Gold nanoparticles decorated with oligo(ethylene glycol) thiols:enhanced Hofmeister effects in colloid−protein mixtures

Oligo(ethylene glycol) (OEG) thiol self-assembled monolayer (SAM) decorated gold nanoparticles (AuNPs) have potential applications in bionanotechnology due to their unique property of preventing the nonspecific absorption of protein on the colloidal surface. For colloid-protein mixtures, a previous study (Zhang et al. J. Phys. Chem. A 2007, 111, 12229) has shown that the OEG SAM-coated AuNPs become unstable upon addition of proteins (BSA) above a critical concentration, c*. This has been explained as a depletion effect in the two-component system. Adding salt (NaCl) can reduce the value of c*; that is, reduce the stability of the mixture. In the present work, we study the influence of the nature of the added salt on the stability of this two-component colloid-protein system. It is shown that the addition of various salts does not change the stability of either protein or colloid in solution in the experimental conditions of this work, except that sodium sulfate can destabilize the colloidal solutions. In the binary mixtures, however, the stability of colloid-protein mixtures shows significant dependence on the nature of the salt: chaotropic salts (NaSCN, NaClO4, NaNO3, MgCl2) stabilize the system with increasing salt concentration, while kosmotropic salts (NaCl, Na2SO4, NH4Cl) lead to the aggregation of colloids with increasing salt concentration. These observations indicate that the Hofmeister effect can be enhanced in two-component systems; that is, the modification of the colloidal interface by ions changes significantly the effective depletive interaction via proteins. Real time SAXS measurements confirm in all cases that the aggregates are in an amorphous state.

Design and application of nanoscale actuators using block-copolymers

Block copolymers are versatile designer macromolecules where a “bottom-up” approach can be used to create tailored materials with unique properties. These simple building blocks allow us to create actuators that convert energy from a variety of sources (such as chemical, electrical and heat) into mechanical energy. In this review we will discuss the advantages and potential pitfalls of using block copolymers to create actuators, putting emphasis on the ways in which these materials can be synthesised and processed. Particular attention will be given to the theoretical background of microphase separation and how the phase diagram can be used during the design process of actuators. Different types of actuation will be discussed throughout.

Degradable poly(ethylene glycol)-based hydrogels:synthesis, physico-chemical properties and in vitro characterization

Designing degradable hydrogels is complicated by the structural and temporal complexities of the gel and evolving tissue. A major challenge is to create scaffolds with sufficient mechanical properties to restore initial function while simultaneously controlling temporal changes in the gel structure to facilitate tissue formation. Poly(ethylene glycol) was used in this work, to form biodegradable poly(ethylene glycol)-based hydrogels with hydrolyzable poly-l-lactide segments in the backbone. Non-degradable poly(ethylene glycol) was also introduced in the formulation to obtain control of the degradation profile that encompasses cell growth and new tissue formation. The dependence on polymer composition was observed by higher degradation profiles and decreased mechanical properties as the content of degradable segments was increased in the formulation. Based on in vitro tests, no toxicity of extracts or biomaterial in direct contact with human adipose tissue stem cells was observed, and the ultraviolet light treatment did not affect the proliferation capacity of the cells.

Poly(3-hexylthiophene) based block copolymers prepared by "click" chemistry

p-Conjugated block copolymers have been prepared from terminal azide functionalized polystyrenes (PS) and alkyne functionalized poly(3- hexylthiophene)s (P3HT) via a copper(I) catalyzed Huisgen [3 + 2] dipolar cycloaddition reaction. The functionalized a-azido-PS homopolymer was prepared by atom transfer radical polymerization from a specifically designed initiator bearing the azide function, whereas ?-ethynyl-P3HT and a,?-pentynyl-P3HT were synthesized by a modified Grignard metathesis polymerization using alkynyl Grignard derivatives. The electronic environment of the alkynyl end groups was shown to be decisive in determining triazole ring formation.

Soft hydrogels from nanotubes of poly(ethylene oxide)−tetraphenylalanine conjugates prepared by click chemistry

A new poly(ethylene oxide)-tetraphenylalanine polymer-peptide conjugate has been prepared via a “click” reaction between an alkyne-modified peptide and an azide-terminated PEO oligomer. Self-assembled nanotubes are formed after dialysis of a THF solution of this polymer-peptide conjugate against water. The structure of these nanotubes has been probed by circular dichroism, IR, TEM, and SAXS. From these data, it is apparent that self-assembly involves the formation of antiparallel ß-sheets and p-p-stacking. Nanotubes are formed at concentrations between 2 and 10 mg mL-1. Entanglement between adjacent nanotubes occurs at higher concentrations, resulting in the formation of soft hydrogels. Gel strength increases at higher polymer-peptide conjugate concentration, as expected.

The effect of PEO length on the self-assembly of poly(ethylene oxide)−tetrapeptide conjugates prepared by “click” chemistry

Two series of poly(ethylene oxide)-tetrapeptide conjugates have been prepared using a “Click” reaction between an alkyne-modified tetra(phenylalanine) or tetra(valine) and various azide-terminated poly(ethylene oxide) (PEO) oligomers. Three different PEO precursors were used to prepare these conjugates, with number-average molecular weights of 350, 1200, and 1800 Da. Assembly of mPEO-F4-OEt and mPEO-V4-OEt conjugates was achieved by dialysis of a THF solution of the conjugate against water or by direct aqueous rehydration of a thin film. The PEO length has a profound effect on the outcome of the self-assembly, with the F4 conjugates giving rise to nanotubes, fibers, and wormlike micelles, respectively, as the length of the PEO block is increased. For the V4 series, the propensity to form ß-sheets dominates, and hence, the self-assembled structures are reminiscent of those formed by peptides alone, even at the longer PEO lengths. Thus, this systematic study demonstrates that the self-assembly of PEO-peptides depends on both the nature of the peptides and the relative PEO block length.