Preliminary Radiological In Vivo Study of Calcium Metaphosphate Coated Ti-Alloy Implants

In order to evaluate the bone-implant integration behavior of biodegradable c lcium metaphosphate (CMP, [Ca(PO 3)2]n) coated metallic implant, as-machined, blasted, and blasted /CMP-coated Ti6Al4V screw-type implants were prepared and asepti cally implanted into male New Zealand white rabbits. CMP sol was prepared by sol-gel process and coate on each substrate by dip and spin coating. The CMP coated layer was smooth and uniform with fine grai s, compared to that of as-machined and as-blasted specimens. Each specimen was inserted i nto the defects of bilateral intratibial metaphysis bone and then followed up for 1 and 6 weeks. From the radiographs at 1 and 6 weeks after implantation, all the implants were shown to be apparent ly well integrated with surrounding bone tissue without interfacial fracture, bony resorption, or ra di lucent lines. With the combination of histological results, CMP-coated group was noticed that bony bridges were extending from the endosteum onto the implants at 6 weeks after implantation, wi th the showing good osseo-intergration compared to other two groups. Introduction The development of a stable direct bonding between bone and implant surface (osteointegration) is the critical issue for the long-term success of orthopedic and denta l impl nts. The establishment and maintenance of osteointegration depends on wound healing, repairing and remodel ing f hard tissues. The tissue response to an implant involves physical factors such as i mplant design and surface topography, and chemical factors such as composition and structure of the material surface [1]. To improve the implant fixation to a host bone, several strategies have been developed focusing on the surface modification of materials. For example, the physical surf ace modification of implants in roughness by various techniques has been attracted, because it has been de monstrated that the osteoblastic cells tend to attach more easily to rough surface [ 4], consequently increasing the bone apposition [5]. Chemical surface modifications have been also realized by cova lent attachment of an organic monolayer anchored by a siloxane network [2], and immobilization of specific adhesive peptides like arginine-glycine-aspartic acid-serine (RGDS) [3]. In addition, the implants coated with different bioactive materials such as calcium phosphates, bioactive glasses [6], diamond-like carbon, and amorphous C-N film [7] enha nced the bonding to bone. However, it has been currently reported that the coating layer w s sometimes delaminated from the substrates. Therefore, as one of the alternatives to solve this proble m, the biodegradable material coating on implants, which may allow the organism to replace the for eign material by new bone tissue in a balanced time schedule, was conductd [8]. Calcium metaphosphate (CM P, [ a(PO3)2]n) is a Key Engineering Materials Online: 2003-12-15 ISSN: 1662-9795, Vols. 254-256, pp 881-886 doi:10.4028/www.scientific.net/KEM.254-256.881 © 2004 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-13/03/20,19:47:25) Title of Publication (to be inserted by the publisher) promising biodegradable material due to its hydrolytic degradation behavior of PO 4 3polymeric chains. In this study, in order to preliminarily evaluate in-vivo bone-implant osseo-integration behavior and stability of biodegradable CMP coated implants radiologically and hi stologically, Three groups of metallic screws were aseptically implanted into male New Z aland white rabbits and then followed up for 1 and 6 weeks: as-machined, as-blasted, and blasted/CMP-coated Ti6Al4V. Materials and Methods CMP sol was prepared by the reaction of Ca(NO 3)2·4H2O (Aldrich 99%, USA) with P(OC2H5)3 (Fluka 97%, Japan) in methyl alcohol using correct amounts to obtain the s toichiometric Ca/P ratio of 0.5. First, Ca-precursor dissolved in methyl alcohol was dehydrated at 180 °C and then anhydrous calcium precursor was dissolved in methyl alcohol in Ar-atmosphere. P -precursor was pre-hydrolyzed for 1 hour with the addition of HCl and H 2O as catalysts, before the reaction with the Ca-precursor. The prepared CMP sol was aged at 40 °C for 48 hours. As-machined (group 1), grit-blasted with CMP powder (75~150 μm) (group 2), and blasted and then CMP-coated (group 3) screw-shaped Ti-alloy implants were prepared. CMP sol was coate d by dip and spin coating at 5000 rpm for 50 seconds. CMP coated specimens were immediately dried at 70 °C for 12 hours and then heat-treated at 600 °C for 3 hours. All the specimens were sterilized in an autoclave at 120 °C for 10 min before implantation. The surface morphology was observed with SEM a nd the material phases were identified with XRD. Six groups (as-machined, as-blasted and bl sted/ CMP-coated for 1 and 6 weeks, respectively) of skeletally mature male New Zealand w hite rabbits (2.5 ~ 2.8 Kg) were used for aseptic implantation under general anesthesia induced by Xylaxine (Rumpun, Bayer Korea) 11mg/kg and Ketamine (Ketamine, Yuhan, Korea) 10mg/kg intramuscular inj ection. Bilateral intratibial metaphysis bone defects were formed by a round burr, each specimen was inserted into the defects and then followed up radiologically and histologically for 1 and 6 weeks. Results and Discussion Homogeneous and transparent CMP sol was prepared by sol-gel method. Aft er 48 hour-aging at 40 °C, the appropriate viscosity of CMP sol was obtained for dip and spin coa ti g on Ti-alloy dental implants. The viscosity was 12.7 cP at 27 °C. The surface morphology of the coated and heat-treated CMP layer is smooth and uniform with fine grains (about 100nm), compared to that of as-machined and as-blasted specimens (Fig. 2). The phases of the fine grains wer e identified with -CMP (JCPDS #9-363) from XRD study. The radiography of three different groups at 1 and 6 weeks after implantation showed all the implants were apparently well integra d with surrounding bone tissue, without fractures at the CMP-implant interface, bony resorption, or radiolucent line s. (a) as-machined (b) blasted with CMP (c) blasted/CMP-coated Fig. 1 Ti6Al4V screw-type implants with different surface morphology ( ×12). 882 Bioceramics 16