Amorphous calcium phosphate (ACP) in tissue repair process

Assessment of the Osseointegration of Pure-Phase β-Tricalcium Phosphate (β-TCP) Ceramic Cylinder Implants in Critical Segmental Radial Bone Defects in Rabbits

Autografts, allografts, and synthetic bone substitutes are essential in reconstructive orthopedic surgery. Although autografts and allografts provide excellent skeletal integration, their use is limited by host morbidity and graft acquisition challenges. Synthetic materials like β-tricalcium phosphate (β-TCP) offer promising osseoconductive properties as a potential substitute. This study evaluated the osseointegration of β-TCP ceramic cylinder implants in bone defects in rabbits. Eighteen New Zealand rabbits underwent radial diaphysis ostectomy to create a critical segmental defect and were divided into three groups: Group A received β-TCP blocks, Group B received allogenous cortical bone grafts, and Group C underwent ostectomy without defect filling. Postoperative assessments included clinical evaluations, radiographs, micro-computed tomography, and histology at various time points to assess osseointegration and implant resorption. At the 120th postoperative day, Group B showed successful bone integration without infection. In contrast, Group A showed no osseointegration or resorption of the β-TCP implants, and Group C exhibited bone non-union. While β-TCP demonstrated biocompatibility, it lacked osseoconductivity, likely due to low porosity. β-TCP implants did not promote bone consolidation, suggesting that further research on porosity and shape is needed to improve their suitability for veterinary orthopedic reconstructive surgery.

Improved visualisation of ACP-engineered osteoblastic spheroids: a comparative study of contrast-enhanced micro-CT and traditional imaging techniques

This study investigates osteoblastic cell spheroid cultivation methods, exploring flat-bottom, U-bottom, and rotary flask techniques with and without amorphous calcium phosphate (ACP) supplementation to replicate the 3D bone tissue microenvironment. ACP particles derived from eggshell waste exhibit enhanced osteogenic activity in 3D models. However, representative imaging of intricate 3D tissue-engineered constructs poses challenges in conventional imaging techniques due to notable scattering and absorption effects in light microscopy, and hence limited penetration depth. We investigated contrast-enhanced micro-CT as a methodological approach for comprehensive morphological 3D-analysis of thein-vitromodel and compared the technique with confocal laser scanning microscopy, scanning electron microscopy and classical histology. Phosphotungstic acid and iodine-based contrast agents were employed for micro-CT imaging in laboratory and synchrotron micro-CT imaging. Results revealed spheroid shape variations and structural integrity influenced by cultivation methods and ACP particles. The study underscores the advantage of 3D spheroid models over traditional 2D cultures in mimicking bone tissue architecture and cellular interactions, emphasising the growing demand for novel imaging techniques to visualise 3D tissue-engineered models. Contrast-enhanced micro-CT emerges as a promising non-invasive imaging method for tissue-engineered constructs containing ACP particles, offering insights into sample morphology, enabling virtual histology before further analysis.

Thermal, chemical and physical analysis of VDW.1Seal, Fill Root ST, and ADseal root canal sealers

This study aimed to evaluate the thermal, chemical, and physical properties of VDW.1Seal, Fill Root ST, and ADseal sealers. Thermal properties were analyzed using Thermogravimetric analysis (TGA) and Differential thermal analysis (DTA). Attenuated total reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) analysis was performed as a complementary test to confirm TGA/DTA analysis. The chemical composition of the set sealer material was identified using an X-ray powder diffraction (XRD) system. Other physical properties of each sealer were investigated; ten specimens were used to measure the solubility (at 24 h and 28 days), and another ten specimens were used to assess pH changes and calcium ion release (after 7 and 14 days). Film thickness was done according to ISO 6876 specs. The data were analyzed using the two-way ANOVA test. Results showed that for all sealers, TGA analysis revealed a direct relationship between sealer mass loss and temperature rise. In addition, the decomposition of the tested sealers started at 145 °C, 135 °C and 91 °C for VDW.1Seal, ADseal sealer, and Fill Root ST, respectively. XRD analysis revealed a higher degree of crystallinity for VDW.1Seal and ADseal. ADseal showed the least solubility; VDW.1Seal exhibited the highest alkalinity, calcium ion release, and the lowest film thickness.

Intrafibrillar Mineralization and Immunomodulatory for Synergetic Enhancement of Bone Regeneration via Calcium Phosphate Nanocluster Scaffold

Inspired by the bionic mineralization theory, organic-inorganic composites with hydroxyapatite nanorods orderly arranged along collagen fibrils have attracted extensive attention. Planted with an ideal bone scaffold will contribute greatly to the osteogenic microenvironment; however, it remains challenging to develop a biomimetic scaffold with the ability to promote intrafibrillar mineralization and simultaneous regulation of immune microenvironment in situ. To overcome these challenges, a scaffold containing ultra-small particle size calcium phosphate nanocluster (UsCCP) is prepared, which can enhance bone regeneration through the synergetic effect of intrafibrillar mineralization and immunomodulatory. By efficient infiltration into collagen fibrils, the UsCCP released from the scaffold achieves intrafibrillar mineralization. It also promotes the M2-type polarization of macrophages, leading to an immune microenvironment with both osteogenic and angiogenic potential. The results confirm that the UsCCP scaffold has both intrafibrillar mineralization and immunomodulatory effects, making it a promising candidate for bone regeneration.

RF Magnetron Sputtering of Substituted Hydroxyapatite for Deposition of Biocoatings

Functionalization of titanium (Ti)-based alloy implant surfaces by deposition of calcium phosphates (CaP) has been widely recognized. Substituted hydroxyapatites (HA) allow the coating properties to be tailored based on the use of different Ca substitutes. The formation of antibacterial CaP coatings with the incorporation of Zn or Cu by an RF magnetron sputtering is proposed. The influence of RF magnetron targets elemental composition and structure in the case of Zn-HA and Cu-HA, and the influence of substrate's grain size, the substrate's temperature during the deposition, and post-deposition heat treatment (HT) on the resulting coatings are represented. Sintering the targets at 1150 °C resulted in a noticeable structural change with an increase in cell volume and lattice parameters for substituted HA. The deposition rate of Cu-HA and Zn-HA was notably higher compared to stochiometric HA (10.5 and 10) nm/min vs. 9 ± 0.5 nm/min, respectively. At the substrate temperature below 100 °C, all deposited coatings were found to be amorphous with an atomic short-range order corresponding to the {300} plane of crystalline HA. All deposited coatings were found to be hyper-stochiometric with Ca/P ratios varying from 1.9 to 2.5. An increase in the substrate temperature to 200 °C resulted in the formation of equiaxed grain structure on both coarse-grained (CG) and nanostructured (NS) Ti. The use of NS Ti notably increased the scratch resistance of the deposited coatings from18 ± 1 N to 22 ± 2 N. Influence of HT in air or Ar atmosphere is also discussed. Thus, the deposition of Zn- or Cu-containing CaP is a complex process that could be fine-tuned using the obtained research results.

Tunable Behavior in Solution of Amorphous Calcium Ortho/Pyrophosphate Materials: An Acellular In Vitro Study

Amorphous calcium phosphate-based materials are of major interest in the field of bone substitution. Very recently, the low-temperature synthesis of a new family of amorphous calcium phosphate containing both orthophosphate and pyrophosphate ions in controlled proportions has been reported. Despite their interest, especially due to the biochemical role and the hydrolysis of pyrophosphate occurring in vivo, the behavior of such materials when interacting with aqueous media has never been described. Consequently, we herein report the in vitro acellular evolution of three compositions of mixed calcium ortho- and pyrophosphate amorphous materials including a different orthophosphate proportion. As a first step to assess the physicochemical reactivity of these amorphous materials, they were tested in two different media at 37 °C, acidified water and simulated body fluid solution, from 1 h up to 15 days. The results demonstrated that they were quite stable and that they progressively released part of their constitutive ions, highlighting their potential for controlled delivery of bioactive ions (calcium, orthophosphate, and pyrophosphate ions). In addition to these properties, we showed that the material with the highest ortho/(ortho + pyro) phosphate ratio started to crystallize into nanocrystalline apatite analogous to bone mineral within 2 days or 2 weeks depending on the medium. For the other material compositions, no layer of apatite was detected at their surface with SBF testing despite the favorable supersaturation indexes, crystallization being probably inhibited by pyrophosphate ions released in the medium. This varying apatite-forming ability emphasizes the key role of the ortho/(ortho + pyro) phosphate ratio of these materials in their in vitro reactivity and bioactivity, which paves the way for the development of this promising family of amorphous calcium phosphate materials with tunable physicochemical and biological properties.

Synthetic amorphous calcium phosphates (ACPs): preparation, structure, properties, and biomedical applications

Amorphous calcium phosphates (ACPs) represent a metastable amorphous state of other calcium orthophosphates (abbreviated as CaPO4) possessing variable compositional but rather identical glass-like physical properties, in which there are neither translational nor orientational long-range orders of the atomic positions. In nature, ACPs of a biological origin are found in the calcified tissues of mammals, some parts of primitive organisms, as well as in the mammalian milk. Manmade ACPs can be synthesized in a laboratory by various methods including wet-chemical precipitation, in which they are the first solid phases, precipitated after a rapid mixing of aqueous solutions containing dissolved ions of Ca2+ and PO43- in sufficient amounts. Due to the amorphous nature, all types of synthetic ACPs appear to be thermodynamically unstable and, unless stored in dry conditions or doped by stabilizers, they tend to transform spontaneously to crystalline CaPO4, mainly to ones with an apatitic structure. This intrinsic metastability of the ACPs is of a great biological relevance. In particular, the initiating role that metastable ACPs play in matrix vesicle biomineralization raises their importance from a mere laboratory curiosity to that of a reasonable key intermediate in skeletal calcifications. In addition, synthetic ACPs appear to be very promising biomaterials both for manufacturing artificial bone grafts and for dental applications. In this review, the current knowledge on the occurrence, structural design, chemical composition, preparation, properties, and biomedical applications of the synthetic ACPs have been summarized.

Composite Drug Delivery System Based on Amorphous Calcium Phosphate-Chitosan: An Efficient Antimicrobial Platform for Extended Release of Tetracycline

One major warning emerging during the first worldwide combat against healthcare-associated infections concerns the key role of the surface in the storage and transfer of the virus. Our study is based on the laser coating of surfaces with an inorganic/organic composite mixture of amorphous calcium phosphate–chitosan–tetracycline that is able to fight against infectious agents, but also capable of preserving its activity for a prolonged time, up to several days. The extended release in simulated fluids of the composite mixture containing the drug (tetracycline) was demonstrated by mass loss and UV–VIS investigations. The drug release profile from our composite coatings proceeds via two stages: an initial burst release (during the first hours), followed by a slower evolution active for the next 72 h, and probably more. Optimized coatings strongly inhibit the growth of tested bacteria (Enterococcus faecalis and Escherichia coli), while the drug incorporation has no impact on the in vitro composite’s cytotoxicity, the coatings proving an excellent biocompatibility sustaining the normal development of MG63 bone-like cells. One may, therefore, consider that the proposed coatings’ composition can open the prospective of a new generation of antimicrobial coatings for implants, but also for nosocomial and other large area contamination prevention.

Intraosseous Injection of Calcium Phosphate Polymer-Induced Liquid Precursor Increases Bone Density and Improves Early Implant Osseointegration in Ovariectomized Rats

PURPOSE

Osteoporosis, due to bone loss and structural deterioration, is a risk factor for dental implant failure, as it impedes initial stability and osseointegration. We aim to assess the effects of calcium phosphate polymer-induced liquid precursor (CaP-PILP) treatment, which significantly increases bone density and improves early implant osseointegration in ovariectomized rats.

METHODS

In this study, CaP-PILP was synthesized and characterized through TEM, FTIR and XRD. A rat model of osteoporosis was generated by ovariectomy. CaP-PILP or hydroxyapatite (HAP, negative control) was injected into the tibia, and the resulting changes in bone quality were determined. Further, implants were installed in the treated tibias, and implantation characteristics were assessed after 4 weeks.

RESULTS

The CaP-PILP group had superior bone repair. Importantly, CaP-PILP had excellent properties, similar to those of normal bone, in terms of implant osseointegration. In vivo experiment displayed that CaP-PILP group had better bone contact rate (65.97±3.176) than HAP and OVX groups. Meanwhile, a mound of mature and continuous new bone formed. Moreover, the values of BIC and BA showed no significant difference between the CaP-PILP group and the sham group.

CONCLUSION

In summary, CaP-PILP is a promising material for application in poor-quality bones to improve implant success rates in patients with osteoporosis. This research provides new perspectives on the application of nano-apatite materials in bone repair.

Drug Delivery (Nano)Platforms for Oral and Dental Applications: Tissue Regeneration, Infection Control, and Cancer Management

The oral cavity and oropharynx are complex environments that are susceptible to physical, chemical, and microbiological insults. They are also common sites for pathological and cancerous changes. The effectiveness of conventional locally-administered medications against diseases affecting these oral milieus may be compromised by constant salivary flow. For systemically-administered medications, drug resistance and adverse side-effects are issues that need to be resolved. New strategies for drug delivery have been investigated over the last decade to overcome these obstacles. Synthesis of nanoparticle-containing agents that promote healing represents a quantum leap in ensuring safe, efficient drug delivery to the affected tissues. Micro/nanoencapsulants with unique structures and properties function as more favorable drug-release platforms than conventional treatment approaches. The present review provides an overview of newly-developed nanocarriers and discusses their potential applications and limitations in various fields of dentistry and oral medicine.

The incorporation of phosphorylated chitosan/amorphous calcium phosphate nanocomplex into an experimental composite resin

This study evaluated the effect of incorporating phosphorylated chitosan/amorphous calcium phosphate nanocomplex (Pchi/ACP) into an experimental light-cure composite resin on mechanical-chemical properties and human dentin remineralization. The results showed that the mechanical strength and contact angles of the resins decreased with the increase incorporation of Pchi/ACP. Release concentrations of calcium in saline solution were measured at different time points, showing the incorporation of Pchi/ACP significantly increased calcium release within 14 days, and kept steady thereafter. Finally, the demineralized dentin slabs treated with our resins for four weeks were characterized by SEM-EDS. Various amounts of apatite were formed on the dentin slabs which were treated with the resins containing Pchi/ACP, whereas no apatite was formed without Pchi/ACP. In conclusion, the Pchi/ACP-incorporating composite resin can be a promising dental material due to its favorable mechanical and remineralization properties.

Amorphous Calcium Phosphate NPs Mediate the Macrophage Response and Modulate BMSC Osteogenesis

The potential risk associated with ACP nanoparticles (ACP NPs) cultured with immune cells and their indirect effects on osteogenesis have not been studied deeply. This project aims to evaluate the safety of ACP NPs in macrophages, the responses of macrophages (macrophage polarization, the cytokine secretion pattern of macrophages and intracellular homeostasis) to ACP NPs and the effect of ACP NPs/macrophage-modulated environments on the osteogenic ability of BMSCs. The cell proliferation rate and apoptosis were detected by CCK-8 and Annexin V Apoptosis Detection kits. ROS and autophagy expression were evaluated by ROS test kits and Western blot (WB). Macrophage polarization and cytokine expression were determined by SEM, cytoskeletal staining, RT-PCR and ELISA. TMT™ quantitative protein analysis was used to evaluate protein expression. BMSC osteogenic differentiation was detected by ALP staining, Alizarin Red solution staining and RT-PCR. ACP NPs were safe to macrophages but promoted autophagy and induced ROS production at high concentrations. ACP NPs changed morphology of macrophages and induced polarization into M1 type, thus promoting the expression of inflammatory cytokines. ACP NPs/macrophage-modulated environments weakened the osteogenic ability of BMSCs. ACP NPs polarize macrophages into the M1 phenotype and change the cytokine secretion pattern. ACP NPs/macrophage-modulated environments weaken the osteogenic ability of BMSCs. ACP NPs may cause aseptic inflammation and attenuate osteogenesis.

Development of brushite particles synthesized in the presence of acidic monomers for dental applications

OBJECTIVES

To synthesize and characterize brushite particles in the presence of acidic monomers (acrylic acid/AA, citric acid/CA, and methacryloyloxyethyl phosphate/MOEP) and evaluate the effect of these particles on degree of conversion (DC), flexural strength/modulus (FS/FM) and ion release of experimental composites.

METHODS

Particles were synthesized by co-precipitation with monomers added to the phosphate precursor solution and characterized for monomer content, size and morphology. Composites containing 20 vol% brushite and 40 vol% reinforcing glass were tested for DC, FS and FM (after 24 h and 60 d in water), and 60-day ion release. Data were subjected to ANOVA/Tukey tests (DC) or Kruskal-Wallis/Dunn tests (FS and FM, alpha: 5%).

RESULTS

The presence of acidic monomers affected particle morphology. Monomer content on the particles was low (0.1-1.4% by mass). Composites presented similar DC. For FS/24 h, only the composite containing DCPD_AA was statistically similar to the composite containing 60 vol% of reinforcing glass (without brushite, "control"). After 60 days, all brushite-containing materials showed similar FS, statistically lower than the control composite (p<0.01). Composites containing DCPD_AA, DCPD_MOEP or DCPD_U ("unmodified") showed statistically similar FM/24 h, higher than the control composite. After prolonged immersion, all composites were similar to the control composite, except DCPD_AA. Cumulative ion release ranged from 21 ppm to 28 ppm (calcium) and 9 ppm to 17 ppm (phosphate). Statistically significant reductions in ion release between 15 and 60 days were detected only for the composite containing DCPD_MOEP.

SIGNIFICANCE

Acidic monomers added to the synthesis affected brushite particle morphology. After 60-day storage in water, composite strength was similar among all brushite-containing composites. Ion release was sustained for 60 days and it was not affected by particle morphology.

Osteogenesis of 3D printed macro-pore size biphasic calcium phosphate scaffold in rabbit calvaria

To investigate the osteogenesis of macro-pore sized bone scaffolds, biphasic calcium phosphate scaffolds with accurately controlled macro-pore size (0.8, 1.2, and 1.6 mm) and identical porosity of 70% were fabricated by the 3D printing technology. Eight New Zealand rabbits were selected in the present study, while four 8-mm-diameter calvarial defects were created in each rabbit to place BCP scaffolds with different macro-pore size. The harvested specimens of four and eight weeks were used to evaluate the bone forming ability by micro CT and histological examination. All 3D-printed BCP scaffolds exhibited excellent mechanical properties and had better bone-forming ability than the control at both four and eight weeks. Among them, scaffold with 0.8 mm pore size was superior for initial bone formation and maturation, resulting in the highest value of total bone formation.