Comparison of Carboxybetaine with Sulfobetaine as Lipid Headgroup Involved in Intermolecular Interaction between Lipids in the Membrane

Surfactant-Mediated Structural Modulations to Planar, Amphiphilic Multilamellar Stacks

The hydrophobic effect, a ubiquitous process in biology, is a primary thermodynamic driver of amphiphilic self-assembly. It leads to the formation of unique morphologies including two highly important classes of lamellar and micellar mesophases. The interactions between these two types of structures and their involved components have garnered significant interest because of their importance in key biochemical technologies related to the isolation, purification, and reconstitution of membrane proteins. This work investigates the structural organization of mixtures of the lamellar-forming phospholipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and two zwitterionic micelle-forming surfactants, being n-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (Zwittergent 3-12 or DDAPS) and 1-oleoyl-2-hydroxy-sn-glycero-3-phosphocholine (O-Lyso-PC), when assembled by water vapor hydration with X-ray diffraction measurements, brightfield optical microscopy, wide-field fluorescence microscopy, and atomic force microscopy. The results reveal that multilamellar mesophases of these mixtures can be assembled across a wide range of POPC to surfactant (POPC:surfactant) concentration ratios, including ratios far surpassing the classical detergent-saturation limit of POPC bilayers without significant morphological disruptions to the lamellar motif. The mixed mesophases generally decreased in lamellar spacing (D) and headgroup-to-headgroup distance (Dhh) with a higher concentration of the doped surfactant, but trends in water layer thickness (Dw) between each bilayer in the stack are highly variable. Further structural characteristics including mesophase topography, bilayer thickness, and lamellar rupture force were revealed by atomic force microscopy (AFM), exhibiting homogeneous multilamellar stacks with no significant physical differences with changes in the surfactant concentration within the mesophases. Taken together, the outcomes present the assembly of unanticipated and highly unique mixed mesophases with varied structural trends from the involved surfactant and lipidic components. Modulations in their structural properties can be attributed to the surfactant's chemical specificity in relation to POPC, such as the headgroup hydration and the hydrophobic chain tail mismatch. Taken together, our results illustrate how specific chemical complexities of surfactant-lipid interactions can alter the morphologies of mixed mesophases and thereby alter the kinetic pathways by which surfactants dissolve lipid mesophases in bulk aqueous solutions.

Glioma diagnosis and therapy: Current challenges and nanomaterial-based solutions

Glioma is often referred to as one of the most dreadful central nervous system (CNS)-specific tumors with rapidly-proliferating cancerous glial cells, accounting for nearly half of the brain tumors at an annual incidence rate of 30-80 per a million population. Although glioma treatment remains a significant challenge for researchers and clinicians, the rapid development of nanomedicine provides tremendous opportunities for long-term glioma therapy. However, several obstacles impede the development of novel therapeutics, such as the very tight blood-brain barrier (BBB), undesirable hypoxia, and complex tumor microenvironment (TME). Several efforts have been dedicated to exploring various nanoformulations for improving BBB permeation and precise tumor ablation to address these challenges. Initially, this article briefly introduces glioma classification and various pathogenic factors. Further, currently available therapeutic approaches are illustrated in detail, including traditional chemotherapy, radiotherapy, and surgical practices. Then, different innovative treatment strategies, such as tumor-treating fields, gene therapy, immunotherapy, and phototherapy, are emphasized. In conclusion, we summarize the article with interesting perspectives, providing suggestions for future glioma diagnosis and therapy improvement.

Determination of non-freezing water in different nonfouling materials by differential scanning calorimetry

Nonfouling materials have attracted increasing interest for their excellent biocompatibility and low immunogenicity. Strong hydration is believed to be the key reason for their resisting capability to nonspecific protein adsorption. However, little attention has been paid to quantifying their strong water binding capacity. In this study, we synthesized four zwitterionic polymers, including poly(sulfobetaine methacrylate) (pSBMA), poly(carboxybetaine methacrylate) (pCBMA), poly(carboxybetaine acrylamide) (pCBAA) and poly(2-methacryloyloxyethyl phosphorylcholine) (pMPC), and compared non-freezing water of these zwitterionic polymers with typical antifouling polymer poly(ethylene glycol) (PEG) using differential scanning calorimetry (DSC). Non-freezing water of their monomers was also investigated. The non-freezing water of the polymers (per unit) is pMPC (10.7 ± 1.4) ≈ pCBAA (10.8 ± 1.5) > pCBMA (9.0 ± 0.6) > pSBMA (6.6 ± 0.4) > PEG20000 (0.60 ± 0.04). Similar trend is observed for their monomers. For all studied zwitterionic materials, they showed higher binding capacity than PEG. We attribute the stronger hydration of zwitterionic polymers to their strong electrostatic interactions.

Targeted liposomal drug delivery: a nanoscience and biophysical perspective

Liposomes are a unique platform for drug delivery, and a number of liposomal formulations have already been commercialized. Doxil is a representative example, which uses PEGylated liposomes to load doxorubicin for cancer therapy. Its delivery relies on the enhanced permeability and retention (EPR) effect or passive targeting. Drug loading can be achieved using both standard liposomes and also those containing a solid core such as mesoporous silica and poly(lactide-co-glycolide) (PLGA). Developments have also been made on active targeted delivery using bioaffinity ligands such as small molecules, antibodies, peptides and aptamers. Compared to other types of nanoparticles, the surface of liposomes is fluid, allowing dynamic organization of targeting ligands to achieve optimal binding to cell surface receptors. This review article summarizes development of liposomal targeted drug delivery systems, with an emphasis on the biophysical properties of lipids. In both passive and active targeting, the effects of liposome size, charge, fluidity, rigidity, head-group chemistry and PEGylation are discussed along with recent examples. Most of the examples are focused on targeting tumors or cancer cells. Finally, a few examples of commercialized formulations are described, and some future research opportunities are discussed.

Interaction Mechanisms of Zwitterions with Opposite Dipoles in Aqueous Solutions

Zwitterionic groups have been widely used in antibiofouling surfaces to resist nonspecific adsorption of proteins and other biomolecules. The interactions among zwitterionic groups have attracted considerable attention in bioengineering, whereas the understanding of their nanomechanical mechanism still remains limited. In this work, the interaction mechanisms between two zwitterionic groups with opposite dipoles, i.e., phosphorylcholine (PC) and sulfobetaine (SB), have been investigated via direct force measurements using an atomic force microscope (AFM) and dynamic adsorption tests using the quartz crystal microbalance with dissipation monitoring technique (QCM-D) in aqueous solutions. The AFM force measurements show that the adhesive forces between contacted zwitterionic surfaces during separation in both symmetric and asymmetric configurations were close, mainly due to the enforced alignment of opposing dipole pairs via complementary orientations under confinement. The solution salinity and pH had almost negligible influence on the adhesion measured during surface separation. The QCM-D adsorption tests of PC-headed lipid on PC and SB surfaces showed some degree of adsorption of lipid molecules on the SB surface, whereas not on the PC surface. The different adsorption behaviors indicate that because the outermost negatively charged sulfonic group on the SB faced the aqueous solution, this configuration could facilitate it to form an attractive electrostatic interaction with the PC head of lipid molecules in the solution. This work shows that in addition to hydration and steric interactions, the zwitterionic dipole-induced interactions play an important role in the adhesion and antifouling behaviors of the zwitterionic molecules and surfaces. The improved fundamental understanding provides useful insights into the development of new functional materials and coatings with antifouling applications.