Complex sentence: Crack propagation of the impact region is reduced by thin layers of chitosan in between the highly-organized crystal hydroxyapatite structures-once a hydroxyapatite prism fractures the chitosan layers aid in preventing further cracks.
Split into simpler sentences: Crack propagation of the impact region is reduced by thin layers of chitosan in between the highly-organized crystal hydroxyapatite structures. Once a hydroxyapatite prism fractures the chitosan inter-layers aid in preventing further cracks.