Encapsulated boron as an osteoinductive agent for bone scaffolds

Polymer-clay nanofibrous wound dressing materials containing different boron compounds

BACKGROUND

Montmorillonite (MMT) is a biocompatible nanoclay and its incorporation into polymeric matrix not only improves the polymer's wettability/biodegradability, but also enhances cellular proliferation, and differentiation. On the other hand, the positive effect of boron (B) on the healing cascade and its antibacterial properties have drawn the attention of researchers.

MATERIALS & METHODS

In this regard, B compounds in different chemical structures, boron nitride (BN), zinc borate (ZB), and phenylboronic acid (PBA), were adsorbed onto MMT and then, poly (lactic acid) (PLA) based MMT/B including micron/submicron fibers were fabricated by electrospinning.

RESULTS

The incorporation of MMT nanoparticles into the PLA demonstrated a porous fiber topography with enhanced thermal properties, water uptake capacity, and antibacterial effect. Furthermore, the composites including BN, ZB, and PBA showed bacteriostatic effects against Gram-negative and Gram-positive pathogenic bacteria (Escherichia coli and Staphylococcus aureus). In-vitro cell culture studies performed with human dermal fibroblasts (HDF) indicated the non-toxic effect of B compounds. The results showed that incorporation of MMT supported cell adhesion and proliferation, and further addition of B compounds especially PBA increased cell viability for 14 days.

CONCLUSION

The results illustrated the acceptable characteristics of the B-containing composites and their favorable effect on the cells, demonstrating their potential as a skin tissue engineering product.

Osteogenic Differentiation Capacity of Dental Pulp Stem Cells on 3D Printed Polyurethane/Boric Acid Scaffold

Additive manufacturing is growing in the area of dentistry and orthopedics due to the potential for the fabrication of individual implants. In this study, fused deposition modeling which is the most popular method was used to produce 3D scaffolds having a grid pattern from the polyurethane (PU) filament. Then, this scaffold was coated with boric acid (BA) with the thermionic vacuum arc technique. The microstructure analysis showed the macro-pores having a dimension of ~ 0.16 mm2. The BA coating increased the roughness in adverse decreased the wettability. The presence of BA on the scaffold before and after cell culture was confirmed by FESEM-EDS and ATR-FTIR. The Cell proliferation and osteogenic differentiation capacity of dental pulp stem cells (DPSCs) on uncoated and coated printed 3D PU scaffolds were also investigated. On the third day, cell viability was found to be higher (1.3-fold) in the groups containing BA. However, on the seventh day, the increase in cell proliferation in the PU+BA group was found to be less than in the other groups. According to Ca deposition analysis and Alizarin Red staining, PU+BA increased the calcium accumulation in the cells in both osteogenic induced and non-induced conditions at day 14. According to gene expression analysis, the Runx2 expression was not detected in PU+BA groups with and without differentiation medium (p ≤0.05). The expression of OCN was persistently increased up to 21-fold and 48-fold in cells on PU and PU+BA in osteogenic differentiation medium group after 14 days compared to control group (p ≤0.05). DSPP expression was observed only in PU+BA in osteogenic differentiation medium group. In line with the results that we have obtained, our 3D printed scaffolds have properties to trigger the differentiation of DPSCs cells in terms of osteogenicity.

Surface hardening of Ti-Al-V superalloy spinal implant by using the boronization method

BACKGROUND

We compared the raw Ti-Al-V super alloy transpedicular implant screws with boronized and surface-hardened transpedicular implant screws.

OBJECTIVE

To improve patients' postoperative prognosis with the production of harder and less fragile screws.

METHODS

Surface hardening was achieved by applying green-body encapsulation of the specimen with elemental boron paste which is sintered at elevated temperatures to ensure the boron-metal diffusion. Boron transported into the Ti-Al-V super alloy matrix gradually while suppressing aluminum and a homogeneously boronized surface with a thickness of ∼15 microns was obtained. The uniform external shell was enriched with TiB2, which is one of the hardest ceramics. The Ti-Al-V core material, where boron penetration diminishes, shows cohesive transition and ensures intact core-surface structure.

RESULTS

Scanning electron microscope images confirmed a complete homogeneous, uniform and non-laminating surface formation. Energy-dispersive X-ray monitored the elemental structural mapping and proved the replacement of the aluminum sites on the surface with boron ending up the TiB2. The procedure was 8.6 fold improved the hardness and the mechanical resistance of the tools.

CONCLUSIONS

Surface-hardened, boronized pedicular screws can positively affect the prognosis. In vivo studies are needed to prove the safety of use.

Fabrication and Characterisation of Calcium Sulphate Hemihydrate Enhanced with Zn- or B-Doped Hydroxyapatite Nanoparticles for Hard Tissue Restoration

A composite based on calcium sulphate hemihydrate enhanced with Zn- or B-doped hydroxyapatite nanoparticles was fabricated and evaluated for bone graft applications. The investigations of their structural and morphological properties were performed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) spectroscopy techniques. To study the bioactive properties of the obtained composites, soaking tests in simulated body fluid (SBF) were performed. The results showed that the addition of 2% Zn results in an increase of 2.27% in crystallinity, while the addition of boron causes an increase of 5.61% compared to the undoped HAp sample. The crystallite size was found to be 10.69 ± 1.59 nm for HAp@B, and in the case of HAp@Zn, the size reaches 16.63 ± 1.83 nm, compared to HAp, whose crystallite size value was 19.44 ± 3.13 nm. The mechanical resistance of the samples doped with zinc was the highest and decreased by about 6% after immersion in SBF. Mixing HAp nanoparticles with gypsum improved cell viability compared to HAp for all concentrations (except for 200 µg/mL). Cell density decreased with increasing nanoparticle concentration, compared to gypsum, where the cell density was not significantly affected. The degree of cellular differentiation of osteoblast-type cells was more accentuated in the case of samples treated with G+HAp@B nanoparticles compared to HAp@B. Cell viability in these samples decreased inversely proportionally to the concentration of administered nanoparticles. From the point of view of cell density, this confirmed the quantitative data.

Development of Boron-Containing PVA-Based Cryogels with Controllable Boron Releasing Rate and Altered Influence on Osteoblasts

Cryogel formation is an effective approach to produce porous scaffolds for tissue engineering. In this study, cryogelation was performed to produce boron-containing scaffolds for bone tissue engineering. A combination of the synthetic polymer, poly(vinyl alcohol) (PVA), and the natural polymers, chitosan and starch, was used to formulate the cryogels. Boron was used with a dual purpose: as an additive to alter gelation properties, and to exploit its bioactive effect since boron has been found to be involved in several metabolic pathways, including the promotion of bone growth. This project designs a fabrication protocol enabling the competition of both physical and chemical cross-linking reactions in the cryogels using different molecular weight PVA and borax content (boron source). Using a high ratio of high-molecular-weight PVA resulted in the cryogels exhibiting greater mechanical properties, a lower degradation rate (0.6–1.7% vs. 18–20%) and a higher borax content release (4.98 vs. 1.85, 1.08 nanomole) in contrast to their counterparts with low-molecular-weight PVA. The bioactive impacts of the released borax on cellular behaviour were investigated using MG63 cells seeded into the cryogel scaffolds. It was revealed that the borax-containing scaffolds and their extracts induced MG63 cell migration and the formation of nodule-like aggregates, whilst cryogel scaffolds without borax did not. Moreover, the degradation products of the scaffolds were analysed through the quantification of boron release by the curcumin assay. The impact on cellular response in a scratch assay confirmed that borax released by the scaffold into media (~0.4 mg/mL) induced bone cell migration, proliferation and aggregation. This study demonstrated that boron-containing three-dimensional PVA/starch–chitosan scaffolds can potentially be used within bone tissue engineering applications.

Organomodified nanoclay with boron compounds is improving structural and antibacterial properties of nanofibrous matrices

In this study, nanofibrous polymeric matrices were successfully developed with nanoclay, montmorillonite (MMT) and various boron (B) compounds, which were known to have positive effects on the wound healing with elevated antibacterial properties. For this purpose, MMT was modified with quaternary ammonium salt, trimethyl octadecyl ammonium bromide (TMOD), and boron compounds, boron nitride (BN), zinc borate (ZB), or phenylboronic acid (PBA) were adsorbed on organomodified MMT (OMMT). Then, poly (lactic acid) (PLA) based nanofibrous PLA-OMMT/B composites were fabricated via electrospinning. Modification of MMT nanoparticles with TMOD occurred through ion-exchange reaction and led to better homogenous fibrous structures which exhibited dramatic inhibition for gram-positive bacteria. Moreover, composites with ZB and PBA demonstrated both bacteriostatic and bactericidal effects for gram-positive and gram-negative bacteria. The chemical structures of the matrices were evaluated through ATR-FTIR and supported the intercalated composite formation. The thermal and mechanical stabilities of PLA matrices were also enhanced after OMMT and B incorporation. The lowest breaking strain value was recorded for PLA-OMMT/PBA composite compared to other B composites. The 100% and 50% extracts of the PLA-OMMT matrices showed modest cytotoxic effect on the human dermal fibroblasts (NHDF) on the second day culture that probably originated from TMOD. These results demonstrated that PLA-OMMT/B matrices, especially PBA including matrices, can be used as replaceable wound dressings that have limited interaction with cells but exhibit antibacterial activity and support the early stages of wound healing both morphologically and chemically.

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.

Peek dental implants coated with boron-doped nano-hydroxyapatites: Investigation of in-vitro osteogenic activity

BACKGROUND

PEEK is a high-performance thermoplastic that has many potential uses in orthopaedics and dentistry, and it has been shown to be a substitute for titanium (Ti) implants. However, PEEK is an inherently inert material, and that characteristic limits its cellular adhesion and bone integration. The aim of this study is to determine a suitable surface modification method for increasing the osteogenic potential of polyetheretherketone (PEEK) implants used in periodontal applications.

METHODS

In this work, a nanostructured porous surface is created on PEEK material by sulfonation, in sulfuric acid at room temperature for 20 min, and thus SPEEK samples were obtained. Then, PEEK and SPEEK samples were coated with boron (B) doped hydroxyapatite (HAp) nanoparticles (B-nHAp) precipitated from concentrated synthetic body fluid (10xSBF) by a microwave-assisted method conducted at 600 W. In vitro cell culture studies were carried out with periodontal ligament cells (PDL) on the samples. Osteogenic differentiation of PDL cells on PEEK, SPEEK and SPEEK-B-nHAp was evaluated using ALP activity assay, hydroxyproline assay, and RT-qPCR.

RESULTS

In vitro cell culture studies disclosed improved adhesion and proliferation of PDL cells on the SPEEK and B-nHAp coated SPEEK surfaces (SPEEK-B-nHAp). Results of these assays confirmed that treated PEEK surfaces, especially SPEEK-B-nHAp, significantly enhanced osteogenic differentiation of PDL cells in vitro compared with untreated PEEK surfaces.

CONCLUSION

Here a simple, easy to-use, and efficient modification method based on the properties of boron is proposed for increasing osteogenic potential of PEEK implants.

A Review on the Recent Advancements on Therapeutic Effects of Ions in the Physiological Environments

This review focuses on the therapeutic effects of ions when released in physiological environments. Recent studies have shown that metallic ions like Ag+, Sr2+, Mg2+, Mn2+, Cu2+, Ca2+, P+5, etc., have shown promising results in drug delivery systems and regenerative medicine. These metallic ions can be loaded in nanoparticles, mesoporous bioactive glass nanoparticles (MBGNs), hydroxyapatite (HA), calcium phosphates, polymeric coatings, and salt solutions. The metallic ions can exhibit different functions in the physiological environment such as antibacterial, antiviral, anticancer, bioactive, biocompatible, and angiogenic effects. Furthermore, the metals/metalloid ions can be loaded into scaffolds to improve osteoblast proliferation, differentiation, bone development, fibroblast growth, and improved wound healing efficacy. Moreover, different ions possess different therapeutic limits. Therefore, further mechanisms need to be developed for the highly controlled and sustained release of these ions. This review paper summarizes the recent progress in the use of metallic/metalloid ions in regenerative medicine and encourages further study of ions as a solution to cure diseases.

Zebrafish as a Model to Unveil the Pro-Osteogenic Effects of Boron-Vitamin D3 Synergism

The micronutrient boron (B) plays a key role during the ossification process as suggested by various in vitro and in vivo studies. To deepen our understanding of the molecular mechanism involved in the osteogenicity of B and its possible interaction with vitamin D3 (VD), wild-type AB zebrafish (Danio rerio) were used for morphometric analysis and transcriptomic analysis in addition to taking advantage of the availability of specific zebrafish osteoblast reporter lines. First, osteoactive concentrations of B, VD, and their combinations were established by morphometric analysis of the opercular bone in alizarin red-stained zebrafish larvae exposed to two selected concentrations of B (10 and 100 ng/ml), one concentration of VD (10 pg/ml), and their respective combinations. Bone formation, as measured by opercular bone growth, was significantly increased in the two combination treatments than VD alone. Subsequently, a transcriptomic approach was adopted to unveil the molecular key regulators involved in the synergy. Clustering of differentially expressed genes revealed enrichment toward bone and skeletal functions in the groups co-treated with B and VD. Downstream analysis confirmed mitogen-activated protein kinase as the most regulated pathway by the synergy groups in addition to transforming growth factor-β signaling, focal adhesion, and calcium signaling. The best-performing synergistic treatment, B at 10 ng/ml and VD at 10 pg/ml, was applied to two zebrafish transgenic lines, Tg(sp7:mCherry) and Tg(bglap:EGFP), at multiple time points to further explore the results of the transcriptomic analysis. The synergistic treatment with B and VD induced enrichment of intermediate (sp7+) osteoblast at 6 and 9 days post fertilization (dpf) and of mature (bglap +) osteoblasts at 15 dpf. The results obtained validate the role of B in VD-dependent control over bone mineralization and can help to widen the spectrum of therapeutic approaches to alleviate pathological conditions caused by VD deficiency by using low concentrations of B as a nutritional additive.

Bioactive Chitosan-Based Organometallic Scaffolds for Tissue Engineering and Regeneration

Captivating achievements in developing advanced hybrid biostructures through integrating natural biopolymers with inorganic materials (e.g., metals and metalloids) have paved the way towards the application of bioactive organometallic scaffolds (OMSs) in tissue engineering and regenerative medicine (TERM). Of various biopolymers, chitosan (CS) has been used widely for the development of bioactive OMSs, in large part due to its unique characteristics (e.g., biocompatibility, biodegradability, surface chemistry, and functionalization potential). In integration with inorganic elements, CS has been used to engineer advanced biomimetic matrices to accommodate both embedded cells and drug molecules and serve as scaffolds in TERM. The use of the CS-based OMSs is envisioned to provide a new pragmatic potential in TERM and even in precision medicine. In this review, we aim to elaborate on recent achievements in a variety of CS/metal, CS/metalloid hybrid scaffolds, and discuss their applications in TERM. We also provide comprehensive insights into the formulation, surface modification, characterization, biocompatibility, and cytotoxicity of different types of CS-based OMSs.

Boron Nano-hydroxyapatite Composite Increases the Bone Regeneration of Ovariectomized Rabbit Femurs

Osteoporosis is a systemic metabolic disease defined by a decreased bone mineral density, microarchitectural deterioration, and an increased incidence of fragility fractures that may lead to morbidity and mortality. Boron may stimulate new bone formation and regeneration, when combined with nano-hydroxyapatite. We questioned whether injecting boron-containing nano-hydroxyapatite composites with hyaluronan increased the bone mineral density and new bone formation in osteoporotic rabbit femurs. The regenerative effects of injectable boron-containing nano-hydroxyapatite composites from 6 to 12 weeks, which may prevent osteoporotic femoral fractures, were assessed. Boron-containing (10 μg/ml) nano-hydroxyapatite composites were injected into the intramedullary femoral cavity with hyaluronan. These significantly increased the histomorphometric new bone surface to the total bone surface ratio at 6 and 9 weeks. The micro-tomographic bone volume to the total volume ratio and bone mineral density in osteoporotic rabbit femurs increased when compared to the hyaluronan (p = 0.004, p = 0.004, p = 0.004, p = 0.01, respectively) and the sham-control (p = 0.01, p = 0.004, p = 0.01, p = 0.037, respectively) groups. The boron-containing group had a higher bone mineralization and new bone formation compared to the nano-hydroxyapatite group, although the difference was not statistically significant. These findings reveal that intramedullary injection of boron-containing nano-hydroxyapatite with hyaluronan increases new bone formation and mineralization in ovariectomized rabbit femurs. Boron-containing nano-hydroxyapatite composites are promising tissue engineering biomaterials that may have regenerative potential in preventing primary and/or secondary femoral fractures in osteoporosis patients.

Effects of Extracellular Osteoanabolic Agents on the Endogenous Response of Osteoblastic Cells

The complex multidimensional skeletal organization can adapt its structure in accordance with external contexts, demonstrating excellent self-renewal capacity. Thus, optimal extracellular environmental properties are critical for bone regeneration and inextricably linked to the mechanical and biological states of bone. It is interesting to note that the microstructure of bone depends not only on genetic determinants (which control the bone remodeling loop through autocrine and paracrine signals) but also, more importantly, on the continuous response of cells to external mechanical cues. In particular, bone cells sense mechanical signals such as shear, tensile, loading and vibration, and once activated, they react by regulating bone anabolism. Although several specific surrounding conditions needed for osteoblast cells to specifically augment bone formation have been empirically discovered, most of the underlying biomechanical cellular processes underneath remain largely unknown. Nevertheless, exogenous stimuli of endogenous osteogenesis can be applied to promote the mineral apposition rate, bone formation, bone mass and bone strength, as well as expediting fracture repair and bone regeneration. The following review summarizes the latest studies related to the proliferation and differentiation of osteoblastic cells, enhanced by mechanical forces or supplemental signaling factors (such as trace metals, nutraceuticals, vitamins and exosomes), providing a thorough overview of the exogenous osteogenic agents which can be exploited to modulate and influence the mechanically induced anabolism of bone. Furthermore, this review aims to discuss the emerging role of extracellular stimuli in skeletal metabolism as well as their potential roles and provide new perspectives for the treatment of bone disorders.

Boron Contents of German Mineral and Medicinal Waters and Their Bioavailability in Drosophila melanogaster and Humans

SCOPE

Boron is a trace element that naturally occurs in soil, making mineral and medicinal water important contributors to overall intake. Thus, in a systematic screening, the mean boron concentrations of 381 German mineral and medicinal waters are determined.

METHODS AND RESULTS

Boron concentrations in mineral and medicinal waters are analyzed by inductively coupled mass spectrometry (ICP-MS). Highest boron values find in waters from the southwest of Germany. The boron content of the waters is positively correlated with the concentration of most other analyzed bulk elements, including calcium, potassium, magnesium, and sodium. Mineral waters with either low (7.9 µg L^-1 ), medium (113.9 µg L^-1 ), or high (2193.3 µg L^-1 ) boron content are chosen for boron exposure experiments in fruit flies (Drosophila melanogaster) and humans. In flies, boron-rich mineral water significantly increases boron accumulation, with the accumulation predominantly occurring in the exoskeleton. In humans, serum boron and 24-h urinary boron excretion significantly increase only in response to the intake of boron-rich mineral water.

CONCLUSION

Overall, the current data demonstrate that mineral and medicinal waters vary substantially in the content of boron and that boron-rich mineral water can be used to elevate the boron status, both in flies and humans.

Electrospraying as a novel process for the synthesis of particles/nanoparticles loaded with poorly water-soluble bioactive molecules

Hydrophobicity and low aqueous-solubility of different drugs/nutraceuticals remain a persistent challenge for their development and clinical/food applications. A range of nanotechnology strategies have been implemented to address this issue, and amongst which a particular emphasis has been made on those that afford an improved biological performance and tunable release kinetic of bioactives through a one-step process. More recently, the technique of electrospraying (or electrohydrodynamic atomization) has attained notable impulse in virtue of its potential to tune attributes of nano/micro-structured particles (e.g., porosity, particle size, etc.), rendering a near zero-order release kinetics, diminished burst release manner, as well as its simplicity, reproducibility, and applicability to a broad spectrum of hydrophobic and poorly water-soluble bioactives. Controlled morphology or monodispersity of designed particles could be properly obtained via electrospraying, with a high encapsulation efficiency and without unfavorable denaturation of thermosensitive bioactives upon encapsulation. This paper overviews the recent technological advances in electrospraying for the encapsulation of low queues-soluble bioactive agents. State-of-the-art, advantages, applications, and challenges for its implementation in pharmaceutical/food researches are also discussed.

Boron-doped Biphasic Hydroxyapatite/β-Tricalcium Phosphate for Bone Tissue Engineering

Boron-doped hydroxyapatite/tricalcium phosphates (BHTs) were synthesized to study boron uptake and correlate structural alterations of incremental boron addition (0 to 10 mol%). BHTs with a Ca/P ratio of 1.6 were prepared by a wet precipitation/microwave reflux method, sieved (< 70 μm) and characterized. XRD and FTIR analyses revealed that boron slightly distorted apatite crystal, increased crystallinity (95.78 ± 2.08% for 5BHT) and crystallite size (103.39 ± 23.47 nm for 5BHT) and still, boron addition did not show any further detrimental effects. Total surface area (4.05 ± 0.82 m²/g for 10BHT) and mesoporosity (23.90 ± 7.92 μL/g for 10BHT) were expanded as boron content was increased. Moreover, boron addition made grains become smaller (0.21 ± 0.06 μm for 5BHT) and ordered while hardness (10.51 ± 0.86 GPa for 10BHT) increased. Boron incorporation enhanced bioactivity with significantly highest calcium phosphate deposition and protein adsorption (135.29 ± 29.58 μg on 10BHT). In return, boron favored highest alkaline phosphatase activity (4.80 ± 0.40 M_ALP/ng_DNA.min), intracellular calcium (23.61 ± 0.68 g/g_DNA), phosphate (31.84 ± 4.68 g/g_DNA), and protein (23.70 ± 3.46 g/g_DNA) storage in 5BHT without cytotoxicity (128 ± 18% viability compared to pure HT). Compared to literature, it can be pointed out that we successfully employed an optimal procedure for production of BHTs and incorporated significantly higher boron content in HT (5.23 mol%). Additionally, results tended to conclude that 5BHT samples (5 mol% boron in HT) demonstrated a very high potential to be used in composite bone tissue constructs.

Biological Roles and Delivery Strategies for Ions to Promote Osteogenic Induction

Bone is the most studied tissue in the field of tissue regeneration. Even though it has intrinsic capability to regenerate upon injury, several pathologies and injuries could hamper the highly orchestrated bone formation and resorption process. Bone tissue engineering seeks to mimic the extracellular matrix of the tissue and the different biochemical pathways that lead to successful regeneration. For many years, the use of extrinsic factors (i.e., growth factors and drugs) to modulate these biological processes have been the preferred choice in the field. Even though it has been successful in some instances, this approach presents several drawbacks, such as safety-concerns, short release profile and half-time life of the compounds. On the other hand, the use of inorganic ions has attracted significant attention due to their therapeutic effects, stability and lower biological risks. Biomaterials play a key role in such strategies where they serve as a substrate for the incorporation and release of the ions. In this review, the methodologies used to incorporate ions in biomaterials is presented, highlighting the osteogenic properties of such ions and the roles of biomaterials in controlling their release.

Cellulose acetate-gelatin-coated boron-bioactive glass biocomposite scaffolds for bone tissue engineering

In this study, we aimed to prepare and characterize porous scaffolds composed of pure and boron oxide (B₂O₃)-doped bioactive glass (BG) that were infiltrated by cellulose acetate-gelatin (CA-GE) polymer solution for bone tissue engineering applications. Composite scaffolds were cross-linked with glutaraldehyde after polymer coating to protect the structural integrity of the polymeric-coated scaffolds. The impact of B₂O₃ incorporation into BG-polymer porous scaffolds on the cross-sectional morphology, porosity, mechanical properties, degradation and bioactivity of the scaffolds was investigated. Human dental pulp stem cells (hDPSCs) were enzymatically isolated and used for cell culture studies. According to scanning electron microscope analysis, the porous structure of the scaffolds was preserved after polymer coating. After polymer infiltration, the porosity of the scaffolds decreased from 64.2% to 59.35% for pure BG scaffolds and from 67.3% to 58.9% for B₂O₃-doped scaffolds. Meanwhile, their compressive strengths increased from 0.13 to 0.57 MPa and from 0.20 to 0.82 MPa, respectively. After polymer infiltration, 7% B₂O₃-incorporated BG scaffolds had higher weight loss and Ca-P layer deposition than pure BG scaffolds, after 14 d of incubation in simulated body fluid at 37 °C. Higher attachment and proliferation of hDPSCs were observed on 7% B₂O₃-BG-CA/GE scaffolds. In addition, the alkaline phosphatase activity of the cells was about 1.25-fold higher in this group than that observed on BG-CA/GE scaffolds after 14 d of incubation in osteogenic medium, while their intracellular calcium amounts were 1.7-fold higher than observed on BG-CA/GE after 7 d of incubation in osteogenic medium. Our results suggested that porous cellulose acetate-gelatin-coated boron-BG scaffolds hold promise for bone tissue engineering applications.

Substituted hydroxyapatite coatings of bone implants

Surface modification of orthopedic and dental implants has been demonstrated to be an effective strategy to accelerate bone healing at early implantation times. Among the different alternatives, coating implants with a layer of hydroxyapatite (HAp) is one of the most used techniques, due to its excellent biocompatibility and osteoconductive behavior. The composition and crystalline structure of HAp allow for numerous ionic substitutions that provide added value, such as antibiotic properties or osteoinduction. In this article, we will review and critically analyze the most important advances in the field of substituted hydroxyapatite coatings. In recent years substituted HAp coatings have been deposited not only on orthopedic prostheses and dental implants, but also on macroporous scaffolds, thus expanding their applications towards bone regeneration therapies. Besides, the capability of substituted HAps to immobilize proteins and growth factors by non-covalent interactions has opened new possibilities for preparing hybrid coatings that foster bone healing processes. Finally, the most important in vivo outcomes will be discussed to understand the prospects of substituted HAp coatings from a clinical point of view.

Inorganic Biomaterials for Regenerative Medicine

Regenerative medicine leverages the innate potential of the human body to efficiently repair and regenerate damaged tissues using engineered biomaterials. By designing responsive biomaterials with the appropriate biophysical and biochemical characteristics, cellular response can be modulated to direct tissue healing. Recently, inorganic biomaterials have been shown to regulate cellular responses including cell-cell and cell-matrix interactions. Moreover, ions released from these mineral-based biomaterials play a vital role in defining cell identity, as well as driving tissue-specific functions. The intrinsic properties of inorganic biomaterials, such as the release of bioactive ions (e.g., Ca, Mg, Sr, Si, B, Fe, Cu, Zn, Cr, Co, Mo, Mn, Au, Ag, V, Eu, and La), can be leveraged to induce phenotypic changes in cells or modulate the immune microenvironment to direct tissue healing and regeneration. Biophysical characteristics of biomaterials, such as topography, charge, size, electrostatic interactions, and stiffness can be modulated by addition of inorganic micro- and nanoparticles to polymeric networks have also been shown to play an important role in their biological response. In this Review, we discuss the recent emergence of inorganic biomaterials to harness the innate regenerative potential of the body. Specifically, we will discuss various biophysical or biochemical effects of inorganic-based materials in directing cellular response for regenerative medicine applications.

The Effect of Boron-Containing Nano-Hydroxyapatite on Bone Cells

Metabolic diseases or injuries damage bone structure and self-renewal capacity. Trace elements and hydroxyapatite crystals are important in the development of biomaterials to support the renewal of bone extracellular matrix. In this study, it was assumed that the boron-loaded nanometer-sized hydroxyapatite composite supports the construction of extracellular matrix by controlled boron release in order to prevent its toxic effect. In this context, boron release from nanometer-sized hydroxyapatite was calculated by ICP-MS as in large proportion within 1 h and continuing release was provided at a constant low dose. The effect of the boron-containing nanometer-sized hydroxyapatite composite on the proliferation of SaOS-2 osteoblasts and human bone marrow-derived mesenchymal stem cells was evaluated by WST-1 and compared with the effects of nano-hydroxyapatite and boric acid. Boron increased proliferation of mesenchymal stem cells at high doses and exhibited different effects on osteoblastic cell proliferation. Boron-containing nano-hydroxyapatite composites increased osteogenic differentiation of mesenchymal stem cells by increasing alkaline phosphatase activity, when compared to nano-hydroxyapatite composite and boric acid. The molecular mechanism of effective dose of boron-containing hydroxyapatite has been assessed by transcriptomic analysis and shown to affect genes involved in Wnt, TGF-β, and response to stress signaling pathways when compared to nano-hydroxyapatite composite and boric acid. Finally, a safe osteoconductive dose range of boron-containing nano-hydroxyapatite composites for local repair of bone injuries and the molecular effect profile in the effective dose should be determined by further studies to validation of the regenerative therapeutic effect window.

Boron mediated 2D and 3D cultures of adipose derived mesenchymal stem cells

Boron (B), which is a beneficial bioactive element for human, has an increasing interest in tissue engineering for the last 5 years. However, the effective B concentration in cell culture is still unknown. The aim of the present study is to investigate in vitro osteogenic potential of mesenchymal stem cells, isolated from adipose tissue (AdMSCs), on boron containing 2D and 3D cell cultures. At first, the effects of B concentrations between 1 and 20 μg/mL were evaluated on the survival and osteogenic differentiation of AdMSCs cultured on 2D cell cultures. The 3D cultures were established by using chitosan (Ch) scaffolds prepared by freeze-drying and Ch scaffolds combined with hydroxyapatite (HAp) and B containing hydroxyapatite (B-HAp) that are produced by microwave-induced biomimetic method. The proliferation and osteogenic differentiation of AdMSCs on Ch, HAp/Ch and B-HAp/Ch scaffolds were investigated by in vitro cell culture studies. The results were evaluated with respect to cell viability, bone related ECM gene expressions, and cellular morphology. It was demonstrated that cellular functions of AdMSCs were enhanced by boron in both 2D and 3D cultures. Especially, B-HAp/Ch scaffolds, which have both osteoinductive and osteoconductive properties based on presence of B and HAp in its structure, promoted adhesion, proliferation and osteogenic differentiation of AdMSCs.

Stimulatory Effects of Boron Containing Bioactive Glass on Osteogenesis and Angiogenesis of Polycaprolactone: In Vitro Study

Polycaprolactone (PCL) has attracted great attention for bone regeneration attributed to its cost-efficiency, high toughness, and good processability. However, the relatively low elastic modulus, hydrophobic nature, and insufficient bioactivity of pure PCL limited its wider application for bone regeneration. In the present study, the effects of the addition of boron containing bioactive glass (B-BG) materials on the mechanical properties and biological performance of PCL polymer were investigated with different B-BG contents (0, 10, 20, 30, and 40 wt.%), in order to evaluate the potential applications of B-BG/PCL composites for bone regeneration. The results showed that the B-BG/PCL composites possess better tensile strength, human neutral pH value, and fast degradation as compared to pure PCL polymers. Moreover, the incorporation of B-BG could enhance proliferation, osteogenic differentiation, and angiogenic factor expression for rat bone marrow stromal cells (rBMSCs) as compared to pure PCL polymers. Importantly, the B-BG also promoted the angiogenic differentiation for human umbilical vein endothelial cells (HUVECs). These enhanced effects had a concentration dependence of B-BG content, while 30 wt.% B-BG/PCL composites achieved the greatest stimulatory effect. Therefore the 30 wt.% B-BG/PCL composites have potential applications in bone reconstruction fields.

Development of antimicrobial gelatin films with boron derivatives

Food packaging technology has been advancing to provide safe and high quality food products and to minimize food waste. Moreover, there is a dire need to replace plastic materials in order to reduce environmental pollution. The aim of this study was to prepare biodegradable antimicrobial packaging films from gelatin. Boric acid, disodium octaborate tetrahydrate, and sodium pentaborate were incorporated as the antimicrobial agents. Films containing boric acid and its salts showed antibacterial effect against Staphylococcus aureus and Pseudomonas aeruginosa, as well as antifungal and anticandidal effects against Aspergillus niger and Candida albicans. The mechanical strength of the films was mostly enhanced by the addition of boron derivatives. The rheological measurements and Fourier-transform infrared spectroscopy results suggest that boron derivatives did not interfere with the network formation during gelling. The morphology of boron-added antimicrobial films was found to be similar to the morphology of the control . In conclusion, the newly developed gelatin films containing 10% or 15% disodium octaborate (g/g gelatin) might be good candidates for biodegradable antimicrobial packaging materials.

In vitro performance of a nanobiocomposite scaffold containing boron-modified bioactive glass nanoparticles for dentin regeneration

Every year, many dental restoration methods are carried out in the world and most of them do not succeed. High cost of these restorations and rejection possibility of the implants are main drawbacks. For this reason, a regenerative approach for repairing the damaged dentin-pulp complex or generating a new tissue is needed. In this study, the potential of three-dimensional cellulose acetate/oxidized pullulan/gelatin-based dentin-like constructs containing 10 or 20% bioactive glass nanoparticles was studied to explore their potential for dentin regeneration. Three-dimensional nano biocomposite structures were prepared by freeze-drying/metal mold pressing methods and characterized by in vitro degradation analysis, water absorption capacity and porosity measurements, scanning electron microscopy, in vitro biomineralization analysis. During one-month incubation in phosphate buffered saline solution at 37°C, scaffolds lost about 25-30% of their weight and water absorption capacity gradually decreased with time. Scanning electron microscopy examinations showed that mean diameter of the tubular structures was about 420 µm and the distance between walls of the tubules was around 560 µm. Calcium phosphate precipitates were formed on scaffolds surfaces treated with simulated body fluid, which was enhanced by boron-modified bioactive glass addition. For cell culture studies human dental pulp stem cells were isolated from patient teeth. An improvement in cellular viability was observed for different groups over the incubation period with the highest human dental pulp stem cells viability on B7-20 scaffolds. ICP-OES analysis revealed that concentration of boron ion released from the scaffolds was between 0.2 and 1.1 mM, which was below toxic levels. Alkaline phosphatase activity and intracellular calcium amounts significantly increased 14 days after incubation with highest values in B14-10 group. Von Kossa staining revealed higher levels of mineral deposition in these groups. In this work, results indicated that developed dentin-like constructs are promising for dentin regeneration owing to presence of boron-modified bioactive glass nanoparticles.

The Physiological Role of Boron on Health

Boron is an essential mineral that plays an important role in several biological processes. Boron is required for growth of plants, animals, and humans. There are increasing evidences of this nutrient showing a variety of pleiotropic effects, ranging from anti-inflammatory and antioxidant effects to the modulation of different body systems. In the past few years, the trials showed disease-related polymorphisms of boron in different species, which has drawn attention of scientists to the significance of boron to health. Low boron profile has been related with poor immune function, increased risk of mortality, osteoporosis, and cognitive deterioration. High boron status revealed injury to cell and toxicity in different animals and humans. Some studies have shown some benefits of higher boron status, but findings have been generally mixed, which perhaps accentuates the fact that dietary intake will benefit only if supplemental amount is appropriate. The health benefits of boron are numerous in animals and humans; for instance, it affects the growth at safe intake. Central nervous system shows improvement and immune organs exhibit enhanced immunity with boron supplementation. Hepatic metabolism also shows positive changes in response to dietary boron intake. Furthermore, animals and human fed diets supplemented with boron reveal improved bone density and other benefits including embryonic development, wound healing, and cancer therapy. It has also been reported that boron affects the metabolism of several enzymes and minerals. In the background of these health benefits, low or high boron status is giving cause for concern. Additionally, researches are needed to further elucidate the mechanisms of boron effects, and determine the requirements in different species.

A Biomimetic Alternative to Synthetic Hydroxyapatite: "Boron-Containing Bone-Like Hydroxyapatite" Precipitated From Simulated Body Fluid

BACKGROUND

Biological hydroxyapatite (HA), has several mechanical and physical advantages over the commercially available synthetic apatite (CAP-HA). The aim of this in vivo study was to investigate the effect of osteoinductive "bone-like hydroxyapatite" obtained from simulated body fluid (SBF) combined with osteoinductive "boron" (B) on bone healing.

MATERIALS

Bone like nanohydroxyapatite (SBF-HA) was precipitated from 10× simulated body fluid (10×SBF). Thirty Sprague-Dawley rats were randomly divided into 5 experimental groups (n = 6 each). The groups were involving blank defect, chitosan, SBF-HA, SBF-HA/B, and CAP-HA. Two biparietal round critical sized bone defect was created using a dental burr. The rats were sacrificed respectively at the end of second and fourth months after surgery and their calvarium were harvested for further macroscopic, microtomographic, and histologic evaluation.

RESULTS

The SBF-HA/B group demonstrated the highest mineralized matrix formation rates (30.69 ± 3.73 for the second month, 62.68 ± 7.03 for the fourth month) and was significantly higher than SBF-HA and the CAP-HA groups. The SBF-HA/B group demonstrated the highest mineralized matrix formation rates (30.69 ± 3.73 for the second month, 62.68 ± 7.03 for the fourth month) and was significantly higher than SBF-HA and the CAP-HA groups. In means of bone defect repair histologically, the highest result was observed in the SBF-HA/B group (P < 0.001).

CONCLUSIONS

The "bone-like hydroxapatite" obtained from simulated body fluid is worth attention when both its beneficial effects on bone healing and its biological behavior is taken in consideration for further bone tissue engineering studies. It appears to be a potential alternative to the commercially available hydroxyapatite samples.

Enhanced osteogenic activity with boron-doped nanohydroxyapatite-loaded poly(butylene adipate-co-terephthalate) fibrous 3D matrix

In this study, three dimensional (3D) poly(butylene adipate-co-terephthalate) (PBAT) fibrous scaffolds with more than 90% porosity were fabricated via wet electrospinning method. Amorphous hydroxyapatite (HAp) and boron (B) doped hydroxyapatite (B-HAp) nanoparticles were produced by microwave-assisted biomimetic precipitation and encapsulated into PBAT fibres with the ratio of 5% (w/w) in order to enhance osteogenic activity of the scaffolds. Cell culture studies were carried out with human bone marrow derived stem cells (hBMSCs) and they showed that alkaline phosphatase (ALP) activity and the amounts of collagen and calcium were higher on B containing PBAT (B-HAp-PBAT) scaffolds during the 28-day culture period than that of the PBAT scaffolds. Moreover, hBMSCs cultivated on B-HAp-PBAT scaffolds showed significantly higher expression levels of both early and late stage osteogenic genes e.g. ALP, collagen I (COL-I), osteocalcin (OCN) and osteopontin (OPN) at day 28 than that of the PBAT scaffolds. Scanning electron microscope (SEM) photographs and energy dispersive X-ray (EDX) analysis indicated that hBMSCs produced high amounts of mineralized extracellular matrix (ECM) mainly on the surface of the 3 D matrices. This study demonstrates that boron-containing 3 D nanofibrous PBAT scaffolds with their osteoinductive and osteoconductive properties can be used as alternative constructs for bone tissue engineering.

Microwave-induced production of boron-doped HAp (B-HAp) and B-HAp coated composite scaffolds

The aim of the present study is to produce boron (B) doped hydroxyapatite (B-HAp), which has an osteoinductive property, and investigate in-vitro osteogenesis potential of B-HAp coated chitosan (B-HAp/Ch) scaffolds. At first, B-HAp was produced by the interaction of ions within the concentrated synthetic body fluid containing boron (B-SBF) with microwave energy. Boron incorporation into HAp structure was performed by the substitution of borate ions with phosphate and hydroxyl ions. Experiments were carried out with different microwave powers and exposure times, and optimum conditions for the production of B-HAp were determined. B-HAp precipitated from B-SBF by 600W microwave power has 1.15±0.11% (w/w) B, 1.40 (w/w) Ca/P ratio, 4.30±0.07% (w/w) carbonate content, 30±4nm rod-like morphology and bone-like amorphous structure. Then, chitosan scaffolds that were prepared by freeze-drying were coated with B-HAp by performing microwave-assisted precipitation in the presence of scaffolds to improve their bioactivities and mechanical properties. The formation of apatite layer and the penetration of apatites into the pores were observed by scanning electron microscopy (SEM). Fourier Transform Infrared spectroscopy (ATR-FTIR) and X-ray diffraction (XRD) analysis also confirmed the presence of B-HAp layer. As control, hydroxyapatite coated chitosan scaffolds (HAp/Ch) produced at the same conditions were used. The results of cell culture studies indicated that B releasing from scaffolds enhances proliferation and osteoblastic differentiation of MC3T3-E1 cells. This work emphasized the importance of the use of B within the scaffolds for enhancing in-vitro bone tissue engineering applications.