Preparation and characterization of polyaniline/chitosan blend film

Films consisting of a blend of a chitosan hydrogel and a conductive polymer, polyaniline (PANI), were prepared and characterized for their electrical and mechanical properties. Polyaniline in emeraldine base (EB) form was dispersed in chitosan solution and blend films were obtained by solution casting. The PANI particles in the blend films were then doped with HCl where we observed reductions in the film tensile strength and Young's modulus by about 30%, but the films electrical conductivity increased by 6 orders of magnitude. The highest electrical conductivity of the blend films was of the order 10⁻⁴ S/cm. The electrical and mechanical properties of the films varied with polyaniline content, acid dopant type, acid dopant concentration, and doping time.     

FT-IR imaging spectroscopy of phase separation in blends of poly(3-hydroxybutyrate) with poly(L-lactic acid) and poly(epsilon-caprolactone)

The detection of phase separation and identification of miscibility in biopolymer blends is an important aspect for the improvement of their physical properties. In this article, the phase separation in blends of poly(3-hydroxybutyrate) (PHB) with poly(L-lactic acid) (PLA) and poly(epsilon-caprolactone) (PCL), respectively, has been studied as a function of the blend composition by FT-IR imaging spectroscopy. For both polymer blend systems, a miscibility gap has been found around the 50:50% (w/w) composition of the two components. Furthermore, the separating phases have been identified as blends of the two polymer components and their compositions could be determined from calibrations based on the spectra of the blends in the compositional range of miscibility. The data derived from FT-IR spectroscopic imaging were corroborated by additional DSC analyses and mechanical stress-strain measurements of polymer blend films, which exhibited a characteristic fracture behavior as a function of PHB composition.     

Morphology control in co-continuous poly(L-lactide)/polystyrene blends: a route towards highly structured and interconnected porosity in poly(L-lactide) materials

Poly(L-lactide) is a biodegradable polymer primarily used in biomedical applications. In this paper, both the microstructure and the region of dual-phase continuity are examined for binary and compatibilized poly(L-lactide)/polystyrene blends (PLLA/PS) prepared by melt mixing. The blends are shown to be completely immiscible with an interfacial tension of 6.1 mN/m. The PS-b-PLLA (24,000-b-28,000) diblock copolymer compatibilizer has an asymmetric effect on the blend. It is effective at compatibilizing 50/50 PLLA/PS blends but is only a marginal emulsifier for blends where PLLA is the dominant matrix. Percent continuity, as estimated by solvent extraction/gravimetry and also torque/composition diagrams clearly indicate an onset of the region of dual-phase continuity at 40-45%PS. It is demonstrated that highly percolated blends of the above materials exist from 40 to 75% PS and 40 to 60% PS for the binary and compatibilized blends, respectively. The scale of the microstructure of the continuous morphology is measured using BET and mercury intrusion porosimetry techniques, after extraction of the PS phase. Both the pore size and extent of continuity can be controlled through composition and interfacial modification. Static annealing of the blend after melt mixing can also be used to substantially increase the pore size of the system. Extraction of the PS phase in the blend, carried out after the above preparation protocols, is a route to generating completely interconnected porosity of highly controlled morphologies (pore size, void volume) in poly(L-lactide) materials. In this study, the pore diameter was controlled from 0.9 to 72 microm for a constant void volume of 45-47%, and the void volume was modified from 35 to 74% depending on the blend composition.     

Compatibilization effect of poly(epsilon-caprolactone)-b-poly(ethylene glycol) block copolymers and phase morphology analysis in immiscible poly(lactide)/poly(epsilon-caprolactone) blends

The miscibility and phase behavior of two stereoisomer forms of poly(lactide) (PLA: poly (L-lactide) (PLLA) and poly(DL-lactide) (PDLLA)) blends with poly(epsilon-caprolactone)-b-poly(ethylene glycol) (PCL-b-PEG) and PCL-b-monomethoxy-PEG (PCL-b-MPEG) block copolymers have been investigated by differential scanning calorimetry (DSC). The DSC thermal behavior of both the blend systems revealed that PLA is miscible with the PEG segment phase of PCL-b-(M)PEG but is still immiscible with its PCL segment phase although PCL was block-copolymerized with PEG. On the basis of these results, PCL-b-PEG was added as a compatibilizer to PLA/PCL binary blends. The improvement in mechanical properties of PLA/PCL blends was achieved as anticipated upon the addition of PCL-b-PEG. In addition, atomic force microscopy (AFM) measurements have been performed in order to study the compositional synergism to be observed in mechanical tests. AFM observations of the morphological dependency on blend composition indicate that PLA/PCL blends are immiscible but compatible to some extent and that synergism of compatibilizing may be maximized in the compositional blend ratio before apparent phase separation and coarsening.     

A constitutive model for vascular tissue that integrates fibril, fiber and continuum levels with application to the isotropic and passive properties of the infrarenal aorta

A fundamental understanding of the mechanical properties of the extracellular matrix (ECM) is critically important to quantify the amount of macroscopic stress and/or strain transmitted to the cellular level of vascular tissue. Structural constitutive models integrate histological and mechanical information, and hence, allocate stress and strain to the different microstructural components of the vascular wall. The present work proposes a novel multi-scale structural constitutive model of passive vascular tissue, where collagen fibers are assembled by proteoglycan (PG) cross-linked collagen fibrils and reinforce an otherwise isotropic matrix material. Multiplicative kinematics account for the straightening and stretching of collagen fibrils, and an orientation density function captures the spatial organization of collagen fibers in the tissue. Mechanical and structural assumptions at the collagen fibril level define a piece-wise analytical stress-stretch response of collagen fibers, which in turn is integrated over the unit sphere to constitute the tissue's macroscopic mechanical properties. The proposed model displays the salient macroscopic features of vascular tissue, and employs the material and structural parameters of clear physical meaning. Likewise, the constitutive concept renders a highly efficient multi-scale structural approach that allows for the numerical analysis at the organ level. Model parameters were estimated from isotropic mean-population data of the normal and aneurysmatic aortic wall and used to predict in-vivo stress states of patient-specific vascular geometries, thought to demonstrate the robustness of the particular Finite Element (FE) implementation. The collagen fibril level of the multi-scale constitutive formulation provided an interface to integrate vascular wall biology and to account for collagen turnover.     

Miscibility studies of HPMC/PVA blends in water by viscosity, density, refractive index and ultrasonic velocity method

Hydroxy propyl methyl cellulose (HPMC)/polyvinyl alcohol (PVA) blends are edible polymer films used for food packing and directly in foodstuffs. However they are water-soluble in ordinary temperature and have good mechanical properties. The miscibility of HPMC/PVA blend in water was studied by viscosity, ultrasonic velocity, density and refractive index techniques at 30 and 50 °C. Using viscosity data, the interaction parameters μ and α were calculated. These values revealed that HPMC/PVA blend is miscible when the HPMC content is more than 60% in the blend at 30 and 50 °C. And also the result revealed that the change in temperature has no significant effect on the miscibility of HPMC/PVA polymer blend.     

A micromechanical model of skeletal muscle to explore the effects of fiber and fascicle geometry

Computational models of muscle generally lump the material properties of connective tissue, muscle fibers, and muscle fascicles together into one constitutive relationship that assumes a transversely isotropic microstructure. These models do not take into account how variations in the microstructure of muscle affect its macroscopic material properties. The goal of this work was to develop micromechanical models of muscle to determine the effects of variations in muscle microstructure on the macroscopic constitutive behavior. We created micromechanical models at the fiber and fascicle levels based on histological cross-sections of two rabbit muscles, the rectus femoris (RF) and the soleus, to determine the effects of microstructure geometry (fiber and fascicle shapes) on the along-fiber shear modulus of muscle. The two fiber-level models predicted similar macroscopic shear moduli (within 13.5% difference); however, the two fascicle-level models predicted very different macroscopic shear moduli (up to 161% difference). We also used the micromechanical models to test the assumption that the macroscopic properties of muscle are transversely isotropic about the fiber (or fascicle) direction. The fiber-level models exhibited behavior consistent with the transverse isotropy assumption; however, the fascicle-level models exhibited transversely anisotropic behavior. Micromechanical models, combined with fiber and fiber bundle mechanical experiments, are needed to understand how normal or pathological variations in microstructure give rise to the observed macroscopic behavior of muscle.     

Tensile behavior of cortical bone: dependence of organic matrix material properties on bone mineral content

A porous composite model is developed to analyze the tensile mechanical properties of cortical bone. The effects of microporosity (volksman's canals, osteocyte lacunae) on the mechanical properties of bone tissue are taken into account. A simple shear lag theory, wherein tensile loads are transferred between overlapped mineral platelets by shearing of the organic matrix, is used to model the reinforcement provided by mineral platelets. It is assumed that the organic matrix is elastic in tension and elastic-perfectly plastic in shear until it fails. When organic matrix shear stresses at the ends of mineral platelets reach their yield values, the stress-strain curve of bone tissue starts to deviate from linear behavior. This is referred as the microscopic yield point. At the point where the stress-strain behavior of bone shows a sharp curvature, the organic phase reaches its shear yield stress value over the entire platelet. This is referred as the macroscopic yield point. It is assumed that after macroscopic yield, mineral platelets cannot contribute to the load bearing capacity of bone and that the mechanical behavior of cortical bone tissue is determined by the organic phase only. Bone fails when the principal stress of the organic matrix is reached. By assuming that mechanical properties of the organic matrix are dependent on bone mineral content below the macroscopic yield point, the model is used to predict the entire tensile mechanical behavior of cortical bone for different mineral contents. It is found that decreased shear yield stresses and organic matrix elastic moduli are required to explain the mechanical behavior of bones with lowered mineral contents. Under these conditions, the predicted values (elastic modulus, 0.002 yield stress and strain, and ultimate stress and strain) are within 15% of experimental data.     

The influence of tether number and location on the self-assembly of polymer-tethered nanorods

Coarse-grained molecular dynamics simulations were used to investigate the self-assembly of polymer-tethered nanorods with relatively high aspect ratio. The number and location of polymer tethers were varied to determine their influence on nanorod self-assembly. We found that laterally polymer-tethered nanorods self-assemble into structures with flat interfaces; these structures include stepped ribbons, stepped lamellae and lamellae with rods packed into bilayer sheets. The stepped lamellar phase is observed for the first time in this study. End polymer-tethered nanorods are prone to self-assemble into structures with curved interfaces, and the assembled structures observed here include spherical micelles and nematically aligned cylinders. The cylinder phase exists at high number densities, instead of the lamellar phase typically found for end polymer-tethered nanorods with relatively lower aspect ratio.     

Photo-cross-linked hybrid polymer networks consisting of poly(propylene fumarate) and poly(caprolactone fumarate): controlled physical properties and regulated bone and nerve cell responses

Aiming to achieve suitable polymeric biomaterials with controlled physical properties for hard and soft tissue replacements, we have developed a series of blends consisting of two photo-cross-linkable polymers: polypropylene fumarate (PPF) and polycaprolactone fumarate (PCLF). Physical properties of both un-cross-linked and UV cross-linked PPF/PCLF blends with PPF composition ranging from 0% to 100% have been investigated extensively. It has been found that the physical properties such as thermal, rheological, and mechanical properties could be modulated efficiently by varying the PPF composition in the blends. Thermal properties including glass transition temperature (T g) and melting temperature (T m) have been correlated with their rheological and mechanical properties. Surface characteristics such as surface morphology, hydrophilicity, and the capability of adsorbing serum protein from culture medium have also been examined for the cross-linked polymer and blend disks. For potential applications in bone and nerve tissue engineering, in vitro cell studies including cytotoxicity, cell adhesion, and proliferation on cross-linked disks with controlled physical properties have been performed using rat bone marrow stromal cells and SPL201 cells, respectively. In addition, the role of mechanical properties such as surface stiffness in modulating cell responses has been emphasized using this model blend system.     

Inferring spatial variations of microstructural properties from macroscopic mechanical response

Disease alters tissue microstructure, which in turn affects the macroscopic mechanical properties of tissue. In elasticity imaging, the macroscopic response is measured and is used to infer the spatial distribution of the elastic constitutive parameters. When an empirical constitutive model is used, these parameters cannot be linked to the microstructure. However, when the constitutive model is derived from a microstructural representation of the material, it allows for the possibility of inferring the local averages of the spatial distribution of the microstructural parameters. This idea forms the basis of this study. In particular, we first derive a constitutive model by homogenizing the mechanical response of a network of elastic, tortuous fibers. Thereafter, we use this model in an inverse problem to determine the spatial distribution of the microstructural parameters. We solve the inverse problem as a constrained minimization problem and develop efficient methods for solving it. We apply these methods to displacement fields obtained by deforming gelatin–agar co-gels and determine the spatial distribution of agar concentration and fiber tortuosity, thereby demonstrating that it is possible to image local averages of microstructural parameters from macroscopic measurements of deformation.     

Soft Tissue Modelling of Cardiac Fibres for Use in Coupled Mechano-Electric Simulations

The numerical solution of the coupled system of partial differential and ordinary differential equations that model the whole heart in three dimensions is a considerable computational challenge. As a consequence, it is not computationally practical—either in terms of memory or time—to repeat simulations on a finer computational mesh to ensure that convergence of the solution has been attained. In an attempt to avoid this problem while retaining mathematical rigour, we derive a one dimensional model of a cardiac fibre that takes account of elasticity properties in three structurally defined axes within the myocardial tissue. This model of a cardiac fibre is then coupled with an electrophysiological cell model and a model of cellular electromechanics to allow us to simulate the coupling of the electrical and mechanical activity of the heart. We demonstrate that currently used numerical methods for coupling electrical and mechanical activity do not work in this case, and identify appropriate numerical techniques that may be used when solving the governing equations. This allows us to perform a series of simulations that: (i) investigate the effect of some of the assumptions inherent in other models; and (ii) reproduce qualitatively some experimental observations.     

Key parameters controlling stiffness variability within trees: a multiscale experimental–numerical approach

Microstructural properties of wood vary considerably within a tree. Knowledge of these properties and a better understanding of their relationship to the macroscopic mechanical performance of wood are crucial to optimize the yield and economic value of forest stocks. This holds particularly for the end-use requirements in engineering applications. In this study the microstructure–stiffness relationships of Scots pine are examined with a focus on the effects of the microstructural variability on the elastic properties of wood at different length scales. For this purpose, we have augmented microstructural data acquired using SilviScan-3? (namely wood density, cell dimensions, earlywood and latewood proportion, microfibril angle) with local measurements of these quantities and of the chemical composition derived from wide-angle X-ray scattering, light microscopy, and thermogravimetric analysis, respectively. The stiffness properties were determined by means of ultrasonic tests at the clear wood scale and by means of nanoindentation at the cell wall scale. In addition, micro-mechanical modeling was applied to assess the causal relations between structural and mechanical properties and to complement the experimental investigations. Typical variability profiles of microstructural and mechanical properties are shown from pith to bark, across a single growth ring and from earlywood to latewood. The clear increase of the longitudinal stiffness as well as the rather constant transverse stiffness from pith to bark could be explained by the variation in microfibril angle and wood density over the entire radial distance. The dependence of local cell wall stiffness on the local microfibril angle was also demonstrated. However, the local properties did not necessarily follow the trends observed at the macroscopic scale and exhibited only a weak relationship with the macroscopic mechanical properties. While the relationship between silvicultural practice and wood microstructure remains to be modeled using statistical techniques, the influence of microstructural properties on the macroscopic mechanical behavior of wood can now be described by a physical model. The knowledge gained by these investigations and the availability of a new micromechanical model, which allows transferring these findings to non-tested material, will be valuable for wood quality assessment and optimization in timber engineering.     

Concurrent Quantitative Conductivity and Mechanical Properties Measurements of Organic Photovoltaic Materials using AFM

Organic photovoltaic (OPV) materials are inherently inhomogeneous at the nanometer scale. Nanoscale inhomogeneity of OPV materials affects performance of photovoltaic devices. Thus, understanding of spatial variations in composition as well as electrical properties of OPV materials is of paramount importance for moving PV technology forward.^1,2 In this paper, we describe a protocol for quantitative measurements of electrical and mechanical properties of OPV materials with sub-100 nm resolution. Currently, materials properties measurements performed using commercially available AFM-based techniques (PeakForce, conductive AFM) generally provide only qualitative information. The values for resistance as well as Young''s modulus measured using our method on the prototypical ITO/PEDOT:PSS/P3HT:PC₆₁BM system correspond well with literature data. The P3HT:PC₆₁BM blend separates onto PC₆₁BM-rich and P3HT-rich domains. Mechanical properties of PC₆₁BM-rich and P3HT-rich domains are different, which allows for domain attribution on the surface of the film. Importantly, combining mechanical and electrical data allows for correlation of the domain structure on the surface of the film with electrical properties variation measured through the thickness of the film.     

Miscibility studies of HPMC/PEG blends in water by viscosity,density, refractive index and ultrasonic velocity method

Hydroxy propyl methyl cellulose (HPMC)/polyethylene glycol (PEG) blends are edible polymer films used for food packing and directly in foodstuffs. However, they are water-soluble in ordinary temperature and have good mechanical properties. The miscibility of HPMC/PEG blend in water was studied by viscosity, ultrasonic velocity, density and refractive index techniques at 30 and 50 °C. Using viscosity data, the interaction parameters μ and α were calculated. These values revealed that HPMC/PEG blend is miscible when the HPMC content is more than 60 wt.% in the blend at 30 and 50 °C, below which is immiscible. Further the result was also confirmed by ultrasonic velocity, density, refractive index measurements, which also revealed that the change in temperature has no significant effect on the miscibility of HPMC/PEG polymer blend.     

Active accumulation of gold nanorods in tumor in response to near-infrared laser irradiation

Gold nanorods, rod-shaped gold nanoparticles, have strong absorbance in the near-infrared region, and the absorbed light energy can be converted to heat, the so-called photothermal effect. The gold nanorods were coated with thermoresponsive polymers, which have different phase transition temperatures that were controlled by adding comonomers, N,N-dimethylacrylamide (DMAA) or acrylamide (AAm) to N-isopropylacrylamide (NIPAM). The phase transition temperatures of poly(NIPAM-DMAA) and poly(NIPAM-AAm)-coated gold nanorods were 38 and 41 °C, respectively, while polyNIPAM-coated gold nanorods showed phase transition at 34 °C. Irradiation of the coated gold nanorods using the near-infrared laser induced a decrease in their sizes due to a phase transition of the polymer layers. Poly(NIPAM-AAm)-coated gold nanorods stably circulated in the blood flow without a phase transition after intravenous injection. Irradiation of near-infrared light at a tumor after the injection resulted in the gold specifically accumulating in the tumor. This novel accumulation technique which combines a thermoresponsive polymer and the photothermal effect of the gold nanorods should be a powerful tool for targeted delivery in response to light irradiation.     

Characteristics and bending performance of electroactive polymer blend made with cellulose and poly(3-hydroxybutyrate)

This paper describes a novel cellulose/poly(3-hydroxybutyrate) blend based electroactive polymer. The fabrication process, bending actuation test and its characteristics are investigated. To prepare this new EAP, cellulose and PHB were dissolved in trifluoroacetic acid. The solution was cast to form a film followed by depositing thin gold electrode on both sides of the film. The characteristics of the cellulose/PHB film were investigated by Fourier transform infrared spectra, scanning electron microscopy, X-ray diffraction differential scanning calorimetry, tensile test and dynamic mechanical analysis. The bending performance was evaluated in terms of free bending displacement, electrical power consumption output and lifetime test under ambient conditions. Primary results show that this cellulose/PHB blend EAP is less sensitive to humidity and it shows higher bending displacement and longer lifetime than pure cellulose EAP at room humidity condition. These results indicate that this new cellulose/PHB blend EAP has potential for many biomimetic applications.     

Autocatalytic Sets and Biological Specificity

A universal feature of the biochemistry of any living system is that all the molecules and catalysts that are required for reactions of the system can be built up from an available food source by repeated application of reactions from within that system. RAF (reflexively autocatalytic and food-generated) theory provides a formal way to study such processes. Beginning with Kauffman’s notion of “collectively autocatalytic sets,” this theory has been further developed over the last decade with the discovery of efficient algorithms and new mathematical analysis. In this paper, we study how the behaviour of a simple binary polymer model can be extended to models where the pattern of catalysis more precisely reflects the ligation and cleavage reactions involved. We find that certain properties of these models are similar to, and can be accurately predicted from, the simple binary polymer model; however, other properties lead to slightly different estimates. We also establish a number of new results concerning the structure of RAFs in these systems.     

Preparation and Characterization of a Silk Fibroin/Polyurethane Fiber Blend Membrane Containing Actinomycin X2 with Excellent Mechanical Properties and Enhanced Antibacterial Activities

Development of suitable antimicrobial biomaterials for hygienic wound dressing and healing is an important requirement for medical application. Durable mechanical properties increase the application range of biomaterial in different environmental and biological conditions. Due to the inherent brittleness of silk fibroin (SF), polyurethane fiber (PUF) was used to modify SF containing actinomycin X2 (Ac.X2) to prepare silk fibroin@actinomycin X₂/polyurethane fiber (ASF/PUF) blend membranes. The ASF/PUF blend membrane was developed by solution casting method. Incorporation of PUF improved the flexibility of material and introduction of Ac.X2 has increased antibacterial activity of materials. Excellent mechanical properties (tensile strength up to 25.7 MPa and elongation at break up to 946.5 %) of 50 % SF+50 % PUF blend membrane were proved by tensile testing machine. FT-IR spectra, TGA, contact angle and DMA were tested to prove the blend membrane's physico-chemical characteristics. ASF/PUF blend membrane displayed satisfactory antibacterial activity against S. aureus, and the cytotoxicity tests showed that the blend membrane has better biosafety compared to directly applied Ac.X2 in soluble form. These results suggest that the modification of SF through PUF for development of flexible antibacterial membranes has great potential application value in the field of silk-like material fabrication.     

Multiscale modeling of skeletal muscle properties and experimental validations in isometric conditions

In this article, we describe an approach to model the electromechanical behavior of the skeletal muscle based on the Huxley formulation. We propose a model that complies with a well established macroscopic behavior of striated muscles where force-length, force–velocity, and Mirsky–Parmley properties are taken into account. These properties are introduced at the microscopic scale and related to a tentative explanation of the phenomena. The method used integrates behavior ranging from the microscopic to the macroscopic scale, and allows the computation of the dynamics of the output force and stiffness controlled by EMG or stimulation parameters. The model can thus be used to simulate and carry out research to develop control strategies using electrical stimulation in the context of rehabilitation. Finally, through animal experiments, we estimated model parameters using a Sigma Point Kalman Filtering technique and dedicated experimental protocols in isometric conditions and demonstrated that the model can accurately simulate individual variations and thus take into account subject dependent behavior.