Characterization of crosslinking effects on the physicochemical and drug diffusional properties of cationic hydrogels designed as bioactive urological biomaterials

The Role of Superabsorbent Polymers and Polymer Composites in Water Resource Treatment and Management

In the last century, the issue of "water reserves" has become a remarkably strategic topic in modern science and technology. In this context, water resource treatment and management systems are being developed in both agricultural and urban area scenarios. This can be achieved using superabsorbent polymers (SAPs), highly cross-linked hydrogels with three-dimensional, hydrophilic polymer structures capable of absorbing, swelling and retaining huge amounts of aqueous solutions. SAPs are able to respond to several external stimuli, such as temperature, pH, electric field, and solution composition and concentration. They can be used in many areas, from sensor technology to drug delivery, agriculture, firefighting applications, food, and the biomedical industry. In addition, new categories of functional SAP-based materials, mainly superabsorbent polymer composites, can also encapsulate fertilizers to efficiently provide the controlled release of both water and active compounds. Moreover, SAPs have great potential in wastewater treatment for the removal of harmful elements. In this respect, in the following review, the most promising and recent advances in the use of SAPs and composite SAPs as tools for the sustainable management and remediation of water resource are reviewed and discussed by identifying opportunities and drawbacks and highlighting new challenges and aims to inspire the research community.

Chitosan Hydrogels Cross-Linked with Trimesic Acid for the Delivery of 5-Fluorouracil in Cancer Therapy

Chitosan exhibits unique properties making it a suitable material for drug delivery. Considering the rising popularity of hydrogels in this field, this work offers a comprehensive study of hydrogels constituted by chitosan and cross-linked with 1,3,5-benzene tricarboxylic acid (BTC; also known as trimesic acid). Hydrogels were prepared by cross-linking chitosan with BTC in different concentrations. The nature of the gels was studied through oscillatory amplitude strain and frequency sweep tests within the linear viscoelastic region (LVE) limit. The flow curves of the gels revealed shear thinning behavior. High G′ values imply strong cross-linking with improved stability. The rheological tests revealed that the strength of the hydrogel network increased with the cross-linking degree. Hardness, cohesiveness, adhesiveness, compressibility, and elasticity of the gels were determined using a texture analyzer. The scanning electron microscopy (SEM) data of the cross-linked hydrogels showed distinctive pores with a pore size increasing according to increasing concentrations (pore size range between 3–18 µm). Computational analysis was performed by docking simulations between chitosan and BTC. Drug release studies employing 5-fluorouracil (5-FU) yielded a more sustained release profile with 35 to 50% release among the formulations studied in a 3 h period. Overall, this work demonstrated that the presence of BTC as cross-linker leads to satisfactory mechanical properties of the chitosan hydrogel, suggesting potential applications in the sustained release of cancer therapeutics.

Hydrogels in Hand Sanitizers

Hand hygiene can be considered a strategic key useful in the containment of infections such as COVID-19 both at home and in communities because it can dramatically reduce the widespread outbreak of infections. In case of the unavailability of soap and water, "instant" hand sanitizers are recommended because their application can be considered easy, versatile, quick and often less aggressive for the skin. For these reasons, alcoholic and alcohol-free hand rub gels can be considered the best performing formulations on the market. Together with disinfectants and antiseptic agents, hydrogels play a fundamental role in obtaining stable formulations and are easy to disperse, with a pleasant skin feel and an overall good performance. Several compounds commonly used in the pharmaceutical, cosmetic and food industry are available for this purpose, in particular, cellulose derivatives and synthetic polymers derivatives. Each of them is available in several grades, presenting different thickening behavior, rheological properties and compatibility with other ingredients, alcohols in particular. For all these reasons, it is important to explore hydrogel properties and behaviors in different contexts (i.e., hydroalcoholic and aqueous media) in order to develop new and performing hand rub gels, always taking into account the different international legal frameworks regarding disinfectant and sanitizing formulations.

Hydrogel Antimicrobial Capture Coatings for Endotracheal Tubes: A Pharmaceutical Strategy Designed to Prevent Ventilator-Associated Pneumonia

This paper presents a novel strategy for the prevention of ventilator-associated pneumonia that involves coating poly(vinyl chloride, PVC) endotracheal tubes (ET) with hydrogels that may be subsequently used to entrap nebulized antimicrobial solutions. Candidate hydrogels were prepared containing a range of ratios of hydroxyethyl methacrylate (HEMA) and methacrylic acid (MAA) from 100:0 to 70:30 using free radical polymerization and, when required, simultaneous attachment to PVC was performed. The mechanical properties, glass transition temperatures, swelling kinetics, uptake of gentamicin from an aqueous medium, and gentamicin release were characterized. Increasing the MAA content of the hydrogels significantly decreased the ultimate tensile strength, % elongation at break, Young's modulus, and increased the glass transition temperature, the swelling ratio, and gentamicin uptake. Microbial (Staphylococcus aureus and Pseudomonas aeruginosa) adherence to control (drug-free) hydrogels was observed; however, while adherence to gentamicin-containing p(HEMA) occurred, no adherence occurred to gentamicin-containing HEMA:MAA copolymers. Antimicrobial persistence of gentamicin-containing hydrogels was examined by determining the zone of inhibition against each microorganism on successive days. Hydrogel composition affected the observed antimicrobial persistence, with the hydrogel composed of 70:30 HEMA:MAA exhibiting >20 days persistence against S. aureus and P. aeruginosa, respectively. To simulate clinical use, the hydrogels (coated onto PVC) were first exposed to a nebulized solution of gentamicin (4 mL, 80 mg for 20 min), and then to nebulized bacteria (4 mL ca. 1×10(9) colony forming units mL(-1), 30 min). Viable bacteria were not observed on the gentamicin-treated p(HEMA: MAA) copolymers, whereas growth was observed on gentamicin-treated p(HEMA). In light of the excellent antimicrobial activity and physicochemical properties, p(HEMA: MAA) copolymers composed of ratios of 80:20 or 70:30 HEMA: MAA were identified as potentially useful coatings of endotracheal tubes to be used in conjunction with the clinical nebulization of gentamicin and designed for the prevention of ventilator-associated pneumonia.

Non-cytotoxic silver nanoparticle-polyvinyl alcohol hydrogels with anti-biofilm activity: designed as coatings for endotracheal tube materials

Endotracheal intubation is commonly associated with hospital-acquired infections as the intubation device acts as reservoir for bacterial colonization in the lungs. To reduce the incidence of bacterial colonization on the tubes, hydrogel coatings loaded with antimicrobial agents are gaining popularity. The aim of this study was to incorporate silver nanoparticles (AgNPs) into polyvinyl alcohol (PVA) to form stable hydrogels. Embedding AgNPs into PVA resulted in a decreased elongation at break and an increased tensile strength compared to PVA alone. The Ag release profile varied as a function of the degree of hydrolysis of PVA: the higher degree of hydrolysis demonstrated a lower release rate. Fourier infrared transform spectroscopy demonstrated that AgNPs interacted exclusively with the -OH groups of PVA. AgNP-loaded PVA was non-toxic against human normal bronchial epithelial cells while effective against the attachment of Pseudomonas aeruginosa and Staphylococcus aureus with a greater effect on P. aeruginosa.

Enhanced antibacterial and anti-quorum sensing activities of triclosan by complexation with modified β-cyclodextrins

Triclosan (TCS), an antimicrobial agent widely used in consumer and medical products, was complexed with 2-hydroxypropyl-β-cyclodextrin (HPβCD) and methyl-β-cyclodextrin (MβCD). Phase-solubility studies indicated that inclusion complexes of 1:1 stoichiometry were formed and allowed estimation of the associated equilibrium constants and free-energy changes. At the highest cyclodextrin concentrations investigated, an almost 20-fold increase in the apparent water solubility of TCS was determined. Susceptibility tests against Escherichia coli and Staphylococcus aureus showed that the TCS-HPβCD and TCS-MβCD complexes exhibited antibacterial properties higher than those of uncomplexed TCS. The two complexes were also found capable of interfering with cell-to-cell communication mechanisms in the C. violaceum model system relying on N-acylhomoserine lactone autoinducers. The inhibitory activity of TCS increased significantly upon inclusion of the drug in HPβCD or MβCD, with small differences between the two CDs. The results obtained suggest that the investigated complexes could be used for treating infections caused by TCS-susceptible pathogens or for preventing biofilm formation on indwelling medical devices such as catheters, stents and orthopedic implants.

Novel semi-interpenetrating hydrogel networks with enhanced mechanical properties and thermoresponsive engineered drug delivery, designed as bioactive endotracheal tube biomaterials

Thermoresponsive polymeric platforms are used to optimise drug delivery in pharmaceutical systems and bioactive medical devices. However, the practical application of these systems is compromised by their poor mechanical properties. This study describes the design of thermoresponsive semi-interpenetrating polymer networks (s-IPNs) based on cross-linked p(NIPAA) or p(NIPAA-co-HEMA) hydrogels containing poly(ε-caprolactone) designed to address this issue. Using DSC, the lower critical solution temperature of the co-polymer and p(NIPAA) matrices were circa 34°C and 32°C, respectively. PCL was physically dispersed within the hydrogel matrices as confirmed using confocal scanning laser microscopy and DSC and resulted in marked changes in the mechanical properties (ultimate tensile strength, Young's modulus) without adversely compromising the elongation properties. P(NIPAA) networks containing dispersed PCL exhibited thermoresponsive swelling properties following immersion in buffer (pH 7), with the equilibrium-swelling ratio being greater at 20°C than 37°C and greatest for p(NIPAA)/PCL systems at 20°C. The incorporation of PCL significantly lowered the equilibrium swelling ratio of the various networks but this was not deemed practically significant for s-IPNs based on p(NIPAA). Thermoresponsive release of metronidazole was observed from s-IPN composed of p(NIPAA)/PCL at 37°C but not from p(NIPAA-co-HEMA)/PCL at this temperature. In all other platforms, drug release at 20°C was significantly similar to that at 37°C and was diffusion controlled. This study has uniquely described a strategy by which thermoresponsive drug release may be performed from polymeric platforms with highly elastic properties. It is proposed that these materials may be used clinically as bioactive endotracheal tubes, designed to offer enhanced resistance to ventilator associated pneumonia, a clinical condition associated with the use of endotracheal tubes where stimulus responsive drug release from biomaterials of significant mechanical properties would be advantageous.

Antimicrobial peptide incorporated poly(2-hydroxyethyl methacrylate) hydrogels for the prevention of Staphylococcus epidermidis-associated biomaterial infections

The effectiveness of the antimicrobial peptide maximin-4, the ultrashort peptide H-Orn-Orn-Trp-Trp-NH(2), and the lipopeptide C(12)-Orn-Orn-Trp-Trp-NH(2) in preventing adherence of pathogens to a candidate biomaterial were tested utilizing both matrix- and immersion-loaded poly(2-hydroxyethyl methacrylate) (poly(HEMA)) hydrogels. Antiadherent properties correlated to both the concentration released and the relative antimicrobial concentrations of each compound against Staphylococcus epidermidis ATCC 35984, at each time point. Immersion-loaded samples containing C(12)-Orn-Orn-Trp-Trp-NH(2) exhibited the lowest adherence profile for all peptides studied over 1, 4, and 24 h. The results outlined in this article show that antimicrobial peptides have the potential to serve as an important weapon against biomaterial associated infections.

A Novel Salted-out and Subsequently Crosslinked Poly(Lactic-co-Glycolic Acid) Polymeric Scaffold Applied to Monolithic Drug Delivery

This study involved a statistical approach to develop a mechanistic understanding of the salting-out of poly(lactic-co-glycolic acid) (PLGA) and to evaluate the capacity to modulate the physicochemical and physicomechanical properties of PLGA by incorporating electrolytes that produce stochastic fluctuations. The correlation between the three types of salts used and the extent of PLGA chain transitions were established by structural-thermal analysis. Drug-loaded monolithic matrices are prepared by direct compressing salted-out PLGA and a model drug (melatonin). PLGA scaffolds possess fiber diameters and volumes ranging between 0.1—15 μm and 0.0075—14,000 μm3 , respectively. Texture profile analysis reveal a significant increase in the energy absorbed and matrix resilience with increased NaCl2 and AlCl3 concentrations. In vitro drug release studies were performed in phosphate buffered saline (pH 7.4; 37°C); the release media was sampled at pre-determined intervals and analyzed by UV spectroscopy. Ideal zero-order drug release profiles were observed with 20% melatonin over a 30-day period. Monolithic matrices prepared by crosslinking melatonin with PLGA reveal a superior capability to control drug release. The salting-out and subsequent crosslinking of PLGA significantly modified the physicochemical and physicomechanical properties of native PLGA and demonstrated the ability to achieve controlled drug release.

Strategies for the development of the urinary catheter

Indwelling urinary catheters are utilized in the management of a wide range of conditions both in an acute and a chronic setting. However, utilization of this type of device is associated with a number of issues, including an increased propensity to develop bacteriuria, symptomatic infection and also encrusted deposits on the device. The development of novel biomaterials, incorporation of therapeutic agents and other strategies to minimize the issues associated with these devices are discussed in this review.