## 2 Keratin-Based Nanoparticles
### Human Hair Keratin-Based Nanoparticles
Further, the authors demonstrated that INDX@KNPs stimulate glucose metabolism through an AMPK- (insulin independent) and PTP1B (insulin dependent)-mediated signaling pathway, and that the efficiency of glucose metabolism induced by INDX@KNPs in 3T3-L1 adipocytes is significant as compared to antidiabetic drugs such as Metformin and Pioglitazone, overall demonstrating that INDX@KNPs could represent promising antidiabetic systems. Wound healing has a significant economic and social impact, and accelerating its progression represents a central concern for patients, doctors, and caregivers [32]. The use of biomaterials able to promote cell adhesion and proliferation represents a promising approach to face this issue [33], and among these, keratin is considered a very promising option because of its intrinsic cell growth and proliferation ability, biocompatibility, biodegradability, and natural abundance [34]. In 2019, [PERSON] and coworkers investigated the wound healing ability of recombinant human hair keratin proteins in the form of nanoparticles [35]. The authors studied the use of human type I hair keratin 37 and human type II hair keratin 81, obtained using a bacterial expression system. These keratins were then used to produce the corresponding RKNP37 and RKNP81 nanoparticles via ultrasonic dispersion method. In vitro cell proliferation studies demonstrated that RKNP37 and RKNP81 significantly increased the proliferation of HaCaT cells compared to untreated control, and, among the two, RKNP81 displayed a stronger cell proliferation capacity when the nanoparticle concentration was higher than 0.75 mg/mL. The authors also evaluated the wound-healing efficiency of the RKNPs in vivo, as opposed to untreated control and KNPs made from non-recombinant keratin. Results showed that wounds treated with RKNP37, RKNP81, and KNPs had faster closure compared to the control group after seven days of treatment, and the wound size reduction was 49, 56, and 40% for the wounds covered by RKNP37, RKNP81, and KNPs, respectively. On day 14, the control group displayed 69% wound closure, whereas RKNP37, RKNP81, and KNPs showed wound closures of 81, 85, and 74%, respectively (Figure 4). These results indicated that keratin nanoparticles accelerate the wound healing process, and that recombinant KNPs have greater wound-healing ability, most probably due to their higher purity, thus suggesting that this feature plays a key role in the wound-healing process. Histopathological analysis showed that more blood vessels were observed in the RKNP37 and RKNP81 groups compared to the control groups after day 14, indicating a greater formation of vascular networks essential for providing the cells with nutrients and oxygen, and for completing the wound-healing process. Overall, the results from [PERSON] and colleagues represent a very interesting opportunity to exploit recombinant keratin to produce wound healing materials. [PERSON] and coworkers reported the use of human hair keratin for the production of nanoparticles incorporating both rutin (Ru) and quercetin (Qr), with the aim of assessing the role of the keratinous carrier on the biodistribution and site-specific action of these two active ingredients [36]. Rutin and quercetin (Figure 5) are natural flavonoids with promising anticancer properties [37]. In particular, quercetin was identified as an inhibitor of the mutant H-Ras P21 protein in colon cancer cell lines and primary colorectal tumors normally found in humans, thus being potentially effective in arresting cancer cell proliferation [38; 39]. Dual loaded keratin NPs were prepared by solid dispersion method that afforded KNPs of about 50 nm with an encapsulation efficiency and drug loading capacity of Ru of 91% and 8.58%, respectively and of Qr of 86.5% and 9.74%, respectively. The Ru-Qr in vitro release form KNPs was estimated over time, resulting in a sustained behavior within the first observation time (17.5% and 21% within 5 h, respectively), and reaching a higher release extent after 30 h (88% and 85%, respectively).