Many different biofabrication approaches as well as a variety of bioinks have been developed by researchers working in the field of tissue engineering. A main challenge for bioinks often remains the ...difficulty to achieve shape fidelity after printing. In order to overcome this issue, a homogeneous pre-crosslinking technique, which is universally applicable to all alginate-based materials, was developed. In this study, the Young's Modulus after post-crosslinking of selected hydrogels, as well as the chemical characterization of alginate in terms of M/G ratio and molecular weight, were determined. With our technique it was possible to markedly enhance the printability of a 2% (w/v) alginate solution, without using a higher polymer content, fillers or support structures. 3D porous scaffolds with a height of around 5 mm were printed. Furthermore, the rheological behavior of different pre-crosslinking degrees was studied. Shear forces on cells as well as the flow profile of the bioink inside the printing nozzle during the process were estimated. A high cell viability of printed NIH/3T3 cells embedded in the novel bioink of more than 85% over a time period of two weeks could be observed.
Abstract The laydown of aerodynamically stretched fibers during fiber spinning is a key feature of the non‐woven quality. The desired properties of the produced non‐woven are mostly determined by the ...mechanical properties of the single fiber and the homogeneity of the spunbond. While the former is studied widely, the homogeneity is mostly studied by simulations and not experimentally. Cloudiness or formation of non‐wovens is a known phenomenon that describes deviations from the ideal laydown. Thin areas have a huge impact on the mechanical properties of the spunbond; And subsequently, the investigation of the fiber laydown is of great interest. This work presents an experimental approach to optimize the fiber laydown of a pilot plant fiber spinning device consisting of two aerodynamic stretching devices (aspirators) that stretch eight single fibers each. Due to fiber accumulation on the lay‐down belt under each of the aspirators, a metal rod is placed in‐between to deflect the fibers into the center utilizing the Coanda‐effect to achieve a broad homogeneous fiber distribution.
In this study, the poly(methyl methacrylate) (PMMA)/carbon fibers (CFs) composite films with different CFs concentrations have been prepared using the solution casting technique. CFs were modified ...using aqua regia to reduce aggregations. The residual aspect ratios (ARs) of CFs in the composite films are 49, 105, 227, 312, 417, 527 and 616, respectively. Light microscopy and SEM were applied to investigate the morphology of the composite films. The resistance of the film with different ARs of CFs was measured (1) perpendicularly and (2) along the in-plane direction. Both percolation thresholds ϕc,⊥ and ϕc,∥ were determined by fitting the Mclachlan GEM equation. The conductivity in both directions was presented in contour plot versus ARs of CFs and concentration of CFs. A huge amount of experimental data was obtained in this study, seven aspect ratio (AR) of CFs multiply 12 volume fraction of CFs with two measuring directions. Based on Balberg's excluded volume theory, for the first time the pre-factors K⊥ and K∥ were revealed, considering different measuring direction on the film.
Abstract In the context of tissue engineering, biofabrication techniques are employed to process cells in hydrogel-based matrices, known as bioinks, into complex 3D structures. The aim is the ...production of functional tissue models or even entire organs. The regenerative production of biological tissues adheres to a multitude of criteria that ultimately determine the maturation of a functional tissue. These criteria are of biological nature, such as the biomimetic spatial positioning of different cell types within a physiologically and mechanically suitable matrix, which enables tissue maturation. Furthermore, the processing, a combination of technical procedures and biological materials, has proven highly challenging since cells are sensitive to stress, for example from shear and tensile forces, which may affect their vitality. On the other hand, high resolutions are pursued to create optimal conditions for subsequent tissue maturation. From an analytical perspective, it is prudent to first investigate the printing behavior of bioinks before undertaking complex biological tests. According to our findings, conventional shear rheological tests are insufficient to fully characterize the printing behavior of a bioink. For this reason, we have developed optical methods that, complementarily to the already developed tests, allow for quantification of printing quality and further viscoelastic modeling of bioinks.
Polymer material exhibits a trade-off between toughness and stiffness, therefore, it remains difficult to develop a strategy that simultaneously realizes improved mechanical strength and toughness. ...Inspired by the bamboo-like structure, an efficient and simple melt sequential injection molding is proposed to fabricate a controllable skin-core structure of iPP samples with self-reinforcement and toughness. With increasing the melt injection number, the shear layers containing shish-kebabs are progressively thickened, resulting in an effective improvement of mechanical properties. The tensile strength increased from 35.1 to 55.3 MPa for the melt injection number from one to four, meanwhile the toughness was enhanced from 23.1 to 53.6 kJ/m2. A simple theoretical model was derived and utilized to describe the experimental data. Theoretically calculated tensile strength of sample with entirely shish-kebabs can even reach 222.9 MPa via this technology, which is much higher than that of most engineering plastics and polymer composites. This work not only provides an efficient way to fabricate high-performance general plastics for engineering purposes but also a new opportunity to understand the fundamental issues about the mechanism of the self-reinforced polymers.
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•A melt sequential injection molding (MSIM) technology is proposed.•MSIM sample with a thickened shear layer is obtained.•The tensile strength, stiffness and toughness are simultaneously increased.•A simple model is derived and utilized for the description of the tensile strength.
Nanosilica filled polylactide (PLA)/Poly(methyl methacrylate) (PMMA) 50/50 blends with varying silica concentrations were prepared by melt mixing. In this work, the effects of silica concentration ...and the preferential adsorption between silica and the component on the thermo-mechanical and rheological properties of PLA/PMMA blends were systematically investigated. The results of DSC indicate the miscibility of PLA/PMMA/silica nanocomposites in the solid state, and the incorporation of nanosilica does not only increase the glass transition temperature but also extend the broadness of glass transition. Local nanoscale heterogeneities in the miscible blends are proposed due to the self-concentration of the components, and the presence of nanosilica increased the concentration fluctuation and dynamic heterogeneity of the PLA/PMMA blends. A distinct “crater” structure can be observed in the fractured surfaces of the blend nanocomposites. According to the results of SEM and rheological measurements, it was proposed that PLA molecules were selectively adsorbed on the surface of nanosilica, and the preferential adsorption of PLA changed the blend composition in the “crater” structure and the bulk matrix. The phase separation temperature of the filled PLA/PMMA blends was also improved by the incorporation of nanosilica, implying a potential role of nanosilica in improving the phase stability of PLA/PMMA blends. In addition, nanosilica could increase and entanglement density and decrease the entanglement molar mass of the blends in a concentration-dependent manner.
SEM micrographs of the fractured surfaces of P/P/Si 2 nanocomposites. The specific “crater” structure is highlighted by the red circle (left panel). A schematic diagram illustrating the composition of the “crater” structure in which a preferential adsorption of PLA molecules on the surface of nanosilica aggregates is suggested. Display omitted
•Preferential adsorption between nanosilica and PLA molecules in the nanocomposites.•Nanosilica improves the concentration fluctuation and dynamic heterogeneity in PLA/PMMA blends.•The phase separation temperature of PLA/PMMA blends is improved by nanosilica.•Molecular entanglement in PLA/PMMA blends is effected by nanosilica due to the selective adsorption.
A simple model is proposed assuming location of the CB in the PS phase only and continuity of the PS phase. The figure shows the percolation threshold ϕc of PS/PMMA/CB composites as a function of ...PMMA content. Insert: Schematic illustration of the volume for PS/PMMA/CB system. Display omitted
•CB preferentially locates to the PS phase in immiscible PS/PMMA blends.•PS/PMMA (30/70) blends showed the lowest electrical percolation threshold.•A simple model is suggested to describe the percolation behavior.•After annealing, the CB affected the stabilization of the co-continuous structure.
Blends of carbon black (CB)-filled polystyrene (PS) and poly(methyl methacrylate) (PMMA) with different PS/PMMA ratios have been prepared by melt blending in order to obtain conductive polymer composites with a low electrical percolation threshold according to the concept of double percolation. The dependence of the electrical conductivity on the morphology of the composite was examined before and after annealing in the molten state. The electrical conductivity of the composites was highest when the PS and PMMA phases formed a co-continuous structure and CB particles were selectively located and percolated in the PS phase. PS/PMMA (30/70) blends exhibited the lowest electrical percolation threshold of 1.26vol% CB. A simple model is suggested to explain this effect. After annealing, the CB clearly affected the stabilization of the co-continuous structure. Moreover, the electrical conductivity increased after annealing and the percolation threshold decreased to below 1vol% CB regardless of PS content. The largest increase in electrical conductivity after annealing was found with PS/PMMA (70/30) blends filled with 1vol% CB. With increasing PMMA content, this effect became less pronounced. The different behaviors in the composites can be explained by dynamic percolation and decrease in continuity of the CB-filled PS phase induced by structure coarsening.
Electrophoretic deposition (EPD) of composite coatings based on chitosan, gelatin and copper doped bioactive glass (Cu-BG) particles on 316L stainless substrates (SS) was investigated. Despite the ...fact that EPD offers easy control over the thickness and morphology of the produced coatings, the optimization of the EPD process is a tedious task due to the fact that a high number of variables (applied voltage, deposition time, distance between the electrodes, concentration of the suspension and pH of the suspension) is involved. Therefore, we used the Taguchi Design of Experiments (DoE) approach for accurate and economical process (reduced number of experiments) optimization. The suspension composition (chitosan, gelatin and Cu-BG ratio) and electric field related parameters (voltage and time) were optimized by L25 type Taguchi array. The best coatings were obtained at the applied voltage of 30 V, deposition time of 5 min and the concentration ratio between chitosan/gelatin was 50:50 (vol%). Scanning electron microscopy (SEM) images revealed that Cu-BG particles were fairly homogenously dispersed in the chitosan/gelatin matrix. Fourier transform infrared spectroscopy (FTIR) and energy dispersive spectroscopy confirmed the presence of chitosan, gelatin and Cu-BG particles (qualitatively). The tape test (ASTM D3359-97 and B571-97) elucidated the appropriate adhesion strength of coatings (obtained by EPD using optimized parameters) for orthopedic applications. Moreover, chitosan/gelatin/Cu-BG coatings exhibited suitable hydrophilicity.
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•Key parameters for EPD of chitosan/gelatin and bioactive glass particles determined by design of experiment approach•Kinetics of electrophoretic deposition studied by Hamaker's model•EPD mechanism of chitosan/gelatin and bioactive glass proposed•Optimized coatings showed appropriate adhesion strength of coating to the substrate.•Optimized coatings exhibited suitable hydrophilicity.
This paper compares the molecular structure and rheological properties of a commercial poly(ethylene terephthalate) (PET) after reactive processing with different concentrations of either ...pyromellitic dianhydride (PMDA) or a multifunctional epoxide (Joncryl®ADR‐4368) as a chain extender. By size exclusion chromatography with triple detection, an increase of molar mass, a broadening of molar mass distribution, and the generation of long‐chain branched molecules were found for both chain extenders. While gel‐free materials were obtained with PMDA, the processing with Joncryl leads to the formation of gels. The effect of branching, indicated by the Mark–Houwink exponent, is more pronounced for materials with Joncryl compared to PMDA and points to a more compact branching structure of the PET/Joncryl molecules. Rheological measurements in shear and elongation support the analysis from SEC and reveal a complex tree‐like branching structure for both chain extenders. In addition, the role of the two modifiers with respect to processing was assessed.
Posterior lamellar transplantation of the eye' s cornea (DSAEK, DMEK) currently is the gold standard for treating patients with corneal endothelial cell and back surface pathologies resulting in ...functional impairment. An artificial biomimetic graft carrying human corneal endothelium could minimize the dependency on human donor corneas giving access to this vision-restoring surgery to large numbers of patients, thus reducing current long waiting lists. In this study, four groups of electrospun nanofibrous scaffolds were compared: polycaprolactone (PCL), PCL/collagen, PCL/gelatin and PCL/chitosan. Each of the scaffolds were tissue-engineered with human corneal endothelial cells (HCEC-B4G12) and analyzed with regard to their potential application as artificial posterior lamellar grafts. Staining with ZO-1 and Na
/K
-ATPase antibodies revealed intact cell functionalities. It could be shown, that blending leads to decreasing contact angle, whereby a heterogeneous blend morphology could be revealed. Scaffold cytocompatibility could be confirmed for all groups via live/dead staining, whereby a significant higher cell viability could be observed for the collagen and gelatine blended matrices with 97 ± 3% and 98 ± 2% living cells respectively. TEM images show the superficial anchoring of the HCECs onto the scaffolds. This work emphasizes the benefit of blended PCL nanofibrous scaffolds for corneal endothelial keratoplasty.
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