Disposable Molecular Valve Consisting of Alginate Gel

Abstract

A disposable molecular valve, consisting of a membrane coated with alginate gel, which is partially cross-linked with Ca²⁺, was developed based on a volume change and/or dissolution of the gel in response to the cation concentration. The valve automatically opened upon an increase in the concentration of cations such as H⁺, Na⁺, Ca²⁺, Mg²⁺, Cu²⁺, or Al³⁺. The concentration where the valve opens was 1 × 10⁻⁴ to 2 × 10⁻⁴ M for Ca²⁺, Cu²⁺, and Al³⁺, but the solution volume passed vs. concentration increased in the order of Ca²⁺, Cu²⁺, and Al³⁺. For Na⁺ and Mg²⁺ the valve opening concentration was ca. 1 × 10⁻² and 1 × 10⁻³ M, respectively. Two mechanisms were proposed to account for the opening of the valve. One is due to a shrinking of the gel caused by cations; the other is due to dissolution of the gel. The former corresponds for the cases of Ca²⁺, Cu²⁺, and Al³⁺, and the latter does for Na⁺ and Mg²⁺. The valve closed over the pH range from 3 to 12, whereas it opened below and above this range. The effects of anions and pressure were also studied.