Additively manufactured porous scaffolds by design for treatment of bone defects

There has been increasing attention to produce porous scaffolds that mimic human bone properties for enhancement of tissue ingrowth, regeneration, and integration. Additive manufacturing (AM) technologies, i.e., three dimensional (3D) printing, have played a substantial role in engineering porous scaffolds for clinical applications owing to their high level of design and fabrication flexibility. To this end, this review article attempts to provide a detailed overview on the main design considerations of porous scaffolds such as permeability, adhesion, vascularisation, and interfacial features and their interplay to affect bone regeneration and osseointegration. Physiology of bone regeneration was initially explained that was followed by analysing the impacts of porosity, pore size, permeability and surface chemistry of porous scaffolds on bone regeneration in defects. Importantly, major 3D printing methods employed for fabrication of porous bone substitutes were also discussed. Advancements of MA technologies have allowed for the production of bone scaffolds with complex geometries in polymers, composites and metals with well-tailored architectural, mechanical, and mass transport features. In this way, a particular attention was devoted to reviewing 3D printed scaffolds with triply periodic minimal surface (TPMS) geometries that mimic the hierarchical structure of human bones. In overall, this review enlighten a design pathway to produce patient-specific 3D-printed bone substitutions with high regeneration and osseointegration capacity for repairing large bone defects

Effect of Adsorption on Interfacial Energy Transport Across Solid-vapor Interfaces

We have studied the energy transport across solid-vapor interfaces. An experimental apparatus was designed and built to maintain the temperature at the top of the vapor phase at a constant value and the temperature at the bottom of the solid at smaller value. The vapor was water, and three substrates with differerent thermal conductivities were examined: Teon, gold and silica. At the intervening solid-vapor interface, temperature discontinuities were observed. Furthermore, the amount of water vapor adsorbed on gold was compared with the adsorbed amount of water vapor previously measured on Teflon and silica surfaces. The experimental results show that an increase in the amount of vapor adsorbed was observed to decrease the temperature discontinuity and to enhance the thermal energy transport across the solid-vapor interface. We found that for the substrates considered, it is the interfacial energy transport that controls the total energy transport rather than thermal conductivity.M.A.S.2017-06-13 00:00:0

From adsorption to condensation: The Zeta adsorption isotherm approach

The Zeta Adsorption Isotherm is based on the hypothesis that molecules adsorb on a solid surface as a collection of molecular clusters. The theory is extended to the steady, thermal disequilibrium states where a vapour at a temperature T^V is exposed to a solid surface at a lower temperature, T^S, and the adsorption of the vapour on a homogenous solid surface is examined analytically and experimentally. The uv-visible interferometer technique is used to measure the amount of vapour adsorbed under these steady, thermal disequilibrium states and the results give a strong support to the predicted amount adsorbed. The Zeta Adsorption Isotherm which is based on the assumption of the existence of molecular clusters is applied to predict the subcooling required for the adsorbate to make a disorder-order phase transition. The theory was used along with the Gibbsian thermodynamics to develop a method for predicting the wetting condition on a vertically oriented silicon surface exposed to the heptane vapour in a gravitational field. The measurements indicate the larger amount of vapour is adsorbed at the lower potential energies. The wetting condition is taken to be reached when the adsorbed vapour is transformed into a liquid film. Further, the surface tension of solid-vapour interface and the solid-liquid interface are calculated, and the condition for drainage of the liquid from the Si surface is predicted. It is shown that when the surface tension of the solid-liquid interface is reduced to zero, gravity would cause the larger molecular clusters to drain down the surface. The experimental observations support this prediction. Finally, the proposed method is applied to toluene and octane and heptane vapours adsorbing on Si. Dropwise condensation is observed experimentally for toluene vapour while filmwise condensation is observed for the other two vapours. From the distribution of the clusters in the adsorbate, the conditions for the initiation of the liquid phase are predicted and the surface tensions are determined for these three systems of vapours. The results are compared, and the mechanism which determines the condensation mode of the vapour condensing on the Si surface is investigated.Ph.D