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Fabrication of anisotropic hydrogels exhibiting direction-dependent structure and properties has attracted great interest in biomimicking, tissue engineering, and bioseparation. Herein, we report a freeze-casting-based fabrication of structurally and mechanically anisotropic aerogels and hydrogels composed of hydrazone cross-linked poly(oligoethylene glycol methacrylate) (POEGMA) and cellulose nanocrystals (CNCs). We show that, by controlling the composition of the CNC/POEGMA dispersion and the freeze-casting temperature, aerogels with fibrillar, columnar, or lamellar morphologies can be produced. Small-angle X-ray scattering experiments show that the anisotropy of the structure originates from the alignment of the mesostructures, rather than the CNC building blocks. The composite hydrogels show high structural and mechanical integrity and a strong variation in Young's moduli in orthogonal directions. The controllable morphology and hydrogel anisotropy, coupled with hydrazone cross-linking and biocompatibility of CNCs and POEGMA, provide a versatile platform for the preparation of anisotropic hydrogels. [ABSTRACT FROM AUTHOR]

Nanofibrillar supramolecular hydrogels are hierarchical structures formed by physical association of high-aspect-ratio nanoscale building blocks, each containing many molecules held together via supramolecular interactions. Nanofibrils have diameters in the range of tens to hundreds of nanometers, and their lengths can exceed micrometers. The driving forces involved in the formation of nanofibrillar structures include hydrogen bonding, hydrophobic forces, forces of electrostatic origin, and guest–host interactions. Nanofibrillar hydrogels are formed by biopolymers such as proteins and polysaccharides, and by synthetic supramolecular units such as cylindrical micelles of block copolymers and peptide amphiphiles. In the present review, we discuss the hierarchical assembly of nanofibrillar hydrogels, give examples of hydrogels formed by the most important groups of polymers, discuss structure–property relationships of these nanofibrillar hydrogels, and review their current and potential applications in the fields of bioengineering, cell biology, medicine, and cosmetics. [ABSTRACT FROM AUTHOR]

To develop an understanding of thenature of complex, spatiotemporalinteractions between cells and the extracellular matrix (ECM), artificialECMs formed from hydrogels with a particular spectrum of propertiesare being developed at a rapid pace. We report the microfluidic generationof small, monodisperse composite agarose–gelatin hydrogel modules(microgel particles) that can be used for cell encapsulation and canserve as instructive cellular microenvironments. The agarose componentof the microgels gelled under reduced temperature, while gelatin modifiedwith phenolic hydroxyl groups underwent peroxidase-catalyzed gelation.Microgel composition, structure, morphology, and rigidity were tunedin a high-throughput manner. The results of this work are importantfor the generation of libraries of cell-laden polymer microgels forsingle-cell analysis, tissue engineering, and fundamental studiesof the role of local microenvironments in cell fate. [ABSTRACT FROM AUTHOR]

We describe the synthesis of metal chelating polymersbased onpolyaspartamide and polyglutamide backbones as carriers for 111In in radioimmunoconjugates. These polymers [PAsp(DTPA), PGlu(DTPA)]have a biotin end group and diethylenetriaminepentaacetic acid (DTPA)chelators attached to the primary amines of the diethylenetriamine(DET) pendant groups of biotin-poly{N′-[N-(2-aminoethyl)-2-aminoethyl]aspartamide} [PAsp(DET)] andof biotin-poly{N′-[N-(2-aminoethyl)-2-aminoethyl]glutamide}[PGlu(DET)]. Like Asn-containing proteins and polypeptides, polyaspartamidesundergo uncatalyzed degradation under model physiological conditions(10 mM phosphate buffer, pH 7.4, 150 mM NaCl). We studied the uncatalyzeddegradation of the polyaspartamide polymers by size exclusion chromatographyand found that the degradation rate was sensitive to the nature ofthe pendant groups. The metal-free polymer underwent somewhat slowerdegradation than the corresponding polymers in which the DTPA groupswere saturated with Eu3+or In3+, but even after14 days, substantial fractions of the polymers survived. We concludethat these polymers undergo negligible degradation on the time scale(24–48 h) of radioimmunotherapy treatment of tumors with 111In. From a mechanistic perspective, we note that these degradationrates are on the order of the deamidation rates reported [J. Peptide Res. 2004, 63,426] for Asn-containing pentapeptides, with half-times on the orderof 10 days, but much slower than the rapid decay (hours) reportedrecently [Biomaterials2010, 31, 3707] for poly{N′-[N-(2-aminoethyl)-2-aminoethyl]aspartamide} itself. This variationin degradation rate can be explained in terms of the influence ofpositive charges on the pendant group enhancing the acidity of theside-chain amide nitrogen of the aspartamide repeat unit. The DETpendant group is positively charged at pH 7, but in indium-loadedPAsp(DTPA) this charge is offset by the net negative charge of theDTPA-In complex. [ABSTRACT FROM AUTHOR]