Polymeric Calcium Phosphate Cements Research Articles

Preparation and characterization of calcium phosphate cement of α-tricalcium phosphate-tetracalcium phosphate-dicalcium phosphate system incorporated with poly(γ-glutamic acid)

Polymeric calcium phosphate cements (PCPCs) were prepared from cement powders consisting of alphatricalcium phosphate (α-TCP), tetracalcium phosphate (TTCP) and dicalcium phosphate (DCP), and cement liquid with poly(γ-glutamic acid) (γ-PGA). The characteristics of calcium phosphate cements (CPCs), such as paste injectability, initial setting time, and compressive strength, were assessed. The injectability of PCPCs with a 0–30 wt% TTCP/DCP mixture was above 90%. The initial setting time decreased in concert with the amount of incorporated TTCP/DCP mixture and reached approximately 10–13 min when the amount of TTCP/DCP mixture was 10–30 wt%. The compressive strength of PCPC with the 30% equimolar TTCP/DCP mixture was approximately 18.4±3.5 MPa, whereas that of the CPC without the TTCP/DCP mixture was approximately 4.8±0.1 MPa. Open image in new window

Preparation and characterization of alpha-tricalcium phosphate cements incorporated with polyamino acids

Polymeric calcium phosphate cements (PCPCs) derived from biodegradable polyamino acids, such as polyaspartic acid (PAA) and poly-γ-glutamic acid (γ-PGA), were prepared in an attempt to improve their cohesion strength and injectability. The characteristics of the calcium phosphate cements (CPCs), such as dynamic viscosity, paste injectability, initial setting time, compressive strength and cell compatibility, were assessed. The dynamic viscosity increased significantly with γ-PGA incorporation but decreased with PAA incorporation. The injectability increased with the concentration of polyamino acids and that of the CPCs mixed with γ-PGA reached 94%. The initial setting time decreased with the γ-PGA concentration in the cement liquid and reached approximately 10–15 min when the γ-PGA concentration was 1–2 wt%. The compressive strength (CS) of CPCs after 1 week-incubation decreased with the incorporation of PAA and γ-PGA. γ-PGA incorporation deteriorated the CS more than PAA incorporation because the dissolution of alpha-tricalcium phosphate (α-TCP) was retarded. Saos-2 cells grown on CPCs with polyamino acids spread more than those grown on the CPC without them.

Preparation, Physical-Chemical Characterization, and Cytocompatibility of Polymeric Calcium Phosphate Cements

Aim. Physicochemical mechanical and in vitro biological properties of novel formulations of polymeric calcium phosphate cements (CPCs) were investigated. Methods. Monocalcium phosphate, calcium oxide, and synthetic hydroxyapatite were combined with either modified polyacrylic acid, light activated polyalkenoic acid, or polymethyl vinyl ether maleic acid to obtain Types I, II, and III CPCs. Setting time, compressive and diametral strength of CPCs was compared with zinc polycarboxylate cement (control). Specimens were characterized using X-ray diffraction, scanning electron microscopy, and infrared spectroscopy. In vitro cytotoxicity of CPCs and control was assessed. Results. X-ray diffraction analysis showed hydroxyapatite, monetite, and brushite. Acid-base reaction was confirmed by the appearance of stretching peaks in IR spectra of set cements. SEM revealed rod-like crystals and platy crystals. Setting time of cements was 5–12 min. Type III showed significantly higher strength values compared to control. Type III yielded high biocompatibility. Conclusions. Type III CPCs show promise for dental applications.

Polymeric Calcium Phosphate Cements Incorporated with Poly-γ-Glutamic Acid

Polymeric calcium phosphate cements (PCPC) derived from biodegradable poly-g-glutamic acid (g-PGA) were prepared in an attempt to improve the mechanical strength of calcium phosphate cement (CPC). The characteristics of the PCPCs were compared to those of cement incorporated with citric acid. The diametral tensile and compressive strengths of the CPC incorporated with g-PGA were significantly higher than that of cement incorporated with citric acid at equivalent concentrations (p<0.05). The maximal diametral tensile and compressive strengths of the CPC incubated for 1 week in physiological saline solution were approximately 18.0 and 50.0 MPa, respectively. However, the initial setting time of the PCPC was much slower than that of CPC incorporated with citric acid. The formation of ionic complexes between calcium ions and g-PGA was observed using FT-IR spectroscopy. Hydroxyapatite (HA) formation was retarded by g-PGA incorporation according to scanning electronic microscopy (SEM) and powder X-ray diffraction (XRD) observations.

Mechanical properties of calcium phosphate based dental filling and regeneration materials.

The objective of this study was to compare the mechanical properties of calcium phosphate cements (CPC) for possible dental applications with varied liquid and powder compositions under the same testing condition. Cements studied in this experiment were divided into two groups of CPC not containing polymer and polymeric CPC (PCPC). Cement powder was formed by combining equimolar amounts of dicalcium phosphate anhydrous and tetracalcium phosphate, or acrylic resin polymer powder mixture. The CPC specimens for the compressive strength (CS) and diametral tensile strength (DTS) measurements were prepared by mixing powder and liquid for 30 s with a powder/liquid ratio of 3:1, and subsequently packing the paste into a brass mould. The specimens were kept at 37 degrees C and 100% relative humidity for 24 h before measurements were conducted on a Universal Testing Machine with a cross-head speed of 1 mm min-1. The CS of CPC was 0.14-10.29 MPa and that of PCPC was 0.26-117.58 MPa. The DTS of CPC was 0.10-4.56 MPa and that of PCPC was 0.07-22.54 MPa. The CS and DTS were very diverse depending on the composition of powder and liquid. Some compositions showed higher values than commercial liners. Thus compositions of 2% carboxymethyl cellulose + 35% citric acid in phosphate buffered saline (PBS), 20% gelatin in PBS, 2% sodium alginate in PBS, 20-40% aqueous acrylic-maleic copolymer solution, and some of the HPMC and PMVE-Ma solutions exhibited promising formulae for dentine regenerating materials. Acrylic resin-PCPC group showed generally higher CS and DTS values. Based on this study, further studies on the reaction with odontoblast and resultant dentine regeneration should be performed using promising compositions.

Polymeric calcium phosphate cements derived from poly(methyl vinyl ether-maleic acid)

Objectives. The purpose of this study was to assess the feasibility of forming polymeric calcium phosphate cements from a mixed powder of dicalcium phosphate/tetracalcium phosphate or only tetracalcium phosphate and poly(methyl vinyl ether-maleic acid) (PMVE-Ma), and to study their setting reaction. Methods. The setting reaction process of the polymeric cements was evaluated by mechanical strength tests, infrared spectroscopy and x-ray diffraction analysis and compared with that of a water-setting calcium phosphate cement. The mechanical strength data were analyzed using ANOVA and Scheffé's multiple comparisons test. Results. Cements prepared from the mixed powder and 25–30 wt% aqueous solutions of PMVE-Ma had high mechanical strength after 24 h storage in distilled water at 37°C. The hardening mechanism dependended on an acid-base reaction between the carboxyl groups of PMVE-Ma and the mixed powder, especially its tetracalcium phosphate component. The formation of hydroxyapatite in the polymeric calcium phosphate cement was not detected and is apparently inhibited as a result of the competing reaction of PMVE-Ma with the mixed powder. Significance. The cement-forming reaction was significantly faster than that of a water-setting calcium phosphate cement and slower than that observed with the mixed powder and polyacids such as poly(acrylic acid). The characteristics of the polymeric cements suggest that the materials may be useful in cavity lining or endodontic sealing.

Polymeric calcium phosphate cements: setting reaction modifiers

In this study, the effects of several additives on the setting behavior and mechanical properties of polymeric calcium phosphate cements were investigated. The cements were derived from a polycarboxylic acid (PCA) and a calcium phosphate cement (CPC) powder that consisted of equimolar amounts of tetracalcium phosphate (TTCP) and dicalcium phosphate (DCPA). Retardation of the setting reaction in the PCA-CPC cements was observed by adding tribasic sodium phosphate and fluorides such as stannous fluoride, zirconium(IV) fluoride and titanium(IV) fluoride. It was found that increasing the concentration of these additives decreased the mechanical strength of the cements. However, improvements in both setting and mechanical properties for the PCA-CPC cements were observed by the combined use of 8% (w/w) stanous fluoride and 10% (w/w) tartaric acid. The mechanical properties of the PCA-CPC cement also were improved by adding calcium acetate, calcium methacrylate, zirconium(IV) sulfate and phosphonoacetic acid.

Polymeric calcium phosphate cements: analysis of reaction products and properties

Chemical and mechanical properties of water-based polymeric calcium phosphate cements (PCPC) were investigated. These cements were derived from mixing several types of water-soluble polymers, e.g., gelatin, poly(vinyl alcohol), (PVA), and poly(alkenoic acids) such as poly(acrylic acid), with a calcium phosphate cement (CPC) mixture consisting of equimolar amounts of tetracalcium phosphate (TTCP) and anhydrous discalcium phosphate (DCPA) as well as several other TTCP-containing mixtures. Cement formation was observed with all of the PCPCs. With the gelatin and PVA cements, significant amounts of hydroxyapatite (HA) formation were observed within 24h. Their setting times and mechanical properties were similar to those of the purely inorganic CPC that is derived from the reaction of TTCP and DCPA in water. Although the mechanical properties of a gelatin-CPC cement were only slightly improved, its handling characteristics were superior to that of CPC. Significantly faster setting and stronger cements were obtained using polycarboxylic acid polymers with CPC. However, only small amounts of HA were observed in these types of polymeric cements even after 1 mon storage in distilled water at 37°C. This research demonstrates the feasibility of preparing several new types of dental cements based on the interaction of water-soluble polymers with a self-setting calcium phosphate powder mixture.