Development of a Mechanical System for Osteon Isolation

Osteons are small semi cylindrical hard tissues that exist in long bones of humans and some animals.Their diameter is in the range of 250 -300 micrometers approximately.They contain the osteocytes which plays a role in bone mechanotransduction.The boundary that surrounds the osteon from outside is called the cement line.In a summer research project supported by CUNY-LSAMP a group of four students and three professors worked full summer to develop a system that can isolate the osteons thus a mechanical testing could be performed (stress relaxation test) to determine their poroelastic properties.Two sets of osteons are isolated; one contains the cement line and another one without the cement line (diameter less than 250 micrometers).The vision for the device is to be integrated into a microscopic system thus the osteons can be isolated while looking at them in the microscope.Therefore a new platform for the microscope is designed (Auto Desk Inventor software) and machined so that it can carry a hand drill that is free to move upward and downward.Drill bits are used to produce cylindrical samples of diameters of 200 and 450 micrometers thus allowing for isolation of the two sets of osteons.The drill is aligned with the microscope and two external deformable illuminators are used to give better microscopic images.The drill bits were aligned with the microscopic image in the same vertical plane.The isolated samples were tested by the Micro-CT (resolution is 1 micrometer) to check for any micro cracks that might have occurred during the isolation process.The results revealed that no micro cracks and the top and bottom surfaces are flat thus making the unconfined compression test [1] more accurate.A system that developed previously in the lab [2] is used to apply a displacement that is less than 30 nanometers in a stress relaxation test.The analytical approach [1] will be compared with the experiment results to obtain the poroelastic properties and the permeability of a single osteon in the presence and absence of the cement line.