@article{durham_allen_rabiei_2017, title={Preparation, characterization and in vitro response of bioactive coatings on polyether ether ketone}, volume={105}, ISSN={["1552-4981"]}, DOI={10.1002/jbm.b.33578}, abstractNote={Polyether ether ketone (PEEK) is a highly heat-resistant thermoplastic with excellent strength and elastic modulus similar to human bone, making it an attractive material for orthopedic implants. However, the hydrophobic surface of PEEK implants induces fibrous encapsulation which is unfavorable for stable implant anchorage. In this study, PEEK was coated via ion-beam-assisted deposition (IBAD) using a two-layer design of yttria-stabilized zirconia (YSZ) as a heat-protection layer, and hydroxyapatite (HA) as a top layer to improve osseointegration. Microstructural analysis of the coatings showed a dense, uniform columnar grain structure in the YSZ layer and no delamination from the substrate. The HA layer was found to be amorphous and free of porosities in its as-deposited state. Subsequent heat treatment via microwave energy followed by autoclaving crystallized the HA layer, confirmed by SEM and XRD analysis. An in vitro study using MC3T3 preosteoblast cells showed improved bioactivity in heat-treated sample groups. Cell proliferation, differentiation, and mineralization were analyzed by MTT assay and DNA content, osteocalcin expression, and Alizarin Red S (AR-S) content, respectively. Initial cell growth was increased, and osteogenic maturation and mineralization were accelerated most on coatings that underwent a combined microwave and autoclave heat treatment process as compared to uncoated PEEK and amorphous HA surfaces. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 560-567, 2017.}, number={3}, journal={JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART B-APPLIED BIOMATERIALS}, author={Durham, John W., III and Allen, Matthew J. and Rabiei, Afsaneh}, year={2017}, month={Apr}, pages={560–567} }
 @article{durham_rabiei_2016, title={Deposition, heat treatment and characterization of two layer bioactive coatings on cylindrical PEEK}, volume={301}, ISSN={["0257-8972"]}, DOI={10.1016/j.surfcoat.2015.12.045}, abstractNote={Polyether ether ketone (PEEK) rods were coated via ion beam asssisted deposition (IBAD) at room temperature. The coating consists of a two-layer design of yttria-stabilized zirconia (YSZ) as a heat-protection layer, and hydroxyapatite (HA) as a top layer to increase bioactivity. A rotating substrate holder was designed to deposit an even coating on the cylindrical surface of PEEK rods; the uniformity is verified by cross-sectional measurements using scanning electron microscopy (SEM). Deposition is followed by heat treatment of the coating using microwave annealing and autoclaving. Transmission electron microscopy (TEM) showed a dense, uniform columnar grain structure in the YSZ layer that is well bonded to the PEEK substrate, while the calcium phosphate layer was amorphous and pore-free in its as-deposited state. Subsequent heat treatment via microwave energy introduced HA crystallization in the calcium phosphate layer and additional autoclaving further expanded the crystallization of the HA layer. Chemical composition evaluation of the coating indicated the Ca/P ratios of the HA layer to be near that of stoichiometric HA, with minor variations through the HA layer thickness. The adhesion strength of as-deposited HA/YSZ coatings on smooth, polished PEEK surfaces was mostly unaffected by microwave heat treatment, but decreased with additional autoclave treatment. Increasing surface roughness showed improvement of bond strength.}, journal={SURFACE & COATINGS TECHNOLOGY}, author={Durham, John W., III and Rabiei, Afsaneh}, year={2016}, month={Sep}, pages={106–113} }
 @article{durham_montelongo_ong_guda_allen_rabiei_2016, title={Hydroxyapatite coating on PEEK implants: Biomechanical and histological study in a rabbit model}, volume={68}, ISSN={["1873-0191"]}, DOI={10.1016/j.msec.2016.06.049}, abstractNote={A bioactive two-layer coating consisting of hydroxyapatite (HA) and yttria-stabilized zirconia (YSZ) was investigated on cylindrical polyetheretherketone (PEEK) implants using ion beam assisted deposition (IBAD). Post-deposition heat treatments via variable frequency microwave annealing with and without subsequent autoclaving were used to crystallize the as-deposited amorphous HA layer. Microstructural analysis, performed by TEM and EDS, showed that these methods were capable of crystallizing HA coating on PEEK. The in vivo response to cylindrical PEEK samples with and without coating was studied by implanting uncoated PEEK and coated PEEK implants in the lateral femoral condyle of 18 rabbits. Animals were studied in two groups of 9 for observation at 6 or 18weeks post surgery. Micro-CT analysis, histology, and mechanical pull-out tests were performed to determine the effect of the coating on osseointegration. The heat-treated HA/YSZ coatings showed improved implant fixation as well as higher bone regeneration and bone-implant contact area compared to uncoated PEEK. The study offers a novel method to coat PEEK implants with improved osseointegration.}, journal={MATERIALS SCIENCE & ENGINEERING C-MATERIALS FOR BIOLOGICAL APPLICATIONS}, author={Durham, John W., III and Montelongo, Sergio A. and Ong, Joo L. and Guda, Teja and Allen, Matthew J. and Rabiei, Afsaneh}, year={2016}, month={Nov}, pages={723–731} }
 @article{durham_zhu_2013, title={Fabrication of Functional Nanowire Devices on Unconventional Substrates Using Strain-Release Assembly}, volume={5}, ISSN={["1944-8244"]}, DOI={10.1021/am302384z}, abstractNote={We report three representative nanowire (NW) devices for applications in stretchable electronics, strain sensing, and optical sensing. Fabrication of such devices is based on a recently developed strain-release assembly method. NWs are first aligned transversely on an elastomeric substrate using the strain-release assembly. Constant resistance is achieved in silicon (Si) NW devices stretched up to ~40% of axial strain, highlighting a new concept of transverse buckling. Combining the NW assembly with transfer printing extends suitable device substrates beyond elastomers to other unconventional materials (e.g., flexible and transparent materials). Following this combined process, flexible SiNW strain sensors are fabricated on plastics capable of sensing up to 1.6% bending strain and gauge factors >1000; flexible zinc oxide NW ultraviolet sensors are demonstrated with quick recovery (~2 s) and excellent repeatability on plastics. Our results show promise for the strain-release assembly as a simple and cost-effective process to fabricate NW devices on unconventional substrates.}, number={2}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Durham, John W., III and Zhu, Yong}, year={2013}, month={Jan}, pages={256–261} }