Structural changes in living tissues.

Tissues change in many ways in the period that they are part of a living organism. Tissues are created in fairly repeatable structural patterns, and the patterns are due to both the genes and the (mechanical) environment, but we do not know exactly what part or percentage of a particular pattern to consider the genes, or the environment, responsible for. We do not know much about the beginning of tissue construction (morphogenesis) and also the methods of tissue construction. When the tissue structure is altered to accommodate a new loading, it is not known how the decision is made for the structural reconstruction. We know that tissues grow or reconstruct themselves without ceasing to continue with their structural function, but we do not understand the processes that permit them to accomplish this. Tissues change their structures to altered mechanical environments, but we are not sure how. Tissues heal themselves and we understand little of the structural mechanics of the process. With the objective of describing the interesting unsolved mechanics problems associated with these biological processes, some aspects of the formation, growth and adaptation of living tissues are reviewed. Beyond the objective is the hope that the work will stimulate new ideas and new observations in developmental biology.