Preparation of Biologically Active Materials by Biomimetic Process

Vol.17 No. 1Journal of Wuhan University of Technology - Mater. Sci. Ed.Mar. 2002Preparation of Biologically Active Materials by Biomimetic ProcessFAN Dong-huil) XU Zheng' ) LI Shi-pu2YAN Yu-hua2lTongji University ? )Wuhan University of Technology( Received :Aug.2 2001 )Abstract : In order to form the apatie ruclei on a suface of the substrate ,the substrate rwas placed on orin CaO ,sSiO2 -based glass particles which were soaked in a simulated body fluid with ion concentrations nearly e-qual lo those of human blood plasma ,and lo make the apatie nuclei grou on the substrate in situ ,the substratlewas soahked in another solution highly supersaturated with respect to the apatite. The induction period for the ap-atite nucleation uaried from 0 l0o 4 days depending on the kind of the substrate . The thickness of the apatie layerincreases linearly with increasing soahing time in the second solution. The rate of grouth of the apatite layer in-creases rwih increasing degree of the supersaturation and temperature of the second solution , reaching 7um/d in asolution with ion concentrations which is as 1.5 times as those of the simulated body fluid at 60 C . The adhesivestrength of the apatite layer to the substrate varies depending on the kind and roughness of the substrale .Polyethyleneterephthalate and polyethersulfone plates abraded with No . 400 diamond paste show adhesive strengthsof as high as 4 MPa. This lype of composite of the bone- like apatie with metals , ceramics and organic polymersmight be useful not only as highly biouctive hard tsse. repairing materials with analogous mechanical properties tothose of the hard tsses , but also as highly biocompatible soft tsse- repairing materials uwith ductility.Key words: bioactive materials ; biomimetic process ; preparation ; aqpatite nmucles1 Introductionbiomimetic process in vitro at normnal temperature andpressure . The resultant composites could exhibit not only aVarious kinds of bioactive glasses and glass- ceramicshigh bioactivity to bony tissues ,but also an excellent bio-show their bond to living bone through a layer of a biolog-compatiblity even to soft tissues . Their mechanical prop-ically active bone-like apatite ,i. e . hydroxyapatite with aerties could be varied widely in strength , toughness , elas-defective structure and small crystallites , which is formedtic modulus etc . depending on the kind and three- dimen-on their surface in the body121. According to the recentsional structure of the substrate. Hence , the resultantstudies by some scientists , the bone-like apatite layer iscomposites might be useful not only as hard tissue-repair-formed on the surfaces of CaO , SiO2-based glasses anding materials ,but also as soft tissue-repairing materials.glass- ceramics by the following mechanisnt 31 calcium ionIn the present paper , the results of the investigations ondissolved from the glasses and glass-ceramics increase ththe method for preparing such composites , the rates of theionic activity product of the apatite in the surroundingnucleation and growth of the apatite layer on the substratesbody fluid ，which is already supersaturated with respect toand the adhesive strength of the apatite layer to substratesthe apatite even under a nommal condition . The hydratedare reviewed. .silica on the surfaces of the glasses and glass ceramicsprovides favorable sites for the apatite nucleation. Conse-2 Method for Forming Apatite Layerquently, a large number of the apatite nuclei is rapidlyformed on the surfaces of glasses and glass - ceramics .On the basis of the mechanism of apatite formationOnce the apatite nuclei are formed ，they grow sponta-on CaO , SiO2-based glasses and glass- ceramics , the fol-neously by consuming the calcium and phosphate ionslowing biomimetic method consisting of two steps was defrom the surrounding supersaturated body fluid.signed for forming the bone-like apatite layer on variousConsequently ,it is expected that the bone-like ap-substate中国煤化工pressure.In the firstatite layer could be formed on various kinds of materialsstep , inYHCNMHGTr of apatite nuclei oninvolving metals , ceramics and organic polymers byithe surface or a sunsurale ,ie sunsurate was placed on orin granular particles of a CaO SiO2-based glass which wasFAN Dong-hu( 樊东辉) :Borm in 1964 ;Senior Engineer ;Mi-soaked in a simulated body fluid with ion concentrationscrelectmic Materials Institute ,Dept. of Mater. Sci. and Eng. ,nearly equal to those of human blood plasma at 36.5 9C.Tongji Univeit bhaghai 200092 ,ChinaThe particle sizes of the CaO ,SiO2-based glass grains ,20Joumal of Wuhan University of Technology - Mater. Sci. Ed.Mar. 2002with the nominal compositions MgO 4.6, CaO 44. 7 ,was confimed by thin-film X-ray diffraction and FourierSiO2 34.0 ,P2Os 16.2 ,and CaF20.5 wt% ,were 150 totransform infrared reflection spectroscopy that the new ma-300 pμm in diameter.terial formed on the substrates was the bone- like apatite ,The ion concentrations of the simulated body fluidi.e , hydroxyapatite ,with small crystallites and defective( SBF ) are listed in Table 1 , in comparison with those ofstructure, as shown in Figs. 2 and 3. This apatite layerhuman blood plasma. The ratio of the glass particles towas formed even on thin fibers , their woven cloths , andthe fluid is 1.5g to 30mL. In the second step , in order tofine particles .make the apatite nuclei grow on the substrate in situ , thesubstrate was soaked in another solution which was super-1 Apotitesaturated with respect to the apatite. A typical example oflayerthe solution for the second treatment was a solution( 1.5 .SBF ) with ion concentrations 1.5 times as those of SBF ,as shown in Table 1 ,at 36.5 C. Both of SBF and 1.5ZirconinsubstrateSBF are buffered at pH 7.25 at 36 . 59C with trishydrox-ymethyl aminomethane (( CH2OH )》CNH2 ) and hy-drochloric acid( HCl ). The second solution was renewedSpurnevery 12 to 48h. A polystyrene bottle was usually used asa container for the both treatments .For example , when rectangular substrates of 10mmx 15mmX 1 to 0.1mm in size abraded with No. 400 dia-然Apatitelayrmond paste ,were subjected to the first treatment for 6days and then to the second treatment for 6 more days ,adense and uniform layer of a new material was formed onPMMAthe surfaces of all kinds of examined substrates includingstainless steel , titanium metal , Ti-6Al-4V alloy , plat-inum , gold , silica glass，B-quartz single crystal ,sinteredalumina ,sintered zirconia ,polyvinylchloride ,cellulosetri-Spumacetate ,polyethyleneterephthalate ,polymethylmethacrylateFig. 1 SEM photographs of apatite layers formed on variouspolyethersulfone polytetrafluoroethylene ,Nylon ,polyethy-substrateslene and polyvinylalchol hydrogel as shown in Fig.1.ItTable 1 lon Concentrations/mM of SBF and 1.5 SBF in Composition With Those of Human Blood PlasmaNa+<+Ca2+MgZ+HCO* -HPOR”So2-Blood plasma142.05.02.51.527.0103.01.00.5SBF4.2148.01.5 SBF213.07.53.82.6.30.75jecting the substrates to the first treatment for different3 Nucleation Rate of Apatitetime 0 h to 7 days ,and then to the second treatment for 6days. Thus determined induction periods for the apatiteIn general ,if the first treatment is onmitted in the pro-nucleation on various substrates are shown in Tables 2 andcess described above sthe apatite is not formed at all after3. It varied from 0 to 4 days depending on the substratethe second treatment . When the period in the first treat-for inorganic materials . whereas it was about 1 day for or-ment is short ,the apatite is only sparsely formed on theganic中国煤化工slicon single erystalsubstrate. A certain period of time in the first treatment isformedC N M H Girst treatment since arequired for forming a continuous and uniform apatite laythin silica gel layer was formed on the single crystal ,ander after the second treatment. This time in the first treat-the apatite can nucleate on the surface of silica gel layer ,ment was defined as the induction period for the apatiteimmediately after soaked in the second solution .nucleationad数程sured for various substrates ,by sub-Vol.17 No. 1FAN Dong-hui et al Preparation of Biologically Active Materials by...21of the growth rate on the temperature ,was 43.2 kJ/mol .4 Growth Rate of Apatite LayerThis high activation energy indicates that the growth of theapatite layer is controlled by the surface process ratherThe thickness of the apatite layer formed after thethan by ion transport in the solution. When the ion con-second treatment increased with increasing time of soakingcentrations of the second solution were changed from 0.2in the second solution. For example , when a sintered alu-to 1.5 times as those of SBF at 36.5 C ,the rate of themina plate was subjected to the first treatment for 2 daysgrowth of the apatite layer increased from 0. 15 to 1. 7and then to the second treatment for different periods , theum/d with increasing ion concentrations from 0.2 to 1.5thickness of the formed apatite layer increased linearlySBF , as shown in Fig. 5. Their relations are representedwith increasing soaking time in the second solution at aby the equation R= kon ,where R is the growth rate σ israte of 1.7μm/d at 36.5 C( shown in Fig.4 ). The rate ofrelative supersaturatiort4I , and n = 1.3. Here ,n valuethe growth of the apatite layer increased from 0.5 to 7.that indicates that the growth of the apatite layer is con-0um/d with increasing temperatures of the second solutiontrolled by the surface process or ion transport in the solu-from 10 to 60 C. The activation energy for the growth oftion. This is consistent with the result derived from thethe apatite layer ,which was derived from the dependencetemperature dependence of the growth rate.0- -Apatite .0- -Apatite●- -Substrate●-SubstratePMMAPMMA__ ?TitaniumTimium!ZirconiaZironia20305020001500100050020(CuKa)YdegFig.2 Thin-film X-ray difaction patterms ofFig.3 FT-IR rllection spectra of surfacessurfaces of various substratesof various substratesTable 2 Induction Periods for Apatite Nucleation on Various Inorganic SubstratesSubstrateTitanium metalSi-T-C-0 clothCartbon clotha-AluminaSintered aluminasingle crystalPeriod4c4d2d_2da- Alumnina fiberssoda- line slide glassβ-QuartzFused silica glass Silicon single crystal2(d_1ld_0Table 3 Induction Periods for Apatite Nucleation on Varous Polymer SubstratesPolyethylenet-Polymethylmet-PolyinylchlorideCellulosetriacelatePolyehersulfoneerephthalatehacrylate1dPolytetrafluorPolyvinylalcholNylon 6Polyethylenehydrogeloethylen1cld1中国煤化工kind andYHC NMH G. Table 4 shows the5 Adhesive Strength of Apatite Layertensile adhesive strength for some kinds of organic poly-mers. It can be seen from Table 4 that polyvinylalcoholThe adhesive strength of the apatite layer formed byhydrogel , polyethyleneterephthalate and polyethersulfonethe present 5p方数据n the substrate depends largely on theshow relatively higher adhesive strengths. The experi-22Joumal of Wuhan University of Technology - Mater. Sci. Ed.Mar. 2002ments show that the apatite layer formed on fine fibers offormed on a polyethersulfone plate abraded with # 400 di-the polyethyleneterephthalate cloth is not peeled off , evenamond paste can not be peeled off , even though scratchedif the cloth is sharply bent. In addition ,the apatite layerby sharp knife edge.Table 4 Adhesive Strength of the Apatite Layer to the Organic PolymersPolyvinylalchol hydrogeTSubstratePolyethyleneterephthalatePolymethylmethacrylate( cntaining 22% water )Adhesive strength/MPa3.203.481.06PolyethersulfoneNylon 6PolyethyenePolytetafluoroethylene4.400.631.93<1.1x10-23t;60C1.5 SBFSBF36.5 C0.5 SBF0c0.2SBF1436444Soaking time/hourSoaking timeldayFig.4 Thickness of apatite layer formed in 1.5 SBF atFig.5 Thickness of apatite layer formed in solutionsdifferent temperatures as a function of soakingwith different ion concentrations as a functiontimeof soaking timefore，considered as promising materials for repairing not6 Conclusiononly hard tissues , but also soft tissues .It is apparent from the results described above that aReferencesdense and uniform apatite layer can be formed on anykind of materials involving metals , ceramics and organic1 Z Sewlin et al. Healing of Rabbit Calvaral Defects is Aided bypolymers by a biomimetic process using a CaO，SiO2 -Coral/Collagen/rhBMP-2 Composite . Journal of Nanjing Univer-sity ,1999 355 )547-553based glass as a nucleating agent at normal temperature2 s Pllick E C Shors et al . Bone Formation and Implant Degra-and pressure .dation of Caralline Porous Ceramics Place in Bone and EctopicThe bone-like apatite shows a high bonding ability toSite. Journal of Oral Marillofac Surg. ,1995 53( 3) 915- 922living bone as well as an excellent compatibility to living3WJan[0"中国煤化工valuation of Ceramic Calsoft tisues. The composites prepared by the presentcium HGraft. Bone Replacement ,method could be fabricated into three-dimensional struc-;TYHCNMHGtures analogous to those of the natural tissues and hence4 N Surindar ,D C Colonel et al . Biodegradable Ceramic Implantscould show mechanical properties analogous to those of thein Bone. Oral Sury. ,1999 32 2 )336 - 345natural tissues. These types of composites can be ,there-