AVS2004 Session BI+AS+SE-ThM: Surface Modification of Biomaterials

Thursday, November 18, 2004 8:20 AM in Room 210D

Thursday Morning

Start	Invited?	Item
8:20 AM	Invited	BI+AS+SE-ThM-1 Strategies for the Biofunctionalization of Surfaces using Functional Polymer Layers J. Ruehe (University of Freiburg, Germany) The modification of surfaces with polymers for the promotion of cell outgrowth either in a dense layer or following a distinct pre-determined pattern is a challenging field of research with possible applications in the field of medical implants as well as for specific sensor devices. We present results from various studies in our group that range from the modification of bioimplant surfaces (e.g. glutar aldehyde treated porcine heart valves) with polymer monolayers in order to allow for a re-endothelialization of these devices to the arrangement of neuronal cells on a substrate by depositing synthetic and natural polymers on these chips in the form of a microarray. We will put a strong emphasis on synthetic approaches for establishing a strong, i.e. usually covalent interaction between the polymeric coating and the substrate in order to guarantee a sufficient long-term stability of the layer assemblies. These assemblies may be polymer monolayers as well as networks and we will also report on strategies for the incorporation of biological functions such as cell adhesion motifs or peptides. Finally, approaches for the laterally patterned deposition of these layers will be discussed.
9:00 AM	Invited	BI+AS+SE-ThM-3 Interfacial Biomaterials: Guiding Biology on Synthetic Surfaces E.B. Walsh, X. Huang (Duke University); M.W. Grinstaff (Boston University); D.J. Kenan (Duke University Medical Center) Interfacial biomaterials represent a novel coating technology capable of directing biological processes at the interface between a biologic and a synthetic surface. The approach relies on screening combinatorial libraries to identify unique peptides that adhere to a synthetic target such as a plastic or metal, or to a biological target such as a protein or cell. Next, two or more adhesion peptides are synthetically coupled to create an interfacial biomaterial that mediates the interaction of the protein or cell with the synthetic material. Other interfacial biomaterials may be created by coupling known signaling molecules to peptides that bind synthetic materials. Mixtures of interfacial biomaterials may be applied to a surface to achieve a particular desired biological outcome, such as adhesion of a given cell type to the surface, followed by induction of one or more signal transduction pathways. These interfacial biomaterials are amenable to numerous coating and patterning techniques suggesting their use for diverse applications ranging from biomedical device coatings to anti-infectives to tissue engineering.
9:40 AM		BI+AS+SE-ThM-5 Antibacterial Surfaces of Covalently Immobilized Dendrimers D. Weber, N.R. Choudhury, H.J. Griesser (University of South Australia) The need to limit bacterial adhesion to surfaces of biomedical implants, contact lenses, and other devices has prompted considerable recent research into antibacterial compounds and coatings. To ensure long-term efficacy and eliminate concerns about potential adverse biological effects on sensitive organs remote from the implant site, release strategies seem less suitable, and the covalent surface immobilization of antibacterial compounds is the approach of choice in our work. However, the question then becomes whether a covalently immobilized antibacterial is still biologically active, and can maintain activity over extended service life spans. In this study we have principally explored the surface immobilization of dendrimers, which have previously been shown to be antibacterially active in solution (eg CZ Chen and SL Cooper, Biomaterials 23 3359 2002). Another approach involves extracts of some Australian plant species, but their chemical characterization and synthesis is less developed. We have immobilized amine-terminated dendrimers onto aldehyde plasma polymer interlayers via reductive amination and characterized the coatings by XPS, ToF-SIMS, and AFM. Using various plasma conditions the surface density of aldehyde groups can be varied. The surface density of immobilized dendrimers is determined from XPS elemental ratios, using the dendrimer-specific N signal. Following surface immobilization, the remaining amine groups are quaternized in order to produce a cationic surface. The distinct signal arising from quaternary N in the XPS N 1s spectrum enables assessment of this reaction. The plasma approach also enables us to apply this coating strategy onto a wide variety of substrates both polymeric and inorganic (ceramic and metallic).
10:00 AM	Invited	BI+AS+SE-ThM-6 Biomimetic Vascular Engineering: Exploiting Concepts from Nature to Create New Biomaterial Interfaces R.E. Marchant (Case Western Reserve University) The abundance of complex supramolecular structures in Nature provides lessons in structural hierarchy and functional efficiency that are being explored and exploited in the development of novel biomimetic strategies for creating new biomaterial interfaces for biomedical applications. Mimicking and adapting structural concepts from Nature to create tissue compatible interfaces for biomaterials that incorporate molecular recognition and self-assembly will be the central theme of this presentation. We have developed a biomaterial architecture using "surfactant polymers" that undergo surface and self-induced assembly on hydrophobic surfaces. Our biomimetic designs benefit from understanding the structural and functional properties of the corresponding system in Nature. One example is the external region of a cell membrane, known as the glycocalyx, which is dominated by a complex milieu of glycosylated molecules. The glycosylated molecules direct specific interactions such as cell-cell recognition, and provide an important physical basis for maximizing steric repulsion that prevents undesirable non-specific cell and molecular adhesions. Conversely, understanding the nature of a cellâ?Ts adhesive interactions with the extracellular matrix facilitates design of biomimetic materials with cell adhesion properties. Using these biomimetic concepts, we have designed and studied oligosaccharide and peptide surfactant polymers that provide suppression of non-specific protein interactions and facilitate well-controlled interactions with endothelial cells.
10:40 AM		BI+AS+SE-ThM-8 Stability of Polypeptide Multilayers as Studied by in situ Ellipsometry: Effects of Drying and Post-Buildup Changes in Temperature and pH T.J. Halthur (YKI AB, Institute for Surface Chemistry, Sweden); P. Claesson (KTH, Royal Institute of Technology, Sweden); U. Elofsson (YKI AB, Institute for Surface Chemistry, Sweden) Polyelectrolyte Multilayers (PEM) of poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) with a initial layer of polyethyleneimine (PEI) were built on silica and titanium surfaces using the Layer-by-Layer (LbL) technique. The stability of the film during drying/rewetting, temperature cycles and pH shifts was studied in situ by means of ellipsometry. The filmthickness was found to decrease significantly (approximately 70%) upon drying, but the original film-thickness was regained upon rewetting and the buildup could be continued. The dry thickness was found to be extremely sensitive to ambient humidity, needing several hours to equilibrate. Changes in temperature and pH was also found to influence the multilayer thickness, leading to swelling and de-swelling of as much as 8% and 10-20% respectively. The film does not necessarily regain its original thickness as the pH is shifted back, but instead shows clear signs of hysteresis.
11:00 AM		BI+AS+SE-ThM-9 PCA of TOF-SIMS Spectra from p(AAm-co-EG/AAc) IPNS on Quartz D.J. Graham (University of Washington); G.M. Harbers, K.E. Healy (University of California, Berkeley); D.G. Castner (University of Washington) PCA of TOF-SIMS has been carried out on many well defined model surfaces in structured experiments. These studies have shown the utility of PCA in extracting information from TOF-SIMS experiments from a wide variety of substrate surfaces. This work reports on the application of PCA to a more complex interpenetrating polymer network system. The goal of this project was to verify each step in the IPN synthesis procedure on a quartz substrate. This system presents a challenge to PCA due to the similarity of the polymers used in the IPN and the addition of a peptide chain. PCA of the entire data set (including all synthesis steps for the IPN) showed that PC1 was able to separate most samples. The PC1 loadings were dominated by the overall differences between the hydrocarbons on the bare quartz and the PEG related peak fragments after the addition of the IPN onto the quartz surface. This is likely due to the high PEG content of the IPN polymers. PCA comparing each successive synthesis step gave further insight into the success of the IPN chemistry. PCA was able to distinguish each surface modification up until the addition of the peptide precursor and peptide. The presence of the peptide was verified in subsequent experiments where it was shown that RGD-peptide modified p(AAm-co-EG/AAc) surfaces supported rat calvarial osteoblast adhesion, proliferation, and matrix mineralization. Consequently,surfaces without the RGD peptide or with a control RGE peptide did not support cell attachment. PCA also gave insight into the uniformity of the surface modifications by way of the scores plots. Increasing scatter was seen in the last few synthesis steps suggesting that a less uniform surface chemistry was achieved. The trends seen in the PCA of the TOF-SIMS data were consistent with those seen by XPS.
11:20 AM		BI+AS+SE-ThM-10 Development of an Antimicrobial Polymer Surface Coating for the Prevention of Staphylococcal Infections M. Anderle, L. Pasquardini, L. Lunelli, R. Canteri, P. Villani, C. Pederzolli (ITC-irst, Italy) The proliferation of pathogenic microorganisms on polymer surfaces is one of the most widespread causes of failure of biomedical devices such as catheters, medical implants, vascular graft and joint prostheses. The inhibition of pathogenesis and subsequent mechanisms of protection are possible by killing bacteria in the first steps of colonization. This work describes a polymeric surface coating with liposomes as method to provide a sustained delivery of antibiotics into the local micro-environment of the implant. In this study liposome formulations composed of Phosphatidylcholine (PC), Distearoyl-sn-Glycero-3-Phosphoethanolamine-N-MethoxyPolyethylene glycol (DSPE-PEG) and cholesterol are utilized. Liposomes, different in size, are attached to an amine activated substrate through the formation of covalent bonds with the distal end of the PEG (Polyethylene glycol) derivative molecules. Data on the surface coating using large unilamellar vesicles (LUV) and multilamellar vesicles (MLV) will be shown. The AFM analysis is performed to study the nanoscale structure of the coated surface while the fluorescence spectroscopy and microscopy are engaged to determine the immobilisation efficacy adding a fluorescent lipid (L-α-Phosphatidylethanolamine-N-lissamine rhodamine B sulfonyl) to the liposome composition. The MLV coating on polystyrene shows a more uniform distribution with a lipid concentration of about 2x10¹⁵ mol/cm². Finally drug (rifampicin) release and bacterial colonisation rates with their correlation will be reported.
11:40 AM		BI+AS+SE-ThM-11 Spectroscopic Characterization of Surface-Immobilized Antibacterial Furanone Coatings S. Al-Bataineh, H.J. Griesser (University of South Australia); M. Willcox (University of New South Wales, Australia); L.G. Britcher (University of South Australia) The colonisation by bacteria of biomedical devices presents a serious concern for human implant surgery. In this study, we explore how bacterial colonisation can be prevented by the appropriate design and fabrication of antibacterial coatings, with a major focus on surface-immobilised furanone molecules. These compounds are produced naturally by the marine algae, Delisea pulchra and are used as defence agents to prevent fouling on their surface¹. Several studies have shown that brominated furanones as well as synthetic analogues possess potent antimicrobial activity against bacteria²^,³. The previously used azide protocol was adopted to prepare furanone coatings⁴. XPS and ToF-SIMS results showed successful surface modifications and furanone immobilisation. Detailed analysis of the C 1s and N 1s XPS spectra using constrained curve fitting showed that they are more complicated than anticipated from the theoretical reaction scheme. In addition, the presence of a Br^- peak partially overlapped with a C-Br peak indicated that furanones are partially degraded on UV illumination. More surface characterisations are needed for full understanding of the chemical reactions that occurred. Seven furanone compounds used in this study were tested for their ability to inhibit biofilm formation and growth of two bacterial strains, Staphylococcus aureus (Saur19) and Pseudomonas aeruginosa (Paur6206). Initial results are promising; detailed investigation of the efficacy of the coatings is ongoing. Furthermore, none of the compounds used in this study showed any cytotoxicity potential at the tested concentrations. ¹ de Nys R. et al., 1995, 4:259-71. ² Kjelleberg S. et al., Patent No. PCT/AU99/00284, 1999. ³ Read R. et al. PCT international application PQ6812, 2001. ⁴ Muir B. et al., Proc. 6th World Biomat. Congr., Hawaii, May 2000, p. 596.