Abstract
Biopolymers extracted from renewable resources like chitosan and collagen exhibit interesting properties for the elaboration of materials designed for tissue engineering applications, among which are their hydrophilicity, biocompatibility and biodegradability. In many cases, functional recovery of an injured tissue or organ requires oriented cell outgrowth, which is particularly critical for nerve regeneration. Therefore, there is a growing interest for the elaboration of materials exhibiting functionalization gradients able to guide cells. Here, we explore an original way of elaborating such gradients by assembling particles from a library of functionalized microspheres. We propose a simple process to prepare chitosan-collagen hybrid microspheres by micro- and milli-fluidics, with adaptable dimensions and narrow size distributions. The adhesion and survival rate of PC12 cells on hybrid microspheres were compared to those on pure chitosan ones. Finally, functionalized microspheres were assembled into membranes exhibiting a functionalization gradient.
Highlights
Materials can be elaborated with physical, chemical and biochemical cues designed to orient the behavior of cells [1,2,3,4]
The microspheres were obtained by the initial formation of an emulsion with the biopolymers in the aqueous phase at acidic pH followed by solidification of the droplets. Both chitosan and collagen are soluble in acidic aqueous media but insoluble at neutral pH
The simplest way of solidifying the droplets was to induce a pH increase, which can be obtained by placing the acidic emulsion in the presence of ammonia vapors. This process allowed for the preparation of pure chitosan microspheres (Figure 2b) and of hybrid chitosan-collagen microspheres (Figure 2d) without chemical crosslinking agent, provided the initial biopolymers concentration was high enough to produce solids upon precipitation [31]
Summary
Materials can be elaborated with physical (topology, dimensionality, rigidity), chemical and biochemical cues designed to orient the behavior of cells [1,2,3,4]. To avoid the use of potentially toxic chemicals for the formation of stable microspheres, we studied the possibility to process chitosan solutions into microspheres by microfluidics and incorporate small amounts of collagen. This hybrid composition is attractive because it combines the relatively low viscosity of chitosan solutions with the property of collagen to promote cell adhesion. The assembly of microparticles provides an opportunity to generate materials with multiple functionalities without the necessity of site-specific postmodifications This approach can be an interesting alternative to microprocessing techniques, like bioprinting, when the sensibility of biopolymers to processing conditions (high temperature, electric fields, light irradiation...) can be an issue. The proof of concept was demonstrated with a fluorescent dye covalently attached to the microspheres and extended to a model protein
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