A popular candidate for bioceramics for bone tissue regeneration is hydroxyapatite (HAp), which is known for its biocompatibility [1] due to its resemblance to the inorganic component of bone. However, for optimal performance the ceramic scaffolds should not only be chemically biocompatible, but also match the structure of bone tissue which consists of a highly anisotropic network of interconnected channels that ensure proper flow of blood and nutrients to the bone cells. One of the challenges when reproducing this structure is the size of the channels. While spanning a length of centimetres, the diameter is of the micrometre scale [2], posing difficulties for many shaping techniques. Traditional techniques, such as extrusion, can produce aligned porosities with millimetre-sized channels, but at the micrometre scale it is challenging to go beyond a random network of pores.

Freeze-casting allows the production of microchannels. In freeze-casting, ice is used to create vertical micron-sized channels by growing them from the bottom and upwards in an aqueous powder suspension. After sublimating the ice and firing the green body, a porous structure is obtained with channels where the ice was. Currently the technique is undergoing rapid development and has been used to create bone scaffolding in biofriendly materials [3, 4], but so far focus has been on realising high mechanical strength of the structures and not on obtaining a network structure with a resemblance to human bone [3].

In our study, we are investigating the control of microchannel growth in freeze-casted bioceramics for bone tissue regeneration. During the freeze-casting process, the HAp suspension is placed directly on a copper plate connecting the suspension to the cooling source and acting as a nucleation site for the ice crystals. By varying the shape of the plate, the nucleation and growth of ice throughout the suspension is affected, which directly changes the porous structure of the final ceramic. Here we investigate copper plates with five different patterns: A slope with a 10° angle, a pyramid, a spiral, parallel lines, and a plate with four tops distributed evenly along the circumference of the circular plate. The influence of the patterned surfaces on the freeze-casted channels, their orientation, and any domains within the pores are presented.
 
 
[1]      Q. Fu, M. N. Rahaman, B. S. Bal, and R. F. Brown, “In vitro cellular response to hydroxyapatite scaffolds with oriented pore architectures,” Mater. Sci. Eng. C, vol. 29, no. 7, pp. 2147–2153, Aug. 2009.
[2]      L. M. Ross and E. D. Lamperti, Eds., General Anatomy and Musculoskeletal System. Thieme, 2006.
[3]      S. Deville, “Freeze-Casting of Porous Biomaterials: Structure, Properties and Opportunities,” Materials (Basel)., vol. 3, no. 3, pp. 1913–1927, Mar. 2010.
[4]      U. G. K. Wegst, H. Bai, E. Saiz, A. P. Tomsia, and R. O. Ritchie, “Bioinspired structural materials,” Nat. Mater., vol. 14, pp. 23–36, 2015.