Impact of poly(ethylene glycol) functionalized lipids on ordering and fluidity of colloid supported lipid bilayers.

Colloid supported lipid bilayers (CSLBs) are highly appealing building blocks for functional colloids. In this contribution, we critically evaluate the impact on lipid ordering and CSLB fluidity of inserted additives. We focus on poly(ethylene glycol) (PEG) bearing lipids, which are commonly introduced to promote colloidal stability. We investigate whether their effect on the CSLB is related to the incorporated amount and chemical nature of the lipid anchor. To this end, CSLBs were prepared from lipids with a low or high melting temperature (Tm), DOPC, and DPPC, respectively. Samples were supplemented with either 0, 5 or 10 mol% of either a low or high Tm PEGylated lipid, DOPE-PEG2000 or DSPE-PEG2000, respectively. Lipid ordering was probed via differential scanning calorimetry and fluidity by fluorescence recovery after photobleaching. We find that up to 5 mol% of either PEGylated lipids could be incorporated into both membranes without any pronounced effects. However, the fluorescence recovery of the liquid-like DOPC membrane was markedly decelerated upon incorporating 10 mol% of either PEGylated lipids, whilst insertion of the anchoring lipids (DOPE and DSPE without PEG2000) had no detectable impact. Therefore, we conclude that the amount of incorporated PEG stabilizer, not the chemical nature of the lipid anchor, should be tuned carefully to achieve sufficient colloidal stability without compromising the membrane dynamics. These findings offer guidance for the experimental design of studies using CSLBs, such as those focusing on the consequences of intra- and inter-particle inhomogeneities for multivalent binding and the impact of additive mobility on superselectivity.

Correction: Directional-dependent pockets drive columnar-columnar coexistence.

Correction for 'Directional-dependent pockets drive columnar-columnar coexistence' by Álvaro González García et al., Soft Matter, 2020, DOI: 10.1039/d0sm00802h.

On the Colloidal Stability of Spherical Copolymeric Micelles.

Using self-consistent field (SCF) calculations, we systematically quantify the pair interactions between spherical diblock copolymer micelles following a bottom-up approach. From the equilibrium properties of self-assembling micelles at different separation distances, a simple yet insightful pair interaction can be extracted. The SCF results match with an analytical model based upon closed expressions for the free energy change per diblock copolymer in the micelle. To gain insights into the colloidal stability of dilute micelle suspensions, the second virial coefficient normalized by the undistorted micelle volume (B 2 *) is evaluated. For stable micelles (B 2 * ≳ -6), we find a weak dependence of B 2 * on solvophilic block length for varying core-forming block properties (core solvation and block length). The micelle suspension gets unstable (B 2 * ≲ -6) when the corona-forming block crosses Θ-solvent conditions toward poor solvency. In contrast with what is expected from models where the soft nature of the micelle is not taken into account, increasing the effective grafting density of solvophilic tails from the core then leads to colloidal destabilization of the micelle suspension.