Figure 4.

Examples of commercially relevant injectable polymer-based drug release formulations for chemotherapy (lower half) and immunotherapy (upper half). First injectable formulations in the 1980’s were mostly based on degradable and non-degradable microparticle suspensions (1^st block from left). On the nanoscale, functional groups on the polymer backbone (such as polycarboxylic acid polymers) or at the end groups (typically PEG) can be used to make drug-polymer-conjugates that can reduce systemic toxicity and increase targe accumulation (2^nd block). Amphiphilic block-copolymers such as PEG-PLA’s will self-assemble around hydrophobic drugs, enabling improved target uptake through decoration of target-specific functionalities on the resulting corona surface (3^rd block). Hydrogels are another platform technology to facilitate encapsulation, injectability, local retention and extended release of chemo and immunotherapy agents, through either medium- to long-chain viscosity increasing polymers, such as PEG or hyaluronic acid, or stimuli-responsive gelling co-polymers such as PLGA-PEG-PLGA. Towards the paradigm of personalized medicine, implementing imaging modalities and thus the live trackability of an injected payload is a desired feature of the future for which not many examples exist yet. Adapted with permission from Kamaly et al. Copyright 2016 and modified. American Chemical Society [29]