In recent years, the development of codelivery systems based on combination strategies has provided an effective approach for reducing side effect and retaining drug bioactivity of anti-cancer drugs. Cancer is one of the most serious diseases endangering human health. There are some significant changes between normal tissues and cancerous tissues, and such changes have motivated researchers to design multiple intelligent hydrogel-based dual drug carriers for drug controlled release. Meanwhile, with the development of effective treatment, modulating multiple targets simultaneously can be achieved through a combination of anticancer drug and biological factor in hydrogel. The dual-drug controlled release from hydrogel is also realized. In the review, the recent advance on the intelligent hydrogel-based dual drug delivery system are summarized, which are classified referring to the mechanism of hydrogel loaded dual drugs, the release principles of drugs and the means of combination of drugs. In addition, some personal perspectives on this field are also presented.

Contents
1 Introduction
2 Intelligent hydrogel-based dual drug delivery carriers
2.1 Temperature-sensitive carriers
2.2 pH sensitive carriers
2.3 Redox sensitive carriers
3 The means of drug combination in hydrogel
3.1 Combination of two anticancer drugs
3.2 Combination of anticancer drug and growth factor
3.3 Combination of anticancer drug and gene
4 Conclusion