Dual Setting β-tricalcium Phosphate Composite Cement

twofold Setting -tricalcium Phosphate Composite CementDual Setting -tricalcium Phosphate Composite Cement Obtained by 3D notionAbstractCalcium inorganic phosphate cements (CPCs) could be employed as celluloid deck up graft substitutes or in the manufacture of scaffolds for tissue engineering. The limitations of these systems argon their misfortunate robot equal medium, which limits its use to places with small mechanized separate outes however, the use of polymeric additives such us acrylamide (AA) and ammonium ion polyacrylate (PA), reinforced the system done in situ polymerisation and add the mechanical properties of the utmost piece. Moreover, the imposition of the cement scaffolds through rapid prototyping technologies at low temperatures such as 3D printing, volition allows the fabrication of more multifactorial anatomys and customization of implants. Thus, the objective of this work was the evaluation of the -tricalcium phosphate/AA/PA system in the fabricat ion of scaffolds by rapid prototyping technology. The results showed sparse differences between the porosities of the printed pieces (61% for cylindrical test bodies and 59% for rectangular) but wet assiduity was signifi bottomtly different for each type of printed form. Mechanical strength (1.3MPa) and flexural strain (3.2MPa) were lower than expected due to the richly porosity of the samples although the morphology of the final real(a) showed the presence of homogeneous and interlinked network of hydroxyapatite crystals. Nevertheless, printed materials might be utilise as spongy graft substitutes or scaffolds for tissue engineering in low-mechanical solicitation.Calcium phosphate cements (CPCs) could be employed as synthetic overdress graft substitutes or scaffolds for tissue engineering allowing the fabrication of more complex geometries and the customization of the implants mainly due to the possibility of be molded 1. Moreover, the use of additive manufacturing technolo gies at low temperatures such as 3D printing permits the fabrication of pieces with enhanced performance over traditional techniques 2-3. Usually, the obtained pieces have low mechanical strength, which limits its use to places with small mechanical stresses however, the use of polymeric additives such as acrylamide (AA) and ammonium polyacrylate (PA), could reinforce the system through in situ polymerization and increase the mechanical properties of the final piece 4.Some studies reports the use of calcium phosphate powders such as -tricalcium phosphate, tetracalcium phosphate, and -tricalcium phosphate -Ca3(PO4)2 -TCP as row material in the manufacture of scaffolds by means of 3D printing technology 5-8. However, none of the reported studies refer the use of dual pointting -TCP-based cement hydraulic system as proposed by the authors.Thus, the aim of this work was the fabrication and impersonation of a dual setting composite cement based on -tricalcium phosphate (-TCP)/AA/PA by 3D printing technology.A Z310 cocksure Printer Prototyper was used to print the pieces. Previously shyntethized -TCP powder 9, was mixed with ammonium persulfate (NH4)2S2O8 and placed in the printer chamber. Powder layer thickness was set to 0.0875mm and binder liquid/powder ratio was 0.31mL/g. The binder was composed by a solution of 5%wt Na2HPO4, 10%wt acrylamide (AA), 1% N,N methylenebisacrylamide and 0.5% N,N,N,N- tetramethylethylenediamide 4. Pieces in the form of cylinders and rectangles for compressive and 4 point bending assays were prototyped.Phase composition of the samples was determined by X-Ray Diffraction (XRD) in a PHILLIPS diffractometer (XPert MPD). Morphological differences were observed by Scanning Electron Microscopy (SEM) using a JEOL microscope (JSM-6060). Compressive strength (CS) and pleating stress (FS) were measured in servohydraulic Universal Testing Machine (Instron 3369) with a weight measuring cell of 2kN and a loading rate of 1 mm/min.Figure 1 shows a photograph of the printed materials after removing powder excess. youngster differences were observed in relation to the original sample size.Figure 2 shows the XRD patterns of -TCP powder and prototyped cement after 7 days in water/37.5C. After setting and aging, round -TCP peaks (JCPDS 09-0348) could be identified in improver to the characteristics peaks of CDHA (JCPDS 46-0905).Mechanical properties, water absorption apparent porosity and density can be observed in Table 1. Values of both compressive strength, and flexure stress were very low. Slight differences between the set of apparent porosity of the samples were prime as a function of the arraignment of prototyped piece on the opposite hand, apparent density values were the same regardless of the format of the piece.Microstructural features of the prototyped material are shown in Figure 4. Typical petal-like plates distinctive of setting and bent -TCP-based cements can be observed both on the surface and the erupt surface. However, the size of the crystals in the inside of the material is higher (5) than those found in the surface and a greater homogeneity is observed. In addition, some unreacted -TCP grains and macropores from about 5 microns of diameter can be observed at the outward of materials. No evidence of the presence of the hydrogel formed during the in situ polymerization of acrylamide was observed.Usually, strength is difficult to reproduce for -TCP-based CPCs because of the variability of -TCP phosphate properties from different sources. Factors like mean particle size and distribution, specific surface area, wettability, and phase impurities markedly influence the properties of the resulting cement.Since the precipitation of CHDA is responsible for the adherence and interlocking of the crystalline grains, which results in hardening the fall of the mechanical strength can be attributed to the low transformation of -TCP into CDHA (Eq 1) according to the results of XRD. The value of the apparent density was close to the hypothetical density of -TCP (2.86g/cm3), confirming no transformation of this phase into CHDA.When polymerization is conducted in aqueous slurry of ceramic powder, the resulted crosslinked polyacrilamide hydrogel is able to bind the ceramic particles and provide strength to the resulting system 10. However, the addition of acrylamide to the system apparently did not work as reinforcement of the -TCP-based cement as expected. Moreover, the presence of the hydrogel after polymerization could be prevented the solubilization of the -TCP particles and subsequently inhibited the precipitation of the CDHA so the strength of materials decreases. Furthermore, the high porosity of the prototyped materials also negatively influences the mechanical strength obtained.Water absorption values were not significantly different from those found for samples of cement without additions hydrogel 11, which reinforces the idea that it could be assertable that th e in situ polymerization of the acrylamide have not occurred.SEM results showed the presence of big(a) number of plate-like crystals of aged CDHA in both surface and fracture surface. Differences in the sizes of the crystals are due to the mechanism of hydrolysis which is dependent on the diffusion of melted through the layer formed and occurs from the inside to the outside of the material. However, even though the presence of this entanglement of CDHA is responsible for the mechanical strength, the existence of unreacted -tricalcium phosphate and the high porosity of the prototyped materials are critical factors in the final properties of the cement.In conclusion, it is possible to obtaining scaffolds of dual setting hydraulic cement by 3D printing. The mechanical properties thereof are low for applications where high mechanical stresses were required. Nevertheless, the obtained pieces were high porosity and could be used as scaffolds for cellular growth and cancellous bone repla cement.AcknowledgmentThe authors acknowledge the financial support from CNPq-the National Science and engineering science Development Council (Research Grant 190005/2013-0).1