Like most thriving human endeavors, the field of implant materials and devices intersects with a universe of populations and professions. Nearly everyone will “get into the act” in one way or another, resulting in a variety of perspectives that have more, or less, foundation in fact and genuine concern for the patient. Even the scope of the points of view of scientists and engineers is relatively broad. One reason for the richness of the field in which we work is the increasing number of sites in the body to which implants are being delivered for the treatment of disease and replacement or augmentation of natural tissues. Another reason is the diversity of materials used in implants and diagnostic devices.

The primary goal of the biomaterials scientist and tissue engineer is to create a biocompatible implant which mimics the mechanical and morphological properties of the tissue being replaced. In vitro experimentation has documented the propensity of soluble type I collagen to self-assemble and form microscopic collagen fibrils with periodic banding analogous to native collagen fiber. Our laboratory has further investigated in vitro self-assembly by incorporating several of the “natural” processes into a multi-step fiber formation procedure which generates macroscopic collagen fiber from its molecular constituents. Results of uniaxial tensile tests and ultrastructural analyses indicate that these coextruded and stretched collagen fibers have mechanical properties and fibrillar substructure comparable to that observed in native collagen fiber.

Despite the high initial success rate with metallic stents for the treatment of a variety of vascular lesions, problems have included occlusion due to thrombus formation or intimal proliferation. Improving the biological behavior of these and other other implantable metallic devices may require the use of biomimetic peptide coatings which promote specific cellular responses at the biological-materials interface.

Thiol-terminated peptides, without the addition of a cysteine residue, were synthesized by a modification of standard solid phase methodology. Gold/mica or gold/glass surfaces were exposed for 6 hours at 23 °C to one of three peptide solutions: GRGD(βA)3YNH(CH2)2SH (RGD); (βA)6NH (CH2)2SH (bAla); or a 1:1 mix of both peptides. Peptide films were examined by external reflectance infrared (IR) spectroscopy and atomic force microscopy (AFM) which confirmed the presence of unique close-packed structures for bAla and the 1:1 mix. Endothelial cell proliferative, migratory, and adhesive behavior were evaluated using 3H-thymidine and 51Cr labeling techniques, respectively. Cell proliferation, migration, and adhesion were significantly higher on RGD containing peptide films.

Well-ordered protein assemblies on metallic substrates can be produced with the proper choice of peptide chain structure and terminal residues. Biological activity is a function of film composition and oligopeptide pendant structure.

We have developed processing schemes for depositing three-dimensionally tailored layers of protein polymers on a variety of solid substrates. One of our goals is to create stable, biocompatible coatings on silicon devices for implantation in the central nervous system. Our research has identified several candidate coatings whose morphologies lie in the biologically significant 0.1 to 100 micrometer length scale. Using electric field mediated deposition, we are able to process polypeptides into biologically-responsive films and coatings. Quantitative analysis of the structural evolution of the coating enables us to fine-tune its morphology by varying the field strength and geometry or solution concentration. The interaction of the coated substrates with neurons and glial cells are examined in vivo and in vitro. Data collected from light optical microscopy, atomic force microscopy, transmission electron microscopy, and scanning electron microscopy provide insight about the relationship between the microstructure of these coatings and their macroscopic properties.

Collagen fibers self-assembled from solutions of molecular type I collagen were mineralized at pH 9.5, by exposure to super-saturated solutions of calcium and phosphate for a one week period in a double diffusion chamber. Uniaxial tensile mechanical properties increased with mineralization and electron microscopy of the mineral formed within the fiber was morphologically similar to the mineral phase of calcified tissues. Selected area electron diffraction confirms the presence of hydroxyapatite crystal. Further, the aligned fibrillar substructure serves as a template for the orientation of the c-axis diffraction maxima of the hydroxyapatite. These results indicate that an aligned system composed exclusively of selfassembled type I collagen fibrils serves as a scaffold for oriented growth of mineral analogous to calcification in vertebrate bone.

Calcium phosphate nucleation on colloidal oxide surfaces, such as TiO2, SiO2 and Al2MO3, has been studied as a model system to understand the role of surface chemistry on crystal nucleation kinetics and phase formation. The nucleation induction times have been measured using Constant Composition (CC) technique and calcium phosphate phases formation have been determined mainly by X-ray diffraction. The results indicated TiO2 not only significantly reduces the nucleation induction time and interfacial energy but also stimulates octacalcium phosphate formation over dicalcium phosphate dihydrate. SiO2 and Al2O3 have little effect on both nucleation kinetics and phase formation.

Synthetic biomaterials are widely used for a variety of in vivo and in vitro biomedical applications. However, the performance, safety, and cost effectiveness of medical products are determined by desirable interactions between the physiological environments and biomaterial surfaces. Hence, development of surface modifications for biomaterials is strongly demanded by the biomedical industry. High energy techniques, such as glow discharge plasma, have been developed to impart specific chemical functionality to the biomaterial surfaces or to deposit new polymer films with desired properties. The use of plasma surface modification for biomedical applications is reviewed in this paper.

Polymer surfaces terminated with a specific chemical functionality are attractive for biomaterial applications because of the predictability and selectivity of surface reactions towards the anchoring of a biochemical agent to the polymer. In the present work, engineering of surface functionality was performed using OH radicals generated in gas phase by the reaction between a hot filament and water molecules in vacuum. The generation of OH was confirmed by laser induced fluorescence spectroscopy. The incorporation of oxygen and formation of alcohol groups on polystyrene were confirmed by x-ray photoelectron spectroscopy. High resolution electron energy loss spectroscopic data also showed that for polystyrene with an uptake of less than a monolayer equivalent of oxygen, C-OH was the only detectable surface functionality containing oxygen.

A new method has been developed for the covalent attachment of poly(ethylene oxide) to various polymeric surfaces for use in biomedical applications. Methacrylic acid (MA) monomer was first grafted to low-density polyethylene (LDPE) or polystyrene (PS) sheets by placing them in a solution of 10–20% (v/v) methacrylic acid in water followed by electron beam irradiation of 2–4 megarads. The methacrylic acid was grafted to the surface and polymerized, resulting in the polymer surface being extremely hydrophilic. The MA-treated samples were placed in a solution of PEO in water (MW 8000 – lx106 g/mol, concentration 0.05–15 % w/v), where the PEO strongly hydrogen bonds to the MA on the surface. The pieces were either rinsed with water (monolayer formation) or drained of excess solution (multilayer formation), then placed under the electron beam for a dose of 2 megarads to graft the PEO to the MA-treated surface. The grafted PEO was stable on the surface, unable to be removed despite extensive washing with water, soaking in basic solution (which would break the hydrogen bonding of the PEO with the acid), or scraping of excess hydrogel from the surface. The monolayer thickness was found to have no dependence on the molecular weight or concentration of the PEO in solution, nor did it have any dependence on the time that the MA-treated samples were soaking in the PEO solution before the second irradiation. This indicates that the PEO molecules immediately lie flat on the surface with few loops or tails, with no exchange taking place after the initial adsorption. All surfaces were analyzed using X-ray photoelectron spectroscopy (XPS), with high resolution carbon Is scans being the principle means of MA and PEO detection in the top 50 angstroms of the surface.

Thin films of collagen were prepared by pulsed laser deposition (PLD) at room temperature on Si substrates using a KrF laser (248 nm) over a fluence range from 0.2–1.5 Jcm-2. The effects on film composition and morphology of ambient gas (Ar, Ar/H2O vapor), quenching atmosphere (Ar, Ar/H2O vapor), and fluence were examined. Fourier transform infrared spectroscopy (FT- IR) demonstrated that, independent of deposition parameter, the PLD films contained the characteristic Amide I and II functionalities of the collagen target and indicated that the secondary structure was altered by the PLD process. The surface morphology of the films was a function of the laser fluence and the gas environment during either film deposition or quenching at the end of deposition. Preliminary gel electrophoresis examination of deposited films suggested the collagen had not maintained the triple helical structure of the native collagen. X-Ray diffraction (XRD) indicated that all of the films, deposited under any conditions, were predominantly amorphous.

Calcium phosphates are widely used as implantable materials in both dental andorthopaedic applications. Seven different bone substitutes (BS), including Interpore CorallineHAP, Cortical Bio-Oss, Endobon, Cancellous Bio-Oss, Dense HAP (hydroxyapatite), Collagraftgranules, and Porous HAP, have been evaluated using the Dual Constant Composition (DCC)kinetics methods. DCC measurements of the kinetics of dissolution and re-mineralization of theBS materials offer considerable advantages for the characterization of minor calcium-containingsurface species due to the insensitivity of conventional physical chemical methods such as X-raydiffraction and ESCA. Each sample was pre-conditioned (PC) in 0.15 M NaCl prior to the DCCkinetics procedures. The fastest dissolving material, Collagraft granules, showed a dissolution ratemore than two orders of magnitude larger than Dense HAP. Interestingly, the relativesupersaturation with respect to HAP (σ) following PC was normally negative, whereas withplasma sprayed HAP coated implants, these a values were as high as 20. Surface impurities mayplay a major role following in vivo implantation, since resorption is probably a major reparativemechanism. It is therefore essential to understand the dissolution behavior. Moreover, in a remineralizationmode, trace surface phases may determine the phase and morphology of the newlydeposited bone mineral.

A method for producing titanium dioxide (TiO2) containing hydroxyapatite (HA) crystallite isproposed. Solutions of CaCI2+H3PO4 and TiCL4+HCI combined with KOH are used to precipitatefirst the HA and then the TiO2.The precipitate is then sintered between 900°C and 1000°C for 18 to48 hours. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Energy DispersiveX-ray Analysis (EDX) and scanning electron microscopy (SEM) have been used to determine thecrystallinity, the chemical composition and structure of the samples.

Calcium phosphate based thin films prepared by colloidal sol-gel slow draw dipping of quartz substrates are bioactive to both osteoclast resorption and osteoblast deposition. The bioactivity is related to the presence of mixed crystalline phases in the films generated under different sintering conditions. As the sintering temperature was increased from 800°C to 1000°C, a transition in film composition from calcium hydroxylapatite to alpha-tricalcium phosphate is achieved.

We present in this paper the surface derivatization of polyanhydrides with triethylamine for labeling the hydroxyl group. The reaction was verified with diffuse reflectance FTIR spectroscopy. Surface derivatization of poly(fumaric-co-sebacic)anhydride of 50:50 and 20:80 compositions was performed and ESCA measurements showed the surface nitrogen concentration in good agreement with stoichiometry values.

Silicon-based clean-room technology is employed for the microfabrication of a particle filter with uniform pore dimensions in the 20-40-nm range. Surface and bulk micromachining are integrated in the fabrication process, resulting in a filtering membrane with large active area, flow rate and resistance to pressure. The microfabricated membrane is especially suitable for biofluid purification, including viral elimination. The nanofilter is a technological precursor for a microfabricated, silicon-based capsule to be employed in the reaction-free xenotransplantation of cells. Results are presented below that address the issue of biocompatibility of the microfabricated capsule components and materials.

Lithium was introduced into pyrolyzed phenolic resins by dissolving lithium nitrate (5, 10, and 15% by mass) in a resol precursor. Impregnated specimens were pyrolyzed at 500°C, 575°C, and 650°C in inert atmosphere. After pyrolysis, samples were placed in 5 ml of phosphate buffered saline solution, refrigerated at 5°C, for various Li release times. Inductively coupled plasmaatomic spectroscopy was used to analyze these solutions, which were tested every 24 hours for 5 days; another set was tested after 60 days. Samples containing 5% lithium salt, fired to 500°C, released Li+ at a lower rate than those fired at higher temperature. At the early stages of exposure to saline, samples fired at 575°C and 650°C released Li+ at a higher rate, which fell to that of 500°C samples after many days. After leaching, nuclear reaction analysis using alpha radiation, with an exposure time of I hour, allowed us to analyze [Li+] and gradient up to 121μm below the surface. This indicates that a smaller [Li+] remains in 650°C samples than in those fired at 575°C and 500°C. For 500°C samples, [Li+] near the surface was lower than that for samples fired at 575°C and 650°C. This indicates that 500°C samples release Li+ from near the surface, whereas samples fired at higher temperature release Li+ from deep below the surface, probably because of higher permeability. Li+ release rates of samples fired at 500°C and below 650°C follow a simple diffusion law, with diffusivities between 1017 and 10-18m2/s. Li+ rate may controlled over long time by a multilayered sprayed precursor with variable concentration.

The proposed research is aimed at gaining a fundamental understanding of in vitro nerve cellbiomaterials interactions, with the immediate goal of engineering materials to specifically enhance expression of the neuronal phenotype. Long term goals include (1) optimizing the innervation (connection) of the host neurons with implanted bioartificial tissue constructs and, (2) facilitating the regeneration of damaged peripheral and central nerves. In this study, the interactions of neuronal like PC-I12 cells with the electrically conducting polymer, polypyrrole, (PP) have been investigated. It has been shown by quantitative image analysis that neurite extensions of PC-12 cells are more pronounced on PP surfaces as compared to tissue culture polystyrene. Application of an electrical stimulus to cells cultured on PP film significantly increased (based on morphological evaluation) the expression of neurites in these cells compared to controls. Tissue compatibility and transected sciatic nerve regeneration studies in rat models show that PP films invoke little negative response and support nerve regeneration.

The electrochemical properties of o-dianisidine have been studied in both aqueous and organic solvents. This aryl diamine has been electrochemically polymerized on ITO coated glass electrodes and it was determined that the optical properties of these films are influenced by the polymerization conditions. The use of this polymer film as substrate for chemical coupling of biomaterials has been demonstrated with the light harvesting protein, phycoerythrin. Fabrication and bioanalytical application of enzyme electrodes by electrochemical copolymerization of odianisidine with the enzymes glucose oxidase and horseradish peroxidase, modified with odianisidineis described.

We have developed a technique to immobilize a multilayer enzyme assembly on an optical fiber surface. The technique utilizes a bifunctional amino coupling agent to link between different layers of enzymes. The method offers the flexibility of controlling the number of enzymes on a fiber surface. Multilayers of enzyme — Alkaline Phosphatase have been characterized using ellipsometry and surface plasma resonance. Chemiluminecence experiments have been conducted as a function of number of enzyme layers. The results indicated that at least 3 layers of enzyme can be assembled on a fiber surface. Utilising the new immobilization technique, a novel fiber optic biosensor system for the detection of organophosphorous-based pesticide has been developed. The detection mechanism is the pesticide inhibition of alkaline phosphatase catalyzed chemiluminescence. As a model analyte, paraoxon with ppb level concentration has been detected.

Cells are sensitive to topological, chemical and electrical properties of substrates on which they are grown. However, most studies of cell-surface interactions have neglected electrical effects or confounded them with other substrate properties. The use of nanofabrication technology has made it possible to fabricate optically transparent surfaces, with controlled chemistry and topology, with active, controllable surface charge density in domains as small as 1–4 um1. Human monocytes incubated on polystyrene with 3.3 um wide strip domains alternately charged, so as to maintain overall charge neutrality, show significant charge density and time dependent increases (greater than twofold) in cell area and cell perimeter after challenge with a phagocytic trigger (human IgG opsonized Zymosan particles). Additional ultrastructural studies on silicon dioxide substrates show charge density dependent qualitative morphological differences. The human monocytes exhibited significant charge density and time dependent hyper-phagocytosis (> 25fold increase over control) of human IgG opsonized Zymosan particles. The charge-induced surfaces modulated the amplitude of the secreted extracellular levels of cytokines and also induced a temporal shift in the kinetics of cytokine release2.

These studies demonstrate that human blood peripheral monocytes respond in-vitro to the peak magnitude of local surface charge heterogeneity in the absence of substrate topology and compositional variation.