Indwelling catheters and medical implants with FXIIIa inhibitors: A novel approach to the treatment of catheter and medical device-related infections

Evaluating antimicrobial efficacy in medical devices: The critical role of simulating in use test conditions

Biofilm infections represent the greatest risk associated with medical devices and implants, constituting 65 %-70 % of all device associated infections. Efforts to develop antimicrobial technologies for biomedical applications aim to reduce infection rates, antibiotic use, and the induction of antimicrobial resistance. However, standard laboratory test conditions often overestimate efficacy, highlighting the need for experimental designs that simulate real-world settings. To this end, we evaluated four commercially available antimicrobial materials containing silver (AG1, AG2, AG3) or zinc (ZN1) to assess their ability to mitigate microbial proliferation in for longer duration or multi-use medical devices. The materials' homogeneity and surface topography were characterized through Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS) and Atomic Force Microscopy (AFM). Antimicrobial efficacy was tested using a modified ISO 22196 protocol under clinically relevant conditions and a dry contact test developed to mimic in-use conditions for many extracorporeal medical devices. Results revealed homogeneous elemental distributions in AG1, AG2, and ZN1, and heterogeneous clusters for AG3. Surface roughness was highest for AG2 (170.1 nm), followed by TPE control (155.3 nm), ZN1 (83.51 nm) and silicone control (66.74 nm). All test materials demonstrated antimicrobial efficacies against S. aureus and E. coli, but not against C. albicans. In the dry contact assay, only AG2 proved effective against E. coli, and P. aeruginosa, underlining the role of humidity in antimicrobial action. Results were further corroborated by measurement of ion release by the materials at various temperatures, revealing greater release at higher temperatures. These outcomes emphasize the importance of testing antimicrobial materials under in use conditions to minimize discrepancies between laboratory results and clinical outcomes. Our findings provide a valuable framework for testing and integrating these materials into next-generation multi-use medical devices.

Comparative activity of silver-based antimicrobial composites for urinary catheters

Biomedical polymers are an integral component in a wide range of medical devices because of their many desirable properties. However, extensive use of polymer materials in medical devices has been associated with an increasing incidence of patient infections. Efforts to address this issue have included incorporating antimicrobial additives to develop novel antimicrobial polymeric materials. Silver, with its high toxicity towards bacteria, oligodynamic effect and good thermal stability, has been employed as an additive for polymeric medical devices. In the present study, commercially available elemental (Biogate) and ionic (Ultrafresh 16) silver additives were incorporated into a Polyamide 11 (PA 11) matrix using a compression press. These polymer composites were evaluated for their antimicrobial and ion-release properties. Elemental silver composites were shown to retain their antimicrobial properties for extended periods and actively released silver ions for 84 days; whereas ionic silver composites lost their ion-release activity and, therefore, their antibacterial activity after 56 days. Bacterial log reduction units of 3.87 for ionic silver and 2.41 for elemental silver were identified within 24 h, when tested in accordance with the ISO 22196 test standard; this indicates that ionic silver is more efficient for short-term applications than elemental silver.

Characterisation of polyamide 11/copper antimicrobial composites for medical device applications

Direct incorporation of antimicrobial additive into the polymer matrix is a cost effective approach for the development of polymer/metal antimicrobial composites. Application of these antimicrobial composite systems for manufacturing medical devices addresses the issue of device related infections. In the present study, commercially available inorganic copper based additive, Plasticopper, was incorporated into a Polyamide 11(PA 11) matrix during the polymer processing stage. These polymer composites were evaluated for their morphological, mechanical, antimicrobial and ion release properties. Isothermal crystallisation studies showed that the copper additive acted as a nucleating agent and promoted faster crystallisation. Short term mechanical studies confirmed that the incorporation of copper has reinforcing effect on the composites with 5 and 10% copper loadings and did not adversely affect the short-term mechanical performance of the polymer composites. These composite systems were shown to be active against Escherichia coli ATCC 8739 with >99.99% reduction in bacterial population. Corresponding ion release profiles for these composites indicated long term antimicrobial activity.

How to adjust dexamethasone mobility in silicone matrices: A quantitative treatment

Silicone-based drug delivery systems offer a great potential to improve the therapeutic efficacy and safety of a large variety of medical treatments, e.g. allowing for local long-term delivery of active agents to the inner ear. Different formulation parameters can be varied to adjust desired drug release kinetics. However, often only qualitative information is available on their effects, and product optimization is cumbersome. The aim of this study was to provide a quantitative analysis, allowing also for theoretical predictions of the impact of the device design on system performance. Dexamethasone was incorporated into thin films based on different types of silicones (e.g. varying in the type of side chains and contents of amorphous silica), optionally containing different types and amounts of poly(ethylene glycol) (PEG) (5% or 10%). Furthermore, the initial drug content was altered (from 10% to 50%). In most cases, an analytical solution of Fick's second law could be used to describe the resulting drug release kinetics from the films and to determine the respective "apparent" diffusion coefficient of the drug (which varied from 2×10(-14) to 2×10(-12)cm(2)/s, depending on the system's composition). Thus, the impact of the investigated formulation parameters on drug mobility in the polymeric matrices could be quantitatively described. Importantly, the knowledge of the "apparent" drug diffusivity can be used to theoretically predict the resulting release kinetics from dosage forms of arbitrary size and shape. For instance, dexamethasone release was theoretically predicted from cylindrical extrudates based on a selection of different silicone types. Interestingly, these predictions could be confirmed by independent experiments. Hence, this type of quantitative analysis can replace time-consuming and cost-intensive series of trial-and-error experiments during product optimization. This is particularly helpful, if long-term drug release (e.g., during several weeks, months or years) is targeted.

Silicone surface with drug nanodepots for medical devices

An ideal surface of poly(dimethylsiloxane) (PDMS) medical devices requires sustained drug release to combat various tissue responses and infection. At present, a noncovalent surface coating with drug molecules using binders possesses a detachment problem, while covalently linking drug molecules to the surface provides no releasable drug. Here, a platform that allows the deposition of diverse drugs onto the PDMS surface in an adequate quantity with reliable attachment and a sustained-release character is demonstrated. First, a PDMS surface with carboxyl functionality (PDMS-COOH) is generated by subjecting a PDMS piece to an oxygen plasma treatment to obtain silanol moieties on its surface, then condensing the silanols with (3-aminopropyl)triethoxysilane molecules to generate amino groups, and finally reacting the amino groups with succinic anhydride. The drug-loaded carriers with hydroxyl groups on their surface can then be esterified to PDMS-COOH, resulting in a PDMS surface covalently grafted with drug-filled nanocarriers so that the drugs inside the securely grafted carriers can be released. Demonstrated here is the covalent linking of the surface of a PDMS endotracheal tube with budesonide-loaded ethylcellulose nanoparticles. A secure and high drug accumulation at the surface of the tubes (0.025 mg/cm2) can be achieved without changes in its bulk property such as hardness (Shore-A), and sustained release of budesonide with a high release flux during the first week followed by a reduced release flux over the subsequent 3 weeks can be obtained. In addition, the grafted tube possesses more hydrophilic surface and thus is more tissue-compatible. The grafted PDMS pieces show a reduced in vitro inflammation in cell culture and a lower level of in vivo tissue responses, including a reduced level of inflammation, compared to the unmodified PDMS pieces, when implanted in rats. Although demonstrated with budesonide and a PDMS endotracheal tube, this platform of grafting a PDMS surface with drug-loaded particles can be applied to other drugs and other devices.

Digital Drug Delivery: On-Off Ultrasound Controlled Antibiotic Release from Coated Matrices with Negligible Background Leaching

Hydrogels, such as crosslinked poly(2-hydroxyethyl methacrylate) (pHEMA) have been used extensively in controlled release drug delivery systems. Our previous work demonstrated an ultrasound (US)-responsive system based on pHEMA coated with a self-assembled multilayer of C12-C18 methylene chains. The resulting coating was predominantly crystalline and relatively impermeable, forming an US-activated switch that controlled drug release on-demand, and kept the drug within the matrix in the absence of US. The device, as developed did, however, show a low background drug-leaching rate independent of US irradiation. For some applications, it is desirable to have very low or zero background release rates. This was achieved here by a combination of new processing steps, and by copolymerizing HEMA with a relatively hydrophobic monomer, hydroxypropyl methacrylate (HPMA). These advances produced systems with undetectable ciprofloxacin background release rates that are capable of US-facilitated drug release - up to 14-fold increases relative to controls both before and after US exposure. In addition, these observations are consistent with the hypothesis that US-mediated disorganization of the coating allows a transient flux of water into the matrix where its interaction with bound and dissolved drug facilitates its movement both within and out of the matrix.