# Biomedical Applications of Polymeric Cryogels
## 3 Cryogels in Medical Applications
### Controlled Drug Delivery  
Drug delivery systems (DDs) are designed to deliver various drugs by using polymeric carriers at a certain time and specific sites. DDs are methods for applying a pharmaceutical compound to achieve a therapeutic effect. DDs improve therapeutic effects and reduce the toxicity of drugs. DDs have recently gained great attention of scientists in the fields of biomedicine and pharmacy. Four types of DDs can be reported such as diffusion-controlled, swelling-controlled, erosion-controlled and \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Metal Ion** & _Functional Monomer/Ligand_ & **Method** &
\begin{tabular}{c} **Adsorption** \\ **Capacity** \\ \end{tabular} & **Reference** \\ \hline Iron(III) & \(N\)-_methacryloyl-(l)-cysteine_ & Ion-imprinted cryogel & 75 \(\mu\)g/g & [43] \\ Iron(III) & \(N\)-_methacryloyl-(l)-histidine_ & Affinity-based cryogel & 1.79 mg/g & [44] \\ Aluminum(III) & \(N\)-_methacryloyl-L-glutamic acid_ & Ion-imprinted polymer & 0.76 mg/g & [42] \\ Iron(III) & \(N\)-_Methacryloyl-(l)-glutamic acid_ & Ion-imprinted polymer & 92.6 \(\mu\)mol/g & [45] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Some examples of cryogel applications for the removal of metal ions. Figure 4: Schematic illustration of preparation of hemoglobin imprinted supermacroporous cryogels and SEM photographs of hemoglobin imprinted supermacroporous cryogels [33]. stimulus-controlled. Various polymeric biomaterials have been developed to deliver drugs to human body [46]. DDs are classified as polymeric capsules, micelles, liposomes and gels according to dosage formulation of drugs. A core containing therapeutic drug and a polymer membrane outside the core are defined for a polymeric capsule. Thus, drug can be released by diffusion from the core through the membrane [47]. Supermacroporous cryogels are developed to deliver drugs to human body. The biocompatibility and controllable permeability of cryogels have caused extensively using in DDs for bioactive compounds in the last few decades. Stimuli-responsive cryogels have attracted a great deal of attention of researchers because of their sensitive response to a variety of physical and chemical changes. The structure of cryogels has been defined as smart DDs to fulfill the desired drug release profiles [19]. Supermacroporous polymeric structures have decent advantages such as high water content, non-toxicity, user-friendly, mild and efficient nature. Their reusability and easy storage offer added advantages. Therefore, these materials can be used in drug delivery due to their mechanical and chemical robustness, easy production, mechanical strength, and low cost. Cryogels offer distinctive three-dimensional structure materials for local delivery of therapeutic drugs. High blood-compatibility and resistance to degradation are great properties of these materials. These materials have good alternatives for implantable systems to deliver a large dose of drugs close to the tumor for sustained drug delivery. These materials also greatly decrease the toxic effects of the drug, and increase the therapeutic effect of chemotherapy [48]. Presently, researchers are working on the design of effective and low-cost gel-based drug delivery systems. [PERSON] et al. prepared three-dimensional biocomposites based on chitosan and clinoptilolite by cryogelation and investigated their potential application as drug carriers for diclofenac sodium and indomethacin. They reported the cumulative release of diclofenac sodium from the monoliths lower than 5% at pH 1.2 and higher than 70% at pH 7.4. In addition, they reported cumulative release 6% of indomethacin within the first hour in phosphate buffered saline (PBS) from composite cryogels [48]. The group of [PERSON] [19; 49] prepared mitomycin C (MMC) imprinted cryogels for the delivery of MMC.