The effect of pore size and porosity on mechanical properties and biological response of porous titanium scaffolds

Abstract

The effect of pore size and porosity on elastic modulus, strength, cell attachment and cell proliferation was studied for Ti porous scaffolds manufactured via powder metallurgy and sintering. Porous scaffolds were prepared in two ranges of porosities so that their mechanical properties could mimic those of cortical and trabecular bone respectively.Space-holder engineered pore size distributions were carefully determined to study the impact that small changes in pore size may have on mechanical and biological behaviour. The Young's moduli and compressive strengths were correlated with the relative porosity.Linear, power and exponential regressions were studied to confirm the predictability in the characterisation of the manufactured scaffolds and therefore establish them as a design tool for customisation of devices to suit patients' needs. The correlations were stronger for the linear and the power law regressions and poor for the exponential regressions. The optimal pore microarchitecture (i.e. pore size and porosity) for scaffolds to be used in bone grafting for cortical bone was set to <212m with volumetric porosity values of 27-37%, and for trabecular tissues to 300-500m with volumetric porosity values of 54-58%. The pore size range 212-300m with volumetric porosity values of 38-56% was reported as the least favourable to cell proliferation in the longitudinal study of 12 days of incubation.

Influence of macroporosity on NIH/3T3 adhesion, proliferation, and osteogenic differentiation of MC3T3‐E1 over bio‐functionalized highly porous titanium implant material

“…In vitro studies reported in the literature revealed that different ranges of porosity can promote different bio‐functions. A recent study showed that Ti scaffolds with pore range between 45 and 106 μm presented the best microarchitecture for early stages of attachment, presenting the higher number of cells, whereas pore range higher than 300 μm exhibited the most favorable conditions for cell proliferation. On the other hand, Hollister stated that macropores up to 1000 μm are crucial for tissue regeneration since they preserve tissue volume, provide temporary mechanical function, and allow the vascularization.…”

“…On the other hand, Prananingrum et al showed that the pore size of 100 µm presented the greatest amount of bone ingrowth, and the rate of bone ingrowth significantly decreased as the pore size increased on Ti scaffolds. Torres‐Sanchez et al concluded that small pores offer a larger surface area and at early days of culture this pore size is favorable for the attachment stage. However, when cell proliferation was dominant, larger pore size ranges also presented the largest growth rate, which confirms that large pore size supports cell growth.…”

Taguchi's methods to optimize the properties and bioactivity of 3D printed polycaprolactone/mineral trioxide aggregate scaffold: Theoretical predictions and experimental validation

“…Porosity influences cell infiltration, nutrient transfer, tissue growth, and scaffold mechanical properties (Rosa et al, ; Torres‐Sanchez et al, ). Figures and show that the porosity of the scaffold was significantly affected by all four input parameters.…”

“…The Taguchi's methods can identify noise sources that affect sample variability and allow to predict and optimize the outcomes without testing all the interactions among inputs (Rao et al, 2008;Taguchi & Yokoyama, 1993 Porosity influences cell infiltration, nutrient transfer, tissue growth, and scaffold mechanical properties (Rosa et al, 2012;Torres-Sanchez et al, 2017). Figures 2 and 3 show that the porosity of the scaffold was significantly affected by all four input parameters.…”

“…Notably, numerous parameters (e.g., composition, pore size, fibre diameter) impact the properties of scaffolds. For instance, increased porosity (>55% vol) decreased the compressive strength and modulus of elasticity of titanium scaffolds (Torres-Sanchez et al, 2017). Also, increase in fiber diameter from 0.1 to 3.4 μm decreased the Young's modulus and percentage of strain at break of PCL mats (Kim, Kim, Ryu, Ki, & Park, 2016).…”