Permeability Of Gels Research Articles

Pore-scale prediction of the effective mass diffusivity and apparent permeability of carbon gels with adjustable nanoporous characteristics

To explore the structural effects on transport properties in carbon gels, an improved method has been introduced to regenerate their nanostructure and numerically illustrate the adjustability of their porous characteristics with the variation of synthesis parameters. Two lattice Boltzmann equations are applied to investigate the permeation and diffusion in the gel structures at the pore scale, and the apparent permeability is formulated to describe the total mass flux using the dusty gas model. The structural properties of the reconstructed models and calculated apparent permeabilities have been fully validated by various experiments. A decoupled analysis of the impact of structural parameters on transport properties demonstrates that increasing porosity and pore size, while decreasing geometric tortuosity, leads to more pronounced changes in intrinsic permeability compared to gas diffusivity. By utilizing a database that encompasses 240 reconstructed gels, a structural–functional relationship for transport properties in carbon gels could be proposed. Concerning the intrinsic permeability, a near quadratic relationship with the porosity and mean pore size, independent of particle size, could be concluded. For the nondimensional effective diffusivity, a power exponent of 1.85 associated with porosity is proposed, and its independence of pore size could be revealed. In addition, for gels with porosities under 0.65 and mean pore sizes less than 133 nm, diffusion supersedes permeation as the dominant term in total mass transfer, indicating that particle sizes have a more pronounced influence on the apparent permeability. The predictive model offers guidance for tailoring the transfer properties of carbon gels at the stage of preparation.

Asymmetry of tensile versus compressive elasticity and permeability contributes to the regulation of exchanges in collagen gels.

The Starling principle describes exchanges between blood and tissues based on the balance of hydrostatic and osmotic flows. However, the permeation properties of the main constituent of tissues, namely, collagen, in response to the stress exerted by blood pressure remain poorly characterized. Here, we develop an instrument to determine the elasticity and permeability of collagen gels under tensile and compressive stress based on measuring the temporal change in pressure in an air cavity sealed at the outlet of a collagen slab. Data analysis with an analytical model reveals a drop in the permeability and enhanced strain stiffening of native collagen gels under compression versus tension, both effects being essentially lost after chemical cross-linking. Furthermore, we report the control of the permeability of native collagen gels using sinusoidal fluid injection, an effect explained by the asymmetric response in tension and compression. We lastly suggest that blood-associated pulsations could contribute to exchanges within tissues.

Gelatin-Based Colloidal Versus Monolithic Gels to Regulate Macrophage-Mediated Inflammatory Response.

Unlike conventional monolithic hydrogels with covalent cross-linkage that are typically elastic, colloidal gels assembled by reversibly assembled particles as building blocks have shown fascinating viscoelastic properties. They follow a gel-sol transition upon yielding and recover to the initial state upon the release of the shear force (so-called shear-thinning and self-healing behavior); this makes them an ideal candidate as injectable and moldable biomaterials for tissue regeneration. The immune response provoked by the implantation of the colloidal gels with special viscoelastic and structural features is critical for the successful integration of the implants with the host tissues, which, however, remains little explored. Since macrophages are known as the primary immune cells in determining the inflammatory response against the implants, we herein investigated in vitro macrophage polarization and in vivo inflammatory response induced by gelatin-based colloidal gels as compared to monolithic gels. Specifically, self-healing colloidal gels composed of pure gelatin nanoparticles, or methacrylate gelatin (GelMA) nanoparticles to allow secondary covalent cross-linkage were compared with GelMA bulk hydrogels. We demonstrated that hydrogel's elasticity plays a more dominant role rather than the structural feature in determining in vitro macrophage polarization evidenced by the stiffer gels inducing pro-inflammation M2 macrophage phenotype as compared to soft gels. However, subcutaneous implantation revealed a significantly alleviated immune response characterized by less fibrous capsule formation for the colloidal gels as compared to bulk gels of similar matrix elasticity. We speculated this can be related to the improved permeability of the colloidal gels for cell penetration, thereby leading to less fibrosis. In general, this study provided in-depth insight into the biophysical regulator of hydrogel materials on macrophage behavior and related inflammatory response, which can further direct future implant design and predict biomaterial-host interactions for immunotherapy and regenerative medicine. Impact statement Macrophages response to implanted biomaterials is a highly regulated process that influences device functionality and clinical outcome. Nowadays, the viscoelastic properties of colloidal versus monolithic hydrogels on macrophage phenotype in vitro and the host inflammatory response are not known. Our study found that colloidal hydrogels composed of nanoparticles of gelatin and methacrylate gelatin (GelMA) led to more anti-inflammatory polarization especially on soft colloidal gel (5.9 KPa) compared to bulk GelMA hydrogels. It suggested that macrophage response can be mechanically regulated by the viscoelastic signals of the hydrogels, which could be a promising strategy for the future design and application of novel biomaterials.

Computational and experimental comparison on the effects of flow-induced compression on the permeability of collagen gels

Collagen is a naturally occurring polymer and is popular in tissue engineering due to its high biocompatibility, ubiquity throughout the body, and its porous nature. The transport properties of collagen help dictate the delivery of nutrients to tissues, and the mechanical properties can help improve the function of engineered tissues. The objective of this study is to investigate experimentally the change in permeability as collagen gels undergo flow-induced compression and compare these results with model predictions using a finite element model. We developed a horizontal apparatus to measure the hydraulic permeability of collagen gels undergoing flow-induced compression. The permeability of 1.98 mg/mL, 3.5 mg/mL, and 5 mg/mL collagen Type I rat tail hydrogels were determined experimentally by tracking the pressure drop across the gels as water flowed through the samples, which simultaneously compressed them under pressure. The Holmes-Mow model was used to fit the permeability as the gels underwent compression. A finite element model was created using FEBio to estimate the Young's modulus of collagen gels at the macroscopic level by fitting the experimental pressure vs. the compressive stretch ratio to the model. Our results suggest that the initial permeability of collagen gels decreased with increasing concentration, as expected. However, gels with a lower initial concentration compressed to a greater degree, resulting in smaller final permeabilities once fully compressed. Taken together, our work suggests that the treatment of a collagen gel as an isotropic, elastic material is sufficient to model its transport properties on a macroscopic level but is inadequate if more localized transport properties, which are dependent on network architecture (such as collagen alignment or inhomogeneous densification), are required.

Dynamics-based assessment of nanoscopic polymer-network mesh structures and their defects.

Polymer-network gels often exhibit complex nanoscopic architectures. First, the polymer-network mesh topology on scales of 1-10 nm is usually not uniform and regular, but disordered and irregular. Second, on top of that, many swollen polymer networks display spatial inhomogeneity of their polymer segmental density and crosslinking density on scales of 10-100 nm. This multi-scale structural complexity affects the permeability, mechanical strength, and optical clarity of the polymer gels, which is of central relevance for their performance in popular applications. As a result, there is a need to characterize the polymer network structures on multiple scales. On the scale of the spatial inhomogeneity of crosslinking, 10-100 nm, scattering of neutrons, X-rays, and light has extraordinary utility and is well established. On the scale of the mesh topology, 1-10 nm, in contrast, experimental techniques are less established. This review intends to close this gap by reviewing two intrinsically dynamic methods that yield information on polymer network mesh structures. First, NMR-based assessment of residual dipolar proton-spin couplings, which arise upon the introduction of crosslinks into a liquidlike polymer system to impart partial solidlike characteristics, is suitable to quantitatively assess network meshes and local network defects. Second, diffusive penetration of molecular, macromolecular, and mesoscopic colloidal probes through a polymer gel provides insight into its obstructing network mesh structure and its potential irregularity. Either method is highly synergistic to scattering-based assessment of the network structures on larger scales, and in concert, a rich picture on the nano- and mesoscopic gel topology is obtained.

Experimental work to determine the effect of load pressure on the gel pack permeability of strong and weak preformed particle gels

Preformed particle gels (PPGs) have been widely applied to reduce the permeability of super-high permeability streaks/fractures. PPGs have an ability to decrease water production and increase sweep efficiency in mature oilfields. Either the success or failure of a PPG treatment depends largely on whether or not PPGs can effectively reduce the permeability of the fluid channels to an anticipated level. This work sought to investigate the influence of several factors on PPG blocking efficiency. A filtration model was designed to determine the permeability of PPGs packed in channels/fractures. Two types of PPGs were used for these filtration experiments: Daqing (DQ) and LiquiBlock™ 40K. Particle sizes fell between 30 and 120 meshes. Results indicate PPG permeability decreased as load pressure increased. Additionally, PPGs with a larger particle size exhibited higher PPG pack permeability than PPGs with a smaller particle size. The PPG permeability with a lower brine concentration was more than the PPG pack permeability with a higher brine concentration when the PPG pack was not compressed by a piston. However, PPG pack permeability was less when using a lower brine concentration whether the PPG pack was compressed because the PPGs with higher brine concentration loss more water than the PPGs with the lower brine concentrations. According to our paper results the optimum gel pack with a preferred permeability can be designed by the right selection of the gel strength and correct particle size at reservoir pressure.

Permeability of gels is set by the impulse applied on the gel

To better understand sensory perception of foods, water exudation studies on protein-based gels are of a high importance. It was aimed to study the interplay of gel coarseness and gel stiffness on water holding (WH) and water flow kinetics from the gel once force is applied onto the material. Ovalbumin heat-set gels were used as a model system, where protein volume fraction was kept constant and ionic strength was varied to obtain a range of different gel morphologies and stiffness. WH of gels was measured both as a function of time and force applied. From experimental data (i) an effective gel permeability coefficient and (ii) an effective water flux coefficient were obtained and related to gel coarseness and stiffness. Gel coarseness determined maximum amount of water removed from the gel at defined conditions, where lower (≤0.1 μm) and upper (≥0.4 μm) limiting scales for water removal were identified. Gel stiffness is the major determinant for water removal kinetics from the gel. The combination of gel coarseness and gel stiffness showed a cooperative effect on gel WH. The insights can be exploited in product development to predict and tune oral perception properties of (new) products.

Nanostructural heterogeneity in polymer networks and gels

Many polymer gels display network defects and crosslinking inhomogeneity. This review reflects and interrelates investigations on the characterization of such polymer-network heterogeneity and on its impact on the swelling, elasticity, and permeability of polymer gels.

Effect of whey protein aggregates of various sizes on the formation and properties of rennet-induced milk gels

Whey protein (WP) aggregates that ranged in diameter from 41 to 299 nm but had the same composition were produced by varying the protein concentration at heating at neutral pH and low ionic strength, followed by dilution. The effect of WP aggregates on the formation and properties of rennet-induced milk gels were evaluated. Whey protein aggregates had no effect on the kinetics of caseinomacropeptide release during renneting but significantly affected the clotting of casein micelles and the properties of milk gels. The maximum clotting rate and the strength of rennet-induced milk gels decreased as the dose of WP aggregates added to milk increased. However, WP aggregates with larger diameter and higher voluminosity had a less detrimental effect on milk clotting than smaller aggregates did. The higher surface hydrophobicity and faster diffusion of smaller WP aggregates could have been responsible for adsorption onto renneted casein micelles, which reduced milk clotting rate and gel strength. The permeability of rennet-induced milk gels decreased as the dose of WP aggregates added to milk increased, but the protein concentration at heating had no effect. Whey protein aggregates reduced the contraction capacity of the gels during cooking (42 °C). Drained curd mass fraction and curd moisture increased as the dose of added WP aggregates increased and were affected less by larger WP aggregates. The results of this study suggest that small WP aggregates (<100 nm) interact with casein micelles and interfere with rennet gel formation and contraction.

The Hydraulic Permeability of Blood Clots as a Function of Fibrin and Platelet Density

Interstitial fluid flow within blood clots is a biophysical mechanism that regulates clot growth and dissolution. Assuming that a clot can be modeled as a porous medium, the physical property that dictates interstitial fluid flow is the hydraulic permeability. The objective of this study was to bound the possible values of the hydraulic permeability in clots formed in vivo and present relationships that can be used to estimate clot permeability as a function of composition. A series of clots with known densities of fibrin and platelets, the two major components of a clot, were formed under static conditions. The permeability was calculated by measuring the interstitial fluid velocity through the clots at a constant pressure gradient. Fibrin gels formed with a fiber volume fraction of 0.02–0.54 had permeabilities of 1.2 × 10−1–1.5 × 10−4μm2. Platelet-rich clots with a platelet volume fraction of 0.01–0.61 and a fibrin volume fraction of 0.03 had permeabilities over a range of 1.1 × 10−2–1.5 × 10−5μm2. The permeability of fibrin gels and of clots with platelet volume fraction of <0.2 were modeled as an array of disordered cylinders with uniform diameters. Clots with a platelet volume fraction of >0.2 were modeled as a Brinkman medium of coarse solids (platelets) embedded in a mesh of fine fibers (fibrin). Our data suggest that the permeability of clots formed in vivo can vary by up to five orders of magnitude, with pore sizes that range from 4 to 350 nm. These findings have important implications for the transport of coagulation zymogens/enzymes in the interstitial spaces during clot formation, as well as the design of fibrinolytic drug delivery strategies.

Rheological properties and permeability of soy protein-stabilised emulsion gels made by acidification with glucono-δ-lactone

Soy protein, an important efficient emulsifier, is widely used by the food industry for incorporation into milk, yogurts, ice cream, salad dressings, dessert products, etc. The objective of this study was to investigate the rheological and physical properties of soy protein-stabilised emulsion gels as affected by protein concentration and gelation temperature. The rheological properties and permeability were determined using oscillatory rheometry, permeability and whey separation. The modulus (G' and G″), fracture stress and fracture strain of acid-induced emulsion gels after 20 h of glucono-δ-lactone addition depended strongly on soy protein concentration and gelation temperature. At increasing soy protein concentrations, acid-induced emulsion gels had shorter gelation times but higher storage moduli (G'), fracture stresses and strains. Increasing gelation temperature decreased the gelation time, G', fracture stresses and strains. Permeability and whey separation were significantly affected by the protein concentration and the gelation temperature. A significant positive correlation was observed between whey separation and permeability coefficient in emulsion gels formed at different temperatures. The rheological properties and permeability of soy protein-stabilised emulsion gels were significantly influenced by protein concentration and gelation temperature.

Effect of Fortification with Various Types of Milk Proteins on the Rheological Properties and Permeability of Nonfat Set Yogurt

Yogurt base was prepared from reconstituted skim milk powder (SMP) with 2.5% protein and fortified with additional 1% protein (wt/wt) from 4 different milk protein sources: SMP, milk protein isolate (MPI), micellar casein (MC), and sodium caseinate (NaCN). Heat-treated yogurt mixes were fermented at 40 degrees C with a commercial yogurt culture until pH 4.6. During fermentation pH was monitored, and storage modulus (G') and loss tangent (LT) were measured using dynamic oscillatory rheology. Yield stress (sigma(yield)) and permeability of gels were analyzed at pH 4.6. Addition of NaCN significantly reduced buffering capacity of yogurt mix by apparently solubilizing part of the indigenous colloidal calcium phosphate (CCP) in reconstituted SMP. Use of different types of milk protein did not affect pH development except for MC, which had the slowest fermentation due to its very high buffering. NaCN-fortified yogurt had the highest G' and sigma(yield) values at pH 4.6, as well as maximum LT values. Partial removal of CCP by NaCN before fermentation may have increased rearrangements in yogurt gel. Soluble casein molecules in NaCN-fortified milks may have helped to increase G' and LT values of yogurt gels by increasing the number of cross-links between strands. Use of MC increased the CCP content but resulted in low G' and sigma(yield) at pH 4.6, high LT and high permeability. The G' value at pH 4.6 of yogurts increased in the order: SMP = MC < MPI < NaCN. Type of milk protein used to standardize the protein content had a significant impact on physical properties of yogurt. Practical Application: In yogurt processing, it is common to add additional milk solids to improve viscosity and textural attributes. There are many different types of milk protein powders that could potentially be used for fortification purposes. This study suggests that the type of milk protein used for fortification impacts yogurt properties and sodium caseinate gave the best textural results.

Optical responses, permeability and diol-specific reactivity of thin polyacrylamide gels containing immobilized phenylboronic acid

Thin semitransparent gels were prepared by radical copolymerization of N-acryloyl-m-aminophenylboronic acid (NAAPBA) and acrylamide (AAm) taken in molar ratios from 8:92 to 16:84, respectively, in water. The gels were characterized by the content of immobilized NAAPBA and monomer conversion. Scanning electron microscopy revealed the micrometer size pores in the dried gels. The wet gels displayed a linear optical response to sugars with sensitivity decreasing in the series: d-fructose, d-galactose, d-glucose, d-mannose, N-acetyl-d-glucosamine in the sugar concentration range from 1 to 40–60mM at pH 7.3. Cross-linking of the gels with N,N-methylene-bis-acrylamide decreased the strength of optical response. Specific binding capacity of a diol-containing dye Alizarin Red S in the gels at pH 7.0 coincided with the content of immobilized NAAPBA indicating the 1:1 stoichiometry of the reaction and, therefore, good accessibility of the boronic acid ligands for water-soluble diols. Permeability of the gels was studied with a non-interacting dye Ethyl Orange exhibiting the pore diffusion coefficient of 1.4×10−7cm2/s. The rate of optical response of the gels to glucose was found to be determined by diffusion of sugar into the relatively thick gels (l=0.35–1mm) with effective diffusion coefficients of 2×10−7cm2/s. In the thinner gels (l=0.1mm) the input of other kinetic processes, such as affinity binding or structural rearrangements of the gel, was noticeable.

Effects of penetration enhancers on in vitro permeability of meloxicam gels

Meloxicam (MLX) was formulated as a 0.3% hydroxypropylcellulose (Klucel ®) gel. The effect of four different combinations of co-solvents (ethanol, glycol-PEG-400, propylene glycol, and water) on MLX permeability was determined in vitro throughout isopropyl myristate (IPM)-saturated cellulose membranes. The gel consisting of 2.5% Klucel, propylene glycol, ethanol, and water (1:1:1) showed superior permeability properties and it was selected as the base-gel to investigate the effect of three levels of the penetration enhancers: dimethylsulfoxide (1, 5, and 10% DMSO), tween20 (1, 2, and 5% TW20), oleic acid (0.4, 1, and 5% OA), and menthol (1, 2.5, and 5% MT). In vitro permeability was determined throughout IPM-saturated cellulose membranes and human cadaver skin. DMSO and TW20 did not improve permeability of MLX compared to the control gel at any of the levels tested. Menthol produced a statistically significant ( P < 0.001), dose proportional increase in MLX flux with a peak at 5% (2.43 ± 0.47 μg/cm 2/h). Conversely, addition of OA peaked at 1% but decreased at the higher level (5%). There was no significant difference between the MLX amount recovered in stratum corneum and dermis across the different formulations tested. These findings show that the 0.3% MLX gel formulation containing 5% menthol can possibly deliver therapeutically relevant doses of MLX.

A contact mechanics method for characterizing the elastic properties and permeability of gels

AbstractWhen a saturated gel immersed in the same liquid is suddenly brought into contact with a smooth rigid indenter, the liquid cannot immediately flow out of the pores, and so the gel initially behaves as an incompressible material. This gives rise to a pressure gradient in the liquid phase and the liquid flows until the pressure in it goes to zero everywhere, and all the stresses are transferred to the elastic network. As a result of the flow, the force needed to maintain a constant contact area relaxes with time. In this work, we study the feasibility of using an indentation test to measure this time‐dependent force and to determine the elastic modulus, the Poisson's ratio, and the permeability, Dp, of the network. Specifically, we consider a two‐dimensional Hertz contact problem of a rigid circular cylinder indenting on a half space consisting of an elastic gel. The network of the gel is assumed to be linearly elastic and isotropic, and liquid flow within the gel is assumed to obey Darcy's law, which states that the flux is proportional to the pressure gradient. Exact expressions are obtained for the initial and final force required to maintain a given contact length. These expressions allow us to determine the elastic constants of the network. The permeability of the network can be obtained from the time‐dependent relaxation of the load, which is obtained by solving the exact continuum equations. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 359–370, 2006

Effect of temperature and inoculum concentration on gel microstructure, permeability and syneresis kinetics. Cottage cheese-type gels

Abstract Effects of coagulation temperature and inoculum concentration on microstructure, permeability and syneresis of cottage cheese gels were investigated. Relationships between coagulation parameters (obtained by rheology and near infrared light backscatter) and rate and extent of syneresis were studied. Mass of drained whey was fitted to first order equation W = W ∞ ( 1 - e - k whey t ) (determination coefficient, R 2 = 0.994 ± 0.005 ). Temperature coefficient and activation energy for syneresis were estimated. Increasing temperature significantly enhanced the rate of syneresis, due to bond relaxation. Increasing inoculum concentration decreased rate of syneresis, suggesting that faster acidification rate inhibited network rearrangement during whey expulsion. Syneresis parameters were highly correlated with the rates of acidification and network formation and with the loss tangent. Permeability coefficient, mass of whey drained and kinetic rate constant for syneresis were predicted by equations that included temperature and coagulation parameters. The close interactions between coagulation and syneresis kinetics suggested that it may be possible to develop optical sensors to simultaneously monitor both of these processes.

Marked increase of fibrin gel permeability with very low dose ASA treatment

Previous data from our group show that acetylsalicylic acid (ASA), especially at low dose, alters the network structure of fibrin, rendering it more porous. The present study was performed to extend the dose-response curve for effects of ASA on fibrinogen clotting properties and to examine the variability of these effects during a 24-h dose interval. Fifteen healthy volunteers received ASA 37.5 mg daily (low dose) for 10 days and, after an interval of 2 weeks, 320 mg daily (medium dose) for 7 days, followed by a single bolus dose of 640 mg (high dose). The plasma fibrinogen concentrations were determined and the permeability of fibrin gels (Ks) was assayed with a recently modified flow measurement technique. Three-dimensional (3D) structure of the fibrin network was studied by confocal microscopy. ASA therapy did not influence fibrinogen concentrations. Compared to baseline, Ks levels were increased by 21% and 31% in samples during medium and high dose ASA treatment (p<0.01) and, even more markedly, by 44% (p<0.0001) with very low dose ASA treatment (p<0.01, compared to the higher doses). The effects of ASA on fibrin gel permeability were stable over a 24-h dose interval. During ASA treatment, thicker fibrin fibers and larger network pores with irregular structure were observed by confocal microscopy. Acetylation of lysine residues in the fibrinogen molecule may explain the alterations in its clotting property, resulting in altered fibrin gel permeability. The mechanism(s) behind the greater increase in fibrin gel permeability and alterations in 3D structure of the fibrin network observed, and why this phenomenon is more pronounced at low compared to intermediate or high ASA doses, deserve further investigations.

Improvement of the silica aerogel strengthening process for scaling-up monolithic tile production

Previously published results have shown that washing and aging treatments (respectively in water/ethanol and water/polyethoxydisiloxane solutions) of silica gels (synthesized from polyethoxydisiloxane precursors through HF catalysis) significantly enhance both the permeability and mechanical properties of the wet gels. Unfortunately, scaling-up the process induces severe cracks during supercritical drying. This phenomenon has been related to a pore-size distribution gradient between the surface and the bulk of the gel that appears after aging of thick gels. We report efforts to optimize the aging step. Aging in less-concentrated polyethoxydisiloxane solutions yields gels with a more homogeneous pore-size distribution and has enabled us to obtain large monolithic and crack-free aerogels that remain light and transparent.

Structure and Physical Properties of Yogurt Gels: Effect of Inoculation Rate and Incubation Temperature

The effects of inoculation rates and incubation temperatures on the physical properties and microstructure of yogurt gels were investigated. A 2-factor experimental design with 3 replicates was used for data analysis. Yogurt gels were made with 0.5, 1, 2, 3, or 4% (wt/wt) inoculation rates and incubated at 40 or ∼46°C. Dynamic low amplitude oscillatory rheology was performed to monitor the formation of yogurt gels. Gel permeability and the amount of surface whey were determined. Gel structure was examined by confocal scanning laser microscopy. Higher storage modulus values were observed in yogurt gels made at higher inoculation rates and lower incubation temperatures. Gels made at higher inoculation rates and incubation temperatures exhibited higher yield stress and maximum loss tangent values, respectively. Permeability, pore size, and whey separation of yogurt gels increased with decreased inoculation rate and increased incubation temperature. An increase in the inoculation rate resulted in a decrease in the pH where the maximum in the loss tangent occurs, presumably reflecting less efficient solubilization of colloidal calcium phosphate (which is a slow process) and the need to attain a lower pH to complete the solubilization. Significant positive correlations were observed between whey separation and the value of maximum in loss tangent (r = 0.94) and permeability (r = 0.89). Whey separation was negatively correlated with storage modulus (r = −0.48). It was concluded that rearrangements of casein particles in the gel network and the rate at which the solubilization of colloidal calcium phosphate occurred were important driving forces for whey separation and weak gel.

Short collagen fibers provide control of contraction and permeability in fibroblast-seeded collagen gels.

Tissue engineering may allow for the reconstruction of breast, facial, skin, and other soft tissue defects in the human body. Cell-seeded collagen gels are a logical choice for creating soft tissues because they are biodegradable, mimic the natural tissue, and provide a three-dimensional environment for the cells. The main drawback associated with this approach, however, is the subsequent contraction of the gel by the constituent cells, which severely reduces permeability, initiates apoptosis, and precludes control of the resulting shape and size of the construct. In this study, type I collagen gels were seeded with fibroblasts and cast either with or without the addition of short collagen fibers. Gel contraction was monitored and permeability was assessed after 7 and 14 days in culture. The addition of short collagen fibers both significantly limited contraction and increased permeability of fibroblast-seeded collagen gels. The addition of short collagen fibers had no detrimental effect on cell proliferation, and there were a high number of viable fibroblasts in gels with fibers and gels without fibers. Gels containing short collagen fibers demonstrated permeabilities that were 100 to 1000 times greater than controls and also closely maintained their casting dimensions (never less than 96% of original). By limiting contraction and maintaining permeability, the incorporation of short collagen fibers should enable the creation of larger constructs by allowing for greater nutrient diffusion, and permit the creation of more complicated shapes during gel casting.