Vancomycin ocular delivery systems based on glycerol monooleate reversed hexagonal and reversed cubic liquid crystalline phases

Recent Advances in Ocular Drug Delivery: Insights into Lyotropic Liquid Crystals

Background/Objectives: This review examines the evolution of lyotropic liquid crystals (LLCs) in ocular drug delivery, focusing on their ability to address the challenges associated with traditional ophthalmic formulations. This study aims to underscore the enhanced bioavailability, prolonged retention, and controlled release properties of LLCs that significantly improve therapeutic outcomes. Methods: This review synthesizes data from various studies on both bulk-forming LLCs and liquid crystal nanoparticles (LCNPs). It also considers advanced analytical techniques, including the use of machine learning and AI-driven predictive modeling, to forecast the phase behavior and molecular structuring of LLC systems. Emerging technologies in biosensing and real-time diagnostics are discussed to illustrate the broader applicability of LLCs in ocular health. Results: LLCs are identified as pivotal in promoting targeted drug delivery across different regions of the eye, with specific emphasis on the tailored optimization of LCNPs. This review highlights principal categories of LLCs used in ocular applications, each facilitating unique interactions with physiological systems to enhance drug efficacy and safety. Additionally, novel applications in biosensing demonstrate LLCs' capacity to improve diagnostic processes. Conclusions: Lyotropic liquid crystals offer transformative potential in ocular drug delivery by overcoming significant limitations of conventional delivery methods. The integration of predictive technologies and biosensing applications further enriches the utility of LLCs, indicating a promising future for their use in clinical settings. This review points to continued advancements and encourages further research in LLC technology to maximize its therapeutic benefits.

Bioinspired drug delivery strategies for repurposing conventional antibiotics against intracellular infections

Bacteria have developed a wealth of strategies to avoid and resist the action of antibiotics, one of which involves pathogens invading and forming reservoirs within host cells. Due to the poor cell membrane permeability, stability and retention of conventional antibiotics, this renders current treatments largely ineffective, since achieving a therapeutically relevant antibiotic concentration at the site of intracellular infection is not possible. To overcome such challenges, current antibiotics are 'repurposed' via reformulation using micro- or nano-carrier systems that effectively encapsulate and deliver therapeutics across cellular membranes of infected cells. Bioinspired materials that imitate the uptake of biological particulates and release antibiotics in response to natural stimuli are recently explored to improve the targeting and specificity of this 'nanoantibiotic' approach. In this review, the mechanisms of internalization and survival of intracellular bacteria are elucidated, effectively accentuating the current treatment challenges for intracellular infections and the implications for repurposing conventional antibiotics. Key case studies of nanoantibiotics that have drawn inspiration from natural biological particles and cellular uptake pathways to effectively eradicate intracellular pathogens are detailed, clearly highlighting the rational for harnessing bioinspired drug delivery strategies.

Vancomycin-loaded N,N-dodecyl,methyl-polyethylenimine nanoparticles coated with hyaluronic acid to treat bacterial endophthalmitis: Development, characterization, and ocular biocompatibility

Vancomycin-loaded N,N-dodecyl,methyl-polyethylenimine nanoparticles coated with hyaluronic acid (VCM-DMPEI nanoparticles/HA) were synthesized as an adjuvant for the treatment of bacterial endophthalmitis. The nanoparticles were formulated by experimental statistical design, thoroughly characterized, and evaluated in terms of bactericidal activity and both in vitro and in vivo ocular biocompatibility. The VCM-DMPEI nanoparticles/HA were 154 ± 3 nm in diameter with a 0.197 ± 0.020 polydispersity index; had a + 26.4 ± 3.3 mV zeta potential; exhibited a 93% VCM encapsulation efficiency; and released 58% of the encapsulated VCM over 96 h. VCM and DMPEI exhibited a synergistic bactericidal effect. The VCM-DMPEI nanoparticles/HA were neither toxic to ARPE-19 cells nor irritating to the chorioallantoic membrane. Moreover, the VCM-DMPEI nanoparticles/HA did not induce modifications in retinal functions, as determined by electroretinography, and in the morphology of the ocular tissues. In conclusion, the VCM-DMPEI nanoparticles/HA may be a useful therapeutic adjuvant to treat bacterial endophthalmitis.

Comparison of three in-situ gels composed of different oil types

A phospholipid-based phase separation in-situ gel (PPSG) system, which consists of phospholipids, medium chain oil (triglyceride) and ethanol as basic ingredients, has been previously developed in our lab. In addition, glycerol monooleate (monoglyceride) and glycerol dioleate (diglyceride) were also reported to be able to form liquid crystal gels. Monoglyceride, diglyceride and triglyceride have different degrees of hydroxyl substitution in glycerol and therefore different amphiphilic properties, which may cause different properties of gels composed of them. In this experiment, glycerol monooleate (GMO), glycerol dioleate (GDO) and glycerol trioleate (GTO) were selected to prepare three kinds of PPSGs. We systematically studied their in-vitro and in-vivo physicochemical properties and investigated their drug release behavior with octreotide (OCT) as the model drug. The results showed that PPSG composed of GTO (GTO-gel) had a different microstructure, a slower solvent diffusion speed and the less irritation to skin. In addition, the drug release result showed that the GTO-gel group had a lower initial release rate and a more stable release profile. All results above indicated that GTO-gel had a greater potential as a drug delivery system.

The Evaluations of Menthol and Propylene Glycol on the Transdermal Delivery System of Dual Drug-Loaded Lyotropic Liquid Crystalline Gels

This study aimed to evaluate the effects of two different structural alcohol permeation enhancers (menthol and propylene glycol) on the internal structure and in vitro properties of the dual drug-loaded lyotropic liquid crystalline (LLC) gels. The LLC gels were prepared and characterized by polarized light microscopy, small-angle X-ray scattering, differential scanning calorimetry, attenuated total reflectance-Fourier transform infrared spectrum, and rheology. Based on the results, the inner structure of the gels was Q_II mesophase and exhibited a pseudoplastic fluid behavior. The level of internal order in the LLC mesophase would be affected by introduced 2 wt% menthol (MEN) and propylene glycol (PG). The in vitro release experiment showed that the release behavior of sinomenine hydrochloride (SH) and cinnamaldehyde (CA) from the LLC system was dominated by Fickian diffusion (n < 0.43). MEN and PG had the opposite effects on the release of hydrophilic SH, while the MEN and PG both increased the release of lipophilic drug CA. Furthermore, in vitro permeation studies indicated that MEN and PG could both improve the skin permeability of SH and CA, and MEN displayed more pronounced enhancement. All the samples showed no skin irritation on the normal rat skin. Collectively, in our research, monoterpenoid MEN exhibited a better penetration-promoting effect than straight-chain fatty alcohol PG on the dual drug-loaded LLC system.

Vancomycin Loaded Glycerol Monooleate Liquid Crystalline Phases Modified with Surfactants

The influence of two tuning agents, polyglycerol ester (PE) and triblock copolymer (TC), on the properties of glycerol monooleate (MO) liquid crystalline phase (LCP) was investigated to achieve the therapeutic concentration of vancomycin hydrochloride (VHCl) into the eye, topically during 60 min (1 h) and intravitreally during 2880 min (48 h). Different techniques were used to elucidate the impact of surfactants on the structure of the LCP: polarized light microscopy (PLM), small-angle X-ray scattering (SAXS), and in vitro release tests I and II (simulating local and intravitreal application in the eye). The structure analysis by SAXS depicts that the inclusion of PE into the MO LCP provided partial transition of a hexagonal phase into a lamellar phase, and TC induced a partial transition of a hexagonal phase into an LCP which identification was difficult. The LCP modulated with PE and TC demonstrated different VHCl's release patterns and were evaluated by comparing our release data with the literature data. The comparison indicated that the LCP modulated with 30% w/w PE could be a promising VHCl delivery system intravitreally during 2880 min.

Stimuli-Responsive Lyotropic Liquid Crystalline Nanosystems with Incorporated Poly(2-Dimethylamino Ethyl Methacrylate)-b-Poly(Lauryl Methacrylate) Amphiphilic Block Copolymer

There is an emerging need to evolve the conventional lyotropic liquid crystalline nanoparticles to advanced stimuli-responsive, therapeutic nanosystems with upgraded functionality. Towards this effort, typically used stabilizers, such as Pluronics^®, can be combined or replaced by smart, stimuli-responsive block copolymers. The aim of this study is to incorporate the stimuli-responsive amphiphilic block copolymer poly(2-(dimethylamino)ethyl methacrylate)-b-poly(lauryl methacrylate) (PDMAEMA-b-PLMA) as a stabilizer in lipidic liquid crystalline nanoparticles, in order to provide steric stabilization and simultaneous stimuli-responsiveness. The physicochemical and morphological characteristics of the prepared nanosystems were investigated by light scattering techniques, cryogenic-transmission electron microscopy (cryo-TEM), X-ray diffraction (XRD) and fluorescence spectroscopy. The PDMAEMA-b-PLMA, either individually or combined with Poloxamer 407, exhibited different modes of stabilization depending on the lipid used. Due to the protonation ability of PDMAEMA blocks in acidic pH, the nanoparticles exhibited high positive charge, as well as pH-responsive charge conversion, which can be exploited towards pharmaceutical applications. The ionic strength, temperature and serum proteins influenced the physicochemical behavior of the nanoparticles, while the polymer concentration differentiated their morphology; their micropolarity and microfluidity were also evaluated. The proposed liquid crystalline nanosystems can be considered as novel and attractive pH-responsive drug and gene delivery nanocarriers due to their polycationic content.