Synthesis of hydroxyapatite for biomedical applications

Synthesis of Biocompatible Composite Material Based on Cryogels of Polyvinyl Alcohol and Calcium Phosphates

At the moment, the field of biomedical materials science is actively developing, which aims at creating new functional materials. A developing direction in biomedical materials science is that towards the treatment of diseases associated with bone tissue disorders, using biodegradable composite materials based on polymer and calcium phosphate materials. We developed a material based on polyvinyl alcohol cryogel, mineralized with calcium phosphate. A material based on cryogel of polyvinyl alcohol mineralized with calcium phosphate was developed. The composites were obtained by the method of cyclic freezing-thawing, and the synthesis of calcium phosphates was carried out in situ with heating, stirring, and exposure to microwave radiation. The phase composition, as well as the composition of functional groups, was determined by IR spectroscopy and X-ray phase analysis. Monocytes isolated from human blood showed higher viability compared to the controls.

Functionalized 3D scaffolds for engineering the hematopoietic niche

Hematopoietic stem cells (HSCs) reside in a subzone of the bone marrow (BM) defined as the hematopoietic niche where, via the interplay of differentiation and self-renewal, they can give rise to immune and blood cells. Artificial hematopoietic niches were firstly developed in 2D in vitro cultures but the limited expansion potential and stemness maintenance induced the optimization of these systems to avoid the total loss of the natural tissue complexity. The next steps were adopted by engineering different materials such as hydrogels, fibrous structures with natural or synthetic polymers, ceramics, etc. to produce a 3D substrate better resembling that of BM. Cytokines, soluble factors, adhesion molecules, extracellular matrix (ECM) components, and the secretome of other niche-resident cells play a fundamental role in controlling and regulating HSC commitment. To provide biochemical cues, co-cultures, and feeder-layers, as well as natural or synthetic molecules were utilized. This review gathers key elements employed for the functionalization of a 3D scaffold that demonstrated to promote HSC growth and differentiation ranging from 1) biophysical cues, i.e., material, topography, stiffness, oxygen tension, and fluid shear stress to 2) biochemical hints favored by the presence of ECM elements, feeder cell layers, and redox scavengers. Particular focus is given to the 3D systems to recreate megakaryocyte products, to be applied for blood cell production, whereas HSC clinical application in such 3D constructs was limited so far to BM diseases testing.

Pre-Clinical Study: Immunohistochemical evaluation of matrix metalloproteinase-13 on rabbit (Oryctolagus cuniculus) socket healing after application of platelet-rich fibrin with and without hydroxyapatite

Background: Tissue engineering technology has been used globally and proven to accelerate wound healing. This study aimed to analyse the effect of adding hydroxyapatite (HA) as a scaffold to platelet-rich fibrin (PRF) as a growth factor in accelerating the wound healing process as seen from the expression of matrix metalloproteinase-13 (MMP-13). Methods: This research is an animal experiment conducted on 18 rabbits (Oryctolagus cuniculus). Rabbits were randomly divided into the following three groups of treatment: (G1) the application of PRF group, (G2) the application of PRF+HA group and (C) the control group without any application. Furthermore, each treatment group was split randomly into three groups of observation time. Periodontal tissue biopsy was performed to analyse the histopathological features that were examined on the basis of the level of MMP-13 immunoexpression. Results: MMP-13 immunoexpression in the PRF+HA group showed better histoscore results, indicating a substantial reduction in MMP-13 values compared with other groups. The healing process was shown to increase with increasing observation time (p<0.05), and the PRF+HA group outperformed the PRF and control groups. On day 3, MMP-13 exhibited a dark brown colour of Immunohistochemistry (IHC), which indicated an increase in the expression value of MMP-13 in the early stages of healing, namely, inflammation. On day 14, light brown IHC was seen, especially in group 2, as a reference that the remodeling process had begun. Conclusions: This study indicates that the administration of PRF and HA was capable of reducing the MMP-13 expression that significantly accelerates the socket healing process. Hydroxyapatite is an alloplastic material that has inherent bioactive properties that support osteoconduction, can bind MMPs, and showed faster healing results based on the observation time as documented by immunohistochemistry.

Gallium containing calcium phosphates: potential antibacterial agents or fictitious truth

Amidst an ever-increasing demand for the enhancement of the lifestyle and the modulation of modern diseases, the functionalization of biomaterials is of utmost importance. One of the leading materials for the aforementioned purpose have been calcium phosphates (CaPs). They have been widely used in bone regeneration displaying favourable regenerative potential and biological properties. Many studies have placed their entire focus on facilitating the osteogenic differentiation of stem cells and bone progenitor cells, while the aspect of antibacterial properties has been surmounted. Nevertheless, increasing antibiotic resistance of bacteria requires the development of new materials and the usage of alternative approaches such as ion doping. Gallium (Ga) has been the potential star on the rise among the ions. However, the obstacle that accompanies gallium is the scarcity of research performed and the variety of amalgamations. The question that imposes itself is how a growing field of therapeutics can be further entwined with advances in material science, and how will the incorporation of gallium bring a new outlook. The present study offers a comprehensive overview of state-of-the-art gallium containing calcium phosphates (GaCaPs), their synthesis methods, antibacterial properties, and biocompatibility. Considering their vast potential as antibacterial agents, the need for a methodical perspective is highly necessary to determine if it is a direction on the brink of recognition or a fruitless endeavour. STATEMENT OF SIGNIFICANCE: : Although several studies have been published on various metal ions-containing calcium phosphates, to this date there is no systematic overview pointing out the properties and benefits of gallium containing calcium phosphates. Here we offer a critical overview, including synthesis, structure and biological properties of gallium containing calcium phosphates.

Composite Coatings for Osteoblast Growth Attachment Fabricated by Matrix-Assisted Pulsed Laser Evaporation

The bioactive and biocompatible properties of hydroxyapatite (HAp) promote the osseointegration process. HAp is widely used in biomedical applications, especially in orthopedics, as well as a coating material for metallic implants. We obtained composite coatings based on HAp, chitosan (CS), and FGF2 by a matrix-assisted pulsed laser evaporation (MAPLE) technique. The coatings were physico-chemically investigated by means of X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Infrared Microscopy (IRM), and Scanning Electron Microscopy (SEM). Further, biological investigations were performed. The MAPLE-composite coatings were tested in vitro on the MC3T3-E1 cell line in order to endorse cell attachment and growth without toxic effects and to promote pre-osteoblast differentiation towards the osteogenic lineage. These coatings can be considered suitable for bone tissue engineering applications that lack toxicity and promotes cell adhesion and proliferation while also sustaining the differentiation of pre-osteoblasts towards mature bone cells.

Morphological Changes, Antibacterial Activity, and Cytotoxicity Characterization of Hydrothermally Synthesized Metal Ions-Incorporated Nanoapatites for Biomedical Application

The objective of this study was to prepare hydroxyapatite (HA) with potential antibacterial activity against gram-negative and gram-positive bacteria by incorporating different atomic ratios of Cu²⁺ (0.1–1.0%), Mg²⁺ (1.0–7.0%), and Zn²⁺ (1.0–7.0%) to theoretically replace Ca²⁺ ions during the hydrothermal synthesis of grown precipitated HA nanorods. This study highlights the role of comparing different metal ions on synthetic nanoapatite in regulating the antibacterial properties and toxicity. The comparisons between infrared spectra and between diffractograms have confirmed that metal ions do not affect the formation of HA phases. The results show that after doped Cu²⁺, Mg²⁺, and Zn²⁺ ions replace Ca²⁺, the ionic radius is almost the same, but significantly smaller than that of the original Ca²⁺ ions, and the substitution effect causes the lattice distance to change, resulting in crystal structure distortion and reducing crystallinity. The reduction in the length of the nanopatites after the incorporation of Cu²⁺, Mg²⁺, and Zn²⁺ ions confirmed that the metal ions were mainly substituted during the growth of the rod-shape nanoapatite Ca²⁺ distributed along the longitudinal site. The antibacterial results show that nanoapatite containing Cu²⁺ (0.1%), Mg²⁺ (3%), and Zn²⁺ (5–7%) has obvious and higher antibacterial activity against gram-positive bacteria Staphylococcus aureus within 2 days. The antibacterial effect against the gram-negative bacillus Escherichia coli is not as pronounced as against Staphylococcus aureus. The antibacterial effect of Cu²⁺ substituted Ca²⁺ with an atomic ratio of 0.1~1.0% is even better than that of Mg²⁺- and Zn²⁺- doped with 1~7% groups. In terms of cytotoxicity, nanoapatites with Cu²⁺ (~0.2%) exhibit cytotoxicity, whereas Mg²⁺- (1–5%) and Zn²⁺- (~1%) doped nanoapatites are biocompatible at low concentrations but become cytotoxic as ionic concentration increases. The results show that the hydrothermally synthesized nanoapatite combined with Cu²⁺ (0.2%), Mg²⁺ (3%), and Zn²⁺ (3%) exhibits low toxicity and high antibacterial activity, which provides a good prospect for bypassing antibiotics for future biomedical applications.

Chemical Bonding of Biomolecules to the Surface of Nano-Hydroxyapatite to Enhance Its Bioactivity

Hydroxyapatite (HA) is a significant constituent of bones or teeth and is widely used as an artificial bone graft. It is often used to replace the lost bones or in reconstructing alveolar bones before dental implantation. HA with biological functions finds its importance in orthopedic surgery and dentistry to increase the local concentration of calcium ions, which activate the growth and differentiation of mesenchymal stem cells (MSC). To make relevant use of HA in bone transplantation, the surfaces of orthopedic and dental implants are frequently coated with nanosized hydroxyapatite (nHA), but its low dispersibility and tendency to form aggregates, the purpose of the surface modification of bone implants is defeated. To overcome these drawbacks and to improve the histocompatibility of bone implants or to use nHA in therapeutic applications of implants in the treatment of bone diseases, various studies suggested the attachment of biomolecules (growth factors) or drugs through chemical bonding at the surface of nHA. The growth factors or drugs bonded physically at the surface of nHA are mostly unstable and burst released immediately. Therefore, reported studies suggested that the surface of nHA needs to be modified through the chemical bonding of biologically active molecules at the surface of bone implants such as proteins, peptides, or naturally occurring polysaccharides to prevent the aggregation of nHA and to get homogenous dispersion of nHA in solution. The role of irradiation in producing bioactive and antibacterial nHA through morphological variations in surfaces of nHA is also summarized by considering internal structures and the formation of reactive oxygen species on irradiation. This mini-review aims to highlight the importance of small molecules such as proteins, peptides, drugs, and photocatalysts in surface property modification of nHA to achieve stable, bioactive, and antibacterial nHA to act as artificial bone implants (scaffolds) in combination with biodegradable polymers.

Synergistic effects of nanoattapulgite and hydroxyapatite on vascularization and bone formation in a rabbit tibia bone defect model

Hydroxyapatite (HA) is a promising scaffold material for the treatment of bone defects. However, the lack of angiogenic properties and undesirable mechanical properties (such as fragility) limits the application of HA. Nanoattapulgite (ATP) is a nature-derived clay mineral and has been proven to be a promising bioactive material for bone regeneration due to its ability to induce osteogenesis. In this study, polyvinyl alcohol/collagen/ATP/HA (PVA/COL/ATP/HA) scaffolds were printed. Mouse bone marrow mesenchymal stem/stromal cells (BMSCs) and human umbilical vein endothelial cells (HUVECs) were used in vitro to assess the biocompatibility and the osteogenesis and vascularization induction potentials of the scaffolds. Subsequently, in vivo micro-CT and histological staining were carried out to evaluate new bone formation in a rabbit tibial defect model. The in vitro results showed that the incorporation of ATP increased the printing fidelity and mechanical properties, with values of compressive strengths up to 200% over raw PC-H scaffolds. Simultaneously, the expression levels of osteogenic-related genes and vascularization-related genes were significantly increased after the incorporation of ATP. The in vivo results showed that the PVA/COL/ATP/HA scaffolds exhibited synergistic effects on promoting vascularization and bone formation. The combination of ATP and HA provides a promising strategy for vascularized bone tissue engineering.

Development and characterization of mupirocin encapsulated in animal bone-derived hydroxyapatite for management of chronic wounds

Background

Hydroxyapatite is an important biomedical material used in drug delivery owing to its excellent bioactivity and biocompatibility. In this study, hydroxyapatite isolated from bovine and caprine bones was capped and used as a drug carrier to encapsulate mupirocin as an active pharmaceutical product in hydrogel formulations which were utilized in wound healing application using animal model (Wistar Rats).

Results

Characterization of the mupirocin-encapsulated hydroxyapatite using Fourier transform infrared spectroscopy, and X-ray diffractometer revealed the active presence of mupirocin after encapsulation. The in-vitro drug release study revealed that the capped hydroxyapatite obtained from caprine bone loaded with mupirocin gave drug release rate of 84.67% of the drug within 75 min while conventional mupirocin ointment had the lowest at 27.04% within the same time. The capped hydroxyapatite obtained from bovine bone loaded with mupirocin had the highest encapsulation efficiency of 73.67%. However, the animals treated with formulation prepared from capped hydroxyapatite obtained from caprine bone loaded with mupirocin had the highest wound closure area of 377.8 mm2, while conventional mupirocin ointment had 231.5 mm2 in 16 days of treatment. All the formulations with mupirocin except the ointment showed excellent resistance against Klebsiella pneumonia and Staphylococcus aureus of about 40 mm of inhibition zone.

Conclusions

The mupirocin encapsulated in hydroxyapatite extracted from bovine and caprine bones has been demonstrated to be more superior to the conventional ointment in the management of chronic wound conditions.

Permanently polarized hydroxyapatite, an outstanding catalytic material for carbon and nitrogen fixation

Hydroxyapatite (HAp) is a well-known ceramic material widely used in the biomedical field. This review summarizes the very recent developments on permanently polarized HAp (pp-HAp), a HAp variety with tuned electrical properties that confer remarkable catalytic activity. pp-HAp is obtained by applying a thermal stimulation polarization process (TSP), which consists on a DC electric voltage of 500 V at 1000 °C, to previously sintered HAp. The TSP not only increases the crystallinity, reducing the defects in the crystal lattice, but also creates charges that accumulate at the crystalline boundaries and at the surface of microscopic grains, boosting the electrical conductivity. Finally, the successful utilization of pp-HAp in the catalytic fixation of carbon and nitrogen from CO₂ and N₂ gases, respectively, is reported and the formation of different products of chemical interest (e.g. amino acids, ethanol and ammonium) as a function of the reaction conditions (i.e. feeding gases and presence/absence of UV illumination) and catalyst plasticity is discussed. pp-HAp exhibits important advantages with respect to other consolidated catalysts, which drastically increases the final energetic net balance of the reactions.

Recent Progress of Rare Earth Doped Hydroxyapatite Nanoparticles: Luminescence Properties, Synthesis and Biomedical Applications

Hydroxyapatite nanoparticles (HAP NPs) are host materials and can be modified with various substrates and dopants. Among them, rare earth (RE) ions doped HAP NPs have gathered attention due to their unique physicochemical and imaging properties. Compared to other fluorescence probes, RE-doped HAP NPs display advantages in high brightness, high contrast, photostability, nonblinking, and narrow emission bands. Meanwhile, their intrinsic features (composition, morphology, size, crystallinity, and luminescence intensity) can be adjusted by changing the dopant ratio, synthesizing temperature, reaction time, and techniques. And they have been used in various biomedical applications, including imaging probe, drug delivery, bone tissue engineering, and antibacterial studies. This review surveys the luminescent properties, fluorescence enhancement, synthetic methods, and biocompatibility of various RE-doped HAP NPs consolidated from different research works, for their employments in biomedical applications. For this literature review, an electronic search was conducted in the Pubmed, Web of Science, Google Scholar, Scopus and SciFinder databases, using the keywords: hydroxyapatite, rare earth, lanthanide, fluorescence, and imaging. Literature searches of English-language publications from 1979 with updates through April, 2022, and a total of 472 potential papers were identified. In addition, a few references were located by noting their citation in other studies reviewed. STATEMENT OF SIGNIFICANCE: Hydroxyapatite nanoparticles (HAP NPs) have a broad range of promising biological applications. Although prospective biomedical applications are not limited to rare earth-doped hydroxyapatite nanoparticles (RE-doped HAP NPs), some cases do make use of the distinctive features of RE-elements to achieve the expected functions for HAP families. This review surveys the luminescent properties, synthetic methods, and biocompatibility of various RE-doped HAP NPs consolidated from different research works, for their employments in biomedical applications, including imaging probe, drug delivery, bone tissue repair and tracking, and anti-bacteria. Overall, we expect to shed some light on broadening the research and application of RE-doped HAP NPs in biomedical field.

Synthesis, Characterization, Functionalization and Bio-Applications of Hydroxyapatite Nanomaterials: An Overview

Hydroxyapatite (HA) is similar to natural bone regarding composition, and its structure favors in biomedical applications. Continuous research and progress on HA nanomaterials (HA-NMs) have explored novel fabrication approaches coupled with functionalization and characterization methods. These nanomaterials have a significant role in many biomedical areas like sustained drug and gene delivery, bio-imaging, magnetic resonance, cell separation, and hyperthermia treatment due to their promising biocompatibility. This review highlighted the HA-NMs chemical composition, recent progress in synthesis methods, characterization and surface modification methods, ion-doping, and role in biomedical applications. HA-NMs have a substantial role as drug delivery vehicles, coating material, bone implant, coating, ceramic, and composite materials. Here, we try to summarize an overview of HA-NMs with the provision of future directions.

Complete Genome Sequence of Bacillus toyonensis Strain HA0190, Isolated from a Commercial Hydroxyapatite Product Extensively Used as a Synthetic Bone Graft Substitute

Bacillus toyonensis is a member of the Bacillus cereus group and is used as a probiotic in animal feeds and biological applications. We report the 5.8-Mbp genome sequence of strain HA0190, an isolate from a commercial hydroxyapatite nanoparticle product. The genome contains a circular chromosome and two plasmids, pBT001 and pBT002.

Fabrication of novel bio-adsorbent and its application for the removal of Cu(II) from aqueous solution

As eco-friendly adsorption material, hydroxyapatite (Ca₅(PO₄)₃OH, HA) has been extensively applied to the removal of heavy metal ions. However, separating and recovering of HA powder after the adsorption process limits their application. Alginate-based composite beads (HCA) encapsulated with HA and cellulose were designed to remove Cu(II) from aqueous solution. Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) were used for characteristic analysis. An extensive discussion in terms of HCA adsorption capacity, effect of various Cu(II) concentration, and analysis of the involved mechanisms of Cu(II) removal on the biosorption. HCA beads showed that the maximum adsorption capacity for Cu(II) of 64.14 mg/g at pH = 5 with 8 h contact time. The Langmuir adsorption isotherm and second-order kinetic model gave the closest fit. HCA beads display good regeneration ability after four cycles and offer potentiality for practical application.

A 3D-Bioprinted Multiple Myeloma Model

Multiple myeloma (MM) is a malignancy of plasma cells accounting for ≈12% of hematological malignancies. In this study, the fabrication of a high-content in vitro MM model using a coaxial extrusion bioprinting method is reported, allowing formation of a human bone marrow-like microenvironment featuring an outer mineral-containing sheath and the inner soft hydrogel-based core. MM cells are mono-cultured or co-cultured with HS5 stromal cells that can release interleukin-6 (IL-6), where the cells show superior behaviors and responses to bortezomib in 3D models than in the planar cultures. Tocilizumab, a recombinant humanized anti-IL-6 receptor (IL-6R), is investigated for its efficacy to enhance the chemosensitivity of bortezomib on MM cells cultured in the 3D model by inhibiting IL-6R. More excitingly, in a proof-of-concept demonstration, it is revealed that patient-derived MM cells can be maintained in 3D-bioprinted microenvironment with decent viability for up to 7 days evaluated, whereas they completely die off in planar culture as soon as 5 days. In conclusion, a 3D-bioprinted MM model is fabricated to emulate some characteristics of the human bone marrow to promote growth and proliferation of the encapsulated MM cells, providing new insights for MM modeling, drug development, and personalized therapy in the future.

The Synthesis of Hydroxyapatite by Hydrothermal Process with Calcium Lactate Pentahydrate: The Effect of Reagent Concentrations, pH, Temperature, and Pressure

Hydroxyapatite and other calcium phosphates in the form of whiskers are lately widely considered as fillers for biocomposites due to their special biological and reinforcing properties. Depending on the method of synthesis, apatite whiskers of various sizes and phase composition can be obtained. In our work, hydroxyapatite (HAp) whiskers were successfully prepared in reaction between calcium lactate pentahydrate and orthophosphoric acid. The advantage of the proposed technique is the simple but precise control of the HAp crystal morphology and high product purity which is necessary for biomedical applications. The effect of reagent concentrations, pH, reaction temperature, and pressure on HAp whiskers' morphology and composition was investigated. In the result, we obtained hydroxyapatite of different morphology such as whiskers, hexagonal rods, and nanorods. The products were characterized by SEM, XRD, and FTIR. In this work, the synthesis of HAp whiskers by direct decomposition of calcium lactate pentahydrate chelates under hydrothermal conditions was showed for the first time.

Combination of Nanocrystalline Hydroxyapatite and Injectable Platelet-Rich Fibrin on Bone Graft Materials for Alveolar Bone Preservation

Alveolar bone resorption is one of post-extraction complications with a reduction in the dimensions and quality of the alveolar bone, which will make it challenging to install dental implants in the future. The resorption can be prevented by preserving the alveolar bone using bone grafts. Nanocrystalline hydroxyapatite (HA) is a widely developed material as a bone graft. However, there are still some limitations because it only has osteoconductive properties. The addition of injectable platelet-rich fibrin to HA can increase this material’s osteoinductive, antibacterial, and anti-inflammatory properties, making it suitable for use as bone graft material for the preservation of alveolar bone.

Pectin Microspheres: Synthesis Methods, Properties, and Their Multidisciplinary Applications

There is great contemporary interest in using cleaner technologies through green chemistry and utilizing biopolymers as raw material. Pectin is found on plant cell walls, and it is commonly extracted from fruit shells, mostly apples or citrus fruits. Pectin has applications in many areas of commercial relevance; for this reason, it is possible to find available information about novel methods to transform pectin and pursuing enhanced features, with the structuring of biopolymer microspheres being highly cited to enhance its activity. The structuring of polymers is a technique that has been growing in recent decades, due to its potential for diverse applications in various fields of science and technology. Several techniques are used for the synthesis of microspheres, such as ionotropic gelation, extrusion, aerosol drying, or emulsions, with the latter being the most commonly used method based on its reproducibility and simplicity. The most cited applications are in drug delivery, especially for the treatment of colon diseases and digestive-tract-related issues. In the industrial field, it is used for protecting encapsulated compounds; moreover, the environmental applications mainly include the bioremediation of toxic substances. However, there are still many possibilities for expanding the use of this biopolymer in the environmental field.

Bioperformance Studies of Biphasic Calcium Phosphate Scaffolds Extracted from Fish Bones Impregnated with Free Curcumin and Complexed with β-Cyclodextrin in Bone Regeneration

Fish bones are a natural calcium phosphate (CaP) sources used in biomaterials production for bone regeneration. CaP scaffolds can be enriched with other substances with biological activity to improve bone repair. This study aimed to evaluate the physicochemical properties and bone regeneration potential of biphasic calcium phosphate (BCP) scaffolds impregnated with free curcumin (BCP-CL) or complexed with β-cyclodextrin (BCP-CD) compared to BCP scaffolds. Rietveld’s refinement showed that BCP is composed of 57.2% of HAp and 42.8% of β-TCP and the molar ratio of Ca/P corresponds to 1.59. The scaffolds presented porosity (macro and microporosity) of 57.21%. Apatite formation occurred on the BCP, BCP-CL, and BCP-CD surface, in vitro, in SBF. Micro-Raman technique showed a reduction in the dissolution rate of β-TCP in the curcumin-impregnated scaffolds over time, and in vivo studies on critical-size defects, in rat calvaria, had no additional regenerative effect of BCP-CL and BCP-CD scaffolds, compared to BCP scaffolds. Despite this, the study showed that curcumin impregnation in BCP scaffolds prolongs the release of the β-TCP phase, the BCP- phase with the higher osteoinductive potential, representing an advantage in tissue engineering.

Novel Trends into the Development of Natural Hydroxyapatite-Based Polymeric Composites for Bone Tissue Engineering

In recent years, the number of people needing bone replacements for the treatment of defects caused by chronic diseases or accidents has continuously increased. To solve these problems, tissue engineering has gained significant attention in the biomedical field, by focusing on the development of suitable materials that improve osseointegration and biologic activity. In this direction, the development of an ideal material that provides good osseointegration, increased antimicrobial activity and preserves good mechanical properties has been the main challenge. Currently, bone tissue engineering focuses on the development of materials with tailorable properties, by combining polymers and ceramics to meet the necessary complex requirements. This study presents the main polymers applied in tissue engineering, considering their advantages and drawbacks. Considering the potential disadvantages of polymers, improving the applicability of the material and the combination with a ceramic material is the optimum pathway to increase the mechanical stability and mineralization process. Thus, ceramic materials obtained from natural sources (e.g., hydroxyapatite) are preferred to improve bioactivity, due to their similarity to the native hydroxyapatite found in the composition of human bone.

Structuring and functionalization of non-metallic materials using direct laser interference patterning: a review

Direct laser interference patterning (DLIP) is a laser-based surface structuring method that stands out for its high throughput, flexibility and resolution for laboratory and industrial manufacturing. This top-down technique relies on the formation of an interference pattern by overlapping multiple laser beams onto the sample surface and thus producing a periodic texture by melting and/or ablating the material. Driven by the large industrial sectors, DLIP has been extensively used in the last decades to functionalize metallic surfaces, such as steel, aluminium, copper or nickel. Even so, DLIP processing of non-metallic materials has been gaining popularity in promising fields such as photonics, optoelectronics, nanotechnology and biomedicine. This review aims to comprehensively collect the main findings of DLIP structuring of polymers, ceramics, composites, semiconductors and other non-metals and outline their most relevant results. This contribution also presents the mechanisms by which laser radiation interacts with non-metallic materials in the DLIP process and summarizes the developed surface functions and their applications in different fields.

A Study of Vanadate Group Substitution into Nanosized Hydroxyapatite Doped with Eu3+ Ions as a Potential Tissue Replacement Material

In this study, nanosized vanadate-substituted hydroxyapatites doped with 1 mol% and 2 mol% Eu3+ ions were obtained via the precipitation method. To evaluate the structure and morphology of the obtained compounds, the XRPD (X-ray powder diffraction) technique, Rietveld refinement, SEM-EDS (scanning electron microscopy-energy-dispersive spectrometry) and TEM (transmission electron microscopy) techniques as well as FTIR (Fourier transform infrared) spectroscopy were performed. Moreover, the chemical formula was confirmed using the ICP-OES (Inductively coupled plasma optical emission spectroscopy spectroscopy). The calculated average grain size for powders was in the range of 25 to 90 nm. The luminescence properties of vanadium-substituted hydroxyapatite were evaluated by recording emission spectra and excitation spectra as well as luminescence kinetics. The crucial step of this research was the evaluation of the biocompatibility of the synthesized nanomaterials. Therefore, the obtained compounds were tested toward sheep red blood cells and normal human dermal fibroblast to confirm the nontoxicity and biocompatibility of new nanosized Eu3+ ion-doped vanadate-hydroxyapatite. Moreover, the final step of the research allowed us to determine the time dependent ion release to the simulated body fluid environment. The study confirmed cytocompatibility of vanadium hydroxyapatite doped with Eu3+ ions.

Zn/Sr dual ions-collagen co-assembly hydroxyapatite enhances bone regeneration through procedural osteo-immunomodulation and osteogenesis

The immune microenvironment induced by biomaterials played vital roles in bone regeneration. Hydroxyapatite (HA) and its ion-substituted derivates represent a large class of core inorganic materials for bone tissue engineering. Although ion substitution was proved to be a potent way to grant HA more biological functions, few studies focused on the immunomodulatory properties of ion-doped HA. Herein, to explore the potential osteoimmunomodulatory effects of ion-doped HA, zinc and strontium co-assembled into HA through a collagen template biomimetic way (ZnSr-Col-HA) was successfully achieved. It was found that ZnSr-Col-HA could induce a favorable osteo-immune microenvironment by stimulating macrophages. Furthermore, ZnSr-Col-HA demonstrated a procedural promoting effect on osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) in vitro. Specifically, the osteo-immune microenvironment acted as a dominant factor in promoting osteogenic gene expressions at the early stage through OSM signal pathway. Whereas the direct stimulating effects on BMSCs by Zn²⁺/Sr²⁺ were more effectively at the later stage with Nfatc1/Maf and Wnt signals activated. In vivo study confirmed strong promoting effects of ZnSr-Col-HA on critical-sized cranial defect repair. The current study indicated that such a combined biomaterial design philosophy of dual ion-doping and biomimetic molecular co-assembly to endow HA applicable osteoimmunomodulatory characteristics might bring up a new cutting-edge concept for bone regeneration study.

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Zn/Sr dual ions-collagen co-assembly hydroxyapatite (ZnSr-Col-HA) was achieved via a molecular template biomimetic way.

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A procedural promoting effect of ZnSr-Col-HA on osteogenic differentiation of BMSCs was firstly found.

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A novel material design philosophy was proposed for dual ions-doped biomimetic HA with osteoimmunomodulatory properties.

Effect of Hydroxyapatite Microspheres, Amoxicillin-Hydroxyapatite and Collagen-Hydroxyapatite Composites on Human Dental Pulp-Derived Mesenchymal Stem Cells

In this study, the preparation and characterization of three hydroxyapatite-based bioactive scaffolds, including hydroxyapatite microspheres (HAps), amoxicillin–hydroxyapatite composite (Amx–HAp), and collagen–hydroxyapatite composite (Col–HAp) were performed. In addition, their behavior in human dental pulp mesenchymal stem cell (hDPSC) culture was investigated. HAps were synthesized through the following methods: microwave hydrothermal, hydrothermal reactor, and precipitation, respectively. hDPSCs were obtained from samples of third molars and characterized by immunophenotypic analysis. Cells were cultured on scaffolds with osteogenic differentiation medium and maintained for 21 days. Cytotoxicity analysis and migration assay of hDPSCs were evaluated. After 21 days of induction, no differences in genes expression were observed. hDPSCs highly expressed the collagen IA and the osteonectin at the mRNA. The cytotoxicity assay using hDPSCs demonstrated that the Col–HAp group presented non-viable cells statistically lower than the control group (p = 0.03). In the migration assay, after 24 h HAps revealed the same migration behavior for hDPSCs observed compared to the positive control. Col–HAp also provided a statistically significant higher migration of hDPSCs than HAps (p = 0.02). Migration results after 48 h for HAps was intermediate from those achieved by the control groups. There was no statistical difference between the positive control and Col–HAp. Specifically, this study demonstrated that hydroxyapatite-based bioactive scaffolds, especially Col-Hap, enhanced the dynamic parameters of cell viability and cell migration capacities for hDPSCs, resulting in suitable adhesion, proliferation, and differentiation of this osteogenic lineage. These data presented are of high clinical importance and hold promise for application in therapeutic areas, because Col–HAp can be used in ridge preservation, minor bone augmentation, and periodontal regeneration. The development of novel hydroxyapatite-based bioactive scaffolds with clinical safety for bone formation from hDPSCs is an important yet challenging task both in biomaterials and cell biology.

Facile synthesis of a three-dimensional hydroxyapatite monolith for protein adsorption

Hydroxyapatite (HA) shows promising applications in the clinical treatment of bone defects owing to its excellent physicochemical properties, such as biocompatibility, bioactivity, and osteoconductivity. However, it is difficult to maintain a porous structure in HA materials because of processing difficulties. In this study, a hard template method was developed to prepare a porous HA monolith with a hierarchical pore structure and high porosity. The cellulose monolith template was prepared from cellulose acetate using a thermally induced phase separation method. The cellulose monoliths were then immersed into the HA slurry to form a cellulose_HA composite monolith, which was converted to an HA monolith by burning in air to remove the cellulose monolith. Owing to the hierarchically porous structure of the cellulose monolith template, the obtained HA monolith demonstrated a hierarchically porous structure. Furthermore, the HA monolith was explored to study the adsorption and release properties of bovine serum albumin (BSA), which indicated that the HA monolith had a high adsorption capacity (388.6 mg g^-1) and sustained release from the BSA-loaded HA monolith. Thus, HA monoliths have potential applications in the field of protein purification and biomaterials.

Injectable and self-healing nanocomposite hydrogel loading needle-like nano-hydroxyapatite and graphene oxide for synergistic tumour proliferation inhibition and photothermal therapy

Non-chemotherapeutic tumour treatment has received extensive attention due to its having fewer side effects as compared to chemotherapy. However, nanomaterials-based non-chemotherapy still faces limitations such as poor targeting and low retention. Therefore, a Schiff base cross-linked hydrogel was designed and prepared using aldehyde-modified polyethylene glycol (PEG) and carboxymethyl chitosan (CMC). This hydrogel has good injectable and self-healing properties and can carry graphene oxide (GO) as a photothermal agent and needle-like nano-hydroxyapatite (HAP) as a tumour inhibitor. Combined with tumour proliferation inhibition therapy and photothermal therapy, the nanocomposite hydrogel system can avoid the side effects of chemotherapy and improve the accuracy of tumour treatment. The PEG-CMC/HAP/GO nanocomposite hydrogel system has a porous structure, good injectability and self-healing properties to meet the mechanical requirements. In vitro cell characterization showed that GO is phototoxic to tumour cells, HAP can inhibit the proliferation of tumour cells, the nanocomposite hydrogel remained in the tumour site, and the encapsulated GO and HAP did not transfer to the normal site and cause cell damage. In the in vivo investigation, the breast cancer tumour-bearing mice, the model animals for tumour treatment, were treated with an intratumoral injection of the PEG-CMC/HAP/GO nanocomposite hydrogel. This functional self-healing hydrogel loaded with GO and HAP effectively inhibited tumour cell proliferation and realized the synergistic effect of photothermal therapy, which is expected to become a new effective treatment approach for tumours.

Changes in Spectral Fluorescence Properties of a Near-Infrared Photosensitizer in a Nanoform as a Coating of an Optical Fiber Neuroport

In this work, we tested a new approach to assess the presence of inflammatory process in the implant area using spectral methods and the technique of fiber fluorescence analysis of photosensitizers in nanoform. First of all, the spectral characteristics of the photosensitizer when interacting with the porous surface of the implant, based on hydroxyapatite under in vitro and in vivo conditions, were determined. Thus, it was shown that spectral characteristics of photosensitizers can be used for judgement on the process of inflammation in the implant area and thus on the local presence of the immunocompetent cells. The analysis was performed at a sufficient depth in the biotissue by using the near-infrared spectral region, as well as two different methods: fiber-based laser spectroscopy and fiber-optic neuroscopy, which served to monitor the process and regular fluorescence diagnosis of the studied area. Fluorescence spectroscopic analysis was performed on experimental animals in vivo, i.e., under conditions of active immune system intervention, as well as on cell cultures in vitro in order to judge the role of the immune system in the interaction with the implant in comparison. Thus, the aim of the study was to determine the relationship between the fluorescence signal of nanophotosensitizers in the near infrared spectral region and its parameters with the level of inflammation and the type of surface with which the photosensitizer interacts in the implant area. Thus, fiber-optic control opens up new approaches for further diagnosis and therapy in the implant area, making immune cells a prime target for advanced therapies.

Injectable nanocomposite hydrogels as an emerging platform for biomedical applications: A review

Hydrogels have attracted much attention for biomedical and pharmaceutical applications due to the similarity of their biomimetic structure to the extracellular matrix of natural living tissues, tunable soft porous microarchitecture, superb biomechanical properties, proper biocompatibility, etc. Injectable hydrogels are an exciting type of hydrogels that can be easily injected into the target sites using needles or catheters in a minimally invasive manner. The more comfortable use, less pain, faster recovery period, lower costs, and fewer side effects make injectable hydrogels more attractive to both patients and clinicians in comparison to non-injectable hydrogels. However, it is difficult to achieve an ideal injectable hydrogel using just a single material (i.e., polymer). This challenge can be overcome by incorporating nanofillers into the polymeric matrix to engineer injectable nanocomposite hydrogels with combined or synergistic properties gained from the constituents. This work aims to critically review injectable nanocomposite hydrogels, their preparation methods, properties, functionalities, and versatile biomedical and pharmaceutical applications such as tissue engineering, drug delivery, and cancer labeling and therapy. The most common natural and synthetic polymers as matrices together with the most popular nanomaterials as reinforcements, including nanoceramics, carbon-based nanostructures, metallic nanomaterials, and various nanosized polymeric materials, are highlighted in this review.

Gallium-Containing Hydroxyapatite as a Promising Material for Photocatalytic Performance

The development of photocatalystsor their modification to obtain new photocatalytic performances for the removal of contaminants is a challenge. Hydroxyapatite (HAp), (Ca10(PO4)6(OH)2), is an inorganic component with a high superficial area and low toxicity and the presence of metal in its structure can be an interesting strategy for the photocatalytic approach. This work aimed to synthesize gallium-containing HAp (Ga-HAp) as a promising material for photocatalytic performance. The synthesis was performed by the suspension–precipitation method. The material was characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Morphological analysis employed field emission scanning electron microscope (FESEM) and the elemental analysis by energy-dispersive spectroscopy (EDS). To evaluate the photocatalytic activity, methylene blue (MB) dye was used as a pollutant model under UV light for 120 min. The influence of Ga-HAp concentration (0.25, 0.50, and 1.00 g·L−1) and kinetic reaction was also studied. The Ga-HAp was successfully obtained by the suspension–precipitation method. The structural characterization by XRD and FESEM-EDS elucidated the presence of gallium in the structure of hydroxyapatite. The XPS results indicated the substitution of gallium in the crystal lattice of the material. The discoloration rate of MB dye using Ga-Hap was calculated by pseudo first-order kinetics, and the best rate constant was 7.5 × 10−3 min−1 using 1.00 g·L−1 of photocatalyst. The concentration of Ga-HAp influenced the photocatalytic process, because the discoloration rate increased as a function of the concentration of material. Therefore, Ga-HAp is a promising material for environmental remediation.

Mechanistically Scoping Cell-Free and Cell-Dependent Artificial Scaffolds in Rebuilding Skeletal and Dental Hard Tissues

Rebuilding mineralized tissues in skeletal and dental systems remains costly and challenging. Despite numerous demands and heavy clinical burden over the world, sources of autografts, allografts, and xenografts are far limited, along with massive risks including viral infections, ethic crisis, and so on. Per such dilemma, artificial scaffolds have emerged to provide efficient alternatives. To date, cell-free biomimetic mineralization (BM) and cell-dependent scaffolds have both demonstrated promising capabilities of regenerating mineralized tissues. However, BM and cell-dependent scaffolds have distinctive mechanisms for mineral genesis, which makes them methodically, synthetically, and functionally disparate. Herein, these two strategies in regenerative dentistry and orthopedics are systematically summarized at the level of mechanisms. For BM, methodological and theoretical advances are focused upon; and meanwhile, for cell-dependent scaffolds, it is demonstrated how scaffolds orchestrate osteogenic cell fate. The summary of the experimental advances and clinical progress will endow researchers with mechanistic understandings of artificial scaffolds in rebuilding hard tissues, by which better clinical choices and research directions may be approached.

Anti-tuberculosis drug delivery for tuberculous bone defects

INTRODUCTION

Traditional therapy methods for treating tuberculous bone defects have several limitations. Furthermore, systemic toxicity and disease recurrence in tuberculosis (TB) have not been effectively addressed.

AREAS COVERED

This review is based on references from September 1998 to September 2021 and summarizes the classification and drug-loading methods of anti-TB drugs. The application of different types of biological scaffolds loaded with anti-TB drugs as a novel drug delivery strategy for tuberculous bone defects has been deeply analyzed. Furthermore, the limitations of the existing studies are summarized.

EXPERT OPINION

Loading anti-TB drugs into the scaffold through various drug-loading techniques can effectively improve the efficiency of anti-TB treatment and provide an effective means of treating tuberculous bone defects. This methodology also has good application prospects and provides directions for future research.

Physical Gold Nanoparticle-Decorated Polyethylene Glycol-Hydroxyapatite Composites Guide Osteogenesis and Angiogenesis of Mesenchymal Stem Cells

In this study, polyethylene glycol (PEG) with hydroxyapatite (HA), with the incorporation of physical gold nanoparticles (AuNPs), was created and equipped through a surface coating technique in order to form PEG-HA-AuNP nanocomposites. The surface morphology and chemical composition were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), UV–Vis spectroscopy (UV–Vis), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and contact angle assessment. The effects of PEG-HA-AuNP nanocomposites on the biocompatibility and biological activity of MC3T3-E1 osteoblast cells, endothelial cells (EC), macrophages (RAW 264.7), and human mesenchymal stem cells (MSCs), as well as the guiding of osteogenic differentiation, were estimated through the use of an in vitro assay. Moreover, the anti-inflammatory, biocompatibility, and endothelialization capacities were further assessed through in vivo evaluation. The PEG-HA-AuNP nanocomposites showed superior biological properties and biocompatibility capacity for cell behavior in both MC3T3-E1 cells and MSCs. These biological events surrounding the cells could be associated with the activation of adhesion, proliferation, migration, and differentiation processes on the PEG-HA-AuNP nanocomposites. Indeed, the induction of the osteogenic differentiation of MSCs by PEG-HA-AuNP nanocomposites and enhanced mineralization activity were also evidenced in this study. Moreover, from the in vivo assay, we further found that PEG-HA-AuNP nanocomposites not only facilitate the anti-immune response, as well as reducing CD86 expression, but also facilitate the endothelialization ability, as well as promoting CD31 expression, when implanted into rats subcutaneously for a period of 1 month. The current research illustrates the potential of PEG-HA-AuNP nanocomposites when used in combination with MSCs for the regeneration of bone tissue, with their nanotopography being employed as an applicable surface modification approach for the fabrication of biomaterials.

Combining Materials Obtained by 3D-Printing and Electrospinning from Commercial Polylactide Filament to Produce Biocompatible Composites

The design of scaffolds to reach similar three-dimensional structures mimicking the natural and fibrous environment of some cells is a challenge for tissue engineering, and 3D-printing and electrospinning highlights from other techniques in the production of scaffolds. The former is a well-known additive manufacturing technique devoted to the production of custom-made structures with mechanical properties similar to tissues and bones found in the human body, but lacks the resolution to produce small and interconnected structures. The latter is a well-studied technique to produce materials possessing a fibrillar structure, having the advantage of producing materials with tuned composition compared with a 3D-print. Taking the advantage that commercial 3D-printers work with polylactide (PLA) based filaments, a biocompatible and biodegradable polymer, in this work we produce PLA-based composites by blending materials obtained by 3D-printing and electrospinning. Porous PLA fibers have been obtained by the electrospinning of recovered PLA from 3D-printer filaments, tuning the mechanical properties by blending PLA with small amounts of polyethylene glycol and hydroxyapatite. A composite has been obtained by blending two layers of 3D-printed pieces with a central mat of PLA fibers. The composite presented a reduced storage modulus as compared with a single 3D-print piece and possessing similar mechanical properties to bone tissues. Furthermore, the biocompatibility of the composites is assessed by a simulated body fluid assay and by culturing composites with 3T3 fibroblasts. We observed that all these composites induce the growing and attaching of fibroblast over the surface of a 3D-printed layer and in the fibrous layer, showing the potential of commercial 3D-printers and filaments to produce scaffolds to be used in bone tissue engineering.

Hydroxyapatite grafted chitosan/laponite RD hydrogel: Evaluation of the encapsulation capacity, pH-responsivity, and controlled release behavior

In this study, a pH-responsive drug carrier was developed for the controllable release of drugs in the gastric environment. Chitosan (CS), a pH-sensitive biopolymer, and laponite RD (LAP), a nano-clay with a high drug-loading capability, were used to design the new carrier. Hydroxyapatite (HA) was grafted into CS/LAP matrix through a simple co-precipitation technique to overcome the burst release of the CS/LAP. The structural analysis and swelling tests of products demonstrated that the co-precipitation method has led to the penetration of HA nanoparticles inside the CS/LAP matrix and occupying its hollow pores. Occupation of the empty pores can lead to the entrapment of drug molecules, thereby reducing the release rate. The nanocomposite showed a high loading capacity to ofloxacin as a drug model. The effects of HA content on release behavior of nanocomposite were investigated at simulated gastric (pH 1.2) and intestine (pH 7.4) environments. The results indicated a high pH sensitivity for CS/LAP/HA. HA grafting reduced the release rate remarkably regardless of pH. The release rate of CS/LAP/HA decreased by 44-63% in pH 1.2 and 41-51% in pH 7.4 compared to CS/LAP. Kinetic studies indicated that grafting the HA in CS/LAP has changed the drug release mechanism.

Exposure to hydroxyapatite nanoparticles enhances Toll-like receptor 4 signal transduction and overcomes endotoxin tolerance in vitro and in vivo

Emerging studies indicate hydroxyapatite nanoparticles (HANPs) exhibit modest immunogenicity to elicit innate immune response which might involve Toll-like receptor 4 (TLR4) activation. This study was proposed to elucidate how HANPs direct over TLR4 signal activity in macrophage in response to TLR4 ligand, lipopolysaccharide (LPS). The present study for the first time reveals that HANPs themselves can induce TLR4 endocytosis and activate pathways both of nuclear factor-kappa B (NF-κB) and interferon regulatory factor 3 (IRF3), which potentially trigger the production of inflammatory cytokine by macrophage. Further, HANPs dose-dependently reprogram over LPS driven TLR4 signaling transduction in macrophage, leading to synergistically augmented innate immune response. In particular, HANPs synergize with LPS to promote macrophage polarization toward M1 phenotype. Moreover, HANPs abrogate the endotoxin tolerance in macrophages by restoring the production of inflammatory cytokines from macrophage in response to secondary LPS stimulation, and enhance the responsiveness of the body to LPS re-challenge in the endotoxin tolerance mice model. Therefore, this study sheds a new light on the mechanism by which HANPs drive the innate immune response, and offers a powerful strategy to potentiate LPS mediated TLR4 signaling activation in macrophage. STATEMENT OF SIGNIFICANCE: In recent years, increasing attention has been given to hydroxyapatite nanoparticles (HANPs) on how they interact with immune cells for achieving appropriate biological effect such as bone tissue repair, soft tissue filler, tumor treatment, vaccine delivery, et al. This study indicated HANPs can induce TLR4 signaling activation. In the further, HANPs dose-dependently synergize with LPS to program over LPS induced TLR4 signaling transduction in macrophage, to favor macrophage polarizing toward M1 phenotype, as well as to abrogate immune tolerance in macrophage in response to repeated LPS stimulation. This work opens a window for the intrinsic mechanism of HANPs to drive immune response and facilitate to direct the rational use or design of HANPs for their better biomedical application.