Orthopedic Scaffolds: Evaluation of Structural Strength and Permeability of Fluid Flow via an Open Cell Neovius Structure for Bone Tissue Engineering.

The ability of bone to regenerate itself through mechanobiological responses is its dynamic property. Mechanical cues from a neighboring environment produce the structural strain to promote blood flow and bone marrow mobility that in turn aids the bone regeneration process. Occurrences of these phenomena are crucial for the success of metallic scaffolds implanted in the host bone tissue. Thus, permeability and fluid flow-induced wall shear stress (WSS) are two parameters that directly influence cell bioactivities inside a scaffold and are crucial for effective bone tissue regeneration. Given that the scaffolds shall be implanted in the body, permeability assessment was carried out using non-Newtonian fluid. In this work, the triply periodic minimal surface scaffolds with Neovius architectures were fabricated by using selective laser melting technology. The estimation of fluid flow was carried out using computational fluid dynamics (CFD) analysis with a non-Newtonian blood fluid model. Further, the structural strength of various open cell Neovius lattices was evaluated using a static compression test, and in vitro cell culture using Alamar blue assay was evaluated. Results revealed that the values of intrinsic blood flow permeability of the three-dimensional (3D)-printed open cell porous scaffold with Neovius architecture were of the same order of magnitude as those of human bone, ranging from 0.0025 × 10-9 to 0.0152 × 10-9 m2. The structural elastic modulus and compressive strength of NOCL40, NOCL50, and NOCL60 lattices range from 3.27 to 3.71 GPa and 194 to 205 MPa, respectively. All of the values are comparable to the human bone, thus making these lattices a suitable alternative for orthopedic applications.

Cellular studies and sustained drug delivery via nanostructures fabricated on 3D printed porous Neovius lattices of Ti6Al4V ELI.

Site-specific drug delivery has the potential to reduce drug dosage by 3- to 5-folds. Given the propensity of drugs used in the treatment of tuberculosis and cancers, the increased drug dosages via oral ingestion for several months to a few years of medication is often detrimental to the health of patients. In this study, the sustained delivery of drugs with multiscale structured novel Neovius lattices was achieved. 3D Neovius open cell lattices (NOCL) with porosities of 40%, 45%, and 50% were fabricated layer-by-layer on the laser bed fusion process. Micron-sized Ti6Al4V ELI powder was used for 3D printing. The Young's modulus achieved from the novel Neovius lattices were in the range of 1.2-1.6 GPa, which is comparable to human cortical bone and helps to improve implant failure due to the stress shielding effect. To provide sustained drug delivery, nanotubes (NTs) were fabricated on NOCLs via high-voltage anodization. The osteogenic agent icariin was loaded onto the NOCL-NT samples and their release profiles were studied for 7 d. A significantly steady and slow release rate of 0.05% per hour of the drug was achieved using NOCL-NT. In addition, the initial burst release of NOCL-NT was 4 fold lower than that of the open-cell lattices without NTs. Cellular studies using MG63 human osteoblast-like cells were performed to determine their biocompatibility and osteogenesis which were analyzed using Calcein AM staining and Alamar Blue after 1, 5, and 7 d. 3D printed NOCL samples with NTs and with Icariin loaded NTs demonstrated a significant increase in cell proliferation as compared to as printed NOCL samples.

Static and Fatigue Load Bearing Investigation on Porous Structure Titanium Additively Manufactured Anterior Cervical Cages.

This study investigates the static and fatigue behavior of porous and conventional anterior cervical cages. Porous structure titanium anterior cervical cages were manufactured using direct selective laser sintering technique. Four different types of cervical cages were designed and manufactured, among which three designs consist of porous structure (type 1, type 2, and type 3) and manufactured using metal 3D printing. Remaining one design (type 4) was manufactured using conventional machining and did not consist any porous structure. All types of manufactured cages were tested in compression under static and fatigue loading conditions as per ASTM F2077 standard. Static and fatigue subsidence testing was performed using ASTM F2267 standard. Static compression testing results of type 1 and type 4 cages reported higher yield load when compared to the type 2 and type 3 cages. Static subsidence testing results reported almost 11% less subsidence rate for additively manufactured cages than the conventional cages. Fatigue subsidence testing results showed that type 2 and type 3 cages can withstood approximately 21% higher number of cycles before subsidence as compare to the type 1 and type 4 cages. During fatigue testing, all the cages design survived 5 million cycles at the 3000 N loading. For 6000 N and 8000 N, loading rate type 2 and type 3 cages showed lower fatigue life when compared to other cages design. Since fatigue life of type 2 and type 3 cage designs were reported lower than other cages design, it is concluded that the performance of the additively manufactured porous cages can be significantly varied based upon the cage design features.

Finite element study on the influence of pore size and structure on stress shielding effect of additive manufactured spinal cage.

The stress shielding effect occurs when the orthopedic implant reduces the load delivered to the bone, causing inefficient stress transfer to the host bone. The usage of porous additive manufactured (AM) cages reduces the stress shielding effect and promotes bone ingrowth also. The purpose of this work is to study the stress and deformation on porous hybrid spinal cages under different loading conditions using Finite Element Analysis (FEA). The spinal cages consisting of three porous structures with pore sizes ranging from 0.4 to 0.6 mm were investigated for stress shielding and fatigue strength. The results showed a significant reduction in stress shielding for the studied designs and conclude that the pore size has a greater significant effect on stress shielding than the porous structure in spinal cages.

Electro-deposition of bactericidal and corrosion-resistant hydroxyapatite nanoslabs.

Herein, nanoscale hydroxyapatite (HA) with a slab-like morphology was synthesized, and its size was calculated to be in the range of 80-150 nm, as confirmed via scanning electron microscopy (SEM) and atomic force microscopy (AFM). The nanoscale HA with a slab-like structure has been referred as HA nanoslabs in the manuscript. The composition, crystallinity, wettability, bacterial resistance porosity, surface roughness and corrosion resistance of these HA nanoslabs were studied using energy dispersive spectroscopy (EDAX), X-ray diffraction (XRD), contact angle, colony count BET analyzer and profilometer and polarization techniques, respectively. The contact angle of the HA nanoslabs was found to be 22.6°, which indicated the hydrophilic nature of these nanoslabs. Their bacterial resistance was studied against the Salmonella typhi strain, and it was found that in the presence of the HA nanoslabs, the growth of the bacteria was hindered. For the corrosion resistance study, the HA nanoslabs were electro-deposited on a titanium alloy, used as a substrate. The deposition was carried out at varying currents, viz, 1 mA, 3 mA and 5 mA. The open circuit potential (OCP) and polarization were used for the estimation of the corrosion resistance of the bare and coated substrates. The corrosion potential started shifting towards noble potential, and the current density started decreasing with an increase in the electrochemical deposition current. This indicated good corrosion resistance of these nanoslabs.