Porous materials based on nanopolysaccharides for medical applications: Effect of crosslinking on pore structure and mechanical performance

Sammanfattning: The objective of this work was to develop nanochitin- and nanocellulose-based crosslinked porous nanostructured materials for wound dressing and cartilage repair with suitable porosity and mechanical properties to facilitate cell growth. In the first part of the work (papers I-III), chitosan-based nanocomposites loaded with a high concentration (50 wt%) of chitin nanocrystals (ChNC) and cellulose nanocrystals (CNC) were prepared via electrospinning for use as wound dressing materials. The electrospinning process resulted in highly interconnected porous mats and improved mechanical properties with the addition of nanocrystals and subsequent crosslinking using genipin, a bio-based crosslinking agent. The electrospinning solutions containing chitin nanocrystals showed the best spinnability, and the resultant fibers were continuous and homogeneous, with the highest strength and modulus due to better compatibility with the matrix. The effects of the surface chemistry of the nanocrystals on the electrospinning solution’s properties and the processability and properties of the resulting fibers were studied in detail. Poor spinnability of the cellulose nanocrystal system having sulfate surface groups was attributed to the coagulation between negatively charged cellulose nanocrystals and positively charged chitosan, as well as the high surface tension. Furthermore, the functional properties of the mats, including the water vapor transmission rate, O2/CO2 permeability and cytocompatibility toward adipose-derived stem cells (ASCs), were favorable for wound dressing applications.The second part of the work (papers IV and V) focused on the development of nanocellulose-based porous scaffolds for cartilage application. The first approach was to develop 3-dimensional (3D) porous scaffolds based on cellulose nanofibers (CNF), 70-90 wt%, in a matrix of gelatin/chitosan and in situ crosslinking using genipin. The compression modulus of the scaffolds was found to be in the range of natural cartilage. Although the modulus decreased significantly in phosphate-buffered saline (PBS) at 37°C, the mechanical properties were suitable for chondrogenesis. In the second approach, oven drying prior to the freeze-drying step was employed to achieve improved mechanical stability in wet conditions. Cellulose nanocrystals from a bioethanol process plant (CNCBE), 50 wt%, with carboxyl surface groups were used as reinforcement in a sodium alginate/gelatin (SA/G) hydrogel stabilized using CaCl2 and genipin. The mechanical performance of the hydrogels in moist conditions was comparable to that of natural cartilage. In both studies, the scaffolds showed interconnected pores and nanoscaled pore-wall roughness favorable for chondrocyte attachment. Furthermore, the scaffolds’ high porosity and good cytocompatibility toward chondrocytes and mesenchymal stem cells (MSCs) were considered beneficial for cell growth and extracellular matrix (ECM) production.This work demonstrated that fully bio-based porous nanocomposites can be successfully tailored for biomedical applications.