Self-Regenerating Antimicrobial Polymer Surfaces via Multilayer-Design - Sequential and Triggered Layer Shedding under Physiological Conditions

Dynamic Antimicrobial Poly(disulfide) Coatings Exfoliate Biofilms On Demand Via Triggered Depolymerization

Bacterial biofilms are notoriously problematic in applications ranging from biomedical implants to ship hulls. Cationic, amphiphilic antibacterial surface coatings delay the onset of biofilm formation by killing microbes on contact, but they lose effectiveness over time due to non-specific binding of biomass and biofilm formation. Harsh treatment methods are required to forcibly expel the biomass and regenerate a clean surface. Here, a simple, dynamically reversible method of polymer surface coating that enables both chemical killing on contact, and on-demand mechanical delamination of surface-bound biofilms, by triggered depolymerization of the underlying antimicrobial coating layer, is developed. Antimicrobial polymer derivatives based on α-lipoic acid (LA) undergo dynamic and reversible polymerization into polydisulfides functionalized with biocidal quaternary ammonium salt groups. These coatings kill >99.9% of Staphylococcus aureus cells, repeatedly for 15 cycles without loss of activity, for moderate microbial challenges (≈105 colony-forming units (CFU) mL-1, 1 h), but they ultimately foul under intense challenges (≈107 CFU mL-1, 5 days). The attached biofilms are then exfoliated from the polymer surface by UV-triggered degradation in an aqueous solution at neutral pH. This work provides a simple strategy for antimicrobial coatings that can kill bacteria on contact for extended timescales, followed by triggered biofilm removal under mild conditions.

Architecturally designed sequential-release hydrogels

Drug synergy has made significant strides in clinical applications in recent decades. However, achieving a platform that enables "single administration, multi-stage release" by emulating the natural physiological processes of the human body poses a formidable challenge in the field of molecular pharmaceutics. Hydrogels, as the novel generation of drug delivery systems, have gained widespread utilization in drug platforms owing to their exceptional biocompatibility and modifiability. Sequential drug delivery hydrogels (SDDHs), which amalgamate the advantages of hydrogel and sequential release platforms, offer a promising solution for effectively navigating the intricate human environment and accomplishing drug sequential release. Inspired by architectural design, this review establishes connections between three pivotal factors in SDDHs construction, namely mechanisms, carrier spatial structure, and stimuli-responsiveness, and three aspects of architectural design, specifically building materials, house structures, and intelligent interactive furniture, aiming at providing insights into recent developments in SDDHs. Furthermore, the dual-drug collocation and cutting-edge hydrogel preparation technologies as well as the prevailing challenges in the field were elucidated.

Death at the interface: Nanotechnology’s challenging frontier against microbial surface colonization

The emergence of antimicrobial-resistant bacterial strains has led to novel approaches for combating bacterial infections and surface contamination. More specifically, efforts in combining nanotechnology and biomimetics have led to the development of next-generation antimicrobial/antifouling nanomaterials. While nature-inspired nanoscale topographies are known for minimizing bacterial attachment through surface energy and physicochemical features, few studies have investigated the combined inhibitory effects of such features in combination with chemical alterations of these surfaces. Studies describing surface alterations, such as quaternary ammonium compounds (QACs), have also gained attention due to their broad spectrum of inhibitory activity against bacterial cells. Similarly, antimicrobial peptides (AMPs) have exhibited their capacity to reduce bacterial viability. To maximize the functionality of modified surfaces, the integration of patterned surfaces and functionalized exteriors, achieved through physical and chemical surface alterations, have recently been explored as viable alternatives. Nonetheless, these modifications are prone to challenges that can reduce their efficacy considerably in the long term. Their effectiveness against a wider array of microbial cells is still a subject of investigation. This review article will explore and discuss the emerging trends in biomimetics and other antimicrobials while raising possible concerns about their limitations and discussing future implications regarding their potential combined applications.

Synthesis of Polymer Brushes Via SI-PET-RAFT for Photodynamic Inactivation of Bacteria

Biofilms are a persistent issue in healthcare and industry. Once formed, the eradication of biofilms is challenging as the extracellular polymeric matrix provides protection against harsh environmental conditions and physically enhances resistance to antimicrobials. The fabrication of polymer brush coatings provides a versatile approach to modify the surface to resist the formation of biofilms. Herein, the authors report a facile synthetic route for the preparation of surface-tethered polymeric brushes with antifouling and visible light activated bactericidal properties using surface-initiated photoinduced electron transfer-reversible addition-fragmentation chain transfer polymerization (SI-PET-RAFT). Bactericidal property via the generation of singlet oxygen, which can be temporally and spatially controlled, is investigated against both Gram-positive and Gram-negative bacteria. In addition, the antibacterial properties of the surface can be recycled. This work paves the way for the preparation of polymer films that can resist and kill bacterial biofilms.

Solvent-Free Fabrication of Self-Regenerating Antibacterial Surfaces Resisting Biofilm Formation

Biofilm formation on indwelling medical devices is a major cause of hospital-acquired infections. Monofunctional antibacterial surfaces have been developed to resist the formation of biofilms by killing bacteria on contact, but the adsorption of killed bacterial cells and debris gradually undermines the function of these surfaces. Here, we report a facile approach to produce an antibacterial surface that can regenerate its function after contamination. The self-regenerating surface was achieved by sequential deposition of alternating antibacterial and biodegradable layers of coating using a solvent-free initiated chemical vapor deposition method. As the top antibacterial layer gradually loses its killing ability due to the accumulation of debris, the underlying biodegradable layer degrades, shedding off the top surface layers and exposing another fresh antibacterial surface. Urinary catheters coated with monofunctional and self-regenerating antibacterial coatings both showed more than 99% bacterial killing ability at the initial antibacterial test, but the monofunctional surface lost its killing ability after continued exposure to concentrated bacterial solution, whereas the self-regenerating surfaces regained strong bacterial killing ability after prolonged exposure. Employing poly(methacrylic anhydride) and its copolymers with varied composition as the degrading layer, the degradation kinetics can be well-tailored and the self-regeneration duration spanned from minutes to days. The designed self-regenerating antibacterial surfaces could provide an effective approach to resist biofilm formation and extend the service life of indwelling medical devices.

Antimicrobial surfaces for use on inhabited space craft: A review

Biodegradation of materials on crewed spacecraft can cause disruption, loss of function and lost crew time. Cleaning of surfaces is only partially effective due in accessibility and resource concerns. Commonly affected surfaces are hand-touch sites, waste disposal systems and liquid-handling systems, including condensing heat exchangers. The use of materials on and within such affected systems that reduce the attachment of and degradation by microbes, is an innovative solution to this problem. This review aims to examine both terrestrial and space-based experiments that have aimed to reduce microbial growth which are applicable to the unique conditions of crewed spacecraft. Traditional antimicrobial surfaces such as copper and silver, as well as nanoparticles, long-chain organic molecules and surface topographical features, as well as novel "smart" technologies are discussed. Future missions to cis-lunar and Martian destinations will depend on materials that retain their function and reliability for their success; thus, the use of antimicrobial and antifouling materials is a pivotal one.

Degradable Polymer Films Made from Poly(salicylic-acid-co-sebacic acid) and Poly(sebacic anhydride)/Poly(adipic anhydride) Blends: Degradation Kinetics and Use as Sacrificial Layers for Polymer Multilayer Systems

Two approaches to obtain fast-degrading polymer films based on poly(sebacic anhydride) (PSA) are presented, both of which target polymer films with a lower degree of crystallinity than pure PSA homopolymer: first, thin films were prepared from poly(adipic anhydride)/poly(sebacic anhydride) blends at different ratios, and second, films were made from the copolymer poly(salicylic acid-co-sebacic acid). These films are intended as sacrificial layers for self-regenerating functional coatings, for example to regenerate antimicrobial surface activity. The degradation kinetics of these films were analyzed by surface plasmon resonance spectroscopy (SPR). The results of the blends approach indicate that the blend degradation rate was accelerated only in the initial degradation phase (compared to PSA). The degradation kinetics study of the poly(salicylic-acid-co-sebacic acid) film shows that this copolymer degraded faster than poly(sebacic anhydride) initially, releasing antimicrobial salicylic acid in the process. However, its degradation rate slowed down at a mass loss > 60% and approached the PSA degradation curve at longer degradation times. When tested as sacrificial layer in self-regenerating antimicrobial polymer stacks, it was found that the degradation rate was too low for successful layer shedding.

Biomimetic Self-Renewal Polymer Brushes with Protein Resistance Inspired by Fish Skin

Inspired by fish skin, biomimetic self-renewal poly[(ethylene oxide)-co-(ethylene carbonate)] (PEOC) brushes with protein resistance had been prepared via surface-initiated ring-opening polymerization (ROP). The results of hydrolytic degradation indicated that the PEOC brushes could degrade in artificial seawater. Ellipsometry, X-ray photoelectron spectrometry, and contact angle results demonstrated that the PEOC brushes degrade uniformly. By using a quartz crystal microbalance with dissipation, we studied the protein adsorption on the surfaces in artificial seawater at different degradation times. After 24, 48, 96, and 168 h of degradation, the PEOC surfaces showed nearly zero Δf and ΔD for bovine serum albumin, lysozyme, and fibrinogen. More importantly, there was a notably lower density of microorganisms adhered to the surface modified with PEOC compared with that of the surface without PEOC in natural seawater. The current study showed that the PEOC brushes exhibit a self-renewal property with persistent protein resistance and prevent the adhesion of microorganisms. Such a biomimetic polymer had a great potential in marine antibiofouling.