Original Article Journal of Intelligent Material Systems and Structures 1–14 Ó The Author(s) 2020 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/1045389X20932212 journals.sagepub.com/home/jim Synthesis, characterization, crystallinity, mechanical properties, and shape memory behavior of polyurethane/hydroxyapatite nanocomposites Maryam Jalili Marand 1,2 , Mostafa Rezaei 1,2 , Amin Babaie 1,2 and Reza Lotfi 1,2 Abstract Herein, polycaprolactone diols with diverse molecular weights were synthesized by ring-opening method. Then, polyur- ethanes were synthesized through two-step pre-polymerization method by polyaddition of hydroxyl and –NCO groups. Afterward, a set of polyurethanes/hydroxyapatite nanocomposites were synthesized through solution casting as well as in situ polycondensation methods. The exact nominal molecular weights of the synthesized polycaprolactones were determined by proton nuclear magnetic resonance (hydrogen-1 nuclear magnetic resonance). Hydrogen bonding index of ester and urethane carbonyl groups (HBI (C = O) ) of samples was determined through Fourier-transform infrared spec- troscopy. Results showed that the incorporating of the hydroxyapatite nanoparticles has reduced HBI (C = O) . X-ray dif- fraction patterns and differential scanning calorimetry thermographs confirmed the barrierity and nucleation performance of hydroxyapatite nanoparticles, and the variation of phase mixing degree of polyurethane’s hard and soft segments has altered the crystals size and degree of crystalline in polyurethane/hydroxyapatite nanocomposites. Field emission scanning electron microscope images showed that hydroxyapatite nanoparticles have been uniformly dispersed through in situ polymerization method. Mechanical properties were studied in the terms of HBI (C = O) , hydroxyapatite nanoparticles content, and degree of crystallinity. Two different programming procedures were used to evaluate shape fixity and recovery ratios of samples at room temperature and 60°C. Keywords Shape memory polyurethane nanocomposite, hydroxyapatite nanoparticles, crystallinity, thermally-activated, mechanical properties 1. Introduction Healing and replacement of damaged tissue are one of the greatest subjects in medical science. Nowadays, tis- sue engineering is considered as a novel method to restore the structure and function of damaged tissue (Marzec et al., 2017; Yu et al., 2018). In the reconstruc- tion of bone tissue, the proper selection of bio-material is an important step in designing and manufacturing biocompatible materials with desirable properties such as bioactivity and biodegradability (Dvir et al., 2011; Salgado et al., 2004). Among various polymers, shape memory polyurethane (SMPU) has attracted considerable attention in tissue engineering regarding its biocompatibility, biodegradability, and antimicro- bial properties (Armentano et al., 2010; Kishan et al., 2017; Pandini et al., 2016; Wang et al., 2018; Zhang et al., 2019). Over the course of the last years, several researches have been conducted on the development of SMPU nanocomposites and different nanofillers for various applications and improvement of mechanical, 1 Institute of Polymeric Materials, Sahand University of Technology, Tabriz, Iran 2 Polymer Engineering Department, Sahand University of Technology, Tabriz, Iran Corresponding author: Mostafa Rezaei, Polymer Engineering Department, Sahand University of Technology, P.O. Box 51335-1996, Tabriz, Iran. Email: rezaei@sut.ac.ir