Text

theses

Polycarbonates are a class of degradable polymers used in biomedical applications including vehicles for drug-delivery and sca olds for tissue engineering. They can be classi ed into two groups i.e. aliphatic and aromatic polycarbonates, each with distinctive mechanical properties and degradation mechanisms. Aliphatic polycarbonates are soft and flexible materials most suitable for cartilage or blood vessel repair. Aromatic polycarbonates are strong and stiff , useful for hard tissue applications such as bone regeneration. While aliphatic polycarbonates may undergo a surface erosion process mediated by biological activity, aromatic polycarbonates as for example tyrosine-derived compositions undergo hydrolytic degradation and slow mass erosion. In this thesis, aromatic-aliphatic polycarbonates from natural (hydroxyalkyl)phenols such as tyrosol were explored with the rationale of combining the advantages of both classes of polycarbonates. Copolymers of tyrosol and homovanillyl alcohol had high tensile strength, and showed enzymatic surface erosion by lipase, in vitro. During erosion, mechanical properties were retained for at least 18 weeks: The wet modulus of E = 0.9 +/- 0.1GPa was retained at 65% (w/w) mass loss (rate = 0.14 +/- 0.01 mgcm−2 d−1). The aromatic-aliphatic polycarbonates from (hydroxyalkyl)phenols showed sequence isomerism of diaryl, dialkyl, and aryl alkyl carbonate bonds. In order to control the carbonate isomer sequence, a selective synthesis methodology for diaryl and dialkyl carbonate diols as pre-programmed monomers was developed. An alternating sequence (alt) of diaryl and dialkyl carbonates demonstrated dramatic changes of the phase behavior and erosion as compared to the scrambled sequence (scr): A faster erosion rate of 0.36+/-0.01 mgcm−2d−1 for amorphous alt was observed. When heated, alt readily attained a 3-dimensional crystalline order, whereas scr showed sluggish transition into a 1-dimensional mesophase. Oriented and annealed lms of alt had improved sti ness with E = 5.4 +/- 0.3GPa as compared to scr and poly(l-lactic acid) with E = 3.8+/- 0.2 GPa and E = 3.8 +/- 0.3 GPa, respectively. The in vivo subcutaneous implantation of polymer discs resulted in slow mass loss after 3 months. However, the surface morphology appeared strikingly similar to in vitro samples. Further investigation into implant location and specimen dimensions may help to identify conditions for the in vivo resorbability.

ETD_6008

Ph.D.

Includes bibliographical references

by Sven Daniel Sommerfeld

doi:10.7282/T3NK3GN9

ETD doctoral

The author owns the copyright to this work.