Biomaterial-Based Nanocomposite for Osteogenic Repurposing of Doxycycline

Stable self-assembled oral metformin-bridged nanocochleates against hepatocellular carcinoma

Despite its established anti-diabetic activity, Metformin hydrochloride (MET) has been repurposed for the management of hepatocellular carcinoma (HCC). Owing to MET high aqueous solubility and poor oral permeability, a novel nanoplatform is sought to overcome the current challenges of traditional formulations. In this study, we developed MET-bridged nanocochleates (MET-CO) using a direct bridging method followed by optimization and assessment using various in-vitro and in-vivo pharmacokinetic methods. The optimized nanocochleates MET-CODCP 19, containing dicetyl phosphate (DCP), displayed uniform snail-shaped nano-rolls measuring 136.41 ± 2.11 nm with a PDI of 0.241 ± 0.005 and a highly negative ζ-potential of -61.93 ± 2.57 mV. With an impressive MET encochleation efficiency (> 75%), MET-CODCP 19 exhibited a controlled biphasic release profile, with minimal initial burst followed by prolonged release for 24 h. Importantly, they showed significant MET permeation in both in-vitro Caco-2 and ex-vivo intestinal models compared to non-DCP containing formula or MET solution. The in-vivo oral bioavailability study demonstrated pronounced improvements in the pharmacokinetic parameters with a 5.5 relative bioavailability compared to MET solution. Notably, a significant reduction in IC50 values in HepG2 cells after 24 h of treatment was observed. Furthermore, the optimized formulation showed a significant downregulation of anti-apoptotic and cancer stemness genes, with 12- and 2-fold lower expression compared to MET solution. These promising results highlight the efficacy of the novel MET-bridged nanocochleates as a stable nanoplatform for enhancing the oral bioavailability of MET and boosting its anticancer potential against HCC.

Multifunctional human serum albumin-crosslinked and self-assembling nanoparticles for therapy of periodontitis by anti-oxidation, anti-inflammation and osteogenesis

Periodontitis is a chronic inflammatory disease that can result in the irreversible loss of tooth-supporting tissues and elevate the likelihood and intensity of systemic diseases. The presence of reactive oxygen species (ROS) and associated related oxidative stress is intricately linked to the progression and severity of periodontal inflammation. Targeted removal of local ROS may serve to attenuate inflammation, improve the unfavorable periodontal microenvironment and potentially reverse ensuing pathological cascades. These ROS scavenging nanoparticles, which possess additional characteristics such as anti-inflammation and osteogenic differentiation, are highly sought after for the treatment of periodontitis. In this study, negative charged human serum albumin-crosslinked manganese-doped self-assembling Prussian blue nanoparticles (HSA-MDSPB NPs) were fabricated. These nanoparticles demonstrate the ability to scavenge multiple ROS including superoxide anion, free hydroxyl radicals, singlet oxygen and hydrogen peroxide. Additionally, HSA-MDSPB NPs exhibit the capacity to alleviate inflammation in gingiva and alveolar bone both in vitro and in vivo. Furthermore, HSA-MDSPB NPs have been shown to play a role in promoting the polarization of macrophages from the M1 to M2 phenotype, resulting in reduced production of pro-inflammatory cytokines. More attractively, HSA-MDSPB NPs have been demonstrated to enhance cellular osteogenic differentiation. These properties of HSA-MDSPB NPs contribute to decreased inflammation, extracellular matrix degradation and bone loss in periodontal tissue. In conclusion, the multifunctional nature of HSA-MDSPB NPs provides a promising therapeutic approach for the treatment of periodontitis.

Alendronate/lactoferrin-dual decorated lipid nanocarriers for bone-homing and active targeting of ivermectin and methyl dihydrojasmonate for leukemia

Chronic myeloid leukemia is a hematological cancer, where disease relapse and drug resistance are caused by bone-hosted-residual leukemia cells. An innovative resolution is bone-homing and selective-active targeting of anticancer loaded-nanovectors. Herein, ivermectin (IVM) and methyl dihydrojasmonate (MDJ)-loaded nanostructured lipid carriers (IVM-NLC) were formulated then dually decorated by lactoferrin (Lf) and alendronate (Aln) to optimize (Aln/Lf/IVM-NLC) for active-targeting and bone-homing potential, respectively. Aln/Lf/IVM-NLC (1 mg) revealed nano-size (73.67 ± 0.06 nm), low-PDI (0.43 ± 0.06), sustained-release of IVM (62.75 % at 140-h) and MDJ (78.7 % at 48-h). Aln/Lf/IVM-NLC afforded substantial antileukemic-cytotoxicity on K562-cells (4.29-fold lower IC50), higher cellular uptake and nuclear fragmentation than IVM-NLC with acceptable cytocompatibility on oral-epithelial-cells (as normal cells). Aln/Lf/IVM-NLC effectively upregulated caspase-3 and BAX (4.53 and 15.9-fold higher than IVM-NLC, respectively). Bone homing studies verified higher hydroxyapatite affinity of Aln/Lf/IVM-NLC (1 mg; 22.88 ± 0.01 % at 3-h) and higher metaphyseal-binding (1.5-fold increase) than untargeted-NLC. Moreover, Aln/Lf/IVM-NLC-1 mg secured 1.35-fold higher in vivo bone localization than untargeted-NLC, with lower off-target distribution. Ex-vivo hemocompatibility and in-vivo biocompatibility of Aln/Lf/IVM-NLC (1 mg/mL) were established, with pronounced amelioration of hepatic and renal toxicity compared to higher Aln doses. The innovative Aln/Lf/IVM-NLC could serve as a promising nanovector for bone-homing, active-targeted leukemia therapy.

Antibacterial and Osteogenic Doxycycline Imprinted Bioglass Microspheres to Combat Bone Infection

Currently, postoperative infection is a significant challenge in bone and dental surgical procedures, demanding the exploration of innovative approaches due to the prevalence of antibiotic-resistant bacteria. This study aims to develop a strategy for controlled and smart antibiotic release while accelerating osteogenesis to expedite bone healing. In this regard, temperature-responsive doxycycline (DOX) imprinted bioglass microspheres (BGMs) were synthesized. Following the formation of chitosan-modified BGMs, poly N-isopropylacrylamide (pNIPAm) was used for surface imprinting of DOX. The temperature-responsive molecularly imprinted polymers (MIPs) exhibited pH and temperature dual-responsive adsorption and controlled-release properties for DOX. The temperature-responsive MIP was optimized by investigating the molar ratio of N,N'-methylene bis(acrylamide) (MBA, the cross-linker) to NIPAm. Our results demonstrated that the MIPs showed superior adsorption capacity (96.85 mg/g at 35 °C, pH = 7) than nonimprinted polymers (NIPs) and manifested a favorable selectivity toward DOX. The adsorption behavior of DOX on the MIPs fit well with the Langmuir model and the pseudo-second-order kinetic model. Drug release studies demonstrated a controlled release of DOX due to imprinted cavities, which were fitted with the Korsmeyer-Peppas kinetic model. DOX-imprinted BGMs also revealed comparable antibacterial effects against Staphylococcus aureus and Escherichia coli to the DOX (control). In addition, MIPs promoted viability and osteogenic differentiation of MG63 osteoblast-like cells. Overall, the findings demonstrate the significant potential of DOX-imprinted BGMs for use in bone defects. Nonetheless, further in vitro investigations and subsequent in vivo experiments are warranted to advance this research.

Doxycycline-Loaded Calcium Phosphate Nanoparticles with a Pectin Coat Can Ameliorate Lipopolysaccharide-Induced Neuroinflammation Via Enhancing AMPK

Neuroinflammation occurs in response to different injurious triggers to limit their hazardous effects. However, failure to stop this process can end in multiple neurological diseases. Doxycycline (DX) is a tetracycline, with potential antioxidant and anti-inflammatory properties. The current study tested the effects of free DX, DX-loaded calcium phosphate (DX@CaP), and pectin-coated DX@CaP (Pec/DX@CaP) nanoparticles on the lipopolysaccharide (LPS)-induced neuroinflammation in mice and to identify the role of adenosine monophosphate-activated protein kinase (AMPK) in this effect. The present study was conducted on 48 mice, divided into 6 groups, eight mice each. Group 1 (normal control), Group 2 (blank nanoparticles-treated), Group 3 (LPS (untreated)), Groups 4, 5, and 6 received LPS, then Group 4 received free DX, Group 5 received DX-loaded calcium phosphate nanoparticles (DX@CaP), and Group 6 received DX-loaded calcium phosphate nanoparticles with a pectin coat (Pec/DX@CaP). At the end of the experimentation period, behavioral tests were carried out. Then, mice were sacrificed, and brain tissue was extracted and used for histological examination, and assessment of interleukin-6 positive cells in different brain areas, in addition to biochemical measurement of SOD activity, TLR-4, AMPK and Nrf2. LPS can induce prominent neuroinflammation. Treatment with (Pec/DX@CaP) can reverse most behavioral, histopathological, and biochemical changes caused by LPS. The findings of the current study suggest that (Pec/DX@CaP) exerts a significant reverse of LPS-induced neuroinflammation by enhancing SOD activity, AMPK, and Nrf2 expression, in addition to suppression of TLR-4.

Engineering tanshinone-loaded, levan-biofunctionalized polycaprolactone nanofibers for treatment of skin cancer

Skin cancer is a challenging condition of the highest prevalence rate among other types of cancer. Thus, advancement of local therapeutic approaches for skin cancer is highly needed. Recently, the use of phytotherapeutics, like tanshinone IIA (Tan), as anticancer agents has become promising. In this work, we engineered Tan-loaded polycaprolactone nanofibers, biofunctionalized with levan and egg-lecithin (Tan@Lev/EL/PCL-NF) for local skin cancer therapy. Novel Tan@Lev/EL/PCL-NF were prepared using w/o-emulsion electrospinning, employing a 23-factorial design. Composite NF exhibited nanofiber diameter (365.56 ± 46.25 nm), favorable surface-hydrophilicity and tensile strength. Tan@Lev/EL/PCL-NF could achieve favorably controlled-release (100% in 5 days) and Tan skin-deposition (50%). In vitro anticancer studies verified prominent cytotoxicity of Tan@Lev/EL/PCL-NF on squamous-cell-carcinoma cell-line (SCC), with optimum cytocompatibility on fibroblasts. Tan@Lev/EL/PCL-NF exerted high apoptotic activity with evident nuclear fragmentation, G2/M-mitosis cell-cycle-arrest and antimigratory efficacy. In vivo antitumor activity was established in mice, confirming pronounced inhibition of tumor-growth (224.25 ± 46.89%) and relative tumor weight (1.25 ± 0.18%) for Tan@Lev/EL/PCL-NF compared to other groups. Tan@Lev/EL/PCL-NF afforded tumor-biomarker inhibition, upregulation of caspase-3 and knockdown of BAX and MKi67. Efficient anticancer potential was further confirmed by histomorphometric analysis. Our findings highlight the promising anticancer functionality of composite Tan@Lev/EL/PCL-NF, as efficient local skin cancer phytotherapy.

Targeted Fisetin-Encapsulated β-Cyclodextrin Nanosponges for Breast Cancer

Fisetin (FS) is considered a safer phytomedicine alternative to conventional chemotherapeutics for breast cancer treatment. Despite its surpassing therapeutic potential, its clinical utility is hampered by its low systemic bioavailability. Accordingly, as far as we are aware, this is the first study to develop lactoferrin-coated FS-loaded β-cyclodextrin nanosponges (LF-FS-NS) for targeted FS delivery to breast cancer. NS formation through cross-linking of β-cyclodextrin by diphenyl carbonate was confirmed by FTIR and XRD. The selected LF-FS-NS showed good colloidal properties (size 52.7 ± 7.2 nm, PDI < 0.3, and ζ-potential 24 mV), high loading efficiency (96 ± 0.3%), and sustained drug release of 26 % after 24 h. Morphological examination using SEM revealed the mesoporous spherical structure of the prepared nanosponges with a pore diameter of ~30 nm, which was further confirmed by surface area measurement. Additionally, LF-FS-NS enhanced FS oral and IP bioavailability (2.5- and 3.2-fold, respectively) compared to FS suspension in rats. Antitumor efficacy evaluation in vitro on MDA-MB-231 cells and in vivo on an Ehrlich ascites mouse model demonstrated significantly higher activity and targetability of LF-FS-NS (30 mg/kg) compared to the free drug and uncoated formulation. Consequently, LF-FS-NS could be addressed as a promising formulation for the effective management of breast cancer.

Doxycycline-doped collagen membranes accelerate in vitro osteoblast proliferation and differentiation

OBJECTIVE

The aim of the study was to evaluate the effect of doxycycline- and dexamethasone-doped collagen membranes on the proliferation and differentiation of osteoblasts.

BACKGROUND

Collagen barrier membranes are frequently used to promote bone regeneration and to boost this biological activity their functionalization with antibacterial and immunomodulatory substances has been suggested.

METHODS

The design included commercially available collagen membranes doped with doxycycline (Dox-Col-M) or dexamethasone (Dex-Col-M), as well as undoped membranes (Col-M) as controls, which were placed in contact with cultured MG63 osteoblast-like cells (ATCC). Cell proliferation was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) assay and differentiation by measuring the alkaline phosphatase (ALP) activity using spectrophotometry. Real-time quantitative polymerase chain reaction was used to study the expression of the genes: Runx-2, OSX, ALP, OSC, OPG, RANKL, Col-I, BMP-2, BMP-7, TGF-β1, VEGF, TGF-βR1, TGF-βR2, and TGF-βR3. Scanning electron microscopy was used to study osteoblast morphology. Data were assessed using one-way analysis of variance or Kruskal-Wallis tests, once their distribution normality was assessed by Kolmogorov-Smirnov tests (p > .05). Bonferroni for multiple comparisons were carried out (p < .05).

RESULTS

Osteoblast proliferation was significantly enhanced in the functionalized membranes as follows: (Col-M < Dex-Col-M < Dox-Col-M). ALP activity was significantly higher on cultured osteoblasts on Dox-Col-M. Runx-2, OSX, ALP, OSC, BMP-2, BMP-7, TGF-β1, VEGF, TGF-βR1, TGF-βR2, and TGF-βR3 were overexpressed, and RANKL was down-regulated in osteoblasts cultured on Dox-Col-M. The osteoblasts cultured in contact with the functionalized membranes demonstrated an elongated spindle-shaped morphology.

CONCLUSION

The functionalization of collagen membranes with Dox promoted an increase in the proliferation and differentiation of osteoblasts.

Evaluation of drug release, monomer conversion and surface properties of resin composites containing chlorhexidine-loaded mesoporous and nonporous hydroxyapatite nanocarriers

The aim of this study was to evaluate drug release, degree of conversion (DC), and surface properties of resin composites containing chlorhexidine (CHX)-loaded mesoporous (mHAP) and nonporous hydroxyapatite (HAP) nanocarrier. CHX loaded mHAP and HAP, or CHX without nanocarrier was added into the resin composite in 1% and 5% concentrations. After characterization of experimental materials with XRD, EDX, FT-IR, and SEM, the CHX release on the 1st, 7th, 30th, and 120th days were evaluated by UV-vis spectroscopy. DC, surface roughness, and surface hardness of the samples were also evaluated. The data was statistically analyzed. While mHAP groups released significantly higher CHX on the 30th day (p < .05), there was no statistically significant difference between the HAP and mHAP groups on the 120th day (p > .05). DCs of all groups were similar (p > .05). While mHAP and HAP groups containing 5% CHX showed significantly higher roughness than the other groups (p < .05), no statistically significant difference was observed between the other groups (p > .05). The 1% and 5% CHX groups without nanocarrier showed significantly lower surface hardness (p < .05). However, no statistically significant difference was observed between the other groups in terms of surface hardness (p > .05). A controlled CHX release was achieved by mHAP and HAP nanocarriers for 120 days. The nanocarrier addition up to 5% did not negatively affect the DC and the surface hardness which is one of the surface properties of the resin composites. Although the addition of 5% nanocarrier to the resin composite increased the surface roughness, while adding 1% of these nanocarriers did not change.

Nano zinc oxide-functionalized nanofibrous microspheres: A bioactive hybrid platform with antimicrobial, regenerative and hemostatic activities

Bioactive hybrid constructs are at the cutting edge of innovative biomaterials. PLA nanofibrous microspheres (NF-MS) were functionalized with zinc oxide nanoparticles (nZnO) and DDAB-modified nZnO (D-nZnO) for developing inorganic/nano-microparticulate hybrid constructs (nZnO@NF-MS and D-nZnO@NF-MS) merging antibacterial, regenerative, and haemostatic functionalities. The hybrids appeared as three-dimensional NF-MS frameworks made-up entirely of interconnecting nanofibers embedding nZnO or D-nZnO. Both systems achieved faster release of Zn²⁺ than their respective nanoparticles and D-nZnO@NF-MS exhibited significantly greater surface wettability than nZnO@NF-MS. Regarding bioactivity, D-nZnO@NF-MS displayed a significantly greater and fast-killing effect against Staphylococcus aureus. Both nZnO@NF-MS and D-nZnO@NF-MS showed controllable concentration-dependent cytotoxicity to human gingival fibroblasts (HGF) compared with pristine NF-MS. They were also more effective than pristine NF-MS in promoting migration of human gingival fibroblasts (HGF) in the in vitro wound healing assay. Although D-nZnO@NF-MS showed greater in vitro hemostatic activity than nZnO@NF-MS, (blood-clotting index 22.82 ± 0.65% vs.54.67 ±2.32%) both structures exhibited instant hemostasis (0 s) with no blood loss (0 mg) in the rat-tail cutting technique. By merging the multiple therapeutic bioactivities of D-nZnO and the 3D-structural properties of NF-MS, the innovative D-nZnO@NF-MS hybrid construct provides a versatile bioactive material platform for different biomedical applications.

Dexamethasone and Doxycycline Doped Nanoparticles Increase the Differentiation Potential of Human Bone Marrow Stem Cells

Non-resorbable polymeric nanoparticles (NPs) are proposed as an adjunctive treatment for bone regenerative strategies. The present in vitro investigation aimed to evaluate the effect of the different prototypes of bioactive NPs loaded with zinc (Zn-NPs), doxycycline (Dox-NPs) or dexamethasone (Dex-NPs) on the viability, morphology, migration, adhesion, osteoblastic differentiation, and mineralization potential of human bone marrow stem cells (hBMMSCs). Cell viability, proliferation, and differentiation were assessed using a resaruzin-based assay, cell cycle analysis, cell migration evaluation, cell cytoskeleton staining analysis, Alizarin Red S staining, and expression of the osteogenic-related genes by a real-time quantitative polymerase chain reaction (RT-qPCR). One-Way ANOVA and Tukey’s test were employed. The resazurin assay showed adequate cell viability considering all concentrations and types of NPs at 24, 48, and 72 h of culture. The cell cycle analysis revealed a regular cell cycle profile at 0.1, 1, and 10 µg/mL, whereas 100 µg/mL produced an arrest of cells in the S phase. Cells cultured with 0.1 and 1 µg/mL NP concentrations showed a similar migration capacity to the untreated group. After 21 days, mineralization was increased by all the NPs prototypes. Dox-NPs and Dex-NPs produced a generalized up-regulation of the osteogenic-related genes. Dex-NPs and Dox-NPs exhibited excellent osteogenic potential and promoted hBMMSC differentiation. Future investigations, both in vitro and in vivo, are required to confirm the suitability of these NPs for their clinical application.

Translating Material Science into Bone Regenerative Medicine Applications: State-of-The Art Methods and Protocols

In the last 20 years, bone regenerative research has experienced exponential growth thanks to the discovery of new nanomaterials and improved manufacturing technologies that have emerged in the biomedical field. This revolution demands standardization of methods employed for biomaterials characterization in order to achieve comparable, interoperable, and reproducible results. The exploited methods for characterization span from biophysics and biochemical techniques, including microscopy and spectroscopy, functional assays for biological properties, and molecular profiling. This review aims to provide scholars with a rapid handbook collecting multidisciplinary methods for bone substitute R&D and validation, getting sources from an up-to-date and comprehensive examination of the scientific landscape.

Preparation and Characterization of Doxycycline-Loaded Electrospun PLA/HAP Nanofibers as a Drug Delivery System

The present study aimed to prepare nanofibers by electrospinning in the system polylactic acid-hydroxyapatite-doxycycline (PLA-HAP-Doxy) to be used as a drug delivery vehicle. Two different routes were employed for the preparation of Doxy-containing nanofibers: Immobilization on the electrospun mat’s surface and encapsulation in the fiber structure. The nanofibers obtained by Doxy encapsulation were characterized using Fourier transform infrared (FTIR) spectroscopy, thermogravimetric (TG) and differential thermal analyses (DTA) and scanning electron microscopy (SEM). The adsorption properties of pure PLA and PLA-HAP nanofibers were investigated for solutions with different Doxy concentrations (3, 7 and 12 wt%). Moreover, the desorption properties of the active substance were tested in two different fluids, simulated body fluid (SBF) and phosphate buffer solution (PBS), to evidence the drug release properties. In vitro drug release studies were performed and different drug release kinetics were assessed to confirm the use of these nanofiber materials as efficient drug delivery vehicles. The obtained results indicate that the PLA-HAP-Doxy is a promising system for biomedical applications, the samples with 3 and 7 wt% of Doxy-loaded PLA-HAP nanofibers prepared by physical adsorption are the most acceptable membranes to provide prolonged release in PBS/SBF rather than an immediate release of Doxy.

3D printed bioinspired scaffolds integrating doxycycline nanoparticles: Customizable implants for in vivo osteoregeneration

3D printing has revolutionized pharmaceutical research, with applications encompassing tissue regeneration and drug delivery. Adopting 3D printing for pharmaceutical drug delivery personalization via nanoparticle-reinforced hydrogel scaffolds promises great regenerative potential. Herein, we engineered novel core/shell, bio-inspired, drug-loaded polymeric hydrogel scaffolds for pharmaceutically personalized drug delivery and superior osteoregeneration. Scaffolds were developed using biopolymeric blends of gelatin, polyvinyl alcohol and hyaluronic acid and integrated with composite doxycycline/hydroxyapatite/polycaprolactone nanoparticles (DX/HAp/PCL) innovatively via 3D printing. The developed scaffolds were optimized for swelling pattern and in-vitro drug release through tailoring the biphasic microstructure and wet/dry state to attain various pharmaceutical personalization platforms. Freeze-dried scaffolds with nanoparticles reinforcing the core phase (DX/HAp/PCL-LCS-FD) demonstrated favorably controlled swelling, preserved structural integrity and controlled drug release over 28 days. DX/HAp/PCL-LCS-FD featured double-ranged pore size (90.4 ± 3.9 and 196.6 ± 38.8 µm for shell and core phases, respectively), interconnected porosity and superior mechanical stiffness (74.5 ± 6.8 kPa) for osteogenic functionality. Cell spreading analysis, computed tomography and histomorphometry in a rabbit tibial model confirmed osteoconduction, bioresorption, immune tolerance and bone regenerative potential of the original scaffolds, affording complete defect healing with bone tissue. Our findings suggest that the developed platforms promise prominent local drug delivery and bone regeneration.

Engineering 3D-printed core-shell hydrogel scaffolds reinforced with hybrid hydroxyapatite/polycaprolactone nanoparticles for in vivo bone regeneration

The versatility of 3D printing has rendered it an indispensable tool for the fabrication of composite hydrogel scaffolds, offering bone biomimetic features through inorganic and biopolymeric components as promising platforms for osteoregeneration. In this work, extrusion-based 3D printing was employed for the realization of osteoconductive composite biopolymer-based hydrogel scaffolds reinforced with hybrid bioactive hydroxyapatite/polycaprolactone nanoparticles (HAp/PCL NPs) for osteoregeneration. The printing technique was optimized for ink printability and viscosity and crosslinking parameters, where a biopolymeric blend of gelatin, polyvinyl alcohol and hyaluronic acid was developed as innovative plain polymeric ink (PPI). Scaffolds were fabricated by 3D printing adopting a biphasic core/shell geometry, where the core phase of the scaffolds was reinforced with HAp/PCL NPs; the scaffolds were then freeze-dried. Novel composite freeze-dried, loaded-core scaffolds, HAp/PCL NPs-LCS-FD exhibited controlled swelling and maintained structural integrity for 28 days. The developed HAp/PCL NPs-LCS-FD also demonstrated double-ranged pore size, interconnected porosity and efficient mechanical stiffness and strength, favorable for osteoconductive actions. Cell infiltration studies, computed tomography and histomorphometry demonstrated that HAp/PCL NPs-LCS-FD afforded osteoconduction, biodegradation, biocompatibility and bone healing in rabbit tibial model, acting as a template for new bone formation. Our findings suggest that HAp/PCL NPs-LCS-FD could offer prominent bone regeneration and could be involved in various bone defects.