Both chitosan and polylactide/polyglycolide have good biocompatibility and can be used to produce tissue engineering scaffolds for cultured cells. However the synthetic scaffolds lack groups that would facilitate their modification, whereas chitosan has extensive active amide and hydroxyl groups which would allow it to be subsequently modified for the attachment of peptides, proteins and drugs. Also chitosan is very hydrophilic, whereas PLGA is relatively hydrophobic. Accordingly there are many situations where it would be ideal to have a copolymer of both, especially one that could be electrospun to provide a versatile range of scaffolds for tissue engineering. Our aim was to develop a novel route of chitosan-g-PLGA preparation and evaluate the copolymers in terms of their chemical characterization, their performance on electrospinning and their ability to support the culture of fibroblasts as an initial biological evaluation of these scaffolds. Chitosan was first modified with trimethylsilyl chloride, and catalyzed by dimethylamino pyridine. PLGA-grafted chitosan copolymers were prepared by reaction with end-carboxyl PLGA (PLGA-COOH). FT-IR and(1)H-NMR characterized the copolymer molecular structure as being substantially different to that of the chitosan or PLGA on their own. Elemental analysis showed an average 18 pyranose unit intervals when PLGA-COOH was grafted into the chitosan molecular chain. Differential scanning calorimetry results showed that the copolymers had different thermal properties from PLGA and chitosan respectively. Contact angle measurements demonstrated that copolymers became more hydrophilic than PLGA. The chitosan-g-PLGA copolymers were electrospun to produce either nano- or microfibers as desired. A 3D fibrous scaffold of the copolymers gave good fibroblast adhesion and proliferation which did not differ significantly from the performance of the cells on the chitosan or PLGA electrospun scaffolds. In summary this work presents a methodology for making a hybrid material of natural and synthetic polymers which can be electrospun and reacts well as a substrate for cell culture.
The Pearl River Estuary is in the geometric center of Guangdong-Hong Kong-Macao Greater Bay Area, which is one of the main battlefields to drive the high-quality development of China’s economy. This paper uses seven sets of typical satellite images in Pearl River Estuary for nearly half a century (from 1973 to 2021) to analyze the changes of coastline and sea reclamation. The results show that from 1973 to 2021, the total length of the coastline of the Pearl River Estuary increased from 240.09 km to 416.00 km, and that of the continental coastline from 186.87 km to 246.21 km (but the length of natural coastline in the continental coastline decreased from 136.91 km to 15.17 km). In the same period, the total reclamation area of the Pearl River Estuary increased by 28,256.06 ha. Before 2012, the growth rate of reclamation was generally fast. After 2012, the reclamation in China has entered a period of reflection. With reclamation was strictly controlled in the new era, only the previously approved reclamation projects and national major projects have been guaranteed, which makes the average annual growth rate of the coastline length and the reclamation area in the region show a significant downward trend. The reclamation in early days was largely for agriculture and pond culture purposes, but is shifting to transportation, industrial development, and urban construction in recent decades. This study scientifically analyzes the coastline and reclamation changes of the Pearl River Estuary in the past half century, which has a very important reference value for the next step to formulate marine ecological protection and restoration strategies, and construct a new pattern of marine space development and protection.
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