Details

Autor(en) / Beteiligte

• Liu, Mingjie
• Ishida, Yasuhiro
• Ebina, Yasuo
• Sasaki, Takayoshi
• Hikima, Takaaki
• Takata, Masaki
• Aida, Takuzo

Titel

An anisotropic hydrogel with electrostatic repulsion between cofacially aligned nanosheets

Ist Teil von

• Nature (London), 2015-01, Vol.517 (7532), p.68-72

Ort / Verlag

London: Nature Publishing Group UK

Erscheinungsjahr

2015

Quelle

EBSCO - Psychology & Behavioral Sciences Collection

Beschreibungen/Notizen

• Usually materials design focuses on attractive interactions, but here a hydrogel is described whose properties are dominated by electrostatic repulsion between negatively charged titanate nanosheets embedded within it; the material, inspired by articular cartilage, deforms easily when sheared parallel to the sheets but resists compressive forces applied orthogonally. A hydrogel modelled on articular cartilage Materials design focuses overwhelmingly on attractive interactions, as in advanced polymer-based composites that exploit interactions between inorganic fillers and a polymer matrix. Electrostatic repulsion can be also harnessed to good effect, as demonstrated by the articular cartilage that covers the ends of bones where they form joints, providing near-frictionless mechanical motion. Taking this cartilage as the model, Mingjie Liu and colleagues have developed a hydrogel with mechanical properties dominated by repulsion between negatively charged titanate nanosheets embedded within it. The material deforms easily when sheared parallel to the sheets but resists compressive forces applied orthogonally. Composites of this type should open new possibilities for developing soft materials with unusual functions. Machine technology frequently puts magnetic or electrostatic repulsive forces to practical use, as in maglev trains, vehicle suspensions or non-contact bearings 1 , 2 . In contrast, materials design overwhelmingly focuses on attractive interactions, such as in the many advanced polymer-based composites, where inorganic fillers interact with a polymer matrix to improve mechanical properties. However, articular cartilage strikingly illustrates how electrostatic repulsion can be harnessed to achieve unparalleled functional efficiency: it permits virtually frictionless mechanical motion within joints, even under high compression 3 , 4 . Here we describe a composite hydrogel with anisotropic mechanical properties dominated by electrostatic repulsion between negatively charged unilamellar titanate nanosheets 5 embedded within it. Crucial to the behaviour of this hydrogel is the serendipitous discovery of cofacial nanosheet alignment in aqueous colloidal dispersions subjected to a strong magnetic field, which maximizes electrostatic repulsion 6 and thereby induces a quasi-crystalline structural ordering 7 , 8 over macroscopic length scales and with uniformly large face-to-face nanosheet separation. We fix this transiently induced structural order by transforming the dispersion into a hydrogel 9 , 10 using light-triggered in situ vinyl polymerization 11 . The resultant hydrogel, containing charged inorganic structures that align cofacially in a magnetic flux 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , deforms easily under shear forces applied parallel to the embedded nanosheets yet resists compressive forces applied orthogonally. We anticipate that the concept of embedding anisotropic repulsive electrostatics within a composite material, inspired by articular cartilage, will open up new possibilities for developing soft materials with unusual functions.