# Lignin to Materials: A Focused Review on Recent Novel Lignin Applications
## 3 Medical Applications
### Pharmaceuticals  
There are specific compounds derived from lignin that can not only be used to construct pharmaceuticals to alleviating the symptoms of diseases, but can also be used to construct drug delivery materials. While sulfite and Kraft lignins are more commonly used lignins to synthesize pharmaceutical products, recently lignins obtained from steam explosion and the organosolv process have been investigated for pharmaceutical use. The mechanism commonly employed to utilize lignin is to depolymerize lignin and obtain derivatives to construct biologically active compounds. These biologically active compounds can be used to treat the Herpes simplex virus, influenza virus, and other viruses [27]. Since the toxicity of drugs is an important factor in the drug discovery phase, the cytotoxicity of lignin was studied; findings from a study show that lignins are generally safe to consume and no not disrupt cell viability [27]. When synthesizing pharmaceutical drugs,  
Figure 2: Meshes 3D-printed from poly(lactic acid) (PLA) and 2 wt % lignin with grid sizes of 1.5 mm and 1 mm. The middle column shows the side view of each mesh when slightly bent, while the right column shows the close-ups of each mesh. Reprinted from reference [26], with permission from the MDPI. the antioxidant property of lignins is highly valued because its hydroxyl functional groups in their phenolic rings neutralize free radicals and protect molecules from oxidation [27]. For instance, lignins isolated from Bagasse, steam explosion lignins, and lignosulfonates have half maximal inhibitory concentrations of 44.9 \(\upmu\)g/mL, 74.6 \(\upmu\)g/mL, and 133.6 \(\upmu\)g/mL, respectively. Compared to a common antioxidant present in tea, epicatechin, which has a half maximal inhibitory concentration of 42.3 \(\upmu\)g/mL, these lignins have enhanced antioxidant properties [28]. Lignin-derived components and products, including polyphenols, may help in controlling diseases, like diabetes, coronary heart disease, and Alzheimer's disease. Results of a study suggest that lignosulfonic acid can be taken with glucose to cause a delay in the uptake of glucose to potentially treat diabetes [29]. The study administered a combination of lignosulfonic acid and glucose as well as glucose alone to determine their effects on 2-deoxyglucose uptake in human colorectal adenocarcinoma cells. Since lignosulfonic acid is a non-competitive inhibitor of \(\upalpha\)-glucosidaseidase, lignosulfonic acid can inhibit \(\upalpha\)-glucosidase activity and delay the absorption of glucose in the intestines. Lignosulfonic acid was also demonstrated to inhibit human immunodeficiency virus (HIV) and herpes simplex virus (HSV) transmission when tested with human T-cell leukemia cells, human embryonic kidney cells, and peripheral blood mononuclear cells [30]. Furthermore, lignosulfonates have the potential to be developed into drugs that could decrease oxidative activity, thereby boosting the immune system [3]. Lignin may also helpful in controlling obesity. Out of the dietary fiber components, lignin is reported to be the strongest bile acid adsorbent due to the presence of methoxyl and \(\upbeta\)-carbonyl groups in lignin. When the lignin binds to the bile, micelles are unable to be produced, thereby resulting in decreased lipid absorption [27]. Table 1 summarizes several studies describing the value products that can be synthesized from technical lignins. In a study, lignophenols derived from the native lignin of Japanese cedar were shown to decrease oleate-induced apolipoprotein-B secretion and reduce cholesterol in HepG2 cells (human liver cells), thereby potentially preventing coronary heart disease [31]. These lignophenols were derived using a phase separation process that included cresol and sulfuric acid; lignophenols were then dissolved in dimethyl sulfoxide before being cultured with HepG2 cells.