Graphene Oxide Functionalized Gelatin Methacryloyl Microgel for Enhanced Biomimetic Mineralization and in situ Bone Repair

Introduction

The formation of bone-like apatite (Ap) on natural polymers through biomimetic mineralization using simulated body fluid (SBF) can improve osteoconductivity and biocompatibility, while lowering immunological rejection. Nonetheless, the coating efficiency of the bone-like Ap layer on natural polymers requires improvement. Carbonyls (-COOH) and hydroxyls (-OH) are abundant in graphene oxide (GO), which may offer more active sites for biomimetic mineralization and promote the proliferation of rat bone marrow stromal cells (BMSCs).

Methods

In this study, gelatin methacryloyl (GelMA) microgels were infused with GO (0, 0.5, 1, and 2 mg/mL) and embedded into microgels in SBF for 1, 7, and 14 days. Systematic in vitro and in vivo experiments were performed to evaluate the structure of the microgel and its effect on cell proliferation and ability to repair bone defects in rats.

Results

The resulting GO-GelMA-Ap microgels displayed a porous, interconnected structure with uniformly coated surfaces in bone-like Ap, and the Ca/P ratio of the 1 mg/mL GO-GelMA-Ap group was comparable to that of natural bone tissue. Moreover, the 1 mg/mL GO-GelMA-Ap group exhibited a greater Ap abundance, enhanced proliferation of BMSCs in vitro and increased bone formation in vivo compared to the GelMA-Ap group.

Discussion

Overall, this study offers a novel method for incorporating GO into microgels for bone tissue engineering to promote biomimetic mineralization.

Assessment of Titanate Nanolayers in Terms of Their Physicochemical and Biological Properties

The surface modification of titanium substrates and its alloys in order to improve their osseointegration properties is one of widely studied issues related to the design and production of modern orthopedic and dental implants. In this paper, we discuss the results concerning Ti6Al4V substrate surface modification by (a) alkaline treatment with a 7 M NaOH solution, and (b) production of a porous coating (anodic oxidation with the use of potential U = 5 V) and then treating its surface in the abovementioned alkaline solution. We compared the apatite-forming ability of unmodified and surface-modified titanium alloy in simulated body fluid (SBF) for 1–4 weeks. Analysis of the X-ray diffraction patterns of synthesized coatings allowed their structure characterization before and after immersing in SBF. The obtained nanolayers were studied using Raman spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), and scanning electron microscopy (SEM) images. Elemental analysis was carried out using X-ray energy dispersion spectroscopy (SEM EDX). Wettability and biointegration activity (on the basis of the degree of integration of MG-63 osteoblast-like cells, L929 fibroblasts, and adipose-derived mesenchymal stem cells cultured in vitro on the sample surface) were also evaluated. The obtained results proved that the surfaces of Ti6Al4V and Ti6Al4V covered by TiO₂ nanoporous coatings, which were modified by titanate layers, promote apatite formation in the environment of body fluids and possess optimal biointegration properties for fibroblasts and osteoblasts.

Effect of doping different Si source on Ca-P bioceramic coating fabricated by laser cladding

The doping of silicon (Si) has been proved to improve the bioactivity of Ca-P ceramics. In light of this thinking, in the present study, Ca-P coatings with La₂O₃ by addition of 10 wt% SiO₂ and 10 wt% diatomaceous earth (DE) were fabricated by laser cladding on Ti6Al4V, respectively. Coating doped without Si was also fabricated as the comparison group for the experiment. The effect of two different Si sources on the surface morphology, microstructure, microhardness, and bioactivity was systematically studied. The experimental results show that the Si-doped coating is of rough surface morphology, and the addition of DE significantly reduces the number of cracks and improves the microhardness. The X-ray diffraction results reveal that the amount of bioactive phase tricalcium-phosphate (TCP) and hydroxyapatite (HA) reaches maximum in the DE-doped coating. After soaking in simulated body fluid (SBF), the precipitate of bone-like apatite in the DE-doped coating is significantly higher than that of the other coatings.

Polylactide Composite Pins Reinforced with Bioresorbable Continuous Glass Fibers Demonstrating Bone-like Apatite Formation and Spiral Delamination Degradation

The emergence of polylactide composites reinforced with bioresorbable silicate glass fibers has allowed for the long-term success of biodegradable polymers in load-bearing orthopedic applications. However, few studies have reported on the degradation behavior and bioactivity of such biocomposites. The aim of this work was to investigate the degradation behavior and in vitro bioactivity of a novel biocomposite pin composed of bioresorbable continuous glass fibers and poly-L-D-lactide in simulated body fluid for 78 weeks. As the materials degraded, periodic spiral delamination formed microtubes and funnel-shaped structures in the biocomposite pins. It was speculated that the direction of degradation, from both ends towards the middle of the fibers and from the surface through to the bulk of the polymer matrix, could facilitate bone healing. Following immersion in simulated body fluid, a bone-like apatite layer formed on the biocomposite pins which had a similar composition and structure to natural bone. The sheet- and needle-like apatite nanostructure was doped with sodium, magnesium, and carbonate ions, which acted to lower the Ca/P atomic ratio to less than the stoichiometric apatite and presented a calcium-deficient apatite with low crystallinity. These findings demonstrated the bioactivity of the new biocomposite pins in vitro and their excellent potential for load-bearing applications.

Improving Hydrophilicity and Inducing Bone-Like Apatite Formation on PPBES by Polydopamine Coating for Biomedical Application

Copoly(phthalazinone biphenyl ether sulfone) (PPBES) as a commercially available polyarylether is a promising orthopaedic implant material because its mechanical properties are similar to bone. However, the bioinert surface of polyarylether causes some clinical problems after implantation, which limits its application as an implant material. In this study, the surface of PPBES was modified by a biomineralization method of polydopamine-assisted hydroxyapatite formation (pHAF) to enhance its cytocompatibility. Polydopamine (PDA) coating, inspired by the adhesion mechanism of mussels, can readily endow PPBES with high hydrophilicity and the ability to integrate via the bone-like apatite coating. PPBES and PDA-coated PPBES were evaluated by scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and contact angle measurement. The water contact angles were reduced significantly after coating with PDA. PDA was successfully synthesized on PPBES and more PDA was obtained by increasing the temperature. Bone-like apatite on PPBES (apatite-coated PPBES) was confirmed by SEM and transmission electron microscopy (TEM). The cytotoxicity of pristine PPBES and apatite-coated PPBES were characterized by culturing of NIH-3T3 cells. Bone-like apatite synthesized by pHAF could further enhance cytocompatibility in vitro. This study provides a promising alternative for biofunctionalized PPBES with improved cytocompatibility for bone implant application.

Biodegradation Resistance and Bioactivity of Hydroxyapatite Enhanced Mg-Zn Composites via Selective Laser Melting

Mg-Zn alloys have attracted great attention as implant biomaterials due to their biodegradability and biomechanical compatibility. However, their clinical application was limited due to the too rapid degradation. In the study, hydroxyapatite (HA) was incorporated into Mg-Zn alloy via selective laser melting. Results showed that the degradation rate slowed down due to the decrease of grain size and the formation of protective layer of bone-like apatite. Moreover, the grain size continually decreased with increasing HA content, which was attributed to the heterogeneous nucleation and increased number of nucleation particles in the process of solidification. At the same time, the amount of bone-like apatite increased because HA could provide favorable areas for apatite nucleation. Besides, HA also enhanced the hardness due to the fine grain strengthening and second phase strengthening. However, some pores occurred owing to the agglomerate of HA when its content was excessive, which decreased the biodegradation resistance. These results demonstrated that the Mg-Zn/HA composites were potential implant biomaterials.

Tuning the surface microstructure of titanate coatings on titanium implants for enhancing bioactivity of implants

Biological performance of artificial implant materials is closely related to their surface characteristics, such as microtopography, and composition. Therefore, convenient fabrication of artificial implant materials with a cell-friendly surface structure and suitable composition was of great significance for current tissue engineering. In this work, titanate materials with a nanotubular structure were successfully fabricated through a simple chemical treatment. Immersion test in a simulated body fluid and in vitro cell culture were used to evaluate the biological performance of the treated samples. The results demonstrate that the titanate layer with a nanotubular structure on Ti substrates can promote the apatite-inducing ability remarkably and greatly enhance cellular responses. This highlights the potential of such titanate biomaterials with the special nanoscale structure and effective surface composition for biomedical applications such as bone implants.

Mesoscopically ordered bone-mimetic nanocomposites

A sustainable approach that highly mimics bone-material deposition is reported to produce mechanically stable, degradable composites with nanostructures resembling that of natural bone. Molecular self-assembly combining intermolecular crosslinking leads to resilient matrices possessing long-range ordered aqueous domains, inside which moderately aligned poorly crystalline apatite is converted from the transient amorphous calcium phosphate phase.