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Computational Colloids

Design of the pressure vessel

17 Nov , 2016   Gallery

As described in the previous post, Computational colloids proposes a genetically modified organism that responds to pressure by synthesising material. A transitional stage involves finding a gene that will respond to pressure, amplify its response, and connect it to a luminescence module. The physical demonstrator is intended to operate, initially, in this transitional stage by using a translucent pressure vessel—showing how the hydrogel matrix glows as pore pressure builds up and bacteria responds.

There are several challenges in designing the system. The vessel needs to be strong enough to contain the hydrogel volume when pressured to 1 MN, or around 100kg of even force. To achieve this, we are using a Formlabs Form 2 printer to prototype the vessel in clear, photo-polymer resin. To test resistance, we have produced vessels with a range of wall thicknesses, from 5mm to 15mm.

Another challenge in integrating the transparent vessel with the press mechanism is in creating water-tight conditions. The press should integrate a ‘plunge’ of nearly the same diameter as the inner cavity of the vessel. The offset between internal faces of the vessel and plunge is crucial. Too tight a gap won’t allow to slide in the chamber, and too loose provides a wider channel for water to escape. Efficiency of the system depends on applying an even pressure to the volume of hydrogel. The vessel contains the volume on the sides and bottom, and the plunge applies an even pressure to the upper side. To transmit force to bacteria, hydrogel molecules are collapsed and, forcing water out. To avoid this, we need to create a barrier to hold water in. Our initial approach has been to include a rubber seal, which rings the plunge and holds water in.

The series of photographs below show some of the initial prototypes for the vessel. Difference in colour correspond to different finishing techniques. Generally, we wet-sand printing artefacts using sanding paper in a progression of grit values, from 200 to 2400. To avoid yellowing, we finish vessels with a UV blocking coat, which improves optical qualities of the piece. This finishing process contributes in creating a vessel with the mechanical qualities to operate in the required pressure range, while translucent enough to show luminescent bacteria response.

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