In this paper, a facile and novel method was developed to fabricate high toughness and stiffness double network hydrogels made of ionical-linked natural hydrogel and synthetic hydrogel. The synthetic hydrogel network is formed firstly, and then the gel is soaked in the ionic solution to build second network to form double network hydrogel with high toughness and stiffness. Two different natural polymers, alginate and chitosan, are employed to build rigid and brittle network and poly(acrylamide) is used as soft network in double network hydrogel. The compressive strength of Calcium alginate/poly(acrylamide) double network hydrogels is increased twice than that of poly(acrylamide) single network hydrogels, and the Ca2+ ionically cross-linked alginate is the key to improve the compressive property of double network hydrogels as a sacrificial bond. However, the chitosan/poly(acrylamide) double network hydrogels exhibit no enhancement of compressive strength comparing to poly(acrylamide) single network hydrogels.

Poly(N-isopropylacrylamide) (PNIPAM) has been used extensively for numerous biomedical applications. However, there is not enough information in the literature on the wettability and hygroscopic properties of electrospun PNIPAM fibers, relevant for water harvesting applications. This study focuses on investigating the wettability and hygroscopic properties of electrospun PNIPAM fibers at room temperature and elevated temperature. The wettability properties of electrospun PNIPAM fibers were compared to spin-coated PNIPAM thin films. The wettability properties of the electrospun fibers were enhanced by 56% compared to spin-coated films. Water contact angle (WCA) measured on electrospun fibers was determined to be 137° at elevated temperatures while WCA on spin cast PNIPAM film was determined to be 81° at elevated temperatures. Furthermore, hygroscopic properties of the electrospun PNIPAM fibers were studied using thermogravimetric analysis (TGA). The PNIPAM fibers are seen to exhibit moisture absorption capacity of about 16.6 wt. % under humid conditions.

Decorin is a small leucine-rich repeat proteoglycan supporting collagen fibril formation by controlling the rate of collagen fibrillogenesis and fibril dimensions. Peptides derived from the inner surface of decorin have been shown to bind to collagen, while peptides derived from the outer surface do not display such binding affinity. As typical secondary structural elements such as β-sheets and α-helical regions were found in the decorin X-ray crystal structure, here it was investigated by Circular Dichroism (CD) spectroscopy in solution, whether the same structural elements can be found in the derived peptides. Here it is shown that the peptide derived from decorin’s outer surface has the propensity to adopt helical conformation, as it was found in the crystal structure. The results were more pronounced in 80 vol% TFE solution, which led to an increase in the number as well as the length of helices. In contrast, peptides derived from the inner surface had a higher tendency to adopt β-sheet conformation, also in TFE, which corresponds to the conformation of the original sequence in the crystal structure of decorin. This suggests that the peptides derived from decorin adopt the structures present in the native protein.

For biological and mechanical systems involving moving parts, surface slipperiness is often a critical attribute for their optimal functions. Surface grafting with hydrophilic polymers is a powerful means to render materials slippery in aqueous environment. In “inverted grafting-to approach”, the hydrophilic polymer chains of amphiphilic diblock copolymers dispersed within a poly(dimethylsiloxane) (PDMS) network are selectively segregated upon exposure to aqueous solution. This allows formation of extremely stable brush-like polymer layers. Tribological application of inverted grafting-to approach was successfully demonstrated with PDMS-block-poly(acrylic acid) (PDMS-b-PAA) dispersed within thin PDMS films on PDMS blocks by showing friction coefficients (µ) of ca 10-2 to 10-3, depending on the load, pH and buffer salinity in the absence of other external re-supply of PAA chains. Further manipulations of the thin PDMS film incorporating PDMS-b-PAA to optimize the tribological properties are presented. Lastly, first trials to employ PAA-grafted PDMS surface to generate in-vitro mucosae model are also presented and discussed.

A water-developable sugar-based negative resist material was developed. This material enables the use of pure water in the development process of electron beam (EB) green lithography instead of conventionally used aqueous alkaline developers and organic solvents. The sugar-based negative resist material was developed by replacing the hydroxyl groups in alpha-linked disaccharides with EB-sensitive 2-methacryloyloxyethyl groups. The sugar-based negative resist material features highly efficient crosslinking and low film thickness shrinkage under EB irradiation. It is demonstrated to be applicable to green lithography with a 100– 500 nm line-and-space pattern and an EB exposure dose of 18 μC/cm2.

Microstructured polymeric surfaces capable of a thermally-induced shape-memory effect (SME) can perform on demand changes of surface properties such as wettability or adhesion.

In this study, we explored the influence of the applied compression direction during programming, i.e. vertical compression and tilted compression, on the SME of microstructured crosslinked poly[ethylene-co-(vinyl acetate)] (cPEVA) films comprising arrays of micro-cylinders with a height of 10 µm and different diameters of 10 µm, 25 µm, and 50 µm. The shape recovery of the microstructures during heating was visualized online by optical microscopy, while atomic force microscopy (AFM) was utilized to investigate the temperature-induced shape change of single micro-cylinders. Here, the changes in micro-cylinder height and the characteristic angle θ were followed and analyzed for quantification of the shape-memory performance. Both compression modes resulted in almost flat programmed surfaces as indicated by high shape fixity ratios of Rf ≥ 93±1%. A nearly complete recovery of the micro-cylinders was obtained for all investigated cPEVA samples documented by high shape recovery values of Rr ≥ 97±1%, while the obtained shape change of the micro-cylinders during recovery almost reversely recalled the applied deformation during programming. The presented capability of SMP microstructured substrates to memorize the way of deformation during programming could be a new tool for controlling particular shape changes of microstructures during recovery and in such a way the generated local recovery forces can be adjusted.

Preparation of three-dimensionally architectured porous biomaterials can be achieved in a one-step process by stabilizing gelatin with L-lysine diisocyanate ethyl ester (LDI) in water. The reaction of gelatin with LDI in presence of water leads to the formation of oligourea bridges between gelatin molecules and oligourea chains grafted on gelatin. The number and the length of the bridges, as well as of the grafted chains strongly depend on the concentration of the LDI used for the stabilization, and this has huge influence on the mechanical properties of the material on different hierarchical levels. Higher LDI concentrations yield materials with increased deformation resistance in tensile tests due to the higher number of covalent and physical netpoints in the material. However, mechanical properties determined on the micro-level by AFM indentation showed the opposite trend, i.e. a decrease of Young’s modulus with increasing LDI content. This was interpreted by a decreasing number of shorter oligourea bridges between gelatin chains with decreasing LDI content.

Depsipeptide-based multiblock copolymers synthesized from dihydroxy telechelic oligodepsipeptide precursors are promising candidate materials for biomedical and pharmaceutical applications. High molecular weight polymers in polyaddition reactions e.g. of diols with diisocyanates can only be reached when reactive groups are equivalent and a high conversion for this step growth polymerization is obtained. However, in depsipeptide-based multiblock urethanes reported so far, the stoichiometric ratio of the diisocyanate compound exceeded the theoretical value of 100% by far. In order to investigate the influence of the dosing system in this unusual behavior of the stoichiometric reaction two dosing devices, a solid dosing unit (SDU) and a gravimetric dosing unit (GDU) were used for a gravimetric transfer of an oligo(3-sec-butylmorpholine-2.5-dione) (OBMD) as model oligodepsipeptide. The OBMD precursor, which was transferred as a solid or as a highly viscous solution, was reacted with an isomeric mixture of 2,2,4- and 2,4,4-trimethylhexamethylene diisocyanate (TMDI) as chain extender. Two series of 49 reactions were performed and the chain extension efficacy of the building block was compared between the SDU and GDU as well as with respect to the Carothers equation. When the GDU was used the chain extension yielded higher molecular weights, proving the high accuracy of the dosing device, and the molar ratio of TMDI required for the high-throughput synthesis of the depsipeptide-based multiblock copolymers was similar to depsipeptide-based multiblock copolymers created in a classical synthesis approach.

Shape-memory hydrogels (SMHs) are potential candidate materials for biomedical applications as they can mimic the elastic properties of soft tissue and exhibit shape transformations at body temperature. Here we explored, whether architectured SMHs can be designed by incorporating oligo(ε-caprolactone) (OCL, ${\overline M _n}$ = 4500 g·mol-1, Tm = 54 °C) side chains as switching segment into hydrophilic polymer networks based on N-vinylpyrrolidone as backbone forming component and oligo(ethylene glycol)divinylether (OEGDVE, ${\overline M _n}$ = 250 g·mol-1) as crosslinker. By utilizing NaCl and NaHCO3 as porogene during thermal crosslinking architectured hydrogels having pore diameters between 30 and 500 µm and wall thicknesses ranging from 10 to 190 µm in the swollen state were synthesized. According to the porous microstructure, a macroscopic form stability was obtained when the polymer networks were swollen until equilibrium in water. Material properties were investigated as function of the OCL content, which was varied between 20 and 40 wt%. In compression experiments the architectured hydrogels exhibited strain fixity and strain recovery ratios above 80%. These architectured SMHs might enable biomaterial applications as smart implants with the recovery of bulky structures from compact shapes.

The microfluidic production of droplets is a well controllable process, which allows templating small spherical containers that can subsequently be transferred into uniformly sized polymer microgel particles by a crosslinking reaction. Recently, the per-channel production rate of N-isopropylacrylamide (NIPAAm) droplets (w-phase) dispersed in a low-viscosity fluorocarbon oil (o-phase) could be increased by a delayed surfactant addition, while maintaining the advantageous dripping regime. Here it should be evaluated, if delayed surfactant addition can be applied to enhance droplet production also for high viscosity continuous phases, which is associated with a change to an inviscid drop scenario compared to the previously used setting of viscous drops. It could be illustrated that the concept of delayed surfactant addition holds true also for viscous continuous phases and allows ∼8 fold increased flow rates in the dripping regime. Surprisingly, the droplet size increased at higher total flow rate with constant flow rate ratios of w- and o-phases, which is discussed in the light of viscous dissipation, microchannel bulging and viscosity of the continuous phase. More rigid microchannels such as from glass may allow further exploring this phenomenon in the future.