Original Research Article Proc IMechE Part C: J Mechanical Engineering Science 2021, Vol. 0(0) 1–19 © The Author(s) 2021 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/09544062211050456 journals.sagepub.com/home/pic Mesoscale modeling and biocompatibility of nano-hydroxyapatite reinforced ultra-high molecular weight polyethylene composite Nishant Verma 1 , Anand Kumar Keshri 2 , Himanshu Pathak 1 , Sunny Zafar 1  and Amit Prasad 2 Abstract This work aims to implement an efficient and accurate computational model to predict elastoplastic properties of UHMWPE/ nano-HA bio-composite. Mean-field (MF) homogenization and finite element (FE) techniques are implemented to predict the elastoplastic behavior of composite. The predicted results obtained by MF and FE were compared and validated experi- mentally by fabricating the specimen using microwave-assisted compression molding. The axial and transverse moduli were increased by 49% at a 20% weight fraction of nano-HA. The hardening modulus was also found to be increased by 67%. Further, Degree of crystallinity (X c ) of fabricated composite specimens was determined using differential scanning calorimetry analysis. It was found that the X c increased 34% with the addition of 20% weight fraction of nano-HA. In vitro, direct contact cytotoxicity and antibacterial test were performed to determine cell adhesion and bacterial behavior of the composite. Keywords Mesoscale modeling, mean-field homogenization, ultra-high molecular weight polyethylene, nano-HA, degree of crystallinity, In vitro direct contact cytotoxicity, antibacterial test Date received: 15 May 2021; accepted: 12 September 2021 Introduction Nano-structured materials have been attracting the attention of researchers, scientists, and structure designers due to their excellent mechanical properties. These types of ma- terials include nano-particles, nano-rods, nano-composites, and nano-tubes. Nano-composites are the materials in which the filler particles form the second phase exhibit dimensions in the nano meter range. These composites are also becoming very popular in the field of biomedical applications. Nano-hydroxyapatite (nano-HA) is a popular bio-ceramic due to its excellent biocompatibility. 1–3 Ultra- high molecular weight polyethylene (UHMWPE) is also a popular biopolymer for knee and hip implant applications. The presence of nano-HA in UHMWPE contributes to enhancing Young’ s modulus and bioactivity. 4–6 Nano-HA reinforced UHMWPE composite is a better alternative material for biomedical implants over metallic implants due to their lighter weight, high strength to weight ratio, and low manufacturing cost. 7 Nano-HA contributes more to the increase of Young’ s modulus over micro-HA. This is due to the high surface area to volume ratio of nano-sized HA particles over mico-sized HA particles. 8 The material property of single-phase material can be determined directly by measurement or the first principle of simulation. 9 The multi-phase material can be altered as per the application’ s requirement. These materials are generally subjected to extreme loading conditions during service. Therefore to predict the mechanical property is essential for design and application at a macroscopic level. To perform experiments at different weight fractions, sizes, orientations, and dis- tribution of inclusion is not an economical task due to the high cost of materials and fabrication. 10 The various mi- cromechanics’ approaches have been developed to predict material properties of multi-phase materials. In 1957, Eshelby developed an approximation method to determine the elastic field of elliptical particles. 11 Similarly, in 1962,Hashin 12 and Budiansky 13 developed an approximate method to determine elastic modulus of heterogeneous materials. The formulation of Hashin was based on the theory of elasticity, concentric-spheres model, and varia- tional theorem. Further, Mori Tanaka developed a mean-field (MF) homogenization technique, which predicts better mechan- ical properties of short fiber-reinforced composite (FRC). 13 This method could predict the mechanical properties at different fiber orientations by introducing orientation tensor 1 Composite Design and Manufacturing Research Group, School of Engineering, Indian Institute of Technology Mandi, Mandi, Himachal Pradesh, India-175075 2 School of Basic Sciences, Indian Institute of Technology Mandi, Mandi, Himachal Pradesh, India-175075 Corresponding author: Himanshu Pathak, Composite Design and Manufacturing Research Group, School of Engineering, Indian Institute of Technology Mandi, VPO Kamand, Mandi 175075, Himachal Pradesh, India. Email: himanshu@iitmandi.ac.in