* Corresponding author. Tel.: # 31-50-3633140; fax: # 31-50- 3633159. E-mail address: h.j.busscher@med.rug.nl (H.J. Busscher). Biomaterials 21 (2000) 1981}1987 Surface roughness, porosity and wettability of gentamicin-loaded bone cements and their antibiotic release H. van de Belt, D. Neut, D.R.A. Uges, W. Schenk, J.R. van Horn, H.C. van der Mei, H.J. Busscher* Department of Orthopedic Surgery, University Hospital Groningen, Hanzeplein 1, 9713 GZ Groningen, Netherlands Department of Biomedical Engineering, University of Groningen, Antonius Deusinglaan 1, 9713 AV Groningen, Netherlands Department of Pharmacy, University Hospital Groningen, Hanzeplein 1, 9713 GZ Groningen, Netherlands Received 12 December 1999; accepted 22 March 2000 Abstract In this study, the release of gentamicin as a function of time was measured for six di!erent gentamicin-loaded bone cements and related with the surface roughness, porosity and wettability of the cements. Initial release rates varied little between the six bone cements (CMW1, CMW3, CMW Endurance, CMW 2000, Palacos, and Palamed) and ranged from 8.6 to 14.1 g/cm/h. The total amounts of gentamicin released after 1 week varied between 4.0 and 5.3% of the total amount of antibiotic incorporated for the CMW cements and was 8.4% for Palacos. Palamed released after 1 week signi"cantly more of the gentamicin incorporated (17.0%). The wettability of all cements was similar (water contact angles between 70 and 803), but the surface roughness and the porosity of the cements varied markedly. Initial release rates increased with surface roughness, although the correlation coe$cient was low (0.64), while total amounts released increased linearly (correlation coe$cient 0.97) with the bulk porosity of the cements. Consequently, it can be concluded that the release kinetics of gentamicin from bone cements is controlled by a combination of surface roughness and porosity.  2000 Elsevier Science Ltd. All rights reserved. Keywords: Polymethylmethacrylate; Gentamicin; Bone cement; Surface roughness; Porosity; Wettability 1. Introduction The incorporation of antibiotics in polymethylmethac- rylate (PMMA) bone cements for the treatment and prevention of infection in orthopedics has become com- mon clinical practice during the last two decades and almost 90% of all orthopedic surgeons in the USA use antibiotic-loaded bone cement for the "xation of implants [1]. Apart from implant "xation, antibiotic- loaded bone cements are used in orthopedics for tempo- rary beads and spacers. Incorporation of antibiotics in bone cements and their release over time is thought to yield higher antibiotic concentrations to the (infected) bone or tissue site than can be achieved by systemic routes. The aminoglycoside gentamicin has developed as the most widely used antibiotic in bone cements due to its wide-spectrum antimicrobial activity, excellent solubility and resistance against elevated temperatures, as during polymerization [2]. There are con#icting reports in the literature concerning the gentamicin elution properties of di!erent acrylic bone cements, which are partly due to the lack of a standardized, in vitro test method [3}5]. Release of antibiotics from PMMA bone cements is largely in#uenced by the penetration of dissolution #uids into the polymer matrix, which requires a certain poros- ity of the cement [6,7]. The porosity of the polymer matrix depends on air entrapment during the wetting and stirring of the cement powder during transfer to the cement gun and on e!ects of monomer boiling [8]. Pen- etration of dissolution #uids into pores of the polymer matrices also depends, however, on the wettability of the bone cement surface, which makes antibiotic release es- sentially a surface phenomenon. By consequence, surface roughness is an important characteristic of antibiotic- loaded bone cements. Despite the widespread clinical use of antibiotic- loaded bone cements, there are growing doubts about the 0142-9612/00/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 2 - 9 6 1 2 ( 0 0 ) 0 0 0 8 2 - X