Viscoelastic evaluation of topical creams containing microcrystalline cellulose/sodium carboxymethyl cellulose as stabilizer

The purpose of this study was to examine the viscoelastic properties of topical creams containing various concentrations of microcrystalline cellulose and sodium carboxymethyl cellulose (Avicel(R) CL-611) as a stabilizer. Avicel CL-611 was used at 4 different levels (1%, 2%, 4%, and 6% dispersion) to prepare topical creams, and hydrocortisone acetate was used as a model drug. The viscoelastic properties such as loss modulus (G"), storage modulus (G'), and loss tangent (tan delta) of these creams were measured using a TA Instruments AR 1000 Rheometer and compared to a commercially available formulation. Continuous flow test to determine the yield stress and thixotropic behavior, and dynamic mechanical tests for determining the linear viscosity time sweep data, were performed. Drug release from the various formulations was studied using an Enhancer TM Cell assembly. Formulations containing 1% and 2% Avicel CL-611 had relative viscosity, yield stress, and thixotropic values that were similar to those of the commercial formulation. The elastic modulus (G') of the 1% and 2% formulation was relatively high and did not cross the loss modulus (G"), indicating that the gels were strong. In the commercial formulation, G' increased after preshearing and broke down after 600 seconds. The strain sweep tests showed that for all formulations containing Avicel CL-611, the G' was above G" with a good distance between them. The gel strength and the predominance of G' can be ranked 6% > 4% > 2%. The strain profiles for the 1% and 2% formulations were similar to those of the commercial formulation. The delta values for the 1% and 2% formulations were similar, and the formulations containing 4% Avicel CL-611 had lower delta values, indicating greater elasticity. Drug release from the commercial preparation was fastest compared to the formulations prepared using Avicel CL-611, a correlation with the viscoelastic properties. It was found that viscoelastic data, especially the strain sweep profiles of products containing Avicel CL-611 1% and 2%, correlated with the commercial formulation. Rheological tests that measure the viscosity, yield stress, thixotropic behavior, other oscillatory parameters such as G' and G" are necessary tools in predicting performance of semisolids.     

Development of Novel Microemulsion-Based Topical Formulations of Acyclovir for the Treatment of Cutaneous Herpetic Infections

The present investigation aims at developing microemulsion-based formulations for topical delivery of acyclovir. Various microemulsions were developed using isopropyl myristate/Captex 355/Labrafac as an oil phase, Tween 20 as surfactant, Span 20 as cosurfactant, and water/dimethylsulfoxide (1:3) as an aqueous phase. Transcutol, eucalyptus oil, and peppermint oil were used as permeation enhancers. In vitro permeation studies through laca mice skin were performed using Franz diffusion cells. The optimum formulation containing 2.5% Transcutol as the penetration enhancer showed 1.7-fold enhancement in flux and permeation coefficient as compared to marketed cream and ointment formulation. In vivo antiviral studies were performed in female Balb/c mice against induced herpes simplex virus I infection. A single application of microemulsion formulation containing 2.5% Transcutol given 24 h post-injection resulted in complete suppression of development of herpetic skin lesions.     

Formulation,Characterization, and Clinical Evaluation of Microemulsion Containing Clotrimazole for Topical Delivery

The objective of the present study was to formulate and evaluate microemulsion systems for topical delivery of clotrimazole (CTM). The solubility of CTM in various oils was determined to select the oil phase of the microemulsion systems. Pseudoternary phase diagrams were constructed to identify the area of microemulsion existence. Five CTM microemulsion formulations (M1–M5) were prepared and evaluated for their thermodynamic stability, pH, refractive index, droplet size, viscosity, and in vitro release across cellulose membrane. Among the prepared microemulsion formulations, M3 (lemon oil/Tween 80/n-butanol/water) and M4 (isopropyl myristate/Tween 80/n-butanol/water) microemulsion systems were found to be promising according to their physical properties and CTM cumulative percentage release. Gel form of M3 and M4 were prepared using 1% Carbopol 940 as the hydrogel matrix. Both formulations were evaluated in the liquid and gel forms for drug retention in the skin in comparison to the marketed CTM topical cream and their stability examined after storage at 40°C for 6 months. Microemulsion formulations achieved significantly higher skin retention for CTM over the CTM cream. Stability studies showed that M4 preparations were more stable than M3. The in vitro anti-fungal activity of M4 against Candida albicans was higher than that of the conventional cream. Moreover, clinical evaluation proved the efficacy and tolerability of this preparation in the treatment of various topical fungal infections.     

Formulation of an effective mosquito-repellent topical product from Lemongrass oil

Ointment and cream formulations of lemongrass oil in different classes of base and the oil in liquid paraffin solution have been evaluated for mosquito repellency in a topical application. Mosquito repellency was tested by determining the bite-deterrence of product samples applied on an experimental bird's skin against a 2-day starved culture of Aedes aegypti L. mosquitoes. The 1%v/v solution and 15%v/w cream and ointment preparations of the oil exhibited > or =50% repellency lasting 2-3 h, which may be attributed to citral, a major oil constituent. This activity was comparable to that of a commercial mosquito repellent. Base properties of the lemongrass oil formulations influenced their effectiveness. The oil demonstrated efficacy from the different bases in the order of hydrophilic base > emulsion base > oleaginous base.     

Efficiency of Calamintha officinalis essential oil as preservative in two topical product types

AIMS: To verify the efficiency of Calamintha officinalis essential oil as natural preservative in two current formulations. METHODS AND RESULTS: The 1.0 and 2.0% (v/v) C. officinalis essential oil was assayed for its preservative activity in two product types (cream and shampoo). The microbial challenge test was performed following the standards proposed by the European Pharmacopoeia Commission (E.P.) concerning topical preparations using standard micro-organisms and in addition wild strains, either in single or mixed cultures were used. The results clearly demonstrated that the C. officinalis essential oil at 2.0% concentration reduced the microbial inoculum satisfying the criterion A of the E.P. in the cream formulation and the criterion B in the shampoo formulation. Standard and wild strains showed a behaviour similar, both in cream and in shampoo formulation, with no significant difference (gerarchic variance, P > 0.05). CONCLUSION: C. officinalis essential oil confirmed its preservative properties but at higher concentration than that shown in previous studies on cetomacrogol cream. SIGNIFICANCE AND IMPACT OF THE STUDY: The nature of the formulation in which an essential oil is incorporated as preservative could have considerable effect on its efficacy.     

Dynamics of the head-neck system in response to small perturbations: Analysis and modeling in the frequency domain

The response of the head-neck system to forces of small amplitude (up to 15 N) is described. Sinusoidal (0.6–20 Hz) and impulsive (duration: 100 msec) forces are applied in the sagittal plane to the head of the subject who is instructed to resist the disturbancy. In the case of sinusoidal forces of frequency less than about 2 Hz the active effort to resist the disturbancy results in a largely distorted sinusoidal displacement. Above this frequency the response becomes almost linear. The variations with frequency of the amplitude and the phase of the linear response relative to the applied force (transfer function) are used to characterize the dynamics of the system. The transfer functions evaluated from the impulse response are very similar in shape to those obtained with sinusoidal forces. In both cases the results suggest that the system behaves as a quasi-linear second order system with two degrees of freedom. The most prominent nonlinearities, beyond those present in the low frequency range, are related to the properties of the neck muscles. In particular, the transfer functions clearly show that the rigidity of the system increases as a function of the continuous value of the applied force. On the basis of previous work, both the passive properties of the muscles and those pertaining to the neuronal control system are pooled together in the form of viscoelastic parameters. A simple model of the system is introduced and applied to the experimental results. Its main features are 1) the presence of two centers of rotation. 2) the dependency of the viscoelastic parameters (stiffness and viscosity) on the frequency. It is suggested that both these features are necessary and sufficient to account for the observed behaviour above 2 Hz.     

Effects of Soy Proteins and Hydrolysates on Fat Globule Coalescence and Whipping Properties of Recombined Low-Fat Whipped Cream

The interaction and synergetic effect of soy protein isolate (SPI) and its hydrolysates with different concentrations of monoglycerides were explored at the air-water/oil interfaces in recombined low-fat whipped cream (20%). The creams were made with 20% palm oil, 18% carbohydrate, 0.22% stabilizers, and 0.25–1.00% monoglycerides. The proteins used were native soy protein isolate (NSPI), commercial soy protein isolate (CSPI), soy protein hydrolysates by pepsin (SPHPe), soy protein hydrolysates by papain (SPHPa), and SC (sodium caseinate). Overrun, stability, rheological behavior, and texture of recombined low-fat whipped cream were studied. Results indicated that increasing concentration of monoglycerides was effective in improving the textural, whipping properties, and stability of recombined low-fat whipped cream. Increasing concentration of monoglycerides in the mix prompted the displacement of adsorbed protein from fat globules, built up a firmer structure of fat aggregates, and stabilized the trapped air bubbles in the structure of recombined low-fat whipped cream. At the same level of monoglycerides, SPHPa whipped cream produced a similar overrun, stability, and texture as SC. Due to the high proportion of β-conglycinin in SPHPe, a low degree of fat globule partial coalescence occurred and led to low overrun and weakened structure in recombined low-fat whipped cream.

     

Microemulsion for topical delivery of fenoprofen calcium: in vitro and in vivo evaluation

The aim of this study was to investigate microemulsion (ME) based topical delivery system for fenoprofen calcium (FPCa) to eliminate its oral gastrointestinal adverse effects. ME was prepared by the water titration method using oleic acid as oil phase, tween 80 as a surfactant and propylene glycol as a cosurfactant. Oleic acid was selected as oil phase due to its good solubilizing capacity. ME existence region was determined using pseudo-ternary phase diagrams for preparing different formulations. Six different formulations were selected with various values of oil (25–68%), water (2–3%), and the mixture of surfactant and cosurfactant (1:1) (24–67%). The selected ME formulae were characterized for optical birefringence, transmission electron microscopy (TEM), pH, % transmittance, electronic conductivity, drug content, droplet size, rheological properties and stability evaluation. In vitro release study of FPCa from ME s through the synthetic membrane and hairless rat skin were evaluated. The optimized formula ME5 consisting of 5% w/w FPCa, 60% w/w oleic acid as oil phase, 3% w/w aqueous phase, and 32% w/w of surfactant phase containing Tween 80 and propylene glycol (1:?1) showed the highest transdermal flux and highest skin permeation rate. Finally, the % inhibition of carrageenan-induced rat paw edema of the optimized formula ME5 was highly significant (p?0.001) as compared to plain gel of FPCa. In conclusion, ME is a promising technique for topical delivery of FPCa.     

Microemulsion-based gel of terbinafine for the treatment of onychomycosis: optimization of formulation using D-optimal design

The aim of the present investigation was to evaluate microemulsion as a vehicle for dermal drug delivery and to develop microemulsion-based gel of terbinafine for the treatment of onychomycosis. D-optimal mixture experimental design was adopted to optimize the amount of oil (X ₁), Smix (mixture of surfactant and cosurfactant; X ₂) and water (X ₃) in the microemulsion. The formulations were assessed for globule size (in nanometers; Y ₁) and solubility of drug in microemulsion (in milligrams per milliliter; Y ₂). The microemulsion containing 5.75% oil, 53.75% surfactant–cosurfactant mixture and 40.5% water was selected as the optimized batch. The globule size and solubility of the optimized batch were 18.14 nm and 43.71 mg/ml, respectively. Transmission electron microscopy showed that globules were spherical in shape. Drug containing microemulsion was converted into gel employing 0.75% w/w carbopol 934P. The optimized gel showed better penetration and retention in the human cadaver skin as compared to the commercial cream. The cumulative amount of terbinafine permeated after 12 h was 244.65 ± 18.43 μg cm⁻² which was three times more than the selected commercial cream. Terbinafine microemulsion in the gel form showed better activity against Candida albicans and Trichophyton rubrum than the commercial cream. It was concluded that drug-loaded gel could be a promising formulation for effective treatment of onychomycosis.     

Physicochemical characterization of bioactive polyacrylic acid organogels as potential antimicrobial implants for the buccal cavity

This study describes the formulation and physicochemical characterization of poly(acrylic acid) (PAA) organogels, designed as bioactive implants for improved treatment of infectious diseases of the oral cavity. Organogels were formulated containing a range of concentrations of PAA (3-10% w/w) and metronidazole (2 or 5% w/w, representing a model antimicrobial agent) in different nonaqueous solvents, namely, glycerol (Gly), polyethylene glycol (PEG 400), or propylene glycol (PG). Characterization of the organogels was performed using flow rheometry, compressional analysis, oscillatory rheometry, in vitro mucoadhesion, moisture uptake, and drug release, methods that provide information pertaining to the nonclinical and clinical use of these systems. Increasing the concentration of PAA significantly increased the consistency, compressibility, storage modulus, loss modulus, dynamic viscosity, mucoadhesion, and the rate of drug release. These observations may be accredited to enhanced molecular polymer entanglement. In addition, the choice of solvent directly affected the physicochemical parameters of the organogels, with noticeable differences observed between the three solvents examined. These differences were accredited to the nature of the interaction of PAA with each solvent and, importantly, the density of the resultant physical cross-links. Good correlation was observed between the viscoelastic properties and drug release, with the exception of glycerol-based formulations containing 5 and 10% w/w PAA. This disparity was due to excessive swelling during the dissolution analysis. Ideally, formulations should exhibit controlled drug release, high viscoelasticity, and mucoadhesion, but should flow under minimal stresses. Based on these criteria, PEG 400-based organogels composed of 5% or 10% w/w PAA exhibited suitable physicochemical properties and are suggested to be a potentially interesting strategy for use as bioactive implants designed for use in the oral cavity.     

Formulation development and optimization using nanoemulsion technique: A technical note

Summary and Conclusion  Ramipril nanoemulsion formulations were successfully prepared by the spontaneous emulsification method (titration method). Sefsol 218 was selected as the oil phase for the development of the formulation on the basis of the solubility studies. The differences in the droplet size between the formulations selected from the phase diagram was not statistically significant, although the polydispersity was at a minimum for the formulation containing 20% oil, 27% Smix, and 53% vol/vol aqueous phase. The droplet size was found to be 34.5 nm. Therefore, nanoemulsion, a multipurpose technology, can be exploited in drug delivery for poorly soluble drugs. Nanoemulsions have a higher solubilization capacity than simple micellar solutions, and their thermodynamic stability offers advantages over unstable dispersions, such as emulsions and suspensions, because they can be manufactured with little energy input (heat or mixing) and have a long shelf life. This technical note explains the basis for calculation and construction of pseudoternary phase diagrams and, most important, explains selection of the formulations from the phase diagrams to avoid metastable formulations having minimum surfactant concentration in the least possible time. Published: April 6, 2007     

Precision of nanoindentation protocols for measurement of viscoelasticity in cortical and trabecular bone

Nanoindentation has recently gained attention as a characterization technique for mechanical properties of biological tissues, such as bone, on the sub-micron level. However, optimal methods to characterize viscoelastic properties of bones are yet to be established. This study aimed to compare the time-dependent viscoelastic properties of bone tissue obtained with different nanoindentation methods. Bovine cortical and trabecular bone samples (n=8) from the distal femur and proximal tibia were dehydrated, embedded and polished. The material properties determined using nanoindentation were hardness and reduced modulus, as well as time-dependent parameters based on creep, loading-rate, dissipated energy and semi-dynamic testing under load control. Each loading protocol was repeated 160 times and the reproducibility was assessed based on the coefficient of variation (CV). Additionally, three well-characterized polymers were tested and CV values were calculated for reference.The employed methods were able to characterize time-dependent viscoelastic properties of bone. However, their reproducibility varied highly (CV 9–40%). The creep constant increased with increasing dwell time. The reproducibility was best with a 30 s creep period (CV 18%). The dissipated energy was stable after three repeated load cycles, and the reproducibility improved with each cycle (CV 23%). The viscoelastic properties determined with semi-dynamic test increased with increase in frequency. These measurements were most reproducible at high frequencies (CV 9–10%). Our results indicate that several methods are feasible for the determination of viscoelastic properties of bone material. The high frequency semi-dynamic test showed the highest precision within the tested nanoindentation protocols.     

Nanostructured lipid carriers improve skin permeation and chemical stability of idebenone

Idebenone (IDB) is a synthetic antioxidant and analog of coenzyme Q10. The percutaneous permeation of IDB was investigated in guinea pig skin after application of different formulations. The enhancing effects of various formulations [nanostructured lipid carriers (NLCs), nanoemulsion (NE), or oil solution] on the permeation of IDB were evaluated using ex vivo guinea pig skins. Furthermore, stability of different formulations and in which chemical stability of IDB was determined during storage. Permeation experiments revealed that formulations varied in their ability to enhance the skin permeation of IDB. For NLC formulation, the cumulative amount of IDB in the epidermis, dermis, and acceptor medium of diffusion cells was approximately threefold more than NE or oil solution at the end of 24-h experiment. No significant difference between NE and oil solution was observed in the enhancement of penetration efficacy of IDB. Different formulations resulted in stability with different properties. NLC formulation revealed preferentially more stable than NE. The residual percentage of IDB loaded in NLCs, NE, and oil solution was 90.1%, 65.4%, and 51.3%, respectively, when stored at 40°C under 75% RH and 3,000 lx light conditions for 180 days. The results obtained here demonstrated that the abilities of NLCs to improve the chemical stability of IDB and enhance the skin permeation are much better than NE and oil solution. These suggest that NLCs containing IDB have significant potential use for skin care as an alternative topical formulation.     

Viscoelastic properties of single attached cells under compression

The viscoelastic properties of single, attached C2C12 myoblasts were measured using a recently developed cell loading device. The device allows global compression of an attached cell, while simultaneously measuring the associated forces. The viscoelastic properties were examined by performing a series of dynamic experiments over two frequency decades (0.1-10 Hz) and at a range of axial strains (approximately 10-40%). Confocal laser scanning microscopy was used to visualize the cell during these experiments. To analyze the experimentally obtained force-deformation curves, a nonlinear viscoelastic model was developed. The nonlinear viscoelastic model was able to describe the complete series of dynamic experiments using only a single set of parameters, yielding an elastic modulus of 2120 +/- 900 Pa for the elastic spring, an elastic modulus of 1960 +/- 1350 for the nonlinear spring, and a relaxation time constant of 0.3 +/- 0.12 s. To our knowledge, it is the first time that the global viscoelastic properties of attached cells have been quantified over such a wide range of strains. Furthermore, the experiments were performed under optimal environmental conditions and the results are, therefore, believed to reflect the viscoelastic mechanical behavior of cells, such as would be present in vivo.     

Gum cordia effectively enhances foliage adhesion of neem oil and increases its efficacy against aphids (Homoptera: Aphididae)

The efficiency of pesticides is greatly affected by their ability to adhere and retain on foliage surface. Neem oil, though a very well-known source of many biologically active pesticidal compounds, is very sensitive to environmental parameters, such as UV light. Also, due to volatilization, it is lost in environment and hence fail to reach target and show activity. In this study we attempted to stabilize neem oil emulsion and increase its retention on foliage surface by adding varying concentration of gum cordia. Gum cordia is an anionic polysaccharide derived from Cordia myxa fruits with strong adhesion and emulsification properties. The lethal concentration (LC₅₀) of the final formulations were also determined against aphid species Myzus persicae and Schizaphis graminum. Adhesion was found to be dependent on the concentration of gum cordia as well as type of crop. Increasing gum cordia in neem oil formulations resulted in increase in adhesion of the spray on the leaf surfaces and up to 6 times higher adhesion was observed with 0.5% gum cordia on mustard leaf compared to control. The LC₅₀ decreased with increasing gum cordia concentration. The LC₅₀ values of neem oil sprayed on mustard, spinach, and wheat leaves with 0.5% gum cordia were 0.205, 0.715, and 2.074% respectively while for neem oil control spray (with no gum cordia) LC₅₀ values were 1.833, 2.112, and 4.992% respectively for the above tested leaves. Presence of greater than 0.125% gum cordia in neem formulations provided the barrier against UV irradiation.     

Improved tensile strength of glycerol-plasticized gluten bioplastic containing hydrophobic liquids

The aim of the present work has been to study the influence of hydrophobic liquids on the morphology and the properties of thermo-molded plastics based on glycerol-plasticized wheat gluten (WG). While the total amount of castor oil and glycerol was remained constant at 30 wt%, castor oil with various proportions with respect to glycerol was incorporated with WG by mixing at room temperature and the resultant mixtures were thermo-molded at 120 degrees C to prepare sheet samples. Moisture absorption, morphology, dynamic mechanical properties, and tensile properties (Young's modulus, tensile strength and elongation at break) of the plastics were evaluated. Experimental results showed that the physical properties of WG plastic were closely related to glycerol to castor oil ratio. Increasing in castor oil content reduces the moisture absorption markedly, which is accompanied with a significant improvement in tensile strength and Young's modulus. These observations were further confirmed in 24 wt% glycerol-plasticized WG plastics containing 6 wt% silicone oil or polydimethylsiloxane (PDMS) liquid rubber.     

Development and Characterization of Sorbitan Monostearate and Sesame Oil-Based Organogels for Topical Delivery of Antimicrobials

The current study explains the development of sorbitan monostearate and sesame oil-based organogels for topical drug delivery. The organogels were prepared by dissolving sorbitan monostearate in sesame oil (70°C). Metronidazole was used as a model antimicrobial. The formulations were characterized using phase contrast microscopy, infrared spectroscopy, viscosity, mechanical test, and differential scanning calorimetry. Phase contrast microscopy showed the presence of needle-shaped crystals in the organogel matrix. The length of the crystals increased with the increase in the sorbitan monostearate concentration. XRD studies confirmed the amorphous nature of the organogels. Viscosity study demonstrated shear thinning behavior of the organogels. The viscosity and the mechanical properties of the organogels increased linearly with the increase in the sorbitan monostearate concentration. Stress relaxation study confirmed the viscoelastic nature of the organogels. The organogels were biocompatible. Metronidazole-loaded organogels were examined for their controlled release applications. The release of the drug followed zero-order release kinetics. The drug-loaded organogels showed almost similar antimicrobial activity against Escherichia coli when compared to the commercially available Metrogyl® gel. In gist, it can be proposed that the developed organogels had sufficient properties to be used for controlled delivery of drugs.

Electronic supplementary material

The online version of this article (doi:10.1208/s12249-014-0223-7) contains supplementary material, which is available to authorized users.KEY WORDS: organogel, phase contrast microscopy, sesame oil, sorbitan monostearate     

Exemestane Loaded Self-Microemulsifying Drug Delivery System (SMEDDS): Development and Optimization

The purpose of this research work was to formulate and characterize self-micro emulsifying drug delivery system containing exemestane. The solubility of exemestane was determined in various vehicles. Pseudo ternary phase diagram was used to evaluate the micro-emulsification existence area. SMEDDS formulations were tested for micro-emulsifying properties, and the resultant formulations loaded with exemestane (ME1, ME2, ME3, ME4 and ME5) were investigated for clarity, phase separation, globule size and shape, zeta potential, effect of various diluents and dilutions, thermodynamic and thermal stability. From the results it is concluded that increase in droplet size is proportional to the concentration of oil in SMEDDS formulation. Minor difference in the droplet size and zeta potential was observed by varying the diluents (deionized water and 0.1 N HCl) and dilutions (1:10, 1:50 and 1:100). Formulations, which were found to be thermodynamically stable (ME1, ME2, ME3 and ME4), were subjected to stability studies as per International Conference on Harmonization (ICH) guidelines. No significant variations were observed in the formulations over a period of 3 months at accelerated and long-term conditions. TEM photographs of microemulsions formulations further conformed the spherical shape of globules. Among the various SMEDDS formulations, ME4 offer the advantages of good clarity systems at high oil content and thus offer good solubilization of exemestane. Thus this study indicates that the SMEDDS can be used as a potential drug carrier for dissolution enhancement of exemestane and other lipophilic drug(s).     

Viscoelasticity of human alveolar epithelial cells subjected to stretch

Alveolar epithelial cells undergo stretching during breathing and mechanical ventilation. Stretch can modify cell viscoelastic properties, which may compromise the balance of forces in the alveolar epithelium. We studied the viscoelasticity of alveolar epithelial cells (A549) subjected to equibiaxial distention with a novel experimental approach. Cells were cultured on flexible substrates and subjected to stepwise deformations of up to 17% with a device built on an inverted microscope. Simultaneously, cell storage (G') and loss (G') moduli were measured (0.1-100 Hz) with optical magnetic twisting cytometry. G' and G' increased with strain up to 64 and 30%, respectively, resulting in a decrease in G'/G' (15%). This stretch-induced response was inhibited by disruption of the actin cytoskeleton with latrunculin A. G' increased with frequency following a power law with exponent alpha = 0.197. G' increased proportionally to G' but exhibited a more marked frequency dependence at high frequencies. Stretching (14%) caused a fall in alpha (13%). At high stretching amplitudes, actual cell strain (14.4%) was lower than the applied substrate strain (17.3%), which could indicate a partial cell detachment. These data suggest that cytoskeletal prestress modulates the elastic and frictional properties of alveolar epithelial cells in a coupled manner, according to soft glassy rheology. Stretch-induced cell stiffening could compromise the balance of forces at the cell-cell and cell-matrix adhesions.