| Summary: | 碩士 === 台北醫學院 === 口腔復健醫學研究所 === 86 === Poly-L-lactide(PLLA)is an excellent osteosynthesis material because it has
good biocompatibility and it can be metabolized completely in humam body. On
the other hand, commercial PLLA with a high molecular weight, over 5*10^6, was
difficult to make, resulting in limited mechanical properties and an
insufficient application in stress-bearing fracture sites. In this study,
first, PLLA film samples were made of commercial available PLLA, and immersed
in phosphate buffer solution(PBS) for 0, 1, and 3 weeks. After stretching, the
deformation zones of the film samples produced during the stretching process
were observed and analyzed to investigate the micro-deformation behavior of
PLLA. Then, PLLA reinforced with 0,10wt%,30wt%,50wt% hydroxyapatite(HA) was
fabricated into a block(40*3*4 mm^3) using a compression molding technique
under several processing conditions. The composite samples were tested by
material testing system, differential scanning calorimetry and gel permeability
chromatography, and the morphology of the fracture surfaces were observed by a
scanning electronic microscope to investidate their physical properties.
The results show that the PLLA film samples were deformed by crazing rather
than shear. During 3 weeks, no matter whether the film samples immersed in PBS
or not, the yield strength of the film samples was not affected. There were no
significant differences between the yield strength of crystal and non-crystal
film samples, but the nucleation of the deformation zone of the crystal film
samples happened in the non-crystal areas first.
The flexural strength and the crystallinity of PLLA composite samples
decrease as the HA contents increased, while the Young''s modulus was reversed.
When the HA contents are the same, the Young''s modulus decreased as the HA
particle size became larger, while the crystallinity of PLLA in the samples
was reversed. The morphology of the fracture surfaces of the samples shows
that the fracture of HA/PLLA composites is a mix-type fracture, and the space
between HA nad PLLA interface becomes larger as the HA contents increase. The
decreasing bonding strength between HA and PLLA might be the reason for a
decrease in flexural strength.
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