The Role of Membrane Fluidization in the Gel-Assisted Formation of Giant Polymersomes

Abstract

Polymersomes are being widely explored as synthetic analogs of lipid vesicles based on their enhanced stability and potential uses in a wide variety of applications in (e.g., drug delivery, cell analogs, etc.). Controlled formation of giant polymersomes for use in membrane studies and cell mimetic systems, however, is currently limited by low-yield production methodologies. Here, we describe for the first time, how the size distribution of giant poly(ethylene glycol)-poly(butadiene) (PEO-PBD) polymersomes formed by gel-assisted rehydration may be controlled based on membrane fluidization. We first show that the average diameter and size distribution of PEO-PBD polymersomes may be readily increased by increasing the temperature of the rehydration solution. Further, we describe a correlative relationship between polymersome size and membrane fluidization through the addition of sucrose during rehydration, enabling the formation of PEO-PBD polymersomes with a range of diameters, including giant-sized vesicles (>100 μm). This correlative relationship suggests that sucrose may function as a small molecule fluidizer during rehydration, enhancing polymer diffusivity during formation and increasing polymersome size. Overall the ability to easily regulate the size of PEO-PBD polymersomes based on membrane fluidity, either through temperature or fluidizers, has broadly applicability in areas including targeted therapeutic delivery and synthetic biology.

Self‐Assembly of Giant Unilamellar Vesicles by Film Hydration Methodologies

“…Upon hydration of the polymeric support on the glass surface, the amphiphile film mechanically swells, and is subjected to a higher surface exposure to hydration, facilitating self‐assembly into GUVs. The hydrophilic polymer is initially dissolved in water upon heating, and coated to the coverslip by drop‐casting, dip‐coating or spin‐coating, and dried. The amphiphile solution (in chloroform) is manually spread above the dehydrated hydrogel layer and is dried.…”

“…In terms of coating, the vast majority of protocols rely on the manual expertise of the operator by spreading both the gel and the amphiphilic solution using the length of a pipette tip or a needle . This type of less reproducible protocols is similarly widespread in electroformation as previously discussed.…”

“…Similar to electroformation, the concentrations of amphiphiles varies from 1–4 mg mL −1 for lipids and 3–5 mg mL −1 for polymers of M n from 3000 to 8000 g mol −1 or is sometimes not specified. Gel‐assisted hydration is fast, requires up to 1 h, contrasting with electroformation which exhibits greater variation in reported times (5 min to overnight) and generally takes several hours or longer for gentle hydration . Several gel‐assisted hydration protocols even obtain GUVs within 30 min .…”

“…Gel‐assisted hydration has only been rarely used for amphiphilic polymers. We could only find two accounts of successful GUVs formed by these methods . Both studies have use a few different polymers (PB‐ b ‐PEO, poly(ethyl ethylene)(PEE)‐ b ‐PEO, PEO‐ b ‐poly(propylene oxide)‐ b ‐PEO (PEO‐ b ‐PPO‐ b ‐PEO), and PEO‐ b ‐polydimethylsiloxane (PDMS)‐ b ‐PEO), as an initial proof that gel‐assisted hydration can be used for both triblock and diblock copolymers, with an M n between 3000 and 8000 g mol −1 and were obtained from both agarose and PVA.…”

“…Gel‐assisted hydration is still a relatively novel technique. Consequently it is not surprising that examples with amphiphilic polymers are rare and no hybrid lipid–polymer systems have been reported. Nonetheless, already a variety of lipids have been studied and this method is showing promise for the self‐assembly of all types of lipids .…”