## 2 Keratin-Based Nanoparticles
### Human Hair Keratin-Based Nanoparticles
Figure 4: **(A) Healing progression of full-thickness cutaneous wounds treated with RKNP37, RKNP81, and KNPs. (B) Rate of wound closure on days 0, 7, 14, 21, and 28. * \(p<0.05\), ** \(p<0.01\) relative to control group. Reprinted with permission from [35]. Copyright 2021 American Chemical Society. **  
Figure 5: Chemical structure of rutin and quercetin. The authors also described an in-silico study that accounted for a strong interaction between Ru-Qr-KNPs and the binding pockets of H-Ras P21 proto-oncogene. Results obtained in silico were further supported by experimental studies on HeLa cells, affording 92% cell death after 24 h. Overall, the in vitro anticancer activity of Ru-Qr encapsulated KNPs at different concentrations showed that Ru-Qr encapsulated within NPs can reduce the cells viability in a dose-dependent manner. Mucoadhesion describes the ability of two materials, among which at least one is a biological material, to adhere to each other for a long time by establishing interfacial bonding [40]. Nanotechnology-based drug carriers have been widely exploited for oral and systemic administration of drugs based on their mucoadhesive properties to increase drugs residence time, selectively address the drug to a specific body compartment, reduce the administration frequency, and improve drug bioavailability [41]. On this basis, [PERSON] and coworkers reported the use of human hair keratin as biomaterial for the production of mucoadhesion controlled keratin-based drug delivery systems [42]. The authors described the use of different blends of keratose (KOS) and keratine (KTN), that were obtained according to different extraction methods, for KNPs production. Indeed, the cysteine sulfur atoms of KTN and KOS were in the form of thiols and sulfonic acids, respectively, which resulted in different mucoadhesive and hydrophilic properties, and diverse solubility, surface charge, and degradation rate. The authors reported the preparation of KNPs with different ratios of KOS to KTN and incorporating amoxicillin (AMO) as a model drug to achieve controlled gastric mucoadhesion and drug release. Composite keratin nanoparticles with different mass ratios of KTN/KOS, e.g., 100/0, 75/25, 50/50, and 25/75, were prepared via the ultrasonic dispersion method. The loading capacity of AMO decreased from 15.7 to 8.9% with an increase in the KOS ratio. A possible explanation of this behavior could be related to the higher ability of KTN to agglomerate and form nanoparticles under acidic conditions as opposed to KOS. KTN and KOS nanoparticles displayed positive or negative surface charge in a simulated gastric fluid (SGF), respectively, and a gradual decrease in the zeta potential of KNPs was observed with increasing KOS proportion. The release profiles of AMO from KNPs were investigated in SGF, showing a that higher release rate was achieved by increasing KOS ratio. In summary, KTN/KOS KNPs showed good gastric retention capacity that could be adjusted by changing the ratios of KNT to KOS; importantly, in vivo toxicity studies of KNP (380 mg/kg) indicated no apparent toxicity after oral administration after seven days. The aim of a second study from the same authors was to prepare keratin nanoparticles as a novel kind of hemostatic agents [43]. Based on the observation, KNPs have a great specific surface area, a better film-forming property, and can supply a higher water uptake, and, thus, keratin nanoparticles should represent more efficient hemostatic materials as compared to keratin powders. Keratins were extracted from human hair by a reduction method, and an ultrasonic solidification process was used for KNPs preparation, by varying both keratin concentration and injection speed. KNPs size gradually increased both with growing keratin concentrations and increasing the protein solution injection speed. In vivo hemostasis studies were performed on liver puncture and tail amputation in rat models: 25 mg of keratin extracts and 50 mg of KNPs were used for covering the wound areas.