Fabrication and Characterization of Strontium-Substituted Hydroxyapatite-CaO-CaCO₃ Nanofibers with a Mesoporous Structure as Drug Delivery Carriers

Next-generation antibacterial nanopolymers for treating oral chronic inflammatory diseases of bacterial origin

BACKGROUND

'Periodontitis' refers to periodontal destruction of connective tissue attachment and bone, in response to microorganisms forming subgingival biofilms on the root surface, while 'apical periodontitis' refers to periapical inflammatory processes occurring in response to microorganisms within the root canal system. The treatment of both diseases is based on the elimination of the bacterial challenge, though its predictability depends on the ability of disrupting these biofilms, what may need adjunctive antibacterial strategies, such as the next-generation antibacterial strategies (NGAS). From all the newly developed NGAS, the use of polymeric nanotechnology may pose a potential effective approach. Although some of these strategies have only been tested in vitro and in preclinical in vivo models, their use holds a great potential, and therefore, it is relevant to understand their mechanism of action and evaluate their scientific evidence of efficacy.

OBJECTIVES

To explore NGAS based on polymeric nanotechnology used for the potential treatment of periodontitis and apical periodontitis.

METHOD

A systemic search of scientific publications of adjunctive antimicrobial strategies using nanopolymers to treat periodontal and periapical diseases was conducted using The National Library of Medicine (MEDLINE by PubMed), The Cochrane Oral Health Group Trials Register, EMBASE and Web of Science.

RESULTS

Different polymeric nanoparticles, nanofibres and nanostructured hydrogels combined with antimicrobial substances have been identified in the periodontal literature, being the most commonly used nanopolymers of polycaprolactone, poly(lactic-co-glycolic acid) and chitosan. As antimicrobials, the most frequently used have been antibiotics, though other antimicrobial substances, such as metallic ions, peptides and naturally derived products, have also been added to the nanopolymers.

CONCLUSION

Polymeric nanomaterials containing antimicrobial compounds may be considered as a potential NGAS. Its relative efficacy, however, is not well understood since most of the existing evidence is derived from in vitro or preclinical in vivo studies.

Modern Microbiological Methods to Detect Biofilm Formation in Orthopedy and Suggestions for Antibiotic Therapy, with Particular Emphasis on Prosthetic Joint Infection (PJI)

Biofilm formation is a serious problem that relatively often causes complications in orthopedic surgery. Biofilm-forming pathogens invade implanted foreign bodies and surrounding tissues. Such a condition, if not limited at the appropriate time, often requires reoperation. This can be partially prevented by selecting an appropriate prosthesis material that prevents the development of biofilm. There are many modern techniques available to detect the formed biofilm. By applying them we can identify and visualize biofilm-forming microorganisms. The most common etiological factors associated with biofilms in orthopedics are: Staphylococcus aureus, coagulase-negative Staphylococci (CoNS), and Enterococcus spp., whereas Gram-negative bacilli and Candida spp. also deserve attention. It seems crucial, for therapeutic success, to eradicate the microorganisms able to form biofilm after the implantation of endoprostheses. Planning the effective targeted antimicrobial treatment of postoperative infections requires accurate identification of the microorganism responsible for the complications of the procedure. The modern microbiological testing techniques described in this article show the diagnostic options that can be followed to enable the implementation of effective treatment.

Electrospun nanofiber composite mat based on ulvan for wound dressing applications

Wound dressings can be used to create a temporary healing environment and expedite the wound healing process. Ulvan (ULV) is a sulfated polysaccharide with potent antiviral and anti-inflammatory activities. Polycaprolactone (PCL) is a hydrophobic biodegradable polyester that exhibits slow degradation, strong mechanical strength, and excellent biocompatibility. Electrospun nanofiber matrices mimic the microstructure of the extracellular matrix, allowing them to promote cell proliferation and differentiation. Therefore, the primary objective of this study was to fabricate a polycaprolactone-ulvan fibrous composite mat (PCL-ULV) using the electrospinning technique and to investigate its physical and chemical properties. To assess the characteristics of PCL-ULV, scanning electron microscopy (SEM) was utilized to examine its morphology and diameter distribution. Fourier transform infrared (FTIR) spectroscopy, calcofluor white staining, and monosaccharide analysis were employed to analyze the components of PCL-ULV. Additionally, the water contact angle was measured to evaluate the hydrophilicity. Furthermore, the proliferation and morphology of and gene expression in NIH3T3 fibroblasts on PCL-ULV were assessed. The results showed that the average PCL-ULV fiber diameter was significantly smaller than that of the PCL fibers. The water contact angle measurements indicated that PCL-ULV exhibited better hydrophilicity than the PCL mat. FTIR, calcofluor white staining, and monosaccharide analyses demonstrated that ULV could be successfully coelectrospun with PCL. NIH3T3 fibroblasts cultured on PCL and PCL-ULV showed different cellular behaviors. On PCL-ULV, cell adhesion, proliferation, and stretching were greater than those on PCL. Moreover, the behavior of NIH3T3 fibroblasts on PCL and PCL-ULV differed, as the cells on PCL-ULV exhibited higher proliferation and more stretching. Furthermore, NIH3T3 fibroblasts cultured on ULV-PCL showed higher α-SMA and MMP-9 gene expression and a lower ratio of TIMP-1/MMP-9 than those cultured on PCL. Notably, scarless wounds display lower TIMP/MMP expression ratios than scarring wounds. Thus, the fibrous composite mat PCL-ULV shows potential as a wound dressing for scarless wound healing.

A Comparative Study on Physicochemical Properties and In Vitro Biocompatibility of Sr-Substituted and Sr Ranelate-Loaded Hydroxyapatite Nanoparticles

Synthetic hydroxyapatite nanoparticles (nHAp) possess compositional and structural similarities to those of bone minerals and play a key role in bone regenerative medicine. Functionalization of calcium phosphate biomaterials with Sr, i.e., bone extracellular matrix trace element, has been proven to be an effective biomaterial-based strategy for promoting osteogenesis in vitro and in vivo. Functionalizing nHAp with Sr2+ ions or strontium ranelate (SrRAN) can provide favorable bone tissue regeneration by locally delivering bioactive molecules to the bone defect microenvironment. Moreover, administering an antiosteoporotic drug, SrRAN, directly into site-specific bone defects could significantly reduce the necessary drug dosage and the risk of possible side effects. Our study evaluated the impact of the Sr source (Sr2+ ions and SrRAN) used to functionalize nHAp by wet precipitation on its in vitro cellular activities. The systematic comparison of physicochemical properties, in vitro Sr2+ and Ca2+ ion release, and their effect on in vitro cellular activities of the developed Sr-functionalized nHAp was performed. The ion release tests in TRIS-HCl demonstrated a 21-day slow and continuous release of the Sr2+ and Ca2+ ions from both Sr-substituted nHAp and SrRAN-loaded HAp. Also, SrRAN and Sr2+ ion release kinetics were evaluated in DMEM to understand their correlation with in vitro cellular effects in the same time frame. Relatively low concentration (up to 2 wt %) of Sr in the nHAp led to an increase in the alkaline phosphatase activity in preosteoblasts and expression of collagen I and osteocalcin in osteoblasts, demonstrating their ability to boost bone formation.

Barrier membranes for periodontal guided bone regeneration: a potential therapeutic strategy

Periodontal disease is one of the most common oral diseases with the highest incidence world-wide. In particular, the treatment of periodontal bone defects caused by periodontitis has attracted extensive attention. Guided bone regeneration (GBR) has been recognized as advanced treatment techniques for periodontal bone defects. GBR technique relies on the application of barrier membranes to protect the bone defects. The commonly used GBR membranes are resorbable and non-resorbable. Resorbable GBR membranes are divided into natural polymer resorbable membranes and synthetic polymer resorbable membranes. Each has its advantages and disadvantages. The current research focuses on exploring and improving its preparation and application. This review summarizes the recent literature on the application of GBR membranes to promote the regeneration of periodontal bone defects, elaborates on GBR development strategies, specific applications, and the progress of inducing periodontal bone regeneration to provide a theoretical basis and ideas for the future application of GBR membranes to promote the repair of periodontal bone defects.

Metal Ion-Doped Hydroxyapatite-Based Materials for Bone Defect Restoration

Hydroxyapatite (HA)-based materials are widely used in the bone defect restoration field due to their stable physical properties, good biocompatibility, and bone induction potential. To further improve their performance with extra functions such as antibacterial activity, various kinds of metal ion-doped HA-based materials have been proposed and synthesized. This paper offered a comprehensive review of metal ion-doped HA-based materials for bone defect restoration based on the introduction of the physicochemical characteristics of HA followed by the synthesis methods, properties, and applications of different kinds of metal ion (Ag+, Zn2+, Mg2+, Sr2+, Sm3+, and Ce3+)-doped HA-based materials. In addition, the underlying challenges for bone defect restoration using these materials and potential solutions were discussed.

Spectral Analysis of Strontium-Doped Calcium Phosphate/Chitosan Composite Films

Strontium-doped calcium phosphate/chitosan films were synthetized on silicon substrates using the radio-frequency magnetron sputtering technique and the matrix-assisted pulsed laser evaporation technique. The deposition conditions associated with the radio-frequency magnetron sputtering discharge, in particular, include the high temperature at the substrate, which promotes the formation of strontium-doped tetra calcium phosphate layers. The physical and chemical processes associated with the deposition of chitosan on strontium-doped calcium phosphate layers were investigated using Fourier Transform Infrared Spectroscopy, Energy Dispersive X-ray Spectroscopy, and Scanning Electron Microscopy. Mass spectrometry coupled with laser induced ablation of the composite films proved to be a useful tool in the detection of the molecular ions characteristic to chitosan chemical structure.

Sol-Gel Technologies to Obtain Advanced Bioceramics for Dental Therapeutics

The aim of this work is to review the application of bioceramic materials in the context of current regenerative dentistry therapies, focusing on the latest advances in the synthesis of advanced materials using the sol-gel methodology. Chemical synthesis, processing and therapeutic possibilities are discussed in a structured way, according to the three main types of ceramic materials used in regenerative dentistry: bioactive glasses and glass ceramics, calcium phosphates and calcium silicates. The morphology and chemical composition of these bioceramics play a crucial role in their biological properties and effectiveness in dental therapeutics. The goal is to understand their chemical, surface, mechanical and biological properties better and develop strategies to control their pore structure, shape, size and compositions. Over the past decades, bioceramic materials have provided excellent results in a wide variety of clinical applications related to hard tissue repair and regeneration. Characteristics, such as their similarity to the chemical composition of the mineral phase of bones and teeth, as well as the possibilities offered by the advances in nanotechnology, are driving the development of new biomimetic materials that are required in regenerative dentistry. The sol-gel technique is a method for producing synthetic bioceramics with high purity and homogeneity at the molecular scale and to control the surfaces, interfaces and porosity at the nanometric scale. The intrinsic nanoporosity of materials produced by the sol-gel technique correlates with the high specific surface area, reactivity and bioactivity of advanced bioceramics.

Synthesis and Antimicrobial Analysis of High Surface Area Strontium-Substituted Calcium Phosphate Nanostructures for Bone Regeneration

Continuous microwave-assisted flow synthesis has been used as a simple, more efficient, and low-cost route to fabricate a range of nanosized (<100 nm) strontium-substituted calcium phosphates. In this study, fine nanopowder was synthesized via a continuous flow synthesis with microwave assistance from the solutions of calcium nitrate tetrahydrate (with strontium nitrate as Sr2+ ion source) and diammonium hydrogen phosphate at pH 10 with a time duration of 5 min. The morphological characterization of the obtained powder has been carried out by employing techniques such as transmission electron microscopy, X-ray diffraction, and Brunauer-Emmett-Teller surface area analysis. The chemical structural analysis to evaluate the surface properties was made by using X-ray photoelectron spectroscopy. Zeta potential analysis was performed to evaluate the colloidal stability of the particles. Antimicrobial studies were performed for all the compositions using four bacterial strains and an opportunistic human fungal pathogen Macrophomina phaseolina. It was found that the nanoproduct with high strontium content (15 wt% of strontium) showed pronounced antibacterial potential against M. luteus while it completely arrested the fungal growth after 48 h by all of its concentrations. Thus the synthesis strategy described herein facilitated the rapid production of nanosized Sr-substituted CaPs with excellent biological performance suitable for a bone replacement application.

Preparation of hydroxyapatite nanofibers by using ionic liquids as template and application in enhancing hydrogel performance

Introduction: Hydroxyapatite (HAP or HA) nanofibers are very attractive in the field of biomedical engineering. However, templates used for preparing HAP nanofibers are usually hydrophobic molecules, like fatty acids and/or surfactants, which are difficult to remove and potentially toxic. Therefore, it is important to develop a green approach to prepare HAP nanofibers. Methods: Imidazolium-based ionic liquids (ILs) were used as templates to control the crystallization of HAP. The obtained HAP nanofibers were composited into polyvinyl alcohol-sodium alginate (PVA-Alg) hydrogel (HAP@H). The rheological performance, stretching, and compression properties were tested. Scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), Fourier-transform infrared (FT-IR), and differential scanning calorimetry (DSC) were adopted to characterize the morphology, size, crystallographic orientations, and phase of HAP@H. Results: HAP nanofibers with a length of ∼50 μm were harvested. The DSC results proved that water loss temperature increased from 98°C (for pure hydrogel) to 107°C (for HAP@H). Also, HAP@H hydrogel presented much better porous structure, tensile performance, and compressive performance than that of pure hydrogel. Discussion: The morphology, size, and growth direction of HAP could be modulated easily by altering the alkyl chain length of ILs' cations. This is possibly due to face-specific adsorption of imidazolium moieties on HAP nanocrystals. The enhancing performance of HAP@H is probably due to the composited highly oriented HAP nanofibers.

Influence of the Components and Orientation of Hydroxyapatite Fibrous Substrates on Osteoblast Behavior

Synthetic hydroxyapatite has good biocompatibility, bioactivity and osteoconductive ability because its chemical properties and biological properties are similar to those of bioapatite in bone tissue. Strontium-substituted hydroxyapatite has better degradability than hydroxyapatite and can both promote osteogenesis and inhibit adipogenesis in mesenchymal stem cells. Hence, hydroxyapatite and strontium-substituted hydroxyapatite are widely used as bone graft materials, cell carriers and drug/gene delivery carriers. In addition, osteoblasts cultured on aligned nanofibrous substrates had higher expression of osteogenesis-related genes than did those cultured on random nanofibrous substrates. However, to date, no study has explored the effects of the components and orientation of hydroxyapatite nanofibrous substrates on osteoblastic behavior. In this study, a random hydroxyapatite nanofibrous substrate (R-HANF), a random strontium-substituted hydroxyapatite nanofibrous substrate (R-SrHANF), an aligned hydroxyapatite nanofibrous substrate (A-HANF) and an aligned strontium-substituted hydroxyapatite nanofibrous substrate (A-SrHANF) were successfully fabricated by using the electrospinning technique. The effect of fiber composition on osteoblast-like MG63 cells was assessed by evaluating cell morphology, cell proliferation and osteogenesis-related gene expression. The results showed that MG63 cells cultured on A-SrHANF had higher osteogenesis-related gene expression than those cultured on A-HANF. Additionally, MG63 cells were cultured on R-SrHANF and A-SrHANF to evaluate the effects of fiber orientation on cell behavior. On A-SrHANF, the cells aligned along the direction of the nanofibers, with typical bipolar morphologies, and exhibited higher osteogenesis-related gene expression than cells on R-SrHANF. Hence, the components and orientation of hydroxyapatite nanofibrous substrates are critical parameters affecting the osteogenesis process.

Polycaprolactone/Gelatin/Hydroxyapatite Electrospun Nanomembrane Materials Incorporated with Different Proportions of Attapulgite Synergistically Promote Bone Formation

Purpose

To enhance the osteoinductive effect of Hydroxyapatite (HA) in bone tissue engineering, this study manufactured polycaprolactone (PCL)/gelatin (GEL)/HA nanofibrous scaffolds incorporated with different ratios of attapulgite (ATP): HA (0:3, 0:0, 1:1, 2:1 and 3:0) by high-voltage electrospinning. The synergistic effect exerted by ATP and HA on bone formation was explored both in vivo and in vitro.

Methods and Results

First, we determined the group composition and crystal structure of the nanosheets by Fourier transform infrared (FTIR) and X-ray diffraction (XRD) analyses. Then, the physical properties of the scaffolds, including the modulus of elasticity, porosity and water absorption were evaluated. Moreover, the surface microstructure of the nanofibrous scaffolds was captured by Scanning electron microscopy (SEM) and Transmission Electron Microscope (TEM). The biocompatibility of the fabricated scaffolds represented by cell counting kit 8 (CCK-8) and phalloidin staining was also assessed. Next, in vitro osteogenesis was evaluated. Real-time PCR, alkaline phosphatase (ALP) staining and Alizarin red S (ARS) staining results showed that the materials incorporated with HA and ATP at a ratio of 2:1 synergistically promoted more osteoblastic differentiation and extracellular mineralization than scaffolds doped with HA and ATP alone. Last, in vivo, Hematoxylin-Eosin staining (HE staining) and Masson staining showed that groups treated with HA and ATP acquired optimal patterns of bone regeneration.

Conclusion

This study clarified for the first time that the combination of HA and ATP orchestrated biomaterial-induced osseointegration, and the synergistic effect was more significant when the ratio of ATP/HA was 2:1. This conclusion also provides new ideas and a scientific basis for the development of functionalized nanomaterials in bone tissue engineering.

Ceramic Nanofiber Materials for Wound Healing and Bone Regeneration: A Brief Review

Ceramic nanofibers have been shown to be a new horizon of research in the biomedical area, due to their differentiated morphology, nanoroughness, nanotopography, wettability, bioactivity, and chemical functionalization properties. Therefore, considering the impact caused by the use of these nanofibers, and the fact that there are still limited data available in the literature addressing the ceramic nanofiber application in regenerative medicine, this review article aims to gather the state-of-the-art research concerning these materials, for potential use as a biomaterial for wound healing and bone regeneration, and to analyze their characteristics when considering their application.

The Effect of Strontium-Substituted Hydroxyapatite Nanofibrous Matrix on Osteoblast Proliferation and Differentiation

Natural bone tissue consists primarily of bioapatite and collagen. Synthetic hydroxyapatite (HA) possesses good biocompatibility, bioactivity, and osteoconductivity due to its chemical and biological similarity to bioapatite. Hence, HA has been widely used as a bone graft, cell carrier and drug/gene delivery carrier. Moreover, strontium-substituted hydroxyapatite (SrHA) can enhance osteogenic differentiation and inhibit adipogenic differentiation of mesenchymal stem cells. Hence, SrHA has the potential to be used as a bone graft for bone regeneration. It is widely accepted that cell adhesion and most cellular activities are sensitive to the topography and molecular composition of the matrix. Electrospun polymer or polymer-bioceramic composite nanofibers have been demonstrated to enhance osteoblast differentiation. However, to date, no studies have investigated the effect of nanofibrous bioceramic matrices on osteoblasts. In this study, hydroxyapatite nanofiber (HANF) and strontium-substituted hydroxyapatite nanofiber (SrHANF) matrices were fabricated by electrospinning. The effect of the HANF components on MG63 osteoblast-like cells was evaluated by cell morphology, proliferation, alkaline phosphatase activity (ALP) and gene expression levels of RUNX2, COLI, OCN and BSP. The results showed that MG63 osteoblast-like cells exhibited higher ALP and gene expression levels of RUNX2, COLI, BSP and OCN on the SrHANF matrix than the HANF matrix. Hence, SrHANFs could enhance the differentiation of MG63 osteoblast-like cells.

Mesoporous Mn-doped hydroxyapatite nanorods obtained via pyridinium chloride enabled microwave-assisted synthesis by utilizing Donax variabilis seashells for implant applications

Manganese-doped mesoporous hydroxyapatite (MnHAp) nanorods, a bio-apatite were synthesized via pyridinium chloride mediated microwave approach using bio-waste Donax variabilis seashells to treat orthopedic infections. This is the first report on using pyridinium chloride mediated mesoporous MnHAp nanorods synthesis. Pure and Mn doped HAp samples were examined using Raman spectroscopy, X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) studies to confirm the prepared HAp nanorods. Furthermore, the fabrication of manganese-doped HAp was successful with the formation of a hexagonal crystal lattice without disturbing the HAp phase. It is because, at the time of synthesis, PO₄^3- ions form an electrostatic interaction with the Mn ions. Furthermore, Mn-doped HAp samples showed a reduction in their sizes of 15, 10-15, 5-10 nm width, and 80-100, 10-15, 20-30 nm length with varied pore diameters and surface area. The pure HAp, MnHAp-1, MnHAp-2, and MnHAp-3 nanorods disclose the surface area of 39.4, 18.0, 49.2, and 80.4 m² g^-1, with a pore volume of 0.0102, 0.0047, 0.0143, and 0.0447 cm³ g^-1, the corresponding pore diameter was estimated to be 6, 7, 6, and 4 nm, respectively. Moreover, antibacterial activity reveals effective bactericidal action against infections causing pathogens whereas cytotoxicity examination (MTT assay), and zebrafish results reveal their non-toxic behavior. Therefore, it is evident from the study, that rapid fabrication of mesoporous and diverse structured MnHAp nanorods could be convenient with pyridinium chloride enabled microwave-assisted method as a bactericidal biomaterial for implant applications.

Ce/Sm/Sr-Incorporating Ceramic Scaffolds Obtained via Sol-Gel Route

Three different inorganic scaffolds were obtained starting from the oxide system SiO₂‒P₂O₅‒CaO‒MgO, to which Ce⁴⁺/Sm³⁺/Sr²⁺ cations were added in order to propose novel materials with potential application in the field of hard tissue engineering. Knowing the beneficial effects of each element, improved features in terms of mechanical properties, antibacterial activity and cellular response are expected. The compositions were processed in the form of scaffolds by a common sol-gel method, followed by a thermal treatment at 1000 and 1200 °C. The obtained samples were characterized from thermal, compositional, morphological and mechanical point of view. It was shown that each supplementary component triggers the modification of the crystalline phase composition, as well as microstructural details. Moreover, the shrinkage behavior is well correlated with the attained compression strength values. Sm was proven to be the best choice, since in addition to a superior mechanical resistance, a clear beneficial influence on the viability of 3T3 fibroblast cell line was observed.

Preparation of a New Biocomposite Designed for Cartilage Grafting with Antibiofilm Activity

New polymer–inorganic composites with antibiofilm features based on the granulated poly(tetrafluoroethylene) (PTFE) and apatite materials were obtained using a standard hydraulic press. The study was performed in hydroxy- and fluorapatites doped with different amounts of silver ions and followed by heat treatment at 600 °C. The structural, morphological, and physicochemical properties were determined by X-ray powder diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy-energy-dispersive spectrometry (SEM-EDS), and transition electron microscopy (TEM). The antibacterial properties of the obtained materials were evaluated against Gram-negative pathogens such as Pseudomonas aeruginosa, Klebsiella pneumoniae, and Escherichia coli as well as against Gram-positive bacteria Staphylococcus epidermidis. The cytotoxicity assessment was carried out on the red blood cells (RBC) as a cell model for in vitro study. Moreover, the biofilm formation on the biocomposite surface was studied using confocal laser scanning microscopy (CLSM).

Hydroxyapatite based biocomposite scaffold: A highly biocompatible material for bone regeneration

The conventional approaches for treating bone defects such as autografts donor tissue shortages and allografts transmission of diseases pose many shortcomings. The objective of this study was to design a nano strontium/magnesium doped hydroxyapatite (Sr/Mg-HA) with chitosan (CTS) and multi-walled carbon nanotubes (MWCNT) (Sr/Mg-HA/MWCNT/CTS) biocomposite was created to support the growth of osteoblasts using a solvent evaporation method. To help the growth of osteoblasts, a solvent evaporation technique was used to design a nano strontium/magnesium doped hydroxyapatite with chitosan and multi-walled carbon nanotubes biocomposite. We studied the biocompatibility and efficiency in vitro of biocomposite following physicochemical analyzes. Tests of biocompatibility, cell proliferation, mineralization, and osteogenic differentiation have shown that in-vitro safety and effectiveness of biocomposite are good. The performance of biocomposite was more efficient in in-vitro as well as in vivo experiments than in Sr/Mg-HA nanoparticles. Briefly, the Sr/Mg-HA/MWCNT/CTS biocomposite is an ideal candidate for effective bone repair in clinics with excellent mechanical properties with durable multi-biofunctional antibacterial properties and osteoinductivity.

Hydroxyapatite as a biomaterial - a gift that keeps on giving

The synthetic analogue to biogenic apatite, hydroxyapatite (HA) has a number of physicochemical properties that make it an attractive candidate for diagnosis, treatment of disease and augmentation of biological tissues. Here we describe some of the recent studies on HA, which may provide bases for a number of new medical applications. The content of this review is divided to different medical application modes utilizing HA, including tissue engineering, medical implants, controlled drug delivery, gene therapies, cancer therapies and bioimaging. A number of advantages of HA over other biomaterials emerge from this discourse, including (i) biocompatibility, (ii) bioactivity, (iii) relatively simple synthesis protocols for the fabrication of nanoparticles with specific sizes and shapes, (iv) smart response to environmental stimuli, (v) facile functionalization and surface modification through noncovalent interactions, and (vi) the capacity for being simultaneously loaded with a wide range of therapeutic agents and switched to bioimaging modalities for uses in theranostics. A special section is dedicated to analysis of the safety of particulate HA as a component of parenterally administrable medications. It is concluded that despite the fact that many benefits come with the usage of HA, its deficiencies and potential side effects must be addressed before the translation to the clinical domain is pursued. Although HA has been known in the biomaterials world as the exemplar of safety, this safety proves to be the function of size, morphology, surface ligands and other structural and compositional parameters defining the particles. For this reason, each HA, especially when it comes in a novel structural form, must be treated anew from the safety research angle before being allowed to enter the clinical stage.

A 3D Bioprinted Pseudo-Bone Drug Delivery Scaffold for Bone Tissue Engineering

A 3D bioprinted pseudo-bone drug delivery scaffold was fabricated to display matrix strength, matrix resilience, as well as porous morphology of healthy human bone. Computer-aided design (CAD) software was employed for developing the 3D bioprinted scaffold. Further optimization of the scaffold was undertaken using MATLAB® software and artificial neural networks (ANN). Polymers employed for formulating the 3D scaffold comprised of polypropylene fumarate (PPF), free radical polymerized polyethylene glycol- polycaprolactone (PEG-PCL-PEG), and pluronic (PF127). Simvastatin was incorporated into the 3D bioprinted scaffolds to further promote bone healing and repair properties. The 3D bioprinted scaffold was characterized for its chemical, morphological, mechanical, and in vitro release kinetics for evaluation of its behavior for application as an implantable scaffold at the site of bone fracture. The ANN-optimized 3D bioprinted scaffold displayed significant properties as a controlled release platform, demonstrating drug release over 20 days. The 3D bioprinted scaffold further displayed formation as a pseudo-bone matrix, using a human clavicle bone model, induced with a butterfly fracture. The strength of the pseudo-bone matrix, evaluated for its matrix hardness (MH) and matrix resilience (MR), was evaluated to be as strong as original bone, having a 99% MH and 98% MR property, to healthy human clavicle bones.

Influence of sonication on the physicochemical and biological characteristics of selenium-substituted hydroxyapatites

Selenium-doped hydroxyapatite composite formed by the sonication technique investigated to have superior properties that are specifically advantageous in the tissue engineering, growth, and regeneration sector.

Fabrication and Characteristics of PCL Membranes Containing Strontium-Substituted Hydroxyapatite Nanofibers for Guided Bone Regeneration

Poly(ε-caprolactone) (PCL) membranes have been widely used in guided tissue regeneration (GTR) and guided bone regeneration (GBR). In addition, hydroxyapatite is the major inorganic component and an essential composition of hard bone and teeth. Recently, numerous studies have demonstrated that strontium-substituted hydroxyapatite (SrHA) not only enhances osteogenesis but also inhibits adipogenesis of mesenchymal stem cells. Therefore, SrHA incorporated into PCL could be an alternative material for GBR. In this study, strontium-substituted hydroxyapatite nanofibers (SrHANFs) were fabricated by a sol-gel route followed by electrospinning. We then fabricated PCL-SrHANF membranes as cell culture substrates and assessed the cellular behavior of osteoblast-like cells. Based on the observations of alkaline phosphatase (ALP) activity, bone sialoprotein (BSP) and osteocalcin (OCN) immunofluorescence staining, and Alizarin Red-S staining of cells cultured on the PCL-SrHANF and PCL membranes, we concluded that SrHANFs can promote the differentiation and mineralization of osteoblast-like cells and that PCL-SrHANF membranes have potential for GBR applications.