Calcium orthophosphates (CaPO4): Occurrence and properties

Functionalization of Octacalcium Phosphate Bone Graft with Cisplatin and Zoledronic Acid: Physicochemical and Bioactive Properties

Bones are the fourth most frequent site of metastasis from malignant tumors, including breast cancer, prostate cancer, melanoma, etc. The bioavailability of bone tissue for chemotherapy drugs is extremely low. This requires a search for new approaches of targeted drug delivery to the tumor growth zone after surgery treatment. The aim of this work was to develop a method for octacalcium phosphate (OCP) bone graft functionalization with the cytostatic drug cisplatin to provide the local release of its therapeutic concentrations into the bone defect. OCP porous ceramic granules (OCP ceramics) were used as a platform for functionalization, and bisphosphonate zoledronic acid was used to mediate the interaction between cisplatin and OCP and enhance their binding strength. The obtained OCP materials were studied using scanning electron and light microscopy, high-performance liquid chromatography, atomic emission spectroscopy, and real-time PCR. In vitro and in vivo studies were performed on normal and tumor cell lines and small laboratory animals. The bioactivity of initial OCP ceramics was explored and the efficiency of OCP functionalization with cisplatin, zoledronic acid, and their combination was evaluated. The kinetics of drug release and changes in ceramics properties after functionalization were studied. It was established that zoledronic acid changed the physicochemical and bioactive properties of OCP ceramics and prolonged cisplatin release from the ceramics. In vitro and in vivo experiments confirmed the biocompatibility, osteoconductivity, and osteoinductivity, as well as cytostatic and antitumor properties of the obtained materials. The use of OCP ceramics functionalized with a cytostatic via the described method seems to be promising in clinics when primary or metastatic tumors of the bone tissue are removed.

A novel rapidly mineralized biphasic calcium phosphate with high acid-resistance stability for long-term treatment of dentin hypersensitivity

OBJECTIVES

Treating dental hypersensitivity (DH) rapidly and maintaining long-term effectiveness remains challenging. We aimed to address this problem by fabricating a novel rapidly mineralized biphasic calcium phosphate (RMBCP), which could rapidly elicit mineralization to form hydroxyapatite (HA) and perform excellent acid-resistant stability, thus effectively blocking the exposed dental tubules and protecting them from acid attack.

METHODS

RMBCP was firstly synthesized by precisely adjusting the molar ratio of acetic acid and calcium hydroxide and characterized by X-ray diffraction (XRD), X-ray fluorescence microprobe (XRF), Fourier-transform infrared (FTIR) spectrometer, scanning electron microscope (SEM), and transmission electron microscope (TEM). Subsequently, using a commercialized desensitizing agent, 45S5 bioglass (BG), as the control group, the mineralization performance of RMBCP was investigated in simulated body fluid (SBF), Dulbecco's modified eagle medium (DMEM), and even slightly acidic artificial saliva (pH=6.6). Moreover, the biocompatibility of RMBCP was studied. Finally, the tubule occlusion effect and acid-resistant stability of RMBCP were evaluated in vitro and in vivo.

RESULTS

The rapid mineralization behavior of RMBCP could easily adhere to the dentin surface and block the dentinal tubules completely in vitro and in vivo within 7days. RMBCP performed high acid-resistant stability to maintain the long-term therapeutic effect of DH treatment.

SIGNIFICANCE

Developing novel bioactive calcium phosphate materials with the ability to trigger mineralization for HA formation rapidly will be an effective strategy for the long-term treatment of dentin hypersensitivity.

Nanocrystalline fluorapatite mineralization in the calciphile rock-boring bivalve Lithophaga: functional and phylogenetic significance

Phosphate mineralization as a skeletal material is uncommon in invertebrate animals and rare in Mollusca. Remarkably, apatite minerals were first reported more than 30 years ago in the periostracum of two species of the mytilid bivalve Lithophaga where shells are mostly constructed of calcium carbonate. This discovery extended the range of biominerals secreted by molluscs but has attracted no subsequent research. In this study we review the occurrence of phosphate mineralization in Lithophaga and putatively allied taxa. Lithophagine bivalves, particularly Lithophaga and the more diverse Leiosolenus species, are well known for their endolithic chemical dissolution of calcareous rocks and corals with calcium-binding lipoproteins secreted by mantle glands. Fluorapatite was identified by X-ray diffraction in an outer layer of the periostracum in six species of Lithophaga. Morphological study by scanning electron microscopy of four species showed the fluorapatite crystals embedded in periostracal material in a layer 10–20 µm thick. Dilute bleach treatment revealed the crystals as densely packed euhedral prisms 250–400 nm in size. The succeeding inner layers of the periostracum were unmineralized. Observations of the developing periostracum of Lithophaga teres suggest that the initial mineralization is in the form of amorphous granules that coalesce and transform into euhedral crystals. Periostracal phosphate was not recorded in other members of the Lithophaginae – Leiosolenus, Botula or Zelithophaga species. Leiosolenus species characteristically have extraperiostracal aragonitic encrustations that can be thick and structurally complex. Published molecular phylogenies of Mytilidae bivalves show a division into two major clades with Lithophaga species in one clade and Leiosolenus species in the other, indicating that the subfamily Lithophaginae as presently understood is polyphyletic. This result implies that the two genera have independent evolutionary pathways to endolithic occupation of calcareous substrates although using similar mantle gland secretions to excavate their crypts. Because fluorapatite is considerably less soluble and harder than calcium carbonate, it is suggested that the phosphate layer of Lithophaga is a functional adaptation to protect their shells from self-dissolution from their rock-dissolving glandular secretions and may also act as defence against other shell-eroding organisms.

Second-Generation Phosphorus: Recovery from Wastes towards the Sustainability of Production Chains

Phosphorus (P) is essential for life and has a fundamental role in industry and the world food production system. The present work describes different technologies adopted for what is called the second-generation P recovery framework, that encompass the P obtained from residues and wastes. The second-generation P has a high potential to substitute the first-generation P comprising that originally mined from rock phosphates for agricultural production. Several physical, chemical, and biological processes are available for use in second-generation P recovery. They include both concentrating and recovery technologies: (1) chemical extraction using magnesium and calcium precipitating compounds yielding struvite, newberyite and calcium phosphates; (2) thermal treatments like combustion, hydrothermal carbonization, and pyrolysis; (3) nanofiltration and ion exchange methods; (4) electrochemical processes; and (5) biological processes such as composting, algae uptake, and phosphate accumulating microorganisms (PAOs). However, the best technology to use depends on the characteristic of the waste, the purpose of the process, the cost, and the availability of land. The exhaustion of deposits (economic problem) and the accumulation of P (environmental problem) are the main drivers to incentivize the P’s recovery from various wastes. Besides promoting the resource’s safety, the recovery of P introduces the residues as raw materials, closing the productive systems loop and reducing their environmental damage.

An oligopeptide/aptamer-conjugated dendrimer-based nanocarrier for dual-targeting delivery to bone

Bone targeting is one of the most potentially valuable therapeutic methods for medically treating bone diseases, such as osteoarthritis, osteoporosis, nonunion bone defects, bone cancer, and myeloma-related bone disease, but its efficacy remains a challenge due to unfavorable bone biodistribution, off-target effects, and the lack of cell specificity. To address these problems, we synthesized a new dual-targeting nanocarrier for delivery to bone by covalently modifying the G4.0 PAMAM dendrimer with the C11 peptide and the CH6 aptamer (CH6-PAMAM-C11). The molecular structure was confirmed using ¹H-NMR and FT-IR spectroscopy. CLSM results showed that the novel nanocarrier could successfully accumulate in the targeted cells, mineralized areas and tissues. DLS and TEM demonstrated that CH6-PAMAM-C11 was approximately 40-50 nm in diameter. In vitro targeting experiments confirmed that the C11 ligand had a high affinity for HAP, while the CH6 aptamer had a high affinity for osteoblasts. The in vivo biodistribution analysis showed that CH6-PAMAM-C11 could rapidly accumulate in bone within 4 h and 12 h and then deliver drugs to sites of osteoblast activity. The components of CH6-PAMAM-C11 were well excreted via the kidneys. The accumulation of many more CH6-PAMAM-C11 dual-targeting nanocarriers than single-targeting nanocarriers was observed in the periosteal layer of the rat skull, along with aggregation at sites of osteoblast activity. All of these results indicate that CH6-PAMAM-C11 may be a promising nanocarrier for the delivery of drugs to bone, particularly for the treatment of osteoporosis, and our research strategy may serve as a reference for research in targeted drug, small molecule drug and nucleic acid delivery.

Fabrication and characterization of remineralizing dental composites containing hydroxyapatite nanoparticles

The aim of this study was to fabricate and characterize dental composites containing hydroxyapatite nanoparticles (HApNPs). Four dental composites were produced from the same organic matrix (70 wt% Bis-GMA and 30 wt% TEGDMA), with partial replacement of BaBSi particles (65 wt%) by HApNPs in the following concentrations (wt%): E0 (0) - control, E10 (10), E20 (20) and E30 (30). Ca²⁺ and PO₄^3- release was evaluated in solutions with different pHs (4, 5.5, and 7) using atomic emission spectroscopy with microwave-induced nitrogen plasma while the enamel remineralization potential was evaluated in caries-like enamel lesions induced by S. mutans biofilm using micro-CT. The following properties were characterized: degree of conversion (DC%), microhardness (KHN), flexural strength (FS), elastic modulus (EM) and translucency (TP). The higher the HApNPs content, the higher the Ca²⁺ and PO₄^3- release. The ions release was influenced by pH (4 > 5.5 > 7) (p < 0.05). All composites loaded with HApNPs were able to remineralize the enamel (E30 = E20 > E10) (p < 0.05). Contrarily, E0 was not able of recovering the enamel mineral loss. E0 and E10 presented highest DC%, while E20 and E30 showed similar and lowest DC%. KHN and FS were decreased with the addition of HApNPs, while EM was not influenced by the incorporation of HApNPs. E10 presented statistically similar TP to E0, while this property decreased for E20 and E30 (p < 0.05). Incorporation of HApNPs into dental composites promoted enamel remineralization, mainly at potentially cariogenic pH (= 4), while maintained their overall performance in terms of physicomechanical properties.

Single-walled carbon nanotubes loaded hydroxyapatite-alginate beads with enhanced mechanical properties and sustained drug release ability

Single-walled carbon nanotubes (SWCNTs) containing biomaterial with enhanced mechanical properties for the potential orthopedic application were synthesized and investigated. X-ray diffraction and X-ray fluorescence analysis were indications of the formation of calcium-deficient (Ca/P = 1.65) hydroxyapatite (HA) with a small carbonate content under influence of microwave irradiation. The investigated mechanical properties (maximal relative deformation, compressive strength and Young's modulus) of SWCNT loaded HA-alginate composites confirm their dependence on SWCNTs content. The compressive strength of HA-alginate-SWCNT and the HA-alginate control (202 and 159 MPa, respectively) lies within the values characteristic for the cortical bone. The addition of 0.5% SWCNT, in relation to the content of HA, increases the Young's modulus of the HA-alginate-SWCNT (645 MPa) compared to the SWCNT-free HA-alginate sample (563 MPa), and enhances the material shape stability in simulated physiological conditions. Structural modeling of HA-alginate-SWCNT system showed, that physical adsorption of SWCNT into HA-alginate occurs by forming triple complexes stabilized by solvophobic/van der Waals interactions and H-bonds. The high-performance liquid chromatography demonstrated the influence of SWCNTs on the sustained anaesthesinum drug (used as a model drug) release (456 h against 408 h for SWCNT-free sample). Cell culture assay confirmed biocompatibility and stimulation of osteoblast proliferation of 0.05% and 0.5% SWCNT-containing composites during a 3-day cultivation. All these facts may suggest the potential possibility of using the SWCNT-containing materials, based on HA and alginate, for bone tissue engineering.

Mineral deposition promoted by resin-based sealants with different calcium phosphate additions

The aim of this study was to evaluate the influence of different calcium phosphates (CaPs) on the physical, biological, and remineralizing properties of experimental resin-based sealants (RBSs). Triethylene-glycol dimethacrylate (90wt%) and bisphenol A-glycidyl methacrylate (10wt%) were used to produce resin-based sealants. Hydroxyapatite (SHAp), α-tricalcium phosphate (Sα-TCP) and octacalcium phosphate (SOCP) were added to the sealants in a 10wt% concentration. One group without CaPs was used as the control group (SCG). The degree of conversion (DC) was assessed with Fourier-transformed infrared spectroscopy, whereas cytotoxicity was tested with the HaCaT keratinocyte cell line. The ultimate tensile strength (UTS) was used to assess the mechanical strength of the experimental RBSs. Sealed enamel was used for colorimetric assay. Mineral deposition was assessed with Raman spectroscopy after 7, 14, and 28 days of sample immersion in artificial saliva. Scanning electron microscopy was used to analyze the surface morphology after 28 days of immersion. The addition of 10wt% of fillers significantly reduced the DC of sealants. SOCP groups showed reduced cell viability. Higher UTS was found for Sα-TCP and SHAp. The color analysis showed that SGC and demineralized teeth presented higher mismatches with the sound tissue. Mineral deposition was observed for SHAp and Sα-TCP after 7 days, with increased phosphate content and mineral deposits for SHAp after 28 days. RBS with the addition of 10% HAp promoted increased mineralization in vitro after 28 days, and did not affect cell viability, DC, mechanical properties, or RBS color in the enamel.

Photoluminescent Hydroxylapatite: Eu3+ Doping Effect on Biological Behaviour

Luminescent europium-doped hydroxylapatite (Eu_XHAp) nanomaterials were successfully obtained by co-precipitation method at low temperature. The morphological, structural and optical properties were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier Transform Infrared (FT-IR), UV-Vis and photoluminescence (PL) spectroscopy. The cytotoxicity and biocompatibility of Eu_XHAp were also evaluated using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)) assay, oxidative stress assessment and fluorescent microscopy. The results reveal that the Eu³⁺ has successfully doped the hexagonal lattice of hydroxylapatite. By enhancing the optical features, these Eu_XHAp materials demonstrated superior efficiency to become fluorescent labelling materials for bioimaging applications.

Human macrophages and osteoclasts resorb β-tricalcium phosphate in vitro but not mouse macrophages

β-TCP is a resorbable bony biomaterial but its biodegradation mechanisms in vivo remains unclear. Osteoclast can resorb β-TCP but a role for macrophages has also been suggested by in vivo studies. However no in vitro study has clearly evidenced the action of macrophages in the resorption process. We prepared flat β-TCP tablets with a smooth surface to investigate the in vitro capability of murine (RAW 264.7) and human macrophage cells (PBMCs) to resorb the biomaterial. In parallel, these cells were differentiated into multinucleated osteoclasts with M-CSF and RANK-L. The action of these cells was evaluated by scanning electron microscopy and Raman microspectroscopy after a 21 day culture on the tablets. Human macrophages and osteoclasts derived from PBMCs appeared able to resorb β-TCP by forming resorption pits at the surface of the flat tablets. RAW macrophages were unable to resorb β-TCP but they exhibited this possibility when they have been differentiated into osteoclasts. These cells can engulf β-TCP grains in their cytoplasm as evidenced by light and TEM microscopy with production of carbonic anhydrase (revealed by the immunogold technique in TEM). The resorbed areas were characterized by severe degradation of the grains showing speckled and stick-like aspects indicating a chemical corrosion. The effect was maximal at the grain boundaries which have a slightly different chemical composition. Changes in the Raman spectrum were observed between the resorbed and un-resorbed β-TCP suggesting crystal modifications. In contrast, un-differentiated murine macrophages were not able to chemically attack β-TCP and no resorption pit was observed. RAW cell is not a representative model of the macrophage-biomaterial interactions that occur in human. This in vitro study evidences that both human osteoclasts and macrophages represent active cell populations capable to resorb β-TCP.

In Vitro Activity Assays of Sputtered HAp Coatings with SiC Addition in Various Simulated Biological Fluids

Considering the requirements of medical implantable devices, it is pointed out that biomaterials should play a more sophisticated, longer-term role in the customization and optimization of the material–tissue interface in order to ensure the best long-term clinical outcomes. The aim of this contribution was to assess the performance of silicon carbide–hydroxyapatite in various simulated biological fluids (Dulbecco’s modified Eagle’s medium (DMEM), simulated body fluid (SBF), and phosphate buffer solution (PBS)) through immersion assays for 21 days at 37 ± 0.5 °C and to evaluate the electrochemical behavior. The coatings were prepared on Ti6Al4V alloy substrates by magnetron sputtering method using two cathodes made of hydroxyapatite and silicon carbide (SiC). After immersion assays the coating’s surface was analyzed in terms of morphology, chemical and phase composition, and chemical bonds. According to the electrochemical behavior in the media investigated at 37 ± 0.5 °C, SiC addition inhibits the dissolution of the hydroxyapatite in DMEM acellular media. Furthermore, after adding SiC, the slow degradation of hydroxyapatite in PBS and SBF media as well as biomineralization in DMEM were observed.

Calcium phosphates as ion-releasing fillers in restorative resin-based materials

Calcium phosphates (CaP) are the main constituents of the mineral phase in bones and teeth and, along with calcium silicates and bioactive glasses, have been extensively investigated in remineralization of enamel and dentin. When used as ion-releasing fillers in resin-based materials, they could contribute to extend the service life of adhesive restorations, remineralize caries-affected dentin or prevent caries lesions under sealants and orthodontic brackets. However, the development of resin-based bioactive materials is not straightforward because of the several compositional variables involved in ion release. Also, CaP particles do not reinforce the material; therefore, if high mechanical properties are required, the ratio between CaP particles and reinforcing fillers must be observed. Several research groups have investigated how CaP phase, particle size and content, as well as resin matrix formulation affect remineralization, ion release kinetics and mechanical properties of these materials. This review presents an overview of the main findings reported in the literature.