Fast and continuous preparation of high polymerization degree cellulose nanofibrils and their three-dimensional macroporous scaffold fabrication

C6-carboxy-cellulose with a carboxylate content of 0.8 mmol g(-1) was obtained by oxidation of once-dried cellulose, using the 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)/NaClO/NaClO2 system at pH 6.8 and 60 degrees C for 16 h. This method, with the addition of reagents in the order TEMPO, NaClO and NaClO2, was 38 h faster than a previously published method. Individualized cellulose nanofibrils with a width of 3-5 nm and a length of several hundred nanometers were prepared by homogenizing the C6-carboxy-cellulose-water suspension. Macroporous cellulose nanofibril/poly(vinyl alcohol) scaffolds with interconnected large pores of 20-100 mm diameter and small pores of 2-10 mm diameter were fabricated. The cellulose nanofilaments formed nanofibrous structures on the surface of the PVA wall, which was similar to that of the collagen skeleton of the extracellular matrix. NIH/3T3 cells were cultured in the scaffolds for 4 weeks, SEM observation showed that the cells were anchored and clustered on the cellulose nanofilaments, forming spherical colonies. The extracellular matrix (ECM) was filled with mineralized particles.