Drug-free and non-crosslinked chitosan scaffolds with efficient antibacterial activity against both Gram-negative and Gram-positive bacteria.

•Drug-free and non-crosslinked CS scaffolds were fabricated by freeze-drying.•CS scaffolds showed great antibacterial activity to Gram-negative P. gingivalis.•CS scaffolds showed great antibacterial activity to Gram-positive S. mutans.•CS scaffolds induce time-dependent bacteria clustering.•Crosslinked CS scaffolds showed no antimicrobial activity.