Spray coverage analysis of topical sprays formed by cold thermoreversible hydrogels.

OBJECTIVE: Sprayable hydrogel formulations are promising topical treatments for skin wounds due to their ability to reduce application pain, prolong drug release, and provide moisture to promote skin healing. These viscoelastic materials, however, present challenges in spray ability which can be overcome using a thermoreversible hydrogels sprayed as lower viscosity liquids at cooler temperatures. The purpose of this research was to evaluate the impact of thermoreversible hydrogel formulation and device characteristics on topical spray patterns and to develop metrics to accurately describe surface coverage. METHODS: Cold solutions of Pluronic F127 were prepared at 15, 17, and 20% (w/w) and tested to determine their rheological properties. Formulations were sprayed from hand-held atomizing pump dispersers under cold conditions and two distinct areas of their spray patterns analyzed: the concentrated core and the full spray pattern. Traditional analysis of spray patterns was conducted to determine major and minor axes, ovality, and total area. In addition, new scripts were developed to evaluate the concentrated core. RESULTS: The full spray pattern analysis quantified the total area over which the spray would extend a flat surface, while the concentrated core analysis quantified the continuous region where a drug dose would be concentrated. The combination of formulation viscosity, sprayer nozzle, and spray distance produced spray patterns from highly concentrated to highly dispersed. These parameters can be controlled to generate desired hydrogel spray patterns for application on skin surfaces. CONCLUSION: The developed metrics provide a basis for topical spray analysis that can inform future product performance.

Sprayable ciprofloxacin-loaded poloxamer hydrogels for wound infection treatment.

Topical antimicrobial treatments for severe burns and chronic wounds provide effective treatment against infections, but cause pain and discomfort with application. This study aimed to develop an antimicrobial topical formulation comprising thermoreversible poloxamers (Pluronic F127 and F68) and a broad-spectrum antimicrobial agent (ciprofloxacin hydrochloride, CH), that could be sprayed to eliminate application pain while maintaining antimicrobial activity. Formulations were characterized to determine their sprayability under cold conditions, gelation temperature, final storage modulus at skin temperature, drug release profile, ex vivo permeation through impaired porcine skin, and inhibition against common bacterial pathogens that colonize wounds. All cold formulations were sprayable from simple hand-held, pump-action sprayers due to their low viscosity. Upon heating, 17 and 20% Pluronic F127 formulations produced hydrogels eight to ten degrees below skin temperature, independent of ciprofloxacin loading. Increasing concentrations of Pluronic F127 increased the final storage modulus and viscosity of the gels, while inclusion of Pluronic F68 reduced these properties, showing that hydrogel rheological properties at skin temperature can be tuned via choice of formulation. Drug release was directly correlated to the rheological properties, with stiffer gels resulting in a decrease in drug release rate. Overall, gels released about 65-90% of their load within 12 hours. Ex vivo skin permeation demonstrated that drug was well retained in impaired porcine skin, which is desired to continuously treat bacteria localized to the wound. A well-diffusion assay indicated that the hydrogels had greater bacterial inhibition against Pseudomonas aeruginosa, Escherichia coli, and two strains of Staphylococcus aureus when compared to commercial controls. Overall, the results show the potential of CH-loaded poloxamer formulations as suitable sprayable topical dressings to deliver antimicrobials directly to wounds.

Effect of Salt Form on Gelation and Drug Delivery Properties of Diclofenac-Loaded Poloxamer Gels for Delivery to Impaired Skin.

PURPOSE: Treating chronic wounds is a significant clinical challenge, and a topical product would be ideal for pain management. Poloxamer 407, a thermosensitive polymer, would allow an analgesic drug to be topically applied to a wound as a liquid that transitions to a gel at physiologic temperature. Using diclofenac as a model analgesic drug, our goal was to determine effects of salt form on poloxamer gelation and drug delivery from poloxamer gels applied to excised skin with impaired barrier function. METHODS: Gelation properties of 17% and 20% poloxamer gels loaded with 0.4 to 1.7% diclofenac sodium, potassium, epolamine, or diethylamine were evaluated rheologically. Drug release and delivery were quantified using cellulose membranes, porcine skin, and tape-stripped porcine skin. RESULTS: Poloxamer gelation temperature increased with higher diclofenac concentration, regardless of salt form; the magnitude of increase varied in the following order: sodium>potassium>diethylamine>epolamine. Gelation temperature differences resulting from the various counterions generally matched previously observed trends of ion-specific effects on macromolecule solubility (the Hofmeister series). Despite changes in gelation behavior, we observed minimal corresponding effects on drug release or delivery. There were no significant differences in diclofenac released or delivered through intact porcine skin over 48 h. However, in studies with impaired (tape-stripped) skin, diclofenac delivery was slowest overall with the epolamine salt. CONCLUSION: Varying the salt form of a model analgesic drug can impact gelation and drug delivery characteristics of poloxamer systems. Further study of the mechanisms of these changes will be important for continued development of topical poloxamer products for clinical wound care.

Surface rheological properties alter aerosol formation from mucus mimetic surfaces.

The effects of surface tension and surface viscoelastic properties on the formation of aerosol droplets generated from mucus-like viscoelastic gels (mucus mimetics) during shearing with a high velocity air stream were investigated. Mucus mimetic samples were formulated with similar composition (94% water and 6% dissolved solids, consisting of mucins, proteins, and ions), surface tension (via the addition of surfactant to the mimetic surface) and bulk viscoelastic properties (via crosslinking of mucin macromolecules in the mimetic) to that of native non-diseased tracheal mucus. The surface tension of the mucus mimetic was decreased by spreading one of two surfactants, dipalmitoyl phosphatidylcholine (DPPC) or calf lung surfactant (Infasurf®), on the mimetic surface. Aerosols were generated from the mimetic surfaces during simulated coughing using an enhanced simulated cough machine (ESCM) operating under controlled environmental conditions. The size distribution of aerosol droplets generated during simulated coughing from the surfactant-coated mimetic surfaces was multimodal, while no droplets were generated from the bare mimetic surface due to its high surface viscoelastic properties and high surface tension. The concentration of aerosols generated from the DPPC-coated mimetic was higher than that of the Infasurf®-coated mimetic, even though the surface tension of the two interfaces was the same. The experimental results suggest that a balance of surface elastic behavior and surface viscous behavior is required for the generation of aerosols from the viscoelastic surfaces.

Zwitterionic Polymer Coatings Enhance Gold Nanoparticle Stability and Uptake in Various Biological Environments.

Zwitterionic polymers are a class of materials that have demonstrated utility as non-fouling surfaces for medical devices and drug delivery vehicles. Here, we develop a synthesis protocol to produce zwitterionic polymers as coatings for gold nanoparticles and evaluate nanoparticle stability and biological function after exposure to various biological fluids. Thiol-functionalized polymethacryloyloxyethyl phosphorylcholine polymers (pMPC) were synthesized in nontoxic solvents via photoinitiated free radical polymerization with a radical addition-fragmentation chain transfer (RAFT) agent and coated onto gold nanoparticles. pMPC-coated nanoparticles exhibited reduced particle aggregation, improved suspension stability, and decreased protein adsorption upon exposure to serum and lung lavage fluid (BALF). Cell uptake in A549 cells was greater for pMPC-coated particles than uncoated particles after exposure to serum and BALF, with no observed cell toxicity, but pMPC-coated particles experienced higher levels of cell uptake after serum exposure than BALF exposure, suggesting that differences in the composition of the fluids result in differing impacts on particle fate. These zwitterionic polymers may serve as useful nanoparticle coatings to enhance particle stability and uptake in various biological environments.

Thermosensitive Gels Used to Improve Microneedle-Assisted Transdermal Delivery of Naltrexone.

Transdermal delivery of naltrexone (NTX) can be enhanced using microneedles, although micropores generated this way can reseal by 48 h in humans, which prevents further drug delivery from a formulation. Poloxamer 407 (P407) is a thermosensitive polymer that may extend microneedle-assisted NTX delivery time by creating an in situ gel depot in the skin. We characterized gelation temperature, drug release, and permeation of P407 gels containing 7% NTX-HCl. To investigate microneedle effects on NTX-HCl permeation, porcine skin was treated with microneedles (600 or 750 µm length), creating 50 or 100 micropores. The formulations were removed from the skin at 48 h to simulate the effect of micropores resealing in vivo, when drug delivery is blunted. Gelation temperature increased slightly with addition of NTX-HCl. In vitro NTX-HCl release from P407 formulations demonstrated first order release kinetics. Microneedle treatment enhanced NTX-HCl permeation both from aqueous solution controls and P407 gels. Steady-state flux was overall lower in the P407 conditions compared to the aqueous solution, though ratios of AUCs before and after gel removal demonstrate that P407 gels provide more sustained release even after gel removal. This may be beneficial for reducing the required application frequency of microneedles for ongoing treatment.

Rheological and Drug Delivery Characteristics of Poloxamer-Based Diclofenac Sodium Formulations for Chronic Wound Site Analgesia.

Chronic wounds are a significant and growing health problem, and clinical treatment is often a painful experience. A topical dosage form would be optimal to treat this pain. Poloxamer 407, a thermosensitive polymer that is a liquid at low temperatures but gels at higher temperatures, is well suited to administer topical analgesics to chronic wound sites. The goal of this study was to evaluate the gelation and drug delivery properties of poloxamer 407 gels containing diclofenac sodium for potential use in chronic wound analgesic delivery. The gelation properties of poloxamer formulations were evaluated rheologically. Drug delivery properties of poloxamers loaded with diclofenac sodium were evaluated using snakeskin dialysis membranes, intact porcine ear skin, and porcine ear skin impaired via tape stripping. A commercial gel product and a solution of diclofenac sodium in water were used as control formulations. Poloxamer concentration and gelation temperature varied inversely, and the addition of higher concentrations of diclofenac sodium correlated to significant increases in poloxamer gelation temperature. Poloxamer solutions were effective in limiting the permeation of diclofenac sodium through membranes with impaired barrier properties, and delivery of diclofenac sodium from poloxamer 407 did not vary significantly from delivery observed from the commercial gel product. The amount of drug delivered in 24 h did not change significantly with changes in poloxamer 407 concentration. The results of this study indicate that poloxamer 407 may be a useful formulation component for administration of an analgesic product to a chronic wound site.

Design and Characterization of Spray-Dried Chitosan-Naltrexone Microspheres for Microneedle-Assisted Transdermal Delivery.

Naltrexone (NTX) hydrochloride is a potent opioid antagonist with significant first-pass metabolism and notable untoward effects when administered orally or intramuscularly. Microneedle (MN)-assisted transdermal delivery is an attractive alternative that can improve therapeutic delivery to deeper skin layers. In this study, chitosan-NTX microspheres were developed via spray-drying, and their potential for transdermal NTX delivery in association with MN skin treatment was assessed. A quality-by-design approach was used to evaluate the impact of key input variables (chitosan molecular weight, concentration, chitosan-NTX ratio, and feed flow rate) on microsphere physical characteristics, encapsulation efficiency, and drug-loading capacity. Formulated microspheres had high encapsulation efficiencies (70%-87%), with drug-loading capacities ranging from 10%-43%. NTX flux through MN-treated skin was 11.6 ± 2.2 µg/cm2·h from chitosan-NTX microspheres, which was significantly higher than flux across intact skin. Combining MN-assisted delivery with the chitosan microsphere formulation enabled NTX delivery across the skin barrier, while controlling the dose released to the skin.

Lung cell exposure to secondary photochemical aerosols generated from OH oxidation of cyclic siloxanes.

To study the fate of cyclic volatile methyl siloxanes (cVMS) undergoing photooxidation in the environment and to assess the acute toxicity of inhaled secondary aerosols from cVMS, we used an oxidative flow reactor (OFR) to produce aerosols from oxidation of decamethylcyclopentasiloxane (D5). The aerosols produced from this process were characterized for size, shape, and chemical composition. We found that the OFR produced aerosols composed of silicon and oxygen, arranged in chain agglomerates, with primary particles of approximately 31 nm in diameter. Lung cells were exposed to the secondary organosilicon aerosols at estimated doses of 54-116 ng/cm2 using a Vitrocell air-liquid interface system, and organic gases and ozone exposure was minimized through a series of denuders. Siloxane aerosols were not found to be highly toxic.

The effect of salts in aqueous media on the formation of the BSA corona on SiO2 nanoparticles.

Protein-nanoparticle interactions are garnering attention due to their potential impacts on human health and environmental contamination. The colloidal properties of nanoparticles (NPs) in aqueous media may differ in the presence of natural materials such as salts and proteins. In this study, the interactions between bovine serum albumin (BSA) and fumed hydrophilic silicon dioxide (SiO2) NPs were studied in aqueous solutions under variable pH or ion composition. Investigation of hydrodynamic diameter and zeta potential changes to nanoparticles upon addition of BSA, the adsorption of BSA to the SiO2 NP surface, and the interaction energy between particles revealed that buffered solutions promote protein adsorption onto NPs and particle agglomeration. The effects of ionic salt solutions were dependent on the ion charge, with negatively charged ions stabilizing the system and positively charged ions promoting protein-nanoparticle interactions. These data highlight that physiologically relevant salts affect protein corona formation on non-toxic, amorphous SiO2 NPs and spur the need for well-defined characterization conditions when determining potential toxicity of NPs upon human or animal exposure.

Why inhaling salt water changes what we exhale.

We find that inhaling salt water diminishes subsequently exhaled biomaterial in man and animals due to reversible stabilization of the airway lining fluid (ALF)/air interface as a novel potential means for control of the spread of airborne infectious disease. The mechanism of this phenomenon relates to charge shielding of mucin or mucin-like macromolecules that consequently undergo gelation; this gelation alters the physical properties of the ALF surface and reduces its breakup. Cations in the nebulized solution and apparent surface viscoelasticity of the ALF (more than any other ALF intrinsic physical property) appear to be responsible for the reduced tendency of the ALF to disintegrate into very small droplets. We confirm these effects in vivo and show their reversibility through nebulization of saline solutions to anesthetized bull calves.

Bovine serum albumin adsorption on SiO2 and TiO2 nanoparticle surfaces at circumneutral and acidic pH: A tale of two nano-bio surface interactions.

The interaction of a model protein, bovine serum albumin (BSA) with two different metal oxide nanoparticles, TiO2 (∼22nm) and SiO2 (∼14nm), was studied at both physiological and acidic pH. The pH- and nanoparticle-dependent differences in protein structure and protein adsorption were determined using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and thermogravimetric analysis (TGA). The results indicated that the surface coverage of BSA decreases with decreasing pH on both TiO2 and SiO2 surfaces, and BSA coverage is higher by a factor of ca. 3-10times more on TiO2 compared to SiO2. The secondary structure of BSA changes upon adsorption to either nanoparticle surface at both pH 7.4 and 2. At acidic pH, BSA appears to completely unfold on TiO2 nanoparticles whereas it assumes an extended conformation on SiO2. These differences highlight for the first time the extent to which the protein corona structure is significantly impacted by protein-nanoparticle interactions which depend on the interplay between pH and specific nanoparticle surface chemistry.

Adsorption of bovine serum albumin on silicon dioxide nanoparticles: Impact of pH on nanoparticle-protein interactions.

Bovine serum albumin (BSA) adsorbed on amorphous silicon dioxide (SiO2) nanoparticles was studied as a function of pH across the range of 2 to 8. Aggregation, surface charge, surface coverage, and protein structure were investigated over this entire pH range. SiO2 nanoparticle aggregation is found to depend upon pH and differs in the presence of adsorbed BSA. For SiO2 nanoparticles truncated with hydroxyl groups, the largest aggregates were observed at pH 3, close to the isoelectric point of SiO2 nanoparticles, whereas for SiO2 nanoparticles with adsorbed BSA, the aggregate size was the greatest at pH 3.7, close to the isoelectric point of the BSA-SiO2 complex. Surface coverage of BSA was also the greatest at the isoelectric point of the BSA-SiO2 complex with a value of ca. 3 ± 1 × 1011 molecules cm-2. Furthermore, the secondary protein structure was modified when compared to the solution phase at all pH values, but the most significant differences were seen at pH 7.4 and below. It is concluded that protein-nanoparticle interactions vary with solution pH, which may have implications for nanoparticles in different biological fluids (e.g., blood, stomach, and lungs).

Airborne infectious disease and the suppression of pulmonary bioaerosols.

The current understanding of airborne pathogen spread in relation to the new methods of suppressing exhaled bioaerosols using safe surface-active materials, such as isotonic saline, is reviewed here. We discuss the physics of bioaerosol generation in the lungs, what is currently known about the relationship between expired bioaerosols and airborne infectious disease and current methods of airborne infectious disease containment. We conclude by reviewing recent experiments that suggest the delivery of isotonic saline can significantly diminish exhaled aerosol--generated from airway lining fluid in the course of natural breathing. We also discuss these implications in relation to airborne infectious disease control.

Large Porous Hollow Particles: Lightweight Champions of Pulmonary Drug Delivery.

The deep lungs provide an efficient pathway for drugs to transport into the systemic circulation, as the extremely large surface area and thin epithelial membrane enable rapid drug transport to the blood stream. To penetrate into the deep lungs, aerosol particles with aerodynamic diameters of 1-3 µm are optimal. Large porous hollow particles (LPHPs) can achieve this aerodynamic size range through enhanced porosity within the particles (typically < 0.4 g/cm(3)), which aerodynamically balances the large particle size (> 5 µm, up to 30 µm). The physical properties of these particles provide some key advantages compared to their small, nonporous counterparts through enhanced dispersibility, efficient deep lung deposition, and avoidance of phagocytic clearance. This review highlights the potential of LPHPs in pulmonary delivery of systemic drugs, with a focus on their critical attributes and key formulation aspects. In addition, three examples of LPHPs under development are presented to emphasize the potential of this technology to treat systemic diseases.

Tensiometric and Phase Domain Behavior of Lung Surfactant on Mucus-like Viscoelastic Hydrogels.

Lung surfactant has been observed at all surfaces of the airway lining fluids and is an important contributor to normal lung function. In the conducting airways, the surfactant film lies atop a viscoelastic mucus gel. In this work, we report on the characterization of the tensiometric and phase domain behavior of lung surfactant at the air-liquid interface of mucus-like viscoelastic gels. Poly(acrylic acid) hydrogels were formulated to serve as a model mucus with bulk rheological properties that matched those of tracheobronchial mucus secretions. Infasurf (Calfactant), a commercially available pulmonary surfactant derived from calf lung extract, was spread onto the hydrogel surface. The surface tension lowering ability and relaxation of Infasurf films on the hydrogels was quantified and compared to Infasurf behavior on an aqueous subphase. Infasurf phase domains during surface compression were characterized by fluorescence microscopy and phase shifting interferometry. We observed that increasing the bulk viscoelastic properties of the model mucus hydrogels reduced the ability of Infasurf films to lower surface tension and inhibited film relaxation. A shift in the formation of Infasurf condensed phase domains from smaller, more spherical domains to large, agglomerated, multilayer structures was observed with increasing viscoelastic properties of the subphase. These studies demonstrate that the surface behavior of lung surfactant on viscoelastic surfaces, such as those found in the conducting airways, differs significantly from aqueous, surfactant-laden systems.

Calf Lung Surfactant Recovers Surface Functionality After Exposure to Aerosols Containing Polymeric Particles.

BACKGROUND: Recent studies have shown that colloidal particles can disrupt the interfacial properties of lung surfactant and thus key functional abilities of lung surfactant. However, the mechanisms underlying the interactions between aerosols and surfactant films remain poorly understood, as our ability to expose films to particles via the aerosol route has been limited. The aim of this study was to develop a method to reproducibly apply aerosols with a quantifiable particle dose on lung surfactant films and investigate particle-induced changes to the interfacial properties of the surfactant under conditions that more closely mimic those in vivo. METHODS: Films of DPPC and Infasurf® were exposed to aerosols containing polystyrene particles generated using a Dry Powder Insufflator™. The dose of particles deposited on surfactant films was determined via light absorbance. The interfacial properties of the surfactant were studied using a Langmuir-Wilhelmy balance during surfactant compression to film collapse and cycles of surface compression and expansion at a fast cycling rate within a small surface area range. RESULTS: Exposure of surfactant films to aerosols led to reproducible dosing of particles on the films. In film collapse experiments, particle deposition led to slight changes in collapse surface pressure and surface area of both surfactants. However, longer interaction times between particles and Infasurf® films resulted in time-dependent inhibition of surfactant function. When limited to lung relevant surface pressures, particles reduced the maximum surface pressure that could be achieved. This inhibitory effect persisted for all compression-expansion cycles in DPPC, but normal surfactant behavior was restored in Infasurf® films after five cycles. CONCLUSIONS: The observation that Infasurf® was able to quickly restore its function after exposure to aerosols under conditions that better mimicked those in vivo suggests that particle-induced surfactant inhibition is unlikely to occur in vivo due to an aerosol exposure.

Wetting of a particle in a thin film.

When a particle is placed in a thin liquid film on a planar substrate, the liquid either climbs or descends the particle surface to satisfy its wetting boundary condition. Analytical solutions for the film shape, the degree of particle immersion, and the downward force exerted by the wetting meniscus on the particle are presented in the limit of small Bond number. When line tension is significant, multiple solutions for the equilibrium meniscus position emerge. When the substrate is unyielding, a dewetting transition is predicted; that is, it is energetically favorable for the particle to rest on top of the film rather than remain immersed in it. If the substrate can bend, the energy to drive this bending is found in the limits of slow or rapid solid deflection. These results are significant in a wide array of disciplines, including controlled delivery of drugs to pulmonary airways, the probing of liquid film/particle interface properties using particles affixed to AFM tips and the positioning of small particles in thin films to create patterned media.

New polymeric carriers for controlled drug delivery following inhalation or injection.

Inhalation is gaining increasing acceptance as a convenient, reproducible, and non-invasive method of drug delivery to the lung tissue and/or the systemic circulation. However, sustained drug release following inhalation remains elusive, due in part to the lack of appropriate materials designed specifically for use in the lungs to control the release of bioactive compounds. To address this problem, we have synthesized a new family of ether-anhydride copolymers composed entirely of FDA-approved monomers, including polyethylene glycol (PEG). Sebacic acid, a hydrophobic monomer, was copolymerized with PEG in order to produce water-insoluble polymers capable of providing continuous drug release kinetics following immersion in an aqueous environment. Various amounts of PEG (5-50% by mass) were incorporated into the backbone of the new polymers to allow tuning of particle surface properties for potentially enhanced aerosolization efficiency and to decrease particle clearance rates by phagocytosis in the deep lung. The preparation of large porous particles with these new polymers was systematically approached, utilizing central composite design, to develop improved particle physical properties for deep lung delivery. Microparticles containing model drugs were made with sizes suitable for deposition in various regions of the lung following inhalation as a dry powder. Due to such properties as surface erosion (leading to continuous drug release profiles), erosion times ranging from hours to days (allowing control over drug delivery duration), and ability to incorporate up to 50% PEG in their backbone, these new systems may also find application as "stealth" carriers for therapeutic compounds following intravenous injection.

Poly(ether-anhydride) dry powder aerosols for sustained drug delivery in the lungs.

A new family of biodegradable ether-anhydride polymers was used to develop microparticles capable of controlled drug release and inhalation as a dry powder. The polymers are composed of various ratios of sebacic acid (SA) (to render the polymer insoluble in water) and poly(ethylene glycol) (PEG) (to reduce particle clearance by macrophages and improve aerosolization). Particle aerodynamic diameter was controlled within the respirable range by producing geometrically large, but low density particles as a first step toward reducing particle adhesion forces that limit efficient aerosolization of dry powders. Particles made from a variety of polymer compositions possessed high emitted doses (>80%) from a Spinhaler dry powder inhaler (DPI). Control over particle surface and bulk properties (surface roughness, surface charge, density and water retention) was achieved by varying the percentage of PEG in the polymer backbone. The addition of 10% PEG into the polymer backbone significantly enhanced deposition in the lower stages of an in vitro lung model following aerosolization from the DPI (fine particle fractions [FPF] reached 30%). Efficient aerosolization from an obsolete DPI combined with the ability to evade phagocytic clearance and provide controlled release of various drug molecules make these particles promising for prolonged drug delivery in the lung.