Biomedical Applications of Layer - by - Layer Assembly : From Biomimetics to Tissue

In the second half of the 20th century, scientists have been attracted to the design of thin solid films at the molecular level because of their potential for applications in the fields of biology and medicine. Two techniques dominated research in this area: Langmuir–Blodgett deposition and self-assembled monolayers (SAMs). Both Langmuir–Blodgett deposition, invented by Langmuir and Blodgett, and the SAM technique, developed by Nuzzo and Allara, and by Whitesides and co-workers, have shown remarkable capability for the immobilization of proteins and cells and subsequent application in biocatalysis, drug delivery, and tissue engineering. However, several intrinsic disadvantages of both methods limit their application in the field of biology. For Langmuir–Blodgett deposition, the drawbacks are expensive instrumentation and long fabrication periods for preparation of the biomolecule films, limited types of biomolecules that can be embedded in the film (Langmuir–Blodgett deposition requires the assembly components to be amphiphilic), and the considerable instability of biomolecules resulting from weak physical attraction inside the films. For SAMs, the disadvantages are low loading of biological components in the films because of their monolayer nature, a limited number of substrate types, since SAMs are only fabricated by the adsorption of thiols onto noble metal surfaces or by silanes onto silica surfaces, and the limited stability of films under ambient and physiological conditions. An alternative to Langmuir–Blodgett deposition and SAMs is layer-by-layer (LBL) assembly, introduced by Decher, R EV EW