Formation of lipid vesicles in situ utilizing the thiol-Michael reaction.

Synthetic unilamellar liposomes, functionalized to enable novel characteristics and behavior, are of great utility to fields such as drug delivery and artificial cell membranes. However, the generation of these liposomes is frequently highly labor-intensive and time consuming whereas in situ liposome formation presents a potential solution to this problem. A novel method for in situ lipid formation is developed here through the covalent addition of a thiol-functionalized lysolipid to an acrylate-functionalized tail via the thiol-Michael addition reaction with potential for inclusion of additional functionality via the tail. Dilute, stoichiometric mixtures of a thiol lysolipid and an acrylate tail reacted in an aqueous media at ambient conditions for 48 hours reached nearly 90% conversion, forming the desired thioether-containing phospholipid product. These lipids assemble into a high density of liposomes with sizes ranging from 20 nm to several microns in diameter and include various structures ranging from spheres to tubular vesicles with structure and lamellarity dependent upon the catalyst concentration used. To demonstrate lipid functionalization, an acrylate tail possessing a terminal alkyne was coupled into the lipid structure. These functionalized liposomes enable photo-induced polymerization of the terminal alkyne upon irradiation.

Production of dynamic lipid bilayers using the reversible thiol-thioester exchange reaction.

Thiol lysolipids undergo thiol-thioester exchange with two phenyl thioester-functionalized tails to produce phospholipid structures that assemble into liposomes with differences in exchange rates, temperature sensitivity, permeability, and continued exchange behavior. This in situ formation reaction imparts dynamic characteristics into the membrane for downstream liposome functionalization and mimics native membrane remodeling.

Contact Line Pinning Is Not Required for Nanobubble Stability on Copolymer Brushes.

Whereas nanobubble stability on solid surfaces is thought to be based on local surface structure, in this work, we show that nanobubble stability on polymer brushes does not appear to require contact-line pinning. Glass surfaces were functionalized with copolymer brushes containing mixtures of hydrophobic and hydrophilic segments, exhibiting water contact angles ranging from 10 to 75°. On unmodified glass, dissolution and redeposition of nanobubbles resulted in reformation in mostly the same locations, consistent with the contact line pinning hypothesis. However, on polymer brushes, the nucleation sites were random, and nanobubbles formed in new locations upon redeposition. Moreover, the presence of stable nanobubbles was correlated with global surface wettability, as opposed to local structure, when the surface exceeded a critical water contact angle of 50 or 60° for polymers containing carboxyl or sulfobetaine groups, respectively, as hydrophilic side chains. The critical contact angles were insensitive to the identity of the hydrophobic segments.

Liposomes formed from photo-cleavable phospholipids: in situ formation and photo-induced enhancement in permeability.

Photocleavable liposomes were formed in situ through the coupling of an o-nitrobenzyl-containing azide tail precursor and an alkyne-functionalized lysolipid by the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. Inclusion of the photolabile o-nitrobenzyl-structure enables control over the permeability and morphology of the liposomes. Photolysis of the o-nitrobenzyl group changes the molecular structure of the photolabile phospholipids, inducing phase transitions and permeability increases in the bilayer membrane, ultimately disrupting the liposome entity.

Photoinduced Vesicle Formation via the Copper-Catalyzed Azide-Alkyne Cycloaddition Reaction.

Synthetic vesicles have a wide range of applications from drug and cosmetic delivery to artificial cell and membrane studies, making simple and controlled formation of vesicles a large focus of the field today. Here, we report the use of the photoinitiated copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction using visible light to introduce spatiotemporal control into the formation of vesicles. Upon the establishment of the spatiotemporal control over vesicle formation, it became possible to adjust initiation conditions to modulate vesicle sizes resulting in the formation of controllably small or large vesicles based on light intensity or giant vesicles when the formation was initiated in flow-free conditions. Additionally, this photoinitiated method enables vesicle formation at a density 400-fold higher than initiation using sodium ascorbate as the catalyst. Together, these advances enable the formation of high-density, controlled size vesicles using low-energy wavelengths while producing enhanced control over the formation characteristics of the vesicle.