polymers Article New Approach for Preparing In Vitro Bioactive Scaffold Consisted of Ag-Doped Hydroxyapatite + Polyvinyltrimethoxysilane Marzieh Rabiei 1, * , Arvydas Palevicius 1 , Reza Ebrahimi-Kahrizsangi 2 , Sohrab Nasiri 1 , Andrius Vilkauskas 1 and Giedrius Janusas 1   Citation: Rabiei, M.; Palevicius, A.; Ebrahimi-Kahrizsangi, R.; Nasiri, S.; Vilkauskas, A.; Janusas, G. New Approach for Preparing In Vitro Bioactive Scaffold Consisted of Ag-Doped Hydroxyapatite + Polyvinyltrimethoxysilane. Polymers 2021, 13, 1695. https://doi.org/ 10.3390/polym13111695 Academic Editors: Sajjad Husain Mir, Gaulthier Rydzek and Sameer Hussain Received: 4 May 2021 Accepted: 20 May 2021 Published: 22 May 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Faculty of Mechanical Engineering and Design, Kaunas University of Technology, LT-51424 Kaunas, Lithuania; arvydas.palevicius@ktu.lt (A.P.); sohrab.nasiri@ktu.edu (S.N.); andrius.vilkauskas@ktu.lt (A.V.); giedrius.janusas@ktu.lt (G.J.) 2 Advanced Materials Research Center, Department of Materials Engineering, Najafabad Branch, Islamic Azad University of Najafabad, Najafbad Isfahan P.O. Box 85141-43131, Iran; rezaebrahimi@iaun.ac.ir * Correspondence: marzieh.rabiei@ktu.edu; Tel.: +37-0-6360-5863 Abstract: Recently, researchers have focused on the biocompatibility and mechanical properties of highly porous structures of biomaterials products. Porous composites are a new category of bioengi- neering that possess excellent functional and structural properties. In this study, the physical and mechanical properties of prepared doped silver (Ag)-hydroxyapatite (HA) by the mechanochemical and spark plasma sintering (SPS) methods were investigated. The influence of dopant on phase formation, structural properties, mechanical properties and morphological characteristics was investi- gated. Furthermore, in this case, as a new approach to produce a porous scaffold with an average size of >100 μm, the hair band was used as a mold. According to the Monshi–Scherrer method, the crystal size of scaffold was calculated 38 ± 2 nm and this value was in the good agreement with average value from transmission electron microscopy (TEM) analysis. In addition, the stress–strain compres- sion test of scaffold was considered, and the maximum value of compressive strength was recorded ~15.71 MPa. Taking into account the XRD, TEM, Fourier-transform infrared (FTIR), scanning electron microscope (SEM) and energy dispersive X-Ray analysis (EDAX) analysis, the prepared scaffold was bioactive and the effects of doped Ag-HA and the use of polyvinyltrimethoxysilane (PVTMS) as an additive were desirable. The results showed that the effect of thermal treatment on composed of Ag and HA were impressive while no change in transformation was observed at 850 ◦ C. In addi- tion, PVTMS plays an important role as an additive for preventing the decomposition and creating open-microporous in the scaffold that these porosities can be helpful for increasing bioactivity. Keywords: Ag-doped HA; mechanochemical process; spark plasma sintering; open porosities; simulated body fluid; bioactivity 1. Introduction Taking into account the existence of Calcium Phosphates (CaPs) in the body, re- searchers nowadays have considered CaPs for the replacement and repair of injured bones. One of the most desirable and well-known CaPs groups is associated with hydroxyapatite (HA) [1,2]. The chemical formula of hydroxyapatite is Ca 10 (PO 4 ) 6 (OH) 2 and it differs little from the bone tissue [3]. According to the knowledge of crystallographic structures, there are two types of HA structures: hexagonal and monoclinic. Mostly the hexagonal HA is suitable for the biomaterials industry, as the monoclinic HA is not more stable in bioactive properties [4]. In addition, one of the challenges for using HA as a bioactive component is related to the likelihood of infection; therefore, the use of antibacterial materials is the best way to solve this problem [5]. On the other hand, the studies have proven that silver (Ag) has antibacterial properties [6–8]. Moreover, one of the best elements for biocompatibility Polymers 2021, 13, 1695. https://doi.org/10.3390/polym13111695 https://www.mdpi.com/journal/polymers