Biocompatible Organic Coatings Based on Bisphosphonic Acid RGD-Derivatives for PEO-Modified Titanium Implants

Design, synthesis and analysis of charged RGD derivatives

In the present study, negatively charged N-Biotin-RGD and positively charged C-Biotin-RGD were designed, synthesized, and characterized with docking analysis. The fixation of MDA-MB-231 cells with formalin made their cell surface neutrally charged thus removing the electrostatic interactions between charged biotinylated RGD derivatives and MDA-MB-231 cells. The results of the binding affinity of biotinylated RGD derivatives against MDA-MB-231 cells showed that N-Biotin-RGD had higher binding affinity than C-Biotin-RGD. The cytotoxic effect was analyzed by incubating charged biotinylated RGD derivatives with live MDA-MB-231 cells. MDA-MB-231 cell surface is negatively charged due to high hypersialyliation of polyglycans and Warburg effect. The results of their cytotoxic activities against live MDA-MB-231 cells were found to be electrostatic in nature. C-Biotin-RGD had an attractive interaction with the MDA-MB-231 cell surface resulting in a higher cytotoxic effect. In comparison, N-Biotin-RGD had a repulsive interaction with the MDA-MB-231 cell surface resulting in a lower cytotoxic effect. Hence, positively charged C-Biotin-RGD is a better cytotoxic agent than a negatively charged N-Biotin-RGD against MDA-MB-231 cells.

DMP1 and IFITM5 Regulate Osteogenic Differentiation of MC3T3-E1 on PEO-Treated Ti-6Al-4V-Ca2+/Pi surface

Despite numerous studies on various surface modifications on titanium and its alloys, it remains unclear what kind of titanium-based surface modifications are capable of controlling cell activity. This study aimed to understand the mechanism at the cellular and molecular levels and investigate the in vitro response of osteoblastic MC3T3-E1 cultured on the Ti-6Al-4V surface modified by plasma electrolytic oxidation (PEO) treatment. A Ti-6Al-4V surface was prepared by PEO at 180, 280, and 380 V for 3 or 10 min in an electrolyte containing Ca²⁺/P_i ions. Our results showed that PEO-treated Ti-6Al-4V-Ca²⁺/P_i surfaces enhanced the cell attachment and differentiation of MC3T3-E1 compared to the untreated Ti-6Al-4V control but did not affect cytotoxicity as shown by cell proliferation and cell death. Interestingly, on the Ti-6Al-4V-Ca²⁺/P_i surface treated by PEO at 280 V for 3 or 10 min, MC3T3-E1 showed a higher initial adhesion and mineralization. In addition, the alkaline phosphatase (ALP) activity significantly increased in MC3T3-E1 on the PEO-treated Ti-6Al-4V-Ca²⁺/P_i (280 V for 3 or 10 min). In RNA-seq analysis, the expression of dentin matrix protein 1 (DMP1), sortilin 1 (Sort1), signal-induced proliferation-associated 1 like 2 (SIPA1L2), and interferon-induced transmembrane protein 5 (IFITM5) was induced during the osteogenic differentiation of MC3T3-E1 on the PEO-treated Ti-6Al-4V-Ca²⁺/P_i. DMP1 and IFITM5 silencing decreased the expression of bone differentiation-related mRNAs and proteins and ALP activity in MC3T3-E1. These results suggest that the PEO-treated Ti-6Al-4V-Ca²⁺/P_i surface induces osteoblast differentiation by regulating the expression of DMP1 and IFITM5. Therefore, surface microstructure modification through PEO coatings with Ca²⁺/P_i ions could be used as a valuable method to improve biocompatibility properties of titanium alloys.

Modeling of Biological Activity of PEO-Coated Titanium Implants with Conjugates of Cyclic RGD Peptide with Amino Acid Bisphosphonates

Titanium is considered to be the most essential metal in the field of implantology. The main factors determining metal biocompatibility, among others, include the morphology and chemical composition of the titanium surface. Therefore, the aim of this work was to develop approaches to control the biological activity of the titanium surface by creating coatings that combine both an inorganic phase with a given morphology and organic molecules containing an integrin-selective peptide that regulate cell adhesion and proliferation. As such, we synthesized new c(RGDfC) derivatives of amino acid bisphosphonates (four examples) with different bisphosphonate anchors and maleimide linkers. These molecules were deposited on a highly developed porous surface obtained via the plasma electrolytic oxidation (PEO) of coarse-grained and nanostructured titanium. In vitro studies demonstrated the increase in the viability degree of mesenchymal stem cells and fibroblasts on the surface of coarse-grained or nanostructured titanium modified with PEO and a c(RGDfC) derivative of ε-aminocaproic acid bisphophonate with an SMCC linker. As a result, the use of conjugates of amino acid bisphosphonates with a cyclic RGD peptide for the modification of PEO-coated titanium opens the ways for the effective control of the biological activity of the metal implant surface.

Advanced Surface Modification for 3D-Printed Titanium Alloy Implant Interface Functionalization

With the development of three-dimensional (3D) printed technology, 3D printed alloy implants, especially titanium alloy, play a critical role in biomedical fields such as orthopedics and dentistry. However, untreated titanium alloy implants always possess a bioinert surface that prevents the interface osseointegration, which is necessary to perform surface modification to enhance its biological functions. In this article, we discuss the principles and processes of chemical, physical, and biological surface modification technologies on 3D printed titanium alloy implants in detail. Furthermore, the challenges on antibacterial, osteogenesis, and mechanical properties of 3D-printed titanium alloy implants by surface modification are summarized. Future research studies, including the combination of multiple modification technologies or the coordination of the structure and composition of the composite coating are also present. This review provides leading-edge functionalization strategies of the 3D printed titanium alloy implants.

Investigation of Biocompatible PEO Coating Growth on cp-Ti with In Situ Spectroscopic Methods

The problem of the optimization of properties for biocompatible coatings as functional materials requires in-depth understanding of the coating formation processes; this allows for precise manufacturing of new generation implantable devices. Plasma electrolytic oxidation (PEO) opens the possibility for the design of biomimetic surfaces for better biocompatibility of titanium materials. The pulsed bipolar PEO process of cp-Ti under voltage control was investigated using joint analysis of the surface characterization and by in situ methods of impedance spectroscopy and optical emission spectroscopy. Scanning electron microscopy, X-ray diffractometry, coating thickness, and roughness measurements were used to characterize the surface morphology evolution during the treatment for 5 min. In situ impedance spectroscopy facilitated the evaluation of the PEO process frequency response and proposed the underlying equivalent circuit where parameters were correlated with the coating layer properties. In situ optical emission spectroscopy helped to analyze the spectral line evolutions for the substrate material and electrolyte species and to justify a method to estimate the coating thickness via the relation of the spectral line intensities. As a result, the optimal treatment time was established as 2 min; this provides a 9-11 µm thick PEO coating with Ra 1 µm, 3-5% porosity, and containing 75% of anatase. The methods for in-situ spectral diagnostics of the coating thickness and roughness were justified so that the treatment time can be corrected online when the coating achieves the required properties.

Comparison of Biocompatible Coatings Produced by Plasma Electrolytic Oxidation on cp-Ti and Ti-Zr-Nb Superelastic Alloy

The paper compares the coatings produced by plasma electrolytic oxidation (PEO) on commercially pure titanium and a novel superelastic alloy Ti-18Zr-15Nb (at. %) for implant applications. The PEO coatings were produced on both alloys in the identical pulsed bipolar regime. The properties of the coatings were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDX), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS). The PEO process kinetics was modeled based on the Avrami theorem and Cottrell equation using a relaxation method. The resultant coatings contain TiO2, for both alloys, and NbO2, Nb2O5, ZrO2 for Ti-18Zr-15Nb alloy. The coating on the Ti-18Zr-15Nb alloy has a higher thickness, porosity, and roughness compared to that on cp-Ti. The values of the kinetic coefficients of the PEO process—higher diffusion coefficient and lower time constant for the processing of Ti-18Zr-15Nb—explain this effect. According to the electrochemical studies, PEO coatings on Ti-18Zr-15Nb alloy provide better corrosion protection. Higher corrosion resistance, porosity, and roughness contribute to better biocompatibility of the PEO coating on Ti-18Zr-15Nb alloy compared to cp-Ti.

Chitosan-miRNA functionalized microporous titanium oxide surfaces via a layer-by-layer approach with a sustained release profile for enhanced osteogenic activity

BACKGROUND

The biofunctionalization of titanium implants for high osteogenic ability is a promising approach for the development of advanced implants to promote osseointegration, especially in compromised bone conditions. In this study, polyelectrolyte multilayers (PEMs) were fabricated using the layer-by-layer approach with a chitosan-miRNA (CS-miRNA) complex and sodium hyaluronate (HA) as the positively and negatively charged polyelectrolytes on microarc-oxidized (MAO) Ti surfaces via silane-glutaraldehyde coupling.

METHODS

Dynamic contact angle and scanning electron microscopy measurements were conducted to monitor the layer accumulation. RiboGreen was used to quantify the miRNA loading and release profile in phosphate-buffered saline. The in vitro transfection efficiency and the cytotoxicity were investigated after seeding mesenchymal stem cells (MSCs) on the CS-antimiR-138/HA PEM-functionalized microporous Ti surface. The in vitro osteogenic differentiation of the MSCs and the in vivo osseointegration were also evaluated.

RESULTS

The surface wettability alternately changed during the formation of PEMs. The CS-miRNA nanoparticles were distributed evenly across the MAO surface. The miRNA loading increased with increasing bilayer number. More importantly, a sustained miRNA release was obtained over a timeframe of approximately 2 weeks. In vitro transfection revealed that the CS-antimiR-138 nanoparticles were taken up efficiently by the cells and caused significant knockdown of miR-138 without showing significant cytotoxicity. The CS-antimiR-138/HA PEM surface enhanced the osteogenic differentiation of MSCs in terms of enhanced alkaline phosphatase, collagen production and extracellular matrix mineralization. Substantially enhanced in vivo osseointegration was observed in the rat model.

CONCLUSIONS

The findings demonstrated that the novel CS-antimiR-138/HA PEM-functionalized microporous Ti implant exhibited sustained release of CS-antimiR-138, and notably enhanced the in vitro osteogenic differentiation of MSCs and in vivo osseointegration. This novel miRNA-functionalized Ti implant may be used in the clinical setting to allow for more effective and robust osseointegration.