The appeal of lipid carriers begins with basic biochemistry. The eye’s surfaces are lipid-rich, so nanoparticles built from phospholipids and related molecules interact naturally with the tear film, extending residence time and sustaining drug release in the conjunctival sac. Some lipid ingredients have a high affinity for cell membranes and actively promote absorption, while others function as permeation enhancers in their own right. Liposomes go one step further: their phospholipid bilayers mimic the structure of cell membranes, which facilitates uptake. Crucially, these systems are also well tolerated, rarely irritating the ocular mucosa—a decisive advantage for chronic conditions requiring daily, sometimes lifelong, administration.

Liposomes, spherical vesicles in which an aqueous core is enclosed by one or more phospholipid bilayers, are the most mature of the three technologies. They range from small unilamellar vesicles of 20 to 200 nanometers up to multilamellar structures spanning 1 to 5 micrometers, and they can carry both water-soluble and oil-soluble drugs simultaneously. Their most powerful design trick is surface charge. Positively charged, or cationic, liposomes bind electrostatically to the negatively charged sialic residues of mucin and to sulfated proteoglycans in cell membranes, anchoring the particles to the ocular surface long enough for uptake to occur. This single modification has produced some of the most striking results in the field.

In one recent study, cationic liposomes roughly 300 nanometers in diameter with a surface potential of +30 millivolts were loaded with tacrolimus for dry eye treatment. The formulation prolonged ocular retention and raised corneal drug concentrations substantially, and it outperformed commercial drops on a key clinical metric: tear film break-up time improved by 3.57 seconds versus 1.50 seconds with the marketed product. Inflammation markers fell in parallel—interleukin-1β concentrations dropped to 99.91 picograms per milliliter, compared with 138.98 for commercial drops and 228.99 in the positive control group. Even more strikingly, a separate 2025 investigation showed that cationic liposomes can scavenge cell-free DNA, a molecule elevated in dry eye patients that destabilizes the tear film and drives surface inflammation. After one week of topical treatment in mice with induced dry eye, the liposomal dispersion restored tear secretion, goblet cell counts, and the corneal barrier itself.

The pharmacokinetic gains from liposomal encapsulation can be dramatic. When acyclovir was delivered to rabbits in positively charged phosphatidylcholine-based liposomes, the relative area under the curve in the aqueous humor was 11.9—more than eleven times higher than an equal concentration applied as an ointment, an aqueous solution, or a solution mixed with empty liposomes. Ganciclovir in liposomes showed two- to ten-fold higher distribution in the sclera, cornea, iris, lens, and vitreous humor than a simple solution. Besifloxacin loaded into cationic liposomes achieved lower minimum inhibitory and bactericidal concentrations against Pseudomonas aeruginosa than the commercial product Besivance, while permeating more effectively. Astaxanthin-loaded liposomes with a slight positive charge protected rats against superficial punctate keratopathy better than neutral versions, apparently because electrostatic attraction to the corneal epithelium kept the antioxidant where it was needed rather than letting it diffuse into the stroma.

Perhaps the most consequential frontier is the delivery of protein therapeutics without needles. Bevacizumab, an antibody used for retinal vascular disease, currently requires intraocular injection. Researchers found that associating annexin A5 with bevacizumab-loaded liposomes triggered endocytosis and transcytosis through the corneal epithelium, delivering 127 nanograms per gram of drug to the posterior segment and 18 nanograms per gram to the retina after topical administration in rabbits. Coating strategies amplify these effects further: methacrylated hyaluronic acid on liposomal surfaces promoted adhesion to bovine conjunctival tissue and CD44-mediated uptake in human corneal epithelial cells, while maleimide-terminated PEG formed covalent carbon–sulfur bonds with thiol groups in the glycocalyx to anchor particles in place. Combination products are advancing too—timolol and latanoprost co-loaded in oligoethylenimine-functionalized liposomes reduced intraocular pressure in rats for up to five days from a single drop, and liposomal triamcinolone acetonide reached the vitreous and retina of rabbits and four patients with diabetic macular edema without raising intraocular pressure.

Cubosomes, the second major platform, are liquid-crystalline nanoparticles built from amphiphilic lipids such as glyceryl monooleate and phytantriol, stabilized by poloxamers. Their bicontinuous cubic lipid structure resembles the membranes of the corneal epithelium, easing transport into corneal cells, and their components are themselves permeation enhancers. The numbers are compelling: ketorolac in cubosomes achieved 2.07-fold higher transcorneal permeation and 2.24-fold greater corneal retention than a reference solution, while bromfenac sodium in hyaluronan-enriched cubosomes reached an aqueous humor area under the curve of 18.88 microgram-hours per milliliter versus 7.93 for marketed drops. In the infection arena, gatifloxacin-loaded cubosomes cut the minimum inhibitory concentration against drug-resistant Staphylococcus aureus four-fold, from 16 to 4 micrograms per milliliter, and reduced corneal opacity more effectively than the pure drug in infected rats—likely because the cubosomes fused with or adhered to bacterial membranes, improving drug delivery into the pathogens themselves.

Cubosomes are also proving their worth against glaucoma and reaching deeper ocular tissues. Timolol-loaded glyceryl monooleate cubosomes of 142 nanometers lowered intraocular pressure in rabbits from 27.8–39.7 to 21.4–32.6 millimeters of mercury after one week. A dual-loaded formulation carrying dorzolamide hydrochloride and timolol maleate together reduced pressure from 27.28 to 19.40 within four hours, with higher drug exposure than marketed drops for both agents. Acetazolamide cubosomes achieved a 38.22 percent pressure reduction versus 31.14 percent for commercial Azopt drops and 21.99 percent for oral tablets—without systemic absorption, since the untreated eye showed no pressure change. Most remarkably, cationic cubosomes carrying lutein delivered the antioxidant to retinal cells, protected the retina against oxidative stress, enhanced Nrf2 and HO-1 antioxidant gene expression, and were still detectable in the mouse retina seven days after topical instillation as simple eye drops.

Solid lipid nanoparticles, the third platform, consist of a lipid matrix—long- or medium-chain triglycerides, waxes, or fatty acids solid at physiological temperatures—wrapped in a surfactant shell that prevents aggregation. Their small size and lipid composition allow them to pass through the cornea and vitreous toward the retinal layers, and they suit dry eye therapy by protecting polar tear components from evaporation. The evidence spans antifungals to anti-inflammatories: natamycin in solid lipid nanoparticles showed 2.5-fold lower minimum inhibitory concentrations against Aspergillus fumigatus and Candida albicans; ofloxacin nanoparticles coated with chitosan and polyethylene glycol reached two- to three-fold higher ocular concentrations in rabbits; PEGylated latanoprost nanoparticles loaded into contact lenses sustained release for 96 hours; and econazole drops kept corneal drug concentrations above the minimum inhibitory concentration for three hours after a single administration. Even fragile molecules benefit—lutein, an unstable carotenoid, gained resistance to oxygen, light, and heat along with an increased permeability coefficient after encapsulation.

Challenges remain before these systems fully replace conventional formulations. Liposomes suffer from chemical instability through lipid oxidation and ester hydrolysis, and from physical instability through aggregation and fusion, which can dump the entire drug payload prematurely. Sterilization is awkward—autoclaving destroys the vesicular structure, while sterile filtration fails for particles above 200 nanometers. Cubosomes risk phase changes in tear fluid that compromise release profiles, and their high-energy production methods can damage sensitive actives. Solid lipid nanoparticles undergo polymorphic transitions during storage that trigger drug leakage, and their ordered crystal lattices leave little room for payload—problems that nanostructured lipid carriers blending solid and liquid lipids may solve. Yet the trajectory is clear: only liposomes have so far reached FDA-approved products, including Artelac Rebalance liposomal drops with vitamin B12 and Lacrisek liposomal spray with vitamins A and E for dry eye. As the review’s authors conclude, these dispersions can be formulated as modified eye drops that outperform both rapidly eliminated conventional solutions and blurry oily semisolids—pointing toward a near future where nanotechnology quietly turns the humble eye drop into one of medicine’s most precise delivery tools.

Subject of Research: Lipid-based nanosized drug delivery systems for topical ophthalmic drug administration

Article Title: Lipid-based nanosized drug delivery systems in ophthalmology

Article References: Genov, K., Yoncheva, Y., Pencheva, V., Yoncheva, K., & Veleva-Krasteva, N. (2026). Lipid-based nanosized drug delivery systems in ophthalmology. Pharmacia, 73, Article e206262. https://doi.org/10.3897/pharmacia.73.e206262

Image Credits: AI Generated

DOI: 10.3897/pharmacia.73.e206262

Keywords: liposomes, cubosomes, solid lipid nanoparticles, ocular drug delivery, dry eye, glaucoma, nanoparticles, corneal permeation, drug bioavailability, ophthalmology, nanomedicine, tear film

The nanoparticles at the heart of the study are built from a simple mixture of phytantriol and a phospholipid called DPPS. By adjusting the salt concentration of the surrounding solution, the researchers could drive the same lipid formulation through a sequence of distinct internal structures. In pure water, the lipids assembled into lamellar vesicles, essentially flat bilayer spheres. Dilution into 0.1-times phosphate-buffered saline transformed them into so-called P-cubosomes, particles whose interiors form a bicontinuous cubic phase with the Im3m symmetry. A further step into full-strength PBS produced D-cubosomes with the Pn3m diamond-type cubic phase. Small-angle X-ray scattering and cryogenic electron microscopy confirmed each transition, and the particles kept their assigned structures even after being transferred into the biological assay medium used for all subsequent experiments.

What makes this platform powerful is that the three particle types are nearly identical in every measurable respect except curvature. Dynamic light scattering showed hydrodynamic diameters of roughly 125 to 142 nanometers, and all three displayed a near-neutral zeta potential of about minus 3 millivolts in the assay medium. Co-administration with the antibiotic daptomycin did not alter these colloidal properties. Yet when the researchers applied the Gauss-Bonnet theorem to the X-ray-derived lattice parameters, they calculated Gaussian curvatures of zero for the vesicles, about minus 0.07 per square nanometer for P-cubosomes, and minus 0.10 per square nanometer for D-cubosomes. The cubic particles expose saddle-shaped openings where internal water channels meet the particle surface, while the vesicle surface is topologically flat. Increasing salt screens electrostatic repulsion between lipid headgroups, reduces the interfacial area per molecule, and pushes the system toward progressively more negative curvature.

With this curvature hierarchy established, the team tested how the blank, drug-free particles interacted with six clinical MRSA strains. Confocal microscopy showed all three formulations gathering near the bacterial membrane, but quantitative assays revealed a clear trend. In the NPN uptake assay, which measures penetration into the hydrophobic membrane interior, D-cubosomes achieved the highest uptake factor of 9.5 at 64 micrograms per milliliter, closely followed by P-cubosomes at 9.4, while vesicles lagged at 8.1. D-cubosomes also triggered the strongest oxidative stress in bacterial cells. The particles alone, however, could not kill the bacteria; their role emerged only in combination with daptomycin, a lipopeptide antibiotic that disrupts Gram-positive membranes by binding to negatively charged lipids.

The combination experiments produced striking results. Adding subinhibitory daptomycin to vesicle suspensions reduced the minimum inhibitory concentration of the drug eight-fold compared with nanoparticle monotherapy. With P-cubosomes the reduction reached 32-fold, and with D-cubosomes it climbed to 64-fold. Similar trends held across all six MRSA strains tested. Notably, the fractional inhibitory concentration indices remained within the conventional indifferent range, meaning the effect is best described as curvature-dependent potentiation rather than formal pharmacodynamic synergy. Control experiments confirmed that ionic strength alone did not explain the enhancement, since daptomycin activity was unchanged in buffers of different salinity without nanoparticles.

Fluorescence live-dead staining quantified the bactericidal consequences. Daptomycin alone left approximately 81 percent of cells viable, comparable to untreated controls. Combined with vesicles, viability fell to about 15 percent; with P-cubosomes, to roughly 7 percent; and with D-cubosomes, to below 2 percent. Electron microscopy added visual weight to these numbers. Untreated MRSA cells showed smooth, uniform surfaces, and neither daptomycin alone nor any nanoparticle alone caused visible damage. The daptomycin-D-cubosome combination, however, produced extensive membrane disruption, with distinctive bread-crumb-like protrusions covering the cell surface, while the vesicle combination left morphology essentially intact and P-cubosomes caused only moderate blebbing. Transmission electron microscopy further showed D-cubosomes in the closest contact with bacterial envelopes, with visible cell lysis in the combination treatment.

To probe the mechanism at molecular resolution, the researchers turned to neutron reflectometry. They first confirmed with fluorescent peptidoglycan labeling that the nanoparticles were not primarily accumulating in the cell wall, justifying a simplified model membrane that recreates the S. aureus cytoplasmic membrane from phosphatidylglycerol, cardiolipin, and lysyl-phosphatidylglycerol in the same 69:12:19 molar ratio found in the bacterium. Using three isotopic contrasts, the team measured how each formulation remodeled this bilayer. Daptomycin with vesicles removed only 9.5 percent of the lipid volume fraction. The P-cubosome combination extracted 17.8 percent, consistent with partial lipid loss. The D-cubosome combination was by far the most destructive, stripping 36 percent of the lipid and allowing water to penetrate the bilayer, and a layer associated with D-cubosomes, roughly 33.5 angstroms thick, was detected deposited on the membrane surface.

The physical explanation draws on well-established membrane biophysics. According to Helfrich’s curvature-elastic energy model, membranes store elastic energy that depends on how far their shape deviates from a spontaneous curvature, and Gaussian curvature contributes directly to this energy landscape. Negative Gaussian curvature, the saddle-like geometry characteristic of the cubic phases, lowers the energetic barrier for membrane remodeling processes such as fusion and pore formation. The MRSA membrane, dominated by lysyl-phosphatidylglycerol, naturally favors positive curvature, so highly negatively curved nanoparticles create a curvature mismatch that generates localized stress, weakens lipid packing, and increases permeability. Daptomycin at subinhibitory levels presumably sensitizes the membrane, while the retained internal curvature of the nanoparticles governs how much remodeling follows.

Safety and in vivo data strengthened the case. Human embryonic kidney cells maintained at least 80 percent metabolic activity after 24 hours of exposure to any formulation alone or combined with daptomycin. In a mouse bacteremia model, intravenous infection with S. aureus followed by intraperitoneal treatment showed a clear curvature-dependent hierarchy of bacterial clearance. Free daptomycin at 10 milligrams per kilogram, chosen to represent a suboptimal therapeutic condition, did not significantly reduce organ bacterial burdens compared with saline. Blank nanoparticles alone produced a modest two log10 reduction. The daptomycin-vesicle combination roughly doubled that effect, the P-cubosome combination lowered counts to between 10,000 and 100,000 colony-forming units per gram, and the D-cubosome combination pushed bacterial counts in the kidney, liver, and spleen close to the detection limit of 100 CFU per gram, a five to six log10 improvement over the free drug.

The authors are careful to frame the animal work as a proof of concept rather than therapeutic validation. Serum proteins, lipoproteins, and endogenous lipases could remodel the nanoparticles before they reach infected tissues, and the study did not include pharmacokinetic analysis, long-term toxicity assessment, or survival endpoints. Future development will require plasma stability studies, quantitative measurement of any daptomycin association with the lipid phases, biodistribution data, dose optimization, and immunogenicity evaluation. Even so, the central message stands out clearly: by isolating curvature as the only structural variable in a matched nanoparticle platform, the study provides direct experimental evidence that nanoscale geometry, tunable through something as simple as salt concentration, can be programmed to amplify antibiotic activity against one of the world’s most dangerous drug-resistant pathogens.

Subject of Research: Curvature-modulated lyotropic liquid crystalline nanoparticles as antibacterial potentiators against MRSA

Article Title: Enhanced Antibacterial Properties of Lyotropic Liquid Crystalline Nanoparticles via Curvature Modulation

Article References: Lai, X., Wang, S., Ding, C., Kostoulias, X., Brun, A. P. L., Hsu, H.-Y., Jiang, J.-H., Wang, Y., Strugnell, R. A., Peleg, A. Y., & Shen, H.-H. (2026). Enhanced Antibacterial Properties of Lyotropic Liquid Crystalline Nanoparticles via Curvature Modulation. Advanced Science, 13(55), Article e76516. https://doi.org/10.1002/advs.76516

Image Credits: AI Generated

DOI: 10.1002/advs.76516

Keywords: antimicrobial resistance, MRSA, lyotropic liquid crystalline nanoparticles, cubosomes, Gaussian curvature, daptomycin, membrane disruption, neutron reflectometry, nanomedicine, Staphylococcus aureus, lipid nanoparticles, antibiotic potentiation