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  • 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 80C 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

    ResultsAlthough 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.

    IntroductionIn 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 37C. To obtain high-purity chitosan, impure chitosan was treated

    using a two step process of recrystallization and deacetylation.