Facile and Efficient Control of Bioadhesion on Poly(dimethylsiloxane) by Using a Biomimetic Approach

Efficient One-Step Passivation of Polyurethane Using Transurethanization

The uncontrolled accumulation of biological materials on the surface of medical devices through protein adsorption or cell adhesion causes adverse biological reactions in the living host system, leading to complications. In this study, poly(ethylene glycol) (PEG) is successfully grafted onto polyurethane (PU) surfaces by using a new strategy through a simple and efficient transurethanization reaction. The PEG hydroxyl group is deprotonated and then reacted with the PU surface to provide antiadhesive hydrophilic surfaces in a single step. Surface analysis techniques proved the grafting to be efficient and the formation of a hydrophilic polymeric layer at the surface of PU. Biological assays showed that the surface modification induced lower protein adsorption, cell, platelet, and bacterial adhesion than untreated surfaces, showing a potential for biomedical applications.

Combining adhesive and nonadhesive injectable hydrogels for intervertebral disc repair in an ovine discectomy model

Background

Intervertebral disc (IVD) disorders (e.g., herniation) directly contribute to back pain, which is a leading cause of global disability. Next-generation treatments for IVD herniation need advanced preclinical testing to evaluate their ability to repair large defects, prevent reherniation, and limit progressive degeneration. This study tested whether experimental, injectable, and nonbioactive biomaterials could slow IVD degeneration in an ovine discectomy model.

Methods

Ten skeletally mature sheep (4-5.5 years) experienced partial discectomy injury with cruciate-style annulus fibrosus (AF) defects and 0.1 g nucleus pulposus (NP) removal in the L1-L2, L2-L3, and L3-L4 lumbar IVDs. L4-L5 IVDs were Intact controls. IVD injury levels received: (1) no treatment (Injury), (2) poly (ethylene glycol) diacrylate (PEGDA), (3) genipin-crosslinked fibrin (FibGen), (4) carboxymethylcellulose-methylcellulose (C-MC), or (5) C-MC and FibGen (FibGen + C-MC). Animals healed for 12 weeks, then IVDs were assessed using computed tomography (CT), magnetic resonance (MR) imaging, and histopathology.

Results

All repaired IVDs retained ~90% of their preoperative disc height and showed minor degenerative changes by Pfirrmann grading. All repairs had similar disc height loss and Pfirrmann grade as Injury IVDs. Adhesive AF sealants (i.e., PEGDA and FibGen) did not herniate, although repair caused local endplate (EP) changes and inflammation. NP repair biomaterials (i.e., C-MC) and combination repair (i.e., FibGen + C-MC) exhibited lower levels of degeneration, less EP damage, and less severe inflammation; however, C-MC showed signs of herniation via biomaterial expulsion.

Conclusions

All repair IVDs were noninferior to Injury IVDs by IVD height loss and Pfirrmann grade. C-MC and FibGen + C-MC IVDs had the best outcomes, and may be appropriate for enhancement with bioactive factors (e.g., cells, growth factors, and miRNAs). Such bioactive factors appear to be necessary to prevent injury-induced IVD degeneration. Application of AF sealants alone (i.e., PEGDA and FibGen) resulted in EP damage and inflammation, particularly for PEGDA IVDs, suggesting further material refinements are needed.

Microbial growth and adhesion of Escherichia coli in elastomeric silicone foams with commonly used additives

Silicone is often used in environments where water repellency is an advantage. Contact with water promotes the adhesion of microorganisms and biofilm formation. Depending on the application, this may increase the possibility of food poisoning and infections, the material's degrading appearance, and the likelihood of manufacturing defects. The prevention of microbial adhesion and biofilm formation is also essential for silicone-based elastomeric foams, which are used in direct contact with human bodies but are often difficult to clean. In this study, the microbial attachment in and the retention from the pores of silicone foams of different compositions is described and compared to those of commonly used polyurethane foams. The growth of the gram-negative Escherichia coli in the pores and their leaching during wash cycles is characterised by bacterial growth/inhibition, adhesion assay, and SEM imaging. The structural and surface properties of the materials are compared. Despite using common antibacterial additives, we have found that non-soluble particles stay isolated in the silicone elastomer layer, thus affecting surface microroughness. Water-soluble tannic acid dissolves into the medium and seems to aid in inhibiting planktonic bacterial growth, with a clear indication of the availability of tannic acid on the surfaces of SIFs.

Layer-by-layer construction of zwitterionic/biguanide polymers on silicone rubber as antifouling/bactericidal coating

Biofilm formation on biomedical devices is the major cause of devices associated infections. Traditional antibiotics treatments on biofilm associated infections is increasing the risk of multidrug resistance. Thus, developing antibiotics-free...

Self-Limiting Mussel Inspired Thin Antifouling Coating with Broad-Spectrum Resistance to Biofilm Formation to Prevent Catheter-Associated Infection in Mouse and Porcine Models

Catheter-associated urinary tract infections (CAUTIs) are one of the most commonly occurring hospital-acquired infections. Current coating strategies to prevent catheter-associated biofilm formation are limited by their poor long-term efficiency and limited applicability to diverse materials. Here, the authors report a highly effective non-fouling coating with long-term biofilm prevention activity and is applicable to diverse catheters. The thin coating is lubricous, stable, highly uniform, and shows broad spectrum prevention of biofilm formation of nine different bacterial strains and prevents the migration of bacteria on catheter surface. The coating method is adapted to human-sized catheters (both intraluminal and extraluminal) and demonstrates long-term biofilm prevention activity over 30 days in challenging conditions. The coated catheters are tested in a mouse CAUTI model and demonstrate high efficiency in preventing bacterial colonization of both Gram-positive and Gram-negative bacteria. Furthermore, the coated human-sized Foley catheters are evaluated in a porcine CAUTI model and show consistent efficiency in reducing biofilm formation by Escherichia coli (E. coli) over 95%. The simplicity of the coating method, the ability to apply this coating on diverse materials, and the high efficiency in preventing bacterial adhesion increase the potential of this method for the development of next generation infection resistant medical devices.

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.

Co-Networks Poly(hydroxyalkanoates)-Terpenes to Enhance Antibacterial Properties

Biocompatible and biodegradable bacterial polyesters, poly(hydroxyalkanoates) (PHAs), were combined with linalool, a well-known monoterpene, extracted from spice plants to design novel antibacterial materials. Their chemical association by a photo-induced thiol-ene reaction provided materials having both high mechanical resistance and flexibility. The influence of the nature of the crosslinking agent and the weight ratio of linalool on the thermo-mechanical performances were carefully evaluated. The elongation at break increases from 7% for the native PHA to 40% for PHA-linalool co-networks using a tetrafunctional cross-linking agent. The materials highlighted tremendous anti-adherence properties against Escherichia coli and Staphylococcus aureus by increasing linalool ratios. A significant decrease in antibacterial adhesion of 63% and 82% was observed for E. coli and S. aureus, respectively.

Microtopographies control the development of basal protrusions in epithelial sheets

Cells are able to develop various types of membrane protrusions that modulate their adhesive, migratory, or functional properties. However, their ability to form basal protrusions, particularly in the context of epithelial sheets, is not widely characterized. The authors built hexagonal lattices to probe systematically the microtopography-induced formation of epithelial cell protrusions. Lattices of hexagons of various sizes (from 1.5 to 19 μm) and 5-10 μm height were generated by two-photon photopolymerization in NOA61 or poly(ethylene glycol) diacrylate derivatives. The authors found that cells generated numerous, extensive, and deep basal protrusions for hexagons inferior to cell size (3-10 μm) while maintaining a continuous epithelial layer above structures. They characterized the kinetics of protrusion formation depending on scaffold geometry and size. The reported formation of extensive protrusions in 3D microtopography could be beneficial to develop new biomaterials with increased adhesive properties or to improve tissue engineering.

Surface modification strategies for combating catheter-related complications: recent advances and challenges

This review summarizes the progress made in addressing bacterial colonization and other surface-related complications arising from catheter use.

Making Silicone Rubber Highly Resistant to Bacterial Attachment Using Thiol-ene Grafting

Biomedical devices are indispensable in modern medicine yet offer surfaces that promote bacterial attachment and biofilm formation, resulting in acute and chronic healthcare-associated infections. We have developed a simple method to graft acrylates to silicone rubber, polydimethylsiloxane (PDMS), a commonly used device material that is often colonized by bacteria. We demonstrate a novel method whereby nontoxic bacteria attachment-resistant polymers can be readily grafted from and grafted to the surface using thiol-ene chemistry, substantially reducing bacterial colonization. With use of this approach, bacterial biofilm coverage can be reduced by 99% compared with standard PDMS in an in vitro assay. This grafting approach offers significant advantages over commonly used physisorbed coatings, especially in areas of high shear or mechanical stress. Furthermore, the approach is versatile such that the grafted material properties can be tailored for the desired final application.

Self-Healing Superhydrophobic Fluoropolymer Brushes as Highly Protein-Repellent Coatings

Superhydrophobic surfaces with micro/nanostructures are widely used to prevent nonspecific adsorption of commercial polymeric and/or biological materials. Herein, a self-healing superhydrophobic and highly protein-repellent fluoropolymer brush was grafted onto nanostructured silicon by surface-initiated atom transfer radical polymerization (ATRP). Both the superhydrophobicity and antifouling properties (as indicated for isolated protein solutions and for 10% blood plasma) are well repaired upon serious chemical degradation (by e.g. air plasma). This brush still maintains excellent superhydrophobicity and good antifouling properties even after 5 damage-repair cycles, which opens a new door to fabricate long-term antifouling coatings on various substrates that can be used in harsh environments.

Modulation of Protein Fouling and Interfacial Properties at Carbon Surfaces via Immobilization of Glycans Using Aryldiazonium Chemistry

Carbon materials and nanomaterials are of great interest for biological applications such as implantable devices and nanoparticle vectors, however, to realize their potential it is critical to control formation and composition of the protein corona in biological media. In this work, protein adsorption studies were carried out at carbon surfaces functionalized with aryldiazonium layers bearing mono- and di-saccharide glycosides. Surface IR reflectance absorption spectroscopy and quartz crystal microbalance were used to study adsorption of albumin, lysozyme and fibrinogen. Protein adsorption was found to decrease by 30–90% with respect to bare carbon surfaces; notably, enhanced rejection was observed in the case of the tested di-saccharide vs. simple mono-saccharides for near-physiological protein concentration values. ζ-potential measurements revealed that aryldiazonium chemistry results in the immobilization of phenylglycosides without a change in surface charge density, which is known to be important for protein adsorption. Multisolvent contact angle measurements were used to calculate surface free energy and acid-base polar components of bare and modified surfaces based on the van Oss-Chaudhury-Good model: results indicate that protein resistance in these phenylglycoside layers correlates positively with wetting behavior and Lewis basicity.

Design of cytocompatible bacteria-repellent bio-based polyester films via an aqueous photoactivated process

The design of cytocompatible bacteria-repellent bio-based polyester surfaces in aqueous media.

Bottom-Up Fabrication of PEG Brush on Poly(dimethylsiloxane) for Antifouling Surface Construction

Poly(dimethylsiloxane) silicones have found many applications in biomedical devices, whereas their surface hydrophobicity always brings about unexpected bioadhesion, causing complications of the implanted biomedical devices. In this work, surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization was utilized to generate PEG brushes on silicone surface, obtaining highly hydrophilic surface coatings. Such PEG brush coated silicone presents excellent antifouling to protein, cells, and bacteria, which may have great potential in implantable biomaterial surface modifications.

Toward the development of a versatile functionalized silicone coating

The development of a versatile silicone copolymer coating prepared by the chemical coupling of trichlorosilane (TCS) to the vinyl groups of poly(vinylmethylsiloxane) (PVMS) is reported. The resultant PVMS-TCS copolymer can be deposited as a functional organic layer on a hydrophobic poly(dimethylsiloxane) substrate and its mechanical modulus can be regulated by varying the TCS coupling ratio. In this paper, several case studies demonstrating the versatile properties of these PVMS-TCS functional coatings on PDMS elastomer substrates are presented. Numerous experimental probes, including optical microscopy, Fourier-transform infrared spectroscopy, surface contact angle, ellipsometry, and nanoindentation, are utilized to interrogate the physical and chemical characteristics of these PVMS-TCS coatings.

Support for the initial attachment, growth and differentiation of MG-63 cells: a comparison between nano-size hydroxyapatite and micro-size hydroxyapatite in composites

Hydroxyapatite (HA) is considered to be a bioactive material that favorably influences the adhesion, growth, and osteogenic differentiation of osteoblasts. To optimize the cell response on the hydroxyapatite composite, it is desirable to assess the optimum concentration and also the optimum particle size. The aim of our study was to prepare composite materials made of polydimethylsiloxane, polyamide, and nano-sized (N) or micro-sized (M) HA, with an HA content of 0%, 2%, 5%, 10%, 15%, 20%, 25% (v/v) (referred to as N0–N25 or M0–M25), and to evaluate them in vitro in cultures with human osteoblast-like MG-63 cells. For clinical applications, fast osseointegration of the implant into the bone is essential. We observed the greatest initial cell adhesion on composites M10 and N5. Nano-sized HA supported cell growth, especially during the first 3 days of culture. On composites with micro-size HA (2%–15%), MG-63 cells reached the highest densities on day 7. Samples M20 and M25, however, were toxic for MG-63 cells, although these composites supported the production of osteocalcin in these cells. On N2, a higher concentration of osteopontin was found in MG-63 cells. For biomedical applications, the concentration range of 5%–15% (v/v) nano-size or micro-size HA seems to be optimum.

Chemical force microscopy of stimuli-responsive adhesive copolymers

Atomic force microscopy with chemically sensitive tips was used to investigate the hydrophobic and electrostatic interaction forces of a stimuli-responsive adhesive polymer, and their dynamic changes in response to water immersion and salt concentration. Block copolymer-filled coatings were obtained by incorporating an amphiphilic block copolymer containing a polydimethylsiloxane (PDMS) block and a poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) block in a PDMS matrix. Topographic images of fresh samples revealed the presence of nanoscale domains associated with the presence of copolymers, covered by a thin layer of PDMS. Prolonged (30 days) immersion in aqueous solution led to the exposure of the hydrophilic PDMAEMA chains on the surface. Using adhesion force mapping with hydrophobic tips, we showed that fresh samples were uniformly hydrophobic, while aged samples exhibited lower surface hydrophobicity and featured nanoscale hydrophilic copolymer domains. Force mapping with negatively charged tips revealed remarkable salt-dependent force plateau signatures reflecting desorption of polyelectrolyte copolymer chains. These nanoscale experiments show how solvent-induced conformational changes of stimuli-responsive copolymers can be used to modulate surface adhesion.