Figure 1.
An illustration of the essential components of the setup (reservoir, conductor and template) and the sequential steps involved in the Dip TIPS process (1: assembling, 2: quenching, 3: coarsening, 4: freeze-drying and 5: collection of the foam).
Table 1.
Parameters under Dip TIPS study with the information about tested variables and other constant conditions followed* (n = 6).
Figure 2.
Macro- and micro- morphological features of the foams.
(a) gross appearance of the open-end capsular, tubular, flat 3D porous PLCL300 scaffolds (5% w/v, quenched at −80°C) with variable foam thickness and inner lumen diameters; (b) schematic of different sections of the scaffold analyzed under SEM; typical SEM images of (c) cross section of the scaffold showing the lengthwise cut elongated pores in direction of the applied thermal gradient (pore walls and overall channeled character of pores are clearly visible), (d) longitudinal section of the scaffold showing interconnected open-cells between particular channels, and (e) outer surface and (g) inner surface of the scaffold revealing the anisotropic nature of the pores. Panel (f) is the middle section of the foam's cross section (black dotted line in the panel c) showing an internal honey-comb like pore architecture.
Figure 3.
Influence of the polymer type.
SEM images of the cross section, the outer and inner surfaces of the foams prepared from PLA, PCL and PLCL300 (5% w/v, quenched at −80°C for 30 s) revealed the relatively superior pore morphology without any micro-cracks of the PLCL foam as compared to that of pure PLA and PCL foams.
Figure 4.
Influence of the polymer molecular weight.
SEM images of the cross section and the outer surface of the foams prepared from PLCL solution (5% w/v, quenched at −80°C for 30 s) of variable molecular weights showed the well-organized pore morphology and increased overall foam thickness in PLCL300 (Mw = 316,000 g/mol and Mn = 120,000 g/mol) as compared to that of PLCL150 (Mw = 162,000 g/mol and Mn = 57,000 g/mol).
Figure 5.
Influence of the polymer concentration.
SEM images of the cross section and the outer surface of the PLCL300 scaffolds prepared from variable concentration (3, 5, 7 and 10% w/v, quenched at −80°C for 30 s) demonstrated that the pore size was inversely proportional, and the pore wall thickness and the overall foam thickness was directly proportional to increase in the polymer concentration. Measurements were performed by Image J (n = 25). The differences in the foam thickness or the pore size between any two groups were found to be statistically significant. The correlation coefficients between the polymer concentration and the outer pore size and the foam thickness were calculated to be −0.99 and +0.92, respectively.
Figure 6.
Influence of the quenching temperature.
SEM images of the cross section and the outer surface of PLCL300 foams (5% w/v) prepared at various quenching temperatures (−25, −80 and −196°C) for 30 s revealed that the increase in the quenching depth promoted the organization of pores with a significant decrease in the average pore size, but with a slight alteration in the overall foam thickness. Measurements were done by Image J (n = 25). The differences in the foam thickness or the pore size between any two groups were found to be statistically significant. The correlation coefficients between the quenching temperature and the outer pore size and the foam thickness were calculated to be −0.99 and +0.42, respectively.
Figure 7.
Influence of the quenching time.
SEM images of the cross section and the outer surface of PLCL300 (5% w/v) foams prepared at −80°C for different quenching times (15, 30, 45 and 60 s) demonstrated the facile fabrication of foams of variable thickness without any significant change in the average pore size but with a slight thickening of the pore wall. Measurements were performed by Image J (n = 25). The differences in the outer pore sizes were statistically not significant, but the differences in the thickness between any two groups were statistically significant. The correlation coefficients between the quenching time and outer pore size and foam thickness were calculated to be +0.98 and +0.99, respectively.
Figure 8.
Influence of the coarsening time.
SEM images of the cross section and the outer surface of the PLCL300 (3% w/v) foams prepared by quenching at −25°C for 30 s and coarsening for various times (0, 0.5, 1 and 2 h) suggested that an increase in the coarsening time resulted in better organization of the solvent rich phase what after solvent removal led to well-ordered pores.
Figure 9.
Influence of the mold diameter.
SEM images of the cross section and the outer surface of the PLCL300 (5% w/v) foams prepared with molds of 2, 3 and 4 mm diameter at −80°C for 30 s demonstrated the ability to fabricate foams with variable inner lumen diameters without any significant change in the average pore size but with a slight thickening of the pore wall and decrease in the overall foam thickness. Measurements were performed by Image J (n = 25). The differences between any two groups were statistically not significant. The correlation coefficients between the mold diameter and outer pore size and foam thickness were calculated to be −0.92 and −0.98, respectively.
Table 2.
DSC analysis of PLCL300 before processing (control) and PLCL300 foams (5% wt, 30 s) prepared under various quenching temperatures (n = 3).
Table 3.
Mercury intrusion porosimetry and BET surface area analysis of PLCL300 foams (5% wt, 30 s) prepared at various quenching temperatures (n = 3).
Figure 10.
The cumulative pore volume (line with markers) and derivative pore size distribution (vertical columns) of PLCL300 foam prepared at −80°C for 30 s (pore range: 0.2 to 116 µm).
Figure 11.
In vivo behavior of the test (a–e) and control (f–j) scaffolds.
(a, f) 4-week old anastomosed scaffolds as seen in the omentum of the model animal; (b, g) low magnification and (c, h) high magnification H&E stained sections showing the host cell infiltration and cell distribution (deep blue-purple nuclei, pink cytoplasmic and extracellular proteins); (d, i) TRI stained sections showing the synthesis of extracellular collagen (blue or green) by the invading cells; and (e, j) anti-CD31 stained sections showing the infiltration of microvascular endothelial cells (brown). The black arrow in the panels (b–e) represents the direction of host cell/tissue infiltration. Scale: 200 µm.
Figure 12.
A schematic illustration of the mechanism of the formation of anisotropic oriented interconnected channeled pores (1: quenching, 2: freeze-drying).
Table 4.
Summary of the effects of various process parameters on the foam properties (n = 6).
Table 5.
Summary of the practical advantages of Dip TIPS in comparison with the state of the art method for the fabrication of anisotropic porous foams of various shapes for various applications.