Enhancement of osteoblast activity on nanostructured NiTi/hydroxyapatite coatings on additive manufactured NiTi metal implants by nanosecond pulsed laser sintering

Additive Manufacturing: An Opportunity for the Fabrication of Near-Net-Shape NiTi Implants

Nickel–titanium (NiTi) is a shape-memory alloy, a type of material whose name is derived from its ability to recover its original shape upon heating to a certain temperature. NiTi falls under the umbrella of metallic materials, offering high superelasticity, acceptable corrosion resistance, a relatively low elastic modulus, and desirable biocompatibility. There are several challenges regarding the processing and machinability of NiTi, originating from its high ductility and reactivity. Additive manufacturing (AM), commonly known as 3D printing, is a promising candidate for solving problems in the fabrication of near-net-shape NiTi biomaterials with controlled porosity. Powder-bed fusion and directed energy deposition are AM approaches employed to produce synthetic NiTi implants. A short summary of the principles and the pros and cons of these approaches is provided. The influence of the operating parameters, which can change the microstructural features, including the porosity content and orientation of the crystals, on the mechanical properties is addressed. Surface-modification techniques are recommended for suppressing the Ni ion leaching from the surface of AM-fabricated NiTi, which is a technical challenge faced by the long-term in vivo application of NiTi.

Induction of Bone Remodeling by Raloxifene-Doped Iron Oxide Functionalized with Hydroxyapatite to Accelerate Fracture Healing

Repairing fractures in the presence of infection is a major challenge that is currently declining using nanotechnology. By producing iron oxide nanoparticles (NPs) containing hydroxyapatite and Raloxifene (R-IONPs-HA), this study tries to target drug delivery, control infection and promotion of the cells proliferation/differentiation to repair damaged tissue. After the production of R-IONPs-HA through co-precipitation, the physicochemical features of the NPs were considered by SEM, TEM, DLS and XRD methods, and the possibility of drug release. The effect of R-IONPs-HA on MC3T3-E1 cell proliferation/differentiation was determined by CCK-assay and microscopic observations. Also, Gram-negative and -positive bacteria were applied to evaluate the antibacterial activity. Finally, cell differentiation biomarkers like an ALP, OCN, and RUNX-2 genes were examined by real time (RT)-PCR. The results showed that R-IONPs-HA was spherical with dimensions of 98.1 ± 1.17 nm. In addition, the results of Zeta and XRD confirmed the loading HA and R on IONPs. Also, the release rate of R and HA in 64 h with pH 6 reached 61.4 and 30.4%, respectively. The anti-bacterial activity of R-IONPs-HA on Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa bacteria showed a significant reduction in infection. Also, MC3T3-E1 cells showed greater proliferation and differentiation by R-IONPs-HA compared to other groups. Increased expression of ossification genes such as OCN, and RUNX-2 confirmed this claim. Finally, R-IONPs-HA with good biocompatibility, antibacterial activity and ossification induction has great potential to repair bone fractures and prevent infection.

Effect of bisphosphonate treatment of titanium surfaces on alkaline phosphatase activity in osteoblasts: a systematic review and meta-analysis

Background

Bisphosphonate coating of dental implants is a promising tool for surface modification aiming to improve the osseointegration process and clinical outcome. The biological effects of bisphosphonates are thought to be mainly associated with osteoclasts inhibition, whereas their effects on osteoblast function are unclear. A potential of bisphosphonate coated surfaces to stimulate osteoblast differentiation was investigated by several in vitro studies with contradictory results. The purpose of this systematic review and meta-analysis was to evaluate the effect of bisphosphonate coated implant surfaces on alkaline phosphatase activity in osteoblasts.

Methods

In vitro studies that assessed alkaline phosphatase activity in osteoblasts following cell culture on bisphosphonate coated titanium surfaces were searched in electronic databases PubMed/MEDLINE, Scopus and ISI Web of Science. Animal studies and clinical trials were excluded. The literature search was restricted to articles written in English and published up to August 2019. Publication bias was assessed by the construction of funnel plots.

Results

Eleven studies met the inclusion criteria. Meta-analysis showed that coating of titanium surfaces with bisphosphonates increases alkaline phosphatase activity in osteoblasts after 3 days (n = 1), 7 (n = 7), 14 (n = 6) and 21 (n = 3) days. (7 days beta coefficient = 1.363, p-value = 0.001; 14 days beta coefficient = 1.325, p-value < 0.001; 21 days beta coefficient = 1.152, p-value = 0.159).

Conclusions

The meta-analysis suggests that bisphosphonate coatings of titanium implant surfaces may have beneficial effects on osteogenic behaviour of osteoblasts grown on titanium surfaces in vitro. Further studies are required to assess to which extent bisphosphonates coating might improve osseointegration in clinical situations.

Evaluation of Microbial Adhesion and Biofilm Formation on Nano-Structured and Nano-Coated Ortho-Prosthetic Materials by a Dynamic Model

The bio-engineering technologies of medical devices through nano-structuring and coating was recently proposed to improve biocompatibility and to reduce microbial adhesion in the prevention of implantable device-related infections. Our aim was to evaluate the ability of new nano-structured and coated materials to prevent the adhesion and biofilm formation, according to the American Standard Test Method ASTM-E2647-13. The materials composition was determined by X-ray Fluorescence and Laser Induced Breakdown Spectroscopy. Silver release was evaluated by Inductively Coupled Plasma Mass Spectrometry analysis. The gene expression levels of the Quorum Sensing Las and Rhl system were evaluated by the ΔΔCt method. The Log bacterial density (Log CFU/cm²) on TiAl6V4 was 4.41 ± 0.76 and 4.63 ± 1.01 on TiAl6V4-AgNPs compared to 2.57 ± 0.70 on CoCr and 2.73 ± 0.61 on CoCr-AgNPs (P < 0.0001, A.N.O.V.A.- one way test). The silver release was found to be equal to 17.8 ± 0.2 µg/L after the batch phase and 1.3 ± 0.1 µg/L during continuous flow. The rhlR gene resulted in a 2.70-fold increased expression in biofilm growth on the silver nanoparticles (AgNPs) coating. In conclusion, CoCr showed a greater ability to reduce microbial adhesion, independently of the AgNPs coating. The silver release resulted in promoting the up-regulation of the Rhl system. Further investigation should be conducted to optimize the effectiveness of the coating.

Effect of hydroxy groups and microtopography generated by a nanosecond-pulsed laser on pure Ti surfaces

In this paper, we study a process for modifying the surface microtopography of the Ti oxide layer using a nanosecond-pulsed laser (NPL). Even now, the mechanism by which hydroxyl groups are generated on the titanium surface treated by NPL is not clear. Hence, we evaluated the surface properties of the NPL defocus distances on pure titanium surfaces, and investigated the relationship between the generation of hydroxyapatites/cell viability and the titanium surface characteristics. The NPL defocus distance was varied from 0 to 4 mm. Defocus distances of 0 and 2 mm generated microtopographical features on the titanium surface, and the resulting surfaces exhibited a greater density of OH groups than the surface treated with a defocus distance of 4 mm. The surfaces treated using defocus distances of 0 and 2 mm were found to be coated with microspherical hydroxyapatite composed of coexisting plate- and needle-like crystals after immersion in simulated body fluid, and alkaline phosphatase activity assays indicated improved cell compatibility. The improvements in biocompatibility and cell compatibility were due to the pocket-like microtopographical structures formed along the processing trace. These pockets contained a large amount of OH groups, and promoted the growth of hydroxyapatite.

Surface Modification of Biomedical Titanium Alloy: Micromorphology, Microstructure Evolution and Biomedical Applications

With the increasing demand for bone implant therapy, titanium alloy has been widely used in the biomedical field. However, various potential applications of titanium alloy implants are easily hampered by their biological inertia. In fact, the interaction of the implant with tissue is critical to the success of the implant. Thus, the implant surface is modified before implantation frequently, which can not only improve the mechanical properties of the implant, but also polish up bioactivity and osseoconductivity on a cellular level. This paper aims at reviewing titanium surface modification techniques for biomedical applications. Additionally, several other significant aspects are described in detail in this article, for example, micromorphology, microstructure evolution that determines mechanical properties, as well as a number of issues concerning about practical application of biomedical implants.