## 6 Future Perspectives  
Chitosan-based carriers have been reported to be effective for the delivery of drugs for the treatment of selected brain diseases in vivo. The charge on chitosan-based drug delivery systems has been reported to result in targeted drug delivery thereby increasing drug concentration at the tumor site and improving the therapeutic outcomes. The design of chitosan-based drug delivery systems influences drug uptake by the brain tissues. Chitosan nanoparticles decorated with antibodies on the surface crossed the brain barrier and also provided neuroprotection when compared with those without antibodies that were characterized by aggregation. The size of the nanoparticles was reported to be either above or below 200 nm. There is a need for more research on the consistency of range of particle size of nanoparticles effective for good brain uptake. The conjugation of antibodies onto the surface of the NPs and the coating of the NPs surface was reported to be a potential approach for the development of formulations for enhanced brain uptake with reduced toxicity. However, there is a pressing need for more in vivo studies on NPs formulations conjugated with antibodies and coated NPs. More studies on the toxicity of these nanoparticles in vivo in long-term use is also very important.  
In the design of in situ gels, the addition of musk ketone to the chitosan-based gel also increased the sensitivity of the nasal cavity, thereby inhibiting the efflux of levodopa through P-glycoprotein efflux pump in the brain and enhanced the concentration of drug uptake to the brain. The addition of polycations to in situ gels also increased the drug uptake and delayed mucociliary clearance. There is a need for more research to be performed on the toxicity of musk ketone used in gels for intranasal administration.  
Chitosan-based liposomes and emulsions are also potential carriers for the nose-to-brain targeting. The nanoscale droplets, low polydispersity index, and high viscosity of emulsions influenced the high drug permeation through the mucosal surfaces. The coating of the liposomes formulation with chitosan promoted electrostatic interactions with negative sialic acid of mucins, thereby increasing the mucoadhesion and extending the residence of the formulation in the nasal cavity, and hence, enhancing the brain uptake. The surface of the liposomes was coated with chitosan also enhanced the stability of the formulations.  
The administration of the chitosan formulations has been reported to result in side effects such as the swelling of glands and the absence of shuffing of the mucosal epithelium. The results reported by several researchers indicate that chitosan-based formulations are potential systems for targeted drug delivery to the brain. Although, there are unique promising results on the treatment of brain diseases using chitosan drug delivery systems, however, more research needs to be conducted in order to enhance and reduce the global issues encountered in treating brain diseases. A study on the potential risk of the nanocarriers to humans in long-term study is very important. The affordability of these carriers should also be thoroughly investigated.