Contents lists available at ScienceDirect Journal of the Mechanical Behavior of Biomedical Materials journal homepage: www.elsevier.com/locate/jmbbm Comprehensive characterization of silica-modified silicon rubbers Ioana Chiulan a,∗∗ , Denis Mihaela Panaitescu a , Elena-Ruxandra Radu a , Adriana Nicoleta Frone a , Raluca Augusta Gabor a , Cristian Andi Nicolae a , George Jinescu b , Vlad Tofan c , Gary Chinga-Carrasco d,∗ a ICECHIM, 202 Splaiul Independentei, 060021, Bucharest, Romania b Carol Davila University of Medicine and Pharmacy, 37 Dionisie Lupu, 020022, Bucharest, Romania c Cantacuzino National Institute of Research and Development for Microbiology and Immunology, 103 Splaiul Independentei, 050096, Bucharest, Romania d RISE PFI, Høgskoleringen 6b, NO-7491, Trondheim, Norway ABSTRACT In this study a commercially liquid silicone rubber was filled with fumed silica particles in different concentrations and evaluated for medical applications. The thermal, morphological and mechanical properties of silicone/silica composite samples were studied before and after aging, flexural tests and immersion in saline environment. Understanding the effect of silica content, aging conditions and thickness (from 0.6 to 2 mm) of the samples on the behavior of these materials in different environments is crucial for applications as implantable devices. Before inducing any mechanical stress, tensile strength was found to increase for samples containing3or5wt%offumedsilica,dependingonthethickness.Asimilartrendwasobservedafter10 6 flexes for tensile strength, storage modulus and hardness at roomtemperature,whichincreasedwiththeconcentrationoffumedsilica.Moreover,tensilestrengthdecreasedwithincreasingthethicknessofthesamplesfrom0.6 to2mm.Thethermaldegradationwasfoundtostartathighertemperatureinthecaseofthecompositesascomparedwithneatsilicone,however,theglasstransition and melting temperatures were only slightly modified by the presence of the silica particles, regardless the mechanical aging. The MTT assay using L929 fibroblasts mouse cells showed a good short-time cytocompatibility for both silicone elastomer and the composite with 3 wt% fumed silica. Similarly, the measurement of the cytokine secretion revealed no inflammatory response. 1. Introduction Silicones are highly versatile materials, suitable for various in- dustries and applications, due to their high elasticity, biocompatibility, easy processability and chemical inertness. In addition, their hydro- phobicity is an advantage for products where the cell adherence is unwanted (Ranella et al., 2010). Silicone is a synthetic polymer, com- monly obtained in the form of a linear chain made of poly- dimethylsiloxane (PDMS). Highly crosslinked silicones or gel-like sili- cones are nowadays used in medical implants. Among them the breast implants are by far the most popular, not only for esthetic reasons, but also for emotionally healing after a mastectomy for breast cancer or other serious illnesses. Silicone elastomers are considered as a material of choice for orthopedic prosthesis, maxillofacial prosthesis, heart valves or hands-free speech valve, cardiopulmonary bypass equipment, finger joint, soft tissue replacement, catheters and canula, tracheal stents (Chen et al., 2013; Hu et al., 2014; Khan et al., 2014; Vearick et al., 2018) etc. However, they are insufficiently exploited for the use inside the human body, especially for long-term implantation of pros- thesis, valves etc. The rupture of an implant may cause significant complications. The risk of rupture of a silicone implant is associated with degradation processes, as consequence of multiple causes: i) au- toimmune response due to the microorganisms present in the implant (Mojsiewicz-Pieńkowska and Krenczkowska, 2018); ii) penetration of lipids into the polymer network; iii) mechanical loading during daily activities (Necchi et al., 2011; Schubert et al., 2018) or iv) swelling of the silicone shell due to the diffusion of the inner gel, in the case of some breast implants (Birkefeld et al., 2004). Elastosil LR 3003/40 is a liquid silicone, which is vulcanized at high temperature and can be processed easily by injection molding, resulting in transparent and flexible objects. It is used for various products, like nipple teats, medical devices and kitchenware (products for foodstuffs). Various fillers were already used to reinforce the silicone elastomers, like silica, clays, metal oxides, hollow microspheres (Kappel et al., 2014; Liu et al., 2013), fibers of polypropylene, polyamide and carbon (Vearick et al., 2018). Silica is a well-known filler for soft silicone elastomers and is used in a concentration of up to 30% (Berry and Davies, 2010). Additionally, according to Bondurant et al. (Institute of Medicine Committee on the Safety of Silicone Breast, 1999) fumed si- lica is an important component of medical rubber-like materials, e.g. https://doi.org/10.1016/j.jmbbm.2019.103427 Received 30 April 2019; Received in revised form 7 September 2019; Accepted 9 September 2019 ∗ Corresponding author. ∗∗ Corresponding author. E-mail addresses: ioana.chiulan@icechim.ro (I. Chiulan), gary.chinga.carrasco@rise-pfi.no (G. Chinga-Carrasco). Journal of the Mechanical Behavior of Biomedical Materials 101 (2020) 103427 Available online 10 September 2019 1751-6161/ © 2019 Elsevier Ltd. All rights reserved. T