Download Phosphate-Calcium Concrets as Bioceramic Drug Delivery Systems

Phosphate-Calcium Cements as Bioceramic Drug Delivery Systems
A. Zima, A. Ślósarczyk, J. Rawska
Faculty of Materials Science and Ceramics, AGH-University of Science and Technology,
30-059 Cracow, Al. Mickiewicza 30, Poland
Implants on the basis of calcium phosphates, mainly hydroxyapatite, HAp
[Ca10(PO4)6(OH)2 ] and TCP [Ca3(PO4)2], have been used for many years to fill bone tissue
losses caused by diseases or mechanical injuries. Bone inflammation states occurring
frequently after surgical treatment are a serious problem in the healing process. Therefore
intense studies on implant materials playing the role of both, bone loss fillers and carriers
for controlled, local drug release are carried out. Granular and porous HAp and TCP –
based implants are the most frequent ones; dense profiles are less common. Powdery
formulations are also sometimes used.
The aim of our studies has been to work out the calcium-phosphate based cements
which can be applied as fillers for bone tissue losses and to test in vitro their applicability
as homogenous drug delivery systems.
αTCP (98 wt. %) and HAp (2 wt. %) have been the main components of the
investigated cements. αTCP prepared in the Bioceramic Laboratory of the Department of
Ceramic Technology at AGH-UST Faculty of Materials Science and Ceramics as well as
produced by Taichei Chemical Industry have been used in the investigations. 3% Na2HPO4
solution has been applied as the binding liquid. Setting time, phase composition,
microstructure, compression strength of the obtained cements have been examined. pH
and conductivity of the solutions surrounding the cement samples maintained for four
months in distilled water and in simulated body fluid (SBF) have been determined. The
cement showing the shortest setting time (8,5 min) and the highest compression strength
(25 MPa) has been selected for kinetic investigations of the release of pentoxyfiline (PTX)
as the model drug. The drug concentration in the samples has been determined
spectrophotometrically using 275 nm as the analytical wavelength.
It has been found that the cement setting process is significantly influenced by the
substrate grain size. Too large grains of αTCP powder produced by Taichei have inhibited
the setting of the cement containing it. As the surface area of the studied powders has
increased the setting time of these powders-based concretes has shortened. In the ageing
process both, the microstructure of the samples after setting and solidification and the type
of αTCP applied played an important role. Mechanical strength studies have shown that
ageing processes have been intense in the material containing the Japanese αTCP powder
(almost three-fold decrease in mechanical strength after five months of maintaining the
samples in distilled water). In the case of other cements the changes have been small. pH
values around the samples placed in aqueous solutions have been equal to ca. 7 what is
closed to the physiological level.
Keywords: TCP, bone cements, drug carriers.