Hydroxyapatite nano-pillars on TI-6Al-4V: Enhancements in cell spreading and proliferation during cell/surface integration.

Despite the attractive combinations of cell/surface interactions, biocompatibility, and good mechanical properties of Ti-6Al-4V, there is still a need to enhance the early stages of cell/surface integration that are associated with the implantation of biomedical devices into the human body. This paper presents a novel, easy and reproducible method of nanoscale and nanostructured hydroxyapatite (HA) coatings on Ti-6Al-4V. The resulting nanoscale coatings/nanostructures are characterized using a combination of Raman spectroscopy, scanning electron microscopy equipped with energy dispersive x-ray spectroscopy. The nanostructured/nanoscale coatings are shown to enhance the early stages of cell spreading and integration of bone cells (hFOB cells) on Ti-6Al-4V surfaces. The improvements include the acceleration of extra-cellular matrix, cell spreading and proliferation by nanoscale HA structures on the coated surfaces. The implications of the results are discussed for the development of HA nanostructures for the improved osseointegration of Ti-6Al-4V in orthopedic and dental applications.

Cell-surface interactions on gold-coated polydimethylsiloxane nanocomposite structures: Localized laser heating on cell viability.

This article presents the results of cell-surface interactions on polydimethylsiloxane (PDMS)-based substrates coated with nanoscale gold (Au) thin films. The surfaces of PDMS and PDMS-magnetite (MNP)-based substrates were treated with UV-ozone, prior to thermal vapor deposition (sputter-coated) of thin films of titanium (Ti) onto the substrates to improve the adhesion of Au coatings. The thin layer of Ti was thermally evaporated to improve interfacial adhesion, which was enhanced by a 40-nm thick film microwrinkled/buckled wavy layer of Au, that was coated to enhance cell-surface interactions and protein absorption. Cell-surface interactions were studied on the hybrid surfaces using a combination of optical and fluorescence microscopy. Consequently, cell proliferation and surface cytotoxicity (of the sputter-coated PDMS surfaces) were elucidated by characterizing the metabolic activity in the presence of breast cancer and normal breast cells. The photothermal conversion efficiency associated with laser-materials interactions with the PDMS/PDMS-magnetite-based composites was shown to have an optimum efficiency of ~31.8%. The implications of the results are discussed for potential applications of PDMS nanocomposites in implantable biomedical devices.

Synthesis and Characterization of Alkylamine-Functionalized Si(111) for Perovskite Adhesion With Minimal Interfacial Oxidation or Electronic Defects.

We investigated synthetic strategies for the functionalization of Si(111) surfaces with organic species containing amine moieties. We employed the functionalized surfaces to chemically "glue" perovskites to silicon with efficient electron transfer and minimal oxidation leading to deleterious recombination at the silicon substrate. A two-step halogenation-alkylation reaction produced a mixed allyl-methyl monolayer on Si(111). Subsequent reactions utilized multiple methods of brominating the allyl double bond including reaction with HBr in acetic acid, HBr in THF, and molecular bromine in dichloromethane. Reaction with ammonia in methanol effected conversion of the bromide to the amine. X-ray photoelectron spectroscopy (XPS) quantified chemical states and coverages, transient-microwave photoconductivity ascertained photogenerated carrier lifetimes, atomic force microscopy (AFM) quantified perovskite-silicon adhesion, and nonaqueous photoelectrochemistry explored solar-energy-conversion performance. The HBr bromination followed by the amination yielded a surface with ∼10% amine sites on the Si(111) with minimal oxide and surface recombination velocity values below 120 cm s-1, following extended exposures to air. Importantly, conversion of amine sites to ammonium and deposition of methylammonium lead halide via spin coating and annealing did not degrade carrier lifetimes. AFM experiments quantified adhesion between perovskite films and alkylammonium-functionalized or native-oxide silicon surfaces. Adhesion forces/interactions between the perovskite and the alkylammonium-functionalized films were comparable to the interaction between the perovskite and native-oxide silicon surface. Photoelectrochemistry of perovskite thin films on alkylammonium-functionalized n+-Si showed significantly higher Voc than n+-Si with a native oxide when in contact with a nonaqueous ferrocene+/0 redox couple. We discuss the present results in the context of utilizing molecular organic recognition to attach perovskites to silicon utilizing organic linkers so as to inexpensively modify silicon for future tandem-junction photovoltaics.