**4. Drug incorporation strategies**

Some MOFs possess rigid and permanent pores, whereas others are flexible and can respond to external/internal stimuli such as temperature, light, pH, etc. by changing their pore size [24]. In addition, MOFs have distinct features such as breathing, linker rotation, swelling, and subnetwork displacements, which are important for drug loading and release management [25]. There are many ways to associate a drug with MOF, which may be a medicine, a gene, a protein, an enzyme, or any other agent of therapeutic importance.


*Drug Delivery Applications of Metal-Organic Frameworks (MOFs) DOI: http://dx.doi.org/10.5772/intechopen.103684*

### **Figure 3.**

*(a) One-pot synthesis of ZIF-8 NMOF encapsulating zinc phthalocyanine, a photosensitizer used for PDT. Reproduced with permission from [26]. Copyright 2018 American Chemical Society. (b) Direct assembly of porphyrin-based DBC ligand in DBC-UiO NMOF for PDT application. Reproduced with permission from [29]. Copyright 2015 American Chemical Society. (c) Coordinative interaction of His-tags with CUS of MOF: (i) basic MOF molecular composition; (ii) formation of coordinate bond between CUS metal ion (Lewis acid) and imidazolate group of histidine (Lewis base); (iii) generation of multifunctional MOFs by attachment of multiple His-tags. Reproduced with permission from [33]. Copyright 2017 American Chemical Society. (d) Post-synthetic covalent attachment of amino group of DOX to aldehyde of ICA linker in ZIF-90, followed by loading of 5-Fluoro uracil into the pores of NMOF. Reproduced with permission from [34]. Copyright 2017 American Chemical Society.*

**Figure 3** gives a schematic illustration of some of these drug-loading techniques. Multimodal and theranostic systems can also be obtained by using one or more loading techniques to incorporate multiple drugs.
