Polymerizable peptide copolymer coatings for the control of biointerfacial interactions.

The effective control over biointerfacial interactions is essential for a broad range of biomedical applications in vitro and in vivo such as biosensors, cell culture tools and implantable devices. Here, our aim was to develop a coating strategy that is transferable between different substrate materials and can effectively suppress nonspecific protein adsorption and hence reduce cell attachment while also presenting bioactive signals to enable specific cell-material interactions. In a first step an allylamine plasma polymer coating was applied, followed by the covalent immobilization of a macroinitiator carrying iniferter functionalities in the side chains. Subsequently, copolymers with different molar ratios of acrylamide and a polymerizable peptide containing the sequence Arg-Gly-Asp (RGD) were grafted via surface initiated free radical polymerization. X-ray photoelectron spectroscopy (XPS) was used to confirm the success of each coating step. The cellular response to these coatings was evaluated using L929 mouse fibroblast cell culture assays for up to 24 h. Cell attachment was significantly reduced on acrylamide homopolymer coatings and negative control surfaces representing a polymerizable peptide containing the nonbioactive Arg-Ala-Asp (RAD) sequence. In contrast, cell attachment was increased with increasing polymerizable RGD peptide ratios in the copolymer. The combination of acrylamide-terminated peptide sequences in combination with acrylamide provides a simple and versatile route to surfaces that combine low nonspecific protein adsorption and the display of controlled densities of bioactive signals and is expected to be translated into a number of biomedical applications in vitro and in vivo.

Inhibition of protein and cell attachment on materials generated from N-(2-hydroxypropyl) acrylamide.

Effective control over biointerfacial interactions is essential for a broad range of biomedical applications. At this point in time, only a relatively small range of radically polymerizable monomers have been described that are able to generate low fouling polymer materials and surfaces. The most important examples that have been successfully used in the context of the reduction of nonspecific protein adsorption and subsequent cell attachment include PEG-based monomers such as poly(ethylene glycol) methacrylate (PEGMA), zwitterionic monomers such as 2-methacryloyloxyethyl phosphorylcholine and noncharged monomers such as acrylamide and N-(2-hydroxypropyl) methacrylamide (HPMAm). However, issues such as oxidative degradation and poor polymerization characteristics limit the applicability of most of these candidates. Here we have synthesized the monomer N-(2-hydroxypropyl) acrylamide (HPAm), examined its polymerization kinetics and evaluated its suitability for RAFT mediated polymerization in comparison to HPMAm. We also synthesized hydrogels using HPMAm and HPAm and evaluated the ability of HPAm polymers to occlude protein adsorption and cell attachment. In RAFT-controlled polymerization, much faster (8×) polymerization was observed for HPAm relative to HPMAm and better control was achieved over the molecular weight distribution. The performance of hydrogels prepared from HPAm in the prevention of protein adsorption and cellular attachment was equivalent to or better than that observed for materials made from HPMAm and PEG. These results open the door for HPAm based polymers in applications where effective control over biointerfacial interactions is required.

Synergistic Polymer Coatings with Antibacterial and Antiviral Properties for Healthcare Applications.

The role of frequently touched surfaces in the transmission of infectious diseases is well-documented, and the urgent need for effective surface technologies with antipathogen activity has been highlighted by the recent global pandemic and rise in antimicrobial resistance. Here, we have explored combinations of up to 3 different classes of compounds within a polymeric matrix to enable the fabrication of coatings with broad-spectrum activity. Compounds were either based on metals or metal oxides, namely, copper, silver, and copper oxide, essential oils, namely, cinnamaldehyde, tea tree oil, and carvacrol oil, or cationic polymers, namely, poly(ε-lysine) and poly(hexamethylene biguanide). These compounds were mixed into a polymer matrix, coated, and dried to yield durable coatings. Coatings containing up to 7.5% (w/w) of the compounds were assessed in the zone of inhibition and biofilm assays using Staphylococcus aureus and Pseudomonas aeruginosa, as well as infectivity assays using human coronavirus OC43. Our data demonstrate that a selected combination of additives was able to provide a 5-log reduction in the colony-forming units of both bacteria and a 4-log reduction in viral infectivity. This simple but highly effective technology is expected to find applications in environments such as hospitals, aged care facilities, or public transport.

A surface-independent bioglue using photo-crosslinkable benzophenone moiety.

Surface coating technology is broadly demanded across various fields, including marine and biomedical materials; therefore, a facile and versatile approach is desired. This study proposed an attractive surface coating strategy using photo-crosslinkable benzophenone (BP) moiety for biomaterials application. BP-containing "bioglue" polymer can effectively crosslink with all kinds of surfaces and biomolecules. Upon exposure to ultraviolet (UV) light, free radical reaction from the BP glue facilitates the immobilization of diverse molecules onto different substrates in a straightforward and user-friendly manner. Through either one-step, mixing the bioglue with targeted biomolecules, or two-step methods, pre-coating the bioglue and then adding targeted biomolecules, polyacrylic acid (PAA), cyclic RGD-containing peptides, and proteins (gelatin, collagen, and fibronectin) were successfully immobilized on substrates. After drying the bioglue, targeted biomolecules can still be immobilized on the surfaces preserving their bioactivity. Cell culture on biomolecule-immobilized surfaces using NIH 3T3 fibroblasts and human bone marrow stem cells (hBMSCs) showed significant improvement of cell adhesion and activity compared to the unmodified control in serum-free media after 24 hours. Furthermore, hBMSCs on the fibronectin-immobilized surface showed an increased calcium deposition after 21 days of osteogenic differentiation, suggesting that the immobilized fibronectin is highly bioactive. Given the straightforward protocol and substrate-independent bioglue, the proposed coating strategy is promising in broad-range fields.

Advances in Design and Development of Lumi-Solve: A Novel Drug-Eluting Photo-Angioplasty Device.

PURPOSE: The Lumi-Solve photo-angioplasty drug eluting balloon catheter (DEBc) may afford safety advantages over current DEBc. Lumi-Solve utilises the guidewire (GW) port and lumen to deliver fibre-optic UV365nm light to the angioplasty balloon which may be problematic. We explore and evaluate alternative Lumi-Solve design options to circumvent fibre-optic use of the GW port and lumen which may enhance efficacy and clinical utility. METHODS: Effects of guidewire shadowing (GWS) on visible and UV365nm light transmission were evaluated and modelled in-silico. To evaluate the effect of a dedicated intra-balloon fibre-optic port, modified angioplasty balloons and sections of translucent polyethylene terephthalate (PET) GW port tubing were utilised. Investigation of the effect of GWS on chemical and biological photo-activation of balloon surface drug was performed utilising LCMS analysis and inhibition of histone deacetylase activity (HDACi) was measured in human umbilical vein endothelial cells (HUVEC). RESULTS: Parallel fibre-optic and GW port configurations generated a GWS of approximately 18.0% of the evaluable balloon surface area and attenuated both visible and UV light intensity by 20.0-25.0% and reduced chemical photo-activation of balloon surface drug and HDACi by at least 40-45%. Alternative fibre-optic port configurations including a spiral design significantly mitigated GWS effects on UV light transmission. CONCLUSIONS: To avoid use of the GW port and its associated complications a dedicated third port and lumen for the Lumi-Solve fibre-optic may be required. To maximize balloon surface chemical and biological photo-activation, non-parallel, intra-balloon, fibre-optic lumen trajectories, including a spiral design may be useful.

Design, Development, In Vitro and Preliminary In Vivo Evaluation of a Novel Photo-Angioplasty Device: Lumi-Solve.

PURPOSE: Paclitaxel (PTX)-coated drug eluting balloon catheters (DEBc) used in the management of neointimal hyperplasia (NIH) have been associated with safety concerns. Alternative coating agents and targeted delivery systems may improve safety and DEBc efficacy. Utilizing a multi-platform approach we designed, developed and evaluated Lumi-Solve, a novel DEBc, coated with ultraviolet (UV) 365 nm-activated caged metacept-3 (c-MCT-3), an epigenetic agent from the histone deacetylase inhibitor (HDACi) class. METHODS: In vitro catheter and contrast media transmission of UV365nm was evaluated spectroscopically. UV365nm conversion of c-MCT-3 to MCT-3 was evaluated chromatographically. Cellular toxicity and HDACi activity of c-MCT-3 ∓UV365nm was evaluated in vitro. In vivo UV365nm conversion of c-MCT-3 to MCT-3 was evaluated in an ovine carotid artery model. RESULTS: Catheter material and dilute contrast media did not attenuate UV365nm transmission or c-MCT-3 activation. c-MCT-3 demonstrated less cellular toxicity than MCT-3 and PTX. UV365nm-activated c-MCT-3 demonstrated HDACi activity. In vivo activation of c-MCT-3 produced MCT-3. CONCLUSIONS: Lumi-Solve, a novel DEBc device developed utilizing a combination of chemical, fibre-optic and catheter based technology platforms, demonstrated potential for targeted delivery of bioactive HDACi to the blood vessel wall supporting direct application to the management of NIH and warranting additional in vivo studies.

Cell microarrays for the screening of factors that allow the enrichment of bovine testicular cells.

Cell microarrays can serve as high-throughput platforms for the screening of a diverse range of biologically active factors and biomaterials that can induce desired cellular responses such as attachment, proliferation, or differentiation. Here, we demonstrate that surface-engineered microarrays can be used for the screening and identification of factors that allow the enrichment and isolation of rare cells from tissue-derived heterogeneous cell populations. In particular, we have focused on the enrichment of bovine testicular cells including type A spermatogonia and Sertoli cells. Microarray slides were coated with a copolymer synthesized from poly(ethylene glycol) methacrylate and glycidyl methacrylate to enable both the prevention of cell attachment between printed spots and the covalent anchoring of various factors such as antibodies, lectins, growth factors, extracellular matrix proteins, and synthetic macromolecules on printed spots. Microarrays were incubated with mixed cell populations from freshly isolated bovine testicular tissue. Overall, cell attachment was evaluated using CellTracker staining, whereas differential attachment of testicular cells was determined by immunohistochemistry staining with Plzf and vimentin antibodies as markers for type A spermatogonia and Sertoli cells, respectively. The results indicate that various surface immobilized factors, but in particular Dolichos biflorus lectin, allowed the enrichment of Plzf positive cells. Furthermore, Pisum sativum lectin, concanavalin A, collagen type IV, and vitronectin were identified as suitable negative selection factors. To our best knowledge, this work is the first to demonstrate the utility of surface engineered cell-based microarrays for the identification of factors that allow the selective capture of rare cells from tissue isolated heterogeneous mixtures.

Evaluation of the Novel Antimicrobial BCP3 in a Coating for Endotracheal Tubes.

Ventilator-associated pneumonia (VAP) is a highly common hospital-acquired infection affecting people that require mechanical ventilation. The endotracheal tube (ETT) used during the ventilation process provides a surface that can allow bacterial colonization and biofilm formation, which can lead to VAP. Although various approaches, including ETT design and material selection, as well as antimicrobial coatings have been employed to minimize adverse events, VAP remains a significant unresolved clinical issue. In this study, we have utilized a novel styrylbenzene-based antimicrobial (BCP3) in a simple and robust coating that allows its long-term release at an effective level. BCP3 was applied onto PVC ETT segments blended together with poly(lactic-co-glycolic acid) via a facile dip-coating process with controlled loadings. In vitro studies demonstrated concentration-dependent release of BCP3 from the coatings for at least 31 days. Bacterial assays using major VAP culprits, Staphylococcus aureus and Pseudomonas aeruginosa, demonstrated significant growth inhibition, with a stronger effect on S. aureus. Despite its ability to inhibit bacterial growth, BCP3 showed no cytotoxicity toward mammalian (L929) fibroblasts, which makes it attractive from a clinical perspective. The coating procedure was successfully translated to coat the entire ETTs, making it highly amenable for large-scale manufacturing.

In Situ Surface Modification of Microfluidic Blood-Brain-Barriers for Improved Screening of Small Molecules and Nanoparticles.

Here, we have developed and evaluated a microfluidic-based human blood-brain-barrier (µBBB) platform that models and predicts brain tissue uptake of small molecule drugs and nanoparticles (NPs) targeting the central nervous system. By using a photocrosslinkable copolymer that was prepared from monomers containing benzophenone and N-hydroxysuccinimide ester functional groups, we were able to evenly coat and functionalize µBBB chip channels in situ, providing a covalently attached homogenous layer of extracellular matrix proteins. This novel approach allowed the coculture of human endothelial cells, pericytes, and astrocytes and resulted in the formation of a mimic of cerebral endothelium expressing tight junction markers and efflux proteins, resembling the native BBB. The permeability coefficients of a number of compounds, including caffeine, nitrofurantoin, dextran, sucrose, glucose, and alanine, were measured on our µBBB platform and were found to agree with reported values. In addition, we successfully visualized the receptor-mediated uptake and transcytosis of transferrin-functionalized NPs. The BBB-penetrating NPs were able to target glioma cells cultured in 3D in the brain compartment of our µBBB. In conclusion, our µBBB was able to accurately predict the BBB permeability of both small molecule pharmaceuticals and nanovectors and allowed time-resolved visualization of transcytosis. Our versatile chip design accommodates different brain disease models and is expected to be exploited in further BBB studies, aiming at replacing animal experiments.

Spatially Controlled Surface Modification of Porous Silicon for Sustained Drug Delivery Applications.

A new and facile approach to selectively functionalize the internal and external surfaces of porous silicon (pSi) for drug delivery applications is reported. To provide a surface that is suitable for sustained drug release of the hydrophobic cancer chemotherapy drug camptothecin (CPT), the internal surfaces of pSi films were first modified with 1-dodecene. To further modify the external surface of the pSi samples, an interlayer was applied by silanization with (3-aminopropyl)triethoxysilane (APTES) following air plasma treatment. In addition, copolymers of N-(2-hydroxypropyl) acrylamide (HPAm) and N-benzophenone acrylamide (BPAm) were grafted onto the external pSi surfaces by spin-coating and UV crosslinking. Each modification step was verified using attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, water contact angle (WCA) measurements, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). In order to confirm that the air plasma treatment and silanization step only occurred on the top surface of pSi samples, confocal microscopy was employed after fluorescein isothiocyanate (FITC) conjugation. Drug release studies carried out over 17 h in PBS demonstrated that the modified pSi reservoirs released CPT continuously, while showing excellent stability. Furthermore, protein adsorption and cell attachment studies demonstrated the ability of the graft polymer layer to reduce both significantly. In combination with the biocompatible pSi substrate material, the facile modification strategy described in this study provides access to new multifunctional drug delivery systems (DDS) for applications in cancer therapy.

Replication of a Tissue Microenvironment by Thermal Scanning Probe Lithography.

Thermal scanning probe lithography (t-SPL) is a nanofabrication technique in which an immobilized thermolabile resist, such as polyphthalaldehyde (PPA), is locally vaporized by a heated atomic force microscope tip. Compared with other nanofabrication techniques, such as soft lithography and nanoimprinting lithography, t-SPL is more efficient and convenient as it does not involve time-consuming mask productions or complicated etching procedures, making it a promising candidate technique for the fast prototyping of nanoscale topographies for biological studies. Here, we established the direct use of PPA-coated surfaces as a cell culture substrate. We showed that PPA is biocompatible and that the deposition of allylamine by plasma polymerization on a silicon wafer before PPA coating can stabilize the immobilization of PPA in aqueous solutions. When seeded on PPA-coated surfaces, human mesenchymal stem cells (MSC) adhered, spread, and proliferated in a manner indistinguishable from cells cultured on glass surfaces. This allowed us to subsequently use t-SPL to generate nanotopographies for cell culture experiments. As a proof of concept, we analyzed the surface topography of bovine tendon sections, previously shown to induce morphogenesis and differentiation of MSC, by means of atomic force microscopy, and then "wrote" topographical data on PPA by means of t-SPL. The resulting substrate, matching the native tissue topography on the nanoscale, was directly used for MSC culture. The t-SPL substrate induced similar changes in cell morphology and focal adhesion formation in the MSC compared to native tendon sections, suggesting that t-SPL can rapidly generate cell culture substrates with complex and spatially accurate topographical signals. This technique may greatly accelerate the prototyping of models for the study of cell-matrix interactions.

The in vivo performance of an enzyme-assisted self-assembled peptide/protein hydrogel.

We demonstrate the distribution of the important extracellular matrix protein laminin in a novel biomaterial consisting of a hydrogel underpinned by nanofibrillar networks. These are formed by the immobilised enzyme mediated self-assembly of fmoc-L(3) (9-fluorenylmethoxycarbonyl-tri-leucine). The peptide assembly yields nanofibrils formed of ß-sheets that are locked together via π-stacking interactions. This ordering allows the localisation of the peptide sidechains on the surface, creating a hydrophobic environment. This induces the formation of bundles of these nanofibrils producing a clear hydrogel. This mechanism enables the three dimensional distribution of laminin throughout the network via supramolecular interactions. These forces favour the formation and improve the order of the network itself, as observed by spectroscopic and mechanical testing. In order to test the stability and suitability of this class of material for in vivo applications, we utilise microinjection to deliver the biomaterial under fine spatial control into a dystrophic zebrafish model organism, which lacks laminin as a result of a genetic mutation. Using confocal and transmission electron microscopy, we confirm that the biomaterial remains stable structurally, and is confined spatially to the site of injection.