Jeffrey L. Dalsin

Bioinspired antifouling polymers

Controlling biointerfacial phenomena is crucial to the success of many biomedical technologies. For applications in biosensing, diagnostics, and medical devices, precise control of interactions between material surfaces and the biological milieu is an important but elusive goal 1 . Emerging strategies for manipulating the biological response to medical materials seek to take advantage of specific interactions between designed surfaces, biomolecules, and cells 2 . Limiting nonspecific interaction of cells, proteins, and microorganisms with material surfaces is critical, since these interactions can prove highly problematic for device efficacy and safety. Thus, a central research focus continues to be the development of versatile, convenient, and cost-effective strategies for rendering surfaces resistant to fouling by proteins, cells, and bacteria.

Algal antifouling and fouling-release properties of metal surfaces coated with a polymer inspired by marine mussels.

Abstract The marine antifouling and fouling-release performance of titanium surfaces coated with a bio-inspired polymer was investigated. The polymer consisted of methoxy-terminated poly(ethylene glycol) (mPEG) conjugated to the adhesive amino acid l-3,4-dihydroxyphenylalanine (DOPA) and was chosen based on its successful resistance to protein and mammalian cell fouling. Biofouling assays for the settlement and release of the diatom Navicula perminuta and settlement, growth and release of zoospores and sporelings (young plants) of the green alga Ulva linza were carried out. Results were compared to glass, a poly(dimethylsiloxane) elastomer (Silastic T2) and uncoated Ti. The mPEG-DOPA3 modified Ti surfaces exhibited a substantial decrease in attachment of both cells of N. perminuta and zoospores of U. linza as well as the highest detachment of attached cells under flow compared to control surfaces. The superior performance of this polymer over a standard silicone fouling-release coating in diatom assays and approximately equivalent performance in zoospore assays suggests that this bio-inspired polymer may be effective in marine antifouling and fouling-release applications.

A novel low-friction surface for biomedical applications: Modification of poly(dimethylsiloxane) (PDMS) with polyethylene glycol(PEG)-DOPA-lysine

Aqueous biocompatible tribosystems are desirable for a variety of tissue-contacting medical devices. L-3,4-dihydroxyphenylalanine (DOPA) and lysine (K) peptide mimics of mussel adhesive proteins strongly interact with surfaces and may be useful for surface attachment of lubricating polymers in tribosystems. Here, we describe a significant improvement in lubrication properties of poly (dimethylsiloxane) (PDMS) surfaces when modified with PEG-DOPA-K. Surfaces were characterized by optical and atomic force microscopy, contact angle, PM-IRRAS, and X-ray photoelectron spectroscopy. Such surfaces, tested over the course of 200 rotations ( approximately 8 m in length), maintained an extremely low friction coefficient (mu) (0.03 +/- 0.00) compared to bare PDMS (0.98 +/- 0.02). These results indicate the potential applications of PEG-DOPA-K for the modification of device surfaces. Extremely low mu values were maintained over relatively long length scales and a range of sliding speeds without the need for substrate pre-activation and in the absence of excess polymer in aqueous solution. These results were only obtained when DOPA was bound to lysine (modification with PEG-DOPA did not have an effect on mu) suggesting the critical role of lysine in obtaining a lowered friction coefficient.

Biomimetic Adhesive Polymers Based on Mussel Adhesive Proteins

Nature provides many outstanding examples of adhesive strategies from which chemists and material scientists can draw inspiration in their pursuit of new adhesive materials. As described in other chapters of this book, detailed studies of the adhesive mechanisms of geckos, mussels and other organisms during the past several decades have enhanced our understanding of the underlying physicochemical principles to the extent that direct translation of this knowledge into biomimetic strategies for synthesizing new practical adhesives is now possible. Although new biomimetic adhesives have the potential for impact in many areas of technology, one of the more compelling outlets for these materials is in healthcare delivery, which will be the focus of this chapter. Obvious parallels exist between the marine and human physiologic environment, and a strategy that works well in one context may be useful in the other. Efforts to develop biomimetic adhesives are most effective when guided by detailed understanding of the key features and mechanisms of natural adhesives. A simple example of this is given by recent mimicry of gecko adhesive in photolithographically micropatterned polymers (Geim et al. 2003), an approach made possible by earlier studies elaborating the fine morphological detail and adhesive force of individual gecko foot setae (Autumn et al. 2000). In the case of secreted adhesives such as those employed by marine organisms, biomimetic efforts are only possible when there is basic understanding of the key macromolecular components and their compositions. In the case of barnacle adhesives only limited information is known about the adhesive mechanism and component proteins (Naldrett and Kaplan 1997; Kamino et al. 2000; Kamino 2001), providing little guidance to biomimetic efforts. Such is not the case with mussel adhesive proteins (MAPs), which have been extensively studied and the subject of numerous biomimetic efforts. We begin with a brief review of the unique chemical features of MAPs, a subject that is discussed in greater detail in a recent review (Waite et al. 2005) and in Chap. 7 of the present volume. Several 13 Biomimetic Adhesive Polymers Based on Mussel Adhesive Proteins

Anti-Adhesive Coating and Clearance of Device Associated Uropathogenic Escherichia coli Cystitis

PURPOSE A previous study showed decreased uropathogen adherence using a novel anti-fouling coating consisting of mussel adhesive protein mimics conjugated to poly(ethylene glycol). We assessed the ability of methoxy polyethylene glycol-dihydroxyphenylalanine (Nerites Corp. Ltd., Madison, Wisconsin) coated ureteral stents to resist bacterial adherence, infection development and encrustation in a rabbit model of uropathogenic Escherichia coli cystitis. MATERIALS AND METHODS Sof-Flex stent curls that were uncoated and coated with 3 coatings, including Surphys 002, 008 and 009, respectively, and uncoated Percuflex Plus stents were inserted transurethrally into the bladder of 50 male New Zealand White rabbits (Charles River Laboratories, Montreal, Quebec, Canada), followed by instillation of uropathogenic E. coli strain GR12 (10(7) cfu). Urine was examined for bacteria on days 0, 1, 3 and 7, and for cytokine levels on day 7. On day 7 the animals were sacrificed. Stent curls and bladders were harvested for analysis. In a parallel experiment stents were challenged in vitro for 7 days with GR12 in human urine. RESULTS Surphys 009 coated devices showed decreased urine and stent bacterial counts compared to those in controls. Eight of 10 rabbits in the Surphys 009 group had sterile urine by day 3 vs 1 in each control group (p = 0.013), while stent adherent organisms were decreased by more than 75%. While no statistical differences were found in encrustation and bladder inflammation across the groups, immune scoring was lowest in the uncoated Sof-Flex control and Surphys 009 groups (p = 0.030). CONCLUSIONS Surphys 009 strongly resisted bacterial attachment, resulting in improved infection clearance over that of uncoated devices. However, this did not translate to decreased encrustation, which appeared to be independent of infection in this model.

First Prize: Novel Uropathogen-Resistant Coatings Inspired by Marine Mussels

BACKGROUND AND PURPOSE Success in the prevention of urinary device infections has been elusive, largely due to multiple bacterial attachment strategies and the development of urinary conditioning films. We investigated a novel anti-fouling coating consisting of mussel adhesive protein mimics conjugated to polyethylene glycol (mPEG-DOPA(3)) for its potential to resist conditioning film formation and uropathogen attachment in human urine. METHODS Model TiO(2) -coated silicon disks ( approximately 75 mm(2)) were either coated with mPEG-DOPA(3) or left uncoated and sterilized using ethylene oxide gas. For bacterial attachment experiments, coated and uncoated surfaces were separately challenged with bacterial strains comprising six major uropathogenic species for 24 hours at 37 degrees C in human pooled urine. Starting inoculum for each strain was 10(5) CFU/mL and 0.5 mL was used per disk. Following incubation, the disks were thoroughly rinsed in phosphate buffered saline to remove non-adherent and weakly-adherent organisms and cell scrapers were employed to dislodge those that were firmly attached. Adherent bacteria were quantitated using dilution plating. Representative disks were also examined using scanning electron microscopy, energy dispersive x-ray analysis, and live/dead viability staining. RESULTS The mPEG-DOPA(3) coating significantly resisted the attachment of all uropathogens tested, with a maximum >231-fold reduction in adherence for Escherichia coli GR-12, Enterococcus faecalis 23241, and Proteus mirabilis 296 compared to uncoated TiO(2) disks. Scanning electron microscopy and viability staining analyses also reflected these results and demonstrated the ability of the coating to resist urinary constituent adherence as well. CONCLUSION Model surfaces coated with mPEG-DOPA(3) strongly resisted both urinary film formation and bacterial attachment in vitro. Future in vitro and in vivo studies will be conducted to assess whether similar findings can be demonstrated when these polymer coatings are applied to urologic devices.

Surface Modification for Protein Resistance Using a Biomimetic Approach

In recent years the immobilization of poly(ethylene glycol) (PEG) on surfaces has proved to be one of the most attractive methods to prevent biological fouling of surfaces. We have developed a paradoxical biomimetic PEGylation strategy that exploits the adhesive characteristics of proteins secreted by marine mussels—one of nature’s most notorious foulers. Linear PEGs were coupled to peptides containing 3,4-dihydroxyphenylalanine (DOPA), an unusual amino acid which is found in high concentration in these so-called mussel adhesive proteins. Using surface plasmon resonance, we have demonstrated enhanced resistance to protein adhesion on gold substrates modified with the DOPA-containing PEGs.

Biomimetic Adhesives and Coatings Based on Mussel Adhesive Proteins

Nature provides many outstanding examples of adhesive strategies from which chemists and material scientists can draw inspiration in their pursuit of new adhesive materials. Mussels secrete adhesive proteins, which enable these organisms to bind tightly to various surfaces under water. One of the key structure component of mussel adhesive protein (MAP) is the presence of a catecholic amino acid, 3,4-dihydroxyphenylalanine (DOPA), which plays an important role in the curing and interfacial binding of MAP. The catechol side chain is capable of undergoing various reversible and irreversible interactions with both organic and inorganic substrates. Modification of inert polymer systems with DOPA and other catechol derivatives have imparted these materials with water-resistant adhesive properties and the ability to cure rapidly. This chapter focuses on the various strategies used in developing biomimetic adhesives and coatings, as well as recent developments of self-healing and smart materials that employ MAP chemistry.