User:MTLE4470 grp5 AS/sandbox

LIMPETS ARE SO COOL.... kinda

Function and Formation:
Different limpet species exhibit different overall shapes of their teeth.

Role in Distributing Stress:
The structure, composition, and morphological shape of the teeth of the limpet allow for an even distribution of stress throughout the tooth. The teeth have a self-sharpening mechanism which allows for the teeth to be more highly functional for longer periods of time. Stress wears preferentially on the front surface of the cusp of the teeth, allowing the back surface to stay sharp and more effective.

There is evidence that different regions of the limpet teeth show different mechanical strengths. Measurements taken from the tip of the anterior edge of the tooth show that the teeth can exhibit an elastic modulus of around 140 GPa. Traveling down the anterior edge toward the anterior cusp of the teeth however, the elastic modulus decreases ending around 50 GPa at the edge of the teeth. The orientation of the goethite fibers can be correlated to this decrease in elastic modulus, as towards the tip of the tooth the fibers are more aligned with each other, correlating to a high modulus and vice versa.

Critical length of the goethite fibers is the reason the structural chitin matrix has extreme support. The critical length of goethite fibers has been estimated to be around 610 nm and when compared with the actual length of the fibers found in the teeth, around 3.1 um, shows that the teeth have fibers much larger than the critical length. This paired with orientation of the fibers leads to effective stress distribution onto the goethite fibers and not onto the weaker chitin matrix in the limpet teeth.

Crystallization Process:
The initial event that takes place when the limpet creates a new row of teeth is the creation of the main macromolecular α-chitin component. This serves as an organic matrix or framework for the crystallization of the teeth themselves. The first mineral to be deposited is goethite (α-FeOOH), a soft iron oxide which forms crystals parallel to the chitin fibers. The goethite however has varying different crystal habits. The crystals arrange in various shapes and even thicknesses throughout the chitin matrix. Depending on the formation of the chitin matrix however, this can have varying profound effects on the formation of the goethite crystals. The space in between the crystals and the chitin matrix is filled with an amorphous hydrated silica (SiO2).

Growth and Development:
Development of limpet teeth occurs in a conveyor-belt style manner, where teeth start growing at the back of the radula, and move toward the front of this structure as they mature. The growth rate of the limpet’s teeth is around .51 rows a day. Fully mature teeth are located in the scraping zone, the very front of the radula. The scraping zone is in contact with the substrate that the limpet feeds off of. As a result, the fully mature teeth are subsequently worn down until they are discarded - at a rate equal to the growth rate. To counter this degradation, a new row of teeth begin to grow.