Functional tissue engineering: The role of biomechanics

''Tissue engineering" uses implanted cells, scaffolds, DNA, protein, and/or protein fragments to replace or repair injured or diseased tissues and org ans, Despite its early, success, tissue engineers have faced challenges in repairing or replacing tissues that serve a predominantly biomechanical fun ction. An evolving discipline called "functional tissue engineering" (FTE) seeks to address these challenges. In this paper, the authors present princ iples of functional tissue engineering that should be addressed when engine ering repairs and replacements for load-bearing structures. First, in vivo stress/strain histories need to be measured for a variety of activities. Th ese in vivo data provide mechanical thresholds that tissue repairs/replacem ents will likely encounter after surgery, Second, the mechanical properties of the native tissues must be established for subfailure and failure condi tions. These "baseline data" provide parameters within the expected thresho ld for different in vivo activities and beyond these levels if safety facto rs are to be incorporated. Third, a subset of these these mechanical proper ties must be selected and prioritized. This subset is important, given that the mechanical properties of the designs are not expected to completely du plicate the properties of the native tissues. Fourth, standards must be set when evaluating the repairs/replacements after surgery so as to deter-mine "how good is good enough?" Some aspects of the repair outcome may be infer ior but other mechanical characteristics of the repairs and replacements mi ght be suitable. New and improved methods must also be developed for assess ing the function of engineered tissues. Fifth, the effects of physical fact ors on cellular activity must be determined in engineered tissues. Knowing these signals may shorten the iterations required to replace a tissue succe ssfully and direct cellular activity and phenotype toward a desired end goa l. Finally, to effect a better repair outcome, cell-matrix implants may ben efit from being mechanically stimulated using in vitro "bioreactors" prior to implantation Increasing evidence suggests that mechanical stress, as wel l as other physical factors, may significantly increase the biosynthetic ac tivity of cells in bioartificial matrices, Incorporating each of these prin ciples of functional tissue engineering should result in safer and more eff icacious repairs and replacements for the surgeon and patient. [S0148-0731( 00)00206-5].