Synthesis and In Vitro Activity Assessment of Novel Silicon Oxycarbide-Based Bioactive Glasses

Cytocompatible and osteoconductive silicon oxycarbide glass scaffolds 3D printed by DLP: a potential material for bone tissue regeneration

Bone lesions affect individuals of different age groups, compromising their daily activities and potentially leading to prolonged morbidity. Over the years, new compositions and manufacturing technologies were developed to offer customized solutions to replace injured tissue and stimulate tissue regeneration. This work used digital light processing (DPL) technology for three-dimensional (3D) printing of porous structures using pre-ceramic polymer, followed by pyrolysis to obtain SiOC vitreous scaffolds. The SiOC scaffolds produced had an amorphous structure (compatible with glass) with an average porosity of 72.69% ± 0.99, an average hardness of 935.1 ± 71.0 HV, and an average maximum flexural stress of 7.8 ± 1.0 MPa, similar to cancellous bone tissue. The scaffolds were not cytotoxic and allowed adult stem cell adhesion, growth, and expansion. After treatment with osteoinductive medium, adult stem cells in the SiOC scaffolds differentiated to osteoblasts, assuming a tissue-like structure, with organization in multiple layers and production of a dense fibrous matrix rich in hydroxyapatite. The in vitro analyses supported the hypothesis that the SiOC scaffolds produced in this work were suitable for use as a bone substitute for treating critically sized lesions, with the potential to stimulate the gradual process of regeneration of the native tissue. The data obtained stimulate the continuity of studies with the SiOC scaffolds developed in this work, paving the way for evaluating safety and biological activity in vivo.

Oxygen-Deficient Bioceramics: Combination of Diagnosis, Therapy, and Regeneration

The journey of ceramics in medicine has been synchronized with an evolution from the first generation-alumina, zirconia, etc.-to the third -3D scaffolds. There is an up-and-coming member called oxygen-deficient or colored bioceramics, which have recently found their way through biomedical applications. The oxygen vacancy steers the light absorption toward visible and near infrared regions, making the colored bioceramics multifunctional-therapeutic, diagnostic, and regenerative. Oxygen-deficient bioceramics are capable of turning light into heat and reactive oxygen species for photothermal and photodynamic therapies, respectively, and concomitantly yield infrared and photoacoustic images. Different types of oxygen-deficient bioceramics have been recently developed through various synthesis routes. Some of them like TiO2- x , MoO3- x , and WOx have been more investigated for biomedical applications, whereas the rest have yet to be scrutinized. The most prominent advantage of these bioceramics over the other biomaterials is their multifunctionality endowed with a change in the microstructure. There are some challenges ahead of this category discussed at the end of the present review. By shedding light on this recently born bioceramics subcategory, it is believed that the field will undergo a big step further as these platforms are naturally multifunctional.

Spectroscopic studies on phosphate-modified silicon oxycarbide-based amorphous materials

Vibrational spectroscopy is the most effective, efficient and informative method of structural analysis of amorphous materials with silica matrix and, therefore, an indispensable tool for examining silicon oxycarbide-based amorphous materials (SiOC). The subject of this work is a description of the modification process of SiOC glasses with phosphate ions based on the structural examination including mainly Infrared and Raman Spectroscopy. They were obtained as polymer-derived ceramics based on ladder-like silsesquioxanes synthesised via the sol-gel method. With the high phosphate's volatility, it was decided to introduce the co-doping ions to create [AlPO₄] and [BPO₄] stable structural units. As a result, several samples from the SiPOC, SiPAlOC and SiPBOC systems were obtained with various quantities of the modifiers. All samples underwent a detailed structural evaluation of both polymer precursors and ceramics after high-temperature treatment with Fourier-transformed infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD) and magic angle spinning nuclear magnetic resonance (MAS-NMR). Obtained results proved the efficient preparation of desired materials that exhibit structural parameters similar to the unmodified one. They were X-ray-amorphous with no phase separation and crystallisation. Spectroscopic measurements confirmed the presence of the crucial Si-C bond and how modifying ions are incorporated into the SiOC network. It was also possible to characterise the turbostratic free carbon phase. The modification was aimed to improve the bioperformance of the materials in the context of their future application as bioactive coatings on metallic implants.

Effect of the Content and Ordering of the sp2 Free Carbon Phase on the Charge Carrier Transport in Polymer-Derived Silicon Oxycarbides

The present work elaborates on the correlation between the amount and ordering of the free carbon phase in silicon oxycarbides and their charge carrier transport behavior. Thus, silicon oxycarbides possessing free carbon contents from 0 to ca. 58 vol.% (SiOC/C) were synthesized and exposed to temperatures from 1100 to 1800 °C. The prepared samples were extensively analyzed concerning the thermal evolution of the sp2 carbon phase by means of Raman spectroscopy. Additionally, electrical conductivity and Hall measurements were performed and correlated with the structural information obtained from the Raman spectroscopic investigation. It is shown that the percolation threshold in SiOC/C samples depends on the temperature of their thermal treatment, varying from ca. 20 vol.% in the samples prepared at 1100 °C to ca. 6 vol.% for the samples annealed at 1600 °C. Moreover, three different conduction regimes are identified in SiOC/C, depending on its sp2 carbon content: (i) at low carbon contents (i.e., <1 vol.%), the silicon oxycarbide glassy matrix dominates the charge carrier transport, which exhibits an activation energy of ca. 1 eV and occurs within localized states, presumably dangling bonds; (ii) near the percolation threshold, tunneling or hopping of charge carriers between spatially separated sp2 carbon precipitates appear to be responsible for the electrical conductivity; (iii) whereas above the percolation threshold, the charge carrier transport is only weakly activated (Ea = 0.03 eV) and is realized through the (continuous) carbon phase. Hall measurements on SiOC/C samples above the percolation threshold indicate p-type carriers mainly contributing to conduction. Their density is shown to vary with the sp2 carbon content in the range from 1014 to 1019 cm-3; whereas their mobility (ca. 3 cm2/V) seems to not depend on the sp2 carbon content.

Biological evaluation of preceramic organosilicon polymers for various healthcare and biomedical engineering applications: A review

Preceramic organosilicon materials combining the properties of a polymer and an inorganic ceramic phase are of great interest to scientists working in biomedical sciences. The interdisciplinary nature of organosilicon polymers and their molecular structures, as well as their diversity of applications have resulted in an unprecedented range of devices and synergies cutting across unrelated fields in medicine and engineering. Organosilicon materials, especially the polysiloxanes, have a long history of industrial and medical uses in many versatile aspects as they can be easily fabricated into complex-shaped products using a wide variety of computer-aided or polymer manufacturing techniques. Thus far, intensive research activities have been mainly devoted to the processing of preceramic organosilicon polymers toward magnetic, electronic, structural, optical, and not biological applications. Herein we present innovative research studies and recent developments of preceramic organosilicon polymers at the interface with biological systems, displaying the versatility and multi-functionality of these materials. This article reviews recent research on preceramic organosilicon polymers and corresponding composites for bone tissue regeneration and medical engineering implants, focusing on three particular topics: (a) surface modifications to create tailorable and bioactive surfaces with high corrosion resistance and improved biological properties; (b) biological evaluations for specific applications, such as in glaucoma drainage devices, orthopedic implants, bone tissue regeneration, wound dressing, drug delivery systems, and antibacterial activity; and (c) in vitro and in vivo studies for cytotoxicity, genotoxicity, and cell viability. The interest in organosilicon materials stems from the fact that a vast array of these materials have complementary attributes that, when integrated appropriately with functional fillers and carefully controlled conditions, could be exploited either as polymeric Si-based composites or as organosilicon polymer-derived Si-based ceramic composites to tailor and optimize properties of the Si-based materials for various proposed applications.

In Vitro Cytocompatibility Assessment of Ti-Modified, Silicon-oxycarbide-Based, Polymer-Derived, Ceramic-Implantable Electrodes under Pacing Conditions

Polymer-derived ceramics (PDC) have recently gained increased interest in the field of bioceramics. Among PDC's, carbon-rich silicon oxycarbide ceramics (SiOC) possess good combined electrical and mechanical properties. Their durability in aggressive environments and proposed cytocompatibility makes them an attractive material for fabrication of bio-MEMS devices such as pacemaker electrodes. The aim of the present study is to demonstrate the remarkable mechanical and electrical properties, biological response of PDCs modified with titanium (Ti) and their potential for application as pacemaker electrodes. Therefore, a new type of SiOC modified with Ti fillers was synthesized via PDC route using a Pt-catalyzed hydrosilylation reaction. Preceramic green bodies were pyrolyzed at 1000 °C under an argon atmosphere to achieve amorphous ceramics. Electrical and mechanical characterization of SiC_xO_2(1-x)/TiO_xC_y ceramics revealed a maximum electrical conductivity of 10 S cm^-1 and a flexural strength of maximal 1 GPa, which is acceptable for pacemaker applications. Ti incorporation is found to be beneficial for enhancing the electrical conductivity of SiOC ceramics and the conductivity values were increased with Ti doping and reached a maximum for the composition with 30 wt % Ti precursor. Cytocompatibility was demonstrated for the PDC SiOC ceramics as well as SiOC ceramics modified with Ti fillers. Cytocompatibility was also demonstrated for SiTiOC20 electrodes under pacing conditions by monitoring of cells in an in vitro 3D environment. Collectively, these data demonstrate the great potential of polymer-derived SiOC ceramics to be used as pacemaker electrodes.

Facile Preparative Access to Bioactive Silicon Oxycarbides with Tunable Porosity

In the present work, Ca-containing silicon oxycarbides (SiCaOC) with varying Ca content have been synthesized via sol-gel processing and thermal treatment in inert gas atmosphere (pyrolysis). It has been shown that the as-prepared SiCaOC materials with low Ca loadings (Ca/Si molar ratios = 0.05 or 0.12) were X-ray amorphous; their glassy network contains Q3 sites, indicating the presence of Ca2+ at non-bridging-oxygen sites. SiCaOC with high Ca content (i.e., Ca/Si molar ratio = 0.50) exhibits the presence of crystalline calcium silicate (mainly pseudowollastonite). Furthermore, it has been shown that the incorporation of Ca into the SiOC glassy network has a significant effect on its porosity and specific surface area. Thus, the as-prepared Ca-free SiOC material is shown to be non-porous and having a specific surface area (SSA) of 22.5 m2/g; whereas SiCaOC with Ca/Si molar ratio of 0.05 exhibits mesoporosity and a SSA value of 123.4 m2/g. The further increase of Ca content leads to a decrease of the SSA and the generation of macroporosity in SiCaOC; thus, SiCaOC with Ca/Si molar ratio of 0.12 is macroporous and exhibits a SSA value of 39.5 m2/g. Bioactivity assessment in simulated body fluid (SBF) confirms the hydroxyapatite formation on all SiCaOC samples after seven days soaking, unlike the relatively inert ternary silicon oxycarbide reference. In particular, SiCaOC with a Ca/Si molar ratio of 0.05 shows an increased apatite forming ability compared to that of SiCaOC with Ca/Si molar ratio of 0.12; this difference is considered to be a direct consequence of the significantly higher SSA of the sample with the Ca/Si ratio of 0.05. The present work indicates two effects of Ca incorporation into the silicon oxycarbide glassy network on its bioactivity: Firstly, Ca2+ is shown to contribute to the slight depolymerization of the network, which clearly triggers the hydroxyapatite formation (compare the bioactive behavior of SiOC to that of SiCaOC with Ca/Si molar ratio 0.12 upon SBF exposure); secondly, the Ca2+ incorporation seems to strongly affect the porosity and SSA in the prepared SiCaOC materials. There is an optimum of Ca loading into the silicon oxycarbide glassy network (at a Ca/Si molar ration of 0.05), which provides mesoporosity and reaches maximum SSA, both highly beneficial for the bioactive behavior of the materials. An increase of the Ca loading leads, in addition to the crystallization of calcium silicates, to a coarsening of the pores (i.e., macroporosity) and a significant decrease of the SSA, both negatively affecting the bioactivity.