Co-release of dicloxacillin and thioridazine from catheter material containing an interpenetrating polymer network for inhibiting device-associated Staphylococcus aureus infection

Biomedical applications of stimuli-responsive "smart" interpenetrating polymer network hydrogels

In recent years, owing to the ongoing advancements in polymer materials, hydrogels have found increasing applications in the biomedical domain, notably in the realm of stimuli-responsive "smart" hydrogels. Nonetheless, conventional single-network stimuli-responsive "smart" hydrogels frequently exhibit deficiencies, including low mechanical strength, limited biocompatibility, and extended response times. In response, researchers have addressed these challenges by introducing a second network to create stimuli-responsive "smart" Interpenetrating Polymer Network (IPN) hydrogels. The mechanical strength of the material can be significantly improved due to the topological entanglement and physical interactions within the interpenetrating structure. Simultaneously, combining different network structures enhances the biocompatibility and stimulus responsiveness of the gel, endowing it with unique properties such as cell adhesion, conductivity, hemostasis/antioxidation, and color-changing capabilities. This article primarily aims to elucidate the stimulus-inducing factors in stimuli-responsive "smart" IPN hydrogels, the impact of the gels on cell behaviors and their biomedical application range. Additionally, we also offer an in-depth exposition of their categorization, mechanisms, performance characteristics, and related aspects. This review furnishes a comprehensive assessment and outlook for the advancement of stimuli-responsive "smart" IPN hydrogels within the biomedical arena. We believe that, as the biomedical field increasingly demands novel materials featuring improved mechanical properties, robust biocompatibility, and heightened stimulus responsiveness, stimuli-responsive "smart" IPN hydrogels will hold substantial promise for wide-ranging applications in this domain.

Experimental comparative study of a novel drug-eluting arteriovenous graft in a sheep model

Background

Arteriovenous (AV) grafts often develop severe complications of stenosis due to neointimal proliferation that occurs either at the venous anastomosis site or at the outflow receiving vein. This study compares primary patency during 12 months of follow up for a new experimental Biomodics© interpenetrating polymer network (IPN) drug-eluting graft prototype with state-of-the-art GORE® ACUSEAL (ACUSEAL) in an AV graft model in sheep.

Methods and results

An end-to-end bypass from the common carotid artery to the jugularis vein was performed bilaterally in 12 sheep. The usage of ACUSEAL or the IPN, both 6.0 mm in diameter, was determined via randomization. The sheep were followed up every 4 weeks with ultrasonic duplex scanning to determine patency; the experienced observer was blinded to the randomization. One sheep died after 11 days, and the final sample accordingly consisted of 11 animals. When comparing neointimal hyperplasia after 12 months in the two grafts, Fisher's exact test showed a significant difference with none out of 11 in the IPN grafts and 9 out of 11 in the ACUSEAL graft (p < 0.001). However, the Biomodics© IPN exhibited severe deterioration over time.

Conclusions

Almost all of the grafts occluded during the 12 months of follow up. Although the zwitterion-bounded interpenetrating drug eluting polymer network showed signs to impair neointimal hyperplasia and thrombosis, age-related degeneration hindered demonstrating a potential improvement in patency.

Weaving the next generation of (bio)materials: Semi-interpenetrated and interpenetrated polymeric networks for biomedical applications

Advances in polymer science have led to the development of semi-interpenetrated and interpenetrated networks (SIPN/IPN). The interpenetration procedure allows enhancing several important properties of a polymeric material, including mechanical properties, swelling capability, stimulus-sensitive response, and biological performance, among others. More interestingly, the interpenetration (or semi-interpenetration) can be achieved independent of the material size, that is at the macroscopic, microscopic, or nanometric scale. SIPN/IPN have been used for a wide range of applications, especially in the biomedical field, including tissue engineering, delivery of chemical compounds or biological macromolecules, and multifunctional systems as theragnostic platforms. In the last years, this fascinating field has gained a great interest in the area of polymers for therapeutics; therefore, a comprehensive revision of the topic is timely. In this review, we describe in detail the most relevant synthetic approaches to fabricate polymeric IPN and SIPN, ranging from nanoscale to macroscale. The advantages of typical synthetic methods are analyzed, as well as novel and promising trends in the field of advanced material fabrication. Furthermore, the characterization techniques employed for these materials are summarized from physicochemical, thermal, mechanical, and biological perspectives. The applications of novel (semi-)interpenetrated structures are discussed with a focus on drug delivery, tissue engineering, and regenerative medicine, as well as combinations thereof.

An Antibiotic-Loaded Silicone-Hydrogel Interpenetrating Polymer Network for the Prevention of Surgical Site Infections

Surgical site infections (SSIs) are among the most frequent healthcare-associated infections, resulting in high morbidity, mortality, and cost. While correct hygiene measures and prophylactic antibiotics are effective in preventing SSIs, even in modern healthcare settings where recommended guidelines are strictly followed, SSIs persist as a considerable problem that has proven hard to solve. Surgical procedures involving the implantation of foreign bodies are particularly problematic due to the ability of microorganisms to adhere to and colonize the implanted material and form resilient biofilms. In these cases, SSIs may develop even months after implantation and can be difficult to treat once established. Locally applied antibiotics or specifically engineered implant materials with built-in antibiotic-release properties may prevent these complications and, ultimately, require fewer antibiotics compared to those that are systemically administered. In this study, we demonstrated an antimicrobial material concept with intended use in artificial vascular grafts. The material is a silicone-hydrogel interpenetrating polymer network developed earlier for drug-release catheters. In this study, we designed the material for permanent implantation and tested the drug-loading and drug-release properties of the material to prevent the growth of a typical causative pathogen of SSIs, Staphylococcus aureus. The novelty of this study is demonstrated through the antimicrobial properties of the material in vitro after loading it with an advantageous combination, minocycline and rifampicin, which subsequently showed superiority over the state-of-the-art (Propaten) artificial graft material in a large-animal study, using a novel porcine tissue-implantation model.

Auranofin coated catheters inhibit bacterial and fungal biofilms in a murine subcutaneous model

Microbe entry through catheter ports can lead to biofilm accumulation and complications from catheter-related bloodstream infection and ultimately require antimicrobial treatment and catheter replacement. Although strides have been made with microbial prevention by applying standardized antiseptic techniques during catheter implantation, both bacterial and fungal microbes can present health risks to already sick individuals. To reduce microbial adhesion, murine and human catheters were coated with polyurethane and auranofin using a dip coating method and compared to non-coated materials. Upon passage of fluid through the coated material in vitro, flow dynamics were not impacted. The unique antimicrobial properties of the coating material auranofin has shown inhibitory activity against bacteria such as Staphylococcus aureus and fungi such as Candida albicans. Auranofin coating on catheters at 10mg/mL reduced C. albicans accumulation in vitro from 2.0 x 10⁸ to 7.8 x 10⁵ CFU for mouse catheters and from 1.6 x 10⁷ to 2.8 x 10⁶ for human catheters, showing an impact to mature biofilms. Assessment of a dual microbe biofilm on auranofin-coated catheters resulted in a 2-log reduction in S. aureus and a 3-log reduction in C. albicans compared to uncoated catheters. In vivo assessment in a murine subcutaneous model demonstrated that catheters coated with 10 mg/mL auranofin reduced independent S. aureus and C. albicans accumulation by 4-log and 1-log, respectively, compared to non-coated catheters. In conclusion, the auranofin-coated catheters demonstrate proficiency at inhibiting multiple pathogens by decreasing S. aureus and C. albicans biofilm accumulation.

Development of Cationic Cellulose-Modified Bentonite-Alginate Nanocomposite Gels for Sustained Release of Alachlor

The nanocomposite gel prepared from nanoclay and natural polysaccharides showed a good sustained-release property. Herein, a cationic cellulose-modified bentonite-alginate nanocomposite gel was prepared and used to enhance the sustained release of alachlor. The underlying effect and mechanism of the structure of modified bentonite-alginate nanocomposite gels on the release behavior of alachlor were explored by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric (TG) analysis. The results showed that the release of alachlor from the nanocomposite gels was dominated by Fickian diffusion and closely related to the adsorption capacity and permeability of the matrix. The cationic cellulose intercalated into the interlayer space of bentonite through an ion exchange reaction, which significantly enhanced the hydrophobicity of bentonite and its interaction with alachlor. The stacking aggregation of bentonite nanoplatelets and permeability of the gel network were decreased through the electrostatic interaction between cationic cellulose and alginate molecular chains, thus remarkably enhancing the sustained-release property of the nanocomposite gel. The release kinetics revealed that the release rate of alachlor from the nanocomposite gel first decreased and then increased as the content of bentonite and modified bentonite gradually increased. Also, the best sustained-release property of the nanocomposite gel was obtained at bentonite and modified bentonite additions of about 10%, under which the release time of 50% alachlor (T ₅₀) from bentonite-alginate and modified bentonite-alginate nanocomposite gels was 4.4 and 5.6 times longer than the release time from pure alginate gels, respectively.

A Novel Device-Integrated Drug Delivery System for Local Inhibition of Urinary Tract Infection

Background: Catheter-associated urinary tract infection (CAUTI) is a frequent community-acquired infection and the most common nosocomial infection. Here, we developed a novel antimicrobial catheter concept that utilizes a silicone-based interpenetrating polymer network (IPN) as balloon material to facilitate a topical slow-release prophylaxis of antibacterial agents across the balloon to the urinary bladder.

Methods: The balloon material was achieved by modifying low shore hardness silicone tubes with a hydrogel interpenetrating polymer in supercritical CO₂ using the sequential method. Release properties and antibacterial efficacy of the IPN balloon treatment concept was investigated in vitro and in a porcine CAUTI model developed for the study. In the latter, Bactiguard Infection Protection (BIP) Foley catheters were also assessed to enable benchmark with the traditional antimicrobial coating principle.

Results: Uropathogenic Escherichia coli was undetectable in urinary bladders and on retrieved catheters in the IPN treatment group as compared to control that revealed significant bacteriuria (>10⁵ colony forming units/ml) as well as catheter-associated biofilm. The BIP catheters failed to prevent E. coli colonization of the bladder but significantly reduced catheter biofilm formation compared to the control.

Conclusion: The IPN-catheter concept provides a novel, promising delivery route for local treatment in the urinary tract.

Molecular-Gated Drug Delivery Systems Using Light-Triggered Hydrophobic-to-Hydrophilic Switches

A photoresponsive molecular-gated drug delivery system (DDS) based on silicone-hydrogel (poly(HEMA-co-PEGMEA)) interpenetrating polymer networks (IPNs) functionalized with carboxylated spiropyran (SPCOOH) was designed and demonstrated as an on-demand DDS. The triggered-release mechanism relies on controlling the wetting behavior of the surface by light, exploiting different hydrophobicities between the "closed" and "open" isomers of spiropyran as a photoswitchable molecular gate on the surface of IPN (SP-photogated IPN). Light-triggered release of doxycycline (DOX) as a model drug indicated that the spiropyran (SP) molecules provide a hydrophobic layer around the drug carrier and have a good gate-closing efficiency for IPNs with 20-30% hydrogel content. Upon UV light irradiation, SP converts into an open hydrophilic merocyanine state, which triggers the release of DOX. These results were compared with a previously developed SP-bulk modified IPN using the same hydrogel as a control, proving the efficiency of the gated IPN system. The covalent attachment of SPCOOH to the alcohol groups of the hydrogel and the structural change caused by UV light was indicated with FTIR analysis. XPS results also confirm the presence of SP by indicating the atomic percentage of nitrogen with respect to the hydrogel content.

On-Demand Reversible UV-Triggered Interpenetrating Polymer Network-Based Drug Delivery System Using the Spiropyran-Merocyanine Hydrophobicity Switch

A reversible switchable on-demand UV-triggered drug delivery system (DDS) based on interpenetrating polymer networks (IPNs) with silicone as the host polymer and spiropyran (SP)-functionalized guest polymer is designed and demonstrated. The photo-responsive IPNs provide a new triggered drug delivery concept as they exploit the change in intermolecular interactions (work of adhesion) among the drug, matrix, and solvent when the incorporated hydrophobic SP moieties transform into the hydrophilic merocyanine form upon light irradiation without degradation and disruption of the DDS. The change in how the copolymer composition (hydrophilicity and content) and the lipophilicity of the drug (log P) affect the release profile was investigated. A thermodynamic model, based on Hansen solubility parameters, was developed to design and optimize the polymer composition of the IPNs to obtain the most efficient light-triggered drug release and suppression of the premature release. The developed IPNs showed excellent result for dopamine, l-dopa, and prednisone with around 90-95% light-triggered release. The model was applied to study the release behavior of drugs with different log P and to estimate if the light-induced hydrophobic-to-hydrophilic switch can overcome the work of adhesion between polymers and drugs and hence the desorption and release of the drugs. To the best of our knowledge, this is the first time that work of adhesion is used for this aim. Comparing the result obtained from the model and experiment shows that the model is useful for evaluating and estimating the release behavior of specific drugs merocyanine, IPN, DDS, and spiropyran.

Precisely Structured Nitric-Oxide-Releasing Copolymer Brush Defeats Broad-Spectrum Catheter-Associated Biofilm Infections In Vivo

Gram-negative bacteria cannot be easily eradicated by antibiotics and are a major source of recalcitrant infections of indwelling medical devices. Among various device-associated infections, intravascular catheter infection is a leading cause of mortality. Prior approaches to surface modification, such as antibiotics impregnation, hydrophilization, unstructured NO-releasing, etc., have failed to achieve adequate infection-resistant coatings. We report a precision-structured diblock copolymer brush (H(N)-b-S) composed of a surface antifouling block of poly(sulfobetaine methacrylate) (S) and a subsurface bactericidal block (H(N)) of nitric-oxide-emitting functionalized poly(hydroxyethyl methacrylate) (H) covalently grafted from the inner and outer surfaces of a polyurethane catheter. The block copolymer architecture of the coating is important for achieving good broad-spectrum anti-biofilm activity with good biocompatibility and low fouling. The coating procedure is scalable to clinically useful catheter lengths. Only the block copolymer brush coating ((H(N)-b-S)) shows unprecedented, above 99.99%, in vitro biofilm inhibition of Gram-positive and Gram-negative bacteria, 100-fold better than previous coatings. It has negligible toxicity toward mammalian cells and excellent blood compatibility. In a murine subcutaneous infection model, it achieves >99.99% biofilm reduction of Gram-positive and Gram-negative bacteria compared with <90% for silver catheter, while in a porcine central venous catheter infection model, it achieves >99.99% reduction of MRSA with 5-day implantation. This precision coating is readily applicable for long-term biofilm-resistant and blood-compatible copolymer coatings covalently grafted from a wide range of medical devices.

Supercritical Fluid Applications in the Design of Novel Antimicrobial Materials

Bacterial resistance to antibiotics is one of the biggest problems in the modern world. The prevention of bacterial spreading from hospitals to the community and vice versa is an issue we have to deal with. This review presents a vast potential of contemporary high-pressure techniques in the design of materials with antimicrobial activity. Scientists from all over the world came up with ideas on how to exploit extraordinary properties of supercritical fluids in the production of advantageous materials in an environmentally friendly way. The review summarizes reported methods and results.

Implantable Medical Devices and Tissue Engineering: An Overview of Manufacturing Processes and the Use of Polymeric Matrices for Manufacturing and Coating their Surfaces

Medical devices are important diagnosis and therapy tools for several diseases which include a wide range of products. Technological advances in this area have been proposed to reduce adverse complication incidences. New technologies and manufacturing processes, as well as the development of new materials or medical devices with modified surface and the use of biodegradable polymeric devices such as a substrate for cell culture in the field of tissue engineering, have attracted considerable attention in recent years by the scientific community intended to produce medical devices with superior properties and morphology. This review article focused on implantable devices, addresses the major advances in the biomedical field related to the devices manufacture processes such as 3D printing and hot melting extrusion, and the use of polymer matrices composed of copolymers, blends, nanocomposites or grafted with antiproliferative drugs for manufacturing and/or coating the devices surface.

Facile coating of urinary catheter with bio-inspired antibacterial coating

Formation of bacterial biofilm on indwelling urinary catheters usually causes catheter-associated urinary tract infections (CAUTIs) that represent high percent of nosocomial infections worldwide. Therefore, coating urinary catheter with antibacterial and antifouling coating using facile technique is in great demand. In this study, commercial urinary catheter was coated with a layer of the self-polymerized polydopamine which acts as active platform for the in situ formation of silver nanoparticle (AgNPs) on catheter surface. The formed coating was intensively characterized using spectroscopic and microscopic techniques. The coated catheter has the potential to release silver ion in a sustained manner with a concentration of about 2-4 μg ml-1. Disk diffusion test and colony forming unites assay verified the significant bactericidal potential of the AgNPs coated catheter against both gram-positive and gram-negative bacteria as a consequence of silver ion release. In contrast to commercial catheter, the AgNPs coated catheter prevented the adherence of bacterial cells and biofilm formation on their surfaces. Interestingly, scanning electron microscope investigations showed that AgNPs coated catheter possess greater antifouling potential against gram-positive bacteria than against gram-negative bacteria. Overall, the remarkable antibacterial and antifouling potential of the coated catheter supported the use of such facile approach for coating of different medical devices for the prevention of nosocomial infections.

Fused Deposition Modelling as a Potential Tool for Antimicrobial Dialysis Catheters Manufacturing: New Trends vs. Conventional Approaches

The rising rate of individuals with chronic kidney disease (CKD) and ineffective treatment methods for catheter-associated infections in dialysis patients has led to the need for a novel approach to the manufacturing of catheters. The current process requires moulding, which is time consuming, and coated catheters used currently increase the risk of bacterial resistance, toxicity, and added expense. Three-dimensional (3D) printing has gained a lot of attention in recent years and offers the opportunity to rapidly manufacture catheters, matched to patients through imaging and at a lower cost. Fused deposition modelling (FDM) in particular allows thermoplastic polymers to be printed into the desired devices from a model made using computer aided design (CAD). Limitations to FDM include the small range of thermoplastic polymers that are compatible with this form of printing and the high degradation temperature required for drugs to be extruded with the polymer. Hot-melt extrusion (HME) allows the potential for antimicrobial drugs to be added to the polymer to create catheters with antimicrobial activity, therefore being able to overcome the issue of increased rates of infection. This review will cover the area of dialysis and catheter-related infections, current manufacturing processes of catheters and methods to prevent infection, limitations of current processes of catheter manufacture, future directions into the manufacture of catheters, and how drugs can be incorporated into the polymers to help prevent infection.

Molecular mechanisms of thioridazine resistance in Staphylococcus aureus

Staphylococcus aureus has developed resistance towards the most commonly used anti-staphylococcal antibiotics. Therefore, there is an urgent need to find new treatment opportunities. A new approach relies on the use of helper compounds, which are able to potentiate the effect of antibiotics. A well-studied helper compound is thioridazine, which potentiates the effect of the β-lactam antibiotic dicloxacillin against Methicillin-resistant Staphylococcus aureus (MRSA). In order to identify thioridazine's mechanism of action and how it potentiates the effect of dicloxacillin, we generated thioridazine resistant strains of MRSA USA300 by serial passage experiments. Selected strains were whole-genome sequenced to find mutations causing thioridazine resistance. Genes observed to be mutated were attempted deleted in MRSA USA300. The cls gene encoding a cardiolipin synthase important for synthesis of the membrane lipid cardiolipin was found to be mutated in thioridazine resistant strains. Deletion of this gene resulted in a two-fold increased Minimum inhibitory concentrations (MIC) value for thioridazine compared to the wild type and decreased susceptibility similar to the thioridazine resistant strains. Since cardiolipin likely plays a role in resistance towards thioridazine, it might also be important for the mechanism of action behind the potentiating effect of thioridazine. TDZ is known to intercalate into the membrane and we show here that TDZ can depolarize the plasma membrane. However, our results indicate that the membrane potential reducing effect of TDZ is independent of the resistance mechanism.

Introduction of Nature's Complexity in Engineered Blood-compatible Biomaterials

Biomaterials with excellent blood-compatibility are needed for applications in vascular replacement therapies, such as vascular grafts, heart valves and stents, and in extracorporeal devices such as hemodialysis machines and blood-storage bags. The modification of materials that are being used for blood-contacting devices has advanced from passive surface modifications to the design of more complex, smart biomaterials that respond to relevant stimuli from blood to counteract coagulation. Logically, the main source of inspiration for the design of new biomaterials has been the endogenous endothelium. Endothelial regulation of hemostasis is complex and involves a delicate interplay of structural components and feedback mechanisms. Thus, challenges to develop new strategies for blood-compatible biomaterials now lie in incorporating true feedback controlled mechanisms that can regulate blood compatibility in a dynamic way. Here, supramolecular material systems are highlighted as they provide a promising platform to introduce dynamic reciprocity, due to their inherent dynamic nature.

Controlled Release of Plectasin NZ2114 from a Hybrid Silicone-Hydrogel Material for Inhibition of Staphylococcus aureus Biofilm

Staphylococcus aureus is a major human pathogen in catheter-related infections. Modifying catheter material with interpenetrating polymer networks is a novel material technology that allows for impregnation with drugs and subsequent controlled release. Here, we evaluated the potential for combining this system with plectasin derivate NZ2114 in an attempt to design an S. aureus biofilm-resistant catheter. The material demonstrated promising antibiofilm properties, including properties against methicillin-resistant S. aureus, thus suggesting a novel application of this antimicrobial peptide.

Systemic thioridazine in combination with dicloxacillin against early aortic graft infections caused by Staphylococcus aureus in a porcine model: In vivo results do not reproduce the in vitro synergistic activity

Introduction

Conservative treatment solutions against aortic prosthetic vascular graft infection (APVGI) for inoperable patients are limited. The combination of antibiotics with antibacterial helper compounds, such as the neuroleptic drug thioridazine (TDZ), should be explored.

Aim

To investigate the efficacy of conservative systemic treatment with dicloxacillin (DCX) in combination with TDZ (DCX+TDZ), compared to DCX alone, against early APVGI caused by methicillin-sensitive Staphylococcus aureus (MSSA) in a porcine model.

Methods

The synergism of DCX+TDZ against MSSA was initially assessed in vitro by viability assay. Thereafter, thirty-two pigs had polyester grafts implanted in the infrarenal aorta, followed by inoculation with 10⁶ CFU of MSSA, and were randomly administered oral systemic treatment with either 1) DCX or 2) DCX+TDZ. Treatment was initiated one week postoperatively and continued for a further 21 days. Weight, temperature, and blood samples were collected at predefined intervals. By termination, bacterial quantities from the graft surface, graft material, and perigraft tissue were obtained.

Results

Despite in vitro synergism, the porcine experiment revealed no statistical differences for bacteriological endpoints between the two treatment groups, and none of the treatments eradicated the APVGI. Accordingly, the mixed model analyses of weight, temperature, and blood samples revealed no statistical differences.

Conclusion

Conservative systemic treatment with DCX+TDZ did not reproduce in vitro results against APVGI caused by MSSA in this porcine model. However, unexpected severe adverse effects related to the planned dose of TDZ required a considerable reduction to the administered dose of TDZ, which may have compromised the results.