Study On The Adsorption Of Biological Molecular On Hydroxyapatite Surface

Hydroxyapatite (HAP) is an excellent bio-inorganic material with good biocompatibility and chemical stability. There are a lot of oxygenic species and electron-deficient centers on HAP surface, which can couple with many active hydroxyl and aldehyde-reactive groups of biological molecules by chemical bond or non-bond. Therefore, HAP is also an excellent carrier of many biological molecules and it is expected that HAP or HAP-based material could be widely applied to biology and medicine fields, and their crossing fields with chemistry, materials, electronics, etc.In this paper, we used HAP block material with micron channel structure as a carrier to adsorb soluble starch, a-amylase and pepsin, respectively, and further studied on the performance of HAP towards the adsorption of these three biomolecules. Further, we expect that the theoretical and experimental results could be helpful to develop the applications of HAP and HAP-based material in biomolecular separation, concentration and in vitro detection and testing in vivo, etc.During the experiment, UV-Vis spectrophotometry was respectively used in analyzing the concentration of soluble starch, a-amylase and pepsin before and after adsorption on HAP, for further studying the adsorption efficiency of HAP. SEM and EDS methods were respectively employed to characterize adsorption spectra of the three biomolecule solutions, morphology and chemical elements of HAP before and after the adsorption experiments.The experimental results show that, under the experimental conditions, the performance of HAP in the adsorptions of soluble starch, a-amylase and pepsin are very different. The adsorption efficiency of soluble starch on HAP is more than 90%, which is the highest among the three biomolecules. We think that the aldehyde group, hydroxyl and other active groups in starch molecule chain can couple with oxygenic groups at HAP surface and form chemical bonds or hydrogen bond. Therefore, the starch molecules can adsorb on the inner wall of HAP micro-channel and form a monolayer film.The adsorption of α-amylase on HAP is some limited, and the maximum adsorption efficiency is 46%. The adsorption of pepsin on HAP, however, is completely limited. We think that the difference among the three adsorptions is caused by both the properties of the three bio-macromolecules and the polar surface of HAP. Both α-amylase and pepsin are protein molecules with surface hydrophobicity, therefore, it is not easily to adsorb on the polar surface of HAP. However, α-amylase is a calcium-dependent enzyme, so that the Ca2+ ions on the surface of HAP can improve the stability and activity of α-amylase. On the other hand, Ca2+ is also the main cation composing a lot of electron-deficient centrals at HAP surface. Therefore, α-amylase molecules can adsorb on the electro-deficient centrals by means of charge compensation. Thus α-amylase can adsorb on HAP, but the adsorption is partly limited. The molecule weight of pepsin is much higher than α-amylase, and the molecule surface of pepsin is short of either nucleophilic group or electrophilic group, therefore it is difficult for pepsin molecule to be close to the polar surface and enter into the micro-channel of HAP.