Graduation Year

2020

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Biomedical Engineering

Major Professor

Ryan Toomey, Ph.D.

Co-Major Professor

Nathan Gallant, Ph.D.

Committee Member

William Lee III, Ph.D.

Committee Member

Piyush Koria, Ph.D.

Committee Member

Julie Harmon, Ph.D.

Keywords

Crystallization, Osteoblast Characterization, Poly(lactic-co-glycolic acid), Polymers, Surface Coatings

Abstract

Osteoarthritic and bone degenerative diseases are expected to grow immensely as the aging population, 65 years and older increases. Orthopedic implants are one sub-class of medical devices that are used to treat bone breaks and fractures. Traditionally, internal fixation implants are manufactured using titanium or stainless steel. Magnesium, a bioresorbable and biodegradable material, has been proposed as an alternative to titanium and stainless steel. The goal of this research is to control the degradation behavior of magnesium implants by developing crystallized thin poly(lactic acid) copolymer films as protective coatings. To do this, this work was divided into two aims. Aim I focused on characterizing the crystallization and degradation behavior of the films. Aim II focused on investigating the adhesion behavior of MC3T3 cells to ultrathin films. PLGA films ranging from 50nm to 200nm were prepared by spin casting and were either isothermal annealed to obtain crystallization or thermally erased to remove sample history. To test for degradation, films were immersed in simulated body fluid at 37°C and their dry mass was measured weekly. The glass transition, melt temperature, and thermal expansion coefficient was determined by ellipsometry on a heating stage. The surface morphology of the films was evaluated using atomic force microscopy. The adhesion strength was measured using the spinning disk apparatus. For 200nm films, the glass transition temperature on cooling was 59°C. The degree of crystallization increased with longer annealing times and the films reached maximum crystallinity by five days. The degree of crystallization raised the thin film melt temperature by 6°C, but the glass transition temperature remained unaffected by crystallization. Crystallized films eroded three times slower than thermally erased films, indicating that crystallization can tune the degradation rate of PLGA thin films. Lastly, the adhesion strength of MC3T3 cells increased by 1.5 times when hydroxyapatite was incorporated into the films. Future work should include degradation testing of magnesium coated with crystallized hydroxyapatite-PLGA films.

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