In Vitro Calcification Evaluation of Polycarbonate Urethane-Impact of Production Processes.

Event Abstract Back to Event Ciprofloxacin-based polymer additives interact with degradable polyurethane to alter the hydrolysis kinetics of antibiotic-releasing nanofibres Meghan Wright1, Andrew T. Wong1, Meilin Yang2 and Paul Santerre1, 2 1 University of Toronto, Institute of Biomaterials and Biomedical Engineering, Canada 2 University of Toronto, Faculty of Dentistry, Canada Introduction: Within the field of drug-loaded nanofibres, there has been little investigation into understanding the effect of added drug on electrospun fibre biodegradation characteristics despite evidence that added drugs have the potential to alter the rate of degradation of bulk polymer[1], microparticles[2] and even nanofibres[3],[4]. The goal of the current work was to determine the effect of adding the antibiotic ciprofloxacin (CF) and a proprietary antimicrobial polymer (AP) containing CF on the biodegradation rate of electrospun polycarbonate urethane (PCNU) nanofibre scaffolds. It was hypothesized that the added drug would affect the PCNU biodegradation rate by influencing the unique hydrogen-bonding (H-bonding) and microstructure character of the PCNU[5]. Materials and Methods: PCNU was synthesized with hexane diisocyanate:polycarbonate diol:butane diol in a molar ratio of 3:2:1[5]. The AP (7 and 15% w/w equivalent CF) or free CF-HCl (15% w/w) were incorporated via blend electrospinning. Scaffold H-bonding and microstructure were investigated via attenuated total reflectance Fourier transform IR spectroscopy (ATR-FTIR) and differential scanning calorimetry (DSC). Matrix degradation and antimicrobial release studies were carried out in PBS at 37°C for 28 days; drug release was measured by high performance liquid chromatography (HPLC), and PCNU degradation was measured using gel permeation chromatography (GPC). The cell compatibility of release products was assessed using human gingival fibroblasts (HGF), and the minimum inhibitory concentration (MIC) of released CF was measured against P. gingivalis cultures. Results and Discussion: CF from the AP scaffold was released slowly over the duration of the study, while drug aggregation within the 15% w/w CF-HCl scaffolds led to a burst release (Fig.1). The addition of drug caused an increase in the hydrolytic stability of the PCNU scaffolds, proportional to the amount of drug added, regardless of the form it was added (Fig.2). Fig.1. Cumulative release of CF in PBS (pH ~ 7) at 37°C (μM). Data are mean ± SD (n=9). Fig.2. Reduction in polystyrene equivalent weight average molecular weight (Mw), as a percent (%) of original (t=0 days), determined by GPC. Data are the mean ± SD (n=9). At day 28, H-bonding (FTIR) within the hard-segment and phase mixing (DSC) had decreased for the 0% w/w CF scaffolds and increased for the drug-loaded scaffolds (data not shown). Increased H-bonding and phase mixing for the latter may have led to shielding of the hydrolytically susceptible carbonate soft-segment, with the result that the drug-loaded scaffolds had greater stability. Accumulated PCNU biodegradation products (regardless of drug presence) significantly decreased HGF relative metabolic activity (Fig. 3). The MIC of released CF was higher than that of CF-HCl off-the-shelf (~0.5 µg/mL vs. 0.25 µg/mL respectively). Fig.3. Relative metabolic activity as a % of the growth medium control of Day 7 scaffold release products. * Represents significant difference from growth medium control (p < 0.05). Data are the mean ± SE (n=9). Conclusion: The results indicate the ability to use AP to generate electrospun scaffolds with a sustained (>28 days) release of CF. The combination of sustained drug release and delayed scaffold degradation presents a viable treatment modality for medical device applications requiring long term antimicrobial management (e.g. post-surgical oral wounds). National Science and Engineering Research Council (NSERC) Synergy; NSERC CGS D; IBBME; Interface Biologics Inc. for supply of AP

In children, systemic heart valve replacement with bioprostheses is associated with accelerated valve degeneration, and mechanical prostheses require permanent anticoagulation. Novel "biomechanical" polymeric valve prostheses ("bio" = flexible, "mechanical" = synthetic), solely made of polycarbonate urethane (PCU), were tested in vitro and in a growing animal (calf) model with the aim of improved durability without permanent anticoagulation. The trileaflet aortic prosthesis has diminished pressure loss and reduced stress and strain peaks. The asymmetric bileaflet mitral valve mimics natural nonaxial inflow. The valves underwent long-term in vitro testing and in vivo testing in growing calves for 20 weeks [mitral (7), aortic (7)] with comparison to different commercial bioprostheses [mitral (7), aortic (2)]. In vitro durability of PCU valves was proved up to 20 years. Survival of PCU valves versus bioprostheses was 7 versus 2 mitral and 5 versus 0 aortic valves, respectively. Two animals with PCU aortic valves died of pannus overgrowth causing left ventricular outflow tract obstruction. Degeneration and calcification were mild (mitral) and moderate (aortic) in PCU valves but were severe in biological valves. There was no increased thrombogenicity of the PCU valves compared to bioprostheses. The novel polymeric valve prostheses revealed superior durability compared to current bioprostheses in growing animal model without permanent anticoagulation and thus, may be a future option for pediatric patients.

Recent investigation on biomaterial based tissue engineered heart valve (TEHV)

Wear particles invariably form due to contact and friction between articulating surfaces in orthopedic prosthetic joint replacements. Polycarbonate urethane (PCU) has shown low wear rates and invoked minimal local biological response to wear debris in various orthopedic applications. However, controlled preclinical studies have not yet studied the biological response to PCU particles in synovial joints. This study aims to evaluate the biological response to mostly submicron-sized PCU wear particles in synovial joints in a rabbit model representing a worst-case scenario. PCU and ultra-high-molecular-weight-polyethene (UHMWPE) particles were generated invitro, and particle characterization was performed using scanning electron microscopy (SEM) images. Fifteen New Zealand white rabbits, divided into three groups, received bilateral injections in the knee joint with 10 mg/mL PCU, UHMWPE particles, or saline (all 0.2 mL). After 3 months, the biological response in the joint was evaluated by histopathological reactivity scoring. The generated PCU and UHMWPE wear particles were mainly in the biologically active size range with an average equivalent circle diameter (ECD) of 0.31 μm (±0.48) and 6.99 μm (±16.32), respectively. There was a minimal to non-existing biological response (score ≤ 0.5) to PCU (0.5 ± 1.0), UHMWPE particles (0.6 ± 1.3) and saline (0.0 ± 0.0). Also, the wear particles did not disperse from the injection site. The results of this study support the use of PCU as a bearing surface in orthopedic prosthetic joint replacements by indicating that even in the likelihood that wear particles are generated, they are not likely to trigger a strong inflammatory response.

Tribological evaluation of biomedical polycarbonate urethanes against articular cartilage.

A biomimetic multilayered polymeric material designed for heart valve repair and replacement

Chronic neural implants are usually made from silicon materials and are subject to scar tissue formation at the tissue/implant interface, which interferes with their functionality. Carbon nanofibers are an example of a material that may improve neural implant interactions with native cell populations since these nanofibers have promising cytocompatibility, mechanical, and electrical properties. Neural implants may achieve better tissue interactions simply by incorporating carbon nanofibers into a polymer matrix. Polycarbonate urethane and carbon nanofiber composites have induced neurite extension during in vitro studies. The objective of the present study was to use an electrical field to align carbon nanofibers in a polycarbonate urethane matrix. Polycarbonate urethane was dissolved in chloroform, and then mixed with carbon nanofibers of high and low surface energies separately. When the solution was viscous, it was pored into a parallel copper plate capacitor chamber. Alignment occurred after exposure to 500 to 700 volts. The aligned nanofiber structure was maintained after the polymer cured. These materials have been prepared to determine if neuron axonal extension will be affected by the carbon nanofiber alignment. These materials have promising tunable properties for neural implants such as electrical, nanoscale structure and organization, and surface energy characteristics.

Polycarbonate urethane (PCU) is a new biomaterial, and its mechanical properties can be tailored to match that of vaginal tissue. We aimed to determine whether vaginal host immune and extracellular matrix responses differ after PCU versus lightweight polypropylene (PP) mesh implantation. Hysterectomy and ovariectomy were performed on 24 Sprague-Dawley rats. Animals were divided into 3 groups: (1) PCU vaginal mesh, (2) PP vaginal mesh, and (3) sham controls. Vagina-mesh complexes or vaginas (controls) were excised 90 days after surgery. We quantified responses by comparing: (1) histomorphologic scoring of hematoxylin and eosin- and Masson trichrome-stained slides, (2) macrophage subsets (immunolabeling), (3) pro-inflammatory and anti-inflammatory cytokines (Luminex panel), (4) matrix metalloproteinase (MMP)-2 and -9 using an enzyme-linked immunosorbent assay, and (5) type I/III collagen using picrosirius red staining. There was no difference in histomorphologic score between PCU and PP (P = 0.211). Although the histomorphologic response was low surrounding all mesh fibers, groups with PCU and PP mesh had a higher histomorphologic score than the control group (P < 0.005 and P < 0.002, respectively). There were no differences between groups in terms of macrophage subsets, pro-inflammatory cytokines, anti-inflammatory cytokines, MMP-2 and MMP-9, or collagen ratio. Polycarbonate urethane, an elastomer with material properties similar to those of vaginal tissue, elicits minimal host inflammatory responses in a rat model. Because its implantation does not elicit more inflammation than currently used lightweight PP, using PCU for prolapse mesh warrants further investigation with larger animal models.

Grafting of phosphorylcholine functional groups on polycarbonate urethane surface for resisting platelet adhesion

459 THE TENSION OF ALIGNED NANOFIBROUS POLYURETHANE SCAFFOLDS INFLUENCES ANNULUS FIBROSUS CELL FUNCTION

Retrospective retrieval analysis. To evaluate wear, deformation and biodegradation within retrieved polycarbonate urethane (PCU) components of Dynesys systems. The Dynesys Dynamic Stabilization System (Zimmer Spine) consists of pedicle screws (Ti alloy), polycarbonate urethane (PCU) spacers, and a polyethylene-terephthalate cord. Seventeen retrieved (mean implantation: 2.5 years, range: 0.7-7.0 years) and 2 exemplar implant systems were available. Reasons for revision were persistent pain (16/17), infection (1/17), and/or screw loosening (11/17), with 1/17 case of implant migration. Optical microscopy, microCT, and scanning electron microscopy were conducted to evaluate PCU spacer wear and deformation. Attenuated total reflectance Fourier transform infrared spectroscopy was used to assess spacer surface chemical composition. Retrieved spacer components exhibited permanent bending deformation (mean: 4.3°, range: 0.0°-15.8°). We observed evidence of PCU spacer contact with pedicle screws, cords, and surrounding bony structures (74/75, 69/75, and 51/75 spacers, respectively). Relatively infrequent damage modes included PCU fracture (1/75 spacers) or cracking (2/75 spacers), as well as pedicle screw fracture (3/103 screws). PCU degradation products were identified in 10/75 spacers, which represented retrievals having significantly longer implantation times (mean: 4.3 years, range: 1.0-7.0 years). Of these spacers, 8/10 had degradation peaks identified along the side of the spacer where the material would have been in contact with bodily fluid. PCU spacers from retrieved Dynesys systems exhibited permanent deformation, focal regions of in vivo wear and surface damage. Chemical changes associated with PCU biodegradation were associated with longer-term retrievals. The most frequently observed complication was pedicle screw loosening, with 3 incidences of screw breakage in 2 patients. These retrieval data provide a crucial basis for developing in vitro tests to simulate in vivo damage and degradation of posterior dynamic motion preservation implants. Longer-term retrievals, as well as retrievals that include more recent design features (e.g., HA coating), will be useful to provide a greater context for the clinical implications of our short-term observations.

The Dynesys System for stabilizing the lumbar spine was first surgically implanted in Europe in 1994. In 2003, a prospective, randomized, investigational device exemption clinical trial of the system for non-fusion dynamic stabilization began. Polycarbonate urethane (PCU) and polyethylene terephthalate (PET) components explanted from four patients who had participated in the study were analyzed for biostability. Components had been implanted 9-19months. The explanted components were visually inspected and digitally photographed. Scanning electron microscopy was used to analyze the surface of the spacers. The chemical and molecular properties of the retrieved spacers and cords were quantitatively compared with lot-matched, shelf-aged, components that had not been implanted using attenuated total reflection Fourier transform infrared (FTIR) and gel permeation chromatography (GPC). FTIR analyses suggested that the explanted spacers exhibited slight surface chemical changes but were chemically unchanged below the surface and in the center. New peaks that could be attributed to biodegradation of PCU were not observed. The spectral analyses for the cords revealed that the PET cords were chemically unchanged at both the surface and the interior. Peaks associated with the PET biodegradation were not detected. GPC results did not identify changes to the distributions of molecular weights that might be attributed to biodegradation of either PCU spacers or PET cords. The explanted condition of the retrieved components demonstrated the biostability of both PCU spacers and PET cords that had been in vivo for up to 19months.

Polycarbonate urethanes (PCNUs) have been used as a replacement for traditional biomedical polyether-urethanes due to their reported resistance to oxidative biodegradation. However, relatively little is known about their hydrolytic stability in the presence of inflammatory derived enzymes. This has in part motivated the current study relating to the effect of hard segment chemistry and the microdomain structures generated by such chemistry, on the cholesterol esterase (CE) catalyzed hydrolysis of PCNUs. The bulk structures of the studied materials were characterized using gel permeation chromatography (GPC), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), Fourier transform infrared spectroscopy (FTIR) for their bulk structures, and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) for their subsurface structures. 14C-labeled PCNUs were incubated with CE (400 units/mL), for a period of 10 weeks (pH 7.0 at 37 degrees C), and radiolabel release was used to monitor the degradation. The results showed that all of the polymers synthesized in this study were susceptible to CE-catalyzed hydrolytic degradation, and that the extent of degradation was highly dependent on the nature of hard segment interactions within the polymer and at the surface. More specifically, the degree of phase separation and soft segment crystallinity were found to be less important in comparison to the hydrogen bonding among the carbonate and urethane linkages. The rank of the different chemical groups' susceptibility to hydrolysis was as follows: nonhydrogen bonded carbonate > nonhydrogen bonded urethane > hydrogen bonded carbonate > hydrogen bonded urethane. The findings suggest that the degree of hydrogen bonding, when processed into a polyurethane material could be an important parameter to consider in the design of new biostable polyurethane products.

ABSTRACTPhosphorylcholine glyceraldehyde (PCGA) was used as a phosphorylcholine (PC) group containing compound to graft onto the surface of polycarbonateurethane (PCU) film using 1,6-hexanediamine (HDA) or α,ω-diamino-poly(ethylene glycol) (APEG, Mn = 200) as a spacer, in order to introduce biomimetic structure onto the polymer surface. X-ray photoelectron spectroscopy (XPS) analysis shows that PCGA has been covalently linked to the PCU surface. Water contact angle test suggests that the surface hydrophilicity has been improved after PCGA is grafted onto the surface of PCU film. Scanning electron microscope (SEM) observation of the modified PCU films after contacting with plasma-rich plasma demonstrates that platelets rarely adhere but a large number of platelets adhere to the original PCU surface. The hemocompatibility of the PC modified PCU film has been improved obviously after grafting with PCGA with PEG spacer.

Polymeric heart valves for surgical implantation, catheter-based technologies and heart assist devices