Regular Article Thin films of silk fibroin and its blend with chitosan strongly promote biofilm growth of Synechococcus sp. BDU 140432 Sharbani Kaushik a , Mrinal K. Sarma a , Phurpa Dema Thungon b , Mallesh Santhosh b , Pranab Goswami a,b,⇑ a Centre for Energy, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India b Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India graphical abstract article info Article history: Received 17 May 2016 Revised 27 June 2016 Accepted 27 June 2016 Available online 28 June 2016 Keywords: Biofilm Synechococcus sp. Silk Chitosan Hydrophobicity Surface charge abstract The activating role of different polymer thin films coated over polystyrene support on the Synechococcus sp. biofilm growth was examined concurrently by measuring biofilm florescence using a dye and by mea- suring cell density in the isolated biofilm. Compared to blank (no coating), the increase in biofilm forma- tion (%) on silk, chitosan, silk-chitosan (3:2) blend, polyaniline, osmium, and Nafion films were 27.73 (31.16), 21.55 (23.74), 37.21 (38.34), 5.35 (8.96), 6.70 (6.55) and (nil), respectively with corresponding cell density (%) shown in the parentheses. This trend of biofilm formation on the films did not signifi- cantly vary for Escherichia coli and Lactobacillus plantarum strains. The films of 20 residues long each of glycine-alanine repeat peptide, which mimics a silk fibroin motif, and a hydrophobic glycine-valine repeat peptide, increased the biofilm growth by 13.53 % and 26.08 %, respectively. Silk and blend films showed highest adhesion unit (0.48–0.49), adhesion rate ((4.2–4.8)  10 6 , m/s) and Gibbs energy of adhesion (8.5 to 8.6 kT) with Synechococcus sp. The results confirmed interplay of electrostatic and hydrophobic interaction between cell-surface and polymer films for promoting rapid biofilm growth. This study established that the thin films of silk and the blend (3:2) promote rapid biofilm growth for all the tested microorganisms. Ó 2016 Elsevier Inc. All rights reserved. 1. Introduction Biofilms are microbial communities growing on solid surfaces and frequently embedded in a matrix of extracellular polymeric substances (EPS) [1]. The major driving forces for biofilm research http://dx.doi.org/10.1016/j.jcis.2016.06.065 0021-9797/Ó 2016 Elsevier Inc. All rights reserved. ⇑ Corresponding author at: Department of Biosciences and Bioengineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India. E-mail address: pgoswami@iitg.ernet.in (P. Goswami). Journal of Colloid and Interface Science 479 (2016) 251–259 Contents lists available at ScienceDirect Journal of Colloid and Interface Science journal homepage: www.elsevier.com/locate/jcis