ORIGINAL ARTICLE Thermodynamic Parameters and Influence of Kinetic Factors on the Self-Assembly of Acid-Soluble Collagen Nanofibrils Fatemeh Elmi 1 & Maryam Mitra Elmi 2 & Fatemeh Nasiri Amiri 1 Received: 12 March 2017 /Accepted: 12 June 2017 # Springer Science+Business Media, LLC 2017 Abstract In this study, the acid-soluble collagen (ASC), ex- tracted from the fish scales of the Caspian white fish (Rutilus Firisikutum) was studied. The thermo-gravimetric analysis (TGA) showed the maximum demineralization accomplished after 48 h of EDTA treatment. SDS-PAGE and FT-IR spec- troscopy confirmed that extracted ASC was mainly type I collagen. FE-SEM images confirmed the porous and filamen- tary structure. The denaturation temperature (T d ) of ASC was 19 °C, and the transition heat achieved 9.6 J/g. Collagen self- assembly exhibit important potential because for biomedical applications and green technologies. Various inter- and intra- molecular no-covalent interactions such as hydrogen bonding, hydrophobic, electrostatic and Van der Waals interactions in- fluence the formation of self-assembled collagen. Therefore, critical factors as concentration of ASC, temperature, pH, and ionic strength play crucial role in function integration and structural modulation. The impacts of those external triggers on the kinetic self-assembly of ASC demonstrated a two- phase kinetic process, a sigmoidal plot. ACS showed pro- nounced self-assembly behavior when temperature and concentration reach above 14 °C and 0.125 mg/ml, higher concentration and/or temperature could stimulate the ASC self-assembly. The optimum pH value for ASC self- assembly was pH = 7. The effect of ionic strength on ASC self-assembly showed the turbidity increases significantly in 131.2 mM salt concentration. The process of self-assembly is mainly driven by thermodynamics. The thermodynamic study of collagen self-assembly illustrated that the activation energy, E a = 44.3 kJ/mol, the frequency factor, A = 117 × 10 5 s -1 , the enthalpy transition, ΔH ‡ = 42.98 kJ/mol, and the entropy transition, ΔS ‡ = -0.12 kJ/mol.K, respectively. These find- ings show that kinetics factors not only influence the self- assembly structure of ASC but also regulate the activation complex structure in the transition state. Keywords Collagen . Fish Scale . Nano Fibril . Self- Assembly . Kinetics . Thermodynamic Introduction Collagen is a fibrous protein in connective tissues, widely used for biomedical and pharmaceutical purposes. Type I col- lagen is the main protein of the extracellular matrix (ECM), which can play a critical role in the mechanical protection of tissues [1]. The self-assembling trait of collagen plays a cru- cial role in its physiological functions, and has attracted in- creasing attention due to its great potential for biological and industrial applications. In vivo, the presence of a variety of enzymes, especially for those cross-linking the collagen and other components of ECM, can promote the self-assembly of collagen, which has natural advantages for the regeneration of tissues. However, both in vivo and in vitro, type I collagen Electronic supplementary material The online version of this article (doi:10.1007/s11483-017-9492-5) contains supplementary material, which is available to authorized users. * Fatemeh Elmi f.elmi@umz.ac.ir 1 Department of Marine Chemistry, Faculty of Marine & oceanic sciences, University of Mazandaran, Babolsar, Iran 2 Cellular and Molecular Biology Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, Iran Food Biophysics DOI 10.1007/s11483-017-9492-5