Aligned two- and three-dimensional structures by directional freezing of polymers and nanoparticles

Zhang, Haifei; Hussain, Irshad; Brust, Mathias; Butler, Michael F.; Rannard, Steve P.; Cooper, Andrew I.

doi:10.1038/nmat1487

Cited by 754 publications

(677 citation statements)

References 18 publications

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“…Subsequent sublimation of ice results in the formation of a porous solid material. Freeze casting has been successfully adopted to synthesize a variety of porous ceramic, metallic, polymeric and composite materials, including carbon nanotubes or graphene-based polymer composites 18,[30][31][32][33] . Although previous research on freeze casting has been centred on polymers and spherical particles 28,29 , we were particularly interested in studying how 2D graphene sheets interact with anisotropic ice crystal growth without the interference of other polymer or surfactant additives.…”

Section: Resultsmentioning

confidence: 99%

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Biomimetic superelastic graphene-based cellular monoliths

et al. 2012

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Many applications proposed for graphene require multiple sheets be assembled into a monolithic structure. The ability to maintain structural integrity upon large deformation is essential to ensure a macroscopic material which functions reliably. However, it has remained a great challenge to achieve high elasticity in three-dimensional graphene networks. Here we report that the marriage of graphene chemistry with ice physics can lead to the formation of ultralight and superelastic graphene-based cellular monoliths. Mimicking the hierarchical structure of natural cork, the resulting materials can sustain their structural integrity under a load of 450,000 times their own weight and can rapidly recover from 480% compression. The unique biomimetic hierarchical structure also provides this new class of elastomers with exceptionally high energy absorption capability and good electrical conductivity. The successful synthesis of such fascinating materials paves the way to explore the application of graphene in a self-supporting, structurally adaptive and 3D macroscopic form.

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Section: Resultsmentioning

confidence: 99%

“…In conjunction with the anisotropic structure of GO, the principle of the freeze-casting process that has previously been proposed for other nanoparticle suspensions 30,31 can be extended to elucidate the formation of such a unique cellular structure. As schematically illustrated in Fig.…”

Section: Resultsmentioning

confidence: 99%

Biomimetic superelastic graphene-based cellular monoliths

et al. 2012

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“…For unidirectional freezing, the samples were placed perpendicular to the base and insulated using Poly (dimethyl siloxane) (PDMS) molds to allow longitudinal ice crystal formation (Zhang et al, 2005). Briefly, samples were placed on a stainless steel base in the freeze dryer (Labconco Triad TM , Kansas City, MO USA) and frozen at a constant cooling rate of 1°C/min to a final temperature of -30°C.…”

Section: Freeze Drying To Impart Porosity and Axially Aligned Channelmentioning

confidence: 99%

Decellularized grafts with axially aligned channels for peripheral nerve regeneration

Sridharan

Reilly

Buckley

2015

Journal of the Mechanical Behavior of Biomedical Materials

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At least 2 million people worldwide suffer annually from peripheral nerve injuries (PNI), with estimated costs of $7 billion incurred due to paralysis alone. The current "gold" standard for treatment of PNI is the autograft, which poses disadvantages such as high fiscal cost, possible loss of sensation at donor site and the requirement of two surgeries. Allografts are viable alternatives; however, intensive immunosuppressive treatments are often necessary to prevent host rejection. For this reason, significant efforts have been made to remove cellular material from allografts. These decellularized nerve grafts perform better than other clinically available grafts but not as well as autografts; therefore, current research on these grafts includes the incorporation of additional components such as growth factors and cells to provide chemical guidance to regenerating axons. However, effective cellular and axonal penetration is not achieved due to the small pore size (5-10μm) of the decellularized grafts.The overall objective of this study was to induce axially aligned channels in decellularized nerve grafts to facilitate enhanced cell penetration. The specific aims of this study were to optimize a decellularization method to enhance cellular removal, to induce axially aligned pore formation in decellularized grafts through a novel unidirectional freeze drying method, to study the bulk mechanical properties of these modified decellularized grafts and to assess cell penetration into these grafts. To this end we modified an existing decellularization protocol to improve cellular removal while preserving matrix structure in rat sciatic nerve sections. Standard freeze drying and unidirectional freeze drying were employed to impart the necessary pore architecture, and our results suggest that unidirectional freezing is a pertinent modification to the freeze drying process to obtain axially aligned channels. These highly porous scaffolds obtained using unidirectional freeze-drying possessed similar tensile properties to native nerve tissue and exhibited enhanced cellular penetration after 14 days of culture when compared to non-freeze dried and standard freeze-dried scaffolds. The results of this study not only highlight the importance of aligned pores of diameters ~20-60μm on cellular infiltration, but also presents unidirectional freeze drying as a viable technique for producing this required architecture in decellularized nerves. To the best of our knowledge, this study represents the first attempt to manipulate the physical structure of decellularized nerves to enhance cell penetration which may serve as a basis for future peripheral nerve regenerative strategies using decellularized allografts.

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“…It was also reported that at high polymer concentrations, the architecture of oriented ladder-like (parallel microtubules with thin partitions) structures could be achieved if the solvent type and the temperature gradient were maintained the same. Directional freezing and subsequent freeze-drying can be used to align the structural elements both in the form of three-dimensional porous structures and two-dimensional oriented surface patterns [26].…”

Section: Microstructure Of Scaffoldsmentioning

confidence: 99%