Structural and Chemical Analysis of Hydroxyapatite (HA)-Boron Nitride (BN) Nanocomposites Sintered Under Different Atmospheric Conditions.

Calcium phosphate derivatives have been widely employed in medical and dental applications for hard tissue repair, as they are the main inorganic constitution of hard tissue; such as bones and teeth. Owing to their excellent osteoconductive and bioactive properties, hydroxyapatite- (HA) based ceramics are the best candidates of this group for medical, bioscience, and dental applications. However, when replacing a bone or tooth, HA is not able to sustain similar mechanical properties. In this study, to improve the mechanical properties, nanoscale hexagonal boron nitride with different compositional percentages was added to the nano HA to form composites. The effect of compositional changes and sintering parameters on microstructural and morphological properties of the ceramic composites was comparatively investigated. Detailed chemical characterization of the composite materials was carried out using X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and energy-dispersive X-ray spectroscopy, whereas scanning electron microscopy and atomic force microscopy investigations were employed to monitor morphological and surface features. Additional transmission electron microscopy investigations were carried out to reveal the nanostructure and crystal structure of the composites.

Boron Nitride's Morphological Role in the Design of Injectable Hyaluronic Acid Based Hybrid Artificial Synovial Fluid.

The treatment process of osteoarthritis (OA) is challenging as it affects not only cartilage but also subchondral bone, ligament attachment capsules, synovium, and surrounding muscle tissue. Therefore, the search for preventive treatment or methods to slow the onset of the condition. Hexagonal boron nitride (hBN) has a graphite-like lamellar structure and is thought to facilitate cartilage movement for biomedical applications, just like in bearing systems. Hyaluronic acid (HA) is one of the natural polymers that can be used to transport boron nitride and maintain its presence in joints for a long time. In this study, hybrid hydrogels were formulated by using boron nitride nanoparticles and nanosheets. The rheological properties of the hydrogels were evaluated according to the structural differences of hBN. Characterizations have shown that hybrid hydrogels can be produced in injectable form, and the rheological properties are strongly related to the structural properties of the added particle. It has been determined that hBN added to the hydrogel structure reduces the dynamic viscosity of the zero-shear point and the deformation rate of the hydrogel and also changes the viscoelastic properties of the hydrogel depending on boron nitride's structural differences. The suggested mechanism is the hybrid hydrogel that exhibits lower viscosity as the layers detach from each other or disperses the agglomerates under applied shear stress. hBN, which has been proposed as a new strategy for joint injections, is thought to be a promising candidate for the treatment of OA due to its lamellar structures.

Regenerative Effect of Resorbable Scaffold Embedded Boron-Nitride/Hydroxyapatite Nanoparticles in Rat Parietal Bone.

BN has important roles in several physiological events, including bone growth and immune system. New infection-free cranioplasty and has an osteogenic activities material that are compatible with tissue are being developed. We aimed in our study to examine whether different combinations of Boron-nitride/Hydroxyapatite are embedded into the scaffold in the treatment of calvarial defects. 200 adult female Sprague-Dawley rats divided into 10 equal groups. Osteotomy was made by trepan drill in 8 mm diameter. The scaffolds were placed in the rats and were left to recovery for 2 months. During the experiment, CT scans were taken from the calvarial areas of the rats in the 2nd, 4th and 8th weeks. Significant healing was observed in defect diameters in 2.5% BN+10% HA, 2.5% BN and 5% BN+10% HA, respectively. After 8 weeks, it was seen that the amounts of OPN, BMP-2, RunX2 and ALP mRNA expression significantly decreased in 2.5% BN+10% HA, 2.5% BN, 5% BN+10% HA and 5% BN groups. It was shown that bone recovery was at the best grade in the groups, which contained 2.5% BN and 2.5% BN+10% HA when compared to the other groups. BN is a very promising agent that will be used in reconstructive surgery for the treatment of calvarial bone defects.

Effects of hexagonal boron nitride nanoparticles on antimicrobial and antibiofilm activities, cell viability.

The objective of this work was to investigate the antimicrobial and antibiofilm activities of hBN nanoparticles against Streptococcus mutans 3.3, Staphylococcus pasteuri M3, Candida sp. M25 and S. mutans ATTC 25175. Minimum Inhibitory Concentration (MIC) of hBN nanoparticles were determined against Streptococcus mutans 3.3, Staphylococcus pasteuri M3, Candida sp. M25 growth. In addition, we aimed to evaluate the cytotoxic effects of hBN nanoparticles on human normal skin fibroblast (CCD-1094Sk, ATCC® CRL 2120 ™) and Madin Darby Canine Kidney (MDCK) cells by using various toxicological endpoints. Cell viability was assessed by MTT, SRB and PicoGreen assays. After experimental analyses, it was revealed that hBN nanoparticles show better MIC results. The MIC values were higher for Streptococcus mutans ATTC 25175 and Staphylococcus pasteuri M3 and lower against Streptococcus mutans 3.3, Candida sp. M25. Surprisingly, hBN nanoparticles showed a high antibiofilm activity on preformed biofilm, which inhibited biofilm growth of S. mutans 3.3, S. mutans ATTC 25175 and Candida sp.M25. These results show that hBN nanoparticles may be an option to control oral biofilms. In cell viability tests, the cells were exposed to 0.025-0.4 mg/mL concentrations of hBN nano particle suspension. The exposure time to the hBN nanoparticle suspensions were 24 h and 48 h. The results indicate that there is no cytotoxic effect on CRL 2120 and MDCK cells at the concentration range of 0.025-0.1 mg/mL. However, on both first and second day, hBN caused mild cytotoxicity on CRL-2120 cells at high hBN concentration (0.2-0.4 mg/mL). Considering all the results of this study, in appropriate concentration (0.1 mg/mL) hBN nanoparticles can be considered a potential safe oral care product.

Release characteristics of diclofenac sodium from poly(vinyl alcohol)/sodium alginate and poly(vinyl alcohol)-grafted-poly(acrylamide)/sodium alginate blend beads.

In this study, acrylamide (AAm) was grafted onto poly(vinyl alcohol) (PVA) with UV radiation at ambient temperature. The graft copolymer (PVA-g-PAAm) was characterized by using Fourier transform infrared spectroscopy (FTIR), elemental analysis and differential scanning calorimetry (DSC). Polymeric blend beads of PVA-g-PAAm and PVA with sodium alginate (NaAlg) were prepared by cross-linking with glutaraldehyde (GA) and used to deliver a model anti-inflammatory drug, diclofenac sodium (DS). Preparation condition of the beads was optimized by considering the percentage entrapment efficiency, particle size, swelling capacity of beads and their release data. Effects of variables such as PVA/NaAlg ratio, acrylamide content, exposure time to GA and drug/polymer ratio on the release of DS were discussed at three different pH values (1.2, 6.8, 7.4). It was observed that, DS release from the beads decreased with increasing PVA/NaAlg (m/m) ratio, drug/polymer ratio (d/p) and extent of cross-linking. However, DS release increased with increasing acrylamide content of the PVA-g-PAAm polymer. The highest DS release was obtained to be 92% for 1/1 PVA-g-PAAm/NaAlg ratio beads. It was also observed from release results that DS release from the beads through the external medium is much higher at high pH (6.8 and 7.4) than that at low pH (1.2). The drug release from the beads mostly followed Case II transport.

Electrophoretic deposition of hydroxyapatite-hexagonal boron nitride composite coatings on Ti substrate.

In this study, commercial pure titanium samples were coated with nano hydroxyapatite-nano hexagonal boron nitride (nano HA-nano hBN) composite by electrophoretic deposition (EPD). The effect of process parameters (applied voltage, deposition time and solid concentration) on the coating morphology, thickness and the adhesion behavior were studied systematically and crack free nano hBN-nano HA composite coating production was achieved for developing bioactive coatings on titanium substrates for orthopedic applications. For the examination of structural and morphological characteristics of the coating surfaces, various complementary analysis methods were performed. For the structural characterization, XRD and Raman Spectroscopy were used while, Scanning Electron Microscopy (SEM) equipped with an energy dispersive spectrometer (EDS) and Transmission Electron Microscopy (TEM) techniques were carried out for revealing the morphological characterization. The results showed that nano HA-nano hBN were successfully deposited on Ti surface with uniform, crack-free coating by EPD. The amounts of hBN in suspension are considered to have no effect on coating thickness. By adding hBN into HA, the morphology of HA did not change and hBN has no significant effect on porous structure. These nanostructured surfaces are expected to be suitable for proliferation of cells and have high potential for bioactive materials.

Study of the boron levels in serum after implantation of different ratios nano-hexagonal boron nitride-hydroxy apatite in rat femurs.

Boron and its derivatives are effective in bone recovery and osteointegration. However, increasing the boron levels in body liquids may cause toxicity. The aim of our study is to investigate serum boron levels using ICP-MS after implantation of different ratios of nano-hBN-HA composites in rat femurs. All rats were (n=126) divided into five experimental groups (n=24) and one healthy group (6 rats); healthy (Group1), femoral defect + %100 HA (Group2), femoral defect + %2.5 hBN + %97.5 HA (Group3), femoral defect + %5 hBN + %95 HA (Group4), femoral defect + %10 hBN + %90 HA (Group5), femoral defect + %100 hBN (Group6). The femoral defect was created in the distal femur (3mm drill-bit). Each implant group was divided into four different groups (n=24) also 6 rats sacrificed for each groups in one week intervals during four weeks. In our results; at 1, 2, 3, and 4 weeks after implantation near bone tissue, serum levels of boron were evaluated using ICP-MS. We demonstrated that neither short-term nor long-term implantation of hBN-HA composite resulted in statistically increased serum boron levels in experimental groups compared to healthy group. In conclusion, this study investigated the implant material produced form hBN-HA for the first time. Our data suggest that hBN is a new promising target for biomaterial and implant bioengineers.