Advanced Mg, Zn, Sr, Si Multi-Substituted Hydroxyapatites for Bone Regeneration

Optimization of a tunable process for rapid production of calcium phosphate microparticles using a droplet-based microfluidic platform

Calcium phosphate (CaP) biomaterials are amongst the most widely used synthetic bone graft substitutes, owing to their chemical similarities to the mineral part of bone matrix and off-the-shelf availability. However, their ability to regenerate bone in critical-sized bone defects has remained inferior to the gold standard autologous bone. Hence, there is a need for methods that can be employed to efficiently produce CaPs with different properties, enabling the screening and consequent fine-tuning of the properties of CaPs towards effective bone regeneration. To this end, we propose the use of droplet microfluidics for rapid production of a variety of CaP microparticles. Particularly, this study aims to optimize the steps of a droplet microfluidic-based production process, including droplet generation, in-droplet CaP synthesis, purification and sintering, in order to obtain a library of CaP microparticles with fine-tuned properties. The results showed that size-controlled, monodisperse water-in-oil microdroplets containing calcium- and phosphate-rich solutions can be produced using a flow-focusing droplet-generator microfluidic chip. We optimized synthesis protocols based on in-droplet mineralization to obtain a range of CaP microparticles without and with inorganic additives. This was achieved by adjusting synthesis parameters, such as precursor concentration, pH value, and aging time, and applying heat treatment. In addition, our results indicated that the synthesis and fabrication parameters of CaPs in this method can alter the microstructure and the degradation behavior of CaPs. Overall, the results highlight the potential of the droplet microfluidic platform for engineering CaP microparticle biomaterials with fine-tuned properties.

Comparative In Vitro Dissolution Assessment of Calcined and Uncalcined Hydroxyapatite Using Differences in Bioresorbability and Biomineralization

This study reports the effect of the not-calcining process on the bioresorption and biomineralization of hydroxyapatite through in vitro dissolution assessment. The prepared calcined hydroxyapatite (c-HAp) and uncalcined hydroxyapatite (unc-HAp) have a particle size of 2 μm and 13 μm, surface areas of 4.47 m2/g and 108.08 m2/g, and a Ca/P ratio of 1.66 and 1.52, respectively. In vitro dissolution assessments of c-HAp and unc-HAp were performed for 20 days at 37 °C in a citric acid buffer according to ISO 10993-14. During the dissolution, the c-HAp and unc-HAp confirmed an increase in weight, and the calcium and phosphorous ions were rapidly released. The calcium ions released from c-HAp formed rod-shaped particles with a longer and thinner morphology, while in unc-HAp, they appeared thicker and shorter. In the ICP-OES results, the concentrations of calcium elements were initially increased and then decreased by this formation. The rod-shaped particles identified as calcium citrate (Ca-citrate) through the XRD pattern. The calcium content of Ca-citrate particles from unc-HAp was higher than that from c-HAp. The unc-HAp demonstrated non-toxic properties in a cytotoxicity evaluation. Therefore, due to its higher bioresorption and biomineralization, unc-HAp exhibits enhanced biocompatibility compared to c-HAp.

Zinc-based biomaterials for bone repair and regeneration: mechanism and applications

Zinc (Zn) is one of the most important trace elements in the human body and plays a key role in various physiological processes, especially in bone metabolism. Zn-containing materials have been reported to enhance bone repair through promoting cell proliferation, osteogenic activity, angiogenesis, and inhibiting osteoclast differentiation. Therefore, Zn-based biomaterials are potential substitutes for traditional bone grafts. In this review, the specific mechanisms of bone formation promotion by Zn-based biomaterials were discussed, and recent developments in their application in bone tissue engineering were summarized. Moreover, the challenges and perspectives of Zn-based biomaterials were concluded, revealing their attractive potential and development directions in the future.

Optimization of Functional Toothpaste Formulation Containing Nano-Hydroxyapatite and Birch Extract for Daily Oral Care

This research work aims to develop functional toothpastes with combined enamel remineralization and antibacterial effects using nano-hydroxyapatites (nHAPs) and birch extract. Eleven toothpastes (notated as P1-P11) were designed featuring different concentrations of birch extract and a constant concentration of pure nHAPs or substituted nHAPs (HAP-5%Zn, HAP-0.23%Mg-3.9%Zn-2%Si-10%Sr, and HAP-2.5%Mg-2.9%Si-1.34%Zn). In vitro assessments involved treating artificially demineralized enamel slices and analyzing surface repair and remineralization using Atomic Force Microscopy (AFM). The Agar Disk Diffusion method was used to measure antibacterial activity against Enterococcus faecalis, Escherichia coli, Porphyromonas gingivalis, Streptococcus mutans, and Staphylococcus aureus. Topographic images of enamel structure and surface roughness, as well as the ability of nHAP nanoparticles to form self-assembled layers, revealed excellent restorative properties of the tested toothpastes, with enamel nanostructure normalization occurring as soon as 10 days after treatment. The outcomes highlighted enamel morphology improvements due to the toothpaste treatment also having various efficacious antibacterial effects. Promising results were obtained using P5 toothpaste, containing HAP-5%Zn (3.4%) and birch extract (1.3%), indicating notable remineralization and good antibacterial properties. This study represents a significant advancement in oral care by introducing toothpaste formulations that simultaneously promote enamel health through effective remineralization and bacterial inhibition.

Remineralization Induced by Biomimetic Hydroxyapatite Toothpastes on Human Enamel

This work aimed to compare the effect of four new toothpastes (P1-P4) based on pure and biomimetic substituted nano-hydroxyapatites (HAPs) on remineralization of human enamel. Artificially demineralized enamel slices were daily treated for ten days with different toothpastes according to the experimental design. Tooth enamel surfaces were investigated using atomic force microscope (AFM) images and surface roughness (Ra) determined before and after treatment. The surface roughness of enamel slices was statistically analyzed by one-way ANOVA and Bonferroni's multiple comparison test. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) data revealed the HAP structure with crystal sizes between 28 and 33 nm and crystallinity between 29 and 37%. The average size of HAP particles was found to be between 30 and 40 nm. The Ra values indicated that P3 (HAP-Mg-Zn-Sr-Si) toothpaste was the most effective after 10 days of treatment, leading to the lowest mean roughness. The P3 and P2 (HAP) toothpastes were found to be effective in promoting remineralization. Specifically, their effectiveness can be ranked as follows: P3 = P2 > P4 (HAP-Mg-Zn-Si) > P1 (HAP-Zn), considering both the chemical composition and the size of their constitutive nanoparticles. The proposed toothpastes might be used successfully to treat early tooth decay.

Calcination and ion substitution improve physicochemical and biological properties of nanohydroxyapatite for bone tissue engineering applications

Nanohydroxyapatite (nanoHAP) is widely used in bone regeneration, but there is a need to enhance its properties to provide stimuli for cell commitment and osteoconduction. This study examines the effect of calcination at 1200 °C on the physicochemical and biological properties of nanoHAP doped with magnesium (Mg2+), strontium (Sr2+), and zinc (Zn2+). A synergistic effect of dual modification on nanoHAP biological properties was investigated. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), BET analysis, Fourier-transform spectroscopy, and thermal analysis methods. Furthermore, ion release tests and in vitro biological characterization, including cytocompatibility, reactive oxygen species production, osteoconductive potential and cell proliferation, were performed. The XRD results indicate that the ion substitution of nanoHAP has no effect on the apatite structure, and after calcination, β-tricalcium phosphate (β-TCP) is formed as an additional phase. SEM analysis showed that calcination induces the agglomeration of particles and changes in surface morphology. A decrease in the specific surface area and in the ion release rate was observed. Combining calcination and nanoHAP ion modification is beneficial for cell proliferation and osteoblast response and provide additional stimuli for cell commitment in bone regeneration.

Magnesium (Mg2 +), Strontium (Sr2 +), and Zinc (Zn2 +) Co-substituted Bone Cements Based on Nano-hydroxyapatite/Monetite for Bone Regeneration

New bone cement type that combines Sr2 + /Mg2 + or Sr2 + /Zn2 + co-substituted nano-hydroxyapatite (n-HAs) with calcium phosphate dibasic and chitosan/gelatin polymers was developed to increase adhesion and cellular response. The cements were physicochemically described and tested in vitro using cell cultures. All cements exhibited quite hydrophilic and had high washout resistance. Cement releases Ca2 + , Mg2 + , Sr2 + , and Zn2 + in concentrations that are suitable for osteoblast proliferation and development. All of the cements stimulated cell proliferation in fibroblasts, endothelial cells, and osteoblasts, were non-cytotoxic, and produced apatite. Cements containing co-substituted n-HAs had excellent cytocompatibility, which improved osteoblast adhesion and cell proliferation. These cements had osteoinductive potential, stimulating extracellular matrix (ECM) mineralization and differentiation of MC3T3-E1 cells by increasing ALP and NO production. The ions Ca2 + , Mg2 + , Zn2 + , and Sr2 + appear to cooperate in promoting osteoblast function. The C3 cement (HA-SrMg5%), which was made up of n-HA co-substituted with 5 mol% Sr and 5 mol% Mg, showed exceptional osteoinductive capacity in terms of bone regeneration, indicating that this new bone cement could be a promising material for bone replacement.

Tissue-Engineered Nanomaterials Play Diverse Roles in Bone Injury Repair

Nanomaterials with bone-mimicking characteristics and easily internalized by the cell could create suitable microenvironments in which to regulate the therapeutic effects of bone regeneration. This review provides an overview of the current state-of-the-art research in developing and using nanomaterials for better bone injury repair. First, an overview of the hierarchical architecture from the macroscale to the nanoscale of natural bone is presented, as these bone tissue microstructures and compositions are the basis for constructing bone substitutes. Next, urgent clinical issues associated with bone injury that require resolution and the potential of nanomaterials to overcome them are discussed. Finally, nanomaterials are classified as inorganic or organic based on their chemical properties. Their basic characteristics and the results of related bone engineering studies are described. This review describes theoretical and technical bases for the development of innovative methods for repairing damaged bone and should inspire therapeutic strategies with potential for clinical applications.

Immunomodulatory nanotherapeutic approaches for periodontal tissue regeneration

Periodontitis is an infection-induced inflammatory disease characterized by progressive destruction of tooth supporting tissues, which, if left untreated, can result in tooth loss. The destruction of periodontal tissues is primarily caused by an imbalance between the host immune protection and immune destruction mechanisms. The ultimate goal of periodontal therapy is to eliminate inflammation and promote the repair and regeneration of both hard and soft tissues, so as to restore the physiological structure and function of periodontium. Advancement in nanotechnologies has enabled the development of nanomaterials with immunomodulatory properties for regenerative dentistry. This review discusses the immune mechanisms of the major effector cells in the innate and adaptive immune systems, the physicochemical and biological properties of nanomaterials, and the research advancements in immunomodulatory nanotherapeutic approaches for the management of periodontitis and the regeneration of periodontal tissues. The current challenges, and prospects for future applications of nanomaterials are then discussed so that researchers at the intersections of osteoimmunology, regenerative dentistry and materiobiology will continue to advance the development of nanomaterials for improved periodontal tissue regeneration.

Biomimetic ion substituted and Co-substituted hydroxyapatite nanoparticle synthesis using Serratia Marcescens

Biomimicry is becoming deep-rooted as part of bioceramics owing to its numerous functional advantages. Naturally occurring hydroxyapatite (HA) apart from primary nano structures are also characterised by various ionic substitutions. The ease of accommodating such key elements into the HA lattice is known to enhance bone healing properties of bioceramics. In this work, hydroxyapatite synthesized via biomimetic approach was substituted with individual as well as multiple cations for potential applications in bone repair. Ion substitutions of Sr, Mg and Zn was carried out on HA for the first time by using Serratia grown in a defined biomineralization medium. The individual ions of varying concentration substituted in Serratia HA (SHA) (Sr SHA, Mg SHA and Zn SHA) were analysed for crystallinity, functional groups, morphology and crystal size. All three showed decreased crystallinity, phase purity, large agglomerated aggregates and needle-shaped morphologies. Fourier transform infrared spectroscopy (FTIR) spectra indicated increased carbonate content of 5.8% resembling that of natural bone. Additionally, the reduced O-H intensities clearly portrayed disruption of HA lattice and subsequent ion-substitution. The novelty of this study lies primarily in investigating the co-substitution of a combination of 1% Sr, Zn and Mg in SHA and establishing the associated change in bone parameters. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images clearly illustrated uniform nano-sized agglomerates of average dimensions of 20-50 nm length and 8-15 nm width for Sr SHA; 10-40 nm length and 8-10 nm width for both Zn SHA and Mg SHA and 40-70 nm length and 4-10 nm width in the case of 1% Sr, Zn, Mg SHA. In both individual as well as co-substitutions, significant peak shifts were not observed possibly due to the lower concentrations. However, cell volumes increased in both cases due to presence of Sr²⁺ validating its dominant integration into the SHA lattice. Rich trace ion deposition was presented by energy dispersive X-ray spectroscopy (EDS) and quantified using inductively coupled plasma optical emission spectrometer (ICP-OES). In vitro cytotoxicity studies in three cell lines viz. NIH/3T3 fibroblast cells, MG-63 osteosarcoma cells and RAW 264.7 macrophages showed more than 90% cell viability proving the biocompatible nature of 1% Sr, Zn and Mg in SHA. Microbial biomineralization by Serratia produced nanocrystals of HA that mimicked "bone-like apatite" as evidenced by pure phase, carbonated groups, reduced crystallinity, nano agglomerates, variations in cell parameters, rich ion deposition and non-toxic nature. Therefore ion-substituted and co-substituted biomineralized nano SHA appears to be a suitable candidate for applications in biomedicine addressing bone injuries and aiding regeneration as a result of its characteristics close to that of the human bone.

Recent Trends in Hydroxyapatite Supplementation for Osteoregenerative Purposes

Bone regeneration has gained attention in the biomedical field, which has led to the development of materials and synthesis methods meant to improve osseointegration and cellular bone activity. The properties of hydroxyapatite, a type of calcium phosphate, have been researched to determine its advantages for bone tissue engineering, particularly its biocompatibility and ability to interact with bone cells. Recently, the advantages of utilizing nanomolecules of hydroxyapatite, combined with various substances, in order to enhance and combine their characteristics, have been reported in the literature. This review will outline the cellular and molecular roles of hydroxypatite, its interactions with bone cells, and its nano-combinations with various ions and natural products and their effects on bone growth, development, and bone repair.

Bioinorganic Preparation of Hydroxyapatite and Rare Earth Substituted Hydroxyapatite for Biomaterials Applications

Rare Earth elements in the lanthanide series are regarded as one of the finest options for the cationic substitution of calcium ions in hydroxyapatite (HA) because of their favorable impact on the biological characteristics of substituted HA. Neodymium and cerium were used to substitute 5% of calcium ions in HA, prepared via the wet precipitation method. Characterization tests for pure and substituted HA were conducted using XRD, FTIR, EDS, and FESEM. The results showed that changing part from calcium ions in hydroxyapatite to Nd and Ce ions altered its structure, composition, and morphology. Regarding the biological tests, the cytotoxicity test revealed a change in IC₅₀ for both normal and cancer cell lines, where substitution part of the Ca ions with rare Earth elements led to increasing antitumor activity in comparison with HA without substitution; in addition, antibacterial and fungicide activity was evident for both HA and Nd-Ce/HA, with a modest increase in antibacterial activity of Nd-Ce/HA against S. epidermidis and E. coli in comparison with HA. These findings may shed light on the process by which Nd and Ce ions improve the biological characteristics of pure HA and the increased potential of these bioceramics.

Nanocomposite Based on HA/PVTMS/Cl2FeH8O4 as a Gas and Temperature Sensor

In this paper, a novel nanocrystalline composite material of hydroxyapatite (HA)/polyvinyltrimethoxysilane (PVTMS)/iron(II)chloride tetrahydrate (Cl₂FeH₈-O₄) with hexagonal structure is proposed for the fabrication of a gas/temperature sensor. Taking into account the sensitivity of HA to high temperatures, to prevent the collapse and breakdown of bonds and the leakage of volatiles without damaging the composite structure, a freeze-drying machine is designed and fabricated. X-ray diffraction, FTIR, SEM, EDAX, TEM, absorption and photoluminescence analyses of composite are studied. XRD is used to confirm the material structure and the crystallite size of the composite is calculated by the Monshi-Scherrer method, and a value of 81.60 ± 0.06 nm is obtained. The influence of the oxygen environment on the absorption and photoluminescence measurements of the composite and the influence of vaporized ethanol, N₂ and CO on the SiO₂/composite/Ag sensor device are investigated. The sensor with a 30 nm-thick layer of composite shows the highest response to vaporized ethanol, N₂ and ambient CO. Overall, the composite and sensor exhibit a good selectivity to oxygen, vaporized ethanol, N₂ and CO environments.

Marine plankton exoskeletone-derived hydroxyapatite/polycaprolactone composite 3D scaffold for bone tissue engineering

3D porous scaffolds based on biodegradable polymers are one of the materials for bone tissue regeneration. In this study, a porous scaffold was prepared using a solvent casting/particulate leaching method that used polycaprolactone (PCL) and hydroxyapatite (OceanBone-HAp) extracted from a marine plankton exoskeleton to achieve excellent bone regeneration. In this study, the morphology and physicochemical properties of the PCL/OceanBone-HAp scaffolds were evaluated using scanning electron microscopy, X-ray diffraction, and porosity analysis. The results confirmed the porous structure of the scaffold and removal of the solvent and porogen particles. In vitro test results revealed superior cell adhesion, proliferation, and viability of PCL/OceanBone-HAp scaffolds compared to PCL scaffolds alone. The enhanced alkaline phosphatase activity and expression of bone morphogenetic protein 2, collagen type I α 1, osteocalcin, and bone sialoprotein in the PCL/OceanBone-HAp scaffolds were confirmed through ALP and real-time polymerase chain reaction assays. Moreover, in vivo experiments using a rabbit calvarial defect model showed that the PCL/OceanBone-HAp scaffold exhibited enhanced bone regeneration compared to the PCL scaffold. Therefore, the PCL/OceanBone-HAp scaffold is a promising scaffold for bone repair.

In vitro antibacterial effect of forsterite nanopowder: synthesis and characterization

The aims of this study were the preparation, characterization, and in vitro antibacterial activity evaluation of forsterite (FS, Mg₂SiO₄) nanopowder obtained by two major methods, namely sol-gel (FSsg) and co-precipitation (FSpp). The main aim was to determine the influence of preparation methodologies on physical properties and in vitro antibacterial activity of obtained forsterite nanopowder. To assess the best working temperature for the preparation of FSsg and FSpp, the synthesis and thermal treatment conditions were optimized on the basis of thermal gravimetric (TG) and differential scanning calorimetric (DSC) analysis performed on the dried gel and dried co-precipitated solid, respectively. The FSsg and FSpp powders were characterized by X-ray powder diffraction (XRD), indicating a high purity for both FSsg and FSpp powders. The morphology of FSsg and FSpp nanopowders was explored by scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). In vitro antibacterial activity was investigated using a targeted pathogen, namely Staphylococcus aureus (S. aureus) ATCC 6538 P as tested strain by broth dilution technique and inoculations on nutrient agar to highlight the bactericidal inhibitory effect. FSsg nanopowder has no inhibitory capacity, while FSpp produced inhibition, the effect being bactericidal at a concentration of 10 mg/mL. The superior bactericidal activity of FSpp against FSsg is due to variation in the own surface properties, such as specific surface area (SSA) and nano-regime particle size. The FSpp nanoparticles, NPs, obtained by co-precipitation method are reported for the first time as a novel bactericidal nanomaterial against S. aureus.

Calcium Phosphate Functionalization and Applications in Dentistry

The oral and maxillofacial hard tissues support the maxillofacial shape and serve as the foundation for functional activities. Defects in these tissues not only impair patients’ ability to perform their normal physiological functions but also have a significant negative impact on their psychological well-being. Moreover, these tissues have a limited capacity for self-healing, necessitating the use of artificial materials to repair defects. Calcium phosphate is a fine-grained inorganic biomineral found in vertebrate teeth and bones that has a comparable composition to human hard tissues. Calcium phosphate materials are biocompatible, bioactive, and osteogenic for hard tissue repair, despite drawbacks such as poor mechanical qualities, limiting their clinical efficacy and application. With the advancement of materials science and technology, numerous techniques have been developed to enhance the characteristics of calcium phosphate, and one of them is functionalization. Calcium phosphate can be functionally modified by changing its size, morphology, or composition through various preparation processes to achieve multifunctionality and improve physical and chemical properties, biocompatibility, and osteogenic potential. The purpose of this review is to provide new ideas for the treatment of oralmaxillofacial hard tissue defects and deficiencies by summarizing the functionalization strategies of calcium phosphate materials and their applications in dentistry.

Assessment of protein adhesion behaviour and biocompatibility of magnesium/Co-substituted HA-based composites for orthopaedic application

Protein adsorption has a great influence on Mg-based metallic implants, which affects cell attachment and cell growth. Adsorption of the proteins (via electrostatic interaction, hydrophobic/hydrophilic, and hydrogen-bonding) on the implant surface is greatly influenced by the surface chemistry of the implant. Hydroxyapatite (HA) is a class of CaP ceramic, beneficial for protein adsorption as it possesses Ca²⁺ and PO₄^3- in it, which are believed to be the protein binding sites on the HA surface. Moreover, HA is the popular choice for reinforcement in the magnesium matrix owing to its similarity with bone mineral composition. However, negligible interaction between HA and Mg particles during sintering is the major limitation for frequent usage of Mg-HA implants. Doping of HA with Mg²⁺ and Zn²⁺ (CoHA) ions leads to its chemistry similar to natural apatite in human bone and facilitates comparatively better bonding with the MgZn matrix. This study mainly aims to delve into the protein adsorption behaviour of Magnesium/Co-substituted HA-based Composites (M3Z-CoHA) along with their biocompatibility. Qualitative and quantitative protein adsorption analysis shows that the addition of 15 wt% CoHA to Mg matrix enhanced protein adsorption by ~60% and renders cell viability >90% after day 1, supporting cellular growth and proliferation. The implants also initiated osteogenic differentiation of the cells after day 7. The leached-out products from all the composites showed no toxicity. The morphology of the cells in all the composites was found as healthy as the control cells. Overall, the composite with 15 wt% HA reinforcement (M3Z-15CoHA) has shown favourable protein adsorption behaviour and cytocompatibility.

Electrodeposition of Calcium Phosphate Coatings on Metallic Substrates for Bone Implant Applications: A Review

This review summaries more than three decades of scientific knowledge on electrodeposition of calcium phosphate coatings. This low-temperature process aims to make the surface of metallic bone implants bioactive within a physiological environment. The first part of the review describes the reaction mechanisms that lead to the synthesis of a bioactive coating. Electrodeposition occurs in three consecutive steps that involve electrochemical reactions, pH modification, and precipitation of the calcium phosphate coating. However, the process also produces undesired dihydrogen bubbles during the deposition because of the reduction of water, the solvent of the electrolyte solution. To prevent the production of large amounts of dihydrogen bubbles, the current density value is limited during deposition. To circumvent this issue, the use of pulsed current has been proposed in recent years to replace the traditional direct current. Thanks to breaking times, dihydrogen bubbles can regularly escape from the surface of the implant, and the deposition of the calcium phosphate coating is less disturbed by the accumulation of bubbles. In addition, the pulsed current has a positive impact on the chemical composition, morphology, roughness, and mechanical properties of the electrodeposited calcium phosphate coating. Finally, the review describes one of the most interesting properties of electrodeposition, i.e., the possibility of adding ionic substituents to the calcium phosphate crystal lattice to improve the biological performance of the bone implant. Several cations and anions are reviewed from the scientific literature with a description of their biological impact on the physiological environment.

Biodegradable Zn-2Ag-0.04Mg Alloy for Bone Regeneration In Vivo

To evaluate the bone regeneration capacity of Zn-2Ag-0.04Mg alloy scaffold in vivo. Zn, Zn-2Ag and Zn-2Ag-0.04Mg scaffolds were implanted in the femur of New Zealand rabbits, and the degradation of the scaffolds and the regeneration of the bone were observed at 6th week and 6th month. Two-dimensional and three-dimensional micro-CT results showed the new bone in Zn-2Ag-0.04Mg alloy scaffold group was significant more than Zn scaffold group, the bone volume in Zn-2Ag-0.04Mg was higher. Moreover, the osteogenic index in the Zn-2Ag-0.04Mg alloy scaffold group was also higher than Zn scaffold group. At 6th month, the scaffold of Zn-2Ag-0.04Mg was smaller than Zn group or Zn-2Ag group. HE staining of the liver, kidney, and heart did not detect any abnormalities, confirmed the biosafety of the Zn-2Ag-0.04Mg alloy scaffold. The Zn-Ag-0.04Mg alloy scaffold exhibits good biocompatibility and bone regeneration ability in vivo.

Biomimetic PLGA/Strontium-Zinc Nano Hydroxyapatite Composite Scaffolds for Bone Regeneration

Synthetic bone graft substitutes have attracted increasing attention in tissue engineering. This study aimed to fabricate a novel, bioactive, porous scaffold that can be used as a bone substitute. Strontium and zinc doped nano-hydroxyapatite (Sr/Zn n-HAp) were synthesized by a water-based sol-gel technique. Sr/Zn n-HAp and poly (lactide-co-glycolide) (PLGA) were used to fabricate composite scaffolds by supercritical carbon dioxide technique. FTIR, XRD, TEM, SEM, and TGA were used to characterize Sr/Zn n-HAp and the composite scaffolds. The synthesized scaffolds were adequately porous with an average pore size range between 189 to 406 µm. The scaffolds demonstrated bioactive behavior by forming crystals when immersed in the simulated body fluid. The scaffolds after immersing in Tris/HCl buffer increased the pH value of the medium, establishing their favorable biodegradable behavior. ICP-MS study for the scaffolds detected the presence of Sr, Ca, and Zn ions in the SBF within the first week, which would augment osseointegration if implanted in the body. nHAp and their composites (PLGA-nHAp) showed ultimate compressive strength ranging between 0.4–19.8 MPa. A 2.5% Sr/Zn substituted nHAp-PLGA composite showed a compressive behavior resembling that of cancellous bone indicating it as a good candidate for cancellous bone substitute.

Biomimetic porous scaffolds containing decellularized small intestinal submucosa and Sr2+/Fe3+co-doped hydroxyapatite accelerate angiogenesis/osteogenesis for bone regeneration

The design of bone scaffolds is predominately aimed to well reproduce the natural bony environment by imitating the architecture/composition of host bone. Such biomimetic biomaterials are gaining increasing attention and acknowledged quite promising for bone tissue engineering. Herein, novel biomimetic bone scaffolds containing decellularized small intestinal submucosa matrix (SIS-ECM) and Sr²⁺/Fe³⁺co-doped hydroxyapatite (SrFeHA) are fabricated for the first time by the sophisticated self-assembled mineralization procedure, followed by cross-linking and lyophilization post-treatments. The results indicate the constructed SIS/SrFeHA scaffolds are characterized by highly porous structures, rough microsurface and improved mechanical strength, as well as efficient releasing of bioactive Sr²⁺/Fe³⁺and ECM components. These favorable physico-chemical properties endow SIS/SrFeHA scaffolds with an architectural/componential biomimetic bony environment which appears to be highly beneficial for inducing angiogenesis/osteogenesis both in vitro and in vivo. In particular, the cellular functionality and bioactivity of endotheliocytes/osteoblasts are significantly enhanced by SIS/SrFeHA scaffolds, and the cranial defects model further verifies the potent ability of SIS/SrFeHA to accelerate in vivo vascularization and bone regeneration following implantation. In this view these results highlight the considerable angiogenesis/osteogenesis potential of biomimetic porous SIS/SrFeHA scaffolds for inducing bone regeneration and thus may afford a new promising alternative for bone tissue engineering.

Biomimetic Composite Coatings for Activation of Titanium Implant Surfaces: Methodological Approach and In Vivo Enhanced Osseointegration

Innovative nanomaterials are required for the coatings of titanium (Ti) implants to ensure the activation of Ti surfaces for improved osseointegration, enhanced bone fracture healing and bone regeneration. This paper presents a systematic investigation of biomimetic composite (BC) coatings on Ti implant surfaces in a rat model of a diaphyseal femoral fracture. Methodological approaches of surface modification of the Ti implants via the usual joining methods (e.g., grit blasting and acid etching) and advanced physicochemical coating via a self-assembled dip-coating method were used. The biomimetic procedure used multi-substituted hydroxyapatite (ms-HAP) HAP-1.5 wt% Mg-0.2 wt% Zn-0.2 wt% Si nanoparticles (NPs), which were functionalized using collagen type 1 molecules (COL), resulting in ms-HAP/COL (core/shell) NPs that were embedded into a polylactic acid (PLA) matrix and finally covered with COL layers, obtaining the ms-HAP/COL@PLA/COL composite. To assess the osseointegration issue, first, the thickness, surface morphology and roughness of the BC coating on the Ti implants were determined using AFM and SEM. The BC-coated Ti implants and uncoated Ti implants were then used in Wistar albino rats with a diaphyseal femoral fracture, both in the absence and the presence of high-frequency pulsed electromagnetic shortwave (HF-PESW) stimulation. This study was performed using a bone marker serum concentration and histological and computer tomography (micro-CT) analysis at 2 and 8 weeks after surgical implantation. The implant osseointegration was evaluated through the bone–implant contact (BIC). The bone–implant interface was investigated using FE-SEM images and EDX spectra of the retrieved surgical implants at 8 weeks in the four animal groups. The obtained results showed significantly higher bone–implants contact and bone volume per tissue volume, as well as a greater amount of newly formed bone, in the BC-coated Ti implants than in the uncoated Ti implants. Direct bone–implant contact was also confirmed via histological examination. The results of this study confirmed that these biomimetic composite coatings on Ti implants were essential for a significant enhancement of osseointegration of BC-coated Ti implants and bone regeneration. This research provides a novel strategy for the treatment of bone fractures with possible orthopedic applications.

Incorporation of Barium Ions into Biomaterials: Dangerous Liaison or Potential Revolution?

In the present manuscript, a brief overview on barium, its possible utilization, and the aftermath of its behavior in organisms has been presented. As a bivalent cation, barium has the potential to be used in a myriad of biochemical reactions. A number of studies have exhibited both the unwanted outcome barium displayed and the advantages of barium laden compounds, tested in in vitro and in vivo settings. The plethora of prospective manipulations covered the area of hydrogels and calcium phosphates, with an end goal of examining barium's future in the tissue engineering. However, majority of data revert to the research conducted in the 20th century, without investigating the mechanisms of action using current state-of-the-art technology. Having this in mind, set of questions that are needed for possible future research arose. Can barium be used as a substitute for other biologically relevant divalent cations? Will the incorporation of barium ions hamper the execution of the essential processes in the organism? Most importantly, can the benefits outweigh the harm?

Synthesis and evaluation of magnesium/co-precipitated hydroxyapatite based composite for biomedical application

Owing to its inductive attributes, hydroxyapatite is an ideal reinforcement to tailor the degradation kinetics of magnesium-based temporary orthopedic implants. However, the large difference in the melting temperature of hydroxyapatite and magnesium lead to an insignificant interaction between them during the sintering process, which has been a major limitation in their consolidation. Doping of pure HA with Mg²⁺ and Zn²⁺ ions could be a viable solution by making it coherent with the Mg matrix. Further, such doping also results in a chemistry more similar to the natural apatite in human bone. In this study, Mg²⁺ and Zn²⁺ ions doped hydroxyapatite (CoHA) is synthesized and reinforced to obtain high density in Mg-based composites, fabricated through spark plasma sintering. Composite with 15 wt % CoHA offered ~113% improvement in the ultimate compressive strength. Higher relative density, due to improved consolidation, might be the reason for higher mechanical strength. Hydrogen evolution (up to 64 h) and static immersion studies (up to 28 days) revealed comparatively higher corrosion resistance for 10 wt% CoHA composites. This study gives insight into the potential of fabrication and designing of the M3Z-CoHA composites for temporary orthopedic implants.

Ion release from hydroxyapatite and substituted hydroxyapatites in different immersion liquids: in vitro experiments and theoretical modelling study

Multi-substituted hydroxyapatites (ms-HAPs) are currently gaining more consideration owing to their multifunctional properties and biomimetic structure, owning thus an enhanced biological potential in orthopaedic and dental applications. In this study, nano-hydroxyapatite (HAP) substituted with multiple cations (Sr2+, Mg2+ and Zn2+) for Ca2+ and anion ( Si O 4 4 - ) for P O 4 3 - and OH-, specifically HAPc-5%Sr and HAPc-10%Sr (where HAPc is HAP-1.5%Mg-0.2%Zn-0.2%Si), both lyophilized non-calcined and lyophilized calcined, were evaluated for their in vitro ions release. These nanomaterials were characterized by scanning electron microscopy, field emission-scanning electron microscopy and energy-dispersive X-ray, as well as by atomic force microscope images and by surface specific areas and porosity. Further, the release of cations and of phosphate anions were assessed from nano-HAP and ms-HAPs, both in water and in simulated body fluid, in static and simulated dynamic conditions, using inductively coupled plasma optical emission spectrometry. The release profiles were analysed and the influence of experimental conditions was determined for each of the six nanomaterials and for various periods of time. The pH of the samples soaked in the immersion liquids was also measured. The ion release mechanism was theoretically investigated using the Korsmeyer-Peppas model. The results indicated a mechanism principally based on diffusion and dissolution, with possible contribution of ion exchange. The surface of ms-HAP nanoparticles is more susceptible to dissolution into immersion liquids owing to the lattice strain provoked by simultaneous multi-substitution in HAP structure. According to the findings, it is rational to suggest that both materials HAPc-5%Sr and HAPc-10%Sr are bioactive and can be potential candidates in bone tissue regeneration.