A Physiology-Based Mathematical Model to Understand Drug Delivery from Contact Lenses to the Back of the Eye.

OBJECTIVE: Therapeutic contact lenses, able to store drug and deliver it to the eye surface in a sustained fashion, gained interest as an effective and patient-friendly alternative to eye drops. Recent animal studies also demonstrated the presence of therapeutic drug levels in the back of the eye after wearing drug-loaded contact lenses, thus opening the possibility of treating the posterior segment without need of invasive intraocular injections. The drug pathways from contact lenses to the back of the eye require further investigation. METHODS: A mechanistic mathematical model was developed to evaluate the drug concentration over time in the tears, sclera and choroid, retina, aqueous humor and vitreous humor after the application of a therapeutic contact lens. The main drug transport mechanisms of the eye and the barrier properties of the different tissues were included in the model. Validation was performed by comparison with experimental data in literature. RESULTS: The model predictions of drug concentration over time reflected the experimental data both in the anterior and posterior segment of the eye. The model can differentiate between contributions to transport from different pathways. CONCLUSIONS: The model constitutes a first step towards the possibility of predicting the ocular drug distribution and the treatment efficacy in the early stage of contact lens development, and it may help reduce both the need for in vivo tests (with ethical and economic advantages) and the gap between the lens design and clinical application. It also allows for an improved understanding of drug transport in the eye.

New Protic Ionic Liquids as Potential Additives to Lubricate Si-Based MEMS/NEMS.

The motivation for this work was to develop new protic ionic liquids (PILs) as additives for the lubrication of micro and nanoelectromechanical systems (MEMS and NEMS). Ten PILs based on the combination of methylimidazolium ([MIMH]), 4-picolinium ([4-picH]), pyridinium ([PyrH]), 1,8-diazabicyclo[5.4.0]-undec-7-ene-8-ium ([DBUH]) and tetramethylguanidinium ([TMGH]) cations with hydrogen sulfate([HSO4]) and mesylate ([MeSO3]) anions were tested as additives in polyethylene glycol (PEG200) to lubricate steel/silicon and silicon/silicon contacts. The best additive was [4-picH][HSO4], which adsorbed strongly on the Si surface, leading to a protective film that reduced wear by up to 15 times compared to PEG200.

Molecular Interactions between Ionic Liquid Lubricants and Silica Surfaces: An MD Simulation Study.

The unique physicochemical properties of ionic liquids (ILs) attracted interest in their application as lubricants of micro/nano-electromechanical systems. This work evaluates the feasibility of using the protic ionic liquids [4-picH][HSO4], [4-picH][CH3SO3], [MIMH][HSO4], and [MIMH][CH3SO3] and the aprotic ILs [C6mim][HSO4] and [C6mim][CH3SO3] as additives to model lubricant poly(ethylene glycol) (PEG200) to lubricate silicon surfaces. Additives based on the cation [4-picH]+ exhibited the best tribological performance, with the optimal value for 2% [4-picH][HSO4] in PEG200 (w/w). Molecular dynamics (MD) simulations of the first stages of adsorption of the ILs at the glass surface were performed to portray the molecular behavior of the ILs added to PEG200 and their interaction with the silica substrate. For the pure ILs at the solid substrates, the MD results indicated that weak specific interactions of the cation with the glass interface are lost to accommodate the larger anion in the first contact layer. For the PEG200 + 2% [4-picH][HSO4] system, the formation of a more compact protective film adsorbed at the glass surface is revealed by a larger trans population of the dihedral angle -O(R)-C-C-O(R)- in PEG200, in comparison to the same distribution for the pure model lubricant. Our findings suggest that the enhanced lubrication performance of PEG200 with [4-picH][HSO4] arises from synergistic interactions between the protic IL and PEG200 at the adsorbed layer.

Dexamethasone phosphate and penetratin co-eluting contact lenses: a strategy to enhance ocular drug permeability.

Contact lenses (CLs) have been suggested as drug delivery platforms capable of increasing the drug residence time on the cornea and therefore its bioavailability. However, when targeting the posterior segment of the eye, the drug released from CLs still encounters the barrier effect of the ocular tissues, which considerably reduces the efficacy of administration. This work aims at the development of CLs able to simultaneously deliver an anti-inflammatory drug (dexamethasone sodium phosphate) and a cell-penetrating peptide (penetratin), the latter acting as a drug carrier across the tissues. Hydroxyethyl methacrylate (HEMA)-based hydrogels were functionalized with acrylic acid (AAc) and/or aminopropyl methacrylamide (APMA) to serve as CL materials with increased affinity for the drug and peptide. APMA-functionalized hydrogels sustained the dual release for 8 h, which is compatible with the wearing time of daily CLs. Hydrogels demonstrated suitable light transmittance, swelling capacity and in vitro biocompatibility. The anti-inflammatory activity of the drug was not compromised by the presence of the peptide nor by sterilization. The ocular distribution of the drug after 6 h of CL wearing was evaluated in vivo in rabbits and revealed that the amount of drug in the cornea and aqueous humor significantly increased when the drug was co-delivered with penetratin.

Surface tension of ionic liquids and ionic liquid solutions.

Some of the most active scientific research fronts of the past decade are centered on ionic liquids. These fluids present characteristic surface behavior and distinctive trends of their surface tension versus temperature. One way to explore and understand their unique nature is to study their surface properties. This critical review analyses most of the surface tension data reported between 2001 and 2010 (187 references).

Antiseptic-Loaded Casein Hydrogels for Wound Dressings.

Chronic wound treatment accounts for a substantial percentage of the medical expenses worldwide. Improving and developing novel wound care systems can potentially help to handle this problem. Wound dressings loaded with antiseptics may be an important tool for wound care, as they inhibit bacterial growth at the wound site. The goal of the present work was to investigate the potential of using casein hydrogel dressings loaded with two antiseptic drugs, Octiset® or polyhexanide, to treat chronic wounds. Casein-based hydrogels are inexpensive and have several properties that make them suitable for biomedical applications. Two types of casein were used: casein sodium salt and acid casein, with the formulations being labelled CS and C, respectively. The hydrogels were characterised with respect to their physical properties (swelling capacity, water content, morphology, mechanical resistance, and stability), before and after sterilisation, and they showed adequate values for the intended application. The hydrogels of both formulations were able to sustain controlled drug-release for, at least, 48 h. They were demonstrated to be non-irritant, highly haemocompatible, and non-cytotoxic, and revealed good antimicrobial properties against Staphylococcus aureus and Pseudomonas aeruginosa. Steam-heat sterilisation did not compromise the material's properties. The in vivo performance of C hydrogel loaded with Octiset® was evaluated in a case study with a dog. The efficient recovery of the wounds confirms its potential as an alternative for wound treatment. To our knowledge, this is the first time that wound dressings loaded with Octiset®, one of the most efficient drugs for wound treatment, were prepared and tested.

Peculiar surface behavior of some ionic liquids based on active pharmaceutical ingredients.

The ionic liquids based on biologically active cations and anions, commonly designated by ionic liquids based on active pharmaceutical ingredients (ILs-APIs), are interesting compounds for use in pharmaceutical applications. Lidocaine docusate, ranitidine docusate, and didecyldimethylammonium ibuprofen are examples of promising ILs-APIs that were recently synthesized. They were submitted to biological testing and calorimetric measurements, but nothing is known about their surface properties. In this work, we measured the surface tension and the contact angles on both hydrophilic and hydrophobic surfaces in a temperature range as wide as possible. Based on the wettability data, the polarity fractions were estimated using the Fowkes theory. The peculiar surface behavior observed was tentatively attributed to the presence of mesophases.

Intraocular lenses as drug delivery devices.

Cataract surgery is one of the most common and safe surgical procedures nowadays. However, it is not free of risks as endophthalmitis, ocular inflammation and posterior capsule opacification (PCO) can appear as post-surgery complications. The usual eye drop therapy used as prophylaxis for the former two complications has limited bioavailability. In turn, the prevention of PCO involves an adequate surgical technique and a careful choice of intraocular lens (IOL) design and material. Also, different drugs have been tested to reduce incidence of PCO, but no prophylaxis demonstrated to be completely effective. In the past few years, IOLs have been proposed as drug delivery devices to replace or/assist the usual eye drop therapy in the post-operatory period. The great advantage of drug loaded IOLs would be to ensure a continuous drug delivery, independent of patient's compliance without requiring any further action besides IOL implantation. The biggest challenge of drug loaded IOLs production is to achieve a controlled and extended release that meet therapeutic needs without inducing toxicity to the surrounding ocular tissues or affecting the physical properties of the lens. This review starts by addressing the possible complications after cataract surgery, as well as the most commonly adopted prophylaxis for each of them. The various types of IOLs are described and their main advantages/disadvantages are discussed. The different strategies pursued to incorporate drugs into the IOLs and control their release, which include soaking the IOL in the drugs solution, supercritical impregnation, surface modifications, and attachment of drug reservoirs to the IOL, among others, are reported. For each strategy, a summary of the publications is presented, which includes the target complication, the types and amounts of released drugs and the IOL materials. A brief description of each individual study is given afterwards. Optimization of drug loaded IOLs through mathematical modelling and possible issues raised by their sterilization are also tackled. At the end, the future commercialization of drug loaded IOLs is commented.

Asymmetry in Drug Permeability through the Cornea.

The permeability through the cornea determines the ability of a drug or any topically applied compound to cross the tissue and reach the intraocular area. Most of the permeability values found in the literature are obtained considering topical drug formulations, and therefore, refer to the drug permeability inward the eye. However, due to the asymmetry of the corneal tissue, outward drug permeability constitutes a more meaningful parameter when dealing with intraocular drug-delivery systems (i.e., drug-loaded intraocular lenses, intraocular implants or injections). Herein, the permeability coefficients of two commonly administered anti-inflammatory drugs (i.e., bromfenac sodium and dexamethasone sodium) were determined ex vivo using Franz diffusion cells and porcine corneas in both inward and outward configurations. A significantly higher drug accumulation in the cornea was detected in the outward direction, which is consistent with the different characteristics of the corneal layers. Coherently, a higher permeability coefficient was obtained for bromfenac sodium in the outward direction, but no differences were detected for dexamethasone sodium in the two directions. Drug accumulation in the cornea can prolong the therapeutic effect of intraocular drug-release systems.

The effects of addition of functional monomers and molecular imprinting on dual drug release from intraocular lens material.

Although cataract surgery is considered a safe procedure, post-surgery complications such as endophthalmitis and ocular inflammation, may occur. To prevent this, antibiotics and anti-inflammatories are prescribed in the form of eye drops during the post-operatory period, but they lead to a low drug bioavailability in target tissues. The objective of this work is to develop an intraocular lens (IOL) material to deliver simultaneously one antibiotic, moxifloxacin (MXF), and one anti-inflammatory, diclofenac (DFN), in therapeutic concentrations to prevent both complications. The IOL material was modified through the incorporation of functional monomers, as well as molecular imprinting with both drugs using the same functional monomers, namely acrylic acid (AA), methacrylic acid (MAA), 4-vinylpiridine (4-VP) and a combination of MAA + 4-VP. The best results were obtained with MAA. Molecular imprinting did not influence the drug release, except with AA. Application of a mathematical model predicted that the released MXF and DFN concentrations would stay above the pre-determined MIC of S. aureus and S. epidermidis and the minimum values of IC50 of COX-1 and COX-2, for 9 and 14 days, respectively. Antibacterial tests showed that the released antibiotic remained active. The physical properties of the drug-loaded MAA-hydrogel remained adequate. The developed system proved to be non-irritant and non-cytotoxic.

Drug-Loaded Hydrogels for Intraocular Lenses with Prophylactic Action against Pseudophakic Cystoid Macular Edema.

Pseudophakic cystoid macular edema (PCME), caused by chronic inflammation, is the most common cause of visual impairment in the medium-term after cataract surgery. Therefore, the prophylactic topical administration of combined steroidal and non-steroidal anti-inflammatory drugs is commonly done. Drug-eluting intraocular lenses (IOLs) gained interest as an efficient way to overcome the compliance issues related to the use of ocular drops without the need for additional surgical steps. The incorporation of functional monomers and molecular imprinting were herein applied to design hydrogels suitable as IOLs and able to co-deliver steroidal (dexamethasone sodium phosphate) and non-steroidal (bromfenac sodium) drugs. The incorporation of N-(2-aminopropyl) methacrylamide (APMA) increased the drug uptake and improved the in vitro release kinetics. Imprinting with bromfenac resulted in a decreased drug release due to permanent drug bonding, while imprinting with dexamethasone increased the amount of dexamethasone released after dual-drug loading. The application of a mathematical model to predict the in vivo drug release behavior suggests the feasibility of achieving therapeutic drug concentrations of bromfenac and dexamethasone in the aqueous humor for about 2 and 8 weeks, respectively, which is compatible with the current topical prophylaxis after cataract surgery.

Imprinted hydrogels with LbL coating for dual drug release from soft contact lenses materials.

A combined strategy to control the release of two drugs, one anti-inflammatory (diclofenac sodium, DCF) and one antibiotic (moxifloxacin hydrochloride, MXF), from a soft contact lens (SCL) material, was assessed. The material was a silicone-based hydrogel, which was modified by molecular imprinting with MXF and coated by the layer-by-layer (LbL) method using natural polyelectrolytes: alginate (ALG), poly-l-lysine (PLL) and hyaluronate (HA), crosslinked with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC). Imprinting was used to increase the amount of MXF loaded and to sustain its release, while the LbL coating acted as a diffusion barrier for DCF and improved the surface properties. The drugs were loaded by soaking in a DCF + MXF dual solution. High hydrostatic pressure (HHP) was successfully applied in the sterilization of the drug-loaded hydrogels. The transmittance, refractive index, wettability and ionic permeability of the hydrogels remained within the required levels for SCLs application. The concentrations of the released DCF and MXF stayed above the IC50 and the MIC (for S. aureus and S. epidermidis) values, for 9 and 10 days, respectively. No ocular irritancy was detected by the HET-CAM test. NIH/3T3 cell viability demonstrated that the drug-loaded hydrogels were not toxic, and cell adhesion was reduced.

Moxifloxacin-imprinted silicone-based hydrogels as contact lens materials for extended drug release.

Contact lenses may act as drug release platforms for the treatment of ocular infections, but there is still the need for extending their typical release periods and enhancing ocular bioavailability. The present study aimed to develop a molecularly imprinted silicone-based hydrogel to be used in the manufacturing of contact lenses that can be loaded efficiently and be able to release the antibiotic moxifloxacin hydrochloride (MXF) in a sustained way. A set of hydrogels was prepared by the molecular imprinting method using acrylic acid (AA) as the functional monomer for the specific recognition of MXF. The modified hydrogels loaded a higher amount of MXF, which was released for a longer time. In vitro experiments, using a microfluidic cell to mimic the ocular surface fluid turnover, showed that the imprinted hydrogel TRIS(300)-I prepared with the highest content in AA led to MXF concentrations in the release medium which were effective against S. aureus and S. epidermidis for about 2 weeks. Furthermore, some important properties such as water uptake, wettability, transmittance, ionic permeability, and Young´s modulus of the modified hydrogel remained within the range of values recommended for contact lenses. No cytotoxicity and no potential ocular irritancy effect were detected. Such hydrogel seems to be a promising alternative to the current options for the treatment of ocular infections.

Dual drug delivery from hydrophobic and hydrophilic intraocular lenses: in-vitro and in-vivo studies.

Posterior capsule opacification (PCO) still remains the most frequent long term complication after cataract surgery, while endophthalmitis is rare but severe and should be prevented at all cost. Intraocular lenses (IOLs) with different designs (eg. edge and body-haptics angle) and materials (acrylic hydrophobic and acrylic hydrophilic surfaces) have been studied to reduce PCO. For the prevention of endophthalmitis, intracameral injection followed or not by topical treatment with antibiotics and anti-inflammatories are usually prescribed. The objective of this work was to investigate the use of IOLs as controlled release platforms of two drugs, the antibiotic moxifloxacin (MXF) and the anti-inflammatory ketorolac (KTL) that could advantageously substitute the usual treatment. Two types of IOLs were chosen, hydrophobic and hydrophilic. Hydrophobic IOLs have shown better results in the prevention of PCO because they adhere better to the posterior capsular bag, while hydrophilic IOLs are advised in the case of patients with uveitis, glaucoma or diabetes. The IOLs were loaded with MXF + KTL and sterilized by high hydrostatic pressure. Both IOLs reduced the tendency for adhesion of LECs. In vivo tests were done to compare the concentration of the drugs in the aqueous humor obtained after eye drops administration and drug-loaded IOLs implantation. The developed IOLs were able to release MXF and KTL at therapeutic levels, in a sustained way, which contrasts with the eye drops prophylaxis. No PCO signs were detected and histological analyses demonstrated biocompatibility of these devices.

High Hydrostatic Pressure as Sterilization Method for Drug-Loaded Intraocular Lenses.

Sterilization is a key step in the manufacturing of drug-loaded intraocular lenses (IOLs). Two of the most used methods to sterilize commercial IOLs are steam heat and gamma radiation. However, when the IOLs are loaded with drugs, the adequacy of those methods must be questioned because sterilization may affect the activity of the drugs and/or the drug release. Recently, high hydrostatic pressure (HHP), which is increasingly used in the food industry, has been applied in the sterilization of gels for medical applications. The objective of this work was to assess the performance of HHP in the sterilization of a commercial acrylic material used for the production of IOLs, both without and with loaded drugs. Bare samples and samples loaded with an antibiotic and two anti-inflammatories were tested, and the results were compared to those obtained with conventional sterilization methods. HHP not only sterilized highly contaminated samples but also enhanced drug loading and did not affect significantly the hydrogel properties. Gamma radiation degraded the drugs in solution; thus, it is adequate only for dry sample sterilization. Steam heat did not affect the release profiles but cannot be applied to temperature-sensitive drugs. We concluded that HHP may advantageously substitute steam heat and gamma radiation in the sterilization of drug-loaded IOLs.

Diclofenac sustained release from sterilised soft contact lens materials using an optimised layer-by-layer coating.

A layer-by-layer (LbL) coating was designed using ionic polysaccharides (chitosan, sodium alginate, sodium hyaluronate) and genipin (crosslinker), to sustain the release of diclofenac sodium salt (DCF) from soft contact lens (SCL) materials. The coating was hydrophilic, biocompatible, non-toxic, reduced bacterial growth and had minor effects on the physical properties of the material, such as wettability, ionic permeability, refractive index and transmittance, which remained within the recommended values for SCLs. The coating was applied on a silicone-based hydrogel and on commercial SofLens and Purevision SCLs. The coating attenuated the initial drug burst and extended the therapeutic period for, at least, two weeks. Relevantly, the problems of sterilizing drug loaded SCLs coated with biopolymers, using classic methods that involve high temperature or radiation, were successfully solved through high hydrostatic pressure (HHP) sterilization.

Moxifloxacin-loaded acrylic intraocular lenses: In vitro and in vivo performance.

PURPOSE: To assess the possibility of using acrylic intraocular lenses (IOLs) to ensure controlled and sustained release of moxifloxacin, an antibiotic commonly used for endophthalmitis prophylaxis after cataract surgery. SETTING: Academic, industrial, and clinical partners from Portugal, Belgium, Iceland, and the United States. DESIGN: Experimental study. METHODS: The physical properties of IOLs loaded with moxifloxacin by soaking were characterized. In vitro drug-release studies were performed under hydrodynamic conditions similar to those of the eye, and the activity of the released drug was tested. In vitro cytotoxicity was evaluated, and the in vivo efficacy of the devices was assessed through rabbit experiments in which the effects of topical moxifloxacin drops (control) and moxifloxacin-loaded IOLs were compared. RESULTS: The presence of moxifloxacin in the IOLs had little effect on the evaluated physical properties and did not induce cytotoxicity. In vitro drug release experiments showed that the IOLs provided controlled release of moxifloxacin for approximately 2 weeks. The drug remained active against the tested microorganisms during that period. Moxifloxacin-loaded IOLs and the control treatment induced similar in vivo behavior in terms of inflammatory reactions, capsular bag opacification scores, and uveal and capsule biocompatibility. The drug concentration in the aqueous humor after 1 week was similar in both groups; however, the concentration with the loaded IOLs was less variable. CONCLUSION: The moxifloxacin-loaded IOLs released the drug in a controlled manner, providing therapeutic levels.

Behaviour of wetting films of sodium hyaluronate saline solutions.

The behaviour of wetting films of sodium hyaluronate (NaHA) saline solutions, at physiological conditions, is investigated using interferometry. Concentrations in the range of dilute and semi-dilute regimes were chosen to assess the role of bulk molecular interactions on the surface forces. The transition from dilute to semi-dilute solutions is known to occur at c*=0.59 mg mL(-1). Dilute solutions form stable films whose behaviour is explained by van der Waals interactions. For semi-dilute solutions, the disjoining pressure vs film thickness isotherms show branches attributed to stepwise thinning or film stratification, which is interpreted in terms of a network as predicted by the theory of semi-dilute polyelectrolyte solutions. The distance between branches is 16 nm for the NaHA concentration of 2 mg mL(-1) and 12 nm for the concentration of 3.5 mg mL(-1), in agreement with the calculated correlation lengths of the polymeric network. Since no experimental evidence exists for the presence of a stable network in the bulk, this tendency for self-association should be the result of the liquid confinement. To our knowledge, the existence of oscillatory disjoining pressure isotherms in the presence of excess salt was never observed for other polyelectrolyte solutions.

Antibacterial layer-by-layer coatings to control drug release from soft contact lenses material.

In this study we investigated the possibility of using polyelectrolytes with antibacterial properties to form layer-by-layer (LbL) coatings on contact lens materials with the objective of controlling the release of ophthalmic drugs, while minimizing bacterial growth. A silicone-based hydrogel recently proposed by our group was chosen as a drug releasing soft contact lens (SCL) material and three drugs were tested: moxifloxacin hydrochloride (MXF), chlorhexidine diacetate monohydrate (CHX), and diclofenac sodium salt (DIC). Employed coatings involved combinations of sodium alginate (ALG), chitosan (CHI), sodium hyaluronate (HA) and polylysine hydrobromide (PLL), using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) as a cross-linking agent. Controlled release of DIC was achieved using two double layers of the following combinations: ALG/PLL (EDC), HA (EDC)/CHI and HA/PLL (EDC) + Drug. Furthermore, the physical properties of the coated lens material were kept, or even improved, and bacterial growth was reduced. In contrast, these coatings did not retard the release of MXF and CHX. The specificity of the barrier effect of these LbL films for DIC may be attributed to the formation of reversible interactions between DIC and the polyelectrolyte chains. A top layer of HA was needed to reduce the interaction with tear proteins. The in vivo efficacy of a contact lens coated with ALG/PLL (EDC)//HA and loaded with DIC was predicted using a simplified mathematical model to estimate the drug concentration in the tear fluid. The period of time during which the estimated concentration of DIC remained above the half-maximum inhibitory concentrations for the active enzymes in the process of inflammation, was at least double that obtained with the uncoated sample.

Contactless decontamination of hair samples: cannabinoids.

Room temperature ionic liquids (ILs) have already been shown to provide efficient extraction media for several systems, and to capture volatile compounds, namely opiates. In this work, a novel, contactless, artefact-free extraction procedure for the removal of Δ9 -tetrahrydrocannabinol (THC) from the surface of human hair is presented. To prepare in vitro cannabinoids-contaminated hair, samples were flushed with hashish smoke for 7 h. The decontamination experiments were carried at 100 °C for 24 h, according to the procedure previously described. Fifty-three ILs were screened and presented decontamination efficiencies ranging from 0 to 96 %. Although the majority of the ILs presented efficiencies above 90%, the 1-ethanol-3-methyl tetrafluoroborate (96%) was chosen for further process optimization. The Design of Experiments results demonstrated that all studied variables were significant for the process and the obtained optimum conditions were: 100 °C, 13 h and 175 mg of IL. In the work of Perrotin-Brunel et al. (J. Mol. Struct. 2011, 987, 67), it is demonstrated that, at 100 °C, full conversion of tetrahydrocannabinolic acid (THCA) into THC is obtained after 60 min. Since our decontamination takes place over 13 h at 100 °C, full conversion of THCA into THC is expected. Additionally, our method was compared with the method proposed by Cairns et al. (Forensic Sci. Int. 2004, 145, 97), through the analysis of 15 in vitro contaminated hair samples. The results demonstrated that with our method a mean extraction efficiency of 11 % higher was obtained. Copyright © 2016 John Wiley & Sons, Ltd.