3D-printed biosurfactant-chitosan antibacterial coating for the prevention of silicone-based associated infections

Infections associated with the surfaces of medical devices represent a critical problem due to biofilm formation and the growing resistance towards antibacterial drugs. This is particularly relevant in commonly used invasive devices such as silicone-based ones where a demand for alternative antibiofilm surfaces is increasing. In this work, an antimicrobial chitosan-biosurfactant hydrogel mesh was produced by 3D-printing. The 3D structure was designed to coat polydimethylsiloxane-based medical devices for infection prevention. Additionally, the porous 3D structure allows the incorporation of customized bioactive components. For this purpose, two biosurfactants (surfactin and sophorolipids) were biosynthesized and tested for their antimicrobial activity. In addition, the printing of surfactant-chitosan-based coatings was optimized, and the resulting 3D structures were characterized (i.e., wettability, FTIR-ATR, antimicrobial activity, and biocompatibility). Compared with surfactin, the results showed a better yield and higher antibacterial activity against Gram-positive bacteria for sophorolipids (SLs). Thus, SLs were used to produce chitosan-based 3D-printed coatings. Overall, the SLs-impregnated coatings showed the best antibacterial activity against Staphylococcus aureus planktonic bacteria (61 % of growth inhibition) and antibiofilm activity (2 log units reduction) when compared to control. Furthermore, concerning biocompatibility, the coatings were cytocompatible towards human dermal fibroblasts. Finally, the coating presented a mesh suitable to be filled with a model bioactive compound (i.e., hyaluronic acid), paving the way to be used for customized therapeutics.

Development of a chlorhexidine delivery system based on dental reline acrylic resins

The high recurrence rate of common denture stomatitis after antifungal treatment is still concerning. This condition is caused by low patient compliance and incomplete local elimination of the main etiological factor - Candida albicans, often associated with other microorganisms, such as Streptococcus species. Impregnating denture materials with antimicrobials for local delivery is a strategy that can overcome the side effects and improve the efficacy of conventional treatments (topical and/or systemic). In this work, we describe the development of three hard autopolymerizing reline acrylic resins (Kooliner, Ufi Gel Hard, and Probase Cold) loaded with different percentages of chlorhexidine (CHX). The novel formulations were characterized based on their antimicrobial activity, mechanical, morphological and surface properties, in-vitro drug release profiles, and cytotoxicity. The addition of CHX in all resins did not change their chemical and mechanical structure. Among all the tested formulations, Probase Cold loaded with 5 wt% CHX showed the most promising results in terms of antimicrobial activity and lack of serious detrimental mechanical, morphological, surface, and biological properties.

Novel Organic Solvent Nanofiltration Approaches for Microbial Biosurfactants Downstream Processing

Glycolipid biosurfactants are the most prominent group of microbial biosurfactants, comprising rhamnolipids, sophorolipids and mannosylerythritol lipids (MELs). Usually, large amounts of hydrophobic substrates (e.g., vegetable oils) are used to achieve high titers (~200 g/L) of a crude product of low purity at values limited to 50-60%, contaminated with unconsumed triacylglycerol and residual free fatty acids and monoacylglycerides. The methods reported for the removal of these contaminants use a mixture of organic solvents, compromising solvent recyclability and increasing final process costs. This study reports, for the first time, an innovative downstream method for MELs, in which 90% of the triacylglycerols are separated from the crude MEL mixture in a first stage and the other lipid derivatives (free fatty acids, mono- and diacylglycerols) are removed by organic solvent nanofiltration (OSN). Three commercially available membranes (GMT-oNF-2, PuraMEm-600 and DuramMem-500) and several homemade membranes, casted from 22, 24 or 26% (w/v) polybenzimidazole (PBI) solutions, were assessed for crude MELs purification by diafiltration. A final purity of 87-90% in the MELs was obtained by filtering two diavolumes of methanol or ethyl acetate solutions through a PBI 26% membrane, resulting in MELs losses of 14.7 ± 6.1% and 15.3 ± 2.2%, respectively. Higher biosurfactant purities can be archived using the PBI 26% membrane at higher DV, but at the cost of higher product losses. Namely, in MeOH, the use of 6 DV leads to losses of 32% for MELs and 18% for sophorolipids. To obtain MELs at reagent grade with purities equal or higher than 97%, a two-sequential cascade filtration approach was implemented using the commercial membrane, GMT-oNF. In such a process, MELs with 98% purity was obtained at the cost of 11.6% MELs losses. Finally, decoloration, important in some applications, was successfully assessed using activated carbon. Overall, this study reports a unique solution for microbial biosurfactants production with minimal product losses, enabling solvent recycling and potentially reducing costs.

Assuring the Biofunctionalization of Silicone Covalently Bonded to Rhamnolipids: Antibiofilm Activity and Biocompatibility

Silicone-based medical devices composed of polydimethylsiloxane (PDMS) are widely used all over the human body (e.g., urinary stents and catheters, central venous catheters stents) with extreme clinical success. Nevertheless, their abiotic surfaces, being prone to microorganism colonization, are often involved in infection occurrence. Improving PDMS antimicrobial properties by surface functionalization with biosurfactants to prevent related infections has been the goal of different works, but studies that mimic the clinical use of these novel surfaces are missing. This work aims at the biofunctional assessment of PDMS functionalized with rhamnolipids (RLs), using translational tests that more closely mimic the clinical microenvironment. Rhamnolipids were covalently bonded to PDMS, and the obtained surfaces were characterized by contact angle modification assessment, ATR-FTIR analysis and atomic force microscopy imaging. Moreover, a parallel flow chamber was used to assess the Staphylococcus aureus antibiofilm activity of the obtained surfaces under dynamic conditions, and an in vitro characterization with human dermal fibroblast cells in both direct and indirect characterization assays, along with an in vivo subcutaneous implantation assay in the translational rabbit model, was performed. A 1.2 log reduction in S. aureus biofilm was observed after 24 h under flow dynamic conditions. Additionally, functionalized PDMS lessened cell adhesion upon direct contact, while supporting a cytocompatible profile, within an indirect assay. The adequacy of the biological response was further validated upon in vivo subcutaneous tissue implantation. An important step was taken towards biofunctional assessment of RLs-functionalized PDMS, reinforcing their suitability for medical device usage and infection prevention.

Drug Delivery from PCL/Chitosan Multilayer Coatings for Metallic Implants

Implant-related infections, mainly caused by Staphylococcus aureus, are a major health concern. Treatment is challenging due to multi-resistant strains and the ability of S. aureus to adhere and form biofilms on bone and implant surfaces. The present work involved the preparation and evaluation of a novel dual polymeric film coating on stainless steel. Chitosan and polycaprolactone (PCL) multilayers, loaded with poly(methyl methacrylate) (PMMA) microspheres encapsulating vancomycin or daptomycin, produced by the dip-coating technique, allowed local antibiotic-controlled delivery for the treatment of implant-related infections. Enhanced adhesion of the film to the metal substrate surface was achieved by mechanical abrasion of its surface. Studies have shown that for both drugs the release occurs by diffusion, but the release profile depends on the type of drug (daptomycin or vancomycin), the pH of the solution, and whether the drug is freestanding (directly incorporated into the films) or encapsulated in PMMA microspheres. Daptomycin freestanding films reached 90% release after 1 day at pH 7.4 and 4 days at pH 5.5. In comparison, films with daptomycin encapsulated microspheres reached 90% release after 2 h at pH 5.5 and 2 days at pH 7.4. Vancomycin encapsulated and freestanding films showed a similar behavior reaching 90% release after 20 h of release at pH 5.5 and 2 and 3 days, respectively, at pH 7.4. Furthermore, daptomycin-loaded films showed activity (assessed by agar diffusion assays) against sensitive (ATCC 25923) and clinically isolated (MRSA) S. aureus strains.

Poly(DL-lactic acid) scaffolds as a bone targeting platform for the co-delivery of antimicrobial agents against S. aureus-C. albicans mixed biofilms

New strategies for the treatment of polymicrobial bone infections are required. In this study, the co-delivery of two antimicrobials by poly(D,L-lactic acid) (PDLLA) scaffolds was investigated in a polymicrobial biofilm model. PDLLA scaffolds were prepared by solvent casting/particulate leaching methodology, incorporating minocycline and voriconazole as clinically relevant antimicrobial agents. The scaffolds presented a sponge-like appearance, suitable to support cell proliferation and drug release. Single- and dual-species biofilm models of Staphylococcus aureus and Candida albicans were developed and characterized. S. aureus presented a higher ability to form single-species biofilms, compared to C. albicans. Minocycline and voriconazole-loaded PDLLA scaffolds showed activity against S. aureus and C. albicans single- and dual-biofilms. Ultimately, the cytocompatibility/functional activity of PDLLA scaffolds observed in human MG-63 osteosarcoma cells unveil their potential as a next-generation co-delivery system for antimicrobial therapy in bone infections.

Fighting S. aureus catheter-related infections with sophorolipids: Electing an antiadhesive strategy or a release one?

Staphylococcus aureus medical devices related-infections, such as blood stream catheter are of major concern. Their prevention is compulsory and strategies, not prone to the development of resistance, to prevent S. aureus biofilms on catheter surfaces (e.g. silicone) are needed. In this work two different approaches using sophorolipids were studied to prevent S. aureus biofilm formation on medical grade silicone: i) an antiadhesive strategy through covalent bond of sophorolipids to the surface; ii) and a release strategy using isolated most active sophorolipids. Sophorolipids produced by Starmerella bombicola, were characterized by UHPLC-MS and RMN, purified by automatic flash chromatography and tested for their antimicrobial activity towards S. aureus. Highest antimicrobial activity was observed for C18:0 and C18:1 diacetylated lactonic sophorolipids showing a MIC of 50 μg mL^-1. Surface modification with acidic or lactonic sophorolipids when evaluating the anti-adhesive or release strategy, respectively, was confirmed by contact angle, FTIR-ATR and AFM analysis. When using a mixture of acidic sophorolipids covalently bonded to silicone surface as antiadhesive strategy cytocompatible surfaces were obtained and a reduction of 90 % on biofilm formation was observed. Nevertheless, if a release strategy is adopted with purified lactonic sophorolipids a higher effect is achieved. Most promising compound was C18:1 diacateylated lactonic sophorolipid that showed no cellular viability reduction when a concentration of 1.5 mg mL^-1 was selected and a reduction on biofilm around 5 log units. Results reinforce the applicability of these antimicrobial biosurfactants on preventing biofilms and disclose that their antimicrobial effect is imperative when comparing to their antiadhesive properties.

A Glance at Antimicrobial Strategies to Prevent Catheter-Associated Medical Infections

Urinary and intravascular catheters are two of the most used invasive medical devices; however, microbial colonization of catheter surfaces is responsible for most healthcare-associated infections (HAIs). Several antimicrobial-coated catheters are available, but recurrent antibiotic therapy can decrease their potential activity against resistant bacterial strains. The aim of this Review is to question the actual effectiveness of currently used (coated) catheters and describe the progress and promise of alternative antimicrobial coatings. Different strategies have been reviewed with the common goal of preventing biofilm formation on catheters, including release-based approaches using antibiotics, antiseptics, nitric oxide, 5-fluorouracil, and silver as well as contact-killing approaches employing quaternary ammonium compounds, chitosan, antimicrobial peptides, and enzymes. All of these strategies have given proof of antimicrobial efficacy by modifying the physiology of pathogens or disrupting their structural integrity. The aim for synergistic approaches using multitarget processes and the combination of both antifouling and bactericidal properties holds potential for the near future. Despite intensive research in biofilm preventive strategies, laboratorial studies still present some limitations since experimental conditions usually are not the same and also differ from biological conditions encountered when the catheter is inserted in the human body. Consequently, in most cases, the efficacy data obtained from in vitro studies is not properly reflected in the clinical setting. Thus, further well-designed clinical trials and additional cytotoxicity studies are needed to prove the efficacy and safety of the developed antimicrobial strategies in the prevention of biofilm formation at catheter surfaces.

A scope at antifouling strategies to prevent catheter-associated infections

The use of invasive medical devices is becoming more common nowadays, with catheters representing one of the most used medical devices. However, there is a risk of infection associated with the use of these devices, since they are made of materials that are prone to bacterial adhesion with biofilm formation, often requiring catheter removal as the only therapeutic option. Catheter-related urinary tract infections (CAUTIs) and central line-associated bloodstream infections (CLABSIs) are among the most common causes of healthcare-associated infections (HAIs) worldwide while endotracheal intubation is responsible for ventilator-associated pneumonia (VAP). Therefore, to avoid the use of biocides due to the potential risk of bacterial resistance development, antifouling strategies aiming at the prevention of bacterial adherence and colonization of catheter surfaces represent important alternative measures. This review is focused on the main strategies that are able to modify the physical or chemical properties of biomaterials, leading to the creation of antiadhesive surfaces. The most promising approaches include coating the surfaces with hydrophilic polymers, such as poly(ethylene glycol) (PEG), poly(acrylamide) and poly(acrylates), betaine-based zwitterionic polymers and amphiphilic polymers or the use of bulk-modified poly(urethanes). Natural polysaccharides and its modifications with heparin, have also been used to improve hemocompatibility. Recently developed bioinspired techniques yielding very promising results in the prevention of bacterial adhesion and colonization of surfaces include slippery liquid-infused porous surfaces (SLIPS) based on the superhydrophilic rim of the pitcher plant and the Sharklet topography inspired by the shark skin, which are potential candidates as surface-modifying approaches for biomedical devices. Concerning the potential application of most of these strategies in catheters, more in vivo studies and clinical trials are needed to assure their efficacy and safety for possible future use.

Benefits of Polydopamine as Particle/Matrix Interface in Polylactide/PD-BaSO4 Scaffolds

This work reports the versatility of polydopamine (PD) when applied as a particle coating in a composite of polylactide (PLA). Polydopamine was observed to increase the particle-matrix interface strength and facilitate the adsorption of drugs to the material surface. Here, barium sulfate radiopaque particles were functionalized with polydopamine and integrated into a polylactide matrix, leading to the formulation of a biodegradable and X-ray opaque material with enhanced mechanical properties. Polydopamine functionalized barium sulfate particles also facilitated the adsorption and release of the antibiotic levofloxacin. Analysis of the antibacterial capacity of these composites and the metabolic activity and proliferation of human dermal fibroblasts in vitro demonstrated that these materials are non-cytotoxic and can be 3D printed to formulate complex biocompatible materials for bone fixation devices.

Citrate zinc hydroxyapatite nanorods with enhanced cytocompatibility and osteogenesis for bone regeneration

The development of biomaterials that mimicking the hydroxyapatite nanoparticles existent in the immature bone tissue is crucial, especially to accelerate the bone remodeling and regeneration. In this work, it was developed for the first time, hydroxyapatite nanoparticles (NPs) incorporating citrate and zinc (cit-Zn-Hap) in their composition towards a one-step hydrothermal procedure. For comparison purposes, hydroxyapatite NPs incorporating only zinc (Zn-Hap) or citrate (cit-Hap), as well as hydroxyapatite without any of these elements (Hap) were synthesised. The physicochemical characterization was carried out reveling that, the presence of zinc on hydroxyapatite (cit-Zn-Hap), reduced the size of nanoparticles, changed the phosphate environment and decreased the surface charge when compared with cit-Hap nanoparticles. The osteogenic potential of cit-Zn-Hap NPs was analysed in human bone marrow-derived stromal cells (BMSCs), in the absence of osteoinductive factors. NPs were internalized by endocytosis appearing trapped in endosomes and lysosomes scattered through the cytoplasm. Exposure to these NPs resulted in a significant induction of ALP activity, extracellular matrix mineralization, and gene expression of early and later osteogenic transcription factors, as well as of osteoblastic markers. The osteoinductive effect might be regulated, at least in part, by the increased signalling through the canonical WNT pathway. Evaluation of the cell behaviour following exposure to Zn-Hap and cit-Hap strongly suggested a synergistic effect of citrate and Zn in cit-Zn-Hap NPs towards the induction of the osteogenic commitment and functionality of BMSCs. These findings will allow the design of new biomimetic hydroxyapatite nanoparticles with great potential for bone regeneration.

Evaluating Efficacy of Antimicrobial and Antifouling Materials for Urinary Tract Medical Devices: Challenges and Recommendations

In Europe, the mean incidence of urinary tract infections in intensive care units is 1.1 per 1000 patient-days. Of these cases, catheter-associated urinary tract infections (CAUTI) account for 98%. In total, CAUTI in hospitals is estimated to give additional health-care costs of £1-2.5 billion in the United Kingdom alone. This is in sharp contrast to the low cost of urinary catheters and emphasizes the need for innovative products that reduce the incidence rate of CAUTI. Ureteral stents and other urinary-tract devices suffer similar problems. Antimicrobial strategies are being developed, however, the evaluation of their efficacy is very challenging. This review aims to provide considerations and recommendations covering all relevant aspects of antimicrobial material testing, including surface characterization, biocompatibility, cytotoxicity, in vitro and in vivo tests, microbial strain selection, and hydrodynamic conditions, all in the perspective of complying to the complex pathology of device-associated urinary tract infection. The recommendations should be on the basis of standard assays to be developed which would enable comparisons of results obtained in different research labs both in industry and in academia, as well as provide industry and academia with tools to assess the antimicrobial properties for urinary tract devices in a reliable way.

Acrylic microparticles increase daptomycin intracellular and in vivo anti-biofilm activity against Staphylococcus aureus

Daptomycin (DAP) is a cyclic lipopeptide antibiotic with potential clinical application in orthopedic infections caused by staphylococci. However, it failed to eradicate Staphylococcus aureus in vitro, in intracellular infection studies, as well as in vivo in an experimental model of implant-associated biofilm infections. In this study, the antimicrobial effect of DAP encapsulated in poly(methyl methacrylate)-Eudragit (PMMA-EUD) microparticles (DAP-MPs) on intracellular S. aureus was evaluated in human osteoblast cells using fluorescence in situ hybridization (FISH) analysis. Encapsulated DAP was able to reduce the amount of intracellular S. aureus by 73% compared to blank microparticles (MPs). Then, the advantage of treating with DAP-MPs versus free DAP was evaluated in a murine model of implant-associated biofilm infection. Free DAP showed a >3 log₁₀ decrease in planktonic and adherent bacteria but failed to eradicate adherent methicillin-resistant S. aureus (MRSA), whereas DAP-MPs showed a clearance of planktonic MRSA, significantly reduced adherent MRSA by more than 3 log₁₀ and cured the infection in 60%. This was linked to the prolonged higher DAP concentration within the tissue cage fluid compared to free DAP. To our knowledge, this study provides the first evidence for the high intracellular and in vivo anti-biofilm efficacy of DAP-MPs to target staphylococcal infections.

Novel Antibacterial Agents: An Emergent Need to Win the Battle Against Infections

BACKGROUND

Multiple strategies have been recommended for prevention and control of antibacterial resistance. Solutions will need to be found soon if we are not to run the serious risk of losing the ability to treat bacterial infections, especially the ones arising from multi-resistant strains. Deep knowledge of the resistance mechanisms followed by novel therapeutic drugs and vaccines are needed. A consolidated, multidisciplinary and regulated strategy is required by this challenge.

OBJECTIVE

This review will be focused on new strategies to control infections. Among strategies to tackle antibiotic resistance that have been under investigation, are the use of antimicrobial peptides, phage therapy and phage enzymes, therapeutic antibodies, quorum sensing inhibitors and, finally, the antibacterial nanomedicines. Although all of the approaches seem to be effective, and at least one of them has been in use for relatively a long time (phage therapy), antibacterial nanomedicines show the most diverse range of different approaches regarding potential translation to clinics.

RESULTS & CONCLUSION

Several advances have been made but a great effort is still mandatory in order to reach feasible, effective and marketable novel antimicrobial products.

Can Sophorolipids prevent biofilm formation on silicone catheter tubes?

Given the impact of biofilms in health care environment and the increasing antibiotic resistance and/or tolerance, new strategies for preventing that occurrence in medical devices are obligatory. Thus, biomaterials surface functionalization with active compounds can be a valuable approach. In the present study the ability of the biosurfactants sophorolipids to prevent biofilms formation on silicone rubber aimed for medical catheters was investigated. Sophorolipids produced by Starmerella bombicola, identified by HPLC-MS/MS were used to cover silicone and surface characterization was evaluated through contact angle measurements and FTIR-ATR. Results revealed that sophorolipids presence on silicone surface decreased the hydrophobicity of the material and biofilm formation of Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 25922. Antibiofilm activity was evaluated through different methods and was more pronounced against S. aureus. Furthermore, biocompatibility of silicone specimens with HaCaT cells was also obtained. From this study it was possible to conclude that sophorolipids seem to be a favourable approach for coating silicone catheters. Such compounds may represent a novel source of antibiofilm agents for technological development passing through strategies of permanent functionalization of surfaces.

Insights on the properties of levofloxacin-adsorbed Sr- and Mg-doped calcium phosphate powders

Several types of biodegradable materials have been investigated for the treatment of osteomyelitis. Calcium phosphate (CaP) ceramics are among the most performing materials due to their resemblance to human hard tissues in terms of mineralogical composition, and proven ability to adsorb and deliver a number of drugs. This research work was intended to study the suitability of modified CaP powders loaded with a fluoroquinolone as drug delivery systems for osteomyelitis treatment. Levofloxacin (LEV) was chosen due to the well-recognized anti-staphylococcal activity and adequate penetration into osteoarticular tissues. Substituted CaP powders (5 mol% Sr(2+) or 5 mol% Mg(2+)) were synthesised through aqueous precipitation. The obtained powders were characterised by X-ray diffraction, SEM and FTIR analysis. The X-ray diffraction patterns confirmed the presence of HA and β-tricalcium phosphates (β-TCP) phases in doped compositions, especially in the case of Mg-doped system. The fixation of LEV at the surface of the particles occurred only by physisorption. Both the in vitro microbiological susceptibility, against Staphylococcus spp, and biocompatibility of LEV-loaded CaP powders have not been compromised.

Development of novel sophorolipids with improved cytotoxic activity toward MDA-MB-231 breast cancer cells

Sophorolipids (SLs) are glycolipid biosurfactants, produced as a mixture of several compounds by some nonpathogenic yeast. In the current study, separation of individual SLs from mixtures with further evaluation of their surface properties and biologic activity on MDA-MB-321 breast cancer cell line were investigated. SLs were biosynthesized by Starmerella bombicola in a culture media supplemented with borage oil. A reverse-phase flash chromatography method with an automated system coupled with a prepacked cartridge was used to separate and purify the main SLs. Compositional analysis of SLs was performed by high-performance liquid chromatography with electrospray ionization mass spectrometry and tandem mass spectrometry. The following diacetylated lactonic SLs were isolated and purified: C18:0, C18:1, C18:2, and C18:3. The critical micelle concentration (CMC) and surface tension at CMC (γCMC ) of the purified SLs showed an increase with the number of double bonds. High cytotoxic effect against MDA-MB-231 cells was observed with C18:0 and C18:1 lactonic SLs. The cytotoxic effects of C18:3 lactonic SL on cancerous cells were for the first time studied. This cytotoxic effect was considerably higher than the promoted by acidic SLs; however, it induced a lower effect than the previously mentioned SLs, C18:0 and C18:1. To our knowledge, for the first time, C18:1 lactonic SL, in selected concentrations, proved to be able to inhibit MDA-MB-231 cell migration without compromising cell viability and to increase intracellular reactive oxygen species.

Modelling the adsorption kinetics of erythromycin onto neutral and anionic resins

In this study the selective adsorption method was chosen to enable the recovery of erythromycin. The following sorbents were tested: neutral resins (XAD-4, XAD-7 and XAD-16) and an anionic resin (IRA-410). A mathematical kinetic model for the adsorption of erythromycin against time, on XAD-4, XAD-7 and XAD-16 resins, is proposed. Both Freundlich and Langmuir models showed a good fit for the sorbents XAD-7 and IRA-410 resins. The highest adsorption efficiency was observed when synthetic neutral resin, XAD-7 and XAD-16, were used. The estimated affinity and concentration factors show that the neutral resins tested are adequate for the selective adsorption of erythromycin. The estimated values of enthalpy and free energy of adsorption, lower than 12 kJ mol(-1) and -2 kJ mol(-1), respectively, indicate that a physiosorption process occurred.