Aceh Int. J. Sci. Technol., 10(2) 128-138 August, 2021 doi: 10.13170/aijst.10.2.21982 129 Effect of Silica Addition on Mechanical Properties of Eggshell-Derived Hydroxyapatite Fatma 1 , Desnelli 1 , Fahma Riyanti 1,2 , Mustafa Kamal 3 , Muhammad Ramdan Abdul Mannan 4 , Poedji Loekitowati Hariani 1,2,* 1 Department of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Sriwijaya, Indralaya, Indonesia; 2 Research Centre of Advanced Material and Nanocomposite, Faculty of Mathematics and Natural Sciences, Universitas Sriwijaya, Indralaya, Indonesia ; 3 Department of Biology, Faculty of Mathematics and Natural Sciences, Universitas Sriwijaya, Indralaya, Indonesia; 4 Bachelor Program of Chemistry, Faculty of Mathematics and Natural Sciences, Universitas Sriwijaya, Indralaya, Indonesia *Corresponding author email: puji_lukitowati@mipa.unsri.ac.id Received : August 1, 2021 Accepted : September 17, 2021 Online : September 18, 2021 Abstract –Eggshell is a solid waste that is available in abundance but is being left unused. Eggshell containing calcium in a high amount. Calcium can be used as a precursor for hydroxyapatite (HAp). Modification of HAp with SiO2 is expected to improve its low mechanical properties for biomedical applications. In this study, HAp is synthesized from the eggshell. Then, it was modified by adding SiO2 utilizing the coprecipitation method with concentrations of 10%, 20%, 30%, and 40%, respectively. The HAp and HAp/SiO 2 were characterized using; X-ray diffraction and Fourier transform infrared spectroscopy. The analysis HAp and HAp/SiO2 were density, compressive strength, and hardness. The best mechanical properties of HAp/SiO2 were characterized using SEM-EDS. The HAp were prepared successfully with a ratio of Ca/P was 1.673, close to the theoretical 1.67. The addition of SiO2 caused a decrease in crystallite size and density but increased compressive strength and hardness. The best mechanical properties of HAp/SiO2 were obtained with SiO2 of 30% and 40% with similar values. Keywords: Eggshell, hydroxyapatite, SiO2, mechanical properties Introduction Hydroxyapatite (HAp) is one of the materials that has received considerable attention for its potential to apply in various applications, including biomedical products (Gomes et al., 2019), drug delivery (Taha et al., 2020), and skin regeneration (Pal et al., 2020). Besides, it is also promising in waste treatment (Ibrahim et al., 2020; Hariani et al., 2020) and heterogeneous catalysts (Saha et al., 2018). HAp has the molecular formula Ca10(PO4)6(OH)2, which belongs to the type of apatite material compound [M10(XO4)6Z2], which has a crystal phase of the most stable polycrystalline calcium phosphate compound (Wang et al., 2017). The molar ratio of calcium to phosphorus (Ca/P) is about 1.67. HAp is also beneficial for bone tissue engineering applications such as bio-scaffolds (Xiao et al., 2019), bioactive glasses (Bazli et al., 2017), bioceramics (Hubadillah et al., 2020), and implants (Shakir et al., 2018 ). It is similar to human bones and teeth in crystal structure and composition (Xu et al., 2004; Amaechi et al., 2019). HAp is applicable in biomedicine because it has high biocompatibility (Aktug et al., 2017), osteoconductivity (Bovand et al., 2019), and bioactivity (Szczes et al., 2017), and is non-inflammatory, non-immunogenic, and non-