Polyurethane coatings release bioactive antibodies to reduce bacterial adhesion

A Kinetic Approach to Synergize Bactericidal Efficacy and Biocompatibility in Silver-Based Sol-Gel Coatings

Silver ions are antimicrobial agents with powerful action against bacteria. Applications in surface treatments, as Ag+-functionalized sol-gel coatings, are expected in the biomedical field to prevent contaminations and infections. The potential cytotoxicity of Ag+ cations toward human cells is well known though. However, few studies consider both the bactericidal activity and the biocompatibility of the Ag+-functionalized sol-gels. Here, we demonstrate that the cytotoxicity of Ag+ cations is circumvented, thanks to the ability of Ag+ cations to kill Escherichia coli (E. coli) much faster than normal human dermal fibroblasts (NHDFs). This phenomenon was investigated in the case of two silver nitrate-loaded sol-gel coatings: one with 0.5 w/w% Ag+ cations and the second with 2.5 w/w%. The maximal amount of released Ag+ ions over time (0.25 mg/L) was ten times lower than the minimal inhibition (MIC) and minimal bactericidal (MBC) concentrations (respectively, 2.5 and 16 mg/L) for E. coli and twice lower to the minimal cytotoxic concentration (0.5 mg/L) observed in NHDFs. E. coli were killed 8-18 times, respectively, faster than NHDFs by silver-loaded sol-gel coatings. This original approach, based on the kinetic control of the biological activity of Ag+ cations instead of a concentration effect, ensures the bactericidal protection while maintaining the biocompatibility of the Ag+ cation-functionalized sol-gels. This opens promising applications of silver-loaded sol-gel coatings for biomedical tools in short-term or indirect contacts with the skin.

Anti-Coagulant and Antimicrobial Recombinant Heparin-Binding Major Ampullate Spidroin 2 (MaSp2) Silk Protein

Governed by established structure–property relationships, peptide motifs comprising major ampullate spider silk confer a balance of strength and extensibility. Other biologically inspired small peptide motifs correlated to specific functionalities can be combined within these units to create designer silk materials with new hybrid properties. In this study, a small basic peptide, (ARKKAAKA) known to both bind heparin and mimic an antimicrobial peptide, was genetically linked to a protease-resistant, mechanically robust silk-like peptide, MaSp2. Purified fusion proteins (four silk domains and four heparin-binding peptide repeats) were expressed in E. coli. Successful fusion of a MaSp2 spider silk peptide with the heparin-binding motif was shown using a variety of analytical assays. The ability of the fusion peptide to bind heparin was assessed with ELISA and was further tested for its anticoagulant property using aPTT assay. Its intrinsic property to inhibit bacterial growth was evaluated using zone of inhibition and crystal violet (CV) assays. Using this strategy, we were able to link the two types of genetic motifs to create a designer silk-like protein with improved hemocompatibility and antimicrobial properties.

Nanoantibiotics: A Novel Rational Approach to Antibiotic Resistant Infections

Background:

The main drawbacks for using conventional antimicrobial agents are the development of multiple drug resistance due to the use of high concentrations of antibiotics for extended periods. This vicious cycle often generates complications of persistent infections, and intolerable antibiotic toxicity. The problem is that while all new discovered antimicrobials are effective and promising, they remain as only short-term solutions to the overall challenge of drug-resistant bacteria.

Objective:

Recently, nanoantibiotics (nAbts) have been of tremendous interest in overcoming the drug resistance developed by several pathogenic microorganisms against most of the commonly used antibiotics. Compared with free antibiotic at the same concentration, drug delivered via a nanoparticle carrier has a much more prominent inhibitory effect on bacterial growth, and drug toxicity, along with prolonged drug release. Additionally, multiple drugs or antimicrobials can be packaged within the same smart polymer which can be designed with stimuli-responsive linkers. These stimuli-responsive nAbts open up the possibility of creating multipurpose and targeted antimicrobials. Biofilm formation still remains the leading cause of conventional antibiotic treatment failure. In contrast to conventional antibiotics nAbts easily penetrate into the biofilm, and selectively target biofilm matrix constituents through the introduction of bacteria specific ligands. In this context, various nanoparticles can be stabilized and functionalized with conventional antibiotics. These composites have a largely enhanced bactericidal efficiency compared to the free antibiotic.

Conclusion:

Nanoparticle-based carriers deliver antibiotics with better biofilm penetration and lower toxicity, thus combating bacterial resistance. However, the successful adaptation of nanoformulations to clinical practice involves a detailed assessment of their safety profiles and potential immunotoxicity.

Zwitterionic Polyurethanes with Tunable Surface and Bulk Properties

To address the lack of blood compatibility and antifouling properties of polyurethanes (PUs), a novel zwitterionic poly(carboxybetaine urethane) (PCBHU) platform with excellent antifouling and tunable mechanical properties is presented. PCBHU was synthesized via the condensation polymerization of diisocyanate with carboxybetaine (CB)-based triols. Postpolymerization hydrolysis of triol segments at the interface generates zwitterionic CB functional groups that provide superior antifouling properties via the enhanced hydration capacities of CB groups. Thermogravimetric analysis and differential scanning calorimetry measurement show the high thermal stability of PCBHU with up to 305 °C degradation temperature. Tunable mechanical properties and water uptakes can be finely tuned by controlling the structure and ratio of CB-based triol cross-linkers. This study presents a new strategy to incorporate CB functional groups into PU without significantly changing the synthetic methods and conditions of PU. It also provides a deeper understanding on structure-property relationships of zwitterionic PUs. Because of its superior antifouling properties than existing PUs and similar cost, mechanical properties, stability, and processability, PCBHU has the great potential to replace current PUs and may open a new avenue to PUs for more challenging biomedical applications in which the existing PUs are limited by calcification and poor antifouling properties.

Silver nanoparticle/fibrinogen bilayers - Mechanism of formation and stability determined by in situ electrokinetic measurements

The kinetics of negatively charged silver nanoparticle (AgNP) deposition on the supporting fibrinogen monolayers of well-characterized coverage was determined by the atomic force microscopy (AFM). The kinetics was quantitatively interpreted in terms of the hybrid random sequential adsorption model. The electrokinetic properties of the fibrinogen monolayers and fibrinogen/AgNP bilayers were thoroughly characterized in situ by the streaming potential measurements. These results were interpreted in terms of the general electrokinetic model expressing the particle coverage in terms of the zeta potential of the bilayers. This allowed one to determine the adsorption constants and the binding energy of AgNPs, which was equal to -20.8 and -21.3 kT for pH 3.5 and 7.4, respectively. These results confirmed the end-on mechanism of fibrinogen adsorption and the presence of positively charged spots at its molecule at pH 7.4 where it exhibits an average negative charge. Besides significance to basic science, the obtained results can be exploited for developing a procedure for producing AgNP monolayers of well-defined coverage and controlled particle release profile.

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.

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.

Non-Equilibrium Plasma Processing for the Preparation of Antibacterial Surfaces

Non-equilibrium plasmas offer several strategies for developing antibacterial surfaces that are able to repel and/or to kill bacteria. Due to the variety of devices, implants, and materials in general, as well as of bacteria and applications, plasma assisted antibacterial strategies need to be tailored to each specific surface. Nano-composite coatings containing inorganic (metals and metal oxides) or organic (drugs and biomolecules) compounds can be deposited in one step, and used as drug delivery systems. On the other hand, functional coatings can be plasma-deposited and used to bind antibacterial molecules, for synthesizing surfaces with long lasting antibacterial activity. In addition, non-fouling coatings can be produced to inhibit the adhesion of bacteria and reduce the formation of biofilm. This paper reviews plasma-based strategies aimed to reduce bacterial attachment and proliferation on biomedical materials and devices, but also onto materials used in other fields. Most of the activities described have been developed in the lab of the authors.

Emerging Antibacterial Coated Dental Implants: A Preventive Measure for Peri-implantitis

Dental implants are the modern marvel and are widely accepted as a reconstructive treatment modality for tooth replacement.

In recent times, there has been a marked progress in the clinical success rates of dental implants, but implant failures as a result of infections are continuing at an alarming rate of 8% per year, translating into 1 million failures worldwide.

Perimucositis and peri-implantitis are the chief complications reported postimplant surgery that effects its short- and long-term success. Peri-implantitis is characterized by clinical and radiological bone loss around the implant accompanied with an inflammatory reaction of the peri-implant mucosa and is an irreversible condition, whereas perimucositis is a reversible inflammatory change.

Implant surfaces provide an ideal substrate for bacterial adhesion forming a biofilm. Biofilm performs vast functions ranging from physical defensive barrier against phagocytic predation to working as a selective permeable barrier. This limits the diffusion of systemic antimicrobial agents that are capable of damaging the bacterial complexes. These rapidly growing bacteria give rise to a chronic infection which is difficult to eradicate by conventional antibiotic therapy.

To inhibit peri-implant infections, various functional modifications in the implant surfaces have been suggested. The coatings on the titanium implant are incorporated with disinfectants, antibiotics as well as antimicrobial peptides AMPs.

This paper is an attempt to review all the antibiotic coatings available for a titanium implant and discuss their prospective future to prevent peri-implant infections.

How to cite this article

Yarramaneni V, Aparna IN, Sachdeva A, Balakrishnan D, Prabhu N. Emerging Antibacterial Coated Dental Implants: A Preventive Measure for Peri-implantitis. World J Dent 2016;7(4):195-198.

Biofilm-related infections: bridging the gap between clinical management and fundamental aspects of recalcitrance toward antibiotics

Surface-associated microbial communities, called biofilms, are present in all environments. Although biofilms play an important positive role in a variety of ecosystems, they also have many negative effects, including biofilm-related infections in medical settings. The ability of pathogenic biofilms to survive in the presence of high concentrations of antibiotics is called "recalcitrance" and is a characteristic property of the biofilm lifestyle, leading to treatment failure and infection recurrence. This review presents our current understanding of the molecular mechanisms of biofilm recalcitrance toward antibiotics and describes how recent progress has improved our capacity to design original and efficient strategies to prevent or eradicate biofilm-related infections.

Therapeutic strategies to combat antibiotic resistance

With multidrug resistant bacteria on the rise, new antibiotic approaches are required. Although a number of new small molecule antibiotics are currently in the development pipeline with many more in preclinical development, the clinical options and practices for infection control must be expanded. Biologics and non-antibiotic adjuvants offer this opportunity for expansion. Nevertheless, to avoid known mechanisms of resistance, intelligent combination approaches for multiple simultaneous and complimentary therapies must be designed. Combination approaches should extend beyond biologically active molecules to include smart controlled delivery strategies. Infection control must integrate antimicrobial stewardship, new antibiotic molecules, biologics, and delivery strategies into effective combination therapies designed to 1) fight the infection, 2) avoid resistance, and 3) protect the natural microbiome. This review explores these developing strategies in the context of circumventing current mechanisms of resistance.

Superhydrophobic nitric oxide-releasing xerogels

Superhydrophobic nitric oxide (NO)-releasing xerogels were prepared by spray-coating a fluorinated silane/silica composite onto N-diazeniumdiolate NO donor-modified xerogels. The thickness of the superhydrophobic layer was used to extend NO release durations from 59 to 105h. The resulting xerogels were stable, maintaining superhydrophobicity for up to 1month (the longest duration tested) when immersed in solution, with no leaching of silica or undesirable fragmentation detected. The combination of superhydrophobicity and NO release reduced viable Pseudomonas aeruginosa adhesion by >2-logs. The killing effect of NO was demonstrated at longer bacterial contact times, with superhydrophobic NO-releasing xerogels resulting in 3.8-log reductions in adhered viable bacteria vs. controls. With no observed toxicity to L929 murine fibroblasts, NO-releasing superhydrophobic membranes may be valuable antibacterial coatings for implants as they both reduce adhesion and kill bacteria that do adhere.

Nitric oxide-flux dependent bacterial adhesion and viability at fibrinogen-coated surfaces

Nitric oxide (NO) is an endogenous antibacterial agent produced by immune cells in response to pathogens. Herein, the NO fluxes necessary to reduce bacterial adhesion of different bacteria (S. aureus, methicillin-resistant S. aureus, S. epidermidis, E. faecalis, E. coli, and P. aeruginosa) were investigated to ascertain the sensitivity of these bacteria to NO. S-nitrosothiol NO donor-modified xerogels were selected as a model NO-release surface due to their extended NO-release kinetics relative to other NO donor systems. The xerogels were coated with poly(vinyl chloride) (PVC) to achieve consistent surface energy between NO-releasing and control substrates. Fibrinogen was pre-adsorbed to these materials to more accurately mimic conditions encountered in blood and promote bacteria adhesion. Nitric oxide fluxes ranging from 20-50 pmol cm-2 s-1 universally inhibited the bacterial adhesion by >80% for each strain studied. Maximum bacteria killing activity (reduced viability by 85-98%) was observed at the greatest NO payload (1700 nmol cm-2).

Proteolytically activated anti-bacterial hydrogel microspheres

Hydrogels are finding increased clinical utility as advances continue to exploit their favorable material properties. Hydrogels can be adapted for many applications, including surface coatings and drug delivery. Anti-infectious surfaces and delivery systems that actively destroy invading organisms are alternative ways to exploit the favorable material properties offered by hydrogels. Sterilization techniques are commonly employed to ensure the materials are non-infectious upon placement, but sterilization is not absolute and infections are still expected. Natural, anti-bacterial proteins have been discovered which have the potential to act as anti-infectious agents; however, the proteins are toxic and need localized release to have therapeutic efficacy without toxicity. In these studies, we explore the use of the glutathione s-transferase (GST) to anchor the bactericidal peptide, melittin, to the surface of poly(ethylene glycol) diacrylate (PEGDA) hydrogel microspheres. We show that therapeutic levels of protein can be anchored to the surface of the microspheres using the GST anchor. We compared the therapeutic efficacy of recombinant melittin released from PEGDA microspheres to melittin. We found that, when released by an activating enzyme, thrombin, recombinant melittin efficiently inhibits growth of the pathogenic bacterium Streptococcus pyogenes as effectively as melittin created by solid phase peptide synthesis. We conclude that a GST protein anchor can be used to immobilize functional protein to PEGDA microspheres and the protein will remain immobilized under physiological conditions until the protein is enzymatically released.

Polyethylene glycol-containing polyurethane hydrogel coatings for improving the biocompatibility of neural electrodes

The instability of the interface between chronically implanted neuroprosthetic devices and neural tissue is a major obstacle to the long-term use of such devices in clinical practice. In this study, we investigate the feasibility of polyethylene glycol (PEG)-containing polyurethane (PU) hydrogel as coatings for polydimethylsiloxane (PDMS)-based neural electrodes in order to achieve a stable neural interface. The influence of PU hydrogel coatings on electrode electrochemical behaviour was investigated. Importantly, the biocompatibility of PU hydrogel coatings was evaluated in vitro and in vivo. Changes in the electrochemical impedance of microelectrodes with PU coatings were negligible. The amount of protein adsorption on the PDMS substrate was reduced by 93% after coating. Rat pheochromocytoma (PC12) cells exhibited more and longer neurites on PU films than on PDMS substrates. Furthermore, PDMS implants with (n=10) and without (n=8) PU coatings were implanted into the cortex of rats and the tissue response to the implants was evaluated 6 weeks post-implantation. GFAP staining for astrocytes and NeuN staining for neurons revealed that PU coatings attenuated glial scarring and reduced the neuronal cell loss around the implants. All of these findings suggest that PU hydrogel coating is feasible and favourable for neural electrode applications.

Two-layered injectable self-assembling peptide scaffold hydrogels for long-term sustained release of human antibodies

The release kinetics for human immunoglobulin (IgG) through the permeable structure of nanofiber scaffold hydrogels consisting of the ac-(RADA)(4)-CONH(2) and ac-(KLDL)(3)-CONH(2) self-assembling peptides were studied during a period of 3 months. Self assembling peptides are a class of stimuli-responsive materials which undergo sol-gel transition in the presence of an electrolyte solution such as biological fluids and salts. IgG diffusivities decreased with increasing hydrogel nanofiber density providing a means to control the release kinetics. Two-layered hydrogel structures were created consisting of concentric spheres of ac-(RADA)(4)-CONH(2) core and ac-(KLDL)(3)-CONH(2) shell and the antibody diffusion profile was determined through the 'onion-like' architecture. Secondary and tertiary structure analyses as well as biological assays using single molecule analyses and quartz crystal microbalance of the released IgG showed that encapsulation and release did not affect the conformation of the antibody and the biological activity even after 3 months inside the hydrogel. The functionality of polyclonal human IgG to the phosphocholine antigen was determined and showed that IgG encapsulation and release did not affect the antibody binding efficacy to the antigen. Our experimental protocol allows for 100% IgG loading efficiency inside the hydrogel while the maximum amount of antibody loading depends solely on the solubility of the antibody in water because the peptide hydrogel consists of water up to 99.5%. Our results show that this fully biocompatible and injectable peptide hydrogel system may be used for controlled release applications as a carrier for therapeutic antibodies.

Photoinitiated nitric oxide-releasing tertiary S-nitrosothiol-modified xerogels

The synthesis of a tertiary thiol-bearing silane precursor (i.e., N-acetyl penicillamine propyltrimethoxysilane or NAPTMS) to enable enhanced NO storage stability at physiological temperature is described. The novel silane was co-condensed with alkoxy- or alkylalkoxysilanes under varied synthetic parameters (e.g., water to silane ratio, catalyst and solvent concentrations, and reaction time) to evaluate systematically the formation of stable xerogel films. The resulting xerogels were subsequently nitrosated to yield tertiary RSNO-modified coatings. Total NO storage ranged from 0.87 to 1.78 μmol cm(-2) depending on the NAPTMS concentration and xerogel coating thickness. Steric hindrance near the nitroso functionality necessitated the use of photolysis to liberate NO. The average NO flux for irradiated xerogels (20% NAPTMS balance TEOS xerogel film cast using 30 μL) in physiological buffer at 37 °C was ∼23 pmol cm(-2) s(-1). The biomedical utility of the photoinitiated NO-releasing films was illustrated by their ability to both reduce Pseudomonas aeruginosa adhesion by ∼90% relative to control interfaces and eradicate the adhered bacteria.

Silver nanoparticle (AgNPs) doped gum acacia-gelatin-silica nanohybrid: an effective support for diastase immobilization

An effective carrier matrix for diastase alpha amylase immobilization has been fabricated by gum acacia-gelatin dual templated polymerization of tetramethoxysilane. Silver nanoparticle (AgNp) doping to this hybrid could significantly enhance the shelf life of the impregnated enzyme while retaining its full bio-catalytic activity. The doped nanohybrid has been characterized as a thermally stable porous material which also showed multipeak photoluminescence under UV excitation. The immobilized diastase alpha amylase has been used to optimize the conditions for soluble starch hydrolysis in comparison to the free enzyme. The optimum pH for both immobilized and free enzyme hydrolysis was found to be same (pH=5), indicating that the immobilization made no major change in enzyme conformation. The immobilized enzyme showed good performance in wide temperature range (from 303 to 323 K), 323 K being the optimum value. The kinetic parameters for the immobilized, (K(m)=10.30 mg/mL, V(max)=4.36 μmol mL(-1)min(-1)) and free enzyme (K(m)=8.85 mg/mL, V(max)=2.81 μmol mL(-1)min(-1)) indicated that the immobilization improved the overall stability and catalytic property of the enzyme. The immobilized enzyme remained usable for repeated cycles and did not lose its activity even after 30 days storage at 40°C, while identically synthesized and stored silver undoped hybrid lost its ~31% activity in 48 h. Present study revealed the hybrids to be potentially useful for biomedical and optical applications.

Biofunctionalization of silicone polymers using poly(amidoamine) dendrimers and a mannose derivative for prolonged interference against pathogen colonization

Despite numerous preventive strategies on bacterial adhesion, pathogenic biofilm formation remained the major cause of medical device-related infections. Bacterial interference is a promising strategy that uses pre-established biofilms of benign bacteria to serve as live, protective coating against pathogen colonization. However, the application of this strategy to silicone urinary catheters was hampered by low adherence of benign bacteria onto silicone materials. In this work, we present a general method for biofunctionalization of silicone (PDMS) as one of the most widely used materials for biomedical devices. We used mild CO(2) plasma to activate PDMS surface followed by simple attachment of generation 5 (G5) poly(amidoamine) (PAMAM) dendrimers to generate an amino-terminated surface that were maintained even after storage in PBS buffer for 36 days. We then covalently attach a carboxy-terminated mannose derivative to the modified PDMS to promote the adherence of benign Escherichia coli 83972 expressing mannose-binding type 1 fimbriae. We demonstrated that dense, stable biofilms of E. coli 83972 could be established within 48 h on the mannose-coated PDMS. Significantly, this benign biofilm reduced the adherence of the uropathogenic Enterococcus faecalis by 104-fold after 72 h, while the benign bacteria on the unmodified substrate by only 5.5-fold.

Pluronic-lysozyme conjugates as anti-adhesive and antibacterial bifunctional polymers for surface coating

This paper describes the preparation and characterization of polymer-protein conjugates composed of a synthetic triblock copolymer with a central polypropylene oxide (PPO) block and two terminal polyethylene oxide (PEO) segments, Pluronic F-127, and the antibacterial enzyme lysozyme attached to the telechelic groups of the PEO chains. Covalent conjugation of lysozyme proceeded via reductive amination of aldehyde functionalized PEO blocks (CHO-Pluronic) and the amine groups of the lysine residues in the protein. SDS-PAGE gel electrophoresis together with MALDI-TOF mass spectrometry analysis revealed formation of conjugates of one or two lysozyme molecules per Pluronic polymer chain. The conjugated lysozyme showed antibacterial activity towards Bacillus subtilis. Analysis with a quartz crystal microbalance with dissipation revealed that Pluronic-lysozyme conjugates adsorb in a brush conformation on a hydrophobic gold-coated quartz surface. X-ray photoelectron spectroscopy indicated surface coverage of 32% by lysozyme when adsorbed from a mixture of unconjugated Pluronic and Pluronic-lysozyme conjugate (ratio 99:1) and of 47% after adsorption of 100% Pluronic-lysozyme conjugates. Thus, bifunctional brushes were created, possessing both anti-adhesive activity due to the polymer brush, combined with the antibacterial activity of lysozyme. The coating having a lower degree of lysozyme coverage proved to be more bactericidal.

Plasma-enhanced synthesis of bioactive polymeric coatings from monoterpene alcohols: a combined experimental and theoretical study

This paper describes the synthesis and characterization of a novel organic polymer coating for the prevention of the growth of Pseudomonas aeruginosa on the solid surface of three-dimensional objects. Substrata were encapsulated with polyterpenol thin films prepared from terpinen-4-ol using radio frequency plasma enhanced chemical vapor deposition. Terpinen-4-ol is a constituent of tea tree oil with known antibacterial properties. The influence of deposition power on the chemical structure, surface composition, and ultimately the antibacterial inhibitory activity of the resulting polyterpenol thin films was studied using X-ray photoelectron spectroscopy (XPS), water contact angle measurement, atomic force microscopy (AFM), and 3-D interactive visualization and statistical approximation of the topographic profiles. The experimental results were consistent with those predicted by molecular simulations. The extent of bacterial attachment and extracellular polymeric substances (EPS) production was analyzed using scanning electron microscopy (SEM) and confocal scanning laser microscopy (CSLM). Polyterpenol films deposited at lower power were particularly effective against P. aeruginosa due to the preservation of original terpinen-4-ol molecules in the film structure. The proposed antimicrobial and antifouling coating can be potentially integrated into medical and other clinically relevant devices to prevent bacterial growth and to minimize bacteria-associated adverse host responses.

Recent progress in inorganic and composite coatings with bactericidal capability for orthopaedic applications

This review covers the most recent developments of inorganic and organic-inorganic composite coatings for orthopedic implants, providing the interface with living tissue and with potential for drug delivery to combat infections. Conventional systemic delivery of drugs is an inefficient procedure that may cause toxicity and may require a patient's hospitalization for monitoring. Local delivery of antibiotics and other bioactive molecules maximizes their effect where they are required, reduces potential systemic toxicity and increases timeliness and cost efficiency. In addition, local delivery has broad applications in combating infection-related diseases. Polymeric coatings may present some disadvantages. These disadvantages include limited chemical stability, local inflammatory reactions, uncontrolled drug-release kinetics, late thrombosis and restenosis. As a result, embedding of bioactive compounds and biomolecules within inorganic coatings (bioceramics, bioactive glasses) is attracting significant attention. Recently nanoceramics have attracted interest because surface nanostructuring allows for improved cellular adhesion, enhances osteoblast proliferation and differentiation, and increases biomineralization. Organic-inorganic composite coatings, which combine biopolymers and bioactive ceramics that mimick bone structure to induce biomineralization, with the addition of biomolecules, represent alternative systems and ideal materials for "smart" implants. In this review, emphasis is placed on materials and processing techniques developed to advance the therapeutic use of biomolecules-eluting coatings, based on nanostructured ceramics. One part of this report is dedicated to inorganic and composite coatings with antibacterial functionality.

FROM THE CLINICAL EDITOR

Inorganic and composite nanotechnology-based coating methods have recently been developed for orthopedic applications, with the main goal to provide bactericide and other enhanced properties, which may result in reduced need for pharmaceutical interventions and overall more cost effective orthopedic procedures. This review discusses key aspects of the above developments.

Functional Coatings or Films for Hard-Tissue Applications

Metallic biomaterials like stainless steel, Co-based alloy, Ti and its alloys are widely used as artificial hip joints, bone plates and dental implants due to their excellent mechanical properties and endurance. However, there are some surface-originated problems associated with the metallic implants: corrosion and wear in biological environments resulting in ions release and formation of wear debris; poor implant fixation resulting from lack of osteoconductivity and osteoinductivity; implant-associated infections due to the bacterial adhesion and colonization at the implantation site. For overcoming these surface-originated problems, a variety of surface modification techniques have been used on metallic implants, including chemical treatments, physical methods and biological methods. This review surveys coatings that serve to provide properties of anti-corrosion and anti-wear, biocompatibility and bioactivity, and antibacterial activity.

Polymers as ureteral stents

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

Sustained release of antibiotic from polyurethane coated implant materials

Implant associated infections are of increasing importance. To minimize the risks of implant-associated infections recent biomedical strategies have led to the modification of the medical device surfaces. The modifications are in the terms of increasing surface biocompatibility and decreasing bacterial adherence, which can be achieved by applying a coating of biocompatible polymer onto the said surfaces. Entrapping anti-infective agents in a polymer matrix provides an approach to kill bacteria and combat the possibility of any residual infection. We have prepared a biodegradable polyester urethane coat for implant materials, which have the property to accommodate antibiotics within itself. These polyurethane coating materials were characterized by FTIR spectroscopy, swelling property in SBF, gravimetric analysis, drug release, and biocompatibility study. Drug release rates, bacterial colonization and morphological features were also evaluated to predict and understand the antimicrobial activity of these delivery systems. Drug release characteristics were investigated and the physico-chemical mechanisms of the delivery were discussed. Results suggest that the polyester urethane can be used as an implant coating material and can be used as a matrix for the sustained delivery of anti-infective agent.

Permeation of urea through various polyurethane membranes

BACKGROUND

Controlled-release systems using polymer membranes are very important in agriculture for labour-saving and effective delivery of pesticides and other agents. Polymer-coated granules are one of the most useful formulations, and a study of the factors for polymer design is necessary to achieve various release patterns. A permeation study using plain membranes was carried out in order to clarify parameters, and the results were compared with the release from polymer-coated granules.

RESULTS

The permeation coefficient of urea through a plain polyurethane membrane decreased significantly as the urethane and alkyl side chain content increased. The glass transition temperature and crosslink density of the polyurethanes hardly influenced its permeability. The release rate from polyurethane-coated granules was also reduced by alkyl side chains. However, it was faster than that through a plain membrane because of capsule expansion by continuous water penetration and structural changes in the membrane.

CONCLUSION

The release rate of urea through a polyurethane plain membrane and from polyurethane-coated granules can be controlled by changing the chemical properties of the membrane. In addition, physical properties such as the glass transition temperature T(g) or crosslink density should be considered to assess the release profile from polyurethane-coated granules.

Reduced bacterial adhesion to fibrinogen-coated substrates via nitric oxide release

The ability of nitric oxide (NO)-releasing xerogels to reduce fibrinogen-mediated adhesion of Staphylococcus aureus, Staphylococcus epidermidis, and Escherichia coli is described. A negative correlation was observed between NO surface flux and bacterial adhesion for each species tested. For S. aureus and E. coli, reduced adhesion correlated directly with NO flux from 0 to 30 pmol cm(-2)s(-1). A similar dependence for S. epidermidis was evident from 18 to 30 pmol cm(-2)s(-1). At a NO flux of 30 pmol cm(-2)s(-1), surface coverage of S. aureus, S. epidermidis, and E. coli was reduced by 96, 48, and 88%, respectively, compared to non-NO-releasing controls. Polymeric NO release was thus demonstrated to be an effective approach for significantly reducing fibrinogen-mediated adhesion of both gram-positive and gram-negative bacteria in vitro, thereby illustrating the advantage of active NO release as a strategy for inhibiting bacterial adhesion in the presence of pre-adsorbed protein.

Reduced foreign body response at nitric oxide-releasing subcutaneous implants

The tissue response to nitric oxide (NO)-releasing subcutaneous implants is presented. Model implants were created by coating silicone elastomer with diazeniumdiolate-modified xerogel polymers capable of releasing NO. The host tissue response to such implants was evaluated at 1, 3, and 6 weeks and compared to that of uncoated silicone elastomer blanks and xerogel-coated controls incapable of releasing NO. Delivery of NO (approximately 1.35 micromol/cm2 of implant surface area) reduced foreign body collagen capsule ("scar tissue") thickness by >50% compared to uncoated silicone elastomer after 3 weeks. The chronic inflammatory response at the tissue/implant interface was also reduced by >30% at NO-releasing implants after 3 and 6 weeks. Additionally, CD-31 immunohistochemical staining revealed approximately 77% more blood vessels in proximity to NO-releasing implants after 1 week compared to controls. These findings suggest that conferring NO release to subcutaneous implants may promote effective device integration into healthy vascularized tissue, diminish foreign body capsule formation, and improve the performance of indwelling medical devices that require constant mass transport of analytes (e.g., implantable sensors).

Antibacterial nitric oxide-releasing xerogels: cell viability and parallel plate flow cell adhesion studies

The ability of nitric oxide (NO)-releasing xerogels to reduce adhesion of Pseudomonas aeruginosa under flowing conditions was evaluated using a parallel plate flow chamber. At a controlled bacterial suspension flow rate of 0.2mL/min, the NO-releasing xerogels reduced bacterial adhesion in a flux-dependent fashion, with an NO flux of approximately 21pmolcm(-2)s(-1) reducing P. aeruginosa adhesion by approximately 65% compared to controls. Fluorescent viability staining indicated that bacteria adhered to NO-releasing xerogels were killed within 7h. Quantitative cell-plating viability studies showed that the extent of bactericidal activity was dependent on the total amount of NO released, with 750nmolcm(-2) killing >90% more adhered bacteria than xerogels releasing 25nmolcm(-2). Thus, NO-releasing xerogels were shown to both inhibit P. aeruginosa adhesion and kill adhered bacteria cells, two important steps toward designing anti-infective biomaterial coatings.

Formulation and delivery issues for monoclonal antibody therapeutics

Antibodies can have exquisite specificity of target recognition and thus generate highly selective outcomes following their systemic administration. While antibodies can have high specificity, the doses required to treat patients, particularly for a chronic condition, are typically large. Fortunately, advances in production and purification capacities have allowed for the exceptionally large amounts of highly purified monoclonal antibodies to be produced. Additionally, genetic engineering of antibodies has provided a stable of antibody-like proteins that can be easier to prepare. Together, these advances have made antibody-based therapies one of the most commonly pursued pharmaceuticals in biotechnology pipelines. With this success, however, has come a series of technical challenges in the formulation of antibody-based materials to maintain sufficient stability in a variety of configurations and sometimes at particularly high concentrations. This review focuses on issues related to identifying and verifying stable antibody-based formulations.

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.

Miniaturized glucose biosensor modified with a nitric oxide-releasing xerogel microarray

An enzyme-based glucose biosensor modified to release nitric oxide (NO) via a xerogel microarray is reported. The biosensor design is as follows: (1) glucose oxidase (GOx) is immobilized in a methyltrimethoxysilane (MTMOS) xerogel layer; (2) a blended polyurethane/hydrophilic polyurethane coating prevents enzyme leaching and imparts selectivity for glucose; and (3) micropatterned xerogel lines (5 microm wide) separated by distances of 5 or 20 microm provide NO-release capability. This configuration allows for increased glucose sensitivity relative to sensors modified with NO-releasing xerogel films since significant portions of the sensor surface remain unmodified. Glucose diffusion to the GOx layer is thus less inhibited. The micropatterned NO-releasing biosensors generate sufficient NO levels to reduce both Pseudomonas aeruginosa and platelet adhesion without significantly compromising the enzymatic activity of GOx. The glucose response, linearity and stability of the NO-releasing micropatterned sensors are reported.

Delivery systems for small molecule drugs, proteins, and DNA: the neuroscience/biomaterial interface

Manipulation of cellular processes in vivo by the delivery of drugs, proteins or DNA is of paramount importance to neuroscience research. Methods for the presentation of these molecules vary widely, including direct injection (either systemic or stereotactic), osmotic pump-mediated chronic delivery, or even implantation of cells engineered to indefinitely secrete a factor of interest. Biomaterial-based delivery systems represent an alternative to more traditional approaches, with the possibility of increased efficacy. Drug-releasing biomaterials, either as injectable microspheres or as three-dimensional implants, can deliver a molecule of interest (including small molecule drugs, biologically active proteins, or DNA) over a more prolonged period of time than by standard bolus injection, avoiding the need for repeated administration. Furthermore, sustained-release systems can maintain therapeutic concentrations at a target site, thus reducing the chance for toxicity. This review summarizes applications of polymer-based delivery of small molecule drugs, proteins, and DNA specifically relevant to neuroscience research. We detail the fabrication procedures for the polymeric systems and their utility in various experimental models. The biomaterial field offers unique experimental tools with downstream clinical application for the study and treatment of neurologic disease.