Physically crosslinked hydrogels based on gelatin functionalized with desaminotyrosine (DAT) (giving Gel-DAT) or desaminotyrosyl tyrosine (DATT) (resulting in Gel-DATT) have shown high potential as biomaterials. Here, protein adsorption to the functionalized gelatins in comparison to gelatin was quantified to see if the functionalization and chain organization of gelatins has an influence on the amount of proteins being adsorbed. For this purpose, gelatin, Gel-DAT, and Gel-DATT were incubated with water or aq. solutions of bovine serum albumin (BSA), fibrinogen, or fibronectin, respectively, at physiological concentrations. Protein concentrations in the supernatant were determined with the bicinchoninic acid (BCA) assay before and after the contact. BSA adsorption to the materials was influenced as well by the hydrophobicity of the material as the degree of swelling, with the observation that higher protein concentrations led to lower protein adsorption. The highest amount of fibronectin was adsorbed to Gel-DAT, followed by gelatin and Gel-DATT, with only small differences for different initial protein concentrations. Fibrinogen adsorption increased with increasing concentration. In the future, adsorption studies based on specific antibody-based techniques might enable quantification of the proteins also in competition assays and direct quantification of adsorbed material.

The wetting behavior of polyamide films was modified by depositing electrospun nanofibers manufactured from the same polyamide material. Glycerol contact angles on the film surfaces with low coverage of electrospun nanofibers were successfully predicted using a Cassie-Baxter relationship but could not be predicted for high electrospun nanofiber coverage.

Considerable research has focused on the formation of superhydrophobic surfaces utilizing both the chemical composition of surfaces and geometric effects. In this study, a superhydrophobic polycarbonate (PC) network surface was produced from hydrophilic polycarbonate through electrospinning process. Complex surface geometries often related to material roughness is used to evaluate the wetting behavior of electrospun polycarbonate fiber network. The surface properties of electrospun polycarbonate fibers are therefore examined with the potential to exploit the fibers through enhancing hydrophobic behavior. Characterization and analysis of PC electrospun fiber and PC film surfaces were carried out to compare surface roughness with wetting contact angle. Analytical models are used to describe hydrophobicity in terms of roughness.

The synthesis of semi-interpenetrating networks (SIPN) based on linear poly(ethyl 2-cyanoacrylate) (PECA) and oligo(ethylene glycol) diglycidyl ether (OEGDG) based polymer networks was motivated by the hypothesis that the brittleness of polycyanoacrylates may be overcome by incorporating them into a polymer network architecture. A sequential synthetic route was applied, in which first PECA was prepared by anionic polymerization. Subsequently, OEGDG was crosslinked with different anhydrides and curing catalysts to form networks with hydrolyzable ester bonds and interpenetrating PECA. These SIPNs showed a low water uptake compared to other polyether based networks. Some of the obtained materials were transparent and exhibited a great flexibility, which was maintained also after 24 h of immersion in water and subsequent drying. Such networks could be components of future stimuli-sensitive material systems.

As a novel biomimetic polymer gel, we have been studying polymer gels with an autonomous self-oscillating function, since firstly reported in 1996. For developing the polymer gels, we utilized oscillating chemical reaction, called the Belousov-Zhabotinsky (BZ) reaction, which is recognized as a chemical model for understanding several autonomous phenomena in biological systems. The self-oscillating polymer gel is composed of a poly(N-isopropylacrylamide) network in which the metal catalyst for the BZ reaction is covalently immobilized. Under the coexistence of the reactants, the polymer undergoes spontaneous swelling-deswelling changes (in the case of gel) or cyclic soluble-insoluble changes (in the case of an uncrosslinked polymer) without any on-off switching of external stimuli. Several kinds of functional material systems utilizing self-oscillating polymers and gels such as biomimetic actuators, mass transport surface, etc. are expected. Here recent progress on self-oscillating polymers and gels and the design of functional material systems are summarized.

Shape memory effect in pure ultra-high molecular weight polyethylene (UHMWPE) has been studied using dynamic mechanical analysis. Temperature dependencies of properties that define functional characteristics of shape memory polymers (SMP) such as recovery stress, recovery strain and activation temperature of transition were determined for UHMWPE. The recovery stress in UHMWPE deformed by 200% achieved rather high values, up to 7 MPa.

Modeling of free radical polymerizations of the liquid-crystalline monomer 6-[4-(4-heptyloxyphenylazo)phenoxy]hexylacrylate using the PREDICI software package is reported. The model accounts for all elemental reactions that were identified to be important for radical polymerizations of acrylate-type monomers. On the basis of butyl acrylate kinetic data a remarkable agreement between number average molar masses from modelling (Mn,sim) and from experiments (Mn,exp) is observed: Mn,sim = 17800 g·mol−1 and Mn,exp = 17400 g·mol−1. Similarly, dispersity values of 1.8 and 1.6 were determined via modelling and experiments, respectively. It is shown that the assumption of butyl acrylate kinetics provides a reasonable approximation even for acrylate-based monomers having mesogenic substituents.

Magneto-sensitive shape-memory polymers (SMP) obtained by incorporating magnetic nanoparticles in a SMP matrix are an emerging class of multifunctional materials. The incorporation of the nanoparticles enhanced the mechanical properties and in addition enabled remote actuation by exposure to alternating magnetic fields. Here, we report on the thermallyinduced shape-memory properties of such magneto-sensitive nanocomposites based on poly(ω- pentadecalactone) (PPDL) switching segments and magnetic nanoparticles. A series of nanocomposites were prepared by crosslinking of poly(ω-pentadecalactone)dimethacrylate (Mn = 2800 g·mol-1and 5100 g·mol-1) in the presence of silica encapsulated magnetic nanoparticles. The silica shell of the nanoparticles was selected to enhance the distribution and compatibility of the nanoparticles with the polymer matrix. Thermal and mechanical properties of the nanocomposites were explored as a function of PPDL chain length and nanoparticle weight content. All nanocomposites exhibited excellent shape-memory properties with shape fixity rates between 86% and 93% and shape recovery rates above 97%. Potential applications for such shape-memory nanocomposites include smart implants, medical instruments, which could be controlled on demand by thermal or indirect magnetic heating.

Liquid crystal (in particular, nematic) elastomers consist of cross-linked flexible polymer chains with embedded stiff rod molecules that allow them to behave as a rubber and a liquid crystal. Nematic elastomers are characterized by a phase transition from isotropic to nematic past a temperature threshold. They behave as rubber at high temperature and show nematic behavior below the temperature threshold. Such transition is reversible. While in the nematic phase, the rod molecules are aligned along the direction of the ’’nematic director’’. This molecular rearrangement induces a stretch in the polymer chains and hence macroscopic spontaneous deformations. The coupling between nematic order parameter and deformation gives rise to interesting phenomena with a potential for new interesting applications. In the biological field, the ability to considerably change their length makes them very promising as artificial muscles actuators. Their tunable optical properties make them suitable, for example, as lenses for new imaging systems.

We present a mathematical model able to describe the behavior of nematic elastomers and numerical simulations reproducing such peculiar behavior. We use a geometrically linear version of the Warner and Terentjev model [1] and consider cooling experiments and stretching experiments in the direction perpendicular to the one of the director at cross-linking.

Stimuli-sensitive materials can change properties upon exposure to an external stimulus. Thermoreversible gelation upon heating is one example for such a stimuli sensitivity. Here, it is of significance to tailor the transition temperature and to achieve large changes of G’ and the viscosity. Grafting of the thermosensitive poly(ethylene glycol-b-propylene glycol-b-ethylene glycol)s (PEPEs) to pectin was performed in order to investigate if tailoring of the sol-gel-transition temperature can be achieved by adjusting the grafting ratio. PEPEs were aminated and grafted to the polysaccharide via EDC coupling as shown by FTIR. The sol-gel transition of the pectin, PEPE, and the grafted system (PGP) was investigated by rheology. The gelation temperature (Tgel) of the system could be adjusted by varying the grafting density of PEPE onto pectin as well as by the concentration of the thermosensitive polymer in aqueous solution. A concentration of 15 – 20 wt% of the grafted system in water led to gelation temperatures in the range of 25 – 33 °C and the critical micelle concentration (CMC) and critical micelle temperature (CMT) of the grafted systems were determined by UV spectroscopy. The viscosity and the G’ increased by four orders of magnitudes at Tgel, which is comparable to PEPEs alone, but could be reached at lower PEPE concentrations. In the future, a thorough mechanistic investigation of the gelation process would be of interest.

In this paper we report on the preparation of calix[8]arene functionalized polyglycerol nanogels by miniemulsion polymerization. The gel macromonomers were prepared by anionic ring-opening multibranching polymerization of glycidol using calix[8]arene as initiator. 1,1′,3,3,3′,3′-hexamethyl-2,2′-indotricarbocyanine iodide (HITC) red fluorescent dye was used as a guest molecule. Photobleaching upon strong laser illumination was significantly reduced when the dye was encapsulated inside the nanogel.

Phosphorylcholine glyceraldehyde (PCGA) was used as a phosphorylcholine (PC) group containing compound to graft onto the surface of polycarbonateurethane (PCU) film using 1,6-hexanediamine (HDA) or α,ω-diamino-poly(ethylene glycol) (APEG, Mn = 200) as a spacer, in order to introduce biomimetic structure onto the polymer surface. X-ray photoelectron spectroscopy (XPS) analysis shows that PCGA has been covalently linked to the PCU surface. Water contact angle test suggests that the surface hydrophilicity has been improved after PCGA is grafted onto the surface of PCU film. Scanning electron microscope (SEM) observation of the modified PCU films after contacting with plasma-rich plasma demonstrates that platelets rarely adhere but a large number of platelets adhere to the original PCU surface. The hemocompatibility of the PC modified PCU film has been improved obviously after grafting with PCGA with PEG spacer.

Dielectric polymers with high energy density with low loss at high electric fields are highly desired for many energy storage and regulation applications. A polar-fluoropolymer blend consisting of a high energy density polar-fluoropolymer of poly(vinylidene fluoride-chlorotrifluoroethylene) (P(VDF-CTFE)) with a low dielectric loss polymer of poly(ethylene-chlorotrifluoroethylene) (ECTFE) was developed and investigated. We show that the two polymers are partially miscible which leads to blends with high energy density and low loss. Moreover, by introducing crosslinking to further tailor the nano-structures of the blends a markedly reduction of losses in the blend films at high field can be achieved. The crosslinked blend films show a dielectric constant of 7 with a dielectric loss of 1% at low field. Furthermore, the blends maintain a high energy density and low loss (∼3%) at high electric fields (> 250 MV/m).

Aim of this work was to realize free-standing conductive nanofilms having very large surface area with typical nano-scale thickness (40-120 nm) by modifying existing approaches for nanostructured thin films assembly. We tested and optimized two different fabrication methods for the obtainment of free-standing conductive ultra-thin nanosheets based on the conductive polymer poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT:PSS). Supporting Layer and Sacrificial Layer techniques permitted the obtainment of single layer nanofilms that can be released in water and of LbL multilayer nanosheets (PEDOT:PSS/Polyelectrolytes) that can be released in acetone, respectively. Here we describe the details of both the proposed fabrication methods and compare the properties of the realized nanosheets in terms of thickness, contact angle and conductivity. Interestingly, the realized free-standing nanosheets, despite their low thickness, are very robust and compliant while maintaining their structure and functionality. Possible applications are foreseen in the field of sensing and actuation, as well as in the biomedical field, e.g. as smart conductive substrates for cell culturing and stimulation.

Polyurethanes (PU) have been widely used as biomaterial in recent years, while thrombus may still occur when contacting with blood especially for extended period of time. Poly(ethylene glycol) (PEG) and phosphorylcholine (PC)-based polymers are commonly employed for surface modification to create protein repellent surfaces. PC-based polymers have been investigated as biomimetic materials because PC is the major component in the outer layer of cell membranes. In this study, the biomimetic copolymer brush of PEG-b-poly(2-methacryloyloxyethyl phosphorylcholine) on PU surfaces was synthesized via atom transfer radical polymerization (ATRP) with a surface initiator. The flexible PEG chain was 200 g·mol-1, while the poly(2-methacryloyloxyethyl phosphorylcholine) (poly(MPC)) chain length was controlled by the ratio of monomer to sacrificial initiator in solution. The topology of the modified surfaces was characterized by the phase image of atomic force microscopy (AFM) to study the synergy effect between PEG chains and poly(MPC) chains. The unmodified and modified surfaces were characterized by Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), water contact angle and platelet adhesion. The results demonstrated that efficient grafting of PEG-b-poly(MPC) brushes on the surfaces was achieved. The PU surfaces modified with PEG and phosphorylcholine zwitterionic brushes showed effective resistance to platelet adhesion and high hemocompatibility in vitro. These PEG and PC-grafted PU materials might be potentially applied in blood-contacting materials or devices due to their good mechanical and hemocompatible properties.

We present a hybrid structure of Isotactic Polypropylene (iPP) nanocomposite with multiwall carbon nanotubes (MWCNTs). The polymer component contributes to the optical properties, flexibility and integrity of the polymer film while the carbon nanotubes change the thermal and mechanical stability, electrical and thermal conductivity and sensitivity. The multifunctional characteristics of this nanocomposite material are enhanced by anisotropic organization of the nanotubes and polymer through melt shearing which provides organization of the structural constituents at the molecular, nano, and micro length scales. This results in anisotropy of the macroscopic composite film properties parallel and perpendicular to the direction of shearing. On the molecular scale, the CNTs control the arrangement of the polymer molecules in a crystal lattice. On the nanometer scale, the CNTs couple to and align with the smectic normal of the liquid crystal phase of iPP. On the micron scale and larger, the secondary polymer crystal structure is rearranged due to the pinning of the polymer at the CNT surface to form fibrillar rather than spherulitic structures. These multi-scale rearrangements affect the optical, thermal, electrical, mechanical and chemical properties of the nanocomposite film. Our findings indicate that the CNTs under shear induce a novel anisotropy to the various thermo-physical properties of the iPP/CNTs films. We introduce an approach to extract the shear induced orientational order from the thermal conductivity of the dispersed CNTs. The index of refraction of the nanocomposites was also estimated via ellipsometry and was found to decrease slightly when CNTs were added and also showed shear induced anisotropy. The comparison between the results from the different experiments methods for probing induced anisotropy by melt shearing shows that orientation in iPP/CNTs nanocomposites induces anisotropy in multiple macroscopic properties.

In this work, a novel star 4-arm poly(ethylene glycol-co-lactide) acrylate macromonomer (SPELA) is synthesized, and the effect of macromonomer concentration and architecture on modulus, swelling ratio and sol fraction is investigated. The results show that the storage modulus of the hydrogel had an increasing trend with polymer concentration. Changing the polymer architecture from linear to 4-arm increased the storage modulus by 2.2-fold. The water content depended on the hydrophilic segment density as well as the extent of crosslinking and showed a decreasing trend with macromonomer concentration. The sol fractions of the SPELA hydrogels changed from 13% to 5% when concentration increased from 10% to 25%. The star SPELA hydrogel with high modulus, fast gelation time, and low sol fraction is potential useful as a degradable carrier in cell-based therapies. Results show that the SPELA hydrogel supports viability and osteogenic differentiation of the encapsulated bone marrow stromal cells.

Here the synthesis of hydroxy-telechelic four-arm star-shaped oligotetrahydrofuran (4PTHF) with controllable molecular weight was explored, which was perfomed as living cationic ring-opening polymerization of THF using pentaerythritol and trifluoromethanesulfonicanhydride as initiation system. The molecular weights of the 4PTHF were a function of the reaction time. A polymer network was prepared from the hydroxy-telechelic 4PTHF precursor by crosslinking with diisocyanate and the shape-memory properties were determined. High values for Rf and Rr > 98% were obtained even at high programmed elongations, which suggest the 4PTHF-network as a promising shape-memory material. These materials might have a great potential, as the upscaling of synthesis could be successfully demonstrated.

It is well known that there is a linear electro-mechanical coupling under equilibrium thermodynamics in certain crystalline materials with non-centrosymmetric structures. Since Kogan and Meyer published their seminal papers in 1960s[1, 2], people have gradually realized that an inhomogeneous electro-mechanical coupling also exists in insulating materials, which is often called flexoelectricity. The physical mechanism of flexoelectricity in solid crystalline dielectrics is well known and its phenomenological model can be derived from the electromechanical energy coupling under equilibrium thermodynamics, whereas flexoelectricity in liquid crystals is closely related to the geometrical asymmetry of mesogen molecules or the shape polarity but the relation between the flexoelectric coefficients and molecular structures is far from being understood. Theoretically, flexoelectricity in polymers is similar to that in liquid crystals, which is largely dependent on rotation of molecules; therefore, the flexoelectric responses of polymers are complicated and might be different under external perturbations, such as tensile stretching, bending, electric field poling, etc. In this report, we will discuss experimental observations of the giant direct flexoelectric effect in certain polyvinylidene fluoride (PVDF) films under tensile stretching conditions. Our experimental studies indicate that the physical mechanism behind flexoelectricity in polymers might be more complicated than the one proposed for solid crystalline dielectrics.

We compare the characteristics of ferrogels prepared with and without the presence of a uniform magnetic field using Fe3O4 and Fe2O3 nanoparticles immobilized in hydrogels of N-isopropylacrylamide. The spatial distribution and agglomeration of the nanoparticles within the ferrogels were investigated using ultra small angle x-ray scattering (USAXS) and transmission electron microscopy (TEM). Hydrated ferrogels were also studied for magnetization using direct current superconducting quantum interference device (DC-SQUID). Volume size distribution resulting from USAXS data of the Fe3O4-ferrogel prepared under a uniform 225 G magnetic field showed a single broad peak appreciably different from that prepared without magnetic field with three distinct peaks. Volume size distributions resulting from USAXS data of the Fe2O3-ferrogel prepared with and without the presence of a uniform magnetic field both similarly show two peaks. Nanoparticle agglomeration was also determined by analyzing TEM images of ferrogel samples. DC-SQUID measurements of Fe3O4-ferrogel prepared in the presence of a uniform magnetic field showed 9% higher magnetization compared to the Fe3O4-ferrogel prepared without magnetic field. Similarly, DC-SQUID measurements of Fe2O3-ferrogel prepared in the presence of a uniform magnetic field showed 3% higher magnetization compared to the Fe2O3-ferrogel prepared without magnetic field. Thus, the presence of a uniform magnetic field during ferrogel polymerization can enabled the enhancement of the magnetoelastic property of the ferrogel.