A novel approach to study the cellular response to directional loading in relation to biomedical implants

Many tissues in the human body have a structure with a degree of alignment of the component parts. Tissues are built in this way to allow the body to withstand and exert forces required for posture and movement. A typical example of this is the structure of tendons which attach muscles to bone. Their principle structural components are protein fibres called collagen. These collagen fibres have a hierarchical aligned structure in that the fibres are made up of bundles of collagen fibrils and each collagen fibril is composed of long molecular chains. Thus collagen has a macroscopic and a microscopic aligned structure.When the muscles are stretched during movement the collagen fibres align to the direction of force and withstand the loading allowing the muscle to move the bone. When tissues are damaged a normal repair process occurs in which collagen is laid down by cells to rebuild the structure, however, the degree of alignment of the repaired tissue may not be the same as the original tissue and thus its ability to carry a load will be diminished.A material with an aligned structure is anisotropic. The degree of alignment or anisotropy can be measured using a technique called Reflection Anisotropy Spectroscopy (RAS). RAS is a non-destructive optical technique that measures the degree of anisotropy of a material or the interaction of materials at an interface. A material with a completely random structure will have no RAS spectrum but a spectrum would be produced from a material with a degree of alignment that will provide information on its structure at both the microscopic and macroscopic level. Furthermore as the degree of alignment changes the spectrum will change giving us a sensitive way to evaluate the structure of a material. Key advantages of the RAS technique are that it can analyse opaque materials in many environments including under water and it can also follow changes in the alignment of a structure as it is happening.In this study we will use RAS to study the degree of alignment of collagen as a simple molecule attached to an elastic material when it is relaxed and when it is stretched. This will allow us to investigate the microscopic structure of collagen and whether stretching the molecule increases its anisotropy. We will also use RAS to analyse collagen that has been produced by cells, similar to a tissue repair process, when it is relaxed and when it is stretched. In this part we will study the stretching of the collagen itself but also examine if stretching the cells stimulates them to produce more or less aligned collagen. The importance of this is that if stretching the cells stimulates collagen that is aligned more effectively then this can be used to change the normal tissue repair process following injury. Finally we will use RAS to study collagen in natural tendon, collected from an abattoir, when it is relaxed and when it is stretched and compare these spectra with those described above.This will be the first time RAS has been used to study biological tissue in this way. By combining the expertise of physicists and biomaterials scientists we plan to develop this highly specialised technique to provide a new tool for the evaluation of tissues and their repair processes that could help in the design of medical devices to improve tissue healing and repair.