Methacrylate polymers and copolymers as urinary tract biomaterials: Resistance to encrustation and microbial adhesion

Physical Properties of Electropolished CoCrMo Alloy Coated with Biodegradable Polymeric Coatings Releasing Heparin after Prolonged Exposure to Artificial Urine

In this study, we aimed to determine the effect of long-term exposure to artificial urine on the physical properties of CoCrMo alloy with biodegradable heparin-releasing polymeric coatings. Variants of polymer coatings of poly(L,L-lactide-ɛ-caprolactone) (P(L,L-L/CL)) and poly(D,L-lactide-ɛ-caprolactone) (P(D,L-L/CL)) constituting the base for heparin-releasing (HEP) polyvinyl alcohol (PVA) coatings were analyzed. The coatings were applied by the dip-coating method. Heparin was used to counteract the incrustation process in the artificial urine. The study included tests of wettability, resistance to pitting and crevice corrosion, determination of the mass density of metal ions penetrating into the artificial urine, and the kinetics of heparin release. In addition, microscopic observations of surface roughness and adhesion to the metal substrate were performed. Electrolytically polished CoCrMo samples (as a reference level) and samples with polymer coatings were used for the tests. The tests were conducted on samples in the initial state and after 30, 60, and 90 days of exposure to artificial urine. The analysis of the test results shows that the polymer coatings contribute by improving the resistance of the metal substrate to pitting and crevice corrosion in the initial state and reducing (as compared with the metal substrate) the mass density of metal ion release into the artificial urine. Moreover, the PVA + HEP coating, regardless of the base polymer coatings used, contributes to a reduction in the incrustation process in the first 30 days of exposure to the artificial urine.

Cementos óseos acrílicos modificados con hidroxiapatita/acetato de vinilo: caracterización mecánica, termoanálitica y bioactividad in vitro

Los cementos óseos se han convertido en los últimos años en biomateriales de gran utilidad en la fijación de prótesis y en la reconstrucción del hueso. El objetivo de este trabajo es evaluar las propiedades termoanalíticas tales como temperatura máxima de polimerización y tiempo de fraguado en cementos óseos acrílicos modificados con hidroxiapatita/acetato de vinilo, determinar la resistencia a la compresión axial y realizar ensayos de bioactividad in vitro. Diferentes contenidos de acetato de vinilo fueron incorporados en cementos óseos acrílicos cargados todos con un 30 % de hidroxiapatita CORALINA® HAP-200. Las propiedades mecánicas y los parámetros de curado fueron evaluados cumpliendo lo establecido en la Norma ISO 5833 descrita para cementos óseos acrílicos. Se determinaron los parámetros termoanalíticos, obteniéndose tiempos de fraguados entre 3 y 6 minutos y los valores de temperaturas máximas de polimerización oscilan entre 66 y 88 °C. Se obtuvo formulaciones con valores de resistencia a la compresión superiores a lo establecido en la Norma ISO 5833. Se demostró la bioactividad de las formulaciones mediante la inmersión de las muestras en fluido biológico simulado, observándose en la superficie de las mismas la nucleación y el crecimiento de cristales con morfología similar a las apatitas biológicas.

Polymers as ureteral stents

Ureteral stents find wide application in urology. The majority of patients with indwelling ureteral stents are at an increased risk of urinary tract infection. Stent encrustation and its associated complications lead to significant morbidity. This review critically evaluates various polymers that find their application as ureteral stents with regard to various issues such as encrustation, bacterial colonization, urinary tract infections, and related clinical issues. A complete literature survey was performed, and all the relevant articles were scrutinized thoroughly. We discuss issues of encrustation/biofilm formation, new approaches to their testing, polymers currently available for use, new biomaterials, coatings, and novel ureteral stent designs, thereby providing a complete update on recent advances in the development of stents. Finally, we discuss the future of biomaterial use in the urinary tract.

Influence of lactose addition to gentamicin-loaded acrylic bone cement on the kinetics of release of the antibiotic and the cement properties

The purpose of this study was to characterize a poly(methyl methacrylate) bone cement that was loaded with the antibiotic gentamicin sulphate (GS) and lactose, which served to modulate the release of GS from cement specimens. The release of GS when the cement specimens were immersed in phosphate-buffered saline at 37 degrees Celsius was determined spectrophotometrically. The microstructure, porosity, density, tensile properties and flexural properties of the cements were determined before and after release of GS. A kinetics model of the release of GS from the cement that involved a coupled mechanism based on dissolution/diffusion processes and an initial burst effect was proposed. Dissolution assay results showed that drug elution was controlled by a diffusion mechanism which can be modulated by lactose addition. Density values and mechanical properties (tensile strength, flexural strength, elastic modulus and fracture toughness) were reduced by the increased porosity resulting from lactose addition, but maintained acceptable values for the structural functions of bone cement. The present results suggest that lactose-modified, gentamicin-loaded acrylic bone cements are potential candidates for use in various orthopaedic and dental applications.

Characterization of crosslinking effects on the physicochemical and drug diffusional properties of cationic hydrogels designed as bioactive urological biomaterials

This study examined the effects of concentration and type of crosslinker (tetraethyleneglycol diacrylate, TEGDA; diethyleneglycol dimethacrylate, DEGDMA; and polyethyleneglycol dimethacrylate, PEGDMA) on the mechanical and drug diffusional properties of hydrogels that had been selected as candidate coatings for bioactive medical devices. Hydrogels (dimethylaminoethylmethacrylate-covinylpyrrolidone; 1:1) were prepared by free radical polymerization and characterized using tensile analysis, dynamic contact angle analysis and analysis of swelling at pH 6.0. The release of fusidic acid and chlorhexidine was evaluated using buffered medium at pH 6.0 and, in addition, using dissolution medium that had been buffered to pH 9 in the presence and absence of elevated concentrations of calcium, representative of urinary encrustation. Crosslinker concentration, but not type, affected the advancing and receding contact angles. Conversely, both crosslinker type and concentration affected the mechanical and swelling properties of the hydrogels. Maximum swelling and elongation at break were associated with the PEGDMA-crosslinked hydrogels whereas TEGDA-crosslinked hydrogels exhibited the maximum ultimate tensile strength and Young's modulus. Drug release from all systems occurred by diffusion. The mass of chlorhexidine and fusidic acid released was dependent on crosslinker type and concentration, with hydrogels crosslinked with PEGDMA offering the greatest mass of drug released at each sampling period. The mass of fusidic acid but not chlorhexidine released at pH 9.0 in a calcium augmented medium was lower than that released in the same medium devoid of elevated calcium, due to the formation of the poorly soluble calcium salt. In conclusion, this study has uniquely examined the effects of crosslinker type and concentration on physicochemical and drug release properties essential to the clinical and non-clinical performance of bioactive hydrogels for medical device application.

Gold and gold-palladium coated polypropylene grafts in a S. epidermidis wound infection model

BACKGROUND

The use of non-absorbable mesh grafts in both abdominal wall defects and inguinal hernias are impossible in the presence of contamination. This study was conducted for evaluation of the efficiencies of polypropylene mesh grafts coated with gold and palladium-gold.

MATERIALS AND METHODS

Ten piece of 1 x 2 cm of polypropylene mesh grafts were used in each group of naïve, gold-coated, and palladium-gold-coated. The grafts were incubated in physiological saline buffered and 0.5 McFarland slime positive Staphylococcus epidermidis for 24 h. At intervals of 6, 12, 24, 48, 72 h grafts were washed with saline and vortexed for 2 min in 2 ml of physiological saline. There were 100 microl of samples of vortexed material incubated in blood agar and 24 h later, colony numbers were assessed. In the second part of study, the grafts were implanted below the musculoaponeurotic layer at inguinal region of rats following the same procedure of incubation and washing. On the 8th day, the rats were examined for infection rate and their wound cultures were obtained.

RESULTS

The least amount of bacterial growth was detected in the samples obtained from gold-palladium coated grafts; whereas the highest rate of growth was found in samples of naive grafts. The superficial surgical site infection rate was 0% in gold-palladium coated, 30% in gold-coated and 100% in naïve polypropylene group. The bacterial growth rate from wound cultures confirmed the superficial surgical site infection rates in all groups.

CONCLUSION

Prosthetic graft infection with S. epidermidis can be prevented by coating the graft with gold-palladium or gold.

Physicochemical characterisation and biological evaluation of hydrogel-poly(epsilon-caprolactone) interpenetrating polymer networks as novel urinary biomaterials

Hydrogels are frequently employed as medical device biomaterials due to their advantageous biological properties, e.g. resistance to infection and encrustation, biocompatibility; however, their poor mechanical properties generally limit the scope of application to coatings of medical devices. To address this limitation, this study described the formulation of sequential interpenetrating polymer networks (IPN) of poly(-caprolactone) (PCL) and poly(hydroxyethylmethacrylate) (p(HEMA)). IPN containing 20% w/w PCL, p(HEMA), both in the presence or absence of ethyleneglycol dimethacrylate (EGDMA 1% w/w), were prepared by free radical polymerisation. Following preparation the degradation and the mechanical and surface properties of the biomaterials and, in addition, the resistances to microbial adherence and encrustation in vitro were examined. In comparison to p(HEMA) the various IPN exhibited substantially greater tensile properties (ultimate tensile strength, % elongation, Young's modulus) that were accredited to the discrete distribution of PCL within the hydrogel network. The IPN exhibited two glass transition temperatures that were statistically similar to those of the individual components, thereby providing evidence of the immiscible nature of the two polymers. The IPN possessed higher receding contact angles and lower equilibrium water contents in comparison to p(HEMA), whereas the limited degradation of the IPN at both pH 7 and 9 was deemed suitable for clinical usage for periods of at least 4 weeks. The resistances of the various IPN to bacterial adherence and urinary encrustation were examined using in vitro models. Importantly the resistance of the IPN to encrustation was, in general, similar to that of p(HEMA) but greater than that of PCL whereas, the resistance of the IPN to bacterial adherence was frequently greater than that of p(HEMA) and PCL. Therefore, this study has shown that the mechanical properties of p(HEMA) may be substantially increased by the formation of IPN with PCL whilst maintaining other appropriate physicochemical properties and resistances to urinary encrustation and bacterial adherence. It is suggested that these IPN may be suitable for device fabrication thereby expanding the manufacturing application of hydrogels without compromising their potential clinical efficacy.

The resistance of polyvinylpyrrolidone–Iodine–poly(ε-caprolactone) blends to adherence of Escherichia coli

In this study, the resistance of biodegradable biomaterials, composed of blends of poly(-caprolactone) (PCL) and the polymeric antimicrobial complex, polyvinylpyrrolidone-iodine (PVP-I) to the adherence of a clinical isolate of Escherichia coli is described. Blends of PCL composed of a range of high (50,000 g mol(-1)) to low (5000 g mol(-1)) molecular weight ratios of polymer and either devoid of or containing PVP-I (1% w/w) were prepared by solvent evaporation. Following incubation (4 h), there was no relationship between m. wt. ratio of PCL in films devoid of PVP-I and adherence of E. coli. Conversely, microbial adherence to PCL containing PVP-I decreased as the ratio of high:low m. wt. polymer was decreased and was approximately 1000 fold lower than that to comparator films devoid of PVP-I. Following periods of immersion of PVP-I containing PCL films under sink conditions in phosphate buffered saline, subsequent adherence of E. coli was substantially reduced for 2 days (40:60 m. wt. ratio) and 6 days (100:0 m. wt. ratio). Concurrent exposure of PCL and E. coli to sub-minimum inhibitory concentrations (sub-MIC) of PVP-I significantly reduced microbial adherence to the biomaterial; however, the molecular weight ratio of PCL did not affect this outcome. Pretreatment of PCL with similar sub-MIC of PVP-I prior to inclusion within the microbial adherence assay significantly decreased the subsequent adherence of E. coli. Greatest reduction in adherence was observed following treatment of PCL (40:60 m. wt. ratio) with 0.0156% w/w PVP-I. In conclusion, this study has illustrated the utility of PVP-I as a suitable therapeutic agent for incorporation within PCL as a novel biomaterial. Due to the combined antimicrobial and biodegradable properties, these biomaterials offer a promising strategy for the reduction in medical device related infection.

Synthesis and Characterization of Polymeric Soybean Oil-g-Methyl Methacrylate (and n-Butyl Methacrylate) Graft Copolymers: Biocompatibility and Bacterial Adhesion

Peroxidation, epoxidation, and/or perepoxidation reactions of soybean oil under air at room temperature resulted in cross-linked polymeric soybean oil peroxides on the surface along with the waxy soluble part, sPSB, with a molecular weight of 4690, containing up to 2.3 wt % peroxide. This soluble polymeric oil peroxide, sPSB, initiated the free radical polymerization of either methyl methacrylate (MMA) or n-butyl methacrylate (nBMA) to give PSB-g-PMMA and PSB-g-PnBMA graft copolymers. The polymers obtained were characterized by (1)H NMR, thermogravimetric analysis, differential scanning calorimetry, and gel permeation chromatography techniques. Polymeric oil as a plasticizer lowered the glass transition of the PSB-g-PMMA graft copolymers. PSB-g-PMMA and PSB-g-PnBMA graft copolymer film samples were also used in cell culture studies. Fibroblast and macrophage cells were strongly adhered and spread on the copolymer film surfaces, which is important in tissue engineering. Bacterial adhesion on PSB-g-PMMA graft copolymer was also studied. Both Staphylococcus epidermidis and Escherichia coli adhered on the graft copolymer better than on homo-PMMA. Furthermore, the latter adhered much better than the former.

Gentamicin release from modified acrylic bone cements with lactose and hydroxypropylmethylcellulose

Modified polymethylmethacrylate (PMMA) bone cements formulations were prepared by including different proportions of gentamicin and release modulators such as lactose or hydroxypropylmethylcellulose (HPMC). Surface aspect, gentamicin release and porosity of these modified formulations were studied by means of scanning electron microscopy (SEM), a specially designed system for the dissolution studies of the bone cements, and mercury intrusion porosimetry. Lactose modified cements presented an irregular surface with numerous hollows and voids due to the lactose dissolution. HPMC cements presented a characteristic laminated and flaky surface. The drug release of lactose formulations was up to four-fold greater (13%) than the commercial bone cement CMW1 Gentamicin one (3%). The amount of gentamicin eluted at the first withdrawn sample ranged from 30% to 60% of total gentamicin released over the assay. Gentamicin release from lactose formulations increased as lactose percentage was increased which agree with the porosity results. Nevertheless, the use of release modulator HPMC increased porosity, but did not produce an increase in the gentamicin release. HPMC dissolution creates a surrounding sticky and viscous medium similar to a gel that makes the gentamicin release from the cement matrix difficult.

Poly(epsilon-caprolactone) and poly(epsilon-caprolactone)-polyvinylpyrrolidone-iodine blends as ureteral biomaterials: characterisation of mechanical and surface properties, degradation and resistance to encrustation in vitro

This study describes the physicochemical properties and in vitro resistance to encrustation of solvent cast films composed of either poly(epsilon-caprolactone) (PCL), prepared using different ratios of high (50,000) to low (4000) (molecular weight) m.wt., or blends of PCL and the polymeric antimicrobial complex, poly(vinylpyrrolidone)-iodine (PVP-I). The incorporation of PVP-I offered antimicrobial activity to the biomaterials. Films were characterised in terms of mechanical (tensile analysis, dynamic mechanical thermal analysis) and surface properties (dynamic contact angle analysis, scanning electron microscopy), whereas degradation (at 37 degrees C in PBS at pH 7.4) was determined gravimetrically. The resistance of the films to encrustation was evaluated using an in vitro encrustation model. Reductions in the ratio of high:low-m.wt. PCL significantly reduced the ultimate tensile strength, % elongation at break and the advancing contact angle of the films. These effects were attributed to alterations in the amorphous content and the more hydrophilic nature of the films. Conversely, there were no alterations in Young's modulus, the viscoelastic properties and glass-transition temperature. Incorporation of PVP-I did not affect the mechanical or rheological properties of the films, indicative of a limited interaction between the two polymers in the solid state. Manipulation of the high:low m.wt. ratio of PCL significantly altered the degradation of the films, most notably following longer immersion periods, and resistance to encrustation. Accordingly, maximum degradation and resistance to encrustation was observed with the biomaterial composed of 40:60 high:low m.wt. ratios of PCL; however, the mechanical properties of this system were considered inappropriate for clinical application. Films composed of either 50:50 or 60:40 ratio of high:low m.wt. PCL offered an appropriate compromise between physicochemical properties and resistance to encrustation. This study has highlighted the important usefulness of degradable polymer systems as ureteral biomaterials.

Evaluation of a poly(vinyl pyrollidone)-coated biomaterial for urological use

The associated problems of bacterial biofilm formation and encrustation that may cause obstruction or blockage of urethral catheters and ureteral stents often hinders the effective use of biomaterials within the urinary tract. In this in vitro study, we have investigated the surface properties of a hydrophilic poly(vinyl pyrollidone) (PVP)-coating applied to polyurethane and determined its suitability for use as a urinary tract biomaterial by comparing its lubricity and ability to resist bacterial adherence and encrustation with that of uncoated polyurethane and silicone. The PVP-coated polyurethane was significantly more hydrophilic and more lubricious than either uncoated polyurethane or silicone. Adherence of a hydrophilic Escherichia coli isolate to PVP-coated polyurethane and uncoated polyurethane was similar but significantly less than adherence to silicone. Adherence of a hydrophobic Enterococcus faecalis isolate to PVP-coated polyurethane and silicone was similar but was significantly less than adherence to uncoated polyurethane. Struvite encrustation was similar on the PVP-coated polyurethane and silicone but significantly less than on uncoated polyurethane. Furthermore, hydroxyapatite encrustation was significantly less on the PVP-coated polyurethane than on either uncoated polyurethane or silicone. The results suggest that the PVP-coating could be useful in preventing complications caused by bacterial biofilm formation and the deposition of encrustation on biomaterials implanted in the urinary tract and, therefore, warrants further evaluation.

Gentamicin bone cements: characterisation and release (in vitro and in vivo assays)

Due to the extended use of acrylic bone cements, its necessary to develop improved formulations in order to resolve their many drawbacks. The present work was conducted to make a physical-chemical characterisation of this kind of acrylic cement in order to introduce future changes in the formulations to: (1) improve or at least maintain their mechanical properties; (2) diminish their toxicity, and (3) control the drug release (rate and amount). From the dissolution method we can conclude that the preparation method (with or without pressure) of specimens is not responsible for the erratic release. The cumulative amount of gentamicin released was fitted to a semi-empirical equation to explain the possible release mechanism. The powder size, shape and distribution that could affect several properties of bone cement were studied with the aid of different techniques such as SEM, laser diffraction spectroscopy, and powder X-ray diffraction. From SEM micrographs, it was possible to observe that the surfaces of the specimens were very irregular with numerous small craters that may serve as conduits for eluting the antibiotic. An 'in vitro' drug diffusion model is proposed to elucidate the drug release mechanism. Finally an 'in vivo' study was performed to evaluate the antibiotic release to the neighbouring bone sites.

Assessment of encrustation behaviour on urinary tract biomaterials

The effective clinical use of biomaterials within the urinary tract is often hindered by the associated problems of bacterial biofilm formation and encrustation which may cause obstruction or blockage of urethral catheters and ureteral stents. Methods for assessing encrustation formation on these devices are reviewed and novel urinary tract biomaterials which may be more effective at resisting encrustation are discussed.