Stefan Zschoche

A star-PEG-heparin hydrogel platform to aid cell replacement therapies for neurodegenerative diseases

Biofunctional matrices for in vivo tissue engineering strategies must be modifiable in both biomolecular composition and mechanical characteristics. To address this challenge, we present a modular system of biohybrid hydrogels based on covalently cross-linked heparin and star-shaped poly(ethylene glycols) (star-PEG) in which network characteristics can be gradually varied while heparin contents remain constant. Mesh size, swelling and elastic moduli were shown to correlate well with the degree of gel component cross-linking. Additionally, secondary conversion of heparin within the biohybrid gels allowed the covalent attachment of cell adhesion mediating RGD peptides and the non-covalent binding of soluble mitogens such as FGF-2. We applied the biohybrid gels to demonstrate the impact of mechanical and biomolecular cues on primary nerve cells and neural stem cells. The results demonstrate the cell type-specific interplay of synergistic signaling events and the potential of biohybrid materials to selectively stimulate cell fate decisions. These findings suggest important future uses for this material in cell replacement based-therapies for neurodegenerative diseases.

Macroporous starPEG-heparin cryogels.

Macroporous scaffolds with adaptable mechanical and biomolecular properties can be instrumental in enabling cell-based therapies. To meet these requirements, a cryostructuration method was adapted to prepare spongy hydrogels based on chemically cross-linked star-shaped poly(ethylene glycol) (starPEG) and heparin. Subzero temperature treatment of the gel forming reaction mixtures and subsequent lyophilization of the incompletely frozen gels resulted in macroporous biohybrid cryogels showing rapid swelling, porosity of up to 92% with interconnected large pores (30-180 μm), low bulk stiffness, and high mechanical stability upon compression. The applicability of the cryogel scaffolds was investigated using human umbilical vein endothelial cells. Cell attachment and three-dimensional spreading resulted in evenly distributed viable cells within the macroporous starPEG-heparin materials, demonstrating the significant translational potential of the developed three-dimensional cell carriers.

pH-triggered aggregate shape of different generations lysine-dendronized maleimide copolymers with maltose shell.

Glycopolymers are promising materials in the field of biomedical applications and in the fabrication of supramolecular structures with specific functions. For tunable design of supramolecular structures, glycopolymer architectures with specific properties (e.g., controlled self-assembly) are needed. Using the concept of dendronized polymers, a series of H-bond active giant glycomacromolecules with maleimide backbone and lysine dendrons of different generations were synthesized. They possess different macromolecular size and functionality along the backbone. Their peripheral maltose units lead to solubility under physiological conditions and controlled aggregation behavior. The aggregation behavior was investigated depending on generation number, pH value, and concentration. A portfolio of complementary analytical tools give an insight into the influence of the different parameters in shaping a rod-, coil-, and worm-like molecular structure and their controlled aggregate formation. MD simulation helped us to understand the complex aggregation behavior of the linear polymer chain without dendritic units.

Functionalization of Poly(dimethylsiloxane) Surfaces with Maleic Anhydride Copolymer Films

Combining advantageous bulk properties of polymeric materials with surface-selective chemical conversions is required in numerous advanced technologies. For that aim, we investigate strategies to graft maleic anhydride (MA) copolymer films onto poly(dimethylsiloxane) (PDMS) precoatings. Amino groups allowing the covalent attachment of the MA copolymer films to the PDMS (Sylgard 184) surface were introduced either by low-pressure ammonia plasma treatment, or by attachment of 3-aminopropyltriethoxysilane (APTES) onto air plasma-treated PDMS. The resultant coatings were extensively characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), contact angle measurements, and atomic force microscopy (AFM). The results show that the impact of the plasma treatment on the physical properties on the topmost surface of the PDMS is critically important for the characteristics of the layered coatings.

Surface Modification of Cell Culture Carriers: Routes to Anhydride Functionalization of Polystyrene

Physico-chemical and topographical cues allow to control the behavior of adherent cells. Towards this goal, commercially available cell culture carriers can be finished with a laterally microstructured biomolecular functionalization. As shown in a previous study [Biomacromolecules 4 (2003) 1072], the anhydride moiety facilitates a simple and versatile way to protein binding. The present work addresses the technical issue of anhydride surface functionalization of polystyrene, the most common material for cell culture ware. Different approaches based on low pressure plasma, electron beam and ultraviolet light techniques (i.e. maleic anhydride plasma reactions; plasma, electron beam and UV immobilization of functional polymer thin films; grafting of functional polymers to plasma activated surfaces) are introduced and briefly illustrated with examples. Results are characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and ellipsometry. The different routes are compared in terms of technical feasibility and achievable surface properties.

Low-rate dynamic contact angles on poly[styrene-alt-(hexyl/10-carboxydecyl(90/10)maleimide)] and the determination of solid surface tensions

Low-rate dynamic contact angles of 14 liquids on a poly[styrene-alt-(hexyl/10-carboxydecyl(90/10)maleimide)] P[S-(H/CM)] were measured by means of an automated axisymmetric drop shape analysis-profile (ADSA-P). It was found that 9 liquids yield non-constant contact angles, and/or dissolve the polymer. From the experimental contact angles of the remaining 5 liquids, it was found that the product of the liquid-vapour surface tension and the cosine of the contact angle changes smoothly with the liquid-vapour surface tension, i.e. γ lv cosθ depends only on γ lv for a given solid surface (or solid surface tension). This contact angle pattern is in harmony with those from other inert and non-inert (polar and non-polar) surfaces. The solid-vapour surface tension calculated from the equation-of-state approach for solid-liquid interfacial tensions was found to be 31.0 mJ/m 2 , with a 95% confidence limit of ±0.6 mJ/m 2 from the experimental contact angles of the 5 liquids in Laboratory 1, and γ sv = 29.9 mJ/m 2 from measurements with two liquids in Laboratory 2. The difference is essentially due to actual physical differences between the polymer films prepared in the two laboratories.

pH-stable hyperbranched poly(ethyleneimine)-maltose films for the interaction with phosphate containing drugs

Maltose-decorated hyperbranched poly(ethyleneimine) is a promising candidate as drug carrier attributed by electrostatic interactions. Here, we report the fabrication of stable hyperbranched poly(ethyleneimine)-maltose (PEI-Mal) films capable of swelling and their features to load and release phosphate containing drugs as being observed by ellipsometric study.

Synthesis and characterization of new bi-sensitive copoly(2-oxazolines)

We synthesized new bi-sensitive statistical copolymers and A-B-A triblock copolymers from 2-cyclopropyl-2-oxazoline (CPOxa) and 2-methoxycarbonylethyl-2-oxazoline (MEtOxa) using 1,4-dibromobutene as a bi-functional initiating moiety. These new bi-sensitive polymers were obtained via quasi-living polymerization of the oxazoline monomers and subsequent hydrolysis of the methyl ester of MEtOxa. Their thermal conformational transitions in aqueous solution were between 30 and 60 °C and these values were dependent of the copolymer composition, polymer structure (statistical or block copolymer), and of the pH of the solution, where the polymers were dissolved. The achieved polymers could find application in biomaterial science, in microsystems and sensors, and as smart nanocarriers.

Synthesis and characterization of new pH- and thermo-responsive hydrogels based on N-isopropylacrylamide and 2-oxazolines

New pH- and thermo-responsive hydrogels (HG) were synthesized by free radical polymerization of N-isopropylacrylamide and a macromonomer, which was a hydrolyzed random copolymer of 2-carboxyethyl- and 2-methyl-2-oxazoline, using a bisacrylamide as crosslinker. The polymerization was carried out in a mixture of water and ethanol at room temperature and was initiated by ammonium peroxodisulfate. The HG showed conformational transitions with variation of temperature and/or pH-value and as a function of hydrogel composition. This property was shown macroscopically as hydrogel contraction or expansion. The HG structures were characterized by high-resolution magic angle spinning (HRMAS) NMR spectroscopy. The thermal properties, in particular the lower critical solution temperatures, were determined by temperature-dependent HRMAS NMR measurements and differential scanning calorimetry. The pH responsibility was determined by swelling experiments in water at different pH values.

The influence of cations on the dissociation behaviour of copolymers of propene and maleic acid and their modified products with taurine in salt-free solution

Potentiometric and conductometric titrations were used to study the dissociation behaviour of poly(propene-co-maleic acid) and poly(propene-co-maleic acid) modified with various contents of taurine (2-aminoethanesulfonic acid) in salt-free solution. Copolymers of propene and maleic acid with different molecular weights were titrated with LiOH, NaOH, and KOH. The influence of molecular weight on pKa is ascertainable in both the first and second dissociation step. Of the various alkali metal cations studied, lithium had the most significant effect on the dissociation behaviour. The acidic strength decreased in the order lithium > sodium ≥ potassium. After insertion of sulfonic acid groups into poly(propene-co-maleic acid), the influence of strong acidic groups on the dissociation behaviour of carboxylic groups was studied. The contents of taurine were 10, 25, and 50 mol%. The second dissociation step was analyzed in this case. The pKa values increased with increasing content of taurine for titrations with LiOH and KOH, but not NaOH. When NaOH was used, the pKa decreases if the polymer was modified with 10% taurine. Higher taurine contents had no influence on the magnitude of pKa. The results demonstrate the strong influence of short-range electrostatic interactions on the dissociation behaviour of weak polyacids.