A parallel-plate capacitively-coupled plasma deposition system was designed and built for the growth of polyethylene glycol-like films. Deposition rate, bonding structure and dissolution and swelling behavior was characterized as a function of input RF power, reactor pressure and substrate temperature to provide information on the relationship between input plasma parameters and film properties. For the conditions studied in this thesis, deposition rates increased at increasing input powers and operating pressures and decreasing substrate temperatures. The PEG-like coatings resembled higher molecular weight solution-polymerized PEG films with a higher crosslinked structure. Manipulation of plasma deposition conditions allowed control of film crosslink density and resulted in tunable dissolution and swelling properties of the PEG-like polymer. At higher applied powers, lower operating pressures, and higher substrate temperatures, films had a higher crosslink density, thus leading to slower dissolution rates and smaller extents of swelling. Void space openings of swelled-state, PEG-like films were determined using electrophoretic drift and diffusion-controlled transport of fluorophore-tagged PAMAM dendrimers into the bulk of the coating. PAMAM dendrimers were used because of their well-defined sizes and negatively-charged succinamic acid surface groups as a means to probe pore sizes of the plasma films. It was estimated that the upper bound of pore size diameters in the plasma polymer was approximately equal to ~5.5-6.0 nm. Positron annihilation lifetime spectroscopy was used to determine average pore sizes and was estimated to equal ~0.60-0.65 nm.

Hydrogels, which are polymeric cross-linked networks that swell in aqueous environments, are versatile materials that can contain a variety of chemical functionalities, mechanical properties, and topographical features. Microgels are the stable colloidal form of hydrogel materials that range in size from approximately 100 nm to a few microns in diameter. While they also can exhibit similar properties to those of macrogels, microgels can be used as building blocks in a bottom-up approach to assemble films of higher complexity. In this dissertation, work is focused on understanding the assembly and behavior of microgel thin films as non-fouling surfaces, centrifugally deposited materials, self-healing coatings, and degradable constructs. Non-fouling films were assembled using PEG cross-linked microgels to reduce non-specific protein adsorption and mitigate cellular adhesion. These constructs were assembled in a polyelectrolyte multi-layered fashion, of alternating anionic microgels and cationic linear polymer, to effectively block the substrate from the biological environment and consequently exhibited control over cellular adhesion with the surface. The utility and application of these non-fouling microgel coatings on functional implants was also explored. Centrifugal deposition was used to rapidly generate non-fouling microgel multi-layered interfaces on planar surfaces, and upon closer inspection of the microgel monolayers, it was found that the centrifugally deposited films contained closer-packed microgel assemblies with microgels of smaller footprint size, compared to microgels that are passively adsorbed to the surface. Microgels that are centrifugally deposited may adopt a higher energy chain conformation than passively adsorbed microgels, and this higher energy chain conformation may translate into the multi-layered materials. Nonetheless, the centrifugally deposited non-fouling microgel multi-layered films were found to effectively block macrophage adhesion. Films were also assembled in a polyelectrolyte fashion on soft substrates, and were observed to become significantly damaged under mechanical manipulation (poking, bending, or stretching), but then self-heal upon addition of water. By altering the building blocks of the polyelectrolyte multi-layered films, such as the molecular weight of the polycation between microgel layers or by using anionic rigid spheres as the particle in the assembly, changes in the observed film damage suggest that particle-linear polymer interpenetration and polyvalency likely play an important role in the strength and integrity of the microgel thin films. Fluorescently-labeled microgels were also used to interrogate how the films reorganize in the lateral direction, and these early studies suggest that the microgel multi-layered films reorganize when damaged and also possibly when they are undamaged and simply incubated in an aqueous environment. Additional studies were also conducted on microgels synthesized with a hydrolyzable cross-linker, and by supporting these degradable constructs on substrates, detailed single-particle morphological changes during erosion could be interrogated in complex media such as serum. This work, as a collection, demonstrates the ability to obtain information about microgel thin film assemblies and their behavior using microscopy techniques such as ambient and in liquid atomic force microscopy, brightfield optical microscopy, and fluorescence microscopy. The observations made here illustrate how microgels can be used to fabrication thin films that can be utilized in biological applications (non-fouling, self-healing, and erodable constructs), and how different deposition methods (centrifugal deposition and polyelectrolyte multi-layers) can dictate their behavior.

Thesis (M.S. in M.S.E.)--School of Materials Science and Engineering, Georgia Institute of Technology, 2004. Directed by Rober Narayan. / Includes bibliographical references (leaves 85-92).

Thesis (Ph. D.)--University of Hong Kong, 2010. / Includes bibliographical references (p. 253-274). Also available in print.

Thesis (M.S. in M.S.E.)--School of Materials Science and Engineering, Georgia Institute of Technology, 2004. Directed by Roger J. Narayan. / Includes bibliographical references (leaves 87-88).

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 97-108). Also available in print.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Polyetheretherketone (PEEK), a polymer with mechanical strength comparable to human bone, is gaining popularity in the orthopedic field because it can potentially relieve the clinical complications, such as stress shielding effect and inevitable implantation failure, which are caused by the mismatch of the mechanical strength between the current metallic implants and the implantation sites. However, it is bio-inert and requires supplementary modification. Plasma immersion ion implantation (PIII) has been well documented that it is a good way to improve the bioactivity of a biomaterial. It is a method that introduces new elements to the biomaterial, generating bio-functional groups on the material surface without altering its mechanical properties. Hence, the aim of this study is to improve the bioactivity of PEEK by modifying its surface chemistry with the use of water (H2O) and ammonia (NH3) plasma immersion ion implantation (PIII) without altering its mechanical properties. After PIII treatment, a series of surface characterization tests that provide information about the surface properties, such as surface energy, roughness, surface chemical composition and crystallinity of PIII-treated PEEK were carried out. Results show that both H2O PIII and NH3 PIII-treated PEEK had significantly higher surface energy and roughness than untreated PEEK. There was also no significant change in the crystallinity of the PIII-treated PEEK, indicating that PIII treatment will not alter the mechanical properties of PEEK. Improvement in wetting properties of PEEK samples suggest the formation of polar functional groups on the PIII-treated PEEK materials, while the increased in surface roughness may be due to the energetic bombardments of plasma ions on the material surface. The in vitro bioactivity of plasma-treated PEEK was investigated and confirmed with hMSC-TERT. Initial cell attachment, cell spreading area, cell proliferation and differentiation were studied. Cell adhesion and cell spreading were enhanced on PIII-treated PEEK, and higher cell viability was observed on PIII-treated PEEK. Moreover, cell proliferation was promoted on early time point and cell differentiation was also enhanced particularly on day 7 by measuring the alkaline phosphatase activity. Therefore, H2O-PIII and NH3-PIII treatments were able to promote the bioactivity of PEEK samples. / published_or_final_version / Orthopaedics and Traumatology / Master / Master of Philosophy

Self-assembled monolayers have been proven to be well-ordered and to give stable ultrathin films. They show a remarkably high diversity with respect to their functionalisation giving rise to many possible applications. This thesis is focused on the potential use of these molecular thin films in life sciences. The reproduction of a membrane-like environment with these tightly packed and organized unimolecular layers has led to important breakthroughs in their nanotechnological application as biomaterials. Their straightforward modification allows the chemical and physical properties of biological interfaces to be altered. In particular, Oligo(ethylene glycol) based alkanethiol self-assembled monolayers were intensively studied as biointerfaces for their ability to resist the non specific adsorption of proteins. The electrostatic repulsion which originates from these monolayers was seen as one of the possible factors causing this protein repulsion. On the other hand proteins adsorb on alkanethiol self-assembled monolayers. This can be partially attributed to an attractive hydrophobic interaction between the biomolecules and the surface. As a result of the understanding of these two driving forces which are relevant for non-specific protein adsorption/repulsion, novel self-assembling molecules were tailored in an attempt to adjust the adsorption of proteins at the SAM-liquid interface. This was conceivable with these newly designed SAMs since they allow a combination of these forces. We have chosen the ionic strength of the liquid environment as the external parameter which could act on the amount of adsorbed proteins because the electrostatic force created by oligo(ethylene glycol) groups depends on it. In addition to the synthesis of six new molecules, the preparation and characterisation of the novel self-assembled monolayers are reported in this thesis. The density of the monolayers was estimated by X-ray photoelectron spectroscopy and ellipsometry, and the wettability properties were studied by measuring the contact angle. The total force acting on proteins from the SAMs was studied with an atomic force microscope, equipped with a tip mimicking proteins, by measuring force-distance curves. An in-situ technique was investigated in order to study the influence of the variation of this total force on the quantity of adsorbed proteins by varying the ionic strength.

Nosocomial, or hospital acquired, infections, are ubiquitous within the modern clinical setting leading to over $5 billion annually of related healthcare costs in North America. All indwelling devices are highly susceptible to bacterial colonization where physico-chemical interactions between bacteria and biomaterial surfaces have been implicated as determinant factors in the fate of the initial adhesion processes. It has been proposed that by exploiting interference strategies within this critical step of infection the ability to create 'non-infective' biomaterials may be developed. / This thesis demonstrates the effectivity of North American cranberry (Vaccinium macrocarpon) derived proanthocyanidins in preventing the adhesion of pathogenic bacteria to biomaterial surfaces. Specifically, using a model of catheter associated urinary tract infection, significant reductions in initial adhesion of uropathogenic Escherichia coli and Enterococcus faecalis to PVC and PTFE were observed. With the application of colloidal theory, a mechanism of steric interference was determined as responsible for these effects. / The evidence presented implicates PAC as a molecule of interest for the development of novel biomaterials with increased resistance to bacteria colonization.