Dose-dependent osteogenic effect of octacalcium phosphate on mouse bone marrow stromal cells

Macrophage Polarization Related to Crystal Phases of Calcium Phosphate Biomaterials

Calcium phosphate (CaP) materials influence macrophage polarization during bone healing. However, the effect of the crystal phase of CaP materials on the immune response of bone remains unclear. In this study, the effect of the crystal phases of CaP materials on the regulation of macrophage polarization was investigated. Human THP-1 cells and mouse RAW 264 cells were cultured with octacalcium phosphate (OCP) and its hydrolyzed form Ca-deficient hydroxyapatite to assess the expression of pro-inflammatory M1 and anti-inflammatory M2 macrophage-related genes. OCP inhibited the excessive inflammatory response and switched macrophages to the anti-inflammatory M2 phenotype, which promoted the expression of the interleukin 10 (IL10) gene. In contrast, HL stimulated an excessive inflammatory response by promoting the expression of pro-inflammatory M1 macrophage-related genes. To observe changes in the microenvironment induced by OCP and HL, inorganic phosphate (Pi) and calcium ion (Ca²⁺) concentrations and pH value in the medium were measured. The expression of the pro-inflammatory M1 macrophage-related genes (tumor necrosis factor alpha (TNFα) and interlukin 1beta (IL1β)) was closely related to the increase in ion concentration caused by the increase in the CaP dose. Together, these results suggest that the microenvironment caused by the crystal phase of CaP materials may be involved in the immune-regulation capacity of CaP materials.

Bone Tissue Response to Different Grown Crystal Batches of Octacalcium Phosphate in Rat Long Bone Intramedullary Canal Area

The microstructure of biomaterials influences the cellular and biological responses in the bone. Octacalcium phosphate (OCP) exhibits higher biodegradability and osteoconductivity than hydroxyapatite (HA) during the conversion process from OCP to HA. However, the effect of the microstructure of OCP crystals on long tubular bones has not been clarified. In this study, two types of OCPs with different microstructures, fine-OCP (F-OCP) and coarse-OCP (C-OCP), were implanted in rat tibia for 4 weeks. F-OCP promoted cortical bone regeneration compared with C-OCP. The osteoclasts appearance was significantly higher in the C-OCP group than in the control group (defect only) at 1-week post-implantation. To investigate whether the solubility equilibrium depends on the different particle sizes of OCPs, Nano-OCP, which consisted of nanometer-sized OCPs, was prepared. The degree of supersaturation (DS) tended to decrease modestly in the order of C-OCP, F-OCP, and Nano-OCP with respect to HA and OCP in Tris-HCl buffer. F-OCP showed a higher phosphate ion concentration and lower calcium ion concentration after immersion in the buffer than C-OCP. The crystal structures of both OCPs tended to be converted to HA by rat abdominal implantation. These results suggest that differences in the microstructure of OCPs may affect osteoclastogenesis and result in osteoconductivity of this material in long tubular bone by altering dissolution behavior.

Magnetic 3D scaffolds for tissue engineering applications: bioactive glass (45S5) coated with iron-loaded hydroxyapatite nanoparticles

Magnetic 45S5 bioactive glass (BG) based scaffolds covered with iron-loaded hydroxyapatite (Fe-HA-BG) nanoparticles were obtained and its cytotoxicity investigated. Fe-HA nanoparticles were synthesized by a wet chemical method involving the simultaneous addition of Fe²⁺/Fe³⁺ions. BG based scaffolds were prepared by the foam replica procedure and covered with Fe-HA by dip-coating. Fe-HA-BG magnetic saturation values of 0.049 emu g^-1and a very low remanent magnetization of 0.01 emu g^-1were observed. The mineralization assay in simulated body fluid following Kokubo's protocol indicated that Fe-HA-BG scaffolds exhibited improved hydroxyapatite formation in comparison to uncoated scaffolds at shorter immersion times. The biocompatibility of the materialin vitrowas assessed using human osteoblast-like MG-63 cell cultures and mouse bone marrow-derived stroma cell line ST-2. Overall, the results herein discussed suggest that magnetic Fe-HA coatings seem to enhance the biological performance of 45S5 BG based scaffolds. Thus, this magnetic Fe-HA coated scaffold is an interesting system for bone tissue engineering applications and warrant further investigation.

Stem Cell-Friendly Scaffold Biomaterials: Applications for Bone Tissue Engineering and Regenerative Medicine

Bone is a dynamic organ with high regenerative potential and provides essential biological functions in the body, such as providing body mobility and protection of internal organs, regulating hematopoietic cell homeostasis, and serving as important mineral reservoir. Bone defects, which can be caused by trauma, cancer and bone disorders, pose formidable public health burdens. Even though autologous bone grafts, allografts, or xenografts have been used clinically, repairing large bone defects remains as a significant clinical challenge. Bone tissue engineering (BTE) emerged as a promising solution to overcome the limitations of autografts and allografts. Ideal bone tissue engineering is to induce bone regeneration through the synergistic integration of biomaterial scaffolds, bone progenitor cells, and bone-forming factors. Successful stem cell-based BTE requires a combination of abundant mesenchymal progenitors with osteogenic potential, suitable biofactors to drive osteogenic differentiation, and cell-friendly scaffold biomaterials. Thus, the crux of BTE lies within the use of cell-friendly biomaterials as scaffolds to overcome extensive bone defects. In this review, we focus on the biocompatibility and cell-friendly features of commonly used scaffold materials, including inorganic compound-based ceramics, natural polymers, synthetic polymers, decellularized extracellular matrix, and in many cases, composite scaffolds using the above existing biomaterials. It is conceivable that combinations of bioactive materials, progenitor cells, growth factors, functionalization techniques, and biomimetic scaffold designs, along with 3D bioprinting technology, will unleash a new era of complex BTE scaffolds tailored to patient-specific applications.

Segmental Bone Reconstruction by Octacalcium Phosphate Collagen Composites with Teriparatide

Octacalcium phosphate and collagen composite (OCPcol) demonstrated superior bone regeneration and has been commercialized recently in Japan. Teriparatide (TPTD) is a bioactive recombinant form of parathyroid hormone that is approved for osteoporosis treatment. Because mandibular bone reconstruction after segmental resection is a key clinical problem, it was examined whether single-dose local administration of OCPcol with TPTD can affect recovery after this procedure. OCPcol was prepared, and a commercially available hydroxyapatite and collagen composite (HAPcol) was used as a control. A 15 mm length segmental bone defect was made in the mandibular region of male beagle dogs. The experimental animals were divided in four groups. OCPcol treated with TPTD (OCPcol + TPTD), OCPcol, HAPcol treated with TPTD (HAPcol + TPTD), or HAPcol was implanted into the defect. The radiopaque areas of the implanted site were measured and statistically analyzed, and histological examination was performed after 6 months. The value of radiopaque area in total region of OCPcol + TPTD was highest (90.8 ± 7.3 mm²), followed in order by OCPcol (49.3 ± 21.8 mm²), HAPcol + TPTD (10.6 ± 2.3 mm²), and HAPcol (6.4 ± 2.3 mm²), and that of OCPcol + TPTD was significantly higher than that of HAPcol + TPTD or HAPcol. All segmented mandibles of OCPcol + TPTD and a part of those of OCPcol were bridged with newly formed bone, whereas no bone bridges were observed in HAPcol + TPTD or HAPcol. These results suggested that OCPcol treated with TPTD enabled bone reconstruction after segmental mandibular resection more than other three groups.

Clinical study of octacalcium phosphate and collagen composite in oral and maxillofacial surgery

Octacalcium phosphate and its collagen composite have been recognized as bone substitute materials possessing osteoconductivity and biodegradation properties. We evaluated the effectiveness of octacalcium phosphate and its collagen composite used for bone augmentation in major oral and maxillofacial surgeries in a clinical trial. Octacalcium phosphate and its collagen composite were used in cases of sinus floor elevation in 1- and 2-stage, socket preservation, cyst, and alveolar cleft procedures. A total of 60 patients were evaluated for effectiveness after the implantation of octacalcium phosphate and its collagen composite. Although sinus floor elevation in 1-stage, cyst, and alveolar cleft cases met the criteria for the judgment of success, sinus floor elevation in 2-stage and socket preservation groups did not meet the criteria in the initial evaluation. However, an additional evaluation for reconfirmation revealed the effectiveness of octacalcium phosphate and its collagen composite in those groups, and all evaluation results ultimately indicated the success of this clinical trial. Therefore, this clinical trial suggested that application of octacalcium phosphate and its collagen composite for oral and maxillofacial surgery was safe and effective and that octacalcium phosphate and its collagen composite could be a bone substitute candidate instead of autologous bone.

Vascularized Bone-Mimetic Hydrogel Constructs by 3D Bioprinting to Promote Osteogenesis and Angiogenesis

Bone is a highly vascularized tissue with a unique and complex structure. Long bone consists of a peripheral cortical shell containing a network of channels for vascular penetration and an inner highly vascularized bone marrow space. Bioprinting is a powerful tool to enable rapid and precise spatial patterning of cells and biomaterials. Here we developed a two-step digital light processing technique to fabricate a bone-mimetic 3D hydrogel construct based on octacalcium phosphate (OCP), spheroids of human umbilical vein endothelial cells (HUVEC), and gelatin methacrylate (GelMA) hydrogels. The bone-mimetic 3D hydrogel construct was designed to consist of a peripheral OCP-containing GelMA ring to mimic the cortical shell, and a central GelMA ring containing HUVEC spheroids to mimic the bone marrow space. We further demonstrate that OCP, which is evenly embedded in the GelMA, stimulates the osteoblastic differentiation of mesenchymal stem cells. We refined the design of a spheroid culture device to facilitate the rapid formation of a large number of HUVEC spheroids, which were embedded into different concentrations of GelMA hydrogels. It is shown that the concentration of GelMA modulates the extent of formation of the capillary-like structures originating from the HUVEC spheroids. This cell-loaded hydrogel-based bone construct with a biomimetic dual ring structure can be potentially used for bone tissue engineering.

Efficacy of Octacalcium Phosphate Collagen Composite for Titanium Dental Implants in Dogs

Background: Previous studies showed that octacalcium (OCP) collagen composite (OCP/Col) can be used to repair human jaw bone defects without any associated abnormalities. The present study investigated whether OCP/Col could be applied to dental implant treatment using a dog tooth extraction socket model. Methods: The premolars of dogs were extracted; each extraction socket was extended, and titanium dental implants were placed in each socket. OCP/Col was inserted in the space around a titanium dental implant. Autologous bone was used to fill the other sockets, while the untreated socket (i.e., no bone substitute material) served as a control. Three months after the operation, these specimens were analyzed for the osseointegration of each bone substitute material with the surface of the titanium dental implant. Results: In histomorphometric analyses, the peri-implant bone areas (BA%) and bone-implant contact (BIC%) were measured. There was no difference in BA% or BIC% between OCP/Col and autologous bone. Conclusion: These results suggested that OCP/Col could be used for implant treatment as a bone substitute.

Clinical safety and efficacy of implantation of octacalcium phosphate collagen composites in tooth extraction sockets and cyst holes

It was demonstrated that octacalcium phosphate collagen composite achieved notable bone regeneration in bone defects in preclinical studies. On the basis of the research results, an investigator-initiated exploratory clinical trial was conducted after approval from a local Institutional Review Board. This clinical study was performed as a single-arm non-randomized intervention study. Octacalcium phosphate collagen composite was implanted into a total of 10 cases of alveolar bone defects after tooth extractions and cystectomy. Safety assessment was performed in terms of the clinical course and several consecutive laboratory examinations, and sequential radiographs were used for efficacy assessment. All participants uneventfully completed the clinical trial without major problems in their general condition. Postoperative wound swelling was observed, as also commonly seen in tooth extraction or cystectomy. Although no serious liver dysfunction, renal dysfunction, electrolyte imbalance, or abnormal urinalysis results were recognized, the number of white blood cells and C-reactive protein level temporarily increased after the operation. An increase in radiopacity in the octacalcium phosphate collagen composite–implanted site was observed in all cases. Finally, the border between the original bone and the octacalcium phosphate collagen composite–implanted site became indistinguishable. These results suggest that octacalcium phosphate collagen composite could be utilized safely in clinical situations in the future.

[The impact of octacalcium phosphate on the dynamics of bone matrix formation in experimental bone defects]

The aim of the study was to assess the interaction of of octacalcium phosphate (OCP) with bone matrix and cells and its impact on the process of bone generation. The survey was conducted on animal model: critical hipbone defect was created in 12 230-250 g Wister rats. The animals were then divided in two groups. In group 1 (6 animals) defect was left to heal under blood clot and in group 2 (6 animals) it was filled with OCP. Three animals with no defect served as a control group. It was showed significant (p<0.05) increase of the area of the newly formed bone tissue and its direct correlation with duration of observation.

Evaluation of bioactivity of octacalcium phosphate using osteoblastic cell aggregates on a spheroid culture device

Much attention has been paid to three-dimensional cell culture systems in the field of regenerative medicine, since three-dimensional cellular aggregates, or spheroids, are thought to better mimic the in vivo microenvironments compared to conventional monolayer cultured cells. Synthetic calcium phosphate (CaP) materials are widely used as bone substitute materials in orthopedic and dental surgeries. Here we have developed a technique for constructing a hybrid spheroid consisting of mesenchymal stem cells (MSCs) and synthetic CaP materials using a spheroid culture device. We found that the device is able to generate uniform-sized CaP/cell hybrid spheroids rapidly and easily. The results showed that the extent of osteoblastic differentiation from MSCs was different when cells were grown on octacalcium phosphate (OCP), hydroxyapatite (HA), or β-tricalcium phosphate (β-TCP). OCP showed the greatest ability to increase the alkaline phosphatase activity of the spheroid cells. The results suggest that the spheroids with incorporated OCP may be an effective implantable hybrid consisting of scaffold material and cells for bone regeneration. It is also possible that this CaP-cell spheroid system may be used as an in vitro method for assessing the osteogenic induction ability of CaP materials.

Polymer-ceramic spiral structured scaffolds for bone tissue engineering: effect of hydroxyapatite composition on human fetal osteoblasts

For successful bone tissue engineering, a scaffold needs to be osteoconductive, porous, and biodegradable, thus able to support attachment and proliferation of bone cells and guide bone formation. Recently, hydroxyapatites (HA), a major inorganic component of natural bone, and biodegrade polymers have drawn much attention as bone scaffolds. The present study was designed to investigate whether the bone regenerative properties of nano-HA/polycaprolactone (PCL) spiral scaffolds are augmented in an HA dose dependent manner, thereby establishing a suitable composition as a bone formation material. Nano-HA/PCL spiral scaffolds were prepared with different weight ratios of HA and PCL, while porosity was introduced by a modified salt leaching technique. Human fetal osteoblasts (hFOBs) were cultured on the nano-HA/PCL spiral scaffolds up to 14 days. Cellular responses in terms of cell adhesion, viability, proliferation, differentiation, and the expression of bone-related genes were investigated. These scaffolds supported hFOBs adhesion, viability and proliferation. Cell proliferation trend was quite similar on polymer-ceramic and neat polymer spiral scaffolds on days 1, 7, and 14. However, the significantly increased amount of alkaline phosphatase (ALP) activity and mineralized matrix synthesis was evident on the nano-HA/PCL spiral scaffolds. The HA composition in the scaffolds showed a significant effect on ALP and mineralization. Bone phenotypic markers such as bone sialoprotein (BSP), osteonectin (ON), osteocalcin (OC), and type I collagen (Col-1) were semi-quantitatively estimated by reverse transcriptase polymerase chain reaction analysis. All of these results suggested the osteoconductive characteristics of HA/PCL nanocomposite and cell maturation were HA dose dependent. For instance, HA∶PCL = 1∶4 group showed significantly higher ALP mineralization and elevated levels of BSP, ON, OC and Col-I expression as compared other lower or higher ceramic ratios. Amongst the different nano-HA/PCL spiral scaffolds, the 1∶4 weight ratio of HA and PCL is shown to be the most optimal composition for bone tissue regeneration.

First clinical application of octacalcium phosphate collagen composite in human bone defect

We have previously demonstrated that octacalcium phosphate (OCP) collagen composite (OCP/collagen) promotes bone regeneration in a critical-sized bone defect of a rodent or canine model. This study was designed to investigate the bone regeneration of OCP/collagen in human bone defect as a first clinical trial. Two patients who had a radicular cyst or apical periodontitis consented to participate in our clinical study, and OCP/collagen was implanted into the defects after operation. Radiographic examination showed effective bone healing in each bone defect at 3 or 6 months. Likewise, computed tomography value significantly increased after implantation. Postoperative wound healing was uneventful, and neither infection nor allergic reaction against OCP/collagen was observed for the entire period. This study demonstrated that OCP/collagen would be safely used and enhanced bone regeneration in human bone defects. To reinforce the efficacy of OCP/collagen as a bone substitute material, it should be compared with other suitable comparators in the future.

Bone regeneration in rat cranium critical-size defects induced by Cementum Protein 1 (CEMP1)

Gene therapy approaches to bone and periodontal tissue engineering are being widely explored. While localized delivery of osteogenic factors like BMPs is attractive for promotion of bone regeneration; method of delivery, dosage and side effects could limit this approach. A novel protein, Cementum Protein 1 (CEMP1), has recently been shown to promote regeneration of periodontal tissues. In order to address the possibility that CEMP1 can be used to regenerate other types of bone, experiments were designed to test the effect of hrCEMP1 in the repair/regeneration of a rat calvaria critical-size defect. Histological and microcomputed tomography (µCT) analyses of the calvaria defect sites treated with CEMP1 showed that after 16 weeks, hrCEMP1 is able to induce 97% regeneration of the defect. Furthermore, the density and characteristics of the new mineralized tissues were normal for bone. This study demonstrates that hrCEMP1 stimulates bone formation and regeneration and has therapeutic potential for the treatment of bone defects and regeneration of mineralized tissues.

Recent developments of functional scaffolds for craniomaxillofacial bone tissue engineering applications

Autogenous bone grafting remains a gold standard for the reconstruction critical-sized bone defects in the craniomaxillofacial region. Nevertheless, this graft procedure has several disadvantages such as restricted availability, donor-site morbidity, and limitations in regard to fully restoring the complicated three-dimensional structures in the craniomaxillofacial bone. The ultimate goal of craniomaxillofacial bone reconstruction is the regeneration of the physiological bone that simultaneously fulfills both morphological and functional restorations. Developments of tissue engineering in the last two decades have brought such a goal closer to reality. In bone tissue engineering, the scaffolds are fundamental, elemental and mesenchymal stem cells/osteoprogenitor cells and bioactive factors. A variety of scaffolds have been developed and used as spacemakers, biodegradable bone substitutes for transplanting to the new bone, matrices of drug delivery system, or supporting structures enhancing adhesion, proliferation, and matrix production of seeded cells according to the circumstances of the bone defects. However, scaffolds to be clinically completely satisfied have not been developed yet. Development of more functional scaffolds is required to be applied widely to cranio-maxillofacial bone defects. This paper reviews recent trends of scaffolds for crania-maxillofacial bone tissue engineering, including our studies.

Detection of osteogenic differentiation by differential mineralized matrix production in mesenchymal stromal cells by Raman spectroscopy

Mesenchymal stromal cells (MSCs) hold great potential in skeletal tissue engineering and regenerative medicine. However, conventional methods that are used in molecular biology to evaluate osteogenic differentiation of MSCs require a relatively large amount of cells. Cell lysis and cell fixation are also required and all these steps are time-consuming. Therefore, it is imperative to develop a facile technique which can provide real-time information with high sensitivity and selectivity to detect the osteogenic maturation of MSCs. In this study, we use Raman spectroscopy as a biosensor to monitor the production of mineralized matrices during osteogenic induction of MSCs. In summary, Raman spectroscopy is an excellent biosensor to detect the extent of maturation level during MSCs-osteoblast differentiation with a non-disruptive, real-time and label free manner. We expect that this study will promote further investigation of stem cell research and clinical applications.

Synthetic octacalcium phosphate: a possible carrier for mesenchymal stem cells in bone regeneration

The present paper reviews biomaterial studies of synthetic octacalcium phosphate (OCP) as a scaffold of osteoblastic cells. OCP crystals have been suggested to be one of precursor phases in hydroxyapatite (HA) crystal formation in bone and tooth. The recent intensive biomaterials and tissue engineering studies using synthetic OCP disclosed the potential function of OCP as a bioactive material as well as synthetic HA materials due to its highly osteoconductive and biodegradable properties. In vitro studies showed that OCP crystals exhibit a positive effect on osteoblastic cell differentiation. In vivo studies confirmed that the materials of OCP in a granule forms and OCP-based composite materials with natural polymers, such as gelatin and collagen, enhance bone regeneration if implanted in various model bone defects with critical-sized diameters, defined as a defect which does not heal spontaneously throughout the lifetime of the animals. One of particular characteristics of OCP, found as a mechanism to enhance bone regeneration in vivo, is a process of progressive conversion from OCP to HA at physiological conditions. The OCP-HA conversion is accompanied by progressive physicochemical changes of the material properties, which affects the tissue reaction around the crystals where osteoblastic cells are encountered. Mesenchymal stem cells (MSCs) seeded in an OCP-based material enhanced bone regeneration in the rat critical-sized calvaria defect more than that by the material alone. The overall results reveal that OCP crystals have an effect on osteoblastic cell differentiation including the differentiation of MSCs in vivo. The evidence collected experimentally in the laboratory was presented.

Granule size-dependent bone regenerative capacity of octacalcium phosphate in collagen matrix

The present study was designed to determine whether the osteoconductivity of octacalcium phosphate-collagen (OCP/Col) composite can be improved by controlling the granule size of OCP. The granules of synthetic OCP, with diameters in the range of 53 to 300, 300 to 500, and 500 to 1000 μm, were used as an inorganic source of composite materials mixed with atelo-Col. After vacuum dehydrothemal treatment, OCP/Col disks were implanted into critical-sized calvaria defects in Wistar rats for 4, 8, and 12 weeks and examined radiographically, histologically, histomorphometrically, and histochemically. The materials were characterized according to mercury intrusion porosimetry and scanning electron microscopy. X-ray diffraction was performed before and after implantation. The dissolution of OCP crystals in a Col matrix was determined by immersing OCP/Col disks in a culture medium. OCP/Col had a constant pore size (~30 μm) regardless of OCP granule size. OCP in the Col matrix tended to convert to hydroxyapatite (HA) during the implantation. OCP/Col with the smallest granules of OCP enhances both bone regeneration and biodegradation the most through tartrate-resistant acid phosphatase (TRAP)-positive osteoclastic cellular resorption of OCP granules. The smallest OCP granules in the Col matrix showed the highest dissolution and had the greatest potential to form HA. The results indicated that the size of the included OCP granules can controll the osteoconductivity of OCP/Col. The overall results suggest that the physicochemical property of OCP crystals is a factor that determines the bone regenerative capacity of OCP/Col in critical-sized calvaria large bone defects in rats.