Barbieri Thesis - BioMedical Materials program (BMM)

Chapter 6 – Fluid uptake as instructive factor
Table 7. Statistical comparison of serum protein adsorption and fluid uptake after seven days in 0.1%
FBS. The test used was one–way ANOVA test for means (Tukey’s) where a p–value smaller than 0.05
was considered as significant difference.
MLD–MLDL
MLD–MDL
MLDL–MDL
Serum protein adsorption Fluid uptake
10 –4
10 –4
>0.6 (no)
10 –3
0.7 (no)
6.3.5. Accelerated in vitro degradation of the composites
Samples containing poly(D,L–lactide), i.e. MDL, could not be retrieved after five
weeks as they broke down and fully fragmented. These samples had more swollen
volume than MLD and MLDL after three weeks and could hardly keep their shape
when touched with normal laboratory stainless steel spoons or tweezers. This
indicated that MDL composites degraded and absorbed fluids faster. However, all
three composites degraded during the 5–week period as indicated by their mass loss
(Figure 7a), continuous release of calcium and phosphate ions (Figure 8). We
observed that the apatite phase content decreased compared to the starting
conditions (Table 6). In particular, samples containing PLD had the most stable mass,
whereas MDL degraded most. Consistently, there was a direct link between mass loss
and fluid uptake (Figure 7b), where the larger mass loss corresponded to a large
fluid uptake and vice versa. A fast decline in intrinsic viscosity (and weight average
molecular weight) was observed in MDL composites, followed by MLDL and MDL
(Table 8). The degradation rate constants and the correlation coefficients are in
Figure 9. The validity of the model to estimate the autocatalytic degradation rate is
supported by the high values of the correlation coefficients. The results show that the
polymer phase in MDL had a faster autocatalysed hydrolysis than MLDL and MDL,
and in particular, this last result is in line with the fluid absorption trends confirming the
important role fluid uptake has in degrading the polymer phase.
Table 8. Measured inherent (inh) and intrinsic () viscosity, and weight average molecular weight
(Mw) of the polymer phase over five weeks in PBS at 55°C.
MLD
MLDL
MDL
0 weeks
inh [dL g –1 ]
[dL g –1 ]
Mw [kDa]
0.60±0.01
0.61±0.01
43.5±0.9
0.48±0.01
0.49±0.01
42.9±0.9
0.44±0.01
0.45±0.02
51.5±1.4
1 week
inh [dL g –1 ]
[dL g –1 ]
Mw [kDa]
0.51±0.03
0.52±0.02
34.5±1.7
0.30±0.02
0.30±0.01
22.7±0.3
0.20±0.01
0.20±0.01
17.5±1.1
3 weeks
inh [dL g –1 ]
[dL g –1 ]
Mw [kDa]
0.36±0.02
0.36±0.01
20.4±0.6
0.23±0.01
0.24±0.02
16.1±0.7
0.10±0.02
0.11±0.01
7.3±0.8
134
5 weeks
inh [dL g –1 ]
[dL g –1 ]
Mw [kDa]
0.32±0.01
0.33±0.01
16.9±0.5
0.14±0.02
0.15±0.01
8.8±0.3
not measured