Hamaker Coefficient Concept: The Application to the Mycobacterium Tuberculosis – Macrophage Interactions Mechanism

J. L. Chukwuneke, P. C. Chukwuneke, P. C. Okolie, J. E. Sinebe

Abstract


M-Tb – macrophage interactions were studied using the Hamaker coefficient concept as a surface energetics tool in determining the interaction processes, with the surface interfacial energies explained using van der Waals concept of particle – particle interactions. Using the previous works that established the role of surface thermodynamics in various processes from the balanced electrostatic repulsion, and the van der waals attraction mechanism, that the concept of attraction or repulsion between the interacting particles were modeled. The Lifshitz derivations for van der Waals forces were applied as an alternative to the contact angle approach which has been widely used in other biological systems. The methodology involved sputum sample collection, mycobacterium and macrophages structural studies, and the study of the mechanism of interaction of the bacterium and macrophage. Twenty samples each of infected, uninfected and M-Tb/HIV co-infected sputum were collected and screened using GeneXpert and Ziehl-Neelsen staining method. The absorbance, ā, values of each specimen, for wavelength range of 230-950nm were measured using digital Ultraviolet Visible Spectrophotometer.Matlab software tools were used in the mathematical analysis of the data generated from the absorbance values.The Hamaker constantsand the combined Hamaker coefficientA132were obtained. The values of A132abs = 0.21631x10-21Joule (M-Tb infected sputum) and Ã132abs = 0.18825x10-21Joule (M-Tb/HIV co-infected sputum) were obtained for M-Tb/HIV – infected macrophage. The implication of this result is the positive value of the absolute combined Hamaker coefficient which entails net positive van der waals forces demonstrating an attraction between M-Tb and the macrophage. This however, implies that infection is very likely to occur. It was also shown that in the presence of HIV, the interaction energy is reduced by 13% confirming adverse effects observed in HIV patients suffering from tuberculosis. Negative Hamaker coefficient (-0.22669x10-19mJ/m2) indicated that isolation of M-Tb is realistic. The desired outcome is that the bacteria do not adhere to the macrophage to avoid bacteria penetrating it, in which case a condition for rendering combined Hamaker coefficient negative is required. Thus, condition was sought for repulsion to occur and that condition was based on the value of A33 that would render the absolute combined Hamaker coefficient A132abs negative. Mathematically it was derived as A33≥0.9527x10-21Joule which satisfies this condition for negative A132abs. To achieve the condition of A33 above, possible additive(s) in form of drugs to the sputum should be required.

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