Design of infection-resistant antibiotic-releasing polymers. II. Controlled release of antibiotics through a plasma-deposited thin film barrier

Effective pH-regulated release of covalently conjugated antibiotics from antibacterial hydrogels

pH-regulated release of antibiotics is achieved by conjugation with the hydrogel matrix through the reversible imine bond.

Antibiofilm Nitric Oxide-Releasing Polydopamine Coatings

The growing number of patient morbidity related to nosocomial infections has placed an importance on the development of new antibacterial coatings for medical devices. Here, we utilize the versatile adhesion property of polydopamine (pDA) to design an antibacterial coating that possesses low-fouling and nitric oxide (NO)-releasing capabilities. To demonstrate this, glass substrates were functionalized with pDA via immersion in alkaline aqueous solution containing dopamine, followed by grafting of low-fouling polymer (poly(ethylene glycol) (PEG)) via Michael addition and subsequent formation of N-diazeniumdiolate functionalities (NO precursors) by purging with NO gas. X-ray photoelectron spectroscopy confirmed the successful grafting of PEG and formation of N-diazeniumdiolate on polydopamine-coated substrates. NO release from the coating was observed over 2 days, and NO loading is tunable by the pDA film thickness. The antibacterial efficiency of the coatings was assessed using Gram-negative Pseudomonas aeruginosa (i.e., wild-type PAO1 and multidrug-resistant PA37) and Gram-positive Staphylococcus aureus (ATCC 29213). The NO-releasing PEGylated pDA film inhibited biofilm attachment by 96 and 70% after exposure to bacterial culture solution for 24 and 36 h, respectively. In contrast, films that do not contain NO failed to prevent biofilm formation on the surfaces at these time points. Furthermore, this coating also showed 99.9, 97, and 99% killing efficiencies against surface-attached PAO1, PA37, and S. aureus bacteria. Overall, the combination of low-fouling PEG and antibacterial activity of NO in pDA films makes this coating a potential therapeutic option to inhibit biofilm formation on medical devices.

Mussel-Inspired Surface Functionalization of PET with Zwitterions and Silver Nanoparticles for the Dual-Enhanced Antifouling and Antibacterial Properties

Herein, we designed and constructed a dual functional surface with antimicrobial and antifouling abilities to prevent protein and bacterial attachment that are significant challenges in biomedical devices. Primary amino-group-capped sulfobetaine of DMMSA was synthesized and then grafted onto polydopamine pretreated PET sheets via click chemistry. The sheets were subsequently immersed into silver ion solution, in which the absorbed silver ions were reduced to silver nanoparticles (AgNPs) in situ by a polydopamine layer. The antifouling assays demonstrated that the resultant PET/DMMSA/AgNPs sheets exhibited great antifouling performances against bovine serum albumin (BSA), bovine fibrinogen (BFG), platelets, and bacteria, the critical proteins/microorganisms leading to implant failure. The antibacterial data suggested that the sheets had dual functions as inhibitors of bacterial growth and bactericide and could efficiently delay the biofilm formation. This repelling and killing approach is green and simple, with potential biomedical applications.

Surface modification of polypropylene for enhanced layer-by-layer deposition of polyelectrolytes

We have performed three distinct plasma enhanced chemical vapor deposition procedures that can be widely and consistently used in commercially available plasma systems to modify the surface of hydrocarbon-based biomaterials such as polypropylene. In particular, we have evaluated the feasibility of these procedures to provide consistent and stable charged substrates to perform layer-by-layer (LbL) coatings. Surface characterization of both plasma and LbL coatings were done using X-ray photoelectron spectroscopy, attenuated total reflection-Fourier transform infrared spectroscopy, contact angle measurements and surface staining. Results showed successful surface grafting of functional groups in all plasma procedures that led to increased hydrophilicity and uniform LbL coatings with different efficiencies. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2078-2085, 2018.

A new textured polyphosphazene biomaterial with improved blood coagulation and microbial infection responses

A new poly[bis(octafluoropentoxy) phosphazene] (OFP) was synthesized for the purpose of blood contacting medical devices. OFP was further either developed into crosslinkable polyphosphazene (X-OFP) or blended with polyurethane (PU) as the mixture (OFP/PU) for improvement of mechanical property of polyphosphazene polymers. All the materials were fabricated as smooth films or further textured with submicron pillars for the assay of antimicrobial and antithrombotic properties. Results showed that crosslinkable OFP (X-OFP) and blends of OFP/PU successfully improved the mechanical strength of OFP and fewer defects of pillars were found on the textured polyphosphazene surfaces. The antithrombotic experiments showed that polyphosphazene OFP materials reduced human Factor XII activation and platelet adhesion, thereby being resistant to plasma coagulation and thrombosis. The bacterial adhesion and biofilm experiments demonstrated that OFP materials inhibited staphylococcal bacterial adhesion and biofilm formation. The surface texturing further reduced the platelet adhesion and bacterial adhesion, and inhibited biofilm formation up to 23 days. The data suggested that textured OFP materials may provide a practical approach to improve the biocompatibility of current biomaterials in the application of blood contacting medical devices with significant reduction in risk of pathogenic infection and thrombosis.

STATEMENT OF SIGNIFICANCE

The thromboembolic events and microbial infection have been the significant barriers for the long term use of biomaterials in blood-contacting medical devices. The development of new materials with multiple functions including anti-thrombosis and antibacterial surfaces is a high research priority. This study synthesized new biostable and biocompatible polyphosphazene polymers, poly[bis(octafluoropentoxy)phosphazene] (OFP) and crosslinkable OFP, and successfully improved the mechanical strength of polyphosphazenes. Polymers were fabricated into textured films with submicron pillars on the surfaces. The antimicrobial and antithrombotic assays demonstrated that new materials combined with surface physical modification have significant reduction in risk of pathogenic infection and thrombosis, and improve the biocompatibility of current biomaterials in the application of blood-contacting medical devices. It would be interest to biomaterials and bioengineering related communities.

Biomaterial Strategies to Reduce Implant-Associated Infections

Although the prophylaxis in controlling sterility within the operating room environment has been greatly improved, implant-associated infection is still one of the most serious complications in implant surgeries due to the existence of immune depression in the peri-implant area. The antibacterial ability of materials themselves logically becomes an important factor in preventing implant-associated infections. With the understanding of the pathogenesis of implant-associated infections, many approaches have been developed through providing an anti-adhesive surface, delivering antibacterial agents to disrupt cell-cell communication and preventing bacteria aggregation or biofilm formation, or killing bacteria directly (lysing the cell membrane). In this article, we review the current strategies in improving the antibacterial ability of materials to prevent implant infection and further present promising tactics in materials design and applications.

Proactive Approach for Safe Use of Antimicrobial Coatings in Healthcare Settings: Opinion of the COST Action Network AMiCI

Infections and infectious diseases are considered a major challenge to human health in healthcare units worldwide. This opinion paper was initiated by EU COST Action network AMiCI (AntiMicrobial Coating Innovations) and focuses on scientific information essential for weighing the risks and benefits of antimicrobial surfaces in healthcare settings. Particular attention is drawn on nanomaterial-based antimicrobial surfaces in frequently-touched areas in healthcare settings and the potential of these nano-enabled coatings to induce (eco)toxicological hazard and antimicrobial resistance. Possibilities to minimize those risks e.g., at the level of safe-by-design are demonstrated.

Sustained tobramycin release from polyphosphate double network hydrogels

Sustained local delivery of antibiotics from a drug reservoir to treat or prevent bacterial infections can avoid many of the drawbacks of systemic administration of antibiotics. Prolonged local release of high concentrations of antibiotics may also be more effective at treating bacteria in established biofilm populations that are resistant to systemic antibiotics. A double network hydrogel comprising an organic polyphosphate pre-polymer network polymerized within a polyacrylamide network de-swelled to about 50% of its initial volume when the polyphosphate network was crosslinked with polycationic tobramycin, an aminoglycoside antibiotic. The antibiotic-loaded hydrogels contained approximately 200mg/ml of tobramycin. The hydrogels continuously released daily amounts of tobramycin above the Pseudomonas aeruginosa minimal bactericidal concentration for greater than 50days, over the pH range 6.0-8.0, and completely eradicated established P. aeruginosa biofilms within 72h in a flow cell bioreactor. The presence of physiological concentrations of Mg²⁺ and Ca²⁺ ions doubled the cumulative release over 60days. The polyphosphate hydrogels show promise as materials for sustained localized tobramycin delivery to prevent post-operative P. aeruginosa infections including infections established in biofilms.

STATEMENT OF SIGNIFICANCE

Polyphosphate hydrogels were loaded with high concentrations of tobramycin. The hydrogels provided sustained release of bactericidal concentrations of tobramycin for 50days, and were capable of completely eradicating P. aeruginosa in established biofilms. The hydrogels have potential for localized prevention or treatment of P. aeruginosa infections.

Recent Nanotechnology Approaches for Prevention and Treatment of Biofilm-Associated Infections on Medical Devices

Bacterial colonization in the form of biofilms on surfaces causes persistent infections and is an issue of considerable concern to healthcare providers. There is an urgent need for novel antimicrobial or antibiofilm surfaces and biomedical devices that provide protection against biofilm formation and planktonic pathogens, including antibiotic resistant strains. In this context, recent developments in the material science and engineering fields and steady progress in the nanotechnology field have created opportunities to design new biomaterials and surfaces with anti-infective, antifouling, bactericidal, and antibiofilm properties. Here we review a number of the recently developed nanotechnology-based biomaterials and explain underlying strategies used to make antibiofilm surfaces.

Antibacterial Coatings: Challenges, Perspectives, and Opportunities

Antibacterial coatings are rapidly emerging as a primary component of the global mitigation strategy of bacterial pathogens. Thanks to recent concurrent advances in materials science and biotechnology methodologies, and a growing understanding of environmental microbiology, an extensive variety of options are now available to design surfaces with antibacterial properties. However, progress towards a more widespread use in clinical settings crucially depends on addressing the key outstanding issues. We review release-based antibacterial coatings and focus on the challenges and opportunities presented by the latest generation of these materials. In particular, we highlight recent approaches aimed at controlling the release of antibacterial agents, imparting multi-functionality, and enhancing long-term stability.

Self-assembled aliphatic chain extended polyurethane nanobiohybrids: emerging hemocompatible biomaterials for sustained drug delivery

Novel polyurethanes (PUs) have been synthesized using an aliphatic diisocyanate and aliphatic chain extenders with varying chain length. Nanocomposites of PUs have been prepared by dispersing 2-D nanoclay in poly-ol followed by prepolymerization and subsequent chain extension using various chain extenders. Systematic improvement in toughness and adequate enhancement in stiffness in the presence of nanoclay has been observed for PUs with longer chain extenders, and these new classes of nanocomposites exhibit no toughness-stiffness trade-off. Bottom-up self-assembly starting from the molecular level to micron-scale crystallite has been revealed through electronic structure calculation, X-ray diffraction, small-angle neutron scattering, atomic force microscopy and optical images. The role of hydrogen bonding has been revealed for this type of supramolecular assembly, and in the presence of organically modified nanoclay hydrogen bonding contributes to the formation of bigger clusters of nanocomposites. Controlled biodegradation of PU and its nanocomposites has been investigated in enzymatic media. Biocompatibility of these novel nanocomposites has been extensively verified through platelet adhesion, aggregation and hemolysis assay. Sustained drug delivery by biocompatible pristine PU and its nanocomposites has been demonstrated either by controlling the crystallite size of the polyurethane through alteration of the aliphatic chain length of the extender or by incorporating disc-like nanoclay, creating a tortuous path that results in delayed diffusion. Hence, the developed nanohybrids are potential biomaterials for tissue engineering and drug delivery.

Drug/Medical Device Combination Products with Stimuli-responsive Eluting Surface

Drug-eluting medical devices are designed to improve the primary function of the device and at the same time offer local release of drugs which otherwise might find it difficult to reach the insertion/implantation site. The incorporation of the drug enables the tuning of the host/microbial responses to the device and the management of device-related complications. On the other hand, the medical device acts as platform for the delivery of the drug for a prolonged period of time just at the site where it is needed and, consequently, the efficacy and the safety of the treatment, as well as its cost-effectiveness are improved. This chapter begins with an introduction to the combination products and then focuses on the techniques available (compounding, impregnation, coating, grafting of the drug or of polymers that interact with it) to endow medical devices with the ability to host drugs/biological products and to regulate their release. Furthermore, the methods for surface modification with stimuli-responsive polymers or networks are analyzed in detail and the performance of the modified materials as drug-delivery systems is discussed. A wide range of chemical-, irradiation- and plasma-based techniques for grafting of brushes and networks that are sensitive to changes in temperature, pH, light, ionic strength or concentration of certain biomarkers, from a variety of substrate materials, is currently available. Although in vivo tests are still limited, such a surface functionalization of medical devices has already been shown useful for the release on-demand of drugs and biological products, being switchable on/off as a function of the progression of certain physiological or pathological events (e.g. healing, body integration, biofouling or biofilm formation). Improved knowledge of the interactions among the medical device, the functionalized surface, the drug and the body are expected to pave the way to the design of drug-eluting medical devices with optimized and novel performances.

Evaluation of antimicrobial effects of novel implant materials by testing the prevention of biofilm formation using a simple small scale medium-throughput growth inhibition assay

Staphylococcal colonization of implants is a serious complication of orthopaedic surgery. Anti-infectious modification of implant surfaces may serve to prevent bacterial colonization. The authors set out to develop an in vitro test system for the analysis of prevention of biofilm formation by Staphylococcus epidermidis and Staphylococcus aureus on implant materials. Biofilm growth was monitored over 10 days on titanium disks in order to develop appropriate test parameters. Bacterial cell counts following ultrasonic treatment of the colonized samples were compared with scanning electron microscope images of the specimens. Copper ion containing surfaces (ie copper [Cu] and inter-metallic Ti-Cu films) were used for growth inhibition assays: copper ion releasing specimens led to reduced bacterial numbers in biofilms and decreased bacterial persistence in the model used. The assay used represents an inexpensive and quick in vitro screen for the antibacterial effects of novel implant surface materials.

Controlled drug release through a plasma polymerized tetramethylcyclo-tetrasiloxane coating barrier

A plasma polymerized tetramethylcyclo-tetrasiloxane (TMCTS) coating was deposited onto a metallic biomaterial, 316 stainless steel, to control the release rate of drugs, including daunomycin, rapamycin and NPC-15199 (N-(9-fluorenylmethoxy-carbonyl)-leucine), from the substrate surface. The plasma-state polymerized TMCTS thin film was deposited in a vacuum plasma reactor operated at a radio-frequency of 13.56 MHz, and was highly adhesive to the stainless steel, providing a smooth and hard coating layer for drugs coated on the substrate. To investigate the influence of plasma coating thickness on the drug diffusion profile, coatings were deposited at various time lengths from 20 s to 6 min, depending on the type of drug. Atomic force spectroscopy (AFM) was utilized to characterize coating thickness. Drug elution was measured using a spectrophotometer or high-performance liquid chromatography (HPLC) system. The experimental results indicate that plasma polymerized TMCTS can be used as an over-coating to control drug elution at the desired release rate. The drug-release rate was also found to be dependent on the molecular weight of the drug with plasma coating barrier on top of it. The in vitro cytotoxicity test result suggested that the TMCTS plasma coatings did not produce a cytotoxic response to mammalian cells. The non-cytotoxicity of TMCTS coating plus its high thrombo-resistance and biocompatibility are very beneficial to drug-eluting devices that contact blood.

Candida albicans biofilm formation on peptide functionalized polydimethylsiloxane

In order to prevent biofilm formation by Candida albicans, several cationic peptides were covalently bound to polydimethylsiloxane (PDMS). The salivary peptide histatin 5 and two synthetic variants (Dhvar 4 and Dhvar 5) were used to prepare peptide functionalized PDMS using 4-azido-2,3,5,6-tetrafluoro-benzoic acid (AFB) as an interlinkage molecule. In addition, polylysine-, polyarginine-, and polyhistidine-PDMS surfaces were prepared. Dhvar 4 functionalized PDMS yielded the highest reduction of the number of C. albicans biofilm cells in the Modified Robbins Device. Amino acid analysis demonstrated that the amount of peptide immobilized on the modified disks was in the nanomole range. Poly-d-lysine PDMS, in particular the homopeptides with low molecular weight (2500 and 9600) showed the highest activity against C. albicans biofilms, with reductions of 93% and 91%, respectively. The results indicate that the reductions are peptide dependent.

Plasma polymerized n-butyl methacrylate coating with potential for re-endothelialization of intravascular stent devices

Rapid re-endothelialization at an atherosclerotic lesion after stent employment is essential for reducing or preventing local thrombus formation and restenosis. To prevent these complications via enhanced rapid re-endothelialization, poly n-butyl methacrylate (PPBMA) coating was deposited on the stent surface through a radio-frequency plasma polymerization process, with oxygen as the carrier gas. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) characterization confirmed the occurrence of the plasma polymerization and the chemistry properties of the PPBMA. Scanning electron microscopy (SEM) revealed a smooth and dense surface. The wettability of the polymeric films measured by the contact angle indicated that the surface was more hydrophilic (2.0 +/- 1 degrees ) than the original surface (24 +/- 1 degrees ) by the introduction of the PPBMA coating, with a slight decrease even after 4 days. The results of the culture of human umbilical cord veins endothelial cells (HUVEC) in vitro showed that compared with the control of 316L stainless steel, the attachment and growth of cells on the PPBMA-coated surface was significantly enhanced, and a confluent endothelial cells layer was formed after a 4-day culture. A platelet adhesion experiment revealed that the blood compatibility of the substrate surface after PPBMA deposition was also obviously improved. The PPBMA coating remained intact on the stent surface after expansion according to the clinic protocol, indicating that the adhesive strength of PPBMA coating was high enough to withstand the external force in the process of stent expansion. This in vitro pilot study prior to in vivo experiments suggested that this plasma PPBMA was promising for coating stent materials for rapid re-endothelialization.

The Study of Antibiotic Drug-Loaded Polymer Films for the Prevention of the Infection of External Fixation Devices

The purpose of the present study was to develop a polymer film loaded with drug to effectively prevent pin tract infection. It was found that the polymer, poly ethylene-co-vinyl acetate blended with tetrahydrofuran, showed better flexibility and deformability than the other polymers: poly caprolactone18 and poly caprolactone44. Polymer films, poly ethylene-co-vinyl acetate, were divided into five testing groups dependent on the loading concentration of rifampici (5, 10, 15, and 20 wt %). The surface morphology of polymer films was examined by a scanning electron microscopy. It was found that the concentration of drug was a main factor to determine the roughness of the film. Considering the roughness of polymer films, 5 wt % of rifampicin might be the maximum concentration for further applications. Hence, the antibiotic drug-loaded polymer films were manufactured by mixing poly(ethylene-co-vinylacetate) and tetrahydrofuran with rifampicin(antibiotic drug). The film cast was designed as a shape of disk (inner Ø5mm and outer Ø20mm) to be suitable for pins for external fixation in orhtopaedics. The drug-loaded polymer solvent, the amount of 0.6cc, was molded into the disk-shaped film and dried into a airtight box at 15°C for 24 hrs. The drug release characteristics(1, 2, 3, 4 and 5 wt%) were examined as a function of soaking time in phosphate buffered saline (PBS, 10 ml) using an enzyme-linked immunosorbent assay. Rifampicin was linearly released for first 100 hrs(~4 days) for all antibiotic drug-loaded polymer films. Afterward, the drug was released at a slower pace as a function of square root of time until 1000 hrs (~40 days). This slow drug release can be explained by their hydrophobic characteristics of poly ethylene-co-vinyl acetate and rifampicin. The antibiotic drug-loaded polymer film can be intrinsically able to prevent the bacteria adhesion by wrapping the pin track area, and perform active and effective infection-resistant by a sustained antibiotic-release.

Reducing implant-related infections: active release strategies

Despite sterilization and aseptic procedures, bacterial infection remains a major impediment to the utility of medical implants including catheters, artificial prosthetics, and subcutaneous sensors. Indwelling devices are responsible for over half of all nosocomial infections, with an estimate of 1 million cases per year (2004) in the United States alone. Device-associated infections are the result of bacterial adhesion and subsequent biofilm formation at the implantation site. Although useful for relieving associated systemic infections, conventional antibiotic therapies remain ineffective against biofilms. Unfortunately, the lack of a suitable treatment often leaves extraction of the contaminated device as the only viable option for eliminating the biofilm. Much research has focused on developing polymers that resist bacterial adhesion for use as medical device coatings. This tutorial review focuses on coatings that release antimicrobial agents (i.e., active release strategies) for reducing the incidence of implant-associated infection. Following a brief introduction to bacteria, biofilms, and infection, the development and study of coatings that slowly release antimicrobial agents such as antibiotics, silver ions, antibodies, and nitric oxide are covered. The success and limitations of these strategies are highlighted.

Plasma surface modification of poly vinyl chloride for improvement of antibacterial properties

Plasma immersion ion implantation (PIII) was used to modify medical-grade PVC coated by triclosan and bronopol to enhance the antibacterial properties. The surface was first activated by O2 plasma to produce more hydrophilic groups so that triclosan and bronopol could be coated more effectively on the surface. Subsequently, an argon plasma treatment was conducted under optimal conditions to improve the antibacterial properties of the triclosan and bronopol-coated PVC samples. The modified surfaces were characterized by XPS, ATR-FTIR, SEM, and contact angle measurements. The antibacterial properties were evaluated utilizing the method of plate-counting of Staphylococcus aureus (gram positive) and Escherichia coli (gram negative). Our experimental results show that the plasma-modified PVC with bronopol exhibits good antibacterial properties while the favorable bulk properties of PVC are retained. The plasma-modified PVC with triclosan has better antibacterial performance against E. coli than bronopol. The change in the antibacterial effect on the modified PVC with time was also investigated and the antibacterial effect was observed to decrease with time.

Orientation and confinement of cells on chemically patterned polystyrene surfaces

UV/ozone oxidation was combined with a photomasking technique to produce adjacent regions of different chemistry on polystyrene (PS) surfaces. The surface chemistry and topography were studied using AFM, XPS and contact angle measurements. The physicochemical patterns were visualised by the condensation of water vapour upon the surfaces and by the differential attachment of Chinese hamster ovarian (CHO) cells. The orientation of CHO cells on 55 and 125 microm wide oxidised PS strips were measured and found to be highly dependent on the width of the oxidised feature. CHO cells in relatively close proximity to a linear polar/non-polar border showed significant axial alignment along the border. CHO cells can also be confined to specific regions of the polymer surface. Cells attached to larger areas (75 microm x 75 microm) were found to have a smaller average cell size than cells attached to the smaller (56 microm x 56 microm) areas.

Inhibition of biofilm formation by monoclonal antibodies against Staphylococcus epidermidis RP62A accumulation-associated protein

Staphylococcus epidermidis expresses a 140-kDa cell wall-bound protein accumulation-associated protein (AAP) to adhere to and accumulate as a biofilm on a surface. Potentially blocking AAP with a monoclonal antibody (MAb) could reduce or eliminate S. epidermidis bacterial colonization of biomedical devices. Here, we report on our efforts to (i) isolate AAP, (ii) generate MAbs against AAP, and (iii) determine the efficacy of MAbs to inhibit S. epidermidis biofilm formation. An M7 S. epidermidis mutant, reportedly deficient in AAP expression, was used as a negative control. Postinoculation murine sera, containing polyclonal antibodies against AAP, were able to reduce S. epidermidis biofilm formation by 54%. Select MAbs against AAP were able to reduce S. epidermidis by no more than 66%. Two MAb mixtures, 12C6/12A1 and 3C1/12A1, reduced S. epidermidis accumulation up to 79 and 87%, respectively, significantly more than individual MAbs. Contrary to a previous report, biofilm-deficient S. epidermidis mutant M7 expressed a 200-kDa protein on its cell wall that specifically bound AAP MAbs. Peptide characterization of this M7 protein by microcapillary reversed-phase high-pressure liquid chromatography-nanoelectrospray tandem mass spectrometry resulted in 53% homology with AAP. Ongoing studies will elucidate the dynamic expression of AAP and the M7 200-kDa protein in order to define their roles in biofilm formation.

Cellular attachment and spatial control of cells using micro-patterned ultra-violet/ozone treatment in serum enriched media

Ultra-violet Ozone (UVO) modified polystyrene (PS) surfaces were analyzed by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle (CA), optical microscopy (OM) and cell culture experiments. UV/Ozone treatment up to 900 s was used to increase the surface oxygen concentration of PS surfaces from 0% to approximately 35% (unwashed) and 0% to approximately 27% (washed). The observed differences in oxygen concentration, between washed and unwashed surfaces, have been previously attributed to the removal of low molecular weight debris produced in this treatment process. Surface roughness (Rq) is known to affect cellular attachment and proliferation. AFM studies of the UV/Ozone treated PS surfaces show the surface roughness is an order of magnitude less than that expected to cause an effect. UV/Ozone treatment of PS showed a marked change in CA which decreased to approximately 60 degrees after 900 s treatment. The increased attachment and proliferation of Chinese hamster ovarian (CHO) and mouse embryo 3T3-L1 (3T3) cells on the treated surfaces compared to untreated PS were found to correlate strongly with the increase in surface oxygen concentration. Surface chemical oxidation patterns on the PS were produced using a simple masking technique and a short UV/Ozone treatment time, typically 20-45 s. The chemical patterns on PS were visualized by water condensation and the spatially selective attachment of CHO and 3T3-L1 cells cultured with 10% (v/v) serum. This paper describes an easily reproducible, one step technique to produce a well-defined, chemically heterogeneous surface with a cellular resolution using UV/Ozone modification. By using a variety of cell types, that require different media conditions, we have been able to expand the potential applications of this procedure.

Design of infection-resistant antibiotic-releasing polymers: I. Fabrication and formulation

Biomaterials-related infections are often observed with prosthetic implants and in many cases result in the failure of the devices. To design a biomedically useful polymer that is intrinsically infection-resistant, we have developed a ciprofloxacin-loaded polyurethane (PU) matrix that releases antibiotic locally at the implant surface, thereby minimizing bacterial accumulation. We report here the methods of fabrication and formulation for making such antibiotic-loaded devices, as well as evidence of their bactericidal properties. Specifically, various pore-forming agents and drug loadings were examined. An optimum formulation consisting of BIOSPAN PU, poly(ethylene glycol) and ciprofloxacin offered the longest effective period of sustained release (5 days). The bactericidal efficacy of the released ciprofloxacin against Pseudomonas aeruginosa (PA) was four times that of the control PU without antibiotics. This bactericidal efficiency was due to an increase in the PA detachment from the surface. These observations suggested that the released ciprofloxacin was biologically active in preventing the bacteria from permanently adhering to the substratum, and thus decreasing the possibility of biofilm-related infection.