The other side of me (biar nggak dikira orang theologia...)

Production of Nanophase Hydroxyapatite

by using Bacterial Cellulose Membrane System

Tri Windarti, Parsaoran Siahaan, Rofy Restiyo and Winda Purnama

Chemistry Department, MIPA Faculty, Diponegoro University

Hydroxyapatite (HA) [Ca₁₀(PO₄)₆(OH)₂], has been widely used as bone substitute material in clinic application because of its excellent biocompatibility and osteoconduction ^[1]. The aim of bone substitute is to behave temporary in a manner similar to natural bone. From a biological point of view, this material hopefully can reproduce bone crystals with similar composition, structure, morphology, and crystallinity to natural bone ^[2,3]. Numerous methods have been developed to prepare HA powders, such as chemical co-precipitation, sol–gel process, spray-pyrolysis, hydrothermal synthesis and emulsion techniques. Those methods are usually carried out by heating or after-heat-treating. To increase its purity, synthesized HA powders must be treated under hydrothermal condition at 800-1200^oC ^[4,5,6]. However, heating process can reduce osteoconductivity of HA that caused by agglomeration. Furthermore, HA presence in bone is in the form of nanometer sized needle-like crystal of approximately 5-20 nm width and by 60 nm length. Nanophase HA properties such as surface grain size, pore size, wettability, etc, could control protein interaction (for example, adsorption, configuration and bioactivity); therefore, modulating subsequent enhanced osteoblast adhesion and followed by enhanced osteoblast function such as proliferation, alkaline phosphatase synthesis and calcium deposition ^[7].

Bacterial cellulose is a kind of cellulose that produced by bacteria activity. Bacterial cellulose has good properties such as high crystallinity, high polymerization degree, good in mechanical properties and high in purity ^[8,9]. Also bacterial cellulose has pore diameter about 125 nm and the pore size can be modified by using alkaline solution ^[10]. Membrane system is a reaction method in which reactants are separate in two compartments that connected by a membrane. This research was conducted to produce HA by reaction of Ca²⁺ ions and PO₄^3- ions using membrane system. Ca²⁺ ions slowly diffused through the membrane and reacted with PO₄^3- ions to form oriented crystals of HA. Product’s properties depended on ions concentration and pH of PO₄^3- solution. The effect of Ca²⁺ concentration on hydroxyapatite forming was studied in range of 0.1 – 2 M and the influence of pH was studied in of 8 – 12. Experiments were done at room temperature. By using bacterial cellulose as a membrane, HA with nanosized, semi crystalline phase and micro pores can be produced.

Research was carried out in three steps, that were production of bacterial cellulose by Hestrin-Schramm medium and Acetobacter Xylinum bacteria, production of HA by bacterial cellulose membrane system and products analysis by FTIR, XRD, and SEM-EDS. The product’s weight increased as the increase of Ca²⁺ concentration and pH. At low concentration (0.1 M and 0.3 M) the reaction produced product in form of particulate, at middle concentration (0.5 and 0.7 M) formed short tiny fibrous and at high concentration (1, 1.5 and 2M) formed dense long fibrous. Identification by using FTIR and XRD showed that beside hydroxyapatite, the reaction also produce tricalcium phosphate and dicalcium phosphate dihydrate. Product became more crystalline by increasing Ca²⁺ concentration and pH. The SEM image showed the difference of product’s morphology by membrane system and other method (precipitation method). Membrane system method produced porous hydroxyapatite that agglomerate in smaller size (1-5mm). This agglomeration became denser at higher concentration of Ca²⁺ ion. The products on pH 8, 10, 11, 12 were hydroxyapatite and tricalcium phosphate, and on pH 9 was hydroxyapatite. On pH 8, 9, 10 and 11 products phase were semi crystalline and on pH 12 was amorphous. By Scherrer’s equation counted the particle size was 36 nm. Its can be concluded that production of HA by using bacterial cellulose membrane system with 1 M Ca²⁺ and pH 9 produced HA similar to HA in natural bone. From this research, a new method to produce biocompatible, nanophase and semi crystalline phase hydroxyapatite in one step production is invented. Hopefully this method can reduce cost and risk because heating process at high temperature not required.

Keywords: hydroxyapatite, bacterial cellulose, membrane system

Reference

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