View in EDS

Mechanisms of pore formation in hydrogel scaffolds textured by freeze-drying

Saved in:
Bibliographic Details
Title: Mechanisms of pore formation in hydrogel scaffolds textured by freeze-drying
Authors: Jérôme Grenier, Hervé Duval, Fabrice Barou, Pin Lv, Bertrand David, Didier Letourneur
Contributors: Laboratoire de Génie des Procédés et Matériaux - EA 4038 (LGPM), CentraleSupélec, Laboratoire de mécanique des sols, structures et matériaux (MSSMat), CentraleSupélec-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Recherche Vasculaire Translationnelle (LVTS (UMR_S_1148 / U1148)), Institut National de la Santé et de la Recherche Médicale (INSERM)-Université Paris Cité (UPCité)-Université Sorbonne Paris Nord, Géosciences Montpellier, Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles (UA), Centre Européen de Biotechnologies et Bioéconomie (CEBB), ANR-11-IDEX-0003,IPS,Idex Paris-Saclay(2011)
Source: Acta Biomaterialia. 94:195-203
Publisher Information: Elsevier BV, 2019.
Publication Year: 2019
Subject Terms: 0301 basic medicine, MESH: 3T3 Cells, Polymers, MESH: Freeze Drying, MESH: Solvents, Biocompatible Materials, 02 engineering and technology, MESH: Tissue Engineering, Mice, MESH: Biocompatible Materials, MESH: Tissue Scaffolds, Freezing, MESH: Animals, Scanning, 3D cell culture, Tissue Scaffolds, Hydrogels, 3T3 Cells, MESH: Bone and Bones, MESH: Polymers, Cross-Linking Reagents, Rheology, 0210 nano-technology, Porosity, MESH: Hydrogels, MESH: Microscopy, Polysaccharide-based, MESH: Cross-Linking Reagents, Porous scaffolds, Electron, Bone and Bones, 03 medical and health sciences, MESH: Porosity, MESH: Rheology, Polysaccharides, Animals, [SPI.GPROC]Engineering Sciences [physics]/Chemical and Process Engineering, [SDV.IB.BIO]Life Sciences [q-bio]/Bioengineering/Biomaterials, Ice-templating, MESH: Mice, Tissue Engineering, Hydrogel, MESH: Polysaccharides, [CHIM.POLY]Chemical Sciences/Polymers, Freeze Drying, Freeze-drying, Microscopy, Electron, Scanning, Solvents, MESH: Freezing
Description: Whereas freeze-drying is a widely used method to produce porous hydrogel scaffolds, the mechanisms of pore formation involved in this process remained poorly characterized. To explore this, we focused on a cross-linked polysaccharide-based hydrogel developed for bone tissue engineering. Scaffolds were first swollen in 0.025% NaCl then freeze-dried at low cooling rate, i.e. -0.1 °C min-1, and finally swollen in aqueous solvents of increasing ionic strength. We found that scaffold's porous structure is strongly conditioned by the nucleation of ice. Electron cryo-microscopy of frozen scaffolds demonstrates that each pore results from the growth of one to a few ice grains. Most crystals were formed by secondary nucleation since very few nucleating sites were initially present in each scaffold (0.1 nuclei cm-3 °C-1). The polymer chains are rejected in the intergranular space and form a macro-network. Its characteristic length scale coincides with the ice grain size (160 μm) and is several orders of magnitude greater than the mesh size (90 nm) of the cross-linked network. After sublimation, the ice grains are replaced by macro-pores of 280 μm mean size and the resulting dry structure is highly porous, i.e. 93%, as measured by high-resolution X-ray tomography. In the swollen state, the scaffold mean pore size decreases in aqueous solvent of increasing ionic strength (120 µm in 0.025% NaCl and 54 µm in DBPS) but the porosity remains the same, i.e. 29% regardless of the solvent. Finally, cell seeding of dried scaffolds demonstrates that the pores are adequately interconnected to allow homogenous cell distribution. STATEMENT OF SIGNIFICANCE: The fabrication of hydrogel scaffolds is an important research area in tissue engineering. Hydrogels are textured to provide a 3D-framework that is favorable for cell proliferation and/or differentiation. Optimum hydrogel pore size depends on its biological application. Producing porous hydrogels is commonly achieved through freeze-drying. However, the mechanisms of pore formation remain to be fully understood. We carefully analyzed scaffolds of a cross-linked polysaccharide-based hydrogel developed for bone tissue engineering, using state-of-the-art microscopic techniques. Our experimental results evidenced the shaping of hydrogel during the freezing step, through a specific ice-templating mechanism. These findings will guide the strategies for controlling the porous structure of hydrogel scaffolds.
Document Type: Article
Language: English
ISSN: 1742-7061
DOI: 10.1016/j.actbio.2019.05.070
Access URL: https://hal.archives-ouvertes.fr/hal-02144830/file/Preprint%20-%20Mechanisms%20of%20pore%20formation.pdf
https://pubmed.ncbi.nlm.nih.gov/31154055
https://hal.archives-ouvertes.fr/hal-02144830
https://europepmc.org/article/MED/31154055
https://www.ncbi.nlm.nih.gov/pubmed/31154055
https://www.sciencedirect.com/science/article/pii/S1742706119303976
https://hal.archives-ouvertes.fr/hal-02144830/document
Rights: Elsevier TDM
Accession Number: edsair.doi.dedup.....bf6d615335d9fb503303c7c53fe9d53d
Database: OpenAIRE
Description
Abstract:Whereas freeze-drying is a widely used method to produce porous hydrogel scaffolds, the mechanisms of pore formation involved in this process remained poorly characterized. To explore this, we focused on a cross-linked polysaccharide-based hydrogel developed for bone tissue engineering. Scaffolds were first swollen in 0.025% NaCl then freeze-dried at low cooling rate, i.e. -0.1 °C min-1, and finally swollen in aqueous solvents of increasing ionic strength. We found that scaffold's porous structure is strongly conditioned by the nucleation of ice. Electron cryo-microscopy of frozen scaffolds demonstrates that each pore results from the growth of one to a few ice grains. Most crystals were formed by secondary nucleation since very few nucleating sites were initially present in each scaffold (0.1 nuclei cm-3 °C-1). The polymer chains are rejected in the intergranular space and form a macro-network. Its characteristic length scale coincides with the ice grain size (160 μm) and is several orders of magnitude greater than the mesh size (90 nm) of the cross-linked network. After sublimation, the ice grains are replaced by macro-pores of 280 μm mean size and the resulting dry structure is highly porous, i.e. 93%, as measured by high-resolution X-ray tomography. In the swollen state, the scaffold mean pore size decreases in aqueous solvent of increasing ionic strength (120 µm in 0.025% NaCl and 54 µm in DBPS) but the porosity remains the same, i.e. 29% regardless of the solvent. Finally, cell seeding of dried scaffolds demonstrates that the pores are adequately interconnected to allow homogenous cell distribution. STATEMENT OF SIGNIFICANCE: The fabrication of hydrogel scaffolds is an important research area in tissue engineering. Hydrogels are textured to provide a 3D-framework that is favorable for cell proliferation and/or differentiation. Optimum hydrogel pore size depends on its biological application. Producing porous hydrogels is commonly achieved through freeze-drying. However, the mechanisms of pore formation remain to be fully understood. We carefully analyzed scaffolds of a cross-linked polysaccharide-based hydrogel developed for bone tissue engineering, using state-of-the-art microscopic techniques. Our experimental results evidenced the shaping of hydrogel during the freezing step, through a specific ice-templating mechanism. These findings will guide the strategies for controlling the porous structure of hydrogel scaffolds.
ISSN:17427061
DOI:10.1016/j.actbio.2019.05.070