Native collagen fibrils (CF) were successfully extracted from bovine tendons using two different methods: modified acid-solubilized extraction for A-CF and pepsin-aided method for P-CF. The yields of A-CF and P-CF were up to 64.91% (±1.07% SD) and 56.78% (±1.22% SD) (dry weight basis), respectively. The analyses of both amino acid composition and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) confirmed that A-CF and P-CF were type I collagen fibrils. Both A-CF and P-CF retained the intact crystallinity and integrity of type I collagen’s natural structure by FTIR spectra, circular dichroism spectroscopy (CD) and X-ray diffraction detection. The aggregation structures of A-CF and P-CF were displayed by UV–Vis. However, A-CF showed more intact aggregation structure than P-CF. Microstructure and D-periodicities of A-CF and P-CF were observed (SEM and TEM). The diameters of A-CF and P-CF are about 386 and 282 nm, respectively. Although both A-CF and P-CF were theoretically concordant with the Schmitt hypothesis, A-CF was of evener thickness and higher integrity in terms of aggregation structure than P-CF. Modified acid-solubilized method provides a potential non-enzyme alternative to extract native collagen fibrils with uniform thickness and integral aggregation structure.

Silk fibroin (SF) is a natural protein polymer and promising biomaterial. Chemical modifications have attracted growing interest in expanding SF applications. However, the majority of amino acid residues in SF are non-reactive and most of the reactive ones are in the crystalline region. Herein, a modification was conducted to investigate the possibility of direct modification on the surface of natural SF by a reagent with a mild reactivity, the type and quantity of the residues involved in the reactions, and the structural changes upon modification. Infrared spectrum, ¹H NMR, titration and amino acid analyses, X-ray diffraction, and hemolysis test were used to analyze the materials. The results showed that sulfonic acid groups were grafted onto SF and the reaction occurred mainly at serine residues through hydroxyl groups. In total, 0.0958 mmol/g of residues participated in the modification with a modification efficiency of 7.6%. Moreover, the crystallinity and the content of β-sheet structure in SF increased upon modification. The modified material had good blood-compatibility. In conclusion, surface modification on native SF through serine residues was practicable and had the advantage of increased β-sheet structure. This will provide an alternative way for the modification of fibroin for the desired application in the biomedical field.