Chitosan is one of the most widely investigated and used biopolymers for various biomedical applications ranging from tissue engineering to drug delivery and hemostatic dressings. Besides being highly biocompatible, biodegradable, and non-immunogenic, the cationic property of chitosan has gathered special interest for biomedical applications. Now, its nanocomposites are also being developed successfully as anticancer drug carriers which were proven targeted and effective drug delivery (both active and passive) in cancer treatments (Fig. 1). The biopolymeric nanocomposites of chitosan can hold and protect anticancer drugs quite efficiently and effectively. Unique designs, increased sustainability, ease, safe, and cost-effective production of biopolymeric-like chitosan nanocomposites has made them an extremely popular choice in many medical areas.

Fig. 1

The nanocomposites of chitosan for better delivery of anticancer drugs and targeted cancer therapy

The presence of reactive functional groups in chitosan’s structure, specifically amino groups at C2 and OH groups at C3 and C6, is a prominent feature. The degree of deacetylation (DDA) is inversely proportional to degradation in the body; that is, the higher the DDA (> 85%), the slower the degradation. Therefore, higher DDA value chitosan is prepared to fabricate formulations for sustained drug release. The interaction of the positively charged polymer with the cell membrane forms the basis for the chitosan penetration mechanism as well. The high deacetylation degree and molecular weight of chitosan reveal the relative permeability of the epithelium and can therefore improve the transport of polar drugs across epithelial surfaces. Moreover, chitosan blocks the efflux pump, which pumps out xenobiotics, primarily pharmaceuticals, from intestinal epithelial cells or enterocytes. These transporters are crucial components of the mechanisms underlying drug resistance [14]. Chitosan nanoparticles are typically prepared by the following methods:

(1)

Ionic gelation method: this is the most commonly used method for chitosan nanoparticle preparation. In this method, chitosan is dissolved in an acidic solution, and a cationic cross-linking agent, such as tripolyphosphate (TPP), is added dropwise to the solution under stirring. The resulting chitosan-TPP complexes form nanoparticles via ionic interactions.

(2)

Emulsion-droplet coalescence method: in this method, a chitosan solution is emulsified in an oil phase under high-speed stirring. The resulting emulsion is then subjected to ultrasonication to break the droplets and form chitosan nanoparticles.

(3)

Reverse microemulsion method: this method involves the preparation of a water-in-oil microemulsion containing chitosan and a cross-linking agent. The microemulsion is then subjected to an external stimulus, such as heat or ultrasound, to initiate nanoparticle formation.

(4)

Coacervation method: in this method, chitosan and a counterionic polymer, such as alginate, are mixed in an aqueous solution. The mixture is then subjected to a pH change or a salt addition to induce coacervation and form chitosan nanoparticles [7].

The nanocomposites of chitosan can hold and protect anticancer drugs quite efficiently and effectively. One study showed the development of chitosan nanoparticles loaded with dexamethasone, followed by coating with a pH-dependent interpolymer complex based on poly(acrylic acid)/poly(vinyl pyrrolidone) polyblends complexes that were very effective when it comes to directed drug delivery to the colon as these coated particles have significantly large protection in simulated gastric fluid [15]. Chitosan-magnetic nanoparticle (CS-MNP)-based carrier system is another carrier system that has been studied quite extensively for cancer treatments in the last few years. For instance, doxorubicin-CS-MNP drug carrier systems have been developed and they have a significantly larger inhibitory effect on the growth of cancer cells [16]. Phytic acid (PTA) is a naturally occurring substance found in plant seeds that has a wide range of pharmaceutical properties, including anticancer potential. Unfortunately, PTA has a very short plasma half-life, making its use in cancer treatments extremely difficult. According to one study, using chitosan to fabricate PTA-CS-MNP nanoparticles could solve this problem. PTA-CS-MNP nanoparticles not only had very high efficacy against cancer cells, with no cytotoxicity toward normal fibroblast cells. Furthermore, this chitosan-based nanocomposite also demonstrated sustained release of the drug. Sustained release delivery systems minimized the drug dosage and also the number of dosages [17]. A chitosan-coated superparamagnetic iron oxide nanoparticle was developed to deliver doxorubicin and its potent anticancer effect was reported against human ovarian cancer cells [18]. Our lab has recently reported the formulation of chitosan nanoparticle encapsulating anticancer and antimicrobial drug l-asparaginase and demonstrated its efficacy and stability [19]. Sultan et al. recently reported the preparation of anticancer drug cisplatin-loaded chitosan nanoparticles with the monoclonal antibody rituximab attached to the surface for specific targeting [20]. Savin et al. have reported the preparation of a grafted copolymer of chitosan and methacrylated polyethylene glycol and further encapsulation and successful release of monoclonal antibody bevacizumab [21]. Alassaif et al. recently reported the preparation and anticancer effect of carboplatin-loaded chitosan-PLGA nanoparticles against ovarian cancer cells [22].

Hemocompatibility is always an issue that must be addressed whenever an interventional formulation or device is designed. In the case of fabricating injectable nanoparticles, hemocompatibility is extremely crucial to be considered. The design and operation of the device or formulation in the circulation, as well as interactions with blood components and coagulation biochemistry, all influence this feature. The creation of materials that are compatible with blood continues to be one of the most difficult issues in the field of biomaterials. The hemostatic property of chitosan has been heavily utilized for wound healing in recent years. Chitosan is used as a suitable material for effective wound dressings due to several properties, including chemo-attraction and activation of neutrophils and macrophages, stimulation of granulation tissue and re-epithelialization, restriction of scar formation and retraction, analgesic, hemostatic, and intrinsic antimicrobial activity. However, when considering nano-formulation, it becomes more important to consider hemocompatibility, as non-hemocompatible materials (or their degradation products) might trigger cascades resulting in a critical situation such as thrombosis and hemolysis. Since chitosan has been FDA approved for its applications in wound and hemostatic dressings because the amine group on chitosan promotes blood coagulation, the same coagulation enhancing property can be detrimental if the chitosan is used for interventional purposes, such as nanoparticle formulations. Given these factors, numerous research teams have focused on the problem of chitosan’s hemocompatibility and suggest chitosan functionalization as a way to control how biopolymers behave when they come into contact with blood. There have been numerous attempts to produce chitosan derivates that are more hemocompatible. To generate chitosan derivatives with enhanced hemocompatibility, good water solubility, biocompatibility, increased bioactivities, and even improved antioxidant activity, chitosan acylation is a key functionalization technique. N-Succinyl chitosan is a notable member of the N-acyl chitosan group that demonstrates strong hemocompatibility (N-SCs). This substance maintains several biological features, including biocompatibility, nontoxicity, long-term retention in systemic circulation, and strong transfection efficiency. It is produced via a straightforward reaction between chitosan and succinic anhydride. N-Succinyl chitosan has recently been shown to have an antitumor effect. Sulfate modification was a distinct method for producing chitosan derivatives with improved hemocompatibility. A water-soluble chitosan derivative called sulfated chitosan exhibited good biocompatibility and biological properties such as anticoagulant, hemagglutination inhibitory activity, antibacterial, and antioxidant activity. Because it is well known that the surface of blood cells is negatively charged, chitosan sulfates prevent coagulation by electrostatic repulsion. The immobilization and coating of non-fouling oligomers and polymers is one of the methods used to prevent thrombosis on biomaterials; in this case, PEGylation has been the most popular technique because of PEG’s capacity to increase hydrophilicity, provide sterical hindrance, enhance stability, and subsequently minimize interactions with blood components and RES uptake. Chitosan has a remarkable physicochemical property, i.e., hemocompatibility. Chitosan fibers showed good hemocompatibility, even during prolonged contact with human blood. The addition of chitin nanofibers leads to a decrease in hemoglobin molecules sorption due to the decline in optical density [23]. Jesus et al. recently demonstrated and reported the non-hemolytic nature of chitosan polymer as well as its NP formulation even at 2 mg/mL concentration. They emphasized that the hemolytic activity has probably earlier been reported due to the solvent (usually acetic acid), and they showed that proper washing and removal of acetic acid decreased the hemolysis [24]. However, they demonstrated that chitosan NPs formulated with 80% DDA chitosan demonstrated coagulation but 93% DDA chitosan NPs did not have that effect. Therefore, the macromolecular formulation of chitosan may demonstrate a few other properties when the same chitosan is used to formulate nanoparticles. Hence, these and a few other studies reported in the article by Jesus et al. could probably suggest that the nanoparticle formulations of chitosan should be carefully considered before progressing toward clinical trials [24]. This may, to an extent, show the delay in the clinical translation of chitosan-based nanoparticles. Figure 2 represents drug-loaded surface functionalized chitosan nanoparticles targeted to specific cells. Table 2 lists a few chitosan-based nano-formulations encapsulating various anticancer drugs that have been investigated and reported.

Fig. 2

Targeting drug-loaded surface functionalized chitosan NPs in the target cell

Table 2 Some recently developed chitosan-based carrier systems loaded with the anticancer drug used in cancer therapy