Morten B. Hansen

Constrained and UV-activatable cell-penetrating peptides for intracellular delivery of liposomes.

Herein we report on the development of a novel method of constraining a cell-penetrating peptide, which can be used to trigger transport of liposomes into cells upon in this case radiation with UV-light. A cell-penetrating peptide, which was modified on both termini with an alkyl chain, was anchored to the liposomal surface in a constrained and deactivated form. Since one of the two alkyl chains was connected to the peptide via a UV-cleavable linker, disconnection of this alkyl chain upon irradiation led to the exposure of the cell-penetrating peptide, and mediated the transport of the entire liposome particle into cells.

Oppositely charged gelatin nanospheres as building blocks for injectable and biodegradable gels

www.MaterialsViews.com C O M M Oppositely Charged Gelatin Nanospheres as Building Blocks for Injectable and Biodegradable Gels U N IC A T Huanan Wang , Morten B. Hansen , Dennis W. P. M. Lowik , Jan C. M. van Hest , Yubao Li , John A. Jansen , and Sander C. G. Leeuwenburgh * IO N The emergence of regenerative medicine has led to a paradigm shift in the design of novel biomaterials, which are now increasingly considered as (bio)active scaffolds that induce tissue regeneration as opposed to the more traditional concept of passively accepted implant materials. [ 1 ] In order to present biological stimuli to the physiological environment and to trigger tissue repair, optimal integration of synthetic biomaterials within the surrounding tissue is of paramount importance. In that respect, hydrogels made from biodegradable polymers are ideal candidates, since they are generally biocompatible, biodegradable, and, in some cases, injectable. [ 2–4 ] In addition, polymeric hydrogels can act as a reservoir for sustained release of therapeutic and signaling agents. [ 4 ] Nevertheless, current gelbased materials exhibit a rather poor ability to present multiple signaling molecules at programmed time-points and release rates. Colloidal gels, on the other hand, have recently been identifi ed as a promising “bottom-up” strategy for the design of highly functional scaffolds by employing microor nanometer-scale particles as building blocks to assemble into shape-specifi c bulk materials. [ 5–13 ] To this end, interparticle interactions such as electrostatic forces, [ 14 ] magnetic forces, [ 14 ] hydrophobic interactions [ 15 ] and steric hindrance [ 16 ] can be exploited to induce selfassembly of microor nanoparticles into integrated scaffolds. By incorporation of bioactive agents (e.g., enzymes, growth factors and/or biomineral nanocrystals) into these particulate building blocks of variable biodegradability, injectable gels with micrometer-scale resolution and complexity can be formed. This new class of materials would offer virtually unlimited degree of freedom with respect to their capacity for programmed drug release of multiple biomolecules at predetermined release rates. Charged polymeric microor nanospheres are the most obvious building blocks for the design of such injectable and

Simple and efficient solid-phase preparation of azido-peptides.

A shelf-stable and easily prepared diazotransfer reagent, imidazole-1-sulfonyl azide hydrochloride, was used to transform the N-terminus of a model peptide on solid phase into an azide moiety. It is demonstrated that this conversion was accomplished within 30 min with high efficiency under aqueous conditions on a NovaPEG resin or in DMF on polystyrene beads.

Enzyme-Activatable Cell-Penetrating Peptides through a Minimal Side Chain Modification

Activatable cell-penetrating peptides are of great interest in drug delivery because of their enhanced selectivity which can be controlled by the external stimuli that trigger their activation. The use of a specific enzymatic reaction to trigger uptake of an inert peptide offers a relevant targeting strategy because the activation process takes place in a short time and only in areas where the specific cell surface enzyme is present. To this aim, the lysine side chain of Tat peptides was modified with an enzyme-cleavable domain of minimal size. This yielded blocked Tat-peptides which were inactive but that could be activated by coincubation with the selected enzymes.

Dynamically functionalized polymersomes via hydrazone exchange

Polymersomes composed of block copolymers of which the blocks are coupled via a hydrazone moiety are shown to exchange surface PEG chains with the environment via an aniline-catalyzed transimination under equilibrium conditions. This methodology is used to functionalize polymersomes with a different inner and outer moiety in a dynamic covalent way. Secondly, the exchange of surface properties is also demonstrated between differently functionalized polymersomes. These results, therefore, open new routes to the design of complex vesicular surfaces by dynamic exchange.

Quick-and-easy preparation and purification of quantum dot–loaded liposomes

Quantum dots are very attractive as fluorescent markers because of their excellent optical properties. For this reason, they have also been used to label liposomes by means of encapsulation, though their feasibility as liposome labels is often hampered by the presence of unencapsulated quantum dots. Until now, laborious gradient ultracentrifugation or less efficient size exclusion chromatography has been the methods of choice to remove unencapsulated quantum dots. Of these two strategies, size exclusion chromatography is most commonly used, despite the known poor separation. Consequently, this prompts for a choice between purification methods yielding high-purity quantum dot–loaded liposomes but low yields or vice versa. Herein, we present a novel high-yield and high-purity methodology to remove unencapsulated quantum dots in a quick and efficient manner based on electrostatic binding of quantum dots to ion-exchange beads. This was accomplished either by means of short column chromatography or via a simple pull-down approach. The purification efficiency was easily assessed via analytical gel electrophoresis, and by copper-mediated quenching of quantum dot fluorescence, it was established that the quantum dots were not adhered to the liposomes but encapsulated inside these. Furthermore, the recovery degree of quantum dot-loaded liposomes after ion-exchange purification was found to be excellent compared with size exclusion chromatography. Lastly, a method is presented to quantify the number of quantum dots encapsulated in the liposomes by the combined efforts of particle counting and inductively coupled plasma mass spectrometry.