Biodegradability

In order to assess their biodegradability the materials were immersed for 35 days at 37 °C in three different types of solutions: (i) phosphate-buffered saline (PBS) at a

7.5 pH, (ii) simulated body fluid buffered (SBF) at 7.5 pH, and (iii) 0.01 M NaOH solution. The solution was changed once a week [48]. The weight of the samples was recorded prior to initiation of the tests and thereafter they were weighed once a week, after they were first washed with distilled water and vacuum dried at room temperature. For the tests carried out in PBS and SBF negligible weight loss was observed indicating a low degradation rate. However, in the case where NaOH was used as the immersion fluid a linear decrease in weight was observed throughout the 35 days, indicating a 14% decrease in the initial sample weight. This high degradation rate in NaOH was expected since OH- plays a key role in the degradation of aliphatic polyesters [49, 50]. TGA revealed that after immersion in NaOH the PCL/ PLLA ratio was higher than in the as prepared materials, indicating that PLLA degraded at a faster rate. Raman spectroscopy revealed that during degradation the crystallinity of PLLA increased, while its polymer chains shortened. This is due to the ability of water to penetrate easier into the amorphous parts, which hence degrade first. Also the water attacks the ester back bone, which results in a smaller chain length and the formation of short mobile oligomers that can recrystallize [49, 50].

HOB cells were less active and did not induce morphological changes on the scaffolds during the in vitro tests. The MSC cells however, did have an effect on the surface of the scaffold after 5 weeks of culture. The ability of human cells to induce degradation changes on such polymer composites suggests their possible use for in vivo applications where degradability is desired.

 
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