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Sliding-induced adhesion of stiff polymer microfibre arrays. I. Macroscale behaviour.

ABSTRACT: Gecko-inspired microfibre arrays with 42 million polypropylene fibres cm(-2) (each fibre with elastic modulus 1 GPa, length 20 microm and diameter 0.6 microm) were fabricated and tested under pure shear loading conditions, after removing a preload of less than 0.1 N cm(-2). After sliding to engage fibres, 2 cm2 patches developed up to 4N of shear force with an estimated contact region of 0.44 cm2. The control unfibrillated surface had no measurable shear force. For comparison, a natural setal patch tested under the same conditions on smooth glass showed approximately seven times greater shear per unit estimated contact region. Similar to gecko fibre arrays, the synthetic patch maintains contact and increases shear force with sliding. The high shear force observed (approx. 210 nN per fibre) suggests that fibres are in side contact, providing a larger true contact area than would be obtained by tip contact. Shear force increased over the course of repeated tests for synthetic patches, suggesting deformation of fibres into more favourable conformations.

SUBMITTER: Lee J

PROVIDER: S-EPMC2607469 | biostudies-literature | 2008 Aug

REPOSITORIES: biostudies-literature

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Sliding-induced adhesion of stiff polymer microfibre arrays. I. Macroscale behaviour.

Lee Jongho J Majidi Carmel C Schubert Bryan B Fearing Ronald S RS

Journal of the Royal Society, Interface 20080801 25

Gecko-inspired microfibre arrays with 42 million polypropylene fibres cm(-2) (each fibre with elastic modulus 1 GPa, length 20 microm and diameter 0.6 microm) were fabricated and tested under pure shear loading conditions, after removing a preload of less than 0.1 N cm(-2). After sliding to engage fibres, 2 cm2 patches developed up to 4N of shear force with an estimated contact region of 0.44 cm2. The control unfibrillated surface had no measurable shear force. For comparison, a natural setal pa ...[more]

PMID: 18211864

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Project description:Silk hydrogels have shown potential for tissue engineering applications, but several gaps and challenges, such as a restricted ability to form hydrogels with tuned mechanics and structural features, still limit their utilisation. Here, Bombyx mori and Antheraea mylitta (Tasar) silk microfibres were embedded within self-assembling B. mori silk hydrogels to modify the bulk hydrogel mechanical properties. This approach is particularly attractive because it creates structured silk hydrogels. First, B. mori and Tasar microfibres were prepared with lengths between 250 and 500 μm. Secondary structure analyses showed high beta-sheet contents of 61% and 63% for B. mori and Tasar microfibres, respectively. Mixing either microfibre type, at either 2% or 10% (w/v) concentrations, into 3% (w/v) silk solutions during the solution-gel transition increased the initial stiffness of the resulting silk hydrogels, with the 10% (w/v) addition giving a greater increase. Microfibre addition also altered hydrogel stress relaxation, with the fastest stress relaxation observed with a rank order of 2% (w/v) > 10% (w/v) > unmodified hydrogels for either fibre type, although B. mori fibres showed a greater effect. The resulting data sets are interesting because they suggest that the presence of microfibres provided potential 'flow points' within these hydrogels. Assessment of the biological responses by monitoring cell attachment onto these two-dimensional hydrogel substrates revealed greater numbers of human induced pluripotent stem cell-derived mesenchymal stem cells (iPSC-MSCs) attached to the hydrogels containing 10% (w/v) B. mori microfibres as well as 2% (w/v) and 10% (w/v) Tasar microfibres at 24 h after seeding. Cytoskeleton staining revealed a more elongated and stretched morphology for the cells growing on hydrogels containing Tasar microfibres. Overall, these findings illustrate that hydrogel stiffness, stress relaxation and the iPSC-MSC responses towards silk hydrogels can be tuned using microfibres.

Dataset Information

Sliding-induced adhesion of stiff polymer microfibre arrays. I. Macroscale behaviour.

Publications

Sliding-induced adhesion of stiff polymer microfibre arrays. I. Macroscale behaviour.

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