Comparative studies of mechanical and interfacial properties between jute and bamboo fiber-reinforced polypropylene-based composites

Jute and bamboo fiber-reinforced polypropylene (PP) based composites (50wt% fiber) were fabricated by compression molding. Tensile strength (TS), bending strength (BS), tensile modulus (TM), and bending modulus (BM) of the jutereinforced PP composite were found to be 48, 56, 900, and 1500 MPa, respectively. Then, bamboo fiber-reinforced PP-based composites (50 wt% fiber) were fabricated and the mechanical properties evaluated. The TS, BS, TM, and BM of bambooreinforced PP composites were found to be 60, 76, 4210, and 6210 MPa, respectively. It was revealed that bamboo fiber-based composites had higher TS, BS, TM, and BM compared to jute-based composites. Degradation tests of the composites (jute fiber/PP and bamboo fiber/PP) were performed in soil at ambient conditions for up to 24 weeks. It was revealed that bamboo fiber/PP composite retained its original mechanical properties higher than that of jute fiber/PP composite. The interfacial shear strength of the jute and bamboo fiber-based composites was investigated using the single-fiber fragmentation test and it was found to be 2.14 and 4.91 MPa, respectively. Fracture sides of the composites were studied by scanning electron microscope, and the results revealed poor fiber matrix adhesion for jute fiber-based composites compared to that of the bamboo fiber-based composites

Entwicklung anwendungsspezifischer Hydrogelkonzepte basierend auf der Kombination von Alginat, Gelatine und bioaktivem Glas für das Tissue Engineering

Tissue engineering approaches typically involve an exogenous extracellular matrix (ECM) called a scaffold, isolated cells and biochemical signals. The design of the suitable exogenous ECM is essential for the success of tissue engineering since it regulates cell behavior, cell phenotype and tissue-specific gene expression and can mimic the functions of the native ECM of the host tissue. Hydrogels are attractive materials to develop exogenous ECM for tissue engineering applications since they possess microstructure and basic properties that resemble the native ECM in addition to being biocompatible. Alginate is one of the most widely used hydrogel-based biomaterials for tissue engineering applications because of its favorable ionic gelation property at mild conditions, which is suitable for the encapsulation of living cells and biomolecules. However, the slow and uncontrolled degradation and poor cell adhesion properties of alginate limit its applicability in tissue engineering. In the present study, an experimental approach was developed to overcome the drawbacks of alginate by designing a novel class of hydrogel. An alginate-gelatin crosslinked (ADA-GEL) hydrogel was synthesized through covalent crosslinking of alginate di-aldehyde (ADA) with gelatin (GEL). Using this approach the degradation of the matrix was found to be enhanced due to oxidation of alginate, which was carried out for ADA synthesis. Moreover, degradation of ADA-GEL could be controlled by changing the ratio between ADA and GEL moieties. In this study, two cell culture models (2D and 3D) based on the developed hydrogels were investigated. A 2D cell culture study was carried out on hydrogel films, in which normal human dermal fibroblasts (NHDF) and rat bone marrow derived stem cells (rBMSCs) were studied. Viability, attachment, spreading and proliferation of fibroblasts were significantly increased on ADA-GEL of different compositions compared to pristine alginate. Moreover, in vitro cytocompatibility of ADA-GEL was found to increase with increasing gelatin content. Similar outcomes were also observed for rBMSCs on ADA-GEL with and without 0.1% (w/v) bioactive glass nanoparticles (nBG). Moreover, two different 3D models were studied for in vitro cell culture, namely, microencapsulation and scaffolding approach using freeze-drying techniques. The first approach focused on the fabrication of microcapsules from ADA–GEL. The microencapsulation of cells in biodegradable hydrogels offers numerous attractive features for a variety of biomedical applications including tissue engineering. Microcapsules from ADA-GEL hydrogels of different compositions were achieved by tailoring the oxidation degree of ADA, crosslinking degree of ADA-GEL and concentrations and compositions of the hydrogels. From the in vitro cell study it was established that ADA-GEL hydrogels of different compositions supported spreading, migration and proliferation of encapsulated human adipose-derived mesenchymal stem cells (hADSCs), which, however, were found to be enhanced with increasing gelatin content. The extensive spreading, high cell-cell and cell-material interactions of the cells encapsulated in the ADA-GEL hydrogels demonstrated in this study have not been achieved in alginate-based hydrogels before. Most importantly, osteogenic differentiation of hADSCs was achieved in ADA-GEL microcapsules of all compositions. A preliminary in vivo biocompatibility study was conducted (by collaborators) using a subcutaneous model in rat, in which no significant immune reaction was observed for ADA-GEL microcapsules with and without encapsulated rBMSCs. In analogy to the in vitro degradation study, in vivo degradation of ADA-GEL microcapsules was also apparent. In the second approach, freeze-dried scaffolds were fabricated from ADA-GEL without and with the addition of different amounts of bioactive glass (BG). The scaffolds were used as 3D templates for in vitro cell culture aiming at final applications in bone tissue engineering. Incorporation of bioactive glass into ADA-GEL drew significant effects on the properties of the hydrogel and hydrogel-derived scaffolds. Incorporation of BG enhanced the mechanical properties and in vitro bioactivity of ADA-GEL-derived scaffolds. Osteogenic differentiation of bone marrow stromal cell line (ST-2) was found to occur in the freeze-dried scaffolds even in the absence of any external osteogenic stimulating supplements. These outcomes make the developed materials promising candidates for applications in bone tissue engineering and warrant further in vivo investigations.Forschungen zur Gewebezüchtung beinhalten typischerweise die Synthese der extrazellulären Matrix (EZM) auch Scaffolds genannt, das Verhalten isolierter Zellen und biochemischen Signalen. Eine geeignete EZM ist entscheidend für den Erfolg der Gewebezüchtung, da Sie das Zellverhalten den Phänotyp der Zelle und die Expression gewebespezifischer Gene reguliert sowie die Funktion der natürlichen EZM des Empfängergewebes imitiert. Hydrogele sind attraktive Materialien, um EZM bei der Gewebezüchtung zu erzeugen, da sie die Mikrostruktur und wesentlichen Eigenschaften der natürlichen EZM besitzen. Zusätzlich weisen sie eine hervorragende Biokompatibilität auf. Alginat ist für Anwendungen in der Gewebezüchtung eines der am häufigsten verwendeten hydrogelbasierten Biomaterialien. Aufgrund seiner vorteilhaften Eigenschaften hinsichtlich der ionischen Gelierung unter milden Bedingungen ermöglicht es die Verkapselung von lebenden Zellen sowie bioaktiven Molekülen. Die langsame und unkontrollierte Degradation sowie die unzureichende Zelladhäsion an Alginat limitiert jedoch dessen Anwendbarkeit in der regenerativen Medizin. In dieser Arbeit wurden Versuche entwickelt, um das Alginat hinsichtlich seiner nachteiligen Eigenschaften zu verbessern. Durch die kovalente Bindung von Alginat Dialdehyd (ADA) mit Gelatine (GEL) wurde ein vernetztes Alginat-Gelatine (ADA-GEL) Hydrogel hergestellt. Durch die Oxidation des Alginats wurde die Degradation der Matrix optimiert. Ferner kann das Degradationsverhalten von ADA-GEL durch die Variation des Verhältnisses der funktionellen Gruppen des ADA und der GEL eingestellt werden. In dieser Arbeit wurden zwei Zellkulturmodelle (2D und 3D) mit den entwickelten Hydrogelen untersucht. Die 2D Zellkulturstudie wurde an Hydrogelfilmen durchgeführt, wobei normale humane dermale Fibroblasten (NHDF) und mesenchymale Stammzellen aus dem Knochenmark von Ratten (rBMSCs) analysiert wurden. Im Vergleich zum nicht modifizierten Alginat waren die Vitalität, die Adhäsion, die Spreitung und die Proliferation der Zellen bei verschiedenen Zusammensetzungen des ADA-GELs signifikant verbessert. Weiterhin wurde deutlich, dass die in-vitro Zytokompatibilität von ADA-GEL mit einem steigenden Anteil von Gelatine zunimmt. Ähnliche Resultate wurden für die rBMSCs auf ADA-GEL mit und ohne 0.1% (w/v) nanoskaliger bioaktiver Glaspartikel (nBG) erzielt. Desweiteren wurden zwei verschiedene 3D Modelle für in vitro Zellkulturuntersuchungen herangezogen, nämlich der Ansatz der Mikroverkapselung sowie die Herstellung von Stützgerüsten mit Hilfe der Gefriertrocknungstechnik. Das erste Konzept zielte auf die Herstellung von Mikrokapseln aus ADA-GEL. Die Mikroverkapselung von Zellen in biodegradierbaren Hydrogelen eröffnet zahlreiche Möglichkeiten für eine Vielzahl an biomedizinischen Anwendungen einschließlich der Gewebezüchtung. Durch die Anpassung des Oxidationsgrades von ADA, des Vernetzungsgrades von ADA-GEL und der Konzentration sowie der Zusammensetzung der Hydrogele wurden Mikrokapseln aus ADA-GEL mit verschiedenen Zusammensetzungen gezielt optimiert. Durch die in vitro Zellstudie wurde gezeigt, dass ADA-GEL Hydrogele mit verschiedenen Zusammensetzungen die Spreitung, Migration und Proliferation von verkapselten humanen aus dem Fettgewebe gewonnenen mesenchymalen Stammzellen (hADSCs) stimulieren, was durch die Erhöhung des Gelatineanteils noch gesteigert werden konnte. Die ausgiebige Spreitung, eine hohe Zell-Zell und Zell-Material Wechselwirkung der im ADA-GEL verkapselten Zellen, konnten durch Alginat-basierte Hydrogele vorher nicht erreicht werden. Besonders hervorzuheben ist die osteogene Differenzierung von hADSCs in ADA-GEL Mikrokapseln aller Zusammensetzungen. Ein Vorversuch der in vivo Biokompatibilitätsstudie wurde (von Kollaborateuren) unter Verwendung eines subkutanen Modells an Ratten durchgeführt, wobei keine signifikante Immunreaktion für ADA-GEL Mikrokapseln mit und ohne eingekapselte rBMSCs festgestellt wurde. Analog zur in vitro Degradationsstudie, war auch in vivo Degradation die ADA-GEL Mikrokapseln zu beobachten. In einem zweiten Ansatz wurden gefriergetrocknete ADA-GEL Scaffolds mit und ohne bioaktivem Glas (BG) hergestellt. Die Scaffolds wurden als 3D Gerüststrukturen für in vitro Zellkulturuntersuchungen herangezogen, mit dem Ziel, diese in der Knochengewebezüchtung einzusetzen. Das Einbringen von bioaktivem Glas in ADA-GEL führte zu signifikanten Effekten hinsichtlich der Eigenschaften des Hydrogels und der aus diesem hergestellten Scaffolds. Die Zugabe von BG erhöhte die mechanischen Eigenschaften und die in vitro Bioaktivität von ADA-GEL Scaffolds. Es zeigte sich, dass es in den gefriergetrockneten Scaffolds zur osteogenen Differenzierung der Knochenmark Stroma Zelllinie (ST-2) kommt, obwohl keine externen Zusätze zur osteogenen Differenzierung verwendet wurden. Diese Ergebnisse zeigen, dass die entwickelten Materialien vielversprechende Kandidaten für den Einsatz im Knochen Tissue engineering sind, erfordern jedoch weitere in vivo Untersuchungen

Direct Micropatterning of Extracellular Matrix Proteins on Functionalized Polyacrylamide Hydrogels Shows Geometric Regulation of Cell–Cell Junctions

Microcontact printing of extracellular matrix (ECM) proteins in defined regions of a substrate allows spatial control over cell attachment and enables the study of cellular response to irregular ECM geometries. Over the past decade, numerous micropatterning techniques have emerged that conjugate ECM proteins on hydrogel substrates of tunable stiffness, which have revealed a range of cellular responses to varying matrix stiffness and geometry. However, micropatterning of ECM proteins on polyacrylamide (PA) hydrogel remains inconsistent due to its unreliable conjugation with the commonly used protein cross-linkers, particularly at low stiffness. To address these problems, we developed a micropatterning technique in which the PA gel is functionalized by incorporating oxidized <i>N</i>-hydroxyethylacrylamide, which allows direct protein binding through reactive aldehyde groups without any exogenous cross-linkers. As a result, a uniform and consistent protein transfer onto the hydrogel substrates of defined geometries is achieved, even for soft PA gels. We formed square, rectangular, and triangular patterns of two constant areas on soft and stiff PA gels that provide large and small adhesive areas for the MCF10A human mammary epithelial cell pairs. We measured intercellular E-cadherin (E-cad) expression and found that cell–cell junctions could be deteriorated independently by either the stiff ECM of any shape or the elongated cell morphology, accompanied by increased cell-generated tractions, on rectangular soft ECM patterns. Inhibition of nonmuscle myosin II reduced the E-cad junctional localization in cell pairs. When the cell spreading was restricted by reducing the adhesive area of the patterns, we observed an overall rise in E-cad expression at cell–cell junctions. Our findings present an improved micropatterning technique which reveals a geometric regulation of cell–cell junctions in epithelial cell pairs

Macromolecular interactions in alginate–gelatin hydrogels regulate the behavior of human fibroblasts

Due to the presence of tripeptide arginine–glycine–aspartic acid, gelatin is considered a very promising additive material to improve the cytocompatibility of alginate-based hydrogels. Two different strategies, physical blending and chemical crosslinking with gelatin, are used in this study to modify alginate hydrogel. As the intermolecular interactions between the polysaccharide and protein in the resulting physically blended and chemically crosslinked hydrogels are different, significant differences in the properties of these hydrogel types, regarding especially their surface topography, degradation kinetics, mechanical properties, and protein release behavior, are observed. Cellular behavior on both types of alginate–gelatin hydrogels is investigated using primary human dermal fibroblasts to elucidate the effects of the different structural, mechanical, and degradation properties of the produced hydrogels on fibroblast attachment and growth. The hydrogel that is chemically crosslinked with gelatin exhibits the highest degree of cytocompatibility regarding adhesion, proliferation, metabolic activity, and morphology of growing fibroblasts

Designing Porous Bone Tissue Engineering Scaffolds with Enhanced Mechanical Properties from Composite Hydrogels Composed of Modified Alginate, Gelatin, and Bioactive Glass

The combination of biodegradable polymers and bioactive inorganic materials is being widely used for designing bone tissue engineering scaffolds. Here we report a composite hydrogel system composed of bioactive glass incorporated in covalently cross-linked oxidized alginate-gelatin hydrogel (ADA-GEL) for designing porous scaffolds with tunable stiffness and degradability using freeze-drying technique. Because of the presence of bioactive glass, the cross-linking kinetic and cross-linking degree of the hydrogels are significantly increased, which is the main factor for the measured enhanced mechanical strength of the bioactive glass containing ADA-GEL scaffolds. The hydrogels with high cross-linking degree exhibit low protein release profile and low degradability. Apatite formation on bioactive glass containing hydrogel-based scaffolds is confirmed by FTIR. Bone marrow-derived stromal cell growth is promoted in pristine ADA-GEL and 1% bioactive glass containing ADA-GEL scaffolds compared to the scaffolds of pure alginate, alginate–gelatin blended hydrogel, and 5% bioactive glass containing ADA-GEL. Initial studies indicated that the scaffolds, especially without bioactive glass, support osteogenic differentiation of murine bone marrow stromal cell line in the absence of foreign osteogenic stimulating supplements; however, they exhibit low levels of osteogenic expression

Bioplotting of a bioactive alginate dialdehyde-gelatin composite hydrogel containing bioactive glass nanoparticles

Alginate dialdehyde-gelatin (ADA-GEL) constructs incorporating bioactive glass nanoparticles (BGNPs) were produced by biofabrication to obtain a grid-like highly-hydrated composite. The material could induce the deposition of an apatite layer upon immersion in a biological-like environment to sustain cell attachment and proliferation. Composites were formulated with different concentrations of BGNPs synthetized from a sol-gel route, namely 0.1% and 0.5% (w/v). Strontium doped BGNPs were also used. EDS analysis suggested that the BGNPs loading promoted the growth of bone-like apatite layer on the surface when the constructs were immersed in a simulated body fluid. Moreover, the composite constructs could incorporate with high efficiency ibuprofen as a drug model. Furthermore, the biofabrication process allowed the successful incorporation of MG-63 cells into the composite material. Cells were distributed homogeneously within the hydrogel composite, and no differences were found in cell viability between ADA-GEL and the composite constructs, proving that the addition of BGNPs did not influence cell fate. Overall, the composite material showed potential for future applications in bone tissue engineering.This work was supported by the Portuguese Foundation for Science and Technology (FCT) through the doctoral grant SFRH/BD/73174/2010 of Álvaro J Leite.info:eu-repo/semantics/publishedVersio

Encapsulation of Rat Bone Marrow Derived Mesenchymal Stem Cells in Alginate Dialdehyde/Gelatin Microbeads with and without Nanoscaled Bioactive Glass for In Vivo Bone Tissue Engineering

Alginate dialdehyde (ADA), gelatin, and nano-scaled bioactive glass (nBG) particles are being currently investigated for their potential use as three-dimensional scaffolding materials for bone tissue engineering. ADA and gelatin provide a three-dimensional scaffold with properties supporting cell adhesion and proliferation. Combined with nanocristalline BG, this composition closely mimics the mineral phase of bone. In the present study, rat bone marrow derived mesenchymal stem cells (MSCs), commonly used as an osteogenic cell source, were evaluated after encapsulation into ADA-gelatin hydrogel with and without nBG. High cell survival was found in vitro for up to 28 days with or without addition of nBG assessed by calcein staining, proving the cell-friendly encapsulation process. After subcutaneous implantation into rats, survival was assessed by DAPI/TUNEL fluorescence staining. Hematoxylin-eosin staining and immunohistochemical staining for the macrophage marker ED1 (CD68) and the endothelial cell marker lectin were used to evaluate immune reaction and vascularization. After in vivo implantation, high cell survival was found after 1 week, with a notable decrease after 4 weeks. Immune reaction was very mild, proving the biocompatibility of the material. Angiogenesis in implanted constructs was significantly improved by cell encapsulation, compared to cell-free beads, as the implanted MSCs were able to attract endothelial cells. Constructs with nBG showed higher numbers of vital MSCs and lectin positive endothelial cells, thus showing a higher degree of angiogenesis, although this difference was not significant. These results support the use of ADA/gelatin/nBG as a scaffold and of MSCs as a source of osteogenic cells for bone tissue engineering. Future studies should however improve long term cell survival and focus on differentiation potential of encapsulated cells in vivo