necessary for cartilage regeneration the thicknesses of the components of the template 12 can vary depending upon the circumstances of use for example the thickness of the dense collagen membrane may be in the range of 50 to 200 micrometers or more and the thickness of the porous collagen matrix may be in the range of 0 5 to 8 millimeters or more the collagen matrix component of that template has been developed to allow attachment and growth of cells particularly chondrocytes in vitro studies have been used to determine the optimal pore size of the porous collagen matrix component of the template the collagen matrix can be used to immobilize chondrocytes in vitro and support subsequent cell growth the cell number can then be expanded in vitro and the collagen matrix can be used to transport the cells to the repair site and retain the cells in position following implantation previous studies have shown that the collagen matrix pore size can be controlled by varying the dispersion ph collagen concentration and the lyophilization cycle freezing time temperature range and cycle time dillion et al 1986 the collagen matrices have also been characterized according to their permeability to globular macromolecules for example it was found that a pore structure of approximately 15 micrometers would exclude molecules greater than 10 6 daltons a dense collagen membrane.