Bone-like Apatite Formation Research Articles

Multifunctional Bioinspired Bredigite-Modified Adhesive for Bone Fracture Healing

Despite recent advances in bone adhesives applied for full median sternotomy, the regeneration of bone defects has remained challenging since the healing process is hampered by poor adhesiveness, limited bioactivity, and lack of antibacterial functions. Bioinspired adhesives by marine organisms provide a novel concept to circumvent these problems. Herein, a dual cross-link strategy is employed in designing a multifaceted bioinspired adhesive consisting of a catechol amine-functionalized hyperbranched polymer (polydopamine-co-acrylate, PDA), bredigite (BR) nanoparticles, and Fe3+ ions. The hybrid adhesives exhibit strong adhesion to various substrates such as poly(methyl methacrylate), glass, bone, and skin tissues through synergy between irreversible covalent and reversible noncovalent cross-linking, depending on the BR content. Noticeably, the adhesion strength of hybrid adhesives containing 2 wt % BR nanoparticles to bone tissues is 2.3 ± 0.8 MPa, which is about 3 times higher than that of pure PDA adhesives. We also demonstrate that these hybrid adhesives not only are bioactive and accelerate in vitro bone-like apatite formation but also exhibit antibacterial properties against Staphylococcus aureus, depending on the BR concentration. Furthermore, the superior cellular responses in contact with hybrid adhesives, including improved human osteosarcoma MG63 cell spreading and osteogenic differentiation, are achieved owing to the appropriate ion release and flexibility of the cross-linked double-network adhesive. In summary, multifunctional hybrid PDA/BR adhesives with appreciable osteoconductive, mechanical, and antibacterial properties represent the potential applications for median sternotomy surgery as a bone tissue adhesive.

In situ fabrication of cerium-incorporated hydroxyapatite/magnetite nanocomposite coatings with bone regeneration and osteosarcoma potential.

With the ultimate goal of providing a novel platform able to inhibit bacterial adhesion, biofilm formation, and anticancer properties, cerium-doped hydroxyapatite films enhanced with magnetite were developed via spin-coating. The unique aspect of the current study is the potential for creating cerium-doped hydroxyapatite/Fe3O4 coatings on a titanium support to enhance the functionality of bone implants. To assure an increase in the bioactivity of the titanium surface, alkali pretreatment was done before deposition of the apatite layer. Scanning electron microscopy (SEM) in conjunction with energy-dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD) analysis, and Fourier transform-infrared (FTIR) spectroscopy were used to evaluate coatings. Coatings demonstrated good efficacy against Staphylococcus aureus and Escherichia coli, with the latter showing the highest efficacy. In vitro bioactivity in simulated body fluid solution showed this material to be proficient for bone-like apatite formation on the implant surface. Electrochemical impedance spectroscopy was undertaken on intact coatings to examine the barrier properties of composites. We found that spin-coating at 4000 rpm could greatly increase the total resistance. After seeding with osteoblastic populations, Ce-HAP/Fe3O4 materials the adhesion and proliferation of cells. The heating capacity of the Ce-HAP/Fe3O4 film was optimal at 45 °C at 15 s at a frequency of 318 kHz. Osseointegration depends on many more parameters than hydroxyapatite production, so these coatings have significant potential for use in bone healing and bone-cancer therapy.

Surface modification of polyether ether ketone implant with a novel nanocomposite coating containing poly (vinylidene fluoride) toward improving piezoelectric and bioactivity performance

Polyether ether ketone (PEEK) is an appropriate biomaterial for orthopedic implant applications due to its superior mechanical properties, chemical resistance, nontoxicity, and Magnetic resonance imaging (MRI) compatibility. Unfortunately, the inherent bio-inertness of PEEK restricted its application and required some modification to provide better bioactivity. Besides it, the generated electrical signals in the bone due to its piezoelectricity features have a vital role in regulating bone repair and regeneration. We aimed to modify the surface of PEEK with a dual-functionality nanocomposite that provides surface bioactivity and simulates the piezoelectricity of bone. So, we introduced a novel piezoelectric-bioactive nanocomposite of dispersed poly (vinylidene fluoride) (PVDF) in a sulfonated PEEK (SPEEK) matrix containing Nanohydroxyapatite (nHA) and Carbon nanofiber (CNF) fillers for coating on PEEK substrate to improve its biological activity and simulate the electrical microenvironment for bone tissue. Furthermore, sulfonation of the PEEK surface was conducted as an intermediate layer to prepare better adhesion between the coating nanocomposite and the PEEK sublayer. Surface and cross-section morphology, apatite formation, and cell attachment were investigated on the different treated PEEK surfaces using field-emission scanning electron microscopy (FESEM) and energy dispersive X-ray analysis (EDX). Also, piezoelectric performance, electrical conductivity, contact angle, and mechanical properties were examined on the prepared samples. Moreover, cell viability and cell morphology were investigated for biological evaluation with human osteoblast-like MG-63 cells. Collectively, the hydrophilicity of modified PEEK (mPEEK) coated with nanocomposite was improved due to the synergistic effects of SPEEK functional groups and nHA. Also, comprehensive investigation on the mPEEK treated with nanocomposite indicated a noticeably better bone-like apatite formation, cell proliferation, and cell attachments in the presence of nHA. The transfer of induced piezoelectric charges from dispersed PVDF in the matrix to the surface of nanocomposite containing 2 wt% of CNF increased output voltage to 1893 mV. On the other hand, the presence of CNF in nanocomposites enhanced tensile strength and Young's modulus by 92% and 117%, respectively.

Bone-like apatite formation in phosphate-crosslinked sodium alginate-based hydrogels

• Posphate-crosslinked sodium alginate-based hydrogels was developed. • The hydrogels show interconnected porous networks. • The hydrogels show excellent bone-like apatite formation ability. Bioactive materials exhibiting bone-like apatite formation are crucial for inducing the osteogenic potentials of bone cells in the bone tissue engineering field. Herein, we report the design and synthesis of bioactive phosphate-crosslinked sodium alginate-based (PSA) hydrogels for biomineralization using a calcium-free approach. The hydrogels produced contained interconnected porous networks and exhibited improved swelling and biodegradable properties with excellent bone-like apatite formation abilities under simulated body fluid (SBF) conditions, which were attributed to the presence of phosphate groups. The devised functional phosphate-crosslinked sodium alginate hydrogels provided potential scaffolds for bone tissue engineering applications.

In vitro bioactivity and biocompatibility of magnesium implants coated with poly(methyl methacrylate) - bioactive glass composite

Magnesium (Mg) and its alloys have proved promising as biodegradable candidates for the repair of bone tissue. Despite the encouraging bio-related properties of Mg, its high corrosion rate in contact with body fluids still presents a major challenge. An efficient approach to address this issue is to provide a protective coating on Mg. The present research evaluates, for the first time, in vitro bioactivity and biocompatibility of a novel multifunctional composite coating based on poly(methyl methacrylate) (PMMA) biopolymer and bioactive glass (BG) particles on Mg-based implant. Electrophoretic deposition (EPD) was utilized to obtain this coating from a bi-component suspension. Coatings’ morphological analyses by scanning electron microscopy established that EPD provides a facile route for simultaneous deposition of the biopolymeric matrix and BG in the form of a dense and homogeneous coating on the surface of Mg. Chemical characterizations of the coatings performed by energy-dispersive spectroscopy and FT-IR spectroscopy confirmed the presence of both PMMA and BG components in the composite film. In vitro acellular bioactivity test in simulated body fluid (SBF) verified bone-like apatite formation on coatings due to the presence of BG particles. Additionally, in vitro cellular cytotoxicity using MTT assay demonstrated cellular viability in contact with the composite coatings. Moreover, the corrosion behavior of the pure Mg vs coated Mg samples in SBF was assessed electrochemically using linear polarization and impedance spectroscopy techniques. A significant increase in the polarization resistance from 65.89 Ω.cm 2 for uncoated Mg to 1365.1 Ω.cm 2 for Mg coated with a composite film (obtained from 45 g/L PMMA and 3.5 g/L BG suspension) was observed. This indicated a reduction of 95.17% in the corrosion rate of Mg substrate by application of a composite coating. The dramatic reduction in Mg substrate corrosion rate accompanied by in vitro bioactivity and cytocompatibility of the developed composite, reflect the high potential of the present strategy in the modification of Mg-based implants for successful bone tissue engineering applications. • Novel bioactive and corrosion-resistant composite coating on Mg biomedical implant • PMMA facilitates bioactive glass deposition via a facile electrophoretic method • Composite coatings were bioactive due to apatite formation in simulated body fluid • 95.17% reduction in corrosion rate in composite-coated Mg vs bare Mg • Coatings supported the growth of MG63 cells and were non-cytotoxic

Multifunctional TiO2 coatings developed by plasma electrolytic oxidation technique on a Ti20Nb20Zr4Ta alloy for dental applications.

A newly developed β-Ti alloy based on the Ti-Nb-Zr-Ta system (Ti20Nb20Zr4Ta) has been subjected to Plasma Electrolytic Oxidation (PEO) treatment to obtain a multifunctional ceramic-like (TiO2) coating with superior tribocorrosion (wear and corrosion) resistance and improved biocompatibility. For this aim, elements such as Ca, P, and Ag NPs have been incorporated into the oxide film to obtain bioactive and biocide properties. The chemical composition and morphology of the TiO2-PEO coating was characterized, and its multifunctionality was addressed by several means, including antibacterial activity assessment, formation of bone-like apatite, metallic ion release evaluation, in vitro cellular response analysis, and corrosion and tribocorrosion tests in artificial saliva. The developed coatings enhanced the corrosion and tribocorrosion resistance of the bare alloy and exhibited antibacterial ability with low cytotoxicity and negligible ion release. Furthermore, they were able to sustain MC3T3-E1 preosteoblast viability/proliferation and osteogenic differentiation. Altogether, the results obtained demonstrate the potential of the TiO2 coating incorporating Ca, P, and Ag NPs to be used for dental applications.

Biomimetic and osteogenic natural HAP coated three dimensional implant for orthopaedic application

The excellent biocompatible and osteogenesis ability of multifunctional three-dimensional (3D) polymeric scaffolds have a vital role in bone regeneration application. Our prime focus of the investigation is the synthesis of snail shell-derived hydroxyapatite coated poly[bis(carboxyphenoxy)phosphazene] (PCPP)/poly(ε-caprolactone) (PCL) 3D scaffold. Snail shells are utilized for hydroxyapatite (HAP) synthesis via a modified chemical precipitation method. The interconnected PCPP/PCL polymeric scaffold was fabricated by the conventional solvent-casting/particulate-leaching method. Bioceramic HAP was further coated on the scaffold by the dip-coating technique. The obtained natural HAP from Turritella duplicata has minerals and organic substituents which are essential for biomedical application. HAP reinforcement significantly increases the mechanical property, compressive strength, and porosity of the scaffolds. The SEM image depicted the homogenous dispersion of HAP over the scaffold surface. Mechanical studies of the 3D polymeric scaffold at the 2% TSS-HAP content demonstrated a significant increase in compressive strength with desired porous structure. It showed increasing compressive strength from 1.52 MPa to 2.18 MPa and porosity of 82.26% to 76.18%. Snail shell HAP grafted polymeric scaffold shows mineralization with the formation of bone-like apatite. The HAP grafted bioceramic/polymeric scaffold surface helps in the attachment and proliferation of MG-63 cells. It also explored the biocompatible property and antibacterial against gram-positive/gram-negative bacteria. Overall, the fabricated 3D implant has improved mechanical strength, optimum pore size, and interconnected structure, which helps in mineralization and cancellous bone tissue engineering applications.

Surface enhancement of Ti–6Al–4V fabricated by selective laser melting on bone-like apatite formation

Medical grade Ti–6Al–4V implants fabricated using selective laser melting (SLM) are recognized as a commercial biomaterial used for bone repairs and fracture fixation. However, there have been cases of failed bone remodeling and implant infections caused by deficient osteointegration. To improve osteogenesis, the Ti implants are treated by acid-etching. This study focused on the effect of surface treatment by using different percentages of sulfuric acid (H2SO4), hydrochloric acid (HCL), and hydrofluoric acid (HF) on the SLM Ti–6Al–4V. The microstructure and surface topography before and after treatment were evaluated. Then, the presence of a thicker anatase layer that was detectable on the surface was also observed by X-ray diffraction (XRD). The apatite-forming capabilities which indicated a sample bioactivity were assessed in simulated body fluid (SBF) for periods of 3 days and 7 days. The apatite formed on the surface of sample and XRD scanning revealed the deposition of Ca/P, suggesting successful bone-like apatite. The study discovered that these surface improvements were appropriate for the SLM Ti–6Al–4V prior to clinical applications and were likely to yield higher levels of osseointegration.

Digital light processing (DLP) of nano biphasic calcium phosphate bioceramic for making bone tissue engineering scaffolds

Nano-sized ceramic particles are beneficial for the properties of 3D printed structures via digital light processing (DLP). However, achieving optimal conditions for the preparation and processing of ceramic nanoparticle-based slurry is a significant challenge. In this work, a stable and well dispersed slurry with nano-sized biphasic calcium phosphate (BCP) powders was developed and porous BCP bioceramic scaffolds with good bioactivity were accurately fabricated via the DLP additive manufacturing technology. Effects of dispersant, photoinitiator and solid loading on rheological properties and curing abilities of BCP slurries were systematically studied. The slurry having 65 wt % of nano-sized BCP powders showed a relatively low viscosity of 400 mPa s at the 50 s−1 shear rate. It was found that the optimal photoinitiator concentration was tightly associated with the energy dosage in DLP. Furthermore, the effects of sintering temperature (1100 °C, 1200 °C and 1300 °C) on the surface morphology, shrinkage, phase constitution, hardness, compressive properties, and in vitro biological performance of DLP-formed bioceramics were comprehensively investigated. The results showed that DLP-formed BCP ceramics sintered at 1300 °C had the best mechanical properties, in vitro cytocompatibility, and homogeneous bone-like apatite formation ability. Finally, DLP-formed 3D scaffolds with different pore sizes ranging from 300 μm to 1 mm were successfully fabricated, which exhibited high fidelity and accuracy. The current study has demonstrated the great potential of using DLP technology to construct functional complex BCP bioceramic scaffolds for bone tissue regeneration.

Design of macropore structure and micro-nano topography to promote the early neovascularization and osteoinductivity of biphasic calcium phosphate bioceramics

Early neovascularization and osteoinductivity are two key factors to determine the regenerative abilities of biphasic calcium phosphate (BCP) bioceramics in bone repair. Due to the uncontrolled pore structure and large grain size, the biological performances of the conventional BCP bioceramics is restricted to a large extent. Herein, this study attempted to fabricate BCP bioceramics with appropriately uniform macropores and abundant micropores by combining the advantages of the H2O2 foaming method with the microsphere-sintering method, and different sintering methods were adopted to adjust the micro-nano topography. Due to the optimal design of macropore distribution and nano topography, the obtained BCP bioceramics could well trigger and regulate in vitro biological responses, such as degradation, bone-like apatite formation, protein adsorption, cell spreading, angiogenic and osteogenic differentiation. In vivo canine intramuscular implantation further revealed that the nano topography and appropriately uniform macropores might be responsible for the early neovascularization and osteoinductivity of the prepared BCP bioceramics. Collectedly, the neovascularization and osteoinductivity of BCP bioceramics were further enhanced by optimally designing the pore structure and micro-nano topography, which hold huge potential to be an alternative to the gold standard of autogenous bone in bone repairing applications.

Fabrication and biological evaluation of 3D-printed calcium phosphate ceramic scaffolds with distinct macroporous geometries through digital light processing technology.

Digital light processing (DLP)-based 3D printing technique holds promise in fabricating scaffolds with high precision. Here raw calcium phosphate (CaP) powders were modified by 5.5% monoalcohol ethoxylate phosphate (MAEP) to ensure high solid loading and low viscosity. The rheological tests found that photocurable slurries composed of 50 wt% modified CaP powders and 2 wt% toners were suitable for DLP printing. Based on geometric models designed by computer-aided design (CAD) system, three printed CaP ceramics with distinct macroporous structures were prepared, including simple cube, octet-truss and inverse face-centered cube (fcc), which presented the similar phase composition and microstructure, but the different macropore geometries. Inverse fcc group showed the highest porosity and compressive strength. The in vitro and in vivo biological evaluations were performed to compare the bioactivity of three printed CaP ceramics, and the traditional foamed ceramic was used as control. It suggested that all CaP ceramics exhibited good biocompatibility, as evidence by an even bone-like apatite layer formation on the surface, and the good cell proliferation and spreading. A mouse intramuscular implantation model found that all of CaP ceramics could induce ectopic bone formation, and foam group had the strongest osteoinduction, followed by inverse fcc, while cube and octet-truss had the weakest one. It indicated that macropore geometry was of great importance to affect the osteoinductivity of scaffolds, and spherical, concave macropores facilitated osteogenesis. These findings provide a strategy to design and fabricate high-performance orthopedic grafts with proper pore geometry and desired biological performance via DLP-based 3D printing technique.

Additive Manufacturing of α-Amino Acid Based Poly(ester amide)s for Biomedical Applications.

α-Amino acid based polyester amides (PEAs) are promising candidates for additive manufacturing (AM), as they unite the flexibility and degradability of polyesters and good thermomechanical properties of polyamides in one structure. Introducing α-amino acids in the PEA structure brings additional advantages such as (i) good cytocompatibility and biodegradability, (ii) providing strong amide bonds, enhancing the hydrogen-bonding network, (iii) the introduction of pendant reactive functional groups, and (iv) providing good cell–polymer interactions. However, the application of α-amino acid based PEAs for AM via fused deposition modeling (FDM), an important manufacturing technique with unique processing characteristics and requirements, is still lacking. With the aim to exploit the combination of these advantages in the creation, design, and function of additively manufactured scaffolds using FDM, we report the structure–function relationship of a series of α-amino acid based PEAs. The PEAs with three different molecular weights were synthesized via the active solution polycondensation, and their performance for AM applications was studied in comparison with a commercial biomedical grade copolymer of l-lactide and glycolide (PLGA). The PEAs, in addition to good thermal stability, showed semicrystalline behavior with proper mechanical properties, which were different depending on their molecular weight and crystallinity. They showed more ductility due to their lower glass transition temperature (Tg; 18–20 °C) compared with PLGA (57 °C). The rheology studies revealed that the end-capping of PEAs is of high importance for preventing cross-linking and further polymerization during the melt extrusion and for the steadiness and reproducibility of FDM. Furthermore, our data regarding the steady 3D printing performance, good polymer–cell interactions, and low cytotoxicity suggest that α-amino acid based PEAs can be introduced as favorable polymers for future AM applications in tissue engineering. In addition, their ability for formation of bonelike apatite in the simulated body fluid (SBF) indicates their potential for bone tissue engineering applications.

Surface Enhancement in Ti-6al-4v Fabricated by Selective Laser Melting on Bone-Like Apatite Formation

Surface Enhancement in Ti-6al-4v Fabricated by Selective Laser Melting on Bone-Like Apatite Formation

Effects of strontium and zinc substituted plasma sprayed hydroxyapatite coating on bone-like apatite layer formation and cell-material interaction

Recently the use of Sr2+ and Zn2+ ions substituted HA as an excellent biomaterial has been reported. To expand the usage to load-bearing applications, like hip replacement, it has been proposed that the material should be used in the form of a coating on the implant surface. In this work, we prepared Sr2+ and Zn2+ co-substituted HA plasma spray coating at different concentrations on titanium alloy (Ti–6Al–4V). All coatings showed excellent bonding strength with the substrate. The apatite layer formation on the coatings was studied via immersion in SBF. All samples exhibited great capability to induce the apatite layer formation on the coating surface, however, 10Zn5Sr-HA coating inhibited the apatite layer formation. The cell material interaction on the surfaces of the coatings was examined through MC3T3-E1 cell and demonstrated higher biocompatibility, protein adsorption ability, and significantly higher dissolution rate than pure HA coating. However, 10Zn5Sr-HA coating shows cytotoxicity which is confirmed by cell proliferation, cell adhesion, and ALP activity. Besides, some dead cells and poor cellular morphology were also found on the coating surface. The co-substituted HA coating revealed excellent antibacterial ability against bacterial colonization. The addition of Sr2+ to the Zn-HA coating effectively decreased the thermal instability, cytotoxicity, and increased performance as compared to HA coating. From the results, it is indicated that the 5Zn10Sr-HA coating has good bonding strength, bioactivity, biocompatibility, and antibacterial properties.

Immobilization of bioactive glass ceramics @ 2D and 3D polyamide polymer substrates for bone tissue regeneration

The osteoinductivity of bioactive glass ceramics (BGCs) is dependent on their ability to effectively interact with the surrounding physiological environment and influence the fate of target cells; however, masking and poor dispersion can negatively influence bioactivity. Here, we address this problem via a simple fabrication method of assembling highly ordered and aligned arrays of BGC nanoneedle-like structures (@) on the outer surface of various polyamide 6 (PA6) substrates (casted film, 3D printing filaments, electrospun fibre mats) by ion dissociation. The staggered-like nanoneedles of BGC@PA6 substrates with excellent uniform dispersion showed favourable cell viability, proliferation, and spreading of MC3T3 osteoblast-like cells. Moreover, the immobilized BGC nanoneedles induced osteogenic differentiation and accelerated the expression of late osteoblast marker genes, compared to the control group. Furthermore, the BGC@PA6 composite showed high affinity for bone-like apatite formation when incubated in physiological body fluids. These findings suggest that the unique dispersion of BGCs@PA6 substrates with nanostructure features make them attractive candidates for bone tissue regeneration and open avenues for future investigation into exploiting these properties for bone tissue engineering. Importantly, this work provides a novel concept for in-situ immobilization of BGC with distinctive topographical features onto polymer substrates simulating natural bone structure.

Effect of buffer in simulated body fluid on morphology and crystallinity of hydroxyapatite precipitated on 45S5 bioactive glass-derived glass–ceramic scaffolds: comparison of Good’s buffer systems and TRIS

In vitro tests that verify the ability of a material to form bone-like apatite precipitated (HAp) use a solution that imitates the inorganic part of blood plasma, simulated body fluid (SBF). During such tests, it is necessary to maintain a neutral pH, for which purpose the International Standards Organization recommends the TRIS (tris(hydroxymethyl)aminomethane) buffer (ISO 23,317:2014). To do this, TRIS buffer must remain inert, but, as we have previously reported, TRIS interacts with highly bioreactive materials (such as 45S5 Bioglass-derived scaffolds), thereby accelerating scaffold dissolution. In the search for an alternative to TRIS, we have also recently published results for the 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) and 3-(N-morpholino) propanesulfonic acid (MOPS) buffers, which were also unable to maintain a neutral pH in SBF. Thus, we here continue our search for a more suitable Good’s buffer by comparing BES (N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid) and TES (2-[(2-hydroxy-1,1-bis(hydroxymethyl) ethyl) amino] ethanesulfonic acid) with TRIS. 45S5-derived glass–ceramic scaffolds were tested under static–dynamic conditions for bone-like apatite formation using SBF + BES and SBF + TES solutions. The pH measurements, leachate analysis [atomic absorption spectrophotometry (AAS) (Ca2+, SiIV), UltraViolet-Visible (UV-VIS) spectrophotometry (PO4)3−], and scaffold analysis [X-Ray powder diffraction analysis (XRD), X-ray fluorescent analysis (XRF), scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS), Brunauer.Emmett.Teller specific surface area analysis (BET)] all showed that both BES and TES quickly interacted with the tested material. Moreover, the kinetics of the glass–ceramic dissolution affected the crystallinity and morphology of the precipitated HAp. Based on our previous results and the present data, it appears that Good’s buffers are not suitable for the in vitro testing of bioactivity of highly bioreactive materials.

Excellent Osteoinductivity of Biphasic Calcium Phosphate Bioceramics with the Optimal Design of Pore Size Distribution and Micro-Nano Topography

Further enhance the bioactivity and osteoinductivity of biphasic calcium phosphate (BCP) bioceramics to meet the requirements of regenerative medicine is still a hot topic. Due to the uncontrolled pore structure and large grain size, the osteoinductivity of the conventional BCP bioceramics is restricted to a large extent. Herein, this study introduced a novel pore foaming method to fabricate BCP bioceramics with appropriately ordered macropores and abundant micropores by combing the advantages of the microsphere-sintering method with the H2O2 gas foaming method. Moreover, different sintering methods were adopted to adjust the micro-nano topography of BCP bioceramics. Due to the optimal design of pore size distribution and nano topography, the obtained BCP bioceramics could well trigger and regulate in vitro biological responses, such as degradation, bone-like apatite formation, protein adsorption, cell behaviors, angiogenic and osteogenic differentiation. In vivo canine intramuscular implantation further confirmed that the nanotopography and appropriately ordered pore structure might be responsible for the excellent neovascularization and osteoinductivity of the obtained BCP bioceramics. Collectedly, the osteoinductivity of BCP bioceramics was further enhanced by optimally designing pore structure and micro-nano topography, which hold huge potential to be a potential alternative to the gold standard of autogenous bone in bone repairing applications.

Mechanism of apatite formation on a poorly crystallized calcium phosphate in a simulated body fluid (SBF) at 37 °C

Calcium phosphate-based bioactive materials have recently attracted considerable attention. In particular, poorly crystalline apatites (PCA) are successfully used for bone repair and regeneration, enhancing the osteointegration and osteoconduction properties. Our study aims to better understand the mechanism of apatite formation on the poorly crystallized apatite powders. For this purpose, two PCA samples were synthesized in the same conditions while varying only the maturation time.The most noticeable difference between both samples is that the immature specimen (PCA2h) was richer in both water and HPO42− labile species than the mature specimen (PCA2m). Besides, it has a higher surface area and more negatively charged surface. Both PCA samples were soaked in a simulated body fluid (SBF) for different periods of time at 37 °C, leading to the neoformation of bone-like apatite layer on their surfaces due to their bioactivity. The surface of all samples was investigated using scanning electron microscopy (SEM) coupled with energy-dispersive X-ray (EDX) spectroscopy, zeta-potential measurements and BET analysis. FTIR spectroscopy, XRD, and TG-DTA were used to characterize bulk samples. Thermodynamic calculations of CaP precipitation were also performed. Experimental and theoretical data showed that the bone-like apatite formation mechanism on both samples undergoes by three stages. Only on the PCA2h, did a fast precipitation of positively Ca-rich amorphous phase (ACP) occur at a first time (prenucleation stage). It is converted into Ca-poor ACP by uptaking anions from surrounding media, to promote the formation of apatite nuclei during the second stage (nucleation stage). Then, nascent apatite crystals grew into bone like-apatite coating by poorly crystallized BCO3-apatite which is the most thermodynamically stable CaP phase in SBF (growing and maturation stage). While the bone like-apatite formation process on the mature PCA particles include similar events without Ca-rich ACP deposit. Thus, the formation of the Ca-poor ACP starts immediately at the beginning of soaking (at the 1st stage), followed by apatite nucleation (2nd stage), promoting the growth and maturation of BCO3-apatite crystals (3rd stage). Our results highlight the fact that in the waterlogged conditions of the hydrated shells surrounding the immature PCA nanocrystals, a high density of labile orthophosphate anions leads enriches the PCA-liquid solution interface in Ca2+ ions, momentarily stabilizing them into a positively charged amorphous complex likely to be strongly solvated. Then, this interface becomes more attractive for free orthophosphate anions, enhancing the bioactivity to improve osteointegration. The composition of the hydrated shells coating of the biomimetic apatite crystal in both labile species and hydration water seems to govern their bioactivity via surface charge potential and hydrophilic capacity. These data allow a better understanding of the bioactive behaviour of biomaterials involving biomimetic PCA phases for tissue engineering.

Plasma electrolytic oxidation of Ti-6Al-4V alloys in nHA/GNS containing electrolytes for biomedical applications: The combined effect of the deposition frequency and GNS weight percentage

In this study, nano-hydroxyapatite (nHA) based coatings reinforced with graphene nanosheets (GNS) were successfully synthesized on Ti6Al4V alloys using AC-plasma electrolytic oxidation (PEO) technique. The PEO treatments were carried out at 1000, 1500, and 2000 Hz frequencies in different GNS containing electrolytes (free, 1.0, and 1.5 wt%). The combined effect of the deposition frequency and GNS weight percentage on the morphological and crystallographic properties of the coatings was investigated by SEM, AFM, XRD, EDS, and FT-IR analysis. The in-vitro corrosion susceptibilities of the coatings were compared by using the potentiodynamic scanning (PDS) technique in simulated body fluid (SBF) at body temperature. Besides, surface hydrophilicity and microhardness measurements were made on the coatings. The characterization of the coatings confirmed that GNS was successfully deposited in nHA-matrix with a porous and rough structure. Coating thickness and hardness increased with increasing GNS weight percentage in the coating layers and deposition frequency. A bone-like apatite formation was also observed on the surfaces after electrochemical tests in SBF. The results revealed that bioactive and hard coatings can be obtained by PEO in nHA/GNS baths.

Preface

Anodic oxidation (AO) of titanium is a common electrochemical process for surface modification of metallic surfaces and is conducted in an electrolyte solution. Anodisation of titanium implants can generate a coating with optimal characteristics to accelerate the growth of bone-like apatite. The present work aims to develop a novel AO electrolyte formulation of a CaP base solution containing three different alteration agents. The characteristics of the anodised coating were modified by varying the volume fractions of the alteration agents, namely sulphuric acid, hydrogen peroxide, and acetic acid in a base solution of β-glycerolphosphate disodium salt pentahydrate (β-GP) and calcium acetate monohydrate (CA). The surface morphology, mineralogy, wettability, and bioactivity of these coatings were analysed using scanning electron microscopy (SEM), X-ray diffraction (XRD), contact angle analysis, and in vitro testing using simulated body fluid (SBF). Anodisation in a mixture of β-GP + CA electrolyte resulted in the formation of Ca-P-rich oxide coating (with surface features with a donut-like shape) and when altered with 12.5 vol% sulphuric acid, highly defined spiky needle-like morphology was seen on the surface. These coatings were composed of hydroxyapatite, tricalcium phosphate, and calcium diphosphate. After 7 days of SBF immersion, the surface was observed to contain a dense layer of bone-like apatite. However, alteration using acetic acid did not result in any significant changes to the surface characteristics and no bone-like apatite formation was observed even after soaking in SBF for 7 days. Alteration using hydrogen peroxide resulted in an anodised coating that assisted the growth of bone-like apatite layer on the coating surfaces after soaking in SBF for 7 days. The differences in coating performance are linked to the presence of different functional ions with hydronium groups (from sulphuric acid) being superior compared to the carboxyl ions (from acetic acid). The coating produced by sulphuric acid alteration demonstrated super hydrophilicity and rougher topographies which are ideal characteristics for cell attachment and proliferation in implant applications.