Methods and apparatus for hygromorphic shape control

Abstract

A composite film includes a substrate that is not responsive to relative humidity, and also one or more layers of hygromorphic material. The hygromorphic material expands in response to an increase in relative humidity and contracts in response to a decrease in relative humidity. In some cases, the composite film is bi-layer or tri-layer. The composite films are fabricated such that they undergo a desired bending pattern in response to changes in relative humidity. In some cases, these bending patterns are combinations of two bending primitives: a smooth curve and a sharply angled curve. These two primitives are combined to create a variety of shape transformations including 1D linear transformation, 2D surface expansion and contraction, 2.5D texture change and 3D folding. Any type of hygromorphic material may be employed, including living gram positive and gram negative bacterial cells, yeast cells, plant cells, mammalian cells, cell debris, or hydrogel.

What is claimed is: 
     
         1 . An apparatus comprising a 3D printer, wherein the 3D printer is configured to apply hygromorphic material to a first side of an object, in such a way that:
 (a) the amount of the hygromorphic material that adheres to the first side varies substantially from region to region of the first side;   (b) the hygromorphic material adheres in a first spatial distribution on the first side of the object, which first spatial distribution is the amount of hygromorphic material adhering to the first side as a function of spatial position; and   (c) the hygromorphology of the object, after the hygromorphic material is applied to the first side, (A) depends at least in part on the first spatial distribution, and (B) includes changing from a state in which the shape of the object does not include a sharply angled bend to a state in which the shape of the object includes a sharply angled bend.   
     
     
         2 . The apparatus of  claim 1 , wherein the 3D printer:
 (a) is configured to deposit the hygromorphic material according to computer instructions; and   (b) includes a 3-axis positioning system.   
     
     
         3 . The apparatus of  claim 1 , wherein the hygromorphic material comprises a hydrogel. 
     
     
         4 . The apparatus of  claim 1 , wherein the hygromorphic material comprises a bacterial cell. 
     
     
         5 . The apparatus of  claim 1 , wherein the apparatus further comprises or more humidifiers that are configured to cause changes in relative humidity that is ambient to the object. 
     
     
         6 . The apparatus of  claim 5 , wherein the changes in relative humidity comprise increases in relative humidity of air ambient to the first side. 
     
     
         7 . The apparatus of  claim 1 , wherein the 3D printer is configured to apply hygromorphic material to a second side of the object in such a way that:
 (a) the amount of hygromorphic material that adheres to the second side varies substantially from region to region of the second side;   (b) the hygromorphic material adheres in a second spatial distribution on the second side of the object, which second spatial distribution is the amount of hygromorphic material adhering to the second side as a function of spatial position; and   (c) the hygromorphology of the object, after the hygromorphic material is applied to the second side, depends at least in part on the second spatial distribution;   the second side being different than the first side.   
     
     
         8 . An apparatus comprising a 3D printer, wherein the 3D printer is configured to apply hygromorphic material to a first side of an object and to a second side of the object, in such a way that:
 (a) the amount of the hygromorphic material that adheres to the first side varies substantially from region to region of the first side;   (b) the amount of the hygromorphic material that adheres to the second side varies substantially from region to region of the second side; and   (c) the object is configured to undergo bending in response to a change in relative humidity, which bending includes changing from a state in which the shape of the object does not include a sharply angled bend to a state in which the shape of the object includes a sharply angled bend;   the second side being different than the first side.   
     
     
         9 . The apparatus of  claim 8 , wherein the bending occurs when the object is simultaneously exposed to a first relative humidity on the first side and to a second relative humidity on the second side, the first and second relative humidities being different from each other.