Control of pore structure and size in freeze‐dried collagen sponges

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Abstract
Because of many suitable properties, collagen sponges are used as an acellular implant or a biomaterial in the field of tissue engineering. Generally, the inner three‐dimensional structure of the sponges influences the behavior of cells. To investigate this influence, it is necessary to develop a process to produce sponges with a defined, adjustable, and homogeneous pore structure. Collagen sponges can be produced by freeze‐drying of collagen suspensions. The pore structure of the freeze‐dried sponges mirrors the ice‐crystal morphology after freezing. In industrial production, the collagen suspensions are solidified under time‐ and space‐dependent freezing conditions, resulting in an inhomogeneous pore structure. In this investigation, unidirectional solidification was applied during the freezing process to produce collagen sponges with a homogeneous pore structure. Using this technique the entire sample can be solidified under thermally constant freezing conditions. The ice‐crystal morphology and size can be adjusted by varying the solute concentration in the collagen suspension. Collagen sponges with a very uniform and defined pore structure can be produced. Furthermore, the pore size can be adjusted between 20–40 μm. The thickness of the sponges prepared during this research was 10 mm. © 2001 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 58: 352–357, 2001