Partially nanofibrous architecture of 3D tissue engineering scaffolds

Abstract

An ideal tissue-engineering scaffold should provide suitable pores and appropriate pore surface to induce desired cellular activities and to guide 3D tissue regeneration. In the present work, we have developed macroporous polymer scaffolds with varying pore wall architectures from smooth (solid), microporous, partially nanofibrous, to entirely nanofibrous ones. All scaffolds are designed to have well-controlled interconnected macropores, resulting from leaching sugar sphere template. We examine the effects of material composition, solvent, and phase separation temperature on the pore surface architecture of 3D scaffolds. In particular, phase separation of PLLA/PDLLA or PLLA/PLGA blends leads to partially nanofibrous scaffolds, in which PLLA forms nanofibers and PDLLA or PLGA forms the smooth (solid) surfaces on macropore walls, respectively. Specific surface areas are measured for scaffolds with similar macroporosity but different macropore wall architectures. It is found that the pore wall architecture predominates the total surface area of the scaffolds. The surface area of a partially nanofibrous scaffold increases linearly with the PLLA content in the polymer blend. The amounts of adsorbed proteins from serum increase with the surface area of the scaffolds. These macroporous scaffolds with adjustable pore wall surface architectures may provide a platform for investigating the cellular responses to pore surface architecture, and provide us with a powerful tool to develop superior scaffolds for various tissue-engineering applications.

Figure 1

SEM micrographs of partially nanofibrous PLLA/PDLLA films. (A) PDLLA:PLLA=50:50; (B) PDLLA:PLLA=60:40; (C) PDLLA:PLLA=75:25; (D) PDLLA:PLLA=85:15. The total polymer concentration: 10w/v%. Original magnification: 5,000x.

Figure 2

SEM micrographs of 3D macroporous and partially nanofibrous PLLA/PDLLA scaffolds, phase separated in THF at -20°C. (A,B) 100% PLLA; (C,D) PLLA:PDLLA = 75:25; (E,F) PLLA:PDLLA = 50:50; (G,H) PLLA:PDLLA = 25:75; (I,J,M) PLLA:PDLLA = 15:85; (K,L) 100% PDLLA; (M) Cross section of pore wall to show the distribution of nanofibrous and solid domains (PLLA:PDLLA = 15/85). The total polymer concentration: 10w/v%. Original magnification: 100x for A, C, E, G, I, K; 1,000x for B, D, F, H, J, M; and 5,000x for L.

Figure 2

SEM micrographs of 3D macroporous and partially nanofibrous PLLA/PDLLA scaffolds, phase separated in THF at -20°C. (A,B) 100% PLLA; (C,D) PLLA:PDLLA = 75:25; (E,F) PLLA:PDLLA = 50:50; (G,H) PLLA:PDLLA = 25:75; (I,J,M) PLLA:PDLLA = 15:85; (K,L) 100% PDLLA; (M) Cross section of pore wall to show the distribution of nanofibrous and solid domains (PLLA:PDLLA = 15/85). The total polymer concentration: 10w/v%. Original magnification: 100x for A, C, E, G, I, K; 1,000x for B, D, F, H, J, M; and 5,000x for L.

Figure 3

SEM micrographs of macroporous and partially nanofibrous PLLA/PLGA scaffolds, phase separated in THF at -20°C (PLGA:PLLA=25:75). The total polymer concentration was 10w/v%. Original magnification: 100x for A; 5,000x for B.

Figure 4

SEM micrographs of macroporous and microporous PLLA scaffolds, phase separated in dioxane at different temperatures. (A,B) -20°C; (C,D) Liquid nitrogen (-196°C). Original magnification: A & C, 100x; B, 500x; and D, 1,000x.

Figure 5

SEM micrographs of macroporous and nanofibrous PLLA scaffolds, phase separated in dioxane/THF in liquid nitrogen (-196°C). (A-C) THF:dioxane=100:0; (D-F) THF:dioxane=60:40; (G-I) THF:dioxane=40:60; (J-L) THF:dioxane=20:80. Original magnification: 100x for A, D, G, J; 500x for B, E, H, K; and 20,000x for C, F, I, L.

Figure 6

Specific surface areas of: (A) partially nanofibrous PLLA/PDLLA scaffolds (phase-separated in THF at -20 R°C) as a function of PLLA wt% in the polymer blends; (B) PLLA scaffolds with different pore wall surface morphologies: Nano - nanofibrous, phase separation in THF at -20 C°C; Micro-(-196°C) - microporous, phase separation in dioxane in liquid nitrogen; Micro-(-20°C) - microporous, phase separated in dioxane at -20°C; Solid - solid-walled, generated by solvent evaporation from the polymer solution in dichloromethane; (C) PLLA scaffolds phase separated in the solvent mixture of dioxane/THF with varying ratios, in liquid nitrogen (at -196°C).

Figure 7

Serum protein adsorption on macroporous scaffolds with different pore wall surface architectures. (A) PLLA scaffolds phase separated in different solvents: Nano - nanofibrous, phase separated in THF at -20°C; Micro-(-196 C) - microporous, phase separated in dioxane in liquid nitrogen; Micro-(-20°C) - microporous, phase separated in dioxane at -20°C; Solid - solid-walled, generated by solvent evaporation from the polymer solution in dichloromethane; (B) PLLA/PDLLA partially nanofibrous scaffolds with different PLLA wt% in polymer blends, phase-separated in THF at -20°C.