4, the molecular weights (both Ponatinib TNKS2 Mw and Mn) of all the composites had decreased by 97�C98% to 2�C3% of the initial value of the raw material. Polydispersity of the polymer decreased slightly and steadily throughout the test series, from 1.7�C2.2 at 0 weeks to 1.2�C1.3 at 52 weeks. The decrease indicated that Mw decreased more rapidly than Mn and that the molecular mass distribution was narrowed. The degradation of the aliphatic polyesters is known to occur first in the amorphous sections of the polymer and via random chain scission.41 The random chain scission caused the molecular weight of the polymer to decrease rapidly following first order kinetics with k having values of 2.0 �� 10?3 1/h for the plain copolymer and 1.3 �� 10?3 1/h for PLCL + TCP50 + C and 1.2 �� 10?3 1/h for PLCL + TCP60 + C.
Figure 6. The weight average molar weight (Mw) (A), and mass loss and water absorption (B) of the studied composites as a function of time in vitro. The composites comprised of poly(L-lactide-co-��-caprolactone) (PLCL), ��-tricalcium … The SEC distribution plots showed emerging bimodality at 16 weeks for all the tested materials. In our earlier studies, the same kind of bimodality was present in composites without ciprofloxacin antibiotic (Ahola et al. Accepted to the Journal of Biomaterials Applications) beginning from the 20th week of the test series. Bimodality in the SEC distribution curve can be explained with the blocky structure of the copolymer, which was shown by the 1H NMR analysis.
The random parts of the copolymer degrade first, which might cause an increase in a certain part of the SEC distribution curve as the blocky parts consisting mainly of L-lactide monomers remain in the copolymer. The mass loss of the test samples was steady and started from the very beginning of the test series (Fig. 6B). The first part of the mass loss was due to the drug release as ciprofloxacin was released from the composites. When the mass loss caused by the ciprofloxacin release was taken into account, it could be concluded that the mass loss caused by the polymer erosion started after 6 weeks for PLCL + TCP50 + C and PLCL + TCP60 + C and after 4 weeks for PLCL + C. The mass loss in the very beginning of the test series was greater for PLCL + TCP50 + C and PLCL + TCP60 + C than for PLCL + C, which correlated well with the drug release data.
The dissolution GSK-3 of ��-TCP was very slow as was also noted in our earlier study (Ahola et al. Accepted to the Journal of Biomaterials Applications) and it was not significant in the time scale of this study. The mass loss of the composites was almost linear during the whole 52-week test period (R2 values 0.98). Water absorption in PLCL + TCP50 + C and PLCL + TCP60 + C was greater than in PLCL + C during the first 10 weeks (Fig. 6B). After 20 weeks, this behavior changed as the water absorption of PLCL + C accelerated and it absorbed more water than the other tested composites.