Tumor growth suppression induced by biomimetic silk fibroin hydrogels

Protein-based hydrogels with distinct conformations which enable encapsulation or differentiation of cells are of great interest in 3D cancer research models. Conformational changes may cause macroscopic shifts in the hydrogels, allowing for its use as biosensors and drug carriers. In depth knowledge on how 3D conformational changes in proteins may affect cell fate and tumor formation is required. Thus, this study reports an enzymatically crosslinked silk fibroin (SF) hydrogel system that can undergo intrinsic conformation changes from random coil to β-sheet conformation. In random coil status, the SF hydrogels are transparent, elastic, and present ionic strength and pH stimuli-responses. The random coil hydrogels become β-sheet conformation after 10 days in vitro incubation and 14 days in vivo subcutaneous implantation in rat. When encapsulated with ATDC-5 cells, the random coil SF hydrogel promotes cell survival up to 7 days, whereas the subsequent β-sheet transition induces cell apoptosis in vitro. HeLa cells are further incorporated in SF hydrogels and the constructs are investigated in vitro and in an in vivo chick chorioallantoic membrane model for tumor formation. In vivo, Angiogenesis and tumor formation are suppressed in SF hydrogels. Therefore, these hydrogels provide new insights for cancer research and uses of biomaterials.The authors would like to thank the Portuguese Foundation for Science and Technology (FCT) project grants OsteoCart (PTDC/CTM-BPC/115977/2009) and Tissue2Tissue (PTDC/CTM/105703/2008) which supported this study. Research leading to these results has also received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement no REGPOT-CT2012-316331-POLARIS. Le-Ping Yan was awarded a PhD scholarship from FCT (SFRH/BD/64717/2009). We also would like to thank FCT for the distinction attributed to J.M. Oliveira under the Investigador FCT program (IF/00423/2012). The authors also like to acknowledge Dr. Mariana B. Oliveira for technical assistance on the dynamic mechanical analysis of the cell-laden hydrogels

Stratification period combined with mechanical treatments increase Prunus persica and Prunus armeniaca seed germination

The deep dormancy of the Prunus species seeds is caused by the presence of germination inhibi- tors, mainly abscisic acid (ABA) – in the endocarp, the seed coat and endosperm, and in the embryo. As a consequence, the removal of the endocarp, the seed coat together with the endosperm increases the num- ber of germinated seeds. The effect of different treatments of seeds of three peach cultivars – ‘Madison’, ‘Elberta’ and ‘Rakoniewicka’, and of three apricot cultivars – M II‑42, ‘Bella’ and ‘Somo’, were assessed in terms of seed germination and the growth of obtained young seedlings. Seed treatments involved different duration of stratification period at 5°C and removing endocarp, seed coat with endosperm and the part of cotyledons of the embryo. The best seed/embryo germination, about 96% for the peach cultivars and practically 100% for the apricot cultivars, was obtained by stratifying seeds for 90 days and then removing the seed coat together with the endosperm and subjecting the extracted embryos to a temperature of 20°C. The seedlings obtained from the seeds treated this way have shown good growth. Using these treatments, it was possible to obtain a larger number of apricot and peach seedlings, and thus increase the breeding efficiency of these species