Versatile Wedge-Based System for the Construction of Unidirectional Collagen Scaffolds by Directional Freezing: Practical and Theoretical Considerations

Abstract

Aligned unidirectional collagen scaffolds may aid regeneration of those tissues where alignment of cells and extracellular matrix is essential, as for instance in cartilage, nerve bundles, and skeletal muscle. Pores can be introduced by ice crystal formation followed by freeze-drying, the pore architecture reflecting the ice crystal morphology. In this study we developed a wedge-based system allowing the production of a wide range of collagen scaffolds with unidirectional pores by directional freezing. Insoluble type I collagen suspensions were frozen using a custom-made wedge system, facilitating the formation of a horizontal as well as a vertical temperature gradient and providing a controlled solidification area for ice dendrites. The system permitted the growth of aligned unidirectional ice crystals over a large distance (>2.5 cm), an insulator prolonging the freezing process and facilitating the construction of crack-free scaffolds. Unidirectional collagen scaffolds with tunable pore sizes and pore morphologies were constructed by varying freezing rates and suspension media. The versatility of the system was indicated by the construction of unidirectional scaffolds from albumin, poly(vinyl alcohol) (a synthetic polymer), and collagen-polymer blends producing hybrid scaffolds. Macroscopic observations, temperature measurements, and scanning electron microscopy indicated that directed horizontal ice dendrite formation, vertical ice crystal nucleation, and evolutionary selection were the basis of the aligned unidirectional ice crystal growth and, hence, the aligned unidirectional pore structure. In conclusion, a simple, highly adjustable freezing system has been developed allowing the construction of large (hybrid) bioscaffolds with tunable unidirectional pore architecture.

Self-healing Characteristics of Collagen Coatings with Respect to Surface Abrasion

“…Through this process the frozen water content in the collagen gel coating could be transformed directly to vapor from the solid phase, thereby preserving the integrity of the collagen fibers during the drying process. It should be mentioned that freeze-drying process is typically used to fabricate a porous scaffold structure in collagens for tissue engineering 40 41 42 . The principle of freeze-drying is based on sublimation process in which the frozen water in the collagen gel coating transforms directly to vapor from a solid phase 43 .…”

Anisotropic Materials for Skeletal‐Muscle‐Tissue Engineering

“…12). [102] For example, to produce an aligned microporous scaffold, a thermally insulating cylindrical tube (e.g., Teflon) is filled with an aqueous polymeric solution and a temperature gradient in the freezing range of the solvent is established between the two ends. As the polymer solution freezes, the aqueous phase crystallizes into cylinders with microscale diameters and the polymer phase is deposited between the solvent crystals.…”

Construction of bionic tissue engineering cartilage scaffold based on three‐dimensional printing and oriented frozen technology

“…This method allows for optimizing the scaffold properties at two different levels to better mimic biological cartilage tissues. In addition, PLGA has good biocompatibility; 39 the cross‐linking agent genipin is a natural extract, suitable for biological material treatment; dECM used in this research is a natural pig cartilage extract, displaying better biological activity . These multimaterial scaffolds can be used in in vitro cell experiments and in vivo transplantation experiments.…”

“…In addition, hydrogels, such as decellularized extracellular matrix (dECM), collagen, gelatin, with cartilage stem cells and growth factors added were proven to have biological activity suitable for stem cell growth and tissue regeneration, but their mechanical properties were weak. [11][12][13][14][15][16][17][18][19] By freeze drying, both of these materials can be made into porous structures 17,18 beneficial to cell growth. In further research, by gradient or graded structural designing and oriented freezing, the scaffolds' mechanical properties can be enhanced and bionically optimized.…”