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.

Initiation of condensation of toluene and octane vapours on a Si surface.

The adsorption of toluene and octane vapours on a homogenous silicon surface was measured under steady, thermal disequilibrium conditions where a vapour at a temperature T V is exposed to a solid surface at a lower temperature, T S. Zeta adsorption isotherm theory was used along with Gibbsian thermodynamics to examine the adsorption results analytically and to investigate the wetting conditions for these vapours. Further, from the prediction of the cluster distribution in the adsorbate, the conditions for the initiation of a liquid phase are predicted. Finally, the mechanism that determines the condensation mode of hydrocarbons on a silicon surface is investigated.

Initiation of wetting, filmwise condensation and condensate drainage from a surface in a gravity field.

The zeta adsorption isotherm is based on the hypothesis that a vapour adsorbed on a solid surface consists of a collection of molecular clusters. We use this isotherm to propose a method for determining the wetting condition on a vertically oriented silicon surface exposed to heptane in a gravity field. Measurements indicate the amount adsorbed is larger at positions of smaller potential energy. The wetting condition is taken to be reached when the adsorbed vapour is transformed into the adsorbed liquid phase: adsorption lowers the surface tension of Si from the value in the absence of adsorption to that of liquid heptane at wetting, and then as the Si-heptane is cooled further it is reduced to zero, at a subcooling of 3.7 K. The expectation is that when this subcooling is reached, gravity would cause the larger molecular clusters to drain down the surface. This prediction is supported by experimental observations.

From adsorption to condensation: the role of adsorbed molecular clusters.

The adsorption of heptane vapour on a smooth silicon substrate with a lower temperature than the vapour is examined analytically and experimentally. An expression for the amount adsorbed under steady state conditions is derived from the molecular cluster model of the adsorbate that is similar to the one used to derive the equilibrium Zeta adsorption isotherm. The amount adsorbed in each of a series of steady experiments is measured using a UV-vis interferometer, and gives strong support to the amount predicted to be adsorbed. The cluster distribution is used to predict the subcooling temperature required for the adsorbed vapour to make a disorder-order phase transition to become an adsorbed liquid, and the subcooling temperature is found to be 2.7 ± 0.4 K. The continuum approach for predicting the thickness of the adsorbed liquid film originally developed by Nusselt is compared with that measured and is found to over-predict the thickness by three-orders of magnitude.