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Introduction: The need to optimize therapeutic outcomes while minimizing side effects is a major driving force for research and development in the controlled drug delivery field. Polymer nanocomposites (NCs) are an emerging class of materials with remarkable potential for controlled drug delivery. There are a range of release mechanisms that characterize polymer NC systems, and these may be perturbed not only by the addition of nanofillers, but also by the type of drug and the interactions of the drug with the components of the system., Areas Covered: The focus of this review is on non-degradable polymer NC systems. In particular, the types of drug delivery approach from these polymer NCs and the theoretical models developed to describe those approaches are discussed. The importance of component interactions and factors affecting drug delivery from polymer NCs is also addressed., Expert Opinion: Despite the remarkable potential and extensive research being conducted on polymer NCs for use in drug delivery, commercialization and large-scale production are limited by the cost and difficulty in consistently producing fully exfoliated NCs. A continuing challenge for the field is to understand better the key interactions and structure-property relationships arising from different polymer, filler and drug combinations.

Polymer nanocomposites (NCs) are hypothesised to have enhanced barrier properties compared with pristine polymer, allowing more sustained drug release from the materials. In these NC systems active agents are typically incorporated into the polymer matrix and the release kinetics are theoretically perturbed by well dispersed nanoparticle inclusions. An alternative approach is to exploit active agent interactions with the nanoinclusion. In the proposed NC system, the driving hypothesis is that active agents can have dual functionality, acting as both drug and dispersant. Polyurethane-montmorillonite (PEU-MMT) NCs were prepared in which the antimicrobial agent chlorhexidine diacetate (CHX) was evaluated as an organic modifier for silicate dispersion. CHX was incorporated at various concentrations through organic modification of MMT or within the bulk polymer. X-ray diffraction and transmission electron microscopy analysis suggested that intercalated and partially exfoliated NCs were achieved, with better dispersion occurring in the presence of free CHX within the bulk. Tensile testing results showed that variations in the level of organic modification and nanoparticle loading modulated the mechanical properties. Material stiffness increased with nanoparticle loading relative to pristine PEU, and the ultimate properties decreased with nanoparticle and free CHX incorporation. Antibacterial activity against Staphylococcus epidermidis was significant in materials with higher exchanged MMT and NCs containing free CHX, for which 2-log reductions in adherent bacteria were found after 24h. CHX was successfully used to modulate the material properties in its dual role as a dispersant and antimicrobial agent, suggesting that alternative biocides of similar structure may behave comparably within PEU-MMT NC systems., (Copyright 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

The aim of this study was to prepare stable formulations of poorly water-soluble drugs in amorphous forms to enhance their dissolution rates, promote the bioavailability, minimize the dosage, thereby theoretically decreasing their side effects. A dense gas solvent exchange process was developed for the impregnation of poorly water-soluble drugs such as camptothecin and griseofulvin into a chitosan matrix. The amount of drug impregnated was measured by UV-spectrophotometery and gravimetric techniques. Pore characteristics and the crystallinity of the drugs in the impregnated chitosan were measured. Homogenous nano-sized pores with thin walls were formed in chitosan using the dense gas solvent exchange process. The method was efficient for the impregnation of a drug into chitosan. Results of XRD, Fourier transform infrared spectroscopy and differential scanning calorimetry demonstrated that as a result of interaction between chitosan and the drug, both camptothecin and griseofulvin were in amorphous forms after processing. The dissolution rate of processed griseofulvin was increased threefold due to the hydrophilic properties of chitosan and its interaction with the drug. A new approach was developed for promoting drug bioavailability that has the potential to decrease the required dose and side effects, particularly for chemotherapeutic drugs with narrow therapeutic index., (Crown Copyright (c) 2010. Published by Elsevier B.V. All rights reserved.)

Conducting polymers hold significant promise as electrode coatings; however, they are characterized by inherently poor mechanical properties. Blending or producing layered conducting polymers with other polymer forms, such as hydrogels, has been proposed as an approach to improving these properties. There are many challenges to producing hybrid polymers incorporating conducting polymers and hydrogels, including the fabrication of structures based on two such dissimilar materials and evaluation of the properties of the resulting structures. Although both fabrication and evaluation of structure-property relationships remain challenges, materials comprised of conducting polymers and hydrogels are promising for the next generation of bioactive electrode coatings.

Implantable high-density microelectrode arrays have been successfully fabricated using laser micromachining of conventional implant materials, polydimethylsiloxane (PDMS) and platinum (Pt) foil. This study investigates the impact of modifying PDMS and Pt with high power laser beams and the possible toxicity of by-products that may remain on the implantable device. Materials were characterised both chemically and biologically through x-ray photoelectron spectroscopy (XPS), cell growth inhibition assays and a direct contact cell proliferation assay. It was found that laser micromachining produces oxides of silicon and platinum on the PDMS and Pt respectively. While the chemical properties of materials were altered, there was negligible change in the biological response to either extracts or cell growth directly on the composite electrode array.

Conductive neural interfaces tailored for cell interaction by incorporation of bioactive factors are hypothesized to produce superior neuroprostheses with improved charge transfer capabilities. This study examined the effect of entrapping nerve growth factor (NGF) within the conducting polymer poly(ethylene dioxythiophene) (PEDOT) during electrodeposition to create a polymer capable of stimulating neurite outgrowth from proximal neural tissue. NGF entrapment was performed on polymers doped with laminin peptides DEDEDYFQRYLI and DCDPGYIGSR and, additionally, a conventional dopant, paratoluene sulphonate (pTS). All polymer coatings were analysed for a range of physical, electrical and mechanical properties, with the biological activity of ligands examined using a PC12 neurite outgrowth assay. NGF was successfully entrapped in PEDOT during electrodeposition and was shown to produce a softer interface than conventional conducting polymers and films without the NGF modification. However, it was found that the use of a peptide dopant combined with NGF entrapment resulted in polymers with diminished electrical and mechanical stability. Entrapped NGF was determined to be biologically active, with PEDOT/pTS/NGF producing neurite outgrowth comparable with control films where NGF was supplied via the medium. Future studies will determine the effect of typical neural prosthetic stimulation regimes on the release of neurotrophins and subsequent cell response.

Conducting polymers (CPs) have the potential to provide superior neural interfaces to conventional metal electrodes by introducing more efficient charge transfer across the same geometric area. In this study the conducting polymer poly(ethylene dioxythiophene) (PEDOT) was coated on platinum (Pt) microelectrode arrays. The in vitro electrical characteristics were assessed during biphasic stimulation regimes applied between electrode pairs. It was demonstrated that PEDOT could reduce the potential excursion at a Pt electrode interface by an order of magnitude. The charge injection limit of PEDOT was found to be 15 x larger than Pt. Additionally, PEDOT coated electrodes were acutely implanted in the suprachoroidal space of a cat retina. It was demonstrated that PEDOT coated electrodes also had lower potential excursions in vivo and electrically evoked potentials (EEPs) could be detected within the vision cortex.

Bioactive coatings for neural electrodes that are tailored for cell interactions have the potential to produce superior implants with improved charge transfer capabilities. In this study synthetically produced anionically modified laminin peptides DEDEDYFQRYLI and DCDPGYIGSR were used to dope poly(3,4-ethylenedioxythiophene) (PEDOT) electrodeposited on platinum (Pt) electrodes. Performance of peptide doped films was compared to conventional polymer PEDOT/paratoluene sulfonate (pTS) films using SEM, XPS, cyclic voltammetry, impedance spectroscopy, mechanical hardness and adherence. Bioactivity of incorporated peptides and their affect on cell growth was assessed using a PC12 neurite outgrowth assay. It was demonstrated that large peptide dopants produced softer PEDOT films with a minimal decrease in electrochemical stability, compared to the conventional dopant, pTS. Cell studies revealed that the YFQRYLI ligand retained neurite outgrowth bioactivity when DEDEDYFQRYLI was used as a dopant, but the effect was strongly dependant on initial cell attachment. Alternate peptide dopant, DCDPGYIGSR was found to impart superior cell attachment properties when compared to DEDEDYFQRYLI, but attachment on both peptide doped polymers could be enhanced by coating with whole native laminin.

Injectable hydrogels have potential biomedical applications ranging from tissue fillers to drug delivery vehicles. This study focussed on evaluating the structure of poly(vinyl alcohol) (PVA) hydrogels of variable solid content and high molecular weight model drug release from the networks formed via either conventional photo-polymerization compared with chemical initiation of polymerization using an oxidation-reduction (redox) reaction. Swelling behaviour was characterised in water to assess the structural properties. Model drugs, FITC-Dextran, 20 kDa (FD20) and 4 kDa (FD4) were loaded in the hydrogels prior to curing and drug release studies conducted. Redox-cured hydrogels were more swollen than UV-cured systems, lost approximately 20% of their polymer mass compared to only 5% from UV-cured hydrogels and subsequently exhibited networks of larger mesh sizes. Also, networks of variable solid contents showed different structural properties with systems of higher polymer concentration exhibiting a smaller mesh size. The difference in structural properties of the networks affected release of FD20, being faster in redox-cured than UV-cured hydrogels, and slower from systems of higher solid content. Release of FD4 was faster than FD20 from networks of same solid content. This study suggested that PVA hydrogels can be cured by redox-initiation to function as a controlled delivery system for macromolecular drugs.

Synthetic scaffolds show great promise for use in tissue engineering due to their ability to mimic some aspects of the extracellular matrix, however, their use has been hindered by the lack of inherent recognition sites that are required for protein and cell interactions. Heparan sulfate (HS), a glycosaminoglycan polysaccharide present in the basement membrane and on the cell surface, binds growth factors and cytokines and enhances the signalling of these ligands by forming complexes with their receptors. This study focuses on the formation of photopolymerised hydrogels derived from methacrylated macromers of poly(vinyl alcohol) (PVA) and heparin, with the aim of imparting the growth factor activation property of heparin to the synthetic scaffolds. It was shown that the methacrylate group attachment on heparin did not result in the fragmentation of heparin molecules, and that the biological activity of the methacrylated heparin was preserved as determined by tests on its anticoagulation properties and ability to signal fibroblast growth factor-2 (FGF-2). The addition of heparin into the PVA hydrogels resulted in an increase in mass swelling ratio from 5.8 for pure PVA to 6.5 and 6.6 for PVA/heparin co-hydrogels of 19/1 and 17.5/2.5 (w/w) compositions, respectively. It is believed that heparin molecules can be added into a synthetic PVA scaffold without adversely affecting the structural and mechanical stability of the PVA scaffold. The tensile moduli of the co-hydrogels remained close to that of PVA hydrogels (61 kPa), even up to 2.5% heparin composition (PVA/hep 17.5/2.5). Finally, the co-hydrogels were found to retain the growth factor signalling activity of heparin at equilibrium.

The term nanocomposite refers to organic:inorganic composites where one phase, typically the inorganic phase, has dimensions on the nanoscale. Several authors have noted the potential benefit of biomedical application of nanocomposite technology, and have suggested using quaternary ammonium compounds (QAC) as an organic modification to enhance dispersion of nanoparticles within polymer matrices. This study aimed to examine fibroblast responses in vitro to a range of nanocomposites using different organic modifiers. Composite materials were prepared from a polyether urethane (PEU) and various unmodified and organically modified montmorillonite (MMT) nanoparticles. QAC and amino undecanoic acid (AUA) modified-MMT were added to PEU at loadings ranging from approximately 1 to 15 wt %. Composites with organically modified QAC and AUA particles displayed partially exfoliated and intercalated silicate morphology, respectively. Nanocomposites showed increases in ultimate tensile properties for materials with lower QACMMT loadings. However QAC was shown to significantly inhibit cell growth following release from PEU-QACMMT under extraction conditions mimicking those of the physiological environment. Materials containing silicate modified using AUA were cytocompatible. The results of this study suggest that QAC may be unsuitable as organic modifiers for nanoparticles destined for biomedical use. Alternative modifiers based on AUA confer equivalent dispersion and are of low toxicity.

Metal electrode materials used in active implantable devices are often associated with poor long-term stimulation and recording performance. Modification of these materials with conducting polymer coatings has been suggested as an approach for improving the neural tissue-electrode interface and increasing the effective lifetime of these implants. Neural interfaces ideally have intimate contact between the excitable tissue and the electrode to maintain signal quality and activation of neural cells. The outcomes of current research into conducting polymers as coatings has potential to enhance this tissue-material contact by increasing the electrode surface area and roughness as well as allowing delivery of bioactive signals to neural cells. However, challenges facing conducting polymers include poor electroactive stability and mechanical properties as well as control of the mobility, concentration and presentation of bioactive molecules. The impact of biological inclusions on polymer properties and their ongoing performance in neural prosthetics requires a greater understanding with future research aimed at controlling and optimising film characteristics for long-term performance. Optimising the electrode interface will require a trade-off between desired electrical, mechanical, chemical and biological properties.

Polymers have been used to deliver therapeutic agents in a range of medical devices with drug eluting stents being the most widespread current application. Although polymers enable controlled release of a therapeutic agent, the polymeric surface has been reported to provide suboptimal biocompatibility and haemocompatibility and it has been suggested that currently used polymers may be at least partly responsible for the late adverse events observed in intravascular stent systems. In this study, the biostability and biological performance of a siloxane-based polyurethane elastomer (E2A) demonstrating excellent long-term biostability in the unloaded state was investigated following incorporation of a therapeutic agent. After implantation in an ovine model for 6 months, samples were assessed using SEM and ATR-FTIR to determine changes in the surface chemical structure and morphology of the materials and tensile testing was used to examine changes in bulk characteristics. Biological response was assessed using in vitro cytotoxicity testing and histological analysis. Results indicated that incorporation of 25mg/g dexamethasone acetate (DexA) into the siloxane-based polyurethane resulted in no significant difference in the biostability and biocompatibility of the material. Some level of cytotoxic potential was exhibited which was believed to result from residual DexA leaching from samples during the extraction process. These findings suggest that E2A is a potential candidate for a delivery vehicle of therapeutic agents in implantable drug delivery applications.

Multi-walled carbon nanotubes (MWNTs) can be incorporated into conductive polymers to produce superior materials for neural interfaces with high interfacial areas, conductivity and electrochemical stability. This paper explores the addition of MWNTs to polypyrrole (PPy) through two methods, layering and codeposition. Conductivity of PPy doped with polystyrene sulfonate (PSS), a commonly used dopant, was improved by 50% when MWNTs were layered with PPy/PSS. The film electrochemical stability was improved from 38% activity to 66% activity after 400 cycles of oxidation and reduction. Growth inhibition assays indicated that MWNTs are not growth inhibitory. The electroactive polymer-MWNT composites produced demonstrate properties that suggest they are promising candidates for biomedical electrode coatings.

Poly (vinyl alcohol) (PVA) hydrogels are highly attractive for biomedical applications, especially for controlled release of drugs and proteins. Recently, degradable PVA hydrogels have been described, having the advantage that the material disappears over time from the implantation site. Herein, we report the synthesis of radiopaque degradable PVA, which gives a further advantage that the position of the hydrogel can precisely be determined by X-ray fluoroscopy. Radiopacity has been introduced by replacing 0.5% of the pendent alcohol groups on the PVA with 4-iodobenzoylchloride. This level of substitution rendered the polymer adequately radiopaque. The subsequent modification of 0.8% of the pendent hydroxyl groups with an ester acrylate functional group allowed for cross-linking of the macromers. The radiopaque hydrogels degraded over a time span of 140 days. Rheology data suggested that the macromer solutions were appropriate for injection.

Biocompatible, degradable hydrogel systems that can cure in situ following injection as a liquid are useful as a base for tissue engineering and drug delivery. In this study, poly (vinyl alcohol) (PVA) polymers were modified with degradable crosslinkers and formulated for either ultraviolet (UV) light initiation or chemical initiation using an oxidation/reduction (redox) curing method. A major objective was to compare the properties of degradable PVA hydrogels formed via two routes of curing. The effect of macromer concentration, degree of hydrolysis and functional group density on the degradation profiles was investigated. Also, since the hydrogels have been designed to be injected as a liquid for in situ curing, the effect of modified macromer solutions and degradation products on cell growth was investigated. Total degradation times ranged from approximately 20 days up to 120 days and increased in direct proportion with percent macromer. Initiation method (UV or redox) did not significantly impact on time for total degradation. While aqueous solutions of the modified macromer induced some cell growth inhibition, mainly associated with oxidative solutions, degradation products showed relatively low cell growth inhibition. Degradable PVA hydrogels tailored to produce networks with various degradation profiles can be cured by redox initiation and have potential as injectable polymers for soft-tissue engineering and drug delivery.

Honeycomb-structured porous films were prepared using customized amphiphilic block copolymers, synthesized by RAFT polymerization. Pyrrole was templated along an amphiphilic block copolymer, composed of polystyrene and poly(acrylic acid). Subsequent oxidation of pyrrol to polypyrrole, resulted in the formation of a soluble polypyrrole-containing polymer. Gel permeation chromatography and dynamic light scattering studies confirmed the solubility of the resulting customized amphiphilic block copolymer, in both water and organic solvent, forming either micelles or inverse aggregates. Porous films with a hexagonal array of micron-sized pores were generated with the polymer, using the breath figures templating technique. The resulting films were found to be non-cytotoxic and hence suitable as scaffolds for tissue engineering. Initial fibroblast cell culture studies on these scaffolds demonstrated a dependency of cell attachment on the pore size of scaffolds.

Background and Objectives: Laser tissue repair usually relies on hemoderivate protein solders, based on serum albumin. These solders have intrinsic limitations that impair their widespread use, such as limited tensile strength of repaired tissue, poor solder solubility, and brittleness prior to laser denaturation. Furthermore, the required activation temperature of albumin solders (between 65 and 70 degrees C) can induce significant thermal damage to tissue. In this study, we report on the design of a new polysaccharide adhesive for tissue repair that overcomes some of the shortcomings of traditional solders., Study Design/materials and Methods: Flexible and insoluble strips of chitosan adhesive (elastic modulus approximately 6.8 Mpa, surface area approximately 34 mm2, thickness approximately 20 microm) were bonded onto rectangular sections of sheep intestine using a diode laser (continuous mode, 120 +/- 10 mW, lambda = 808 nm) through a multimode optical fiber with an irradiance of approximately 15 W/cm2. The adhesive was based on chitosan and also included indocyanin green dye (IG). The temperature between tissue and adhesive was measured using a small thermocouple (diameter approximately 0.25 mm) during laser irradiation. The repaired tissue was tested for tensile strength by a calibrated tensiometer. Murine fibroblasts were cultured in extracted media from chitosan adhesive to assess cytotoxicity via cell growth inhibition in a 48 hours period., Results: Chitosan adhesive successfully repaired intestine tissue, achieving a tensile strength of 14.7 +/- 4.7 kPa (mean +/- SD, n = 30) at a temperature of 60-65 degrees C. Media extracted from chitosan adhesive showed negligible toxicity to fibroblast cells under the culture conditions examined here., Conclusion: A novel chitosan-based adhesive has been developed, which is insoluble, flexible, and adheres firmly to tissue upon infrared laser activation., (Copyright 2005 Wiley-Liss, Inc.)

Infection of medical devices causes significant morbidity and mortality and considerable research effort has been directed at solving this problem. The aim of this study was to assess the biological performance of a novel furanone compound that has potential as an anti-infective coating for medical devices. This study examined in vitro leukocyte response following exposure to the antibacterial 3-(1'-bromohexyl)-5-dibromomethylene-2(5H)-furanone and assessed the tissue response following subcutaneous implantation of the furanone compound covalently bound to polystyrene (PS). Peripheral human blood was exposed to furanones in solution for 1h and flow cytometry used to analyse viability and changes in expression of surface receptors CD11b/CD18 and CD44. Flow cytometry results from propidium iodide stained cell suspensions suggested that the leukocytes were viable after exposure to furanones in whole blood. No significant difference was found in the expression of CD11b/CD18 and CD44 between the furanone exposed samples and the negative control for neutrophils suggesting that the furanones themselves do not activate these leukocytes. The positive control lipopolysaccharide significantly up-regulated CD11b/CD18 and slightly down-regulated CD44 on both PMNs and monocytes. In vivo studies of the tissue response to furanone covalently bound to PS showed that there was no significant difference in cellularity of capsules surrounding the disk and no significant increase in myeloperoxidase expression. These results demonstrate negligible acute inflammatory response to synthetic brominated antibacterial furanones. Future studies will focus on chronic responses and examination of in vivo efficacy.

In order to overcome the continuing infection rate associated with biomaterials, the use of covalently bound furanones as an antibiofilm coating for biomaterials has been investigated. Furanones have previously been shown to inhibit growth of Gram-positive and Gram-negative bacteria. The aim of these studies were to covalently bind furanones to polymers and to test their efficacy for inhibiting biofilm formation of Staphylococcus epidermidis and in vivo infection rate. Two methods of covalent attachment of furanones were used. The first, a co-polymerisation with a styrene polymer, and second, a plasma-1-ethyl-3-(dimethylaminopropyl) carbodiimide (EDC) reaction to produce furanone-coated catheters. Biofilm formation by S. epidermidis in vitro was inhibited by 89% for polystryene-furanone disks and by 78% by furanone-coated catheters (p<0.01). In an in vivo sheep model we found furanones were effective at controlling infection for up to 65 days. Furanones have potential to be used as a coating for biomaterials to control infection caused by S. epidermidis.

A major barrier to the long-term use of medical devices is development of infection. Staphylococcus epidermidis is one of the most common bacterial isolates from these infections with biofilm formation being their main virulence factor. Currently, antibiotics are used as the main form of therapy. However with the emergence of staphylococcal resistance, this form of therapy is fast becoming ineffective. In this study, the ability of a novel furanone antimicrobial compound to inhibit S. epidermidis adhesion and slime production on biomaterials was assessed. Furanones were physically adsorbed to various biomaterials and bacterial load determined using radioactivity. Slime production was assessed using a colorimetric method. Additionally, the effect of the furanone coating on material surface characteristics such as hydrophobicity and surface roughness was also investigated. The results of this study indicated that there was no significant change in the material characteristics after furanone coating. Bacterial load on all furanone-coated materials was significantly reduced (p<0.001) as was slime production (p<0.001). There is a potential for furanone-coated biomaterials to be used to reduce medical device-associated infections.

The long-term biostability of a novel thermoplastic polyurethane elastomer (Elast-Eon 2 80A) synthesized using poly(hexamethylene oxide) (PHMO) and poly(dimethylsiloxane) (PDMS) macrodiols has been studied using an in vivo ovine model. The material's biostability was compared with that of three commercially available control materials, Pellethane 2363-80A, Pellethane 2363-55D and Bionate 55D, after subcutaneous implantation of strained compression moulded flat sheet dumbbells in sheep for periods ranging from 3 to 24 months. Scanning electron microscopy, attenuated total reflectance-Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were used to assess changes in the surface chemical structure and morphology of the materials. Gel permeation chromatography, differential scanning calorimetry and tensile testing were used to examine changes in bulk characteristics of the materials. The results showed that the biostability of the soft flexible PDMS-based test polyurethane was significantly better than the control material of similar softness, Pellethane 80A, and as good as or better than both of the harder commercially available negative control polyurethanes, Pellethane 55D and Bionate 55D. Changes observed in the surface of the Pellethane materials were consistent with oxidation of the aliphatic polyether soft segment and hydrolysis of the urethane bonds joining hard to soft segment with degradation in Pellethane 80A significantly more severe than that observed in Pellethane 55D. Very minor changes were seen on the surfaces of the Elast-Eon 2 80A and Bionate 55D materials. There was a general trend of molecular weight decreasing with time across all polymers and the molecular weights of all materials decreased at a similar relative rate. The polydispersity ratio, Mw/Mn, increased with time for all materials. Tensile tests indicated that UTS increased in Elast-Eon 2 80A and Bionate 55D following implantation under strained conditions. However, ultimate strain decreased and elastic modulus increased in the explanted specimens of all three materials when compared with their unimplanted unstrained counterparts. The results indicate that a soft, flexible PDMS-based polyurethane synthesized using 20% PHMO and 80% PDMS macrodiols has excellent long-term biostability compared with commercially available polyurethanes.

Background: Laser tissue soldering (LTS) is an alternative technique to suturing for tissue repair that avoids foreign body reaction and provides immediate sealing of the wound. One of the major drawbacks of LTS, however, is the weak tensile strength of the solder welds when compared to sutures. In this study, a crosslinking agent of low cytotoxicity was investigated for its ability to enhance the bond strength of albumin solders with sheep intestine., Study Design/materials and Methods: Solder strips were welded onto rectangular sections of sheep small intestine using a diode laser. The laser delivered in continuous mode a power of 170 +/- 10 mW at lambda = 808 nm, through a multimode optical fiber (core size = 200 microm) to achieve a dose of 10.8 +/- 0.5 J/mg. The solder thickness and surface area were kept constant throughout the experiment (thickness = 0.15 +/- 0.01 mm, area = 12 +/- 1.2 mm2). The solder was composed of 62% bovine serum albumin (BSA), 0.38% genipin, 0.25% indocyanin green dye (IG), and water. Tissue welding was also performed with a BSA solder without genipin, as a control group. The repaired tissue was tested for tensile strength by a calibrated tensiometer. Murine fibroblasts were also cultured in extracted media from heat-denatured genipin solder to assess cell growth inhibition in a 48 hours period., Results: The tensile strength of the genipin solder was doubled that of the BSA solder (0.21 +/- 0.04 N and 0.11 +/- 0.04 N, respectively; P = 10(-15) unpaired t-test, N = 30). Media extracted from crosslinked genipin solder showed negligible toxicity to fibroblast cells under the culture conditions examined here., Conclusion: Addition of a chemical crosslinking agent, such as genipin, significantly increased the tensile strength of adhesive-tissue bonds. A proposed mechanism for this enhanced bond strength is the synergistic action of mechanical adhesion with chemical crosslinking by genipin.

The objective of this study was to develop and evaluate a hydrogel vehicle for sustained release of growth factors for wound healing applications. Hydrogels were fabricated using ultraviolet photo-crosslinking of acrylamide-functionalized nondegradable poly(vinyl alcohol) (PVA). Protein permeability was initially assessed using trypsin inhibitor (TI), a 21 000 MW model protein drug. TI permeability was altered by changing the solids content of the gel and by adding hydrophilic PVA fillers. As the PVA content increased from 10% to 20%, protein flux decreased, with no TI permeating through 20% PVA hydrogels. Further increase in model drug release was achieved by incorporating hydrophilic PVA fillers into the hydrogel. As filler molecular weight increased, TI flux increased. The mechanism for this is most likely an alteration in protein/gel interactions and transient variations in water content. The percent protein released was also altered by varying protein loading concentration. Release studies conducted using growth factor in vehicles with hydrophilic filler showed sustained release of platelet-derived growth factor (PDGF-beta,beta) for up to 3 days compared with less than 24 hours in the controls. In vitro bioactivity was demonstrated by doubling of normal human dermal fibroblast numbers when exposed to growth factor-loaded vehicle compared to control. The release vehicle developed in this study uses a rapid and simple fabrication method, and protein release can be tailored by modifying solid content, incorporating biocompatible hydrophilic fillers, and varying protein loading concentration.

Healing of chronic wounds such as diabetic foot ulcers is a significant clinical problem. Methods of accelerating healing in these difficult lower extremity sites include use of growth factor-loaded gels, hyperbaric oxygen, grafts, and artificial skin replacements. Nitric oxide (NO) has been proposed as a possible active agent for enhancing wound healing. This study examines the in vitro and in vivo responses to a novel hydrogel that produces therapeutic levels of NO. A hydrogel wound dressing was fabricated using ultraviolet light-initiated polymerization from poly(vinyl alcohol) with a NO donor covalently coupled to the polymer backbone. NO release from the NO-modified hydrogel was shown to occur over a time period of up to 48 hours, and there was no associated decrease in fibroblast growth or viability in vitro associated with NO hydrogels. Fibroblasts in culture with NO hydrogels had an increased production of extracellular matrix compared with cells cultured without the NO hydrogels. Preliminary animal studies in a diabetic mouse, impaired wound healing model were conducted comparing low (0.5 mM) and high (5 mM) doses of NO. Time to complete closure was similar in control wounds and NO-treated wounds; however, at 8 days control wounds were significantly smaller than NO-treated wounds. By days 10 to 13 this delay was no longer apparent. Granulation tissue thickness within the wounds at days 8 and 15 and scar tissue thickness after wound closure were increased in animals exposed to higher dose NO hydrogels. The results of this study suggest that exogenous NO released from a hydrogel wound dressing has potential to modulate wound healing.

A porous polyurethane vascular prosthesis with an internal diameter of 5 mm was studied. The graft carries a coating of immobilized dipyridamole (Persantin(R)) on the surface of its lumen. Dipyridamole is a potent nontoxic inhibitor of platelet activation/aggregation, and also a strong inhibitor of vascular smooth muscle cell proliferation. The polyurethane material is also known as Chronoflex(R), and already finds use as a vascular access graft. The coated vascular graft was studied in vitro (hemocompatibility, interaction with blood platelets and cultured endothelial cells), as well as in two established in vivo models. In the first in vivo study, coated grafts were implanted in goats, as a bypass of the carotid artery (four animals, eight grafts, length of the graft was approximately 12 cm). Four uncoated grafts were used as controls in otherwise identical experiments. In the second in vivo experiment, eight sheep were used. Each animal received one coated and one uncoated prosthesis as an interposition graft in the carotid artery (length of the graft was 4 cm). The in vitro experiments revealed that the dipyridamole coating has three beneficial effects: reduced thrombogenicity, reduced adherence of blood platelets, and accommodation of a confluent monolayer of endothelial cells. The goat experiments showed patency of the coated grafts in three of the eight cases. The sheep experiments were not useful for the evaluation of the dipyridamole coating because deterioration of the polyurethane material was observed. The in vivo results indicate that the dipyridamole coating may positively influence the patency rate, probably because the coating promotes the growth of an endothelial cell lining. The sheep data show, however, that the limited stability of the Chronoflex(R) material precludes its issue for the construction of permanent small-bore vascular grafts., (Copyright 2000 John Wiley & Sons, Inc.)

This study examined the fluid dynamics of a textured blood-contacting surface using a computational fluid-dynamic modeling technique. The texture consisted of a regular array of microfibers of length 50 or 100 microm, spaced 100 microm apart, projecting perpendicularly to the surface. The results showed that the surface texture served as a flow-retarding solid boundary for a laminar viscous flow, resulting in a lowered wall shear stress on the hase-plane surface. However, the maximum wall shear stress on the fibers was much higher than the shear stress on the nontextured phase plane. At all fractions of fiber height down past 10 microm, the permeability of the textured region greatly exceeded the analytically predictable permeability of an equivalent array of infinite-height fihers. The lowered suiface shear stress appears to explain in part the enhanced deposition of formed blood elements on the textured surface.

Textured blood-contacting surfaces can promote the formation of a blood-compatible pseudo-neointima. We hypothesized that by controlling the surface texturing, the pseudo-neointima thickness could be controlled. The hypothesis was tested experimentally by fabricating the polyurethane textured surfaces with three different fiber lengths, and exposing them simultaneously to the flowing blood in an ovine ex vivo carotid-jugular series shunt for periods up to 4 h. The textured surface consisted of regularly spaced tapered micro-fibers of defined length on a smooth base-plane surface. Because of the simple surface topography, detailed computational fluid-dynamic modeling of the surface could be obtained as a parallel study. Experimental results showed that white cell was the predominant cell type deposited on the textured surfaces, whereas macroscopic thrombus formation occurred only in one of nine blood-contacting experiments. White cell density on the textured base-plane surface was subsequently quantified by image-analyzing the electron micrographs of blood-contacted textured surfaces. The statistical analysis of cell densities on individual textured surfaces showed effects of wall shear stress on the textured base plane (which was obtained from the fluid-dynamic modeling), the longitudinal position of the test section in the series shunt, and blood-contact time., (Copyright 2000 John Wiley & Sons, Inc.)

Blood-contacting surface modifications aimed at reduction of thromboembolic complications have included the texturing of surfaces so as to promote the formation of a stable pseudo-neointima. A technique has been developed whereby a textured surface consisting of regularly spaced micro-fibres was produced on a smooth base plane. Polyurethane vascular patches with and without the textured luminal surface were fabricated and implanted bilaterally in ovine carotid arteries for 1- and 3-week implantation periods (n = 6 per period). One of 6 arteries with textured patches in the 1-week group was occluded. All other arteries were patent. At 1 week, all patent textured patches had adherent thrombus covering the entire patch surface. By 3 weeks, the thrombus had organised to form a stable pseudo-neointima. Non-textured patches at 1 week had only partial surface coverage of thrombus. At 3 weeks, 4 of 6 non-textured patches had significant red thrombus in the lumen. At 3 weeks, there was also evidence of cellular migration from artery onto both textured and non-textured patches. These findings suggest that the major role of the textured surface was as a promoter of a stabilised thrombus base onto which subsequent cellular migration and tissue healing occurred more rapidly than onto a smooth polyurethane surface.

Autologous grafts are superior to their synthetic counter-parts for grafting arteries smaller than 6-mm diameter both in terms of acute thrombogenicity and chronic intimal hyperplasia. Endothelial cell (EC) coating of the blood contacting surface may reduce thrombogenicity of synthetic small diameter vascular prostheses. In this study, the survival of EC monolayers on synthetic 4-mm diameter arterial prostheses over short-term implantations (< or = 6 weeks) was examined. Graft types examined were expanded polytetra-fluoroethylene (ePTFE) and microporous polyurethane (PU). Lumenal coverage with ECs was achieved by culturing ovine ECs on prostheses treated by either physical adsorption or covalent binding of ovine fibronectin (Fn). An ovine carotid interposition model was used to examine the performance of EC coated ePTFE and microporous PU over implantation periods of 1, 3, and 6 weeks. Outcomes assessed at the end of each experiment were graft patency, area covered by ECs, and thrombus free surface area (TFSA). Fn concentration, cell density at the time of coating and prostacyclin production in vitro were similar for both graft types. Occlusion occurred more frequently in unseeded grafts compared with EC coated grafts over 3 and 6 week implantation periods; however, the difference was not significant (p = 0.099). In prostheses precoated with ECs, approximately 40-60% of the surface area remained covered with endothelial-like cells following the first postoperative week. Recovery of EC layers occurred rapidly thereafter with 80-90% coverage at 3 weeks. TFSA remained low in comparison to EC cover in these prostheses until between 3 and 6 weeks postoperatively, suggesting a lag phase in recovery of EC function of seeded cells. In contrast, EC cover of unseeded prostheses only achieved 10-30% at 3 weeks, primarily by pannus EC ingrowth from the adjacent artery. TFSA of unseeded grafts increased in direct proportion to EC cover over time suggesting that there was no lag phase in function of these ingrowing cells.

Two forms of bovine pericardium (BPC) were assessed as hernia repair materials: non-cross-linked (lyophilized) and cross-linked through treatment with glutaraldehyde (GA). These were compared with polypropylene mesh (Marlex) in a rabbit model. Over 52 wk implantation, the GA BPC grafts developed a strong, stable, fibrous tissue replacement with good incorporation into the abdominal muscle wall. The lyophilized BPC grafts were substantially resorbed within 12 wk of implantation, however the thin, fibrous replacement tissue was inadequate for abdominal wall support. Marlex grafts provided sufficient abdominal support, however these grafts were associated with extensive adhesion formation and, in this model, fat deposition around the perimeter of the graft. Control (ungrafted) rabbit abdominal muscle in the transverse orientation had an ultimate tensile load (UTL) of 11.4 +/- 5.1 N (x +/- s.d.) and a strain at UTL of 35 +/- 12% (n = 169). At 52 weeks the UTL of the repair sites was 7.3 +/- 4.5 N (n = 6), 5.1 +/- 3.5 N (n = 6) and 5.6 +/- 2.7 N (n = 6) for GA BPC, lypophilized BPC and Marlex grafts, respectively.

124 stable CAPD patients from 8 Australian and 3 New Zealand centers were randomly assigned in a blinded fashion to one of two groups to study the effect of vaccination using commercial preparations consisting of a combined staphylococcus toxoid and whole killed staphylococci (SB) or normal saline solution (SS) on the incidence of peritonitis and exit site infection and S. aureus nasal carriage over a 12-month prospective period. In addition, levels of IgG, IgA, IgM, C3 and C4 were monitored during the trial period in serum and dialysate; serum levels of anti-alpha hemolysin and dialysate levels of fibronectin and specific antistaphylococcal antibodies were also measured. Over the period, treatment with SB or SS did not affect the incidence of peritonitis, catheter-related infection or S. aureus nasal carriage. However, vaccination with SB elicited a significant increase in the level of serum anti-alpha hemolysin throughout the 12 month duration of the study, although the level of increase was unrelated to the subsequent rate of peritonitis. Vaccination with SB but not SS elicited a significant increase in the dialysate level of specific antibodies against S. aureus. Serum levels of IgG, IgA, IgM, complement C3 and C4 were within the normal range in the CAPD patients studied and remained unaffected by vaccination with SB. In addition, dialysate levels of IgG, IgA, IgM, complement C3 and C4 were 50-100 times lower than corresponding serum levels and remained unaffected by vaccination. In summary, immunisation with an anti-staphylococcal agent was not successful in reducing peritonitis or exit site infection in CAPD patients.

Patients treated with continuous ambulatory peritoneal dialysis (CAPD) are constantly exposed to microbial invasion of the peritoneal cavity and rapid microbiological diagnosis of peritonitis is essential. Aseptic peritonitis is diagnosed in a high proportion of episodes when small volumes of dialysate are cultured. The aims of this study were to enumerate the microorganisms associated with clinical peritonitis and compare the efficacy of various culture systems for laboratory diagnosis of peritonitis. Four qualitative culture systems were compared: low (1 ml) volume and high (10 ml) volume inoculations of broth media, centrifugation (10 ml) followed by culture of the sediment and filtration (less than or equal to 100 ml) followed by culture of the filter. The pour plate and drop plate were the 2 quantitative methods used. Results of this study indicate that culture of 10 ml fluid volumes is comparable to culture of larger volumes sampled by filtration. Low volume cultures of fluid resulted in a lower proportion of positive cultures. The low numbers of viable microorganisms often found in dialysate from patients with peritonitis supports the concept of culturing a minimum of 10 ml of fluid.

The laboratory diagnosis of continuous ambulatory peritoneal dialysis-associated peritonitis is often hindered by either the absence of or the recovery of low numbers of viable microorganisms. This may be the result of sequestration of bacteria within phagocytes. Sonication of clinical specimens prior to culturing or culturing on saponin-containing media resulted in the growth of significantly greater numbers of colonies than standard culturing on conventional media. In addition, the demonstration that microorganisms are sequestered in phagocytes helped to establish the pathogenic nature of such isolates and distinguish them from contaminants even when present in low numbers. A variety of physical and chemical techniques can disrupt phagocytes and improve the sensitivity of laboratory methods used to confirm the diagnosis of peritonitis in continuous ambulatory peritoneal dialysis patients.