No abstract

No abstract

Abstract:The term calcium phosphate cement was introduced by Gruninger et al. (1). This type of cement can be prepared by reacting a calcium phosphate salt with an aqueous solution, which causes it to set by the crossing of the precipitated crystals. These cements offer a series of advantages that allow their use as grafts and substitutes of damaged parts of the bone system. However, these cements have low mechanical strength compared to human bones. This work studied the influence of the use of polyamide fibers in the mechanical properties of a calcium phosphate cement based on ␣-tricalcium phosphate as well as the mechanisms involved in the increase of mechanical strength. The results demonstrate the feasibility of the use of polymeric fibers to increase mechanical strength and the need for coupling agents for the effective performance of the fibers as reinforcement in these materials.

Leading international institutions are designing and developing various types of ventricular assist devices (VAD) and total artificial hearts (TAH). Some of the commercially available pulsatile VADs are not readily implantable into the thoracic cavity of smaller size patients because of size limitation. The majority of the TAH dimensions requires the removal of the patients' native heart. A miniaturized artificial heart, the auxiliary total artificial heart (ATAH), is being developed in these authors' laboratories. This device is an electromechanically driven ATAH using a brushless direct current (DC) motor fixed in a center metallic piece. This pusher plate-type ATAH control is based on Frank-Starling's law. The beating frequency is regulated through the change of the left preload, assisting the native heart in obtaining adequate blood flow. With the miniaturization of this pump, the average sized patient can have the surgical implantation procedure in the right thoracic cavity without removing the native heart. The left and right stroke volumes are 35 and 32 ml, respectively. In vitro tests were conducted, and the performance curves demonstrate that the ATAH produces 5 L/min of cardiac output at 180 bpm (10 mmHg of left inlet mean pressure and 100 mm Hg of left outlet mean pressure). Taking into account that this ATAH is working along with the native heart, this output is more than satisfactory for such a device.

The term "Calcium Phosphate Cement" (CPC) was formerly introduced by Gruninger et al. (1), who state that this type of cement can be prepared by mixing a calcium phosphate salt with water or with an aqueous solution so that a paste is formed that can react at ambient or body temperatures to produce a precipitate containing one or more different calcium phosphates, and set by the entanglement of precipitated crystals.CPCs offer several advantages over conventional calcium phosphate bioceramics and acrylic bone cement that permit their use as bone graft and substitute, including moldability; minimum bone cavity; direct in vivo insertion; in situ setting; optimum boneimplant contact; and biocompatibility and bioactivity.Moreover, several substances such as antibiotics, antitumoral, or antinflammatory drugs can be easily added to CPCs generating drug delivery systems (2). The main disadvantage of CPCs is their low mechanical resistance, which in the best of cases is equal to that of trabecular bone, or to 20% of the cortical bone. The literature does not contain sound studies related to the increase of the mechanical strength of CPCs. CPCs with mechanical resistance close to that of human bones would have a considerably broader field of clinical applications, currently limited to some orthopedic and maxillofacial procedures.Driessens et al. developed a kind of CPC based on a-tricalcium phosphate (a-TCP) and hydroxyapatite (HA) seeds, and an aqueous solution of Na 2 HPO 4 as mixing liquid. After mixing powder and liquid, a- Abstract: a-Tricalcium phosphate bone cement, as formerly designed and developed by Driessens et al., consists of a powder composed by a-tricalcium phosphate (a-TCP) and hydroxyapatite (HA) seeds, and an aqueous solution of Na 2 HPO 4 as mixing liquid. After mixing powder and liquid, a-TCP dissolves into the liquid and calcium deficient hydroxyapatite (CDHA), more insoluble than the former, precipitates as an entanglement of crystals, which causes the setting and hardening of the cement. a-TCP bone cement offers several advantages in comparison to calcium phosphate bioceramics and acrylic bone cements as bone graft and repairing material, like perfect adaptability to the defect size and shape, osteotransductibility, and absence of thermal effect during setting. The main handicap is its low mechanical strength. Therefore, approaching its mechanical strength to that of human bone could considerably extend its applications. In the present work, an in situ polymerization system based on acrylamide (AA) and ammonium polyacrylate (PA) as liquid reducer was added to a-TCP cement to increase its mechanical strength. The results showed that the addition of 20 wt% of acrylamide and 1 wt% AP to the liquid increased the compressive and tensile strength of a-TCP bone cement by 149 and 69% (55 and 21 MPa), respectively. The improvement in mechanical strength seems to be caused by a decrease of porosity and the reinforcing effect of a polyacrylamide network coexisting with the entanglement of CDHA crystals. The ...