Covalently Bound Drug Depot Devices

As an alternative to simple depot formulations, drugs can also be covalently bound to the polyphosphazene backbone, being dependent 

One more successful example is the preparation of covalently bound antibiotics onto various amino-acid-ester-substituted polyphosphazenes [99]. The amino acid ester groups could be used to fine-tune the rate of hydrol)n ic degradation and thus drug release, and the antibiotics ciprofloxacin and norfloxacin could be covalently attached to the polyphosphazene backbone via the piperazinyl groups. In aqueous media, the antibiotics released were measured to be between 4 and 30% over a 6-week period for films prepared from 

The codelivery of active agents such as drugs or growth factors, whether covalent or noncovalent, could also be of use in tissue engineering applications, with parallel release of the drug via matrix degradation and is discussed further in Chapter 4. 

Similar polymersomes have also been prepared with a pH triggered release profile designed to selectively release its payload after endocytosis. These were prepared through incorporation of N,N-diisopropylethylendiamine groups, which become protonated at lower pH values causing disruption to the vesicle and thus payload release [114]. 

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