@article{MachatschekLendlein2019,
  author    = {Machatschek, Rainhard Gabriel and Lendlein, Andreas},
  title     = {Fundamental insights in PLGA degradation from thin film studies},
  series = {Journal of controlled release : official journal of the Controlled Release Society and of the Japanese Society of Drug Delivery Systems},
  volume    = {319},
  journal   = {Journal of controlled release : official journal of the Controlled Release Society and of the Japanese Society of Drug Delivery Systems},
  publisher = {Elsevier},
  address   = {New York},
  issn      = {0168-3659},
  doi       = {10.1016/j.jconrel.2019.12.044},
  pages     = {276 -- 284},
  year      = {2019},
  abstract  = {Poly(lactide-co-glycolide)s are commercially available degradable implant materials, which are typically selected based on specifications given by the manufacturer, one of which is their molecular weight. Here, we address the question whether variations in the chain length and their distribution affect the degradation behavior of Poly[(rac-lactide)-co-glycolide]s (PDLLGA). The hydrolysis was studied in ultrathin films at the air-water interface in order to rule out any morphological effects. We found that both for purely hydrolytic degradation as well as under enzymatic catalysis, the molecular weight has very little effect on the overall degradation kinetics of PDLLGAs. The quantitative analysis suggested a random scission mechanism. The monolayer experiments showed that an acidic micro-pH does not accelerate the degradation of PDLLGAs, in contrast to alkaline conditions. The degradation experiments were combined with interfacial rheology measurements, which showed a drastic decrease of the viscosity at little mass loss. The extrapolated molecular weight behaved similar to the viscosity, dropping to a value near to the solubility limit of PDLLGA oligomers before mass loss set in. This observation suggests a solubility controlled degradation of PDLLGA. Conclusively, the molecular weight affects the degradation of PDLLGA devices mostly in indirect ways, e.g. by determining their morphology and porosity during fabrication. Our study demonstrates the relevance of the presented Langmuir degradation method for the design of controlled release systems.},
  language  = {en}
}
@article{MazurekBudzyńskaBehlRazzaqetal.2019,
  author    = {Mazurek-Budzyńska, Magdalena and Behl, Marc and Razzaq, Muhammad Yasar and N{\"o}chel, Ulrich and Rokicki, Gabriel and Lendlein, Andreas},
  title     = {Hydrolytic stability of aliphatic poly(carbonate-urea-urethane)s: Influence of hydrocarbon chain length in soft segment},
  series = {Polymer Degradation and Stability},
  volume    = {161},
  journal   = {Polymer Degradation and Stability},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {0141-3910},
  pages     = {283 -- 297},
  year      = {2019},
  abstract  = {Poly(carbonate-urethane)s (PCUs) exhibit improved resistance to hydrolytic degradation and in vivo stress cracking compared to poly(ester-urethane)s and their degradation leads to lower inflammation of the surrounding tissues. Therefore, PCUs are promising implant materials and are considered for devices such as artificial heart or spine implants. In this work, the hydrolytic stability of different poly(carbonate-urethane-urea)s (PCUUs) was studied under variation of the length of hydrocarbon chain (6, 9, 10, and 12 methylene units) between the carbonate linkages in the precursors. PCUUs were synthesized from isophorone diisocyanate and oligo(alkylene carbonate) diols using the moisture-cure method. The changes of sample weight, thermal and mechanical properties, morphology, as well as the degradation products after immersion in a buffer solution (PBS, pH = 7.4) for up to 10 weeks at 37 degrees C were monitored and analyzed. In addition, mechanical properties after 20 weeks (in PBS, 37 degrees C) were investigated. The gel content was determined based on swelling experiments in chloroform. Based on the DSC analysis, slight increases of melting transitions of PCUUs were observed, which were attributed to structure reorganization related to annealing at 37 degrees C rather than to the degradation of the PCUU. Tensile strength after 20 weeks of all investigated samples remained in the range of 29-39 MPa, whereas the elongation at break e(m) decreased only slightly and remained in the range between 670 and 800\%. Based on the characterization of degradation products after up to 10 weeks of immersion it was assessed that oligomers are mainly consisting of hard segments containing urea linkages, which could be assigned to hindered-urea dissociation mechanism. The investigations confirmed good resistance of PCUUs to hydrolysis. Only minor changes in the crystallinity, as well as thermal and mechanical properties were observed and depended on hydrocarbon chain length in soft segment of PCUUs. (C) 2019 Published by Elsevier Ltd.},
  language  = {en}
}