Daniel D. Burkey

Organosilicon Thin Films Deposited from Cyclic and Acyclic Precursors Using Water as an Oxidant

Pulsed-plasma chemical vapor deposition was used to deposit thin films from four different organosilicon precursors using water as the oxidant. The precursors varied in structure, chemical composition, and type of organic substituent. Differences in film structure were observed based on precursor structure and type of organic substituents. More reactive substituents, such as vinyl groups, facilitated cross-linking. At low power (200 W), film structure was dictated by precursor identity. At high power (400 W) film structure became more uniform and precursor identity was less important. Mechanical and thermal properties correlated with plasma power and could be explained by the continuous random network theory and percolation of rigidity arguments. Low-power samples are relatively soft, with hardness values between 0.13 and 0.54 GPa. High-power samples are more extensively cross-linked and oxidized, resulting in enhanced mechanical properties, and had hardness values between 0.68 and 3.2 GPa, depending upon precursor identity. Thermal stability was strongly correlated to the degree of cross-linking, with non-cross-linked films showing up to 30% thickness loss upon annealing. Cross-linked films exhibited less than 8% thickness loss. Dielectric constants for the films ranged between 2.4 and 4.3 and were primarily dependent upon the extent of oxidation and organic content remaining in the films.

Temperature-resolved Fourier transform infrared study of condensation reactions and porogen decomposition in hybrid organosilicon-porogen films

Composite organosilicon/porogen thin films were deposited via pulsed-plasma chemical vapor deposition. The organosilicon monomer was polymerized using water as the oxidant, allowing incorporation of silanol (Si–OH) moieties for subsequent condensation reactions and crosslinking for enhanced mechanical properties. The porogen monomer [methylmethacrylate (MMA)] was codeposited in the same step, and the degree of MMA incorporation was shown to scale with both the peak plasma power and porogen flow rate. Fourier transform infrared (FTIR) spectroscopy spectra of the composite material show features from both the organosilicon precursor and the porogen species, indicating that both materials are successfully incorporated into the thin film. The kinetics of both the condensation reaction and porogen removal were determined by a temperature/time-resolved FTIR method. The condensation reaction and crosslinking events occur between 100 and 425 °C. Porogen decomposition occurs simultaneously between approximately 32...

Cross-Linking and Degradation Properties of Plasma Enhanced Chemical Vapor Deposited Poly(2-hydroxyethyl methacrylate)

Plasma Enhanced Chemical Vapor Deposition (PECVD) of poly-2-hydroxyethyl methacrylate (pHEMA) biocompatible, biodegradable polymer films were produced alone and cross-linked with ethylene glycol diacrylate (EGDA). Degree of cross-linking was controlled via manipulation of the EGDA flow rate, which influenced the amount of swelling and the extent of degradation of the films in an aqueous solution over time. Noncross-linked pHEMA films swelled 10% more than cross-linked films after 24 h of incubation in an aqueous environment. Increasing degree of film cross-linking decreased degradation over time. Thus, PECVD pHEMA films with variable cross-linking properties enable tuning of gel formation and degradation properties, making these films useful in a variety of biologically significant applications.

Biocompatibility of Plasma Enhanced Chemical Vapor Deposited Poly(2-hydroxyethyl methacrylate) Films for Biomimetic Replication of the Intestinal Basement Membrane

It is recognized that topographical features such as ridges and grooves can dramatically influence cell phenotype, motivating the development of substrates with precisely biomimetic topography for study of the influence on cultured cells. Intestinal basement membrane topography has been precisely replicated using plasma enhanced chemical vapor deposition (CVD) of poly(2-hydroxyethyl methacrylate) (pHEMA) on native tissue. The ability for CVD pHEMA to coat and retain the complex architecture of the intestinal basement membrane at the micrometer scale was demonstrated using electron microscopy and surface chemical analysis (XPS). The suitability of CVD pHEMA as a cell culture substrate was assessed. Caco-2 cells maintained a high (>85%) viability on CVD pHEMA. Cell attachment and proliferation on CVD pHEMA were similar to those observed on materials traditionally used for cell culture and microfabrication purposes. Results indicate that CVD pHEMA is useful for development of precise (micrometer-scale) topographically biomimetic substrates for cell culture.

Complex, multi-scale small intestinal topography replicated in cellular growth substrates fabricated via chemical vapor deposition of Parylene C.

Native small intestine possesses distinct multi-scale structures (e.g., crypts, villi) not included in traditional 2D intestinal culture models for drug delivery and regenerative medicine. The known impact of structure on cell function motivates exploration of the influence of intestinal topography on the phenotype of cultured epithelial cells, but the irregular, macro- to submicron-scale features of native intestine are challenging to precisely replicate in cellular growth substrates. Herein, we utilized chemical vapor deposition of Parylene C on decellularized porcine small intestine to create polymeric intestinal replicas containing biomimetic irregular, multi-scale structures. These replicas were used as molds for polydimethylsiloxane (PDMS) growth substrates with macro to submicron intestinal topographical features. Resultant PDMS replicas exhibit multiscale resolution including macro- to micro-scale folds, crypt and villus structures, and submicron-scale features of the underlying basement membrane. After 10 d of human epithelial colorectal cell culture on PDMS substrates, the inclusion of biomimetic topographical features enhanced alkaline phosphatase expression 2.3-fold compared to flat controls, suggesting biomimetic topography is important in induced epithelial differentiation. This work presents a facile, inexpensive method for precisely replicating complex hierarchal features of native tissue, towards a new model for regenerative medicine and drug delivery for intestinal disorders and diseases.

Photoinitiated chemical vapor deposition of cytocompatible poly(2-hydroxyethyl methacrylate) films

Poly(2-hydroxyethyl methacrylate) (pHEMA) is a widely utilized biomaterial due to lack of toxicity and suitable mechanical properties; conformal thin pHEMA films produced via chemical vapor deposition (CVD) would thus have broad biomedical applications. Thin films of pHEMA were deposited using photoinitiated CVD (piCVD). Incorporation of ethylene glycol diacrylate (EGDA) into the pHEMA polymer film as a crosslinker, confirmed via Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, resulted in varied swelling and degradation behavior. 2-Hydroxyethyl methacrylate-only films showed significant thickness loss (up to 40%), possibly due to extraction of low-molecular-weight species or erosion, after 24 h in aqueous solution, whereas films crosslinked with EGDA (9.25-12.4%) were stable for up to 21 days. These results differ significantly from those obtained with plasma-polymerized pHEMA, which degraded steadily over a 21-day period, even with crosslinking. This suggests that the piCVD films differ structurally from those fabricated via plasma polymerization (plasma-enhanced CVD). piCVD pHEMA coatings proved to be good cell culture materials, with Caco-2 cell attachment and viability comparable to results obtained on tissue-culture polystyrene. Thus, thin film CVD pHEMA offers the advantage of enabling conformal coating of a cell culture substrate with tunable properties depending on method of preparation and incorporation of crosslinking agents.