Projects of the St.F.X. Biomechanics Laboratory

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Most of our best ideas seem to start on the blackboard. From many of these discussions, we are starting to see that the use of primitive animals can be very useful to explore rather complex biological problems. This approach to solving biological problems is now called biomimicry. (Check out the biomimetics mailing list.) This page summarizes what we are now doing in the laboratory.

Tissue Mechanics

Elastin, Lamprin and Myxinin
Articular cartilage consists of a stiff fibrillar network with the interfibrillar space filled with proteoglycan aggregrates and fluid. In articular cartilage, the stiff fibers are collagen. However, a variety of other cartilaginous structures exist in both mammalian and non-mammlian species which contain little or no collagen, but rely for their structural integrity on other fibrillar matrix proteins. Elastin, which forms the matrix of elastic cartilages in mammalian ear and laryngeal tissues, is the most well studied of these proteins. However, the major structural protein from lamprey annular cartilage, lamprin, has also been identified and characterized. The evidence suggests that similar sequence and structural elements impart common properties to the tissues in which they are found. There is growing evidence that similiarites also exist with myxinin, the structural protein found in hagfish lingual type I cartilage.

(Ever see a lamprey up close? Divine creatures, they are, living part of their life as parasites on fish. They use their large sucker to attach to their prey. In our research, we use the annular cartilage that provides structural support for the sucker. Lamprey are the favourite animals of our animal care technicians, especially when they escape!).

Our laboratory has initiated an extensive comparative study on the mechanics of non-collagen based cartilages found in three different systems: (1) bovine ear elastic cartiage, (2) lamprey annular cartilage, and (3) hagfish lingual cartilage. We are examining electromechancial properties of all three tissues, using compressive relaxation tests, measuring the effect of strain rate on the physical properties, the Poisson's ratio, and the optical properties of isolated fibers using quantitative polarizing microscopy (P. MacGillivray). This work has developed into a collaboration with Dr. G. Wright (Department of Anatomy and Physiology, Atlantic Veterinary College, the University of Prince Edward Island), and Dr. F. Keeley (Division of Cardiovascular Research and Biochemistry, Hospital for Sick Children Research Institute, Univeristy of Toronto).

This work is supported by an NSERC Operating Grant, and was supported by NSERC Summer Research Scholarships to B. Mahoney, J. Flynn and P. MacGillivray.

Microfibrils

Arteries close to the heart are elastic. When the heart contracts, blood is pushed into the arteries, which expand. As the heart refills, the arteries recoil, pushing the blood further down the circulatory system. This elastic behaviour is important to dampen pressure fluctuations generated by the contraction of the heart. The expansion of the arteries introduces a mechanical problem, since the stresses in the wall becomes very large (the wall thins as the artery expands). The only solution to this problem is to have arterial walls with nonlinear properties. Mammalian elastic arteries do have nonlinear properties, which have been attributed to the different contribution of the structural proteins that make up the wall, elastin and collagen. We have shown that arteries in primitive vertebrates such as lamprey and hagfish, and some invertebrates, also have elastic arteries with nonlinear mechanical properties. These arterial walls, however, do not contain elastin and collagen as structural components, but contain microfibrils (for example, here is a micrograph of microfibrils found in lobster arteries). They appear similar to mammalian microfibrils, which recently have become increasingly important, since they are now appear to play an important role in a major connective tissue disease called Marfan Syndrome. Very little is known about the physical properties of microfibrils, but we have now used these primitive arteries to show that the modulus of elasticity of microfibrils is about 1 MPa, the same as elastin. These primitive arteries provide an excellent model system to examine the mechanical role of microfibrils. We have now shown that the nonlinear stress-strain curve of the abdominal artery of a lobster can be accounted for with only the microfibrils. This work is a collaboration with Dr. G. Wright (Department of Anatomy and Physiology, Atlantic Veterinary College, the University of Prince Edward Island), who provided us with the micrograph of the microfibrils found in lobster arteries.
We are now isolating and characterizing the microfibrils from arteries of lobsters, lamprey and hagfish (D. Knoechel and G. Wong). We are also attempting to correlate changes in the macroscopic properties of the arteries with changes in the microfibrils themselves (A. Leger, J. Muise). Some of this work will be conducted in the laboratory of L. Graham, Biology, St.F.X.

This work is supported by an NSERC Operating Grant, and was supported by a small research grant from the N.I.H. (U.S.), an NSERC Summer Research Scholarship to I. Davison and D. Knoechel, and a NSERC Postgraduate Research Scholarship to A. Leger. Our most recent work is funded by a Research Grant from the Atlantic Veterinary College to G. Wright and E. DeMont.

Abductin

Abductin is a fibrous protein-rubber found in the inner hinge ligaments of scallops. It is a dark brown triangular shaped block, located centrally, just below the hinge line. It forms part of an elastic system that is the only antagonist to the adductor muscle (the part that we eat!). Contraction of the muscle decreases the gape between the two shells, while simultaneously compressing the abductin. Strain energy stored in the protein-rubber is released to power the refilling process. During jet-propelled swimming, the hinge provides a passive reopening of the shells that is both rapid and efficient. Since protein-rubbers exhibit both temperature and frequency dependent properties, then environmentally induced changes in the temperature of the abductin should influence swimming ability. We are presently examining the importance of environmental temperature on the dynamic physical properties of scallop hinges. The experiment involves dynamically oscillating shells over a range of shell gapes and oscillating frequencies that simulate the natural swimming movements. This research was part of a much larger project on the dynamics and energetics of scallop locomotion (see below).


Swimming Mechanics

Scallop
We have now completed an extensive analysis of the dynamics of swimming in the scallop Placopecten magellanicus. The work includes an analysis of the unsteady fluid forces that act on the outside of the shell, the steady fluid forces, and an analysis of the mechanical properties of the hinge. These were integrated into a dynamic model of the whole locomotor system. This is probably the first complete mechanical analysis of swimming in any aquatic animal, and has provided us with a method to calculate the in vivo force-velocity curve for a muscle while it is functioning in the animal. We also showed that riblets found on the shells may function as a drag reduction mechanism. This work has greatly benefited from our interactions with W. Quinn, in the Engineering Department at St.F.X.
Presently, we are developing techniques to examine the seasonal changes in the catchability of scallops (L. MacNeil-Covin). These changes can be induced by seasonal changes in the capacity of the locomotor muscles to generate force. This is a collaborative project with E. Kenchington, DFO Halifax. L. MacNeil-Covin has been learning relevant techniques at the local hospital - St. Martha's Regional Hospital. We are also initiating a project using the scallop locomotor system to evaluate how continuously loaded tissues grow. This project will be completed by L. MacNeil-Covin and S. MacLellan.

This research is supported by an NSERC Operating Grant, and was supported by an NSERC International Fellowship to J. Cheng, and the Interim Funding Research Programme (ACOA). It is also supported by an NSERC Summer Research Scholarship to L. MacNeil-Covin.

Squid

We are also now applying the theories developed on scallop swimming to a more complex organism, the jet-propelled squid. E. Anderson evaluated the fluid dynamic forces on a swimming squid, and P. MacGillivray studied the dynamic mechanical properties of the mantle. Part of the work was conducted at the Woods Hole Oceanographic Institute, and Marine Biology Laboratory, in the United States (May/June 1997). We are now preparing this work for publication.

This research was supported by an NSERC Operating Grant, and a grant from the Esther A. and Joseph Klingenstein Fund (Woods Hole). It was also supported by an NSERC Summer Research Scholarship to P. MacGillivray.

Fish

We are initiating a new research area this summer, to evalulate fast-start performance of fish. This behaviour typically occurrs when fish are escaping from predators. We will evaluate fast-start performance of fish being studied by three researchers.
This research will be conducted by J. MacKenzie, who is partially funded by a N.S. Links internship.

Lobster Enhancement

Edwin DeMont is involved in a lobster enhancement program with the Guysborough County Inshore Fisherman's Association. He is supervising ISAR student Tyson MacCormack, who is working with the Association on a lobster enhancement project. Tyson is collecting morphometric data which will be used to measure the relative growth of the lobsters. The work is partially funded by a St.F.X. course based service learning/NS Links Summer Intership.

Edwin DeMont, Associate Professor
Biology Department, St. Francis Xavier University
P.O. Box 5000, Antigonish, Nova Scotia, B2G 2W5 Canada
Voice 902-867-5116 FAX 902-867-2389
edemont@stfx.ca - May 24, 1998