Utilization of Directional Freezing for the Construction of Tissue Engineering Scaffolds

Although the field of tissue engineering has advanced significantly in the past decade, the inability to easily produce structured scaffolds continues to hinder its progress. We have proposed a method to create a porous scaffold utilizing directional freezing that is fast, reproducible and can be easily mass produced. Most importantly, this method creates long parallel channels within the scaffold. This should allow cells in the scaffold to grow more easily, and may aid scientists in predicting diffusion rates of nutrients and drugs throughout the scaffold. A cross-linked alginate gel was utilized in a directional freezing apparatus which incorporated a mold based on the horizontal Bridgeman design. The apparatus is designed to allow crystallization to occur in only one direction. The gel was frozen from 0°C to −40°C at a cooling rate of −18.3°C/minute. The samples were then freeze dried (leaving pores where ice dendrites had been), sectioned and viewed under a scanning electron microscope (SEM). Visual inspection revealed clear directionality present within the scaffolds. SEM photos also showed evenly spaced pores on the order of 100 μm present. A lesser magnification photo showed that the pores extended to become parallel channels producing a structured mesh that resembled an air filter. The directional freezing method is successful when used to create porous tissue engineering scaffolds, especially those with a low amount of tortuosity. By altering the cooling rate, it may be possible to create different pore distributions, thereby producing a method which can be utilized to create directional tissue engineering scaffolds quickly and effectively.