The engineering of biomimetic tissue relies on the ability to develop biodegradable scaffolds with functionally graded physical and chemical properties. In this study, a twin-screw-extrusion/spiral winding (TSESW) process was developed to enable the radial grading of porous scaffolds (discrete and continuous gradations) that were composed of polycaprolactone (PCL), beta-tricalciumphosphate (beta-TCP) nanoparticles, and salt porogens. Scaffolds with interconnected porosity, exhibiting myriad radial porosity, pore-size distributions, and beta-TCP nanoparticle concentration could be obtained. The results of the characterization of their compressive properties and in vitro cell proliferation studies using human fetal osteoblast cells suggest the promising nature of such scaffolds. The significant degree of freedom offered by the TSESW process should be an additional enabler in the quest toward the mimicry of the complex elegance of the native tissues.
Large-scale and reproducible manufacturing of scaffolds for tissue engineering applications will necessitate the adoption of methods relying on the processing of the biodegradable polymers directly from the melt. Such solventless processing will give rise to bulk and surface properties that will differ significantly from those generated upon processing from solution-based methods. Thus, detailed understanding of the microstructures that are developed during melt processing and the resulting surface/cell interactions is needed. Here, surfaces of melt-cast poly(L-lactide) (PLLA) were patterned to furnish membrane samples with a wide range of crystallinity and significant differences in surface topographies, ranging from highly crystalline (60%) with spherulitic protrusions at the surface to amorphous with nanoscale indentations. The PLLA membranes were used to culture in vitro mouse 3T3-Swiss albino fibroblast cells and osteoblast-like MC3T3-E1 cells. The growth rates of 3T3 fibroblasts were significantly lower on highly crystalline PLLA membranes with spherulitic protrusions in comparison to crystalline PLLA without spherulitic protrusions and amorphous surfaces with 5-10-nm-deep indentations. However, the differences in the growth rates of osteoblast-like cells cultured on the PLLA membranes with different surface patterns were only marginally different.
Gels made with three different polymers widely used as rheology modifiers in cosmetic formulations (cross-linked poly(acrylic acid), cross-linked poly(maleic acid-alt-methyl vinyl ether) copolymer and cross-linked poly(acrylic acid-co-vinyl pyrrolidone) copolymer) were characterized by rheological and sensory evaluation methods to determine the relationship between sensorial perception and corresponding rheological parameters. Both conventional rheological characterization methods and a more recent method, Fourier Transform Rheology with Large Amplitude Oscillatory Flow data (LAOS), were utilized to characterize the material with and without wall slip. Sensorial analyses were implemented in vivo to evaluate the perceived ease of initial and rub-out spreadability, cushion, pick-up and slipperiness attributes of the gels. Results were statistically analysed by both variance (ANOVA) and principle component analysis (PCA). Sensorial panel testing characteristics discriminated the three materials, and PCA analyses revealed that sensory attributes could be well predicted by rheological methods. Rheological experiments, without wall slip, revealed that gel strength in the linear viscoelastic region (LVR) and yield stress of these materials are similar, but exhibit significantly different wall slip and thixotropy behaviour in the low shear rate region under wall slip conditions. Above the critical shear rate, which corresponds to the yield stress, all tested materials did not slip and behaved as conventional, shear thinning polymeric fluids. In particular, the rheological parameters and sensorial perception of the 1% cross-linked vinyl pyrrolidone/acrylic acid copolymer were significantly affected by wall slip and/or thixotropy-related shear banding phenomena.
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