(192f) Improving Chitosan Fibers for Use As Non-Woven Fibrous Scaffolds:Effects of Fiber Processing On Mesenchymal Stem Cell Growth

IMPROVING CHITOSAN FIBERS FOR USE AS NON-WOVEN FIBROUS SCAFFOLDS:EFFECTS OF FIBER PROCESSING ON MESENCHYMAL STEM CELL GROWTH

Oksana Blowytsky2, Howard W.T. Matthew1,2

Departments of 1Biomedical Engineering, and 2Chemical Engineering and Materials Science,

Detroit, MI

Scaffold strength is an area of concern in current tissue engineering research. Because of superior molecular alignment, chitosan fibers have mechanical properties that allow them to reinforce porous chitosan and other hydrogel scaffolds. Biomaterials like chitosan are practical and favorable for use in tissue engineering due to their biocompatibility, biodegradability, rapid integration with soft tissue, and low cost. However, poor mechanical properties and inability to withstand moderate loads inside the body make these scaffolds infeasible for heart valve tissue engineering. Previous studies showed that chitosan fibers made by extruding chitosan solution into ammonia had increased mechanical strength. Derivitization of chitosan with N-acetyl-L-cysteine has also been shown to improve mechanical properties of chitosan in membranes. The focus of this project is to study ways to further enhance chitosan fiber mechanical properties and to form fibers into a scaffold that has similar mechanical properties as a human heart valve.

Chitosan fibers were produced using polymer fiber extrusion technique. High molecular weight chitosan was dissolved in 2 vol% acetic acid to produce a 1.5 wt% chitosan solution and extruded into ammonia and sodium hydroxide through a 24 gauge catheter. All fibers were created using this method and extruded into the following: (1)Control- 25wt% ammonia, (2) 0.50 M NaOH, (3) 1 M NaOH, and (4) 1.5 M NaOH. In a similar experiment, chitosan was derivatized with NAC and extruded into 25 wt% ammonia while exhibiting the following degrees of substitution: (1) Control- 25 wt% ammonia, (2) 6% (3) 15%, and (4) 20%. Fibers were collected from solution, washed with deionized water, and wrapped around metal frames to dry for 30-40 mins, until completely dry. Tensile testing of various physically modified wet fibers was done on the fibers to determine tensile strength, elasticity, and strain. Chitosan solution extruded into sodium hydroxide produced fibers that exhibited a 5-fold improvement in maximum stress from those extruded into 25 wt% ammonia. The strongest fibers were those extruded into 1M MaOH, exhibiting a maximum stress of about 15 MPa, as compared to about 2.7MPa when extruded into ammonia. Elasticity increased from about 13 MPa (control-ammonia) to about 70 MPa (1M NaOH), presenting a 5-fold improvement in stiffness. Chitosan derivatized with NAC and extruded into ammonia produced fibers that were generally the same strength and stiffness as the control—unaltered chitosan. Thus, derivatizing with NAC does not improve mechanical properties. Hypotheses for these results include: (a) the possibility of premature thiol crosslinking which prevented molecular rearrangement and fiber strengthening during extrusion; or (b) inadequate neutralization and washing of fibers after extrusion, resulting in partial polymer degradation. Procedures for addressing these problems have been discussed and will be implemented in the near future.

A non-woven fibrous scaffold (Figure 1) has been created using a felting technique. A study will be conducted to characterize mechanical properties, measure the degradation kinetics, and evaluate MSCs morphology, proliferation, and cytoskeletal organization of this non-woven chitosan fiber scaffold in a perfusion bioreactor.

Figure1. Nonwoven fiber scaffold made of chitosan extruded into 25wt% ammonia