## 2 Nanotechnology and Nanomedicine
### Drug Delivery System
#### 2.7.2 Mechanism of Release Action of Drug from CSCaCO\({}_{3}\)NPs  
Evaluation of the kinetic release of encapsulated drugs from CSCaCO\({}_{3}\)NPs is the fundamental basis for understanding the release mechanism. The different release pattern of a drug from a nanocariver could either be monophasic, biphasic or tri-phasic [144]. The biphasic release pattern is mostly demonstrated by inorganic nanocarriers which involves the rapid initial burst release at the first phase which is strongly associated with excess surface attached drug molecules on the nanoparticles as a result of the weak bonding [145]. The second phase of the biphasic release involves the consistent slow and sustained release reaching the plateau phase [146]. The kinetic release mechanism of a nanocarriers is strongly influenced by the nature of the candidate drug loaded, nature of the nanomaterial itself and nature of conjugation process which could either be as a result of the ionic interaction or physical entrapment of the drug molecules and its microenvironment [147; 148]. Thus, the decomposition, diffusion rate, solubility and degradation of the candidate drugs also have a strong role to play during the release of the drug molecule from the matrix of the nanocarrier which could either lead to a sustained and controlled release or rapid release [149]. However, fully encapsulated drugs within the nanocarrier regardless of the existing bond, are released from the carrier system by either disintegration, pH of the microenvironment or degradation of the nanocarrier which eventually leads to breakage of the existing bond holding the drugs within the matrix [150]. Temperature, enzymes and pH from the microenvironment usually initiate or trigger the release mechanism of the nanocarrier within the body [151]. The release mechanism of nanocarriers triggered by pH could be as a result of sensitivity of the functional group endings to pH changes; examples of these functional group endings on nanocarriers are sulphonamide group, ammonium salt component, carboxylic group etc. [152]. The carrier molecules undergo different processes of drug release either by dissolution, carrier matrix degradation or breakage of bonds between the nanocarrier and the drug molecules [153]. However,calcium carbonate undergoes degradation through the process of diffusion to release its entrapped matrix contents [154].  
The release of encapsulated drugs from CSCaCO\({}_{3}\)NP is basically pH dependent, which is more responsive to a weak acidic environment than normal physiologic environment and vice versa depending on the type of drug loaded. Thus CSCaCO\({}_{3}\)NP could be called an excellent pH-responsive carrier [98]. A study conducted by [PERSON] et al. [10] suggested that CSCaCO\({}_{3}\)NP loaded with doxorubicin, administered for the purpose of chemotherapy could hardly release its encapsulated materials in the blood stream and normal cells before reaching it targeted area. An effective drug delivery system is said to have achieved an excellent sustained and controlled release phase to liberate its matrix content (drug molecules) at a specific localised site for effective therapeutic purposes [155]. In addition, the regulation of adequate therapeutic blood level of drugs at the minimum effective concentration and the minimum toxic concentration is achieved by the controlled kinetic release [153]. It was documented that CSCaCO\({}_{3}\)NP slowly decomposes in a physiologic state to produce Ca\({}^{2+}\) and CO\({}_{2}\)\({}^{3-}\) thereby releasing the encapsulated material from its inner matrix of which the by-products could be useful in bone remodelling, blood clotting and muscle contraction [21]. However, the exact fate of the control release mechanism of CaCO\({}_{3}\) of biogenic cockle shells origin in low pH remains unknown and yet to be documented.