Improving Biological Functions of Three-Dimensional Printed Ti2448 Scaffolds by Decoration with Polydopamine and Extracellular Matrices.

Extracellular matrices (ECMs) provide important cues for cell proliferation and differentiation in the complex environment, which show a significant influence on cell functions. Herein, cell-derived ECMs were deposited on the polydopamine (PDA)-decorated porous Ti-24Nb-4Zr-8Sn (Ti2448) scaffolds fabricated by the electron beam melting method in order to improve biological functions. The influence of PDA-ECM coatings on cell functions was further investigated. The results demonstrated that the PDA-ECM coating facilitated adhesion, proliferation, and migration of MC3T3-E1 cells on Ti2448 scaffolds. Moreover, Ti2448-PDA-ECM scaffolds promoted osteogenesis differentiation of cells indicated by greater alkaline phosphatase activity and further mineralization, compared to the plain Ti2448 group. Meanwhile, Ti2448-PDA-ECM scaffolds enhanced bone growth after implantation for one month in rabbit femoral bone defects. Our findings suggest that the bioinspired PDA-ECM coating can be implemented on the porous Ti2448 scaffolds, which significantly improve the biological functions of orthopedic implants.

The Significance of Coherent Transformation on Grain Refinement and Consequent Enhancement in Toughness.

Coherent transformation is considered to be an effective approach to refine the microstructure and enhance toughness of structural steels. However, there are gaps in the knowledge on the key aspects of microstructure that govern toughness. In this regard, a low alloyed experimental steel with lean chemistry was subjected to a simple heat treatment involving austenitization at different temperatures, followed by quenching and tempering to obtain bainitic microstructures with different boundary composition. The microstructure of the four experimental steels was characterized by electron backscattered diffraction and mechanical properties were determined. The study indicated that the density of high angle grain boundaries does not adequately reflect the change of ductile-to-brittle transition temperatures (DBTT) of the experimental steels. Thus, we propose here a new mechanism on reducing DBTT from the perspective of misorientation of boundary, which takes into consideration these aspects in defining DBTT. One is inhibition effect on cleavage fracture by boundaries with high {100}-plane misorientation angles, and the other is ductility improvement by boundaries with high {110}-plane misorientation angles. Furthermore, the contribution of prior austenite grain boundary, packet boundary, block boundary, and sub-block boundary on toughness is also analyzed.

Favorable modulation of osteoblast cellular activity on Zr-modified Co-Cr-Mo alloy: The significant impact of zirconium on cell-substrate interactions.

Cobalt-chromium-molybdenum alloys exhibit good mechanical properties (yield strength: ~530 MPa, ultimate tensile strength: ~1114 MPa, elongation-to-failure: ~47.3%, and modulus: ~227 GPa) and corrosion resistance. In recent years, from the perspective of osseointegration, they are considered to be lower in rank in comparison to the widely used titanium alloys. We elucidate here the significant and favorable modulation of cellular activity of Zr-modified Co-Cr-Mo alloys. The average grain size of Co-Cr-Mo alloy samples with and without Zr was 104 ± 27 and ~53 ± 11 µm, respectively. The determining role of small addition of Zr (0.04 wt. %) to the Co-Cr-Mo alloys in favorable modulation of cellular activity was accomplished by combining cellular biology and materials science and engineering. Experiments on the influence of Zr addition to Co-Cr-Mo alloys clearly demonstrated that the cell adhesion, spread and cell-substrate interactions were enhanced in the presence of Zr. The spread/growth rate of cells was ~120% on the Co-Cr-Mo alloy and 190% per day on the Co-Cr-Mo-Zr alloy. While the % area covered by the cells increased from ~5.1 to ~33.6% on Co-Cr-Mo alloy and ~19.2 to ~47.8% on Co-Cr-Mo-Zr alloy after 2 and 24 hr of incubation. Similarly, the cell density increased from ~1354 to ~3424 cells/cm2 on Co-Cr-Mo alloy and ~3583 to ~7804 cells/cm2 on Co-Cr-Mo-Zr alloy after 2 and 24 hr of incubation. Additionally, stronger vinculin focal adhesion contact and signals associated with actin stress fibers together with extracellular matrix protein, fibronectin, were noted.

Interplay of topographical and biochemical cues in regulating osteoblast cellular activity in BMP-2 eluting three-dimensional cellular titanium alloy mesh structures.

The objective of this study is to elucidate the elution response of bone morphogenetic protein (BMP-2) in tuning cellular functions on 3D-printed titanium alloy mesh scaffolds subjected to microarc/plasma electrolytic oxidation process. The microtopographical cues enabled strong interaction with BMP-2 protein, which led to controlled release. Furthermore, the interaction of BMP-2 with the surface microtopographical cue regulated osteoblast cellular activity by contributing to the early phase differentiation and mineralization of osteoblasts. The in vitro BMP-2 release kinetics showed an initial burst of BMP-2 after day 1, followed by a controlled release on plasma electrolytic oxidized mesh structure. The profile represented that the rate of release decreased with increase in time on both as-fabricated and plasma electrolytic oxidized mesh structures after 24 h, with relatively higher degree on plasma electrolytic oxidized mesh structure. Furthermore, the in vitro osteoblast cellular activity indicated enhanced osteogenic induction on BMP-2 adsorbed plasma electrolytic oxidized mesh structure. Cells penetrated into micropores through several filopodia-like cellular extensions by increasing the area of contact, leading to stronger cell adhesion on BMP-2 adsorbed plasma electrolytic oxidized mesh structure. The up-regulation of biochemical markers and quantification of the expression level of cell secreted proteins underscored the determining role of BMP-2 eluting 3D mesh structure in modulating osteoblasts functions. The study emphasizes the potential of BMP-2 in rendering plasma electrolytic oxidized 3D-printed titanium alloy mesh structure osteoinductive and controlled delivery of BMP-2. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 49-60, 2019.

Pulsed electric field mediated in vitro cellular response of fibroblast and osteoblast-like cells on conducting austenitic stainless steel substrate.

This article reports the intermittent pulse electric field stimulus mediated in vitro cellular response of L929 mouse fibroblast/SaOS2 osteoblast-like cells on austenitic steel substrates in reference to the field strength dependent behavior. The cellular density and morphometric analyses revealed that the optimal electric (E) fields for the maximum cell density of adhered L929 (~270 % to that of untreated sample) and SaOS2 (~280 % to that of untreated sample) cells are 1 V (0.33 V/cm) and 2 V (0.67 V/cm), respectively. The trend in aspect ratio of elongated SaOS2 cells did not indicate any significant difference among the untreated and treated (up to 3.33 V/cm) cells. The average cell and nucleus areas (for SaOS2 cells) were increased with an increase in the applied voltage up to 8 V (2.67 V/cm) and reduced thereafter. However, the ratio of nucleus to total cell area was increased significantly on the application of higher voltages (2-10 V), indicating the possible influence of E-field on cell growth. Further, the cell density results were compared with earlier results obtained with sintered Hydroxyapatite (HA) and HA-BaTiO3 composites and such comparison revealed that the enhanced cell density on steel sample occurs upon application of much lower field strength and stimulation time. This indicates the possible role of substrate conductivity towards cell growth in pulsed E-field mediated culture conditions.