Biomedical applications of synthetic, biodegradable polymers for the development of anti-infective strategies

In Vitro Assessment of Bacterial Adhesion and Biofilm Formation on Novel Bioactive, Biodegradable Electrospun Fiber Meshes Intended to Support Tendon Rupture Repair

The surgical repair of a ruptured tendon faces two major problems: specifically increased fibrous adhesion to the surrounding tissue and inferior mechanical properties of the scar tissue compared to the native tissue. Bacterial attachment to implant materials is an additional problem as it might lead to severe infections and impaired recovery. To counteract adhesion formation, two novel implant materials were fabricated by electrospinning, namely, a random fiber mesh containing hyaluronic acid (HA) and poly(ethylene oxide) (PEO) in a ratio of 1:1 (HA/PEO 1:1) and 1:4 (HA/PEO 1:4), respectively. Electrospun DegraPol (DP) treated with silver nanoparticles (DP-Ag) was developed to counteract the bacterial attachment. The three novel materials were compared to the previously described DP and DP with incorporated insulin-like growth factor-1 (DP-IGF-1), two implant materials that were also designed to improve tendon repair. To test whether the materials are prone to bacterial adhesion and biofilm formation, we assessed 10 strains of Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa, and Enterococcus faecalis, known for causing nosocomial infections. Fiber diameter, pore size, and water contact angle, reflecting different degrees of hydrophobicity, were used to characterize all materials. Generally, we observed higher biofilm formation on the more hydrophobic DP as compared to the more hydrophilic DP-IGF-1 and a trend toward reduced biofilm formation for DP treated with silver nanoparticles. For the two HA/PEO implants, a similar biofilm formation was observed. All tested materials were highly prone to bacterial adherence and biofilm formation, pointing toward the need of further material development, including the optimized incorporation of antibacterial agents such as silver nanoparticles or antibiotics.

Anti-COVID-19 Credentials of Chitosan Composites and Derivatives: Future Scope?

Chitosan derivatives and composites are the next generation polymers for biomedical applications. With their humble origins from the second most abundant naturally available polymer chitin, chitosan is currently one of the most promising polymer systems, with wide biological applications. This current review gives a bird’s eye view of the antimicrobial applications of chitosan composites and derivatives. The antiviral activity and the mechanisms behind the inhibitory activity of these components have been reviewed. Specifically, the anti-COVID-19 aspects of chitosan composites and their derivatives have been compiled from the existing scattered reports and presented. Defeating COVID-19 is the battle of this century, and the chitosan derivative-based combat strategies naturally become very attractive. The challenges ahead and future recommendations have been addressed.

The prospects of antimicrobial coated medical implants

The implants are increasingly being a part of modern medicine in various surgical procedures for functional or cosmetic purposes. The progressive use of implants is associated with increased infectious complications and prevention of such infections always remains precedence in the clinical settings. The preventive approaches include the systemic administration of antimicrobial agents before and after the surgical procedures as well as the local application of antibiotics. The relevant literature and existing clinical practices have highlighted the role of antimicrobial coating approaches in the prevention of implants associated infections, although the applications of these strategies are not yet standardized, and the clinical efficacy is not much clear. The adequate data from the randomized control trials is challenging because of the unavailability of a large sample size although it is compulsory in this context to assess the clinical efficacy of preemptive practices. This review compares the efficacy of preventive approaches and the prospects of antimicrobial-coated implants in preventing implant-related infections.

Preparation and Antimicrobial Activity of Chitosan and Its Derivatives: A Concise Review

Despite the advantages presented by synthetic polymers such as strength and durability, the lack of biodegradability associated with the persistence in the environment for a long time turned the attention of researchers to natural polymers. Being biodegradable, biopolymers proved to be extremely beneficial to the environment. At present, they represent an important class of materials with applications in all economic sectors, but also in medicine. They find applications as absorbers, cosmetics, controlled drug delivery, tissue engineering, etc. Chitosan is one of the natural polymers which raised a strong interest for researchers due to some exceptional properties such as biodegradability, biocompatibility, nontoxicity, non-antigenicity, low-cost and numerous pharmacological properties as antimicrobial, antitumor, antioxidant, antidiabetic, immunoenhancing. In addition to this, the free amino and hydroxyl groups make it susceptible to a series of structural modulations, obtaining some derivatives with different biomedical applications. This review approaches the physico-chemical and pharmacological properties of chitosan and its derivatives, focusing on the antimicrobial potential including mechanism of action, factors that influence the antimicrobial activity and the activity against resistant strains, topics of great interest in the context of the concern raised by the available therapeutic options for infections, especially with resistant strains.

Larynx stenosis; a challenge for the ENT surgeons

Laryngo-tracheal stenosis is a complex pathology which requires multiple surgical interventions and diligence from the surgeon and patience from the patient so that normal physiology may be restored. The aim of this paper is to evaluate the factors that can influence the evolution of this pathology. It is presented a retrospective study in which 20 cases of larynx stenosis from 2008 until 2018 were evaluated. The study revealed a predominance of the pathology in men, especially from rural environment. The etiology of larynx stenosis was both iatrogenic and traumatic. Multiple surgical interventions classical and endoscopic were necessary, along with tracheostomy. In 7 cases there was the need for larynx stent to be mounted. There was no significant correlation between age, etiology and the site of stenosis and the removal of the tracheostomy. Larynx stenosis benefit in present by modern surgical techniques. Current therapeutic options include conservative therapy, endoscopic approach and external approach depending on the site, severity, morbidities of the stenosis. Even if technology is of great help in LS management of many patients, unfortunately there are still cases where therapy is very complex and with poor functional results.

Ultra-dense polymer brush coating reduces Staphylococcus epidermidis biofilms on medical implants and improves antibiotic treatment outcome

Staphylococcal biofilm formation is a severe complication of medical implants, leading to high antibiotic tolerance and treatment failure. Ultra-dense poly(ethylene glycol) (udPEG) coating resists adsorption of proteins, polysaccharides and extracellular DNA. It is therefore uniquely resistant to attachment by Staphylococcus epidermidis, which remains loosely adhered to the surface. Our aim was to determine if S. epidermidis remains susceptible to antibiotics when adhering to udPEG, and if udPEG coatings can improve the treatment outcome for implant-associated infections. We tested the in vitro efficacy of vancomycin treatment on recently adhered S. epidermidis AUH4567 on udPEG, conventional PEG or titanium surfaces using live/dead staining and microscopy. udPEG was then applied to titanium implants and inserted subcutaneously in mice and inoculated with S. epidermidis to induce infection. Mice were given antibiotic prophylaxis or a short antibiotic treatment. One group was given immunosuppressive therapy. After five days, implants and surrounding tissue were harvested for CFU enumeration. Only few S. epidermidis cells adhered to udPEG compared to conventional PEG and uncoated titanium, and a much lower fraction of cells on udPEG survived antibiotic treatment in vitro. In vivo, the bacterial load on implants in mice receiving vancomycin treatment was significantly lower on udPEG-coated compared to uncoated implants, also in neutropenic mice. Our results suggest that the improved outcome results from the coating's anti-adhesive properties that leads to less biofilm and increased efficacy of antibiotic treatment. Thus, the combination of udPEG with antibiotics is a promising strategy to prevent acute implant-associated infections that arise due to perioperative contaminations.

STATEMENT OF SIGNIFICANCE

Infections of medical implants is an ever-present danger. Here, bacteria develop biofilms that cannot be eradicated with antibiotics. By using an ultra-dense polymer-brush coating (udPEG), bacterial attachment and the subsequent biofilm formation can be reduced, resulting in increased antibiotic susceptibility of bacteria surrounding the implant. udPEG combined with antibiotics proved to significantly reduce bacteria on implants inserted into mice, in our animal model. As the coating is not antibacterial per se, it does not induce antimicrobial resistance and its effect is independent of the bacterial species. Our results are encouraging for the prospect of preventing and treating implant-associated infections that arise due to perioperative contaminations.

Antifouling and antimicrobial biomaterials: an overview

The use of implantable medical devices is a common and indispensable part of medical care for both diagnostic and therapeutic purposes. However, as side effect, the implant of medical devices quite often leads to the occurrence of difficult-to-treat infections, as a consequence of the colonization of their abiotic surfaces by biofilm-growing microorganisms increasingly resistant to antimicrobial therapies. A promising strategy to combat device-related infections is based on anti-infective biomaterials that either repel microbes, so they cannot attach to the device surfaces, or kill them in the surrounding areas. In general, such biomaterials are characterized by antifouling coatings, exhibiting low adhesion or even repellent properties towards microorganisms, or antimicrobial coatings, able to kill microbes approaching the surface. In this light, the present overview will address the development in the last two decades of antifouling and antimicrobial biomaterials designed to potentially limit the initial stages of microbial adhesion, as well as the microbial growth and biofilm formation on medical device surfaces.

Physicochemical properties of polymers: An important system to overcome the cell barriers in gene transfection

Delivery of the macromolecules including DNA, miRNA, and antisense oligonucleotides is typically mediated by carriers due to the large size and negative charge. Different physical (e.g., gene gun or electroporation), and chemical (e.g., cationic polymer or lipid) vectors have been already used to improve the efficiency of gene transfer. Polymer-based DNA delivery systems have attracted special interest, in particular via intravenous injection with many intra- and extracellular barriers. The recent progress has shown that stimuli-responsive polymers entitled as multifunctional nucleic acid vehicles can act to target specific cells. These nonviral carriers are classified by the type of stimulus including reduction potential, pH, and temperature. Generally, the physicochemical characterization of DNA-polymer complexes is critical to enhance the transfection potency via protection of DNA from nuclease digestion, endosomal escape, and nuclear localization. The successful clinical applications will depend on an exact insight of barriers in gene delivery and development of carriers overcoming these barriers. Consequently, improvement of novel cationic polymers with low toxicity and effective for biomedical use has attracted a great attention in gene therapy. This article summarizes the main physicochemical and biological properties of polyplexes describing their gene transfection behavior, in vitro and in vivo. In this line, the relative efficiencies of various cationic polymers are compared.

The antimicrobial activity of free and immobilized poly (diallyldimethylammonium) chloride in nanoparticles of poly (methylmethacrylate)

Background

Several cationic polymers exhibit a useful antimicrobial property, however the structure–activity relationship still requires a more complete investigation. The main objective of this work is the comparison between the antimicrobial activity and toxicity of free and immobilized poly (diallyldimethylammonium) chloride (PDDA) in biocompatible poly (methylmethacrylate) (PMMA) nanoparticles (NPs).

Results

NPs synthesis by emulsion polymerization is performed over a range of [PDDA] at two methylmethacrylate (MMA) concentrations. The PMMA/PDDA dispersions are characterized by dynamic light-scattering for sizing, polydispersity and zeta-potential analysis, scanning electron microscopy (SEM), plating plus colony forming unities (CFU) counting for determination of the minimal microbicidal concentrations (MMC) against Escherichia coli, Staphylococcus aureus and Candida albicans and hemolysis evaluation against mammalian erythrocytes. There is a high colloidal stability for the cationic PMMA/PDDA NPs over a range of [PDDA]. NPs diverse antimicrobial activity against the microorganisms reduces cell viability by eight-logs (E. coli), seven-logs (S. aureus) or two-logs (C. albicans). The NPs completely kill E. coli over a range of [PDDA] that are innocuous to the erythrocytes. Free PDDA antimicrobial activity is higher than the one observed for PDDA in the NPs. There is no PDDA induced-hemolysis at the MMC in contrast to the hemolytic effect of immobilized PDDA in the NPs. Hemolysis is higher than 15 % for immobilized PDDA at the MMC for S. aureus and C. albicans.

Conclusions

The mobility of the cationic antimicrobial polymer PDDA determines its access to the inner layers of the cell wall and the cell membrane, the major sites of PDDA antimicrobial action. PDDA freedom does matter for determining the antimicrobial activity at low PDDA concentrations and absence of hemolysis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12951-015-0123-3) contains supplementary material, which is available to authorized users.

Biodegradable Materials for Bone Repair and Tissue Engineering Applications

This review discusses and summarizes the recent developments and advances in the use of biodegradable materials for bone repair purposes. The choice between using degradable and non-degradable devices for orthopedic and maxillofacial applications must be carefully weighed. Traditional biodegradable devices for osteosynthesis have been successful in low or mild load bearing applications. However, continuing research and recent developments in the field of material science has resulted in development of biomaterials with improved strength and mechanical properties. For this purpose, biodegradable materials, including polymers, ceramics and magnesium alloys have attracted much attention for osteologic repair and applications. The next generation of biodegradable materials would benefit from recent knowledge gained regarding cell material interactions, with better control of interfacing between the material and the surrounding bone tissue. The next generations of biodegradable materials for bone repair and regeneration applications require better control of interfacing between the material and the surrounding bone tissue. Also, the mechanical properties and degradation/resorption profiles of these materials require further improvement to broaden their use and achieve better clinical results.