The noncovalent assembly of polymeric materials via specific molecular recognition interactions has become increasingly prominent in the production of responsive, reversible, and injectable hydrogels. While protein-protein interactions predominantly have been used for such assembly, 1-4 the use of extracellular matrix (ECM)-derived polysaccharide-peptide interactions has been recently emerging as an assembly approach. 5-9 The interactions of proteins and glycosaminoglycans are critical in mediating the multiple responses of the ECM, and materials in which assembly and mechanical properties are controlled by such molecular recognition events may be useful for biologically directed targeted delivery. Accordingly, the ability of heparin and related glycosaminoglycans to sequester and stabilize growth factors has been exploited in the production of surfaces and covalently crosslinked hydrogels that can mediate cell proliferation and migration, angiogenesis, and wound healing. 10-14 In particular, the controlled delivery of VEGF (vascular endothelial growth factor) and select other growth factors from polymeric matrices has shown potential for use in vascular therapies. 12,15,16 Noncovalently assembled matrices also have similar potential use in this regard. 5-9Here, we report the assembly, rheological properties, and targeted delivery/erosion profiles of noncovalently associated hydrogel networks produced via the interaction of a low-molecularweight heparin-modified star polymer (PEG-LMWH) and a dimeric, heparin-binding growth factor (VEGF). 17 Given that overexpression of VEGF and other growth factor receptors plays a key role in both normal healing and pathological conditions, 18-20 we reasoned that hydrogels assembled via such strategies may provide unique opportunities for stimuli-responsive delivery and erosion via biologically relevant, ligand-exchange mechanisms. A schematic of the assembly and erosion strategy is illustrated in Figure 1. We have focused on LMWH in these investigations in order to maximize intermolecular dimeric growth factor/LMWH binding over intramolecular binding (see Supporting Information). The PEGLMWH employed in these investigations was produced via Michael addition of thiol-terminated four-arm star PEG to maleimidefunctionalized LMWH. 7 NMR characterization of the purified product indicated at least 75% functionalization of PEG-LMWH, indicating that it is of sufficiently high functionality (f > 2) to permit formation of crosslinked networks upon interaction with VEGF (f = 2). The VEGF was expressed from E. coli and purified via heparin-affinity chromatography as previously described (Supporting Information). 16Correspondence to: Kristi L. Kiick. Hydrogels were formed via the mixing of homogeneous, lowviscosity solutions of each component in phosphate buffered saline (PBS). The PEG-LMWH solution was vortexed to ensure homogeneity. Addition of a solution of VEGF (5 μL, 2 mg/mL) to a solution of PEG-LMWH (5 μL, 80 mg/mL) immediately resulted in the formation of a self-supporting, viscoel...

The gelation kinetics of self-assembled hydrogels consisting of the β-hairpin peptide MAX1 are investigated using microrheology and far-UV circular dichroism (CD) spectroscopy. The intramolecular folding of this peptide is engineered to control its self-assembly into β-sheet-rich hydrogels. When the peptide is unfolded, it does not self-assemble, and aqueous solutions have the viscosity of water. Folding and consequent self-assembly are triggered by changes in pH, temperature, or ionic strength. This folding and self-assembly mechanism allows temporal control of the material formation. CD spectroscopy shows that the kinetics of β-sheet structure formation occurs in a concentration-dependent manner but does not provide information on the kinetics of network assembly. Here, multiple particle tracking is used to define exact gelation times as a function of peptide concentration. This allows an empirical relationship to be established between the rheologically defined gelation time and the onset of β-sheet formation as measured by CD. Values of the mean-residue ellipticity at 216 nm between −10 × 103 and −12 × 103 deg dmol-1 cm2 coincide with the formation of a percolating gel. Critically, this empirical relationship allows one to identify the gel time solely from spectroscopic measurements, greatly facilitating the establishment of peptide sequence material−function relationships.

This article reports on the results obtained in an investigation on the application of biodegradable polymeric materials in the agricultural practice of mulching. Particular attention has been devoted to the effect of biobased mulching films generated in situ by low-pressure spraying of polymeric water dispersions on the various cultivars. In a field trial, the effectiveness of the hydromulching (liquid-mulching) technique was assessed by the monitoring of the growth and yield of lettuce and corn, which were used as reference plants. Conventional plastic films and straw mulching (SM) were compared with liquid-mulching treatments based on poly(vinyl alcohol) and natural fillers derived from agroindustrial wastes (sugar cane bagasse, wheat flour, saw dust, and wheat straw). An improvement of the biomass yield of the two selected plants with respect to conventional polyethylene mulching was attained in various liquid-mulching formulations with positive effects on the maintenance of soil structure. Alternative fluid-mulching treatments based on biodegradable components were effective in preserving soil aggregates and improving some crop growth parameters.

No abstract