A composite hydrogel comprises an amphiphilic triblock copolymer (ABA) and a loaded micelle bound by noncovalent interactions. The loaded micelle comprises a biologically active substance and an amphiphilic diblock copolymer (CD). The A blocks comprise a steroidal repeat unit (repeat unit 1) having both a backbone carbonate and a side chain bearing a steroid functional group. Each of the A blocks has a degree of polymerization of about 0.5 to about 4.0. The B block comprises a first poly(alkylene oxide) backbone. The C block comprises a second poly(alkylene oxide) backbone. The D block comprises a steroidal repeat unit (repeat unit 2) having both a backbone carbonate group and a side chain comprising a steroid functional group. The composite hydrogel is capable of controlled release of the biologically active substance.
