# Lignin to Materials: A Focused Review on Recent Novel Lignin Applications
## 6 Perspectives  
In the past decade, there have been more investigations conducted on using lignin to construct medical materials, electrochemical energy materials, and 3D printing composites. From the limited technoeconomic assessments conducted, it is difficult to predict the economic trajectory of lignin valorization. Since lignin valorization is an emerging concept, production costs may be higher than conventional processes [3]. According to a technoeconomic assessment analyzing catechol production from lignin, the lignin depolymerization and product separation stages accounted for a total of 55% [3]. For the production of lignin micro- and nanoparticles, their investment cost was 160 million USD, with an atomizer and separation system costing roughly 65% of the capital investment [56]. Assuming Kraft lignin and lignocellulosic are used, manufacturing costs can vary between 870 and USD 1170 per ton. The production capacity of around 70% of North American Kraft pulp mills is restricted by the operation of recovery boilers. Another challenge is finding the optimal membrane used for the Kraft process that will result in the highest lignin yield and purity [57]. Factors to consider for future scale-up efforts would be the size of the market, price volatility of the desired product [3], and the cost of feedstock in addition to solvents [56]. Lignin commercialization is likely with increased international collaboration, as this will mobilize resources and facilitate the development of innovative pathways [57]. Materials constituting lignin and its derivatives have potential in the medical sector due to their versatility as a wound dressing, pharmaceutical drug, drug delivery system, and drug removal material. However, it is difficult for lignin to be absorbed by the human's small intestine or stomach because of its high molecular weight and polydispersity [27]. There have also been studies suggesting that lignin can adsorb toxins, cholesterol, and surfactants, which can negatively impact human health [27]. Much of the research conducted is still at the proof of concept stage and pharmaceutical drugs will need to go through clinical trials before determining their efficacy. Regulatory bodies, like the US Food and Drug Administration, will need to approve the medical products even before they can be commercialized [58]. Clinical trials are time-consuming and costly; thus, there needs to be sufficient confidence in the research done and the viability of the production process before pursuing clinical trials. While lignin is cheap and eco-friendly as a feedstock material for battery and 3D printing materials, a significant challenge is that it is hard to control or isolate lignin's complex recalcitrant structures. Even when fractionation is employed to isolate a lignin structure, fractionation often results in a mixture of products [59; 60]. The electrochemical performance of bio-based battery materials depends on pore features, surface chemistry, and the structure of the lignin raw material [2]. Even though lignin is a relatively cheap starting material, it is still challenging to produce high performing carbon materials for supercapacitors and batteries. Since some lignins cannot stabilize easily, they convert to carbon nanofibers and consequently their morphologies are difficult to control; this makes high-performing lignin-based electrodes difficult to achieve [61]. Furthermore, lignin reaction mechanisms are not well understood [2]. Incorporating lignin in 3D printing materials decreases the reliance on typical petroleum-based plastic 3D printing materials. Doing so not only makes the 3D printing materials more environmentally friendly, but it also reduces costs as lignin is much cheaper than typical 3D printing materials [62]. Additionally, a myriad of materials can not only be created by 3D printing, but they can also be customized. This is of interest in the medical sector, where wound dressings can be 3D printed and customized to best suit the patients' needs.