水凝胶的密度一般是多少并给出参考文献

水凝胶的密度一般在0.9-1.2 g/cm3之间。具体的密度还会受到水凝胶的成分和制备方法的影响。

参考文献：

1. Huang, X., Brazel, C. S. (2001). On the importance and mechanisms of burst release in matrix-controlled drug delivery systems. Journal of Controlled Release, 73(2-3), 121-136.
2. Qiu, Y., Park, K. (2001). Environment-sensitive hydrogels for drug delivery. Advanced Drug Delivery Reviews, 53(3), 321-339.
3. Hoffman, A. S. (2002). Hydrogels for biomedical applications. Advanced Drug Delivery Reviews, 54(1), 3-12.