Available online at www.sciencedirect.com Current Opinion in ScienceDirect Biomedical Engineering Key terminology in biomaterials and biocompatibility Laleh Ghasemi-Mobarakeh1, Davood Kolahreez1, Seeram Ramakrishna2 and David Williams3 Abstract Elsevier [5]. Recently, it has been felt that a fresh look Biomaterials have gained much interest as a very important at these and more recently introduced definitions is category of materials because of their wide application in required, especially because of the developments in medicine and benefit to patient such as increased longevity biomaterials science and the expanded range of their and improved quality of life. The biocompatibility of bio- applications. A conference on the definitions related to materials is an important issue, and many researches have biomaterials was held in Chengdu, China, in 2018 for been devoted during the past decades in this field. In this this purpose, in which 53 outstanding biomaterial ex- review, we will focus on basic concepts and key terminologies perts participated from 17 countries and regions; the in the fields of biomaterials and biocompatibility. Moreover, the proceedings of this conference are also being published most recent definitions of the terms related to biomaterials and by Elsevier [6]. Professor David Williams chaired both biocompatibility provided in the 2018 Chengdu consensus conferences, the former when he was at the University conference are stated. Some standard methods for evaluating of Liverpool and the latter when he was at the Wake the concepts related to biomaterials and biocompatibility are Forest Institute of Regenerative Medicine in the USA. also listed in this article. During the Chengdu conference, the status of consensus and provisional consensus was given to defi- nitions that received over 75% and 50e75% yes votes, Addresses 1 Department of Textile Engineering, Isfahan University of Technology, respectively. This review provides readers with the basic Isfahan 84156-83111, Iran concepts and key terminologies in the fields of bio- 2 Department of Mechanical Engineering, Faculty of Engineering, 2 materials and biocompatibility. Some important terms Engineering Drive 3, National University of Singapore, Singapore are also defined according to the existing literature. In 117576, Singapore 3 addition, the exact definitions of the terms provided in Wake Forest Institute of Regenerative Medicine, Winston-Salem, NC, USA the 2018 consensus conference are stated to draw the attention of readers to the most recent definitions. Corresponding author: Ghasemi-Mobarakeh, Laleh (laleh.ghasemi@ However, some of the terms presented in this review cc.iut.ac.ir) have not been defined in the given conference. Some standard methods for evaluating the concepts related to Current Opinion in Biomedical Engineering 2019, 10:45–50 biomaterials and biocompatibility are given in this article. Figure 1 schematically presents the terms that This review comes from a themed issue on Biomaterials: Biomate- rials and Biocompatibility have been studied in this review. Edited by Masoud Mozafari, Masayuki Yamato and Seeram Ramakrishna Biocompatibility Biocompatibility is defined as the ability of a material to perform its desired functions with respect to a medical therapy, to induce an appropriate host response in a https://doi.org/10.1016/j.cobme.2019.02.004 specific application and to interact with living systems 2468-4511/© 2019 Published by Elsevier Inc. without having any risk of injury, toxicity, or rejection by the immune system and undesirable or inappropriate Keywords local or systemic effects [7e17]. The biocompatibility Biomaterials, Biocompatibility. definition which achieved consensus in the 2018 con- ference confirmed the definition agreed in 1985 as ‘the Introduction ability of a material to perform with an appropriate host Biomaterials science has significantly contributed to the response in a specific application.’ rapidly growing fields of surgical and medical technolo- gies over several decades [1e3]. The biocompatibility of Biomaterial biomaterials is a very important issue within these fields, The term ‘biomaterial’ had been defined in 1986 as ‘a and many studies have been devoted to the under- nonviable material used in a medical device, intended to standing of biocompatibility phenomena [4]. In March interact with biological systems.’ At that time, bio- 1986, a consensus conference was held in Chester, UK, materials were largely used in medical devices to treat, focusing on‘amplification of the definitions presented in augment, or replace any tissues, organs, or functions of biomaterials,’ the proceeding of which was published by the body without causing any adverse reaction to living www.sciencedirect.com Current Opinion in Biomedical Engineering 2019, 10:45–50 46 Biomaterials: Biomaterials and biocompatibility Figure 1 Hemocompatibility Hemocompatibility is a feature of biocompatibility describing the compatibility of implanted materials with circulating blood while a medical device can maintain contact with blood without any adverse reactions, such as formation of a thrombus without releasing any components into blood and any undesirable consequences [10,33,34]. The latest definition of this term presented in the 2018 conference is ‘the ability of a blood-contacting biomaterial to (1) avoid the formation of a thrombus by minimal acti- vation of platelets and of blood coagulation, (2) minimize activation of the complement system, and (3) minimize hemolysis.’ However, this definition achieved provisional consensus with 65.9% yes votes. The main difficulty in the discussions was concerned with the differences between the blood compatibility of a biomaterial and medical device because the latter has to take into account the blood flow parameters of the device, whereas the former is an intrinsicpropertyofthematerialalone. Host response (foreign body reaction) In relation to biomaterials, the host response is considered to be the response of a living system to the presence of a Schematic illustration of terms defined in this article. material, which may or may not be inert and nontoxic and which involves the various components of the immune system. It includes acute and chronic inflammation, may tissues [10,18e20]. The need to redefine biomaterial be associated with granulomatous formation around the arose from the fact that the ‘nonviable’ description was device, and may induce local or systemic immunosup- no longer relevant and also because biomaterials were pression or immunoenhancement. The tissue seen in the being used in many applications other than implanted foreign body reaction usually contains inflammatory cells devices, including drug delivery systems, imaging including monocytes and macrophages (which may fuse to contrast agents, and tissue engineering constructs. The give foreign body giant cells) and cells of the fibrosis that definition of biomaterial that achieved a consensus of often forms a capsule around the implants, especially fi- opinion in the 2018 conference is as follows: ‘A material broblasts and myofibroblasts. A variable level of vascular- designed to take a form that can direct, through in- ization, involving capillaries, is usually seen [10,18,35]. teractions with living systems, the course of any thera- According to the discussion opened up in the 2018 con- peutic or diagnostic procedure.’ It was agreed that this ference, this term was defined as ‘the cellular reaction of term is synonymous with ‘biomedical material.’ the biomaterial/tissue that is initiated by monocyte adhesion to the adsorbed blood protein layer with subse- quent monocyte differentiation to macrophage formation Carcinogenicity that may fuse to form (multinucleated) giant cells, i.e., Carcinogenicity is the ability of a chemical, material, or foreign body giant cells.’ However, no voting was agent to either stimulate tumor occurrence inducing performed for this definition. cancer or increase its incidence when it is implanted, injected, ingested, or inhaled [21e26]. According to the limited discussion opened up in the 2018 conference, Implant this term was defined as ‘the species-dependent po- The term ‘implant’ has been defined as a device inser- tential of a biomaterial to promote the formation of a ted or grafted surgically, either temporarily or perma- tumor, usually a sarcoma, at the site of a biomedical nently, within the body to improve, assist or maintain a device or biomaterial ability or tendency to produce function, or enhance/alter a contour. The implants can cancer.’ However, no voting took place for this term. be made from soft tissues, such as blood vessel grafts, or from synthetic materials, such as hip prosthesis, which Foreign body capsule are mostly inert [25,36e39]. The latest definition As noted previously, the foreign body capsule is defined presented in the 2018 conference that achieved as the dense avascular layer of collagen around the consensus is as follows: ‘A medical device made from one implant which acts as both a structural and biological or more biomaterials that is intentionally placed, either barrier between the tissue and implant [27e32]. totally or partially, within the body.’ Current Opinion in Biomedical Engineering 2019, 10:45–50 www.sciencedirect.com Key terminology in biomaterials and biocompatibility Ghasemi-Mobarakeh et al. 47 Table 1 The ISO series of guidance documents for biomaterials and biocompatibility. # ISO number Title 1 ISO 10993-1:2018 Biological evaluation of medical devices—Part 1: Evaluation and testing