Octacalcium Phosphate Bone Substitute (Bontree®): From Basic Research to Clinical Case Study

Octacalcium phosphate with incorporated terephthalate ion derivatives: novel guest molecules and unique fluorescence properties

Octacalcium phosphate (OCP), an inorganic compound with a layered structure that can incorporate various carboxylic acids, exhibits fluorescence when aromatic carboxylate ions are present in the interlayers. However, the incorporation of carboxylate ions into OCP involves molecular selectivity, and the synthesis of novel OCP materials with incorporated terephthalate ion derivatives is particularly challenging. In this study, we incorporated 4-(carboxymethyl)benzoate and 1,4-phenylenediacetate ions into OCP for the first time and investigated the resulting fluorescence properties. The relationship between the (100) interplanar spacing and size of the incorporated dicarboxylate ions revealed that 4-(carboxymethyl)benzoate ions have a relaxed structure in the OCP interlayers, whereas the structure of the 1,4-phenylenediacetate ions is elongated by approximately 10% relative to that of the stable conformation. OCP with incorporated 1,4-phenylenediacetate ions showed blue fluorescence at 286 nm under 254 nm excitation. In contrast, distinct from previously reported fluorescent OCPs, OCP with incorporated 4-(carboxymethyl)benzoate ions exhibited two-colour fluorescence, with pink emission under 254 nm excitation and blue emission under 312 and 365 nm excitation. This OCP material exhibiting fluorescence at two wavelengths in the visible-light range offers new possibilities for practical applications. In particular, these unique fluorescence characteristics combined with the excellent biological properties of OCP can be exploited to develop novel biofriendly fluorescent probes. These findings contribute to an improved understanding of fundamental calcium phosphate chemistry and should encourage further research on functional OCP materials.

Comparative Analysis of Bone Regeneration According to Particle Type and Barrier Membrane for Octacalcium Phosphate Grafted into Rabbit Calvarial Defects

This animal study was aimed to evaluate the efficacy of new bone formation and volume maintenance according to the particle type and the collagen membrane function for grafted octacalcium phosphate (OCP) in rabbit calvarial defects. The synthetic bone substitutes were prepared in powder form with 90% OCP and granular form with 76% OCP, respectively. The calvarial defects were divided into four groups according to the particle type and the membrane application. All specimens were acquired 2 weeks (n = 5) and 8 weeks (n = 5) after surgery. According to the micro-CT results, the new bone volume increased at 2 weeks in the 76% OCP groups compared to the 90% OCP groups, and the bone volume ratio was significantly lower in the 90% OCP group after 2 weeks. The histomorphometric analysis results indicated that the new bone area and its ratio in all experimental groups were increased at 8 weeks except for the group with 90% OCP without a membrane. Furthermore, the residual bone graft area and its ratio in the 90% OCP groups were decreased at 8 weeks. In conclusion, all types of OCP could be applied as biocompatible bone graft materials regardless of its density and membrane application. Neither the OCP concentration nor the membrane application had a significant effect on new bone formation in the defect area, but the higher the OCP concentration, the less graft volume maintenance was needed.

Octacalcium phosphate, a promising bone substitute material: a narrative review

Biomaterials have been used to supplement and restore function and structure by replacing or restoring parts of damaged tissues and organs. In ancient times, the medical use of biomaterials was limited owing to infection during surgery and poor surgical techniques. However, in modern times, the medical applications of biomaterials are diversifying owing to great developments in material science and medical technology. In this paper, we introduce biomaterials, focusing on calcium phosphate ceramics, including octacalcium phosphate, which has recently attracted attention as a bone graft material.

Gear-shaped carbonate apatite granules with a hexagonal macropore for rapid bone regeneration

Synthetic bone grafts are in high demand owing to increased age-related bone disorders in the global aging population. Here, we report fabrication of gear-shaped granules (G-GRNs) for rapid bone healing. G-GRNs possessed six protrusions and a hexagonal macropore in the granular center. These were composed of carbonate apatite, i.e., bone mineral, microspheres with ∼1-μm micropores in the spaces between the microspheres. G-GRNs formed new bone and blood vessels (both on the granular surface and within the macropores) 4 weeks after implantation in the rabbit femur defects. The formed bone structure was similar to that of cancellous bone. The bone percentage in the defect recovered to that in a normal rabbit femur at week-4 post-implantation, and the bone percentage remained constant for the following 8 weeks. Throughout the entire period, the bone percentage in the G-GRN-implanted group was ∼10% higher than that of the group implanted with conventional carbonate apatite granules. Furthermore, a portion of the G-GRNs resorbed at week-4, and resorption continued for the following 8 weeks. Thus, G-GRNs are involved in bone remodeling and are gradually replaced with new bone while maintaining a suitable bone level. These findings provide a basis for the design and fabrication of synthetic bone grafts for achieving rapid bone regeneration.

Synthesis of Octacalcium Phosphate Containing Glutarate Ions with a High Incorporation Fraction

Octacalcium phosphate (OCP) has received considerable attention in the field of ceramic biomaterials as an advanced functional material. It exhibits a layered structure composed of apatitic and hydrated layers and can incorporate various dicarboxylate ions into the hydrated layer. Saturated dicarboxylic acids (HOOC(CH2)nCOOH) with an odd number of methylene groups (-CH2-) exhibit lower incorporation fractions than those with an even number of methylene groups, possibly owing to a compositional dependence on the synthetic method. In this study, calcium carbonate, phosphoric acid, and various amounts of glutaric acid were used to produce glutarate-ion-incorporated OCP by a wet chemical method, which is different from the conventional synthetic strategy. While utilising 1-20 mmol of glutaric acid during synthesis did not produce the desired product, using 25 mmol of glutaric acid resulted in the formation of single-phase glutarate-ion-incorporated OCP with a Ca/P molar ratio of 1.57 and a 90% incorporation fraction of glutarate ions. This glutarate-ion-incorporation fraction is significantly higher than that reported in the previous studies (35%). Thus, the synthetic procedure proposed herein was able to produce single-phase OCP containing glutarate ions with a high incorporation fraction. Our findings can contribute to development of novel functional ceramic biomaterials in the future.

Acceleration of bone formation by octacalcium phosphate composite in a rat tibia critical-sized defect

Background

The osteogenic capabilities and biodegradability of octacalcium phosphate (OCP) composites make them unique. Despite the excellent characteristics of OCP, their use is limited due to handling difficulties. In this study, we aimed to evaluate and compare three types of OCPs (cemented OCP (C-OCP), C-OCP with collagen (OCP/Col), and synthetic OCP (S-OCP) with alginate (OCP/Alg)) versus commercially available β-tricalcium phosphate (β-TCP) regarding their potential to accelerate bone formation in defective rat tibias.

Methods

The specimens with OCP composite were manufactured into 5 ​mm cubes and inserted into the segmental defects of rat tibias fixed with an external fixator. In addition, 3 ​mm-hole defects in rat tibias were evaluated to compare the graft material properties in different clinical situations. Serial X-ray studies were evaluated weekly and the tibias were harvested at postoperative 6 weeks or 8 weeks for radiologic evaluation. Histological and histomorphometric analyses were performed to evaluate the acceleration of bone formation.

Results

In the critical-defect model, OCP/Alg showed bone bridges between segmentally resected bone ends that were comparable to those of β-TCP. However, differences were observed in the residual graft materials. Most β-TCP was maintained until 8 weeks postoperatively; however, OCP/Alg was more biodegradable. In addition calcification in the β-TCP occurred at the directly contacted area between graft particles and bony ingrowth was observed in the region adjacent resected surface of tibia. In contrast, no direct bony ingrowth was observed in OCP-based materials, but osteogenesis induced from resected surface of tibia was more active. In the hole-defect model, OCP/Col accelerated bone formation. β-TCP and OCP/Alg showed similar patterns with relatively higher biodegradability. In histology, among the OCP-based materials, directly contacted new bone was formed only in OCP/Alg group. The new bone formation in the periphery area of graft materials was much more active in the OCP-based materials, and the newly formed bone showed a thicker trabecular and more mature appearance than the β-TCP group.

Conclusions

In this study, OCP/Alg was equivalent to β-TCP in the acceleration of bone formation with better biodegradability appropriate for clinical situations in different circumstances. Our OCP/Col composite showed fast degradation, which makes it unsuitable for use in mechanical stress conditions in clinical orthopedic settings.

The Translational Potential of this Article

In our research, we compared our various manufactured OCP composites to commercially available β-TCP in critical-defect rat tibia model. OCP/Col showed acceleration in hole-defect model as previous studies in dental field but in our critical-sized defect model it resorbed fast without acceleration of bony union. OCP/Alg showed matched results compared to β-TCP and relatively fast resorption so we showed market value in special clinical indication depending on treatment strategy. This is the first OCP composite study in orthopaedics with animal critical-sized tibia bone study and further study should be considered for clinical application based on this study.

Calcium Orthophosphate (CaPO4)-Based Bioceramics: Preparation, Properties, and Applications

Various types of materials have been traditionally used to restore damaged bones. In the late 1960s, a strong interest was raised in studying ceramics as potential bone grafts due to their biomechanical properties. A short time later, such synthetic biomaterials were called bioceramics. Bioceramics can be prepared from diverse inorganic substances, but this review is limited to calcium orthophosphate (CaPO4)-based formulations only, due to its chemical similarity to mammalian bones and teeth. During the past 50 years, there have been a number of important achievements in this field. Namely, after the initial development of bioceramics that was just tolerated in the physiological environment, an emphasis was shifted towards the formulations able to form direct chemical bonds with the adjacent bones. Afterwards, by the structural and compositional controls, it became possible to choose whether the CaPO4-based implants would remain biologically stable once incorporated into the skeletal structure or whether they would be resorbed over time. At the turn of the millennium, a new concept of regenerative bioceramics was developed, and such formulations became an integrated part of the tissue engineering approach. Now, CaPO4-based scaffolds are designed to induce bone formation and vascularization. These scaffolds are usually porous and harbor various biomolecules and/or cells. Therefore, current biomedical applications of CaPO4-based bioceramics include artificial bone grafts, bone augmentations, maxillofacial reconstruction, spinal fusion, and periodontal disease repairs, as well as bone fillers after tumor surgery. Prospective future applications comprise drug delivery and tissue engineering purposes because CaPO4 appear to be promising carriers of growth factors, bioactive peptides, and various types of cells.

Effects of Scaffold Shape on Bone Regeneration: Tiny Shape Differences Affect the Entire System

Although studies on scaffolds for tissue generation have mainly focused on the chemical composition and pore structure, the effects of scaffold shape have been overlooked. Scaffold shape determines the scaffold surface area (SA) at the single-scaffold level (i.e., microscopic effects), although it also affects the amount of interscaffold space in the tissue defect at the whole-system level (i.e., macroscopic effects). To clarify these microscopic and macroscopic effects, this study reports the osteogenesis abilities of three types of carbonate apatite granular scaffolds with different shapes, namely, irregularly shaped dense granules (DGs) and two types of honeycomb granules (HCGs) with seven hexagonal channels (∼255 μm in length between opposite sides). The HCGs possessed either 12 protuberances (∼75 μm in length) or no protuberances. Protuberances increased the SA of each granule by 3.24 mm2 while also widening interscaffold spaces and increasing the space percentage in the defect by ∼7.6%. Interscaffold spaces were lower in DGs than HCGs. On DGs, new bone formed only on the surface, whereas on HCGs, bone simultaneously formed on the surface and in intrascaffold channels. Interestingly, HCGs without protuberances formed approximately 30% more new bone than those with protuberances. Thus, even tiny protuberances on the scaffold surface can affect the percentage of interscaffold space, thereby exerting dominant effects on osteogenesis. Our findings demonstrate that bone regeneration can be improved by considering macroscopic shape effects beyond the microscopic effects of the scaffold.

Bone Tissue Engineering in the Treatment of Bone Defects

Bones play an important role in maintaining exercise and protecting organs. Bone defect, as a common orthopedic disease in clinics, can cause tremendous damage with long treatment cycles. Therefore, the treatment of bone defect remains as one of the main challenges in clinical practice. Today, with increased incidence of bone disease in the aging population, demand for bone repair material is high. At present, the method of clinical treatment for bone defects including non-invasive therapy and invasive therapy. Surgical treatment is the most effective way to treat bone defects, such as using bone grafts, Masquelet technique, Ilizarov technique etc. In recent years, the rapid development of tissue engineering technology provides a new treatment strategy for bone repair. This review paper introduces the current situation and challenges of clinical treatment of bone defect repair in detail. The advantages and disadvantages of bone tissue engineering scaffolds are comprehensively discussed from the aspect of material, preparation technology, and function of bone tissue engineering scaffolds. This paper also summarizes the 3D printing technology based on computer technology, aiming at designing personalized artificial scaffolds that can accurately fit bone defects.

Radiographic and Histomorphometric Evaluation of Sinus Floor Augmentation Using Biomimetic Octacalcium Phosphate Alloplasts: A Prospective Pilot Study

This prospective single-arm clinical study aimed to radiographically and histomorphometrically evaluate the efficacy of the lateral approach for sinus floor elevation (LSFE) using biomimetic octacalcium phosphate (OCP) synthetic bone graft (Bontree^®). LSFE using Bontree^® was performed on 10 patients (15 implant placement sites) willing to undergo implant surgery, followed by implant placements after 6 months of the healing period. The vertical bone height (VBH) and Hounsfield unit (HU) values at each implant placement site were evaluated radiographically using cone-beam computed tomography at baseline immediately after surgery (T1) and 6 months after surgery (T2). A histomorphometric evaluation of the bone core biopsy specimen was also performed. The mean VBH and HU changes at all sites included a decrease by 0.91 mm and a statistically significant increase by 431.86, respectively, from T1 to T2. The mean ratio of the newly formed bone (23.34% ± 10.63%) was greater than that of the residual bone graft (19.09% ± 8.74%), indicating that Bontree^® is effective for new bone formation. This pilot study suggests that Bontree^® is a promising bone substitute for LSFE.

Preparation of antimicrobial calcium phosphate/protamine composite powders with fluoride ions using octacalcium phosphate

Calcium phosphates are key biomaterials in dental treatment and bone regeneration. Biomaterials must exhibit antibacterial properties to prevent microbial infection in implantation frameworks. Previously, we developed various types of calcium phosphate powders (amorphous calcium phosphate, octacalcium phosphate (OCP), dicalcium phosphate anhydrate, and hydroxyapatite) with adsorbed protamine (which is a protein with antibacterial property) and confirmed their antibacterial property. In this study, as foundational research for the development of novel oral care materials, we synthesized calcium phosphate composite powders from three starting materials: i) OCP, which intercalates organic compounds, ii) protamine, which has antibacterial properties, and iii) F- ion, which promotes the formation of apatite crystals. Through investigating the preparation concentration of the F- ions and their loading into OCP, it was found that more F- ion could be loaded at higher concentrations regardless of the loading method. It was also observed that the higher the preparation concentration, the more the OCP converted to fluorapatite. The synthesized calcium phosphate composite powders were evaluated for biocompatibility through proliferation of MG-63 cells, with none of the powders exhibiting any growth inhibition. Antimicrobial tests showed that the calcium phosphate composite powders synthesized with protamine and F- ion by precipitation had enhanced antimicrobial properties than those synthesized by protamine adsorption. Thus, the calcium phosphate composite powder prepared from OCP, protamine, and F- ion forms the basis for promising antimicrobial biomaterials. Graphical abstract.

Granular honeycomb scaffolds composed of carbonate apatite for simultaneous intra- and inter-granular osteogenesis and angiogenesis

Granular porous calcium phosphate scaffolds are used for bone regeneration in dentistry. However, in conventional granules, the macropore interconnectivity is poor and has varying size. Herein, we developed a productive method for fabricating carbonate apatite honeycomb granules with uniformly sized macropores based on extrusion molding. Each honeycomb granule possesses three hexagonal macropores of ∼290 ​μm along its diagonal. Owing to these macropores, honeycomb granules simultaneously formed new and mature bone and blood vessels in both the interior and exterior of the granules at 4 weeks after implantation. The honeycomb granules are useful for achieving rapid osteogenesis and angiogenesis.