Artificial Muscle Preparation Procedure Using:
Freeform Fabrication of Polyacrylamide and Polyacrylic acid cross-linked gels
Professor of Materials Science and Engineering
University of Arizona, AML, 4715 E. Fort Lowell Rd, Tucson AZ 85712
Phone: 520 322 2994, Fax 520 322 2993, email@example.com
This method follows the standard recipe for polyacrylamide gels used for electrophoresis, with the addition of a
physical gelling agent to prevent flow as the layers are built up by extrusion freeform fabrication.
Gels are made from solutions of acrylamide or acrylic acid at 200-400 g/l of water. The cross-linking agent is
methylenebisacrylamide at levels from 20-50 g/l. For the acrylamide, the initiator is potassium persulfate,
0.25g/l and the accelerator is tetramethylethylenediamine (TEMED) 3.6g/l.
For the acrylic acid, the catalyst system is a potassium persulfate (1.14g)-potassium metabisulfite (0.94g) redox couple.
Fumed silica (210 g/l) is added as a physical gelling agent and the pH adjusted to 3.8-4.0.
Gel stacks are made by extrusion freeform fabrication. Acrylic monomer, water and catalyst are extruded from
a syringe through a fine (0.2-1 mm diameter) nozzle which writes on a heated substrate at about 60oC.
The composition of the gel can be changed by swapping syringes or by using a Y-junction between two syringe feeds.
To prevent the monomer solution from flowing off the substrate before curing, 8 wt.% of fumed silica is added to the
solution, to give it a toothpaste-like rheology. The solution cures to cross-linked gel by thermally activated free
radical polymerization within a few minutes of being deposited on the plate. 6-layer stacks are formed into bars
5 cm x 0.5 cm (wide) x 0.4 cm (thick), before swelling. A typical stack would have a polyacrylic acid face
with 1-5 (x) layers and a polyacrylamide face of (6-x) layers with a combination of dense and open-mesh layers
(written as a series of spaced lines). When used, wire electrodes are usually placed between layers 1&2 and 5&6.
This system allows interdiffusion and bonding between layers, which allows good stress transfer during the swelling processes.
The early onset of gelation and the physical gelling agent prevent extensive mixing between layers.
This can be shown by cutting apart multilayer stacks and measuring the response of individual layers to acid and base.
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