Porous stainless steel for biomedical applications

Abstract

Porous 316L austenitic stainless steel was synthesized by powder metallurgy with relative density of 0.50 and 0.30 using 15 and 30 wt. (%) respectively of ammonium carbonate and ammonium bicarbonate as foaming agents. The powders were mixed in a planetary ball mill at 60 rpm for 10 minutes. The samples were uniaxially pressed at 287 MPa and subsequently vacuum heat treated in two stages, the first one at 200 °C for 5 hours to decompose the carbonate and the second one at 1150 °C for 2 hours to sinter the steel. The sintered samples had a close porous structure and a multimodal pore size distribution that varied with the foaming agent and its concentration. The samples obtained by addition of 30 wt. (%) of foaming agents had a more homogeneous porous structure than that obtained with 15 wt. (%). The MTT cytotoxicity test (3-[4,5-dimethylthiazol]-2,5-diphenyltetrazolium bromide) was used to evaluate the mitochondrial activity of L929 cells with samples for periods of 24, 48, and 72 hours. The cytotoxicity test showed that the steel foams were not toxic to fibroblast culture. The sample with the best cellular growth, therefore the most suitable for biomedical applications among those studied in this work, was produced with 30 wt. (%) ammonium carbonate. In this sample, cell development was observed after 48 hours of incubation, and there was adhesion and spreading on the material after 72 hours. Electrochemical experiments using a chloride-containing medium were performed on steel foams and compared to massive steel. The massive steel had a better corrosion performance than the foams as the porosity contributes to increase the surface area exposed to the corrosive medium.

Evading the host response: Staphylococcus “hiding” in cortical bone canalicular system causes increased bacterial burden

“…While immune cells may physically engage the larger haversian system (~50 μm), the 100× smaller size of the canaliculus (~0.13-0.39 μm) may provide a physical barrier to host immune cells and therefore provides a likely mechanistic pathway by which S. aureus (0.5-1.0 μm) achieve a "hiding" place from the host immune system, and ultimately, increased infection rates. [49][50][51] Meanwhile, the pore size of the comparison implant materials studied in this experiment, medical grade 316L stainless steel (5-10 μm) 52 and "normal" cancellous bone (300-600 μm) 53 is perhaps permissibly large, enabling inflammatory cell infiltration and clearance of infection. Furthering this concept, Schwarz et al 54 describe the limits to bioavailability of antimicrobial agents within the osteocyticcanalicular network, providing additional support for a mechanism by which otherwise susceptible S. aureus develop resistance to host immunity and immunotherapies within the submicron canalicular network.…”

Effect of 45S5 Bio-Glass Particles on Physical Properties and Corrosion Resistance of the Mg-5Zn Matrix Composite

“…where: ρ i -theoretical density of composite constituent; f i -mass fraction of composite constituent. The bulk density was determined using Equation (2) [16].…”

“…Bulk mass volume ρ = (2) True density of the sintered samples was determined using the gas pycnometer (Model: Micromeritics Ac-cuPyc II 1340) according to the ASTM B923-10 [17]. The relative density and total porosity were determined using Equations (3) [16] and (4)…”

Air Permeability of Maraging Steel Cellular Parts Made by Selective Laser Melting

“…Additive manufacturing (AM) can deliver parts of complex geometries with minimal need for secondary machining. To permit large-scale industrial use [ 1 ], cellular structure-based products are prepared using AM in the fields of biomedical [ 2 , 3 ], heat exchanger [ 4 , 5 ] and aeronautical [ 6 ] applications.…”