Residual Stress Patterns Affect Cell Distributions on Injection-Molded Poly-l-Lactide Substrate

High-manganese and nitrogen stabilized austenitic stainless steel (Fe-18Cr-22Mn-0.65N): a material with a bright future for orthopedic implant devices

The rationale behind the success of nickel free or with extremely low nickel austenitic high manganese and nitrogen stabilized stainless steels is adverse influences of nickel ion on human body. Replacement of nickel by nitrogen and manganese provides a stable microstructure and facilitates better biocompatibility in respect of the conventional 316L austenitic stainless steel (316L SS). In this investigation, biocompatibility of the high-manganese and nitrogen stabilized (Fe-18Cr-22Mn-0.65N) austenitic stainless steel was studied and found highly promising.In vitrocell culture and cell proliferation (MTT) assays were performed on this stainless steel and assessed in respect of the 316L SS. Both the steels exhibited similar cell growth behavior. Furthermore, an enhancement was observed in cell proliferation on the Fe-18Cr-22Mn-0.65N SS after surface modification by ultrasonic shot peening (USP). The mean percent proliferation of the MG-63 cells increased from ≈88% for Un-USP to 98% and 105% for USP 3-2 and USP 2-2 samples, respectively for 5 d of incubation. Interestingly,in vivoanimal study performed in rabbits for 3 and 6 weeks showed callus formation and sign of union without any allergic reaction.

Hydrogel-based methods for engineering cellular microenvironment with spatiotemporal gradients

Natural cellular microenvironment consists of spatiotemporal gradients of multiple physical (e.g. extracellular matrix stiffness, porosity and stress/strain) and chemical cues (e.g. morphogens), which play important roles in regulating cell behaviors including spreading, proliferation, migration, differentiation and apoptosis, especially for pathological processes such as tumor formation and progression. Therefore, it is essential to engineer cellular gradient microenvironment incorporating various gradients for the fabrication of normal and pathological tissue models in vitro. In this article, we firstly review the development of engineering cellular physical and chemical gradients with cytocompatible hydrogels in both two-dimension and three-dimension formats. We then present current advances in the application of engineered gradient microenvironments for the fabrication of disease models in vitro. Finally, concluding remarks and future perspectives for engineering cellular gradients are given.

Enhanced Osteoblast Proliferation and Corrosion Resistance of Commercially Pure Titanium Through Surface Nanostructuring by Ultrasonic Shot Peening and Stress Relieving

This investigation was carried out to study the effect of a novel process of surface modification, surface nanostructuring by ultrasonic shot peening, on osteoblast proliferation and corrosion behavior of commercially pure titanium (c p-Ti) in simulated body fluid. A mechanically polished disc of c p-Ti was subjected to ultrasonic shot peening with stainless steel balls to create nanostructure at the surface. A nanostructure (<20 nm) with inhomogeneous distribution was revealed by atomic force and scanning electron microscopy. There was an increase of approximately 10% in cell proliferation, but there was drastic fall in corrosion resistance. Corrosion rate was increased by 327% in the shot peened condition. In order to examine the role of residual stresses associated with the shot peened surface on these aspects, a part of the shot peened specimen was annealed at 400°C for 1 hour. A marked influence of annealing treatment was observed on surface structure, cell proliferation, and corrosion resistance. Surface nanostructure was much more prominent, with increased number density and sharper grain boundaries; cell proliferation was enhanced to approximately 50% and corrosion rate was reduced by 86.2% and 41% as compared with that of the shot peened and the as received conditions, respectively. The highly significant improvement in cell proliferation, resulting from annealing of the shot peened specimen, was attributed to increased volume fraction of stabilized nanostructure, stress recovery, and crystallization of the oxide film. Increase in corrosion resistance from annealing of shot peened material was related to more effective passivation. Thus, the surface of c p-Ti, modified by this novel process, possessed a unique quality of enhancing cell proliferation as well as the corrosion resistance and could be highly effective in reducing treatment time of patients adopting dental and orthopedic implants of titanium and its alloys.

Development and biocompatibility tests of electrospun poly-l-lactide nanofibrous membranes incorporating oleic acid-coated Fe3O4

The aim of this study was to develop an electrospun poly-l-lactide (PLLA) nanofibrous membrane incorporating oleic acid-coated Fe3O4. The Fe3O4 nanoparticles were prepared using the chemical co-precipitation method, and particle diameters were analyzed using transmission electron microscopy. After mixing the oleic acid-coated Fe3O4 nanoparticles and PLLA, a membrane with nanofibers was manufactured using the electrospinning technique. Our results showed that Fe3O4 nanoparticle diameters fabricated in this study were concentrated at 2–8 nm (84.2%). After magnetizing, there exists an approximately linear relationship between magnetic flux density and membrane thickness (R2=0.7, p<0.05). NIH-3T3 fibroblast cells cultured on the magnetized Fe3O4/PLLA nanomembranes exhibited a more spreading and attached phenotype. These results can serve as a reference for future advanced studies.

Effects of compressive residual stress on the morphologic changes of fibroblasts

Recently, the term tensotaxis was proposed to describe the phenomenon that tensile stress or strain affects cell migration. Even so, less attention has been paid to the effects of compressive stress on cell behavior. In this study, by using an injection-molded method combined with photoelastic technology, we developed residual stress gradient-controlled poly-L-lactide discs. After culturing NIH-3T3 fibroblasts on the stress gradient substrate, the cell distributions for high- and low-stress regions were measured and compared. Our results showed that there were significantly more cells in the low-compressive stress region relative to their high-stress analogs (p < 0.05). In addition, NIH-3T3 fibroblasts in the low-compressive stress region expressed more abundant extensive filopodia. These findings provide greater insight into the interaction between cells and substrates, and could serve as a useful reference for connective tissue development and repair.