Intramedullary implants coated with cubic boron nitride enhance bone fracture healing in a rat model

Characterization and Biocompatibility Assessment of Boron Nitride Magnesium Nanocomposites for Orthopedic Applications

Magnesium (Mg) has been intensively studied as a promising alternative material to inert metallic alloys for orthopedic fixation devices due to its biodegradable nature inside the body and its favorable biocompatibility. However, the low mechanical strength and rapid corrosion of Mg in physiological environments represent the main challenges for the development of Mg-based devices for orthopedic applications. A possible solution to these limitations is the incorporation of a small content of biocompatible nanoparticles into the Mg matrix to increase strength and possibly corrosion resistance of the resulting nanocomposites. In this work, the effect of adding boron nitride (BN) nanoparticles (0.5 and 1.5 vol.%) on the mechanical properties, corrosion behavior, and biocompatibility of Mg-based nanocomposites was investigated. The properties of the nanocomposites fabricated using powder metallurgy methods were assessed using microstructure analyses, microhardness, compression tests, in vitro corrosion, contact angle, and cytotoxicity tests. A significant increase in the microhardness, strength, and corrosion rates of Mg-BN nanocomposites was detected compared with those of pure Mg (0% BN). Crystalline surface post-corrosion byproducts were detected and identified via SEM, EDX, and XRD. Biocompatibility assessments showed that the incorporation of BN nanoparticles had no significant impact on the cytotoxicity of Mg and samples were hydrophilic based on the contact angle results. These results confirm that the addition of BN nanoparticles to the Mg matrix can increase strength and corrosion resistance without influencing cytotoxicity in vitro. Further investigation into the chemical behavior of nanocomposites in physiological environments is needed to determine the potential impact of corrosive byproducts. Surface treatments and formulation methods that would increase the viability of these materials in vivo are also needed.

Investigating effects of locally applied boric acid on fracture healing with and without low-level laser therapy

This study aimed to investigate the effects on fracture healing of locally applied boric acid (BA) with and without low-level laser therapy (LLLT). A unicortical femoral defect was surgically created on the anterolateral surface of proximal femur of each subject. The subjects, totaling 56 Wistar albino rats, were randomly allocated into four groups (n = 14 each): control, LLLT (λ = 905 μm, 10,000 Hz, 25 mW, and peak power 25 W), BA (40 mg/kg), and BA + LLLT groups. On the 30th day, the highest radiological score was recorded for the BA + LLLT group (3.63 [2-4]), followed by the BA (3.38 [2.75-3.75]), control (3 [2-3.25]), and LLLT (2.5 [1.25-3]) groups. On days 15 and 30 post-surgery, malondialdehyde levels were significantly lower among the BA + LLLT group compared to the control group (p < 0.001). On day 30, superoxide dismutase, catalase, and alkaline phosphatase levels were highest in the BA + LLLT group compared to the control group (p < 0.001). When the histopathological, immunofluorescence, and immunohistochemical findings on the 15th and 30th days were compared with the control group, a statistically significant difference was found for the BA and BA + LLLT groups (p ˂ 0.05). This study suggests that locally applied BA with LLLT may accelerate fracture healing.

Histomorphometric and biomechanical evaluation of the osseointegration around micro- and nano-level boron-nitride coated titanium dental implants

INTRODUCTION

Titanium dental implants has been coated with different materials such as polymers and biomimetic agents, bone morphogenetic protein, calcium phosphate to enhance surface properties of the titanium implants for osseointegration. The aim of this study was to evaluate the bone tissue healing around Boron Nitride-coated (BN-coated) titanium implants histomorphometrically and biomechanically and also observe the effect of different coating thicknesses on osseointegration.

MATERIALS AND METHODS

BN was coated on dental titanium implants with two different coating thicknesses by using RF magnetron sputtering system. Totally fifty-four implants were inserted into the tibias' of 12 New Zealand rabbits bilaterally under general anesthesia. All animals were sacrificed after 4-weeks. Bone-implant contact (BIC) and new bone area/total area ratios (BATA) were calculated. Also, the removal torque (RT) test was performed.

RESULTS

The highest new bone area in the medullary cavity was around the nano-BN-coated surface with 15.70%. In micro-BN-coated surface and control group, this ratio was determined as 10.48% and 8.23%, respectively. The BIC ratios in upper-side of implants and cortical-associated BIC ratios in lower-side were found significantly higher in control and micro-BN-coated group than nano-BN-coated group (p < 0.05). Similar BIC values were observed between control and micro-BN-coated groups (p > 0.05). BATA values did not show statistically significant differences between all three groups (p > 0.05). The RT values measured in all groups were found comparable and no statistically significant differences were found (p > 0.05).

CONCLUSION

No inflammatory reaction developed around any implant. Relatively more new bone formation around nano-BN-coated titanium implants indicates the promising osseoinductive effect of BN coating. BN-coated implants showed similar biomechanical and histomorphometrical outcomes to that of the conventional titanium implants through a 4-week evaluation period.

Angle-stable interlocking nailing in a canine critical-sized femoral defect model for bone regeneration studies: In pursuit of the principle of the 3R’s

Introduction: Critical-sized long bone defects represent a major therapeutic challenge and current treatment strategies are not without complication. Tissue engineering holds much promise for these debilitating injuries; however, these strategies often fail to successfully translate from rodent studies to the clinical setting. The dog represents a strong model for translational orthopedic studies, however such studies should be optimized in pursuit of the Principle of the 3R’s of animal research (replace, reduce, refine). The objective of this study was to refine a canine critical-sized femoral defect model using an angle-stable interlocking nail (AS-ILN) and reduce total animal numbers by performing imaging, biomechanics, and histology on the same cohort of dogs.

Methods: Six skeletally mature hounds underwent a 4 cm mid-diaphyseal femoral ostectomy followed by stabilization with an AS-ILN. Dogs were assigned to autograft (n = 3) or negative control (n = 3) treatment groups. At 6, 12, and 18 weeks, healing was quantified by ordinal radiographic scoring and quantified CT. After euthanasia, femurs from the autograft group were mechanically evaluated using an established torsional loading protocol. Femurs were subsequently assessed histologically.

Results: Surgery was performed without complication and the AS-ILN provided appropriate fixation for the duration of the study. Dogs assigned to the autograft group achieved radiographic union by 12 weeks, whereas the negative control group experienced non-union. At 18 weeks, median bone and soft tissue callus volume were 9,001 mm³ (range: 4,939–10,061) for the autograft group and 3,469 mm³ (range: 3,085–3,854) for the negative control group. Median torsional stiffness for the operated, autograft treatment group was 0.19 Nm/° (range: 0.19–1.67) and torque at failure was 12.0 Nm (range: 1.7–14.0). Histologically, callus formation and associated endochondral ossification were identified in the autograft treatment group, whereas fibrovascular tissue occupied the critical-sized defect in negative controls.

Conclusion: In a canine critical-sized defect model, the AS-ILN and described outcome measures allowed refinement and reduction consistent with the Principle of the 3R’s of ethical animal research. This model is well-suited for future canine translational bone tissue engineering studies.

Recent Progress in Fabrication and Application of BN Nanostructures and BN-Based Nanohybrids

Due to its unique physical, chemical, and mechanical properties, such as a low specific density, large specific surface area, excellent thermal stability, oxidation resistance, low friction, good dispersion stability, enhanced adsorbing capacity, large interlayer shear force, and wide bandgap, hexagonal boron nitride (h-BN) nanostructures are of great interest in many fields. These include, but are not limited to, (i) heterogeneous catalysts, (ii) promising nanocarriers for targeted drug delivery to tumor cells and nanoparticles containing therapeutic agents to fight bacterial and fungal infections, (iii) reinforcing phases in metal, ceramics, and polymer matrix composites, (iv) additives to liquid lubricants, (v) substrates for surface enhanced Raman spectroscopy, (vi) agents for boron neutron capture therapy, (vii) water purifiers, (viii) gas and biological sensors, and (ix) quantum dots, single photon emitters, and heterostructures for electronic, plasmonic, optical, optoelectronic, semiconductor, and magnetic devices. All of these areas are developing rapidly. Thus, the goal of this review is to analyze the critical mass of knowledge and the current state-of-the-art in the field of BN-based nanomaterial fabrication and application based on their amazing properties.

Comparative review of piezoelectric biomaterials approach for bone tissue engineering

Bone as a minerals' reservoir and rigid tissue of the body generating red and white blood cells supports various organs. Although the self-regeneration property of bone, it cannot regenerate spontaneously in severe damages and still remains as a challenging issue. Tissue engineering offers several techniques for regenerating damaged bones, where various biomaterials are examined to fabricate scaffolds for bone repair. Piezoelectric characteristic plays a crucial role in repairing and regenerating damaged bone by mimicking the bone niche behavior. Piezoelectric biomaterials show significant potential for bone tissue engineering. Herein we try to have a comparative review on piezoelectric and non-piezoelectric biomaterials used in bone tissue engineering, classified them, and discussed their effects on implanted cells and manufacturing techniques. Especially, Polyvinylidene fluoride (PVDF) and its composites are the most practically used piezoelectric biomaterials for bone regeneration. PVDF and its composites have been summarized and discussed to repair damaged bone tissues.

Bioactive Coatings Loaded with Osteogenic Protein for Metallic Implants

Osteoconductive and osteoinductive coatings represent attractive and tunable strategies towards the enhanced biomechanics and osseointegration of metallic implants, providing accurate local modulation of bone-to-implant interface. Composite materials based on polylactide (PLA) and hydroxyapatite (HAp) are proved beneficial substrates for the modulation of bone cells' development, being suitable mechanical supports for the repair and regeneration of bone tissue. Moreover, the addition of osteogenic proteins represents the next step towards the fabrication of advanced biomaterials for hard tissue engineering applications, as their regulatory mechanisms beneficially contribute to the new bone formation. In this respect, laser-processed composites, based on PLA, Hap, and bone morphogenetic protein 4(BMP4), are herein proposed as bioactive coatings for metallic implants. The nanostructured coatings proved superior ability to promote the adhesion, viability, and proliferation of osteoprogenitor cells, without affecting their normal development and further sustaining the osteogenic differentiation of the cells. Our results are complementary to previous studies regarding the successful use of chemically BMP-modified biomaterials in orthopedic and orthodontic applications.

Boron nitride nanotube scaffolds: emergence of a new era in regenerative medicine

Tissue engineering scaffolds have transformed from passive geometrical supports for cell adhesion, extension and proliferation to active, dynamic systems that can in addition, trigger functional maturation of the cells in response to external stimuli. Such 'smart' scaffolds require the incorporation of active response elements that can respond to internal or external stimuli. One of the key elements that direct the cell fate processes is mechanical stress. Different cells respond to various types and magnitudes of mechanical stresses. The incorporation of a pressure-sensitive element in the tissue engineering scaffold therefore, will aid in tuning the cell response to the desired levels. Boron nitride nanotubes (BNNTs) are analogous to carbon nanotubes and have attracted considerable attention due to their unique amalgamation of chemical inertness, piezoelectric property, biocompatibility and, thermal and mechanical stability. Incorporation of BNNTs in scaffolds confers them with piezoelectric property that can be used to stimulate the cells seeded on them. Biorecognition and solubilization of BNNTs can be engineered through surface functionalization with different biomolecules. Over the years, the importance of BNNT has grown in the realm of healthcare nanotechnology. This review discusses the salient properties of BNNTs, the influence of functionalization on theirin vitroandin vivobiocompatibility, and the uniqueness of BNNT-incorporated tissue engineering scaffolds.

Osteoconductive and Osteoinductive Surface Modifications of Biomaterials for Bone Regeneration: A Concise Review

The main aim of bone tissue engineering is to fabricate highly biocompatible, osteoconductive and/or osteoinductive biomaterials for tissue regeneration. Bone implants should support bone growth at the implantation site via promotion of osteoblast adhesion, proliferation, and formation of bone extracellular matrix. Moreover, a very desired feature of biomaterials for clinical applications is their osteoinductivity, which means the ability of the material to induce osteogenic differentiation of mesenchymal stem cells toward bone-building cells (osteoblasts). Nevertheless, the development of completely biocompatible biomaterials with appropriate physicochemical and mechanical properties poses a great challenge for the researchers. Thus, the current trend in the engineering of biomaterials focuses on the surface modifications to improve biological properties of bone implants. This review presents the most recent findings concerning surface modifications of biomaterials to improve their osteoconductivity and osteoinductivity. The article describes two types of surface modifications: (1) Additive and (2) subtractive, indicating biological effects of the resultant surfaces in vitro and/or in vivo. The review article summarizes known additive modifications, such as plasma treatment, magnetron sputtering, and preparation of inorganic, organic, and composite coatings on the implants. It also presents some common subtractive processes applied for surface modifications of the biomaterials (i.e., acid etching, sand blasting, grit blasting, sand-blasted large-grit acid etched (SLA), anodizing, and laser methods). In summary, the article is an excellent compendium on the surface modifications and development of advanced osteoconductive and/or osteoinductive coatings on biomaterials for bone regeneration.