1. Brendan Eckardt, Ukrit Thamma, Himanshu Jain
Materials Science and Engineering
Purification of chitosan for use in
injectable bioactive glass systems
Acknowledgement(s):
David and Lorraine Freed Undergraduate Research Symposium, Lehigh University
Tia Kowal, Matthias Falk, Jim Roberts, Norm Zheng, Raymond Pearson, Amelia Labak, Binay Patel, Zhen Lin, IMI-NFG (NSF) DMR-0844014
Experimental
• Dissolve impure chitosan in acetic acid and wait 24 hours
• Vacuum filter twice and add NaOH to precipitate chitosan out of the clean solution
• Freeze dry recrystallized chitosan
• Soak in NaOH bath at 80°C for 4 hours to remove acetyl group
• Vacuum dry chitosan
• Characterize using FTIR and titration
Summary
Recent years have seen the use of bioactive glass as a means of regenerating bone
tissue. Glass scaffolds have proved capable of osteo-regeneration, but still require
implantation via surgery. In order to treat small fractures, which make up a larger
percentage of injuries than those treatable by scaffolds, a solution that does not require
invasive surgery is desired. The purpose of this research was to develop an injectable
system containing bioactive glass powder, thereby eliminating the need for surgery.
Future Work
• Vacuum dry chitosan before FTIR tests
• Freeze dry recrystallized chitosan to obtain powder
• Use NMR to corroborate results of titration
Results
Although it was called for, the recrystallized chitosan was not freeze dried
and was instead vacuum dried, resulting in tough chitosan flakes rather than
a fine powder. Due to the low surface area of the chitosan flakes and the
difference in size, purification would at best be non-uniform.
FTIR
• absorption method of characterization
• wavelengths correspond to
different functional groups
• by comparing absorbance of OH
and NH3 peaks the purity can be
calculated
Titration
Acid-base titration was also used to determine the degree of
deacetylation. The results show a much closer spread than the FTIR
calculations above.
Introduction
In addition to being non-toxic to humans, any proposed system for injectable bioactive
glass must meet several requirements.
The Ideal Glass Powder System:
• Injectable at room temperature
• Gels upon heating to keep glass powder at the injured site
• Gels at or just below human body temperature
• Contains bioactive glass powder to regenerate bone
By far the greatest challenge in meeting these goals is the thermal behavior of the
mixture. At room temperature, the mixture must flow like a liquid in order to be
injected. However, upon entering the body the mixture must gel as it heats to keep the
glass at the injection site. An example of gelation is shown below.
This increase in viscosity upon heating is the exact opposite of how most materials
behave. One substance capable of achieving this unusual behavior is chitosan. Placing
chitosan in acidic solution gives a product that increases in viscosity upon heating. The
exact temperature of gelation depends strongly on the purity, or degree of deacetylation,
of the chitosan.
By increasing the purity of the chitosan used as shown above, the gelation temperature
can be lowered to 37°C. To obtain high-purity chitosan, impure chitosan was treated
using a two step process of recrystallization and deacetylation.