A novel technique for mechanical characterization of thin elastomeric membrane

Liu, Kuo-Kang; Ju, Bing Feng

doi:10.1088/0022-3727/34/15/102

Cited by 58 publications

(31 citation statements)

References 15 publications

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“…A sphere was placed at the centre of the hydrogel, and its weight caused the hydrogel to deform. In this study, the diameter ratio of the hydrogel to the sphere was kept constant at 5.0, which was identical to the value used in the previous analyses 6 10 11…”

Section: Methodsmentioning

confidence: 99%

Non-destructive mechanical characterisation of UVA/riboflavin crosslinked collagen hydrogels

Ahearne

Yang

Then

et al. 2007

British Journal of Ophthalmology

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Aims: To establish a non-destructive method of characterising the mechanical properties of collagen hydrogels to model corneal tissue and to examine the effect of photochemical crosslinking on their mechanical properties.Methods: Collagen hydrogels were manufactured, submerged in 0.1% riboflavin solution and crosslinked using two UVA tube bulbs with an intensity of between 2.8 and 3.2 mW/cm 2 . The hydrogels were clamped around their outer edge and deformed using a sphere. The deformation was measured in situ using a long-working-distance microscope connected to a CCD camera, and the deformation displacement was used with a theoretical model to calculate the Young modulus of the hydrogels. Collagen hydrogels seeded with human corneal fibroblasts were used to examine cell viability after UVA irradiation. Results: There was an increase in Young modulus of the collagen hydrogels after UVA/riboflavin treatment that was dependent on the exposure time. UVA irradiation without riboflavin showed decreased mechanical integrity and strength. Cell viability was reduced with increased UVA exposure time. Conclusion:The non-destructive technique demonstrated a new methodology comparable with strip extensiometry for cornea or corneal model specimens but with more convenient features. This approach could be used as an initial step in developing new crosslinking treatments for patients with keratoconus.Keratoconus is a non-inflammatory disease that causes thinning of the corneal stroma which can lead to bulging, reduction of vision and discomfort. Several treatment options are under investigation to stabilise the progression of the disease. One of the most promising approaches involves the crosslinking of collagen fibrils in the cornea using ultraviolet light in the presence of a photosensitiser to improve its mechanical strength. 1-3Extensiometry has been used to characterise the mechanical properties of the corneas under investigation. However, extensiometry has several limitations including destructive measurement, using strips of cornea not whole cornea, the corneal curvature not being taken into consideration, and tension primarily on fibrils that are parallel to the direction of strain. 4 5 In addition, the method used to crosslink cornea for extensiometry differs from the method used to treat patients in vivo where only the centre of cornea is irradiated. 3For these reasons, an alternative approach to mechanical characterisation is desirable.We have developed a long-working-distance microscope spherical microindentation system capable of measuring the mechanical properties of hydrogel materials under cell culture conditions. 6This system can be used to obtain mechanical properties of biological materials on-line, nondestructively and in situ. Previous studies have shown that type 1 collagen can be used to model corneal tissue. [7][8][9] This is particularly useful, since a viable human cornea is difficult to obtain. In this paper, a spherical indentation technique was used to measure the Young modulus of collagen...

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Section: Methodsmentioning

confidence: 99%

Non-destructive mechanical characterisation of UVA/riboflavin crosslinked collagen hydrogels

Ahearne

Yang

Then

et al. 2007

British Journal of Ophthalmology

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“…1G). The tissue explants meant that the surface of the construct was nonhomogeneous; thus, the spherical indenter was unable to spontaneously centre 18 and axisymmetrical deformation did not occur. The elastic modulus was measured every 1-2 days for 14 or 21 days depending on the experimental group being investigated.…”

Section: Modulus Measurementmentioning

confidence: 99%

Corneal Stromal Cell Plasticity: In Vitro Regulation of Cell Phenotype Through Cell-Cell Interactions in a Three-Dimensional Model

Wilson

Yang²,

Haj³

2014

Tissue Engineering Part A

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In vivo, epithelial cells are connected both anatomically and functionally with stromal keratocytes. Co-culturing aims at recapturing this cellular anatomy and functionality by bringing together two or more cell types within the same culture environment. Corneal stromal cells were activated to their injury phenotype (fibroblasts) and expanded before being encapsulated in type I collagen hydrogels constructs. Three different epithelial-stromal co-culture methods were then examined: epithelial explant; transwell; and the use of conditioned media. The aim was to determine whether the native, inactivated keratocyte cell phenotype could be restored in vitro. Media supplementation with transforming growth factor beta-1 (TGF-b1) was then used to determine whether the inactivated stromal cells retained their plasticity in vitro and could be re-activated to the fibroblast phenotype. Finally, media supplementation with wortmannin was used to inhibit epithelial-stromal cell interactions. Two different nondestructive techniques, spherical indentation and optical coherence tomography, were used to reveal how epithelial-stromal co-culturing with TGF-b1, and wortmannin media supplementation, respectively, affect stromal cell behavior and differentiation in terms of construct contraction and elastic modulus measurement. Cell viability, phenotype, morphology, and protein expression were investigated to corroborate our mechanical findings. It was shown that activated stromal cells could be inactivated to a keratocyte phenotype via co-culturing and that they retained their plasticity in vitro. Activated corneal stromal cells that were fibroblastic in phenotype were successfully reverted to a nonactivated keratocyte cell lineage in terms of behavior and biological properties; and then back again via TGF-b1 media supplementation. It was then revealed that epithelial-stromal interactions can be blocked via the use of wortmannin inhibition. A greater understanding of stromal-epithelial interactions and what mediates them offers great pharmacological potential in the regulation of corneal wound healing, with the potential to treat corneal diseases and injury by which such interactions are vital.

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“…For cell-hydrogel constructs, the whole assembly was maintained in a large square petri dish which was placed in an incubator at 37 8C, 5% CO 2 . In this study, the diameter ratio of the hydrogel to the ball was kept constant at 5.0, which is identical with the value used in the previous analyses (Yang & Hsu 1971;Liu & Ju 2001). With this sample holder, large displacements, as high as 5 mm, can be visualized.…”

Section: Measurement Instrumentationmentioning

confidence: 99%

“…Recently, Liu & Ju (2001) and Ju & Liu (2002) have developed a novel experimental technique which enables the viscoelastic properties of polymer membranes to be characterized. It involves a central indention of a circumferentially clamped membrane using a ball of known weight and measurement of the corresponding displacement occurring at the centre.…”

Section: Introductionmentioning

confidence: 99%

Characterizing the viscoelastic properties of thin hydrogel-based constructs for tissue engineering applications

Ahearne

Yang

Haj

et al. 2005

J. R. Soc. Interface.

272

212

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We present a novel indentation method for characterizing the viscoelastic properties of alginate and agarose hydrogel based constructs, which are often used as a model system of soft biological tissues. A sensitive long working distance microscope was used for measuring the time-dependent deformation of the thin circular hydrogel membranes under a constant load. The deformation of the constructs was measured laterally. The elastic modulus as a function of time can be determined by a large deformation theory based on Mooney-Rivlin elasticity. A viscoelastic theory, Zener model, was applied to correlate the time-dependent deformation of the constructs with various gel concentrations, and the creep parameters can therefore be quantitatively estimated. The value of Young's modulus was shown to increase in proportion with gel concentration. This finding is consistent with other publications. Our results also showed the great capability of using the technique to measure gels with incorporated corneal stromal cells. This study demonstrates a novel and convenient technique to measure mechanical properties of hydrogel in a non-destructive, online and realtime fashion. Thus this novel technique can become a valuable tool for soft tissue engineering.

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A novel technique for mechanical characterization of thin elastomeric membrane

Cited by 58 publications

References 15 publications

Non-destructive mechanical characterisation of UVA/riboflavin crosslinked collagen hydrogels

Non-destructive mechanical characterisation of UVA/riboflavin crosslinked collagen hydrogels

Corneal Stromal Cell Plasticity: In Vitro Regulation of Cell Phenotype Through Cell-Cell Interactions in a Three-Dimensional Model

Characterizing the viscoelastic properties of thin hydrogel-based constructs for tissue engineering applications

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