In situ gelation properties of a collagen–genipin sol with a potential for the treatment of gastrointestinal ulcers

Figures & data

Figure 1 Viscosity and deliverability of collagen sols.

Notes: (A) Collagen sol viscosity as a function of collagen concentrations. Collagen sols were dissolved in standard NPB (1 × NPB) without genipin, and viscosity was determined at a shear rate of 1 s⁻¹. (B) A typical load–deformation curve of 1.44% collagen sols through a catheter. Collagen sols were added to 5 mL disposable syringes and were delivered through a catheter (length, 1,600 mm; diameter, 2.8 mm). (C) Delivery loads of collagen sols as a function of sol viscosity in 1 × NPB without genipin.
Abbreviations: NPB, neutral phosphate buffer.

Figure 2 Temperature responsiveness of collagen sol gelation in the absence of genipin.

Notes: (A) Gelation curves of 0.5%–1.44% collagen sols in 1 × NPB. Numbers in the figure indicate collagen concentrations. Broken lines indicate rheometer set temperatures. (B) Gelation curves of 1.44% collagen sols in n × NPB. Numbers in the figure indicate NPB concentrations (n of n × NPB). Broken lines indicate rheometer set temperatures. (C) Gelation times (tg₃₇) of 1.44% collagen sols in n × NPB in the absence of genipin as a function of NPB concentrations. Gelation times were measured after the temperature reached 37°C.
Abbreviations: NPB, neutral phosphate buffer; min, minutes.

Figure 3 Temperature responsiveness of collagen sol gelation in the presence of genipin.

Notes: (A) Gelation curves (solid lines) of 1.44% collagen sols in 2 × NPB. Numbers in the figure indicate genipin concentrations, and broken lines indicate rheometer set temperatures. (B) Gelation times of 1.44% collagen sols in 2 × NPB as a function of genipin concentrations. Gelation times were measured after the temperature reached 37°C. (C) Magnified gelation curves (solid lines) of 1.44% collagen sols in 2 × NPB. Numbers in the figure indicate genipin concentrations.
Abbreviation: NPB, neutral phosphate buffer; min, minutes.

Figure 4 Effects of temperature and NPB concentrations on gelation times of 1.44% collagen sols.

Abbreviation: NPB, neutral phosphate buffer.

Figure 5 Effects of warming on genipin structure and genipin-induced crosslinking activities.

Notes: (A) ¹³C NMR spectra of genipin in pure water. (B) ¹³C NMR spectra of genipin in 5 × NPB at 37°C for 6 h. (C) UV spectra of genipin in pure water (solid line) and in 5 × NPB at 37°C for 6 h (broken line). (D) Effects of warming times on genipin-induced crosslinking activities at 23°C. Genipin solution (5 mM) in 5 × NPB was incubated at 37°C for 0–17 h and was then mixed with 1% collagen solution to prepare collagen sols. Gelation times at 23°C were determined using rheological tests. (E) Gelation curves of collagen sols at 37°C after reaching gel points (G′ = G″) at 23°C. Numbers in the figure indicate warming times of genipin solutions.
Abbreviations: NMR, nuclear magnetic resonance; NPB, neutral phosphate buffer; UV, ultraviolet; min, minutes.

Figure 6 Mechanical properties of collagen gels in penetration tests.

Notes: Representative stress–strain curves of 1.44% collagen gels in 1 × NPB (A), 1.6 × NPB (B), and 2 × NPB (C) after incubation at 37°C for 24 h. Numbers in the figure indicate genipin concentrations in sols. Elastic moduli of 1.44% collagen gels in 1 × NPB (D), 1.6 × NPB (E), and 2 × NPB (F) after incubation at 37°C for 24 h. Data are presented as mean ± SD (n=4). Horizontal bars indicate significant differences between samples (**p<0.01).
Abbreviations: NPB, neutral phosphate buffer; SD, standard deviation.

Figure 7 Ex vivo gelation tests of collagen gels in artificial porcine stomach ulcers.

Notes: (A) Artificial ulcers (30 × 30 mm) were induced in excised stomach tissues and were elongated vertically by gravity. (B) A stomach specimen on an aluminum plate tilted at 60°. (C) Artificial ulcer with 0.5% collagen sol in 1 × NPB containing 4 mM genipin. (D) Artificial ulcer with 1.44% collagen sols in 1.6 × NPB containing 4 mM genipin. Artificial ulcers were elongated by gravity. Stomach specimens (C and D) were stored at 37°C for 2 h after application of collagen sol.
Abbreviation: NPB, neutral phosphate buffer.

Figure 8 H&E-stained histological sections of artificial ulcers with collagen sols.

Notes: Stomach specimens were placed horizontally (A) or were tilted at 60° (B–F). (A and B) 0.5% collagen sol in 1 × NPB. (C) 0.9% collagen sol in 1 × NPB. (D) 1.44% collagen sols in 1 × NPB. (E) 1.44% collagen sols in 1.6 × NPB. (F) 1.44% collagen sols in 2 × NPB. Bars indicate 100 µm. (G) Magnification of (E). (H) Magnification of (F). Bars indicate 50 µm.
Abbreviations: H&E, hematoxylin and eosin; NPB, neutral phosphate buffer.

Figure 9 Thickness of collagen gel coverage on artificial porcine stomach ulcers.

Notes: Thickness (mean ± SD; n=10) was determined from H&E-stained histological sections of artificial ulcers with collagen sols. Numbers on the vertical axis indicate collagen/NPB concentration ratios. ND indicates no gel deposition on artificial ulcers surfaces. Vertical bars indicate significant differences between samples (**p<0.01).
Abbreviations: SD, standard deviation; H&E, hematoxylin and eosin; NPB, neutral phosphate buffer.