Abstract The objective of this work was to produce brushite cement for orthopedic applications, based on the system wollastonite/phosphoric acid with the incorporation of polyethylene glycol (PEG) as a setting and processing additive. Brushite/PEG cement was obtained by the dissolution-precipitation method and its physicochemical properties were characterized by X-ray diffraction, compressive strength, porosimetry, and biological behavior (cell adhesion and bioactivity tests). The results indicated the formation of brushite cement with 21.4 MPa of compressive strength and 30% porosity, similar to human trabecular bone. The surface was shown to be adequate for cell adhesion and growth and bioactive with the formation of apatite layers. The incorporation of PEG improved working conditions without causing undesirable changes in the physicochemical properties and biological behavior of developed cement, thus promising for the repair of bone tissue injuries.

Resumo Microesferas de α-TCP foram obtidas atomizando uma suspensão aquosa contendo 50% em massa de α-TCP com baixa cristalinidade e 1% em massa de ácido cítrico. Poli(etileno glicol) e poli(álcool vinílico) foram testados como ligantes. O processo de spray drying resultou em microesferas com diâmetros médios de aproximadamente 20 μm e esfericidade (razão de comprimentos na horizontal e na vertical) próxima a um, características essenciais para várias aplicações, como a liberação controlada de drogas e cimentos ósseos injetáveis. A adição dos ligantes foi necessária para reduzir a quantidade de partículas soltas e aumentar a fluidez do pó, mas também resultou em uma redução na molhabilidade e na área superficial das microesferas. Os melhores resultados foram obtidos com 3% de PVA já que as microesferas apresentaram a maior área superficial, molhabilidade e esfericidade. As microesferas preparadas neste estudo podem ser utilizadas como precursoras de cimentos ósseos injetáveis, já que a sua geometria esférica e sua fluidez favorecem a homogeneidade e injetabilidade das pastas sobrepujando as principais dificuldades dos cimentos injetáveis atuais.

Abstract a-TCP microspheres were obtained by atomizing aqueous slurries containing 50 wt% of low crystallinity α-TCP and 1 wt% of citric acid. Poly(ethylene glycol) and poly(vinyl alcohol) were tested as a binder. The spray drying process yielded to microspheres with mean diameter around 20 μm and sphericity (horizontal and vertical length ratio) closest to one, which is essential to many applications, such as drug delivery and injectability of cements. The addition of binders was necessary to decrease the amount of loose particles and to improve powder flowability but it also caused a reduction in wettability and surface area. Best results were achieved with 3 wt% of PVA, as the microspheres presented the highest specific surface area, wettability, and sphericity. The microspheres prepared in this study may be used as injectable bone cements precursor since their geometry and flowability would favor paste homogeneity and injectability overcoming many drawbacks of today’s injectable bone cements.

"Dual-setting" calcium phosphate cements (DS-CPCs), characterized by a polymerization reaction that proceeds along with the conventional hydraulic setting, were prepared and studied. Acrylamide (AA), 2-hydroxyethyl methacrylate (HEMA), and N-vinyl-2-pyrrolydone (VP) in 5, 10, and 20 wt./vol.-% were added to the liquid of α-tricalcium phosphate (α-TCP) and tetracalcium phosphate/dicalcium phosphate anhydrous (TTCP/ DCPA) conventional cements. N,N´-methylenebisa-crylamide was used as cross linking agent. N,N,N´,N´-tetramethylethylendiamine in the liquid, and ammonium persulfate in the powder, were employed as polymerization catalyst and initiator, respectively. Diametral tensile strength (DTS), setting time, phase composition, conversion rate, and microstructure of the DS-CPC were compared with those of non-added cements. The DTS increased 22 % for α-TCP and 85 % for TTCP/DCPA DS-CPCs by adding 20 wt./vol.-% AA. The HEMA and VP had no positive effect on DTS. The extent of the hydraulic setting reaction for α-TCP DS-CPC was only slightly decreased by the addition of 20 wt./vol.-% of AA to the mixing liquid.