Hydrogels fabrication techniques

Tsuda Y, Kikuchi A, Yamato M et al (2005) The use of patterned dual thermoresponslve surfaces for the collective recovery as co-cultured cell sheets. Biomaterials 26 1885-1893 Tsuda Y, Shimizu T, Yamato M et al (2007) Cellular control of tissue architectures using a three-dimensional tissue fabrication technique. Biomaterials 28 4939 946 Van Tomme SR, Hennink WE (2007) Biodegradable dextran hydrogels for protein delivery applications. Expert Rev Med Devic 4 147-164... 

In the following, some conventional but also microengineering fabrication techniques for hydrogel scaffolds will be presented. 

Three-dimensional porous scaffolds have been developed in several forms (eg, fibrous meshes, foams, sponge-Uke structures, hydrogels, microparticles, selfassembling peptides) by means of a wide range of fabrication techniques such as... 

In contrast to high density arrays low density arrays are made by deposition of pre-synthesized oligonucleotides or proteins on activated surfaces. There are several printing techniques for fabricating microarrays Non-contact biochip arrayers, commonly based on the piezoelectric effect, can apply controlled sub-nanoliter probe volumes to pre-specified locations on the chip surface. Due to the fact that the dispenser does not touch the surface, a non-contact arrayer provides low risk of contamination and is most suitable for printing on soft materials such as hydrogels. 

The microfluidic chip system for preparing a miniaturized PMBV/PVA hydrogel consists of a two-chamber chip, an aluminum custom-made chip holder, Teflon capillaries, microtubes, and syringes equipped with a microsyringe pump (Fig. 15). The two-chamber chip was fabricated by a photolithographic wet etching technique. Whereas both channels and chambers (200 pm in depth) were fabricated on the top plate, only chambers (200 pm in depth) were fabricated on the bottom plate. 

On-wafer membrane deposition and patterning is an important aspect of the fabrication of planar, silicon based (bio)chemical sensors. Three examples are presented in this paper amperometric glucose and free chlorine sensors and a potentiometric ISRET based calcium sensitive device. For the membrane modified ISFET, photolithographic definition of both inner hydrogel-type membrane (polyHEMA) and outer siloxane-based ion sensitive membrane, of total thickness of 80 pm, has been performed. An identical approach has been used for the polyHEMA deposition on the free chlorine sensor. On the other hand, the enzymatic membrane deposition for a glucose electrode has been performed by either a lift-off technique or by an on-chip casting. 

Depositing polymer membranes from solution is probably the oldest and simplest method for polymer deposition. Typically a solution of the polymer is deposited onto the transducer surface and allowed to dry. Although this technique is simple to practice, it is a fine art to perfect. Polymer concentration, solvent composition, amount of solution deposited, and solvent evaporation rate are all crucial parameters to control in order to obtain films that adhere well to the substrate, are uniform in thickness, and are free from defects. Gregg and Heller have solution cast redox-functional hydrogels containing glucose oxidase on an electrode to fabricate a glucose sensor [19]. 

A number of other polymer deposition techniques may be used in sensor fabrication. Some of the most exciting are techniques adopted from the semiconductor industry. For example, uncross-linked hydrogel precursors can be cast onto the surface of a substrate and UV cross-linked through a shadow mask. This technique allows patterning of the hydrogel to make complex sensor anays on a single sensor substrate, for example, an integrated O2, CO2, and pH sensor array [23]. 

Wu, J., Liang, S., Dai, H. et al. (2010) Structure and properties of cellulose/chitin blended hydrogel membranes fabricated via a solution pre-gelation technique. Carbohydrate Polymers, 79(3), 677-684. 

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