Optimising low molecular weight hydrogels for automated 3D printing.

Michael C Nolan,Stephen M King,Dave J Adams,Michael Barrow,Markus Bleuel,Bart Dietrich,Ana M Fuentes Caparrós,Emily R Cross

doi:10.1039/c7sm01694h

Abstract

Hydrogels prepared from low molecular weight gelators (LMWGs) are formed as a result of hierarchical intermolecular interactions between gelators to form fibres, and then further interactions between the self-assembled fibres via physical entanglements, as well as potential branching points. These interactions can allow hydrogels to recover quickly after a high shear rate has been applied. There are currently limited design rules describing which types of morphology or rheological properties are required for a LMWG hydrogel to be used as an effective, printable gel. By preparing hydrogels with different types of fibrous network structures, we have been able to understand in more detail the morphological type which gives rise to a 3D-printable hydrogel using a range of techniques, including rheology, small angle scattering and microscopy.

Highlights

Gaithersburg, MD 20988-8562, USA e Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742-2115, USA f STFC Pulsed Neutron and Muon Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Campus, Didcot, OX11 0QX, UK † Electronic supplementary information (ESI) available: Fig. S1–S16 and Tables S1, S2
There are currently limited design rules describing which types of morphology or rheological properties are required for a low molecular weight gelators (LMWGs) hydrogel to be used as an effective, printable gel
LMWG which form printable hydrogels are usually found by trial and error

Summary

Introduction

A supramolecular gel network formed via non-covalent interactions would allow for the reversible breaking and recovery of the network.[23] When a gel is pre-formed inside a syringe and extruded, the printing process relies on both thixotropy and the recovery of the mechanical properties of the gel which, in turn, greatly relies on the microstructure of the gel network.[24,25] Huang et al have shown that the recovery after shear in organogel systems can depend on the gel microstructure, which in turn depends on the conditions under which gelation is carried out.[26] Pochan and co-workers studied hydrogel behaviour during and after flow and showed that planar domains of the gel network break apart to allow the gel to flow.[24] Using a preformed gel that recovers quickly reduces the need for the additional treatment of the extruded precursor solution to form a gel This approach opens up opportunities to encapsulate drugs, catalysts and other materials inside the gel which will not leak from the network if the network recovers quickly after extrusion.[24,27] Using hydrogels as cell carriers has been shown to improve cell viability during bio-printing.[28]

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Results

Conclusion