated marine environment containing sediment was determined. Less than 1.1 wt% of the incorporated oil was lost from the coating over one year, and the toxicity of these coatings was shown to be minimal to shrimp and fish. Brush abrasion wear was greater for coatings containing free oil, but the modulus of elasticity was not appreciably decreased by the addition of 10wt% free oil.

Rapid and inexpensive quantification of the combined polar components of surface wettability : application to biofouling

A technique is presented (the SHM method) that rapidly and inexpensively quantifies surface wettability using aqueous methanol solutions. The SHM method, which can be performed using basic, generally available laboratory equipment, yields a single value that is strongly correlated with the combined polar (acid‐base) components of surface wettability. In laboratory studies employing silanised glass surfaces, larval settlement rates of the bryozoan Bugula neritina and the ascidian Ascidia nigra are negatively correlated with surface wettability as quantified by SHM (r = ‐0.79, P < 0.02 for both B. neritina and A. nigra). In contrast, settlement of newly‐metamorphosed cyprid larvae of the acorn barnacle Batanus amphitrite is positively correlated with SHM (r = +0.75, P<0.05). The SHM method is potentially useful to biologists who require initial data regarding the influence of surface wettability on biological processes before proceeding to more sophisticated, in‐depth studies involving collaboration with su...