JOURNAL OF MATERIALS SCIENCE: MATERIALS IN MEDICINE 10 (1999) 383±388 Development of porous spherical hydroxyapatite granules: application towards protein delivery W. PAUL, C. P. SHARMA* Division of Biosurface Technology, Sree Chitra Tirunal Institute for Medical Sciences & Technology, Biomedical Technology Wing, Trivandrum 695 012, India A new method for the preparation of porous spherical hydroxyapatite granules is reported. It may be clinically applied towards orthopaedic or maxillofacial surgery as ®llers or packing materials, and as biological chromatography supports. Its application towards delivery of macromolecules or protein drugs is discussed utilizing human serum albumin (HSA) as a model protein. # 1999 Kluwer Academic Publishers 1. Introduction Hydroxyapatite (HA) is the major component of the skeletal tissue of vertebrates. Studies have shown that synthetic HA is totally biocompatible, non-toxic and osteoconductive [1]. HA-based bone graft materials have considerable potential as bone substitute in medical and dental treatments. HA is also an attractive material for high performance liquid chromatography (HPLC) [2, 3]. Several forms of HA ceramic have been clinically and experimentally used: solid and porous blocks, and solid and porous particulate. Recently the particulate form has received much attention from the research ®eld as well as from industry. Various particulate products are commer- cially available and are widely used as ®llers or packing materials. They are manufactured and sold primarily for the oral surgery market. The different forms of particulate HA include irregular multifaceted particles and rounded smooth particles, with solid or porous structure. They are osteoconductive and help ingrowth and attachment of bone [4, 5], and are clinically used in oral surgical procedures to augment the alveolar ridge [6] and in periodontal repair [7]. Kent et al. [8] reported improved denture stability and retention when dense particulate HA has been used for augmentation of atrophic mandibular and maxillary alveolar ridges. However, irregular morphology caused in¯ammatory reactions [9], and also bone formation was slower compared to smooth particles. A number of studies reported the development of granulates by hydrothermal reaction of corals [10], by crushing sintered blocks, by means of vibration and rolling [11], by dripping [12] and drip casting [13] procedures, etc., with irregular or spherical geometry. In this investigation, a new method to produce porous spherical particulate form of HA is developed, utilizing chitosan as a binding agent. This particulate form could be designed for a wide range of biomedical applications such as ®llers, delivery of antibiotics [14] and macro- molecules or contraceptives, and as a matrix for haemoperfusion [15] or (HPLC), etc. The preparation and characterization of spherical particulate are reported and its application towards the sustained delivery of macromolecular drugs is demonstrated utilizing human serum albumin (HSA) as a model protein. 2. Materials and methods Hydroxyapatite powder was prepared from analytical grades Ca(OH) 2 and H 3 PO 4 by precipitation method similar to that reported earlier at a reaction temperature of 100  C [16, 17]. Chitosan is a biopolymer, a deacetylated product of chitin. Biomedical grade chitosan (degree of deacetylation, 86.98%; viscosity average molecular weight, 6.9 6 10 5 Da; intrinsic visc- osity, 5.77 mPa s) was obtained as a gift from Central Institute of Fisheries Technology, Cochin, India. Glutaraldehyde (25% aqueous solution), sorbitan mono- oleate (Span 80), and human serum albumin (HSA, Fraction V) was from Sigma Chemical Co., USA. Poly(DL -lactic acid) (PLA, M w 100 000) was from Polysciences, USA. Liquid paraf®n (heavy; viscosity 0.009 Pa s at 30  C and light; viscosity 0.0018 Pa s at 30  C) was obtained from SD Fine Chem, Bombay, India. Solvents such as acetic acid, petroleum ether and acetone were of analytical grades. 2.1. Preparation of hydroxyapatite spherical particles Fine HA powders 20 g, was mixed with 40 g of 2% (w/v) chitosan solution in 2% (v/v) acetic acid. Well-mixed HA/chitosan slurry was dispersed in 500 ml of dispersion medium, which was a mixture of heavy and light liquid paraf®n and 0.4 mg of span 80 as stabilizing agent in a 1000 ml reaction ¯ask by stirring at 400 r.p.m. with a halfmoon paddle stirrer. After about 5 min, required amounts of glutaraldehyde were added to harden the spheres obtained. After 30 min spheres were ®ltered, *Author to whom correspondence should be addressed. E-mail: bmtwing@md2.vsnl.net.in. 0957±4530 # 1999 Kluwer Academic Publishers 383