Biocompatibility of sol-gel hydroxyapatite-titania composite and bilayer coatings

Anisotropic hydrogel scaffold by flow-induced stereolithography 3D printing technique

Essential organs, such as the heart and liver, contain a unique porous network that allows oxygen and nutrients to be exchanged, with distinct random to ordered regions displaying varying degrees of strength. A novel technique, referred to here as flow-induced lithography, was developed. This technique generates tunable anisotropic three-dimensional (3D) structures. The ink for this bioprinting technique was made of titanium dioxide nanorods (Ti) and kaolinite nanoclay (KLT) dispersed in a GelMA/PEGDA polymeric suspension. By controlling the flow rate, aligned particle microstructures were achieved in the suspensions. The application of UV light to trigger the polymerization of the photoactive prepolymer freezes the oriented particles in the polymer network. Because the viability test was successful in shearing suspensions containing cells, the flow-induced lithography technique can be used with both acellular scaffolds and cell-laden structures. Fabricated hydrogels show outstanding mechanical properties resembling human tissues, as well as significant cell viability (> 95 %) over one week. As a result of this technique and the introduction of bio-ink, a novel approach has been pioneered for developing anisotropic tissue implants utilizing low-viscosity biomaterials.

Freeze casting of hydroxyapatite-titania composites for bone substitutes

Hydroxyapatite (HA) is commonly used as a bone substitute material, but it lacks mechanical strength when compared to native bone tissues. To improve the efficacy of HA as a bone substitute by improving the mechanical strength and cell growth attributes, porous composite scaffolds of HA and titania (HA-TiO2 ) were fabricated through a freeze-casting process. Three different compositions by weight percent, 25-75 HA-TiO2 , 50-50 HA-TiO2 , and 75-25 HA-TiO2 , were custom-made for testing. After sintering at 1250°C, these composite scaffolds exhibited improved mechanical properties compared to porous HA scaffolds. Substrate mixing was observed, which helped reduce crystal size and introduced new phases such as β-TCP and CaTiO3 , which also led to improved mechanical properties. The composition of 50-50 HA-TiO2 had the highest ultimate compressive strength of 3.12 ± 0.36 MPa and elastic modulus 63.29 ± 28.75 MPa. Human osteoblast cell proliferation assay also increased on all three different compositions when compared to porous HA at 14 days. These results highlight the potential of freeze casting composites for the fabrication of bone substitutes, which provide enhanced mechanical strength and biocompatibility while maintaining porosity.

Citric Acid Catalyst-Assisted Bioactive Glass with Hydrogen Peroxide for In Vitro Bioactivity and Biodegradability Using Sol-Gel Method

In this study, carbon-free and completely soluble hydrogen peroxide (H2O2) was utilized in place of conventional surfactants as a pore-forming agent. Citric acid was also used in low concentration for the hydrolysis reaction. A sol-gel method was used to prepare bioactive glass (BG) specimens of H2O2-untreated BG, 1M, 2M, and 3M H2O2-treated BGs. X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), energy-dispersive spectroscopy (EDS), and nitrogen adsorption/desorption isotherm with the Brunauer-Emmett-Teller (BET) method were used for analyzing the samples' phase, surface morphology, chemical composition, constituent composition, pore size, and specific surface area respectively. In vitro bioactivity, as well as biodegradability tests, was performed on samples by immersing them in simulated body fluid (SBF) solution. According to the results, BG particles treated with 2 M H2O2 exhibited higher specific surface area (SSA), which is 189.55 cc/g, and better in vitro bioactivity and biodegradability.

Manufacturing hydroxyapatite scaffold from snapper scales with green phenolic granules as the space holder material

Hydroxyapatite (HA) scaffold was made using the powder metallurgy with an use of a space holder method with a pore-forming agent from green phenolic (GP) granules. The novelty of this study was the use of GP granules as an agent that does not melt at high temperatures to avoid damaging the tangential contact between the HA powder during the sintering process. HA from snapper scales was added and mixed with polyvinyl alcohol (PVA) and ethanol to form a slurry. The ethanol content was then removed by drying at room temperature. The HA, which contained PVA, was added with GP granules as a pore-forming agent in various amounts to get the desired porosity. The green body was made using a stainless steel mold with the uniaxial pressing process under a pressure of 100 MPa. To make a scaffold sintered body, a sintering process ran at 1200 °C with a holding time of 2 h while maintaining the heating and cooling rates at 5 °C/min. The physical properties of the scaffold sintered body were characterized through linear shrinkage test, pore measurement, porosity test, phase observation by X-ray diffraction (XRD), and microstructure observation by scanning electron microscopy (SEM) and digital microscopy (DM). So were the mechanical ones through a compressive strength test. The results showed that the sintered body had a compressive strength value of 1.6 MPa at a porosity of 60.7% with a pore size of 129-394 μm. The scaffold contained interconnections between pores at a HA:GP ratio of 55:45 wt%, which matched the condition required for cell tissue growth. The conclusion is that GP granules are good enough to be used as a pore-making agent on scaffolds using the space holder method because they do not damage the tangential contact between the HA powder during the sintering process. However, efforts are needed to remove the remaining GP ash on the scaffold.

Catalytic Nanomedicine - A new Approach and Solution for Chronic Ulcers: Case Series

Chronic ulcers are a major public health problem, due to their chronic nature, their poor response to treatment, the high frequency of recurrences, and their affection to the patient's quality of life. Even with the development of new therapies in the field of chronic wound care, chronic ulcers remain a clinical problem. As a novel branch of research, Catalytic Nanomedicine has offered promising results in disinfection and treatment of chronic wounds through the use of bionanocatalysts, organically functionalized mesoporous nanostructured materials with catalytic properties. Particularly, Cu/TiO2-SiO2 mixed oxide bionanocatalysts have shown favorable results for chronic ulcer healing. In this work, we present the treatment of 15 patients (8 females and 7 males, mean age of 69.59 ± 12.07 years old) affected with chronic ulcers (wound age ranging from 4 months to 10 years old, mean size of 12.94 ± 18.20 cm2) by the administration of Cu/TiO2-SiO2 bionanocatalysts embedded in a nanoemulsion matrix. In all cases, complete epithelialization and healing of the lesions was achieved (healing time from 3 to 35 weeks), without the appearance of side effects. Wound healing time was analyzed in the context of initial wound size, wound's age, patient's age, and concomitant conditions, being wound size and patient's age the main factor affecting the duration of the treatment with the bionanocatalysts.

The Role of the Sol-Gel Synthesis Process in the Biomedical Field and Its Use to Enhance the Performance of Bioabsorbable Magnesium Implants

In the present day, the increment in life expectancy has led to the necessity of developing new biomaterials for the restoration or substitution of damaged organs that have lost their functionalities. Among all the research about biomaterials, this review paper aimed to expose the main possibilities that the sol-gel synthesis method can provide for the fabrication of materials with interest in the biomedical field, more specifically, when this synthesis method is used to improve the biological properties of different magnesium alloys used as biomaterials. The sol-gel method has been widely studied and used to generate ceramic materials for a wide range of purposes during the last fifty years. Focused on biomedical research, the sol-gel synthesis method allows the generation of different kinds of biomaterials with diverse morphologies and a high potential for the biocompatibility improvement of a wide range of materials commonly used in the biomedical field such as metallic implants, as well as for the generation of drug delivery systems or interesting biomaterials for new tissue engineering therapies.

Anticorrosion and Cytocompatibility Assessment of Graphene-Doped Hybrid Silica and Plasma Electrolytic Oxidation Coatings for Biomedical Applications

Magnesium AZ31 alloy substrates were coated with different coatings, including sol–gel silica-reinforced with graphene nanoplatelets, sol–gel silica, plasma electrolytic oxidation (PEO), and combinations of them, to improve cytocompatibility and control the corrosion rate. Electrochemical corrosion tests, as well as hydrogen evolution tests, were carried out using Hanks’ solution as the electrolyte to assess the anticorrosion behavior of the different coating systems in a simulated body fluid. Preliminary cytocompatibility assessment of the different coating systems was carried out by measuring the metabolic activity, deoxyribonucleic acid quantification, and the cell growth of premyoblastic C2C12-GFP cell cultures on the surface of the different coating systems. Anticorrosion behavior and cytocompatibility were improved with the application of the different coating systems. The use of combined PEO + SG and PEO + SG/GNP coatings significantly decreased the degradation of the specimens. The monolayer sol–gel coatings, with and without GNPs, presented the best cytocompatibility improvement.

Titania-based sol-gel coatings with Ag, Ca-P applied on titanium substrate developed for implantation

This research work is focused on the investigation of newly developed titania sol-gel coatings containing silver, calcium and phosphate with appropriate abilities to be implanted into the human body. These abilities include adhesion, bioactivity, antibacterial property and cytocompatibility of prepared coatings. Four types of coatings were applied on a titanium substrate by dip-coating technique under different conditions (TCP1, TCP2, TCPA1 and TCPA2). Surfaces of coatings after the firing without silver featured different distribution of circular areas containing Ca. The coatings TCPA1 and TCPA2 were made up of unhomogeneously situated silver. Adhesion of the coatings to the substrates was measured by a tape test. All types of the coatings demonstrated very good adhesion. Isolated cracks that appeared during the firing did not have a negative influence on the adhesion properties. Bioactivity of the coatings was tested in vitro using a simulated body fluid. Three of the four types demonstrated bioactive properties (TCP1, TCP2 and TCPA2), that is, precipitation of crystalline hydroxyapatite as was confirmed by X-ray diffraction. The antibacterial effect (against Escherichia coli and Staphylococcus epidermidis) and cytotoxicity (toward L929 and U-2 OS cell lines, direct and indirect test) were then tested. All the coatings demonstrated very good antibacterial effect against both bacteria after 4- and 24-hr interaction. All the coating types were evaluated as cytocompatible in the indirect test. Cells were able to grow even directly on the coatings.

Effect of Ultrasound Irradiation on the Synthesis of Hydroxyapatite/Titanium Oxide Nanocomposites

Bioceramic materials, such as hydroxyapatite, Ca10(PO4)6(OH)2, (HAp), can be chemically bound to bone tissue; since they are bioactive and biocompatible. HAp, titanium oxide (TiO2), and hydroxyapatite/titanium oxide (HAp/TiO2) nanocomposite nanoparticles were obtained by ultrasound irradiation assisted by sol-gel and co-precipitation methods at different time intervals, using Ca(NO3)2•4H2O, (NH4)2HPO4, and TiOSO4•xH2O as calcium, phosphorus, and titanium sources, respectively. HAp, TiO2, and HAp/TiO2 nanocomposite powders were characterized by X-ray Diffraction (XRD) and Raman Spectroscopy. The percentages of anatase phase for TiO2 and of monoclinic and hexagonal phases for HAp were quantified by Rietveld refinement. Furthermore, sample crystallinity in each material was enhanced by increasing the ultrasound irradiation time. The nanoparticle shape was semi-spherical, agglomerated, and between 17 and 20 nm in size. The agglomeration of particles in the samples was corroborated with a Field Emission Scanning Electron Microscope (FESEM).

Sol-Gel Derived Hydroxyapatite Coatings for Titanium Implants: A Review

With the growing demands for bone implant therapy, titanium (Ti) and its alloys are considered as appropriate choices for the load-bearing bone implant substitutes. However, the interaction of bare Ti-based implants with the tissues is critical to the success of the implants for long-term stability. Thus, surface modifications of Ti implants with biocompatible hydroxyapatite (HAp) coatings before implantation is important and gained interest. Sol-gel is a potential technique for deposition the biocompatible HAp and has many advantages over other methods. Therefore, this review strives to provide widespread overview on the recent development of sol-gel HAp deposition on Ti. This study shows that sol-gel technique was able to produce uniform and homogenous HAp coatings and identified the role of surface pretreatment of Ti substrate, optimizing the sol-gel parameters, substitution, and reinforcement of HAp on improving the coating properties. Critical factors that influence on the characteristics of the deposited sol-gel HAp films as corrosion resistance, adhesion to substrate, bioactivity, morphological, and structural properties are discussed. The review also highlights the critical issues, the most significant challenges, and the areas requiring further research.

IC50 Evaluation of Platinum Nanocatalysts for Cancer Treatment in Fibroblast, HeLa, and DU-145 Cell Lines

Cancer is a major public health problem being one of the main causes of morbidity and mortality today. Recent advances in catalytic nanomedicine have offered new cancer therapies based on the administration of nanoparticles (NPs) of platinum (Pt) dispersed in catalytic mesoporous nanomaterials (titania, TiO2) with highly selective cytotoxic properties and no adverse effects. A half maximal inhibitory concentration (IC50) study was carried out in cancerous cell lines (HeLa, DU-145, and fibroblasts) to evaluate the cytotoxic effect of different nanomaterials [Pt/TiO2, TiO2, and Pt(acac)2] synthesized by the sol-gel method at concentrations 0-1000 μg/mL. The assays showed that IC50 values for Pt in functionalized TiO2 (NPt) in HeLa (53.74 ± 2.95 μg/mL) and DU-145 (75.07 ± 5.48 μg/mL) were lower than those of pure TiO2 (74.29 ± 8.95 and 82.02 ± 6.03 μg/mL, respectively). Pt(acac)2 exhibited no cytotoxicity. Normal cells (fibroblasts) treated with NPt exhibited no significant growth inhibition, suggesting the high selectivity of the compound for cancerous cells only. TiO2 and NPt were identified as antineoplastic compounds in vitro. Pt(acac)2 is not recommendable because of the low cytotoxicity observed.

Hybrid Sol-gel Coatings for Corrosion Mitigation: A Critical Review

The corrosion process is a major source of metallic material degradation, particularly in aggressive environments, such as marine ones. Corrosion progression affects the service life of a given metallic structure, which may end in structural failure, leakage, product loss and environmental pollution linked to large financial costs. According to NACE, the annual cost of corrosion worldwide was estimated, in 2016, to be around 3%-4% of the world's gross domestic product. Therefore, the use of methodologies for corrosion mitigation are extremely important. The approaches used can be passive or active. A passive approach is preventive and may be achieved by emplacing a barrier layer, such as a coating that hinders the contact of the metallic substrate with the aggressive environment. An active approach is generally employed when the corrosion is set in. That seeks to reduce the corrosion rate when the protective barrier is already damaged and the aggressive species (i.e., corrosive agents) are in contact with the metallic substrate. In this case, this is more a remediation methodology than a preventive action, such as the use of coatings. The sol-gel synthesis process, over the past few decades, gained remarkable importance in diverse areas of application. Sol-gel allows the combination of inorganic and organic materials in a single-phase and has led to the development of organic-inorganic hybrid (OIH) coatings for several applications, including for corrosion mitigation. This manuscript succinctly reviews the fundamentals of sol-gel concepts and the parameters that influence the processing techniques. The state-of-the-art of the OIH sol-gel coatings reported in the last few years for corrosion protection, are also assessed. Lastly, a brief perspective on the limitations, standing challenges and future perspectives of the field are critically discussed.

Polydopamine-induced hydroxyapatite coating facilitates hydroxyapatite/polyamide 66 implant osteogenesis: an in vitro and in vivo evaluation

Background

Hydroxyapatite/polyamide 66 (HA/P66) has been clinically used for several years owing to its good biocompatibility and bioactivity. However, it has been found that the osseointegration process of the HA/P66 implant takes a large amount of time because of the small amount of HA on its surface.

Methods

To increase the amount of HA and aid faster osseointegration, we prepared a HA coating using a biomimetic process assisted by polydopamine (PDA) on the HA/P66 substrate. The surface properties of the substrate modified by PDA and HA were characterized, and the capacity of biomaterials for osteogenic induction was investigated both in vitro and in vivo.

Results

The HA coating was successfully prepared on the HA/P66 substrate and verified by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The HA coating remained firmly attached to the underlying PDA-HA/P66 substrate even after strong ultrasound treatment for 1 h, and the calcium and phosphorus of the HA coating was continuously released in vitro in a slow manner. The formation of the HA coating on the PDA film greatly increased the hydrophilicity and surface roughness of HA/P66. In cell-based experiments, as compared with the HA/P66 substrate, the HA coating formation on the PDA film could facilitate the functions of C3H10T1/2 cells, including cell adhesion, proliferation, spreading, alkaline phosphatase activity, calcium nodule formation, and expression of osteogenic differentiation-related proteins. In addition, the HA/P66 scaffolds modified with PDA and HA coatings were implanted in rabbit femoral condyles. At 8 weeks after surgery, micro-computed tomography scanning (micro-CT) and hematoxylin–eosin (HE) staining revealed that more new bones were formed around the HA/P66 scaffold that was modified with a PDA-assisted HA coating.

Conclusion

These results indicate that the preparation of a PDA-assisted HA coating by using a biomimetic process significantly improves the capacity of biomaterials for osteogenic induction.

Synthesis of hydroxyapatite for biomedical applications

The current need for long lasting implants and bone substitutes characterized by biocompatibility, bioactivity and mechanical properties, without the immune rejection is a great challenge for scientists. These bone substitute structures should be prepared for individual patients with all details controlled on the micrometer level. Similarly, nontoxic, biocompatible targeted drug delivery systems which allow controlling the rate and time period of the drug delivery and simultaneously eliminating toxic and side effects on the healthy tissues, are of great interest. Extensive attempts have been made to develop a simple, efficient, and green method to form biofunctional scaffolds and implant coatings possessing the above mentioned significant biocompatibility, bioactivity and mechanical strength. Moreover, that could also serve as drug delivery systems. Hydroxyapatite (HA) which is a major mineral component of vertebrate bones and teeth is an excellent material for these purposes. In this literature review the biologically inspired scaffolds, bone substitutes, implants characterized by mechanical strength and biocompatibility, as well the drug delivery systems, based on hydroxyapatite are discussed.