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From 2013.igem.org

Introduction

Approximately half of all implanted medical devices results in one or more medical complications, such as blood clots, infections, poor healing, and excessive cell growth. Complications lengthen the hospital stay costing the american society an additional $30 billion dollar every year, and an increase in mortality rates by 25%. (ref)

A possible solution is to form a protective biocompatible layer between the implant and the body by means of a coating. Applying a biocompatible, biodegradable coating onto medical implants addresses these problems. Although such coatings are currently being applied for example with collagen, they are still inadequate as complications arise. A potent alternative for the coating is spider silk, besides high tensile strength and extensibility, spider silk has good biocompatibility, cell adhesion, and will not induce immune responses in the human body.

Production of spider silk on a grand scale, however, is infeasible due to the territorial behavior of spiders, and due to the fact that each thread silk has to be extracted individually by hand. Recognizing the potential of spider silk, researchers have begun developing silk producing bacteria. The yield, however, is still low, and the bacteria must be lysed in order to obtain it. Furthermore, the formation of a silk coating requires “polymerized proteins” rather than actual silk threads. To realize this, secretion of silk is required, which will presumably increase to production yield.

Our goal is to develop a silk coating for medical implants and a coating mechanism with the help of bacteria.

Bacillus subtilis is the bacterium of choice, because it is a gram-positive bacteria. Gram positive bacteria are often used in industry for the commercial production of extracellular proteins. A codon optimised silk sequence is transformed to silk to and with the use of the natural secretion pathway the silk will be secreted. With the recent development of porous 3d printed implants, for example cartilage implants. Cartilage implants are used to regrow cartilage inside the human body. They consist of a biodegradable porous polymer (ref). To coat such an implant with such a porous structure is off course hard. A system system has been designed that exploits the chemotaxis system of Bacillus in order to guide Bacillus towards the implant. The environmental control factor for this system is heat, which is sensed by the DesK system, which, in turn, is coupled to the chemotaxis system of Bacillus. In that way the silk will only be produced on site increasing the efficiency and saving energy. So our project consists of two subproject, 1 being the production of silk and 2 the coating mechanism