Amethod of top down preparation of chitosan nano particles and nanofibers is proposed. Chitinnanofibrils
(chitin NFs) were prepared using ultrasonic assisted method from crab shells with an average diameter
of 5 nm and the length less than 3 m as analyzed by atomic force microscopy and transmission electron
microscopy. These chitin nanofibers were used as the precursor material for the preparation of chitosan
nanoparticles and nanofibers. The degree of deacetylation of these prepared chitosan nanostructures
were found to be approximately 98%. In addition these chitosan nanostructures showed amorphous crystallinity.
Transmission electron microscopic studies revealed that chitosan nanoparticles were roughly
spherical in nature and had diameters less than 300 nm. These larger particles formed through selfassembly
of much smaller 25 nm particles as evidenced by the TEM imaging. The diameter and the length
of the chitosan nanofibers were found to be less than 100 nm and 3 m respectively. It is envisaged that
due to the cavitation effect, the deacetylated chitin nanofibers were broken down to small pieces to form
seed particles. These seed particles can then be self-assembled to form larger chitosan nanoparticles.