5 research outputs found
Enzyme‐induced ferrification of hydrogels for toughening of functional inorganic compounds
Enzyme-induced mineralization (EIM) has been shown to greatly enhance the mechanical properties of hydrogels by precipitation of calcium salts. Another feature of such hydrogels is their high toughness even when containing finely nanostructured mineral content of ≈75 wt%. This might be useful for bendable materials with high content of functional inorganic nanostructures. The present study demonstrates that EIM can form homogeneous nanostructures of water-insoluble iron salts within hydrogels. Crystalline iron(II) carbonate precipitates urease-induced within polyacrylate-based hydrogels and forms platelet structures that have the potential of forming self-organized nacre-like architectures. The platelet structure can be influenced by chemical composition of the hydrogel. Further, amorphous iron(II) phosphate precipitates within hydrogels with alkaline phosphatase, forming a nanostructured porous inorganic phase, homogeneously distributed within the double network hydrogel. The high amount of iron phosphate (more than 80 wt%) affords a stiffness of ≈100 MPa. The composite is still bendable with considerable toughness of 400 J m−2 and strength of 1 MPa. The high water content (>50%) may allow fast diffusion processes within the material. This makes the iron phosphate-based composite an interesting candidate for flexible electrodes and demonstrates that EIM can be used to deliberately soften ceramic materials, rendering them bendable
Ionically Cross-Linked Shape Memory Polypropylene
An ionically cross-linked
syndiotactic polypropylene (ix-sPP) was
synthesized by subsequent grafting of maleic anhydride (MA) to the
polymer followed by compounding with ZnO. The polymer network was
investigated by X-ray scattering, transmission electron microscopy,
and various thermal and mechanical analyses. The optimized polymer
network with 1 wt % MA grafting and 20 wt % ZnO exhibits a crystal
melting temperature of 125 °C and rubber elastic behavior up
to 203 °C and becomes a viscous polymer melt at higher temperatures.
This process is fully reversible. Further, ix-sPP is an exceptionally
stable ionic polymer network that matches the stability of the respective
covalently cross-linked polymer in terms of shape memory properties.
Additionally, the ionic cross-linking affords thermoplastic processability
and shape memory assisted self-healing
Cross-Linking of a Hydrophilic, Antimicrobial Polycation toward a Fast-Swelling, Antimicrobial Superabsorber and Interpenetrating Hydrogel Networks with Long Lasting Antimicrobial Properties
A hemocompatible,
antimicrobial 3,4en-ionene (PBI) derived by polyaddition of <i>trans</i>-1,4-dibromo-2-butene and <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethyl-1,3-propanediamine
was cross-linked via its bromine end groups using tris(2-aminoethyl)amine
(TREN) to form a fast-swelling, antimicrobial superabsorber. This
superabsorber is taking up the 30-fold of its weight in 60 s and the
granulated material is taking up 96-fold of its weight forming a hydrogel.
It fully prevents growth of the bacterium <i>Staphylococcus aureus</i>. The PBI network was swollen with 2-hydroxyethyl acrylate and glycerol
dimethacrylate followed by photopolymerization to form an interpenetrating
hydrogel (IPH) with varying PBI content in the range of 2.0 to 7.8
wt %. The nanophasic structure of the IPH was confirmed by atomic
force microscopy and transmission electron microscopy. The bacterial
cells of the nosocomial strains <i>Staphylococcus aureus</i>, <i>Escherichia coli</i>, and <i>Pseudomonas aeruginosa</i> are killed on the IPH even at the lowest PBI concentration. The
antimicrobial activity was retained after washing the hydrogels for
up to 4 weeks. The IPHs show minor leaching of PBI far below its antimicrobial
active concentration using a new quantitative test for PBI detection
in solution. This leaching was shown to be insufficient to form an
inhibition zone and killing bacterial cells in the surroundings of
the IPH