Justyna Krzak

Biological effects of sol–gel derived ZrO2 and SiO2/ZrO2 coatings on stainless steel surface—In vitro model using mesenchymal stem cells

The objective of this study was to determine biocompatibility of zirconia-based coatings obtained by the sol–gel method. Two matrices, ZrO2 and SiO2/ZrO2, were created and applied on stainless steel type 316L with dip-coating technique. The morphology and topography of biomaterials’ surface were characterized using energy-dispersive X-ray spectroscopy and atomic force microscopy, while chemical composition was analyzed by Raman spectroscopy. Additionally, wettability and surface free energy were characterized. Biocompatibility of obtained biomaterials was evaluated using an in vitro model employing mesenchymal stem cells (MSCs) of adipose and bone marrow origin. Biological analysis included determination of proliferation activity and morphology of MSCs in cultures on synthesized biomaterials. Osteoinductive properties of biomaterials were determined both in non-osteogenic, as well as osteogenic conditions. The results showed that investigated biomaterials exerted different impact on MSCs. Biomaterial with ZrO2 layer was more biocompatible for adipose-derived MSCs, while SiO2/ZrO2 layer promoted proliferation of bone marrow derived MSCs. Moreover, hybrid coating exhibited greater osteoinductive properties than ZrO2 coating, both on cultures with adipose-derived stromal (stem) cells and bone marrow stromal cells. Observed biological effects may result not only from different chemical composition, but also from diverse wettability. The ZrO2 coating was characterized as hydrophobic layer, while SiO2/ZrO2 exhibited hydrophilic properties. The results obtained suggest that behavior of MSCs in response to the biomaterial may vary depending on their origin, therefore we postulate, that screening analysis of implants’ biocompatibility, should incorporate model applying both adipose- and bone marrow derived MSCs.

Dynamic mechanical analysis of magnetorheological composites containing silica-coated carbonyl iron powder

This article describes the dynamic mechanical analysis of the behaviour of magnetorheological composites consisting of a magnetically active filler (carbonyl iron powder) and a soft thermoplastic elastomer matrix (styrene-ethylene-butylene-styrene). The carbonyl iron particle surface was coated by a sol–gel silica layer to improve the adhesion between hydrophilic magnetic particles and the hydrophobic polymer. Isotropic magnetorheological composites containing 81.25 wt% unmodified and silica-coated carbonyl iron powder were manufactured. The surface morphology of the carbonyl iron particles was observed using transmission electron microscopy, while its magnetic properties were analysed with a vibrating sample magnetometer. The magnetomechanical properties of the prepared magnetorheological composites were determined through shearing tests performed in various magnetic fields. The magnetorheological composites containing modified carbonyl iron powder have lower magnetorheological effect in comparison to the composites with pure carbonyl iron powder.

In vitro and in vivo evaluation of sol-gel derived TiO 2 coatings based on a variety of precursors and synthesis conditions

The effect of synthesis way of TiO2 coatings on biocompatibility of transplanted materials using an in vitro and in vivo rat model was investigated. TiO2 layers were synthesized by a nonaqueous sol-gel dip-coating method on stainless steel 316L substrates applying two different precursors and their combination. Morphology and topography of newly formed biomaterials were determined as well as chemical composition and elemental distribution of a surface samples. In vitro tests were conducted by adipose-derived mesenchymal stem cells cultured on TiO2 coatings and stainless steel without coatings to assess the bioreactivity of obtained materials. A positive biological effect of TiO2/316L/1 coatings--based on titanium(IV) ethoxide--was found in both in vitro and in vivo models. The TiO2/316L/1 exhibited the highest roughness and the lowest titanium concentration in TiO2 than TiO2/316L/2-- based on titanium(IV) propoxide and TiO2/316L/3--based on both above-mentioned precursors. The proper fibroblast-like morphology and higher proliferation rate of cells cultured on TiO2/316L/1 were observed when compared to the other biomaterials. No inflammatory response in the bone surrounding implant covered by each of the obtained TiO2 was present. Our results showed that improvement of routinely used stainless steel 316L with TiO2/316L/1 layer can stimulate beneficial biological response.

The Osteogenic Properties of Multipotent Mesenchymal Stromal Cells in Cultures on TiO2 Sol-Gel-Derived Biomaterial

The biocompatibility of the bone implants is a crucial factor determining the successful tissue regeneration. The aim of this work was to compare cellular behavior and osteogenic properties of rat adipose-derived multipotent stromal cells (ASCs) and bone marrow multipotent stromal cells (BMSCs) cultured on metallic substrate covered with TiO2 sol-gel-derived nanolayer. The morphology, proliferation rate, and osteogenic differentiation potential of both ASCs and BMSCs propagated on the biomaterials were examined. The potential for osteogenic differentiation of ASCs and BMSCs was determined based on the presence of specific markers of osteogenesis, that is, alkaline phosphatase (ALP), osteopontin (OPN), and osteocalcin (OCL). Additionally, the concentration of calcium and phosphorus in extracellular matrix was determined using energy-dispersive X-ray spectroscopy (SEM-EDX). Obtained results showed that TiO2 layer influenced proliferation activity of ASCs, which manifested by shortening of population doubling time and increase of OPN secretion. However, characteristic features of cells morphology and growth pattern of cultures prompted us to conclude that ultrathin TiO2 layer might also enhance osteodifferentiation of BMSCs. Therefore in our opinion, both populations of MSCs should be used for biological evaluation of biomaterials compatibility, such results may enhance the area of investigations related to regenerative medicine.

The influence of sol-gel-derived silica coatings functionalized with betamethasone on adipose-derived stem cells (ASCs).

Silica-based sol–gel coatings have gained attention in bone therapies and orthopedic applications, due to the biocompatibility and bioactivity, including a high potential for the controlled release both in vitro and in vivo. Bioactive materials are created to facilitate the biocompatibility of orthopedic implants. One of the promising alternatives is biomaterials with immobilized drugs. In this study we demonstrated for the first time novel sol–gel-derived silica coatings with active amino groups (SiO2(NH2)) functionalized with a steroid drug—betamethasone, applied to a substrate 316 L using dip coating technique. The presence of betamethasone in functionalized coatings was directly confirmed by Raman spectroscopy and energy-dispersive X-ray spectroscopic analysis. The wettability was evaluated by the sessile drop method, while the surface free energy was estimated based on the contact angles measured. Our results showed a shift in surface properties from hydrophobic to hydrophilic after application of the coatings. We have investigated the morphology, proliferation factor, and the population doubling time of adipose-derived stem cells for biological purposes. Moreover, the analysis of the distribution and localization of cellular microvesicles was performed to evaluate the influence of functionalized surfaces on cellular cytophysiological activity. Increased proliferation and activation of cells, determined by the observations of microvesicles shedding processes, provided evidence of the availability of the drug. Therefore, we conclude that the sol–gel synthesis proposed here allows to improve the metal substrates and can be successfully used for immobilization of betamethasone. This in turn enables the direct delivery of the drug with implanted material into the wound site, and to stimulate the activity of cells to enhance tissue regeneration.

The effect of a sol–gel derived silica coating doped with vitamin E on oxidative stress and senescence of human adipose-derived mesenchymal stem cells (AMSCs)

Nowadays, a major medical problem concerns the effective treatment of musculoskeletal disorders, especially in elderly patients. Implantable metallic materials have been widely applied in reconstructive medicine, including the field of orthopedics. Many studies have presented the beneficial effects of sol–gel-derived silica coatings in the preparation of bioactive materials, e.g. drug-eluting or mesoporous materials that stimulate tissue regeneration. In the current research, we have fabricated a sol–gel-derived silica coating functionalized with vitamin E for the reduction of oxidative stress (OS) on adipose-derived mesenchymal stem cells (AMSCs) isolated from elderly patients. Elevated levels of endogenous OS, through the mitochondrial secretion of reactive oxygen species (ROS) has an unquestionable impact on the viability and multipotent character of MSCs, which in consequence leads to the decreased therapeutic potential of engrafted cells. In the present study, we used a common antioxidant (vitamin E) and investigated its influence on AMSC proliferation and apoptosis at a concentration of 2% in a functionalized sol. The morphologies of the surfaces and coatings were determined using scanning electron microscopy (SEM), and their elemental composition was determined by SEM-EDX. The immobilization of ascorbic acid in the coatings was confirmed with Raman spectroscopy. Using RT-PCR and multiple cell imaging techniques, we evaluated the influence of the novel biomaterial on AMSCs. We have found that the biomaterial functionalized with vitamin E has a beneficial effect on cell viability and proliferative potential, as it decreased OS and induced the activity of free radical scavengers e.g. SOD in AMSCs.

Cytokine induction of sol–gel-derived TiO 2 and SiO 2 coatings on metallic substrates after implantation to rat femur

Material surface is a key determinant of host response on implanted biomaterial. Therefore, modification of the implant surface may optimize implant–tissue reactions. Inflammatory reaction is inevitable after biomaterial implantation, but prolonged inflammation may lead to adverse reactions and subsequent implant failure. Proinflammatory activities of cytokines like interleukin (IL)-1, IL-6, and tumor necrosis factor-alpha (TNF-α) are attractive indicators of these processes and ultimately characterize biocompatibility. The objective of the study was to evaluate local cytokine production after implantation of stainless steel 316L (SS) and titanium alloy (Ti6Al4V) biomaterials coated with titanium dioxide (TiO2) and silica (SiO2) coatings prepared by sol–gel method. Biomaterials were implanted into rat femur and after 12 weeks, bones were harvested. Bone–implant tissue interface was evaluated; immunohistochemical staining was performed to identify IL-6, TNF-α, and Caspase-1. Histomorphometry (AxioVision Rel. 4.6.3 software) of tissue samples was performed in order to quantify the cytokine levels. Both the oxide coatings on SS and Ti6Al4V significantly reduced cytokine production. However, the lowest cytokine levels were observed in TiO2 groups. Cytokine content in uncoated groups was lower in Ti6Al4V than in SS, although coating of either metal reduced cytokine production to similar levels. Sol–gel TiO2 or SiO2 coatings reduced significantly the production of proinflammatory cytokines by local tissues, irrespective of the material used as a substrate, that is, either Ti6Al4V or SS. This suggests lower inflammatory response, which directly points out improvement of materials’ biocompatibility.

The influence of metal-based biomaterials functionalized with sphingosine-1-phosphate on the cellular response and osteogenic differentaion potenial of human adipose derived mesenchymal stem cells in vitro

In this study, stable, homogenous and thin titania dioxide coatings (TiO2) on stainless steel substrate doped with two dosages of bioactive sphingolipids S1P were fabricated using the sol-gel method. S1P belongs to a family of sphingolipids acting as important extracellular signaling molecules and chemoattractants. This study investigated the effect of TiO2, doped with S1P in two different dosages on cellular response as well as osteogenic differentiation potential of human adipose derived multipotent stromal stem cells (hASC). The authors have shown that S1P mediates hASCs morphology, proliferation activity and population doubling time in a dose-dependent manner. They have also demonstrated that functionalization of TiO2 coating with a higher dosage of S1P, i.e. 80 ng/ml [(TiO2/S1P(CII)] activated both S1PR type 1 and type 2 on mRNA level. The results indicated an increase in secretion of BMP-2, Osteopontin and Osteocalcin by osteoblasts progenitor when cultured on [TiO2/S1P(CIIm)]. In addition, the authors observed the highest extracellular matrix mineralization as well as osteonodules formation by the osteoblasts precursors when cultured onto [TiO2/S1P(CIIm)].

Improvement of Interaction in a Composite Structure by Using a Sol-Gel Functional Coating on Carbon Fibers

The modification of carbon fibers for improving adhesion between fibers and an epoxy resin in composite materials has become the focus of attention. In this work the carbon fiber coating process has been devised in a way preventing the stiffening and clumping of fibers. To improve interactions between coated fibers and a resin in composites, four types of silica coatings with different organic functional groups (3-aminopropyl–coating 1, 3-mercaptopropyl–coating 2, 2-(3,4-epoxycyclohexyl) ethyl–coating 3, methyl–coating 4) were obtained. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to distinguish the changes of a carbon fibers surface after coating deposition. The thickness of the obtained coatings, including the diversity of thickness, was determined by transmission electron microscopy (TEM). The increase in surface free energy (SFE) of modified fibers, including the distinction between the polar and dispersive parts, was examined by wettability measurements using a tensometric test. The developed coating preparation process allowed to cover fibers separately with nanoscale silica layers, which changed their morphology. The introduction of organic functional groups resulted in surface free energy changes, especially an increase in specific polar surface energy components.

Influence of carbonyl iron particle coating with silica on the properties of magnetorheological elastomers

In this paper, the influence of encapsulating carbonyl iron particles with various silica coatings on the properties of magnetorheological elastomers (MREs) was investigated. A soft styrene–ethylene–butylene–styrene thermoplastic elastomer was used as the composites polymer matrix. Spherical carbonyl iron powder (CIP) acted as the ferromagnetic filler. In order to improve the metal–polymer interaction, carbonyl iron particles were coated with two types of single and six types of double silica layers. The first layer was created through a TMOS or TEOS hydrolysis whereas the second one was composed of organosilanes. The mechanical properties of MREs containing 38.5 vol% of CIP were analysed under dynamic loading conditions. To investigate the magnetorheological effect in these composites, a 430 mT magnetic field, generated by an array of permanent magnets, was applied during testing. The results revealed that the magnetomechanical response of the MREs differs substantially, depending on the kind of particle coating.