Bone cement with reduced proportion of monomer in total hip arthroplasty: preclinical evaluation and randomized study of 47 cases with 5 years' follow-up.

Bone cement with reduced amount of monomer and low curing temperature may improve implant fixation due to reduced toxicity. We analyzed the mechanical, chemical and thermal properties of such a cement (Cemex Rx) using Palacos R as control. The in vivo performance of the 2 cements was also evaluated in a prospective randomized study of 47 hips, where either of the cement types was used to fixate Lubinus SP2 prostheses with the stem made of titanium alloy. Cemex Rx had a reduced tensile strength, probably because this cement was manually mixed, as recommended by the manufacturer. A standardized labor tory test showed lower curing temperature for Cemex, but measurements at 37 degrees and with prechilled Palacos R and Cemex Rx, as in clinical work, showed no difference. In the clinical study radiostereometric measurements of cup and stem migration showed similar values in the 2 groups up to 5 years after the operation. The cement mantle was stable in both groups, but the stems migrated similarly inside the cement mantle regardless of the type of cement used. Proximal wear was low (0.04-0.05 mm/year) and tended to be lower in the Cemex group (p = 0.02). Aluminum and vanadium levels in serum increased 5 years after the operation, but no difference was noted between the 2 groups. Collagen markers (PICP, ICTP) showed similar increases in bone turnover 6 weeks and 6 months after operation in both groups.

Polyurethane surfaces modified by amphiphilic polymers: effects on protein adsorption.

Surface modification of polyurethane (PUR) surfaces was carried out by using three different amphiphilic polymers. Two of the polymers were graft copolymers, having backbones consisting of poly(methyl methacrylate-co-ethylhexyl acrylate) and poly(styrene-co-acrylamide), respectively, and poly(ethylene oxide) PEO 2000 grafts. The third polymer was a commercially available poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) block copolymer, Pluronic 9400. The polymers were designated ACRY, STY2, and PE94, respectively. Surface modification was achieved by adsorption of the amphiphilic polymers at PUR surfaces from an aqueous solution, or by blending the amphiphiles into a PUR solution, followed by solution casting of films. The accumulation of the amphiphilic polymers at the PUR surfaces was observed by XPS and contact angle measurements. The ACRY and PE94 polymers were shown to adsorb poorly at the PUR surface, but gave strong surface effects when present in the PUR matrix. Protein adsorption was measured under static as well as under flow conditions. The modified surfaces had generally lower adsorption of blood proteins (HSA, Fg and IgG) than the unmodified PUR surfaces. ACRY blend modified surfaces had the lowest adsorption.

Tissue response to commercial silicone and polyurethane elastomers after different sterilization procedures.

Two different commercial polymeric materials, a silicone and a polyurethane (PUR), were studied with regard to correlations between the chemical and physical compositions of the polymer surfaces and the biological response on implantation. Test specimens of the materials were manufactured according to standard procedures. The specimens were implanted in rats for 10 and 90 days. Before implantation the polymers were sterilized in three different ways, namely, beta irradiation, ethylene oxide sterilization and steam sterilization. The polymers were characterized before and after the implantation with respect to the chemical composition and the morphology of the surfaces. After implantation the biological response was evaluated by counting numbers of macrophages, giant cells, fibroblasts and other cells present at the surfaces. The thickness of the fibrous capsule surrounding the test specimens was measured at the thickest and thinnest parts. PUR surfaces showed signs of degradation already after sterilization and after 10 to 90 days of implantation, pits and cracks appeared, especially in the ethylene oxide sterilized samples. However, differences in the biological responses were small and independent of the sterilization method. After 10 days of implantation the capsule thickness and the amounts of cell material adhering at the surfaces were different, and it appears that the silicone rubber induces more tissue response than PUR. The differences in the early tissue response evened out after 90 days implantation time and a steady state situation evolved, which was similar for the silicone and the polyurethane.

Adsorption behaviour of amphiphilic polymers at hydrophobic surfaces: effects on protein adsorption.

The adsorption of four different amphiphilic polymers to a model surface has been studied, and the effects of the adsorbed amphiphiles on the subsequent adsorption of fibrinogen (Fg) and human serum albumin (HSA) at the surfaces were investigated. The amphiphilic polymers were one commercially available ABA block copolymer, Pluronic PE9400 (PE94), composed of poly(ethylene oxide) (A-blocks) and poly(propylene oxide) (B-block), and three graft copolymers, two with backbones of poly(styrene-co-acrylamide) (STY) and one with a backbone of poly(methyl methacrylate-co-ethylhexyl methacrylate) (ACRY). The backbones carried poly(ethylene oxide) (PEO) grafts. The model surface was a hydrophobic methylated silica surface (HMS). The amphiphilic polymers were adsorbed at the HMS surface from an ethanol/water solution. The adsorption process was monitored by ellipsometry. After rinsing with phosphate buffered saline (PBS), protein was added and the continued adsorption measured by ellipsometry. Surfaces modified by adsorption of the amphiphilic polymers were also characterized by contact angle measurements and X-ray photoelectron spectroscopy (XPS). According to these measurements the amphiphilic polymers adsorbed in significant amounts at the HMS surface. A limited study by atomic force microscopy (AFM), as well as the XPS measurements, suggests that both single molecules and micellar aggregates adsorb at the surface. ACRY and PE94 gave the highest levels of adsorption. As compared to the Pluronic block copolymer the graft copolymers were more strongly attached to the HMS surface, as shown by less desorption on rinsing with solvent. The ellipsometric results show that the adsorption of HSA and Fg at HMS surfaces containing preadsorbed amphiphilic polymer was significantly reduced as compared to the bare HMS surface. ACRY and PE94 showed the largest effects. Both polymers gave more than a 20-fold reduction of the Fg adsorption and a 10-fold reduction of the HSA adsorption. The STY polymers reduced the protein adsorption by a factor of 2-3.

Evaluation of Boneloc. Chemical and mechanical properties, and a randomized clinical study of 30 total hip arthroplasties.

We evaluated the mechanical, chemical and clinical properties of Boneloc cement using radiostereometry and a series of laboratory tests. Compared to a standard cement (Palacos) the new cement displayed reduced tensile strength, elastic modulus, curing and glass transition temperatures. The amount of MMA extracted during 3 weeks in methanol was smaller for the Boneloc, but the total amount of released monomers was larger. The adhesion to stainless steel and bone did not differ. Radiostereometric analysis during the first postoperative year in 30 patients randomized to fixation of hip prostheses using either of the 2 cements displayed increased proximal migration of the cup and increased stem subsidence when Boneloc had been used. Part of the stem subsidence occurred inside the cement mantle. On the basis of these findings, we conclude that the inferior fixation in the Boneloc group is mainly caused by its mechanical properties. Other mechanisms, such as increased release of monomers, may also be important.

Protein adsorption of poly(ether urethane) surfaces modified by amphiphilic and hydrophilic polymers.

A commercial biomedical poly(ether urethane), Pellethane 2363-80AE, was surface modified through the use of amphiphilic polymeric additives, and through surface grafting with poly(ethylene glycol), PEG. Two different amphiphilic polymers, Polymer C and Pluronic PE9400, were used as additives. Polymer C, a segmented polyurethane, was prepared from PEG1500, 4,4'-diphenylmethane diisocyanate and a C16-C18 monoglyceride chain extender. Pluronic PE9400 is a propylene oxide-ethylene oxide tri-block co-polymer obtained from BASF. Adsorption of human albumin and fibrinogen to the modified surfaces was studied by means of radiolabelled proteins. By contact angle measurements and X-ray photoelectron spectra the amphiphilic polymers were shown to accumulate at the polyurethane surfaces. Adsorption of fibrinogen, in particular, was significantly reduced by the amphiphilic additives to levels similar to those obtained for Pellethane surfaces grafted with PEG 20,000. In vitro clotting times for citrate-buffered blood in contact with the amphiphilic surfaces increased as compared with the unmodified ones.

Adhesion of staphylococci to chemically modified and native polymers, and the influence of preadsorbed fibronectin, vitronectin and fibrinogen.

A commercially available poly(ether urethane), polyethylene, and modifications of these polymers have been compared with respect to adsorption of fibronectin, fibrinogen and vitronectin. The adhesion of staphylococcal strains (characterized for ability to bind immobilized proteins, cell surface hydrophobicity and charge) was studied by bioluminescence with and without preadsorption of proteins to the surfaces. The least amount of proteins and the fewest bacteria adhered to the amphiphilic surfaces. When polymers were preincubated with plasma or albumin, lower numbers of bacteria adhered, except to Pellethane grafted with PEG 20,000, to which coagulase-negative staphylococci adhered to a higher extent.