The Role of Implant Surface Geometry on Mineralization In Vivo and In Vitro; A Transmission and Scanning Electron Microscopic Study

The purpose of th.is study was to examine the effect of substratum surface topography on bone formation in vivo and in vitro. Precise control over substratum topography was achieved using micromachining, a technique developed from the fabrication of microelectronic components. In the in vivo studies, titanium-coated epoxy replicas of micromachined surfaces were implanted subcutaneously in the parietal area of rats. After 6 weeks, bone-like tissue was found adjacent to some micromachined surfaces. Detailed observation of this tissue with the transmission electron microscope revealed osteoblast/osteocyte-like cells and a fully or partially mineralized collagenous matrix. Mineralized matrix and collagen bundles were found contacting the titanium coating without any intervening material. Mineralized tissue was not found adjacent to smooth surfaces. In vitro, enzymatically released osteogenic cells from calvarial bone produced large ( ~ 10 μm) and small ( ~ 0.5-3 μm) mineralized globules on the micromachined surfaces, whereas only small mineralized globules formed on the smooth control surfaces after 4 weeks of culture. The mineralized nature of the globules was confirmed by energy dispersive X-ray analysis. In a second osteogenic culture system, micromachined or smooth control surfaces were placed on calvarial explants. After 4 weeks, partially mineralized globules ( ~ 5 μm) were noted interspersed between cells and extracellular matrix on the micromachined surfaces but not on the smooth surfaces. This study suggests that the surface topography of an implant influences bone formation in vivo and in vitro and that micromachined surfaces of the dimensions used in these experiments promote mineralized tissue formation

Numerical framework for transcritical real-fluid reacting flow simulations using the flamelet progress variable approach

An extension to the classical FPV model is developed for transcritical real-fluid combustion simulations in the context of finite volume, fully compressible, explicit solvers. A double-flux model is developed for transcritical flows to eliminate the spurious pressure oscillations. A hybrid scheme with entropy-stable flux correction is formulated to robustly represent large density ratios. The thermodynamics for ideal-gas values is modeled by a linearized specific heat ratio model. Parameters needed for the cubic EoS are pre-tabulated for the evaluation of departure functions and a quadratic expression is used to recover the attraction parameter. The novelty of the proposed approach lies in the ability to account for pressure and temperature variations from the baseline table. Cryogenic LOX/GH2 mixing and reacting cases are performed to demonstrate the capability of the proposed approach in multidimensional simulations. The proposed combustion model and numerical schemes are directly applicable for LES simulations of real applications under transcritical conditions.Comment: 55th AIAA Aerospace Sciences Meeting, Dallas, T

Effects of gas density on the structure of liquid jets in still gases

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77334/1/AIAA-11098-570.pd

Structure of the near-injector region of nonevaporating pressure-atomized sprays

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76883/1/AIAA-23315-239.pd

Continuous- and dispersed-phase structure of dense nonevaporating pressure-atomized sprays

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77144/1/AIAA-23475-448.pd

The Relative Importance of Topography and RGD Ligand Density for Endothelial Cell Adhesion

The morphology and function of endothelial cells depends on the physical and chemical characteristics of the extracellular environment. Here, we designed silicon surfaces on which topographical features and surface densities of the integrin binding peptide arginine-glycine-aspartic acid (RGD) could be independently controlled. We used these surfaces to investigate the relative importance of the surface chemistry of ligand presentation versus surface topography in endothelial cell adhesion. We compared cell adhesion, spreading and migration on surfaces with nano- to micro-scaled pyramids and average densities of 6×102–6×1011 RGD/mm2. We found that fewer cells adhered onto rough than flat surfaces and that the optimal average RGD density for cell adhesion was 6×105 RGD/mm2 on flat surfaces and substrata with nano-scaled roughness. Only on surfaces with micro-scaled pyramids did the topography hinder cell migration and a lower average RGD density was optimal for adhesion. In contrast, cell spreading was greatest on surfaces with 6×108 RGD/mm2 irrespectively of presence of feature and their size. In summary, our data suggest that the size of pyramids predominately control the number of endothelial cells that adhere to the substratum but the average RGD density governs the degree of cell spreading and length of focal adhesion within adherent cells. The data points towards a two-step model of cell adhesion: the initial contact of cells with a substratum may be guided by the topography while the engagement of cell surface receptors is predominately controlled by the surface chemistry