  Next generation in-to-out-of body biomedical applications have adopted
optical wireless communications (OWCs). However, by delving into the published
literature, a gap is recognised in modeling the in-to-out-of channel, since
most published contributions neglect the particularities of different type of
tissues. Towards this direction, in this paper we present a novel pathloss and
scattering models for in-to-out-of OWC links. Specifically, we derive extract
analytical expressions that accurately describe the absorption of the five main
tissues' constituents, namely fat, water, melanin, oxygenated and de-oxygenated
blood. Moreover, we formulate a model for the calculation of the absorption
coefficient of any generic biological tissue. Next, by incorporating the impact
of scattering in the aforementioned model we formulate the complete pathloss
model. The developed theoretical framework is verified by means of comparisons
between the estimated pathloss and experimental measurements from independent
research works. Finally, we illustrate the accuracy of the theoretical
framework in estimating the optical properties of any generic tissue based on
its constitution. The extracted channel model is capable of boosting the design
of optimized communication protocols for a plethora of biomedical applications.
