  Recent molecular communication (MC) research has integrated more detailed
computational models to capture the dynamics of practical biophysical systems.
This research focuses on developing realistic models for MC transceivers
inspired by spheroids - three-dimensional cell aggregates commonly used in
organ-on-chip experimental systems. Potential applications that can be used or
modeled with spheroids include nutrient transport in an organ-on-chip system,
the release of biomarkers or reception of drug molecules by a cancerous tumor
site, or transceiver nanomachines participating in information exchange. In
this paper, a simple diffusive MC system is considered where a spheroidal
transmitter and receiver are in an unbounded fluid environment. These
spheroidal antennas are modeled as porous media for diffusive signaling
molecules, then their boundary conditions and effective diffusion coefficients
are characterized. Further, for either a point source or spheroidal
transmitter, Green's function for concentration (GFC) outside and inside the
receiving spheroid is analytically derived and formulated in terms of an
infinite series and confirmed by a particle-based simulator (PBS). The provided
GFCs enable computation of the transmitted and received signals in the
spheroidal communication system. This study shows that the porous structure of
the receiving spheroid amplifies diffusion signals but also disperses them,
thus there is a trade-off between porosity and information transmission rate.
Also, the results reveal that the porous arrangement of the transmitting
spheroid not only disperses the received signal but also attenuates it. System
performance is also evaluated in terms of bit error rate (BER). Decreasing the
porosity of the receiving spheroid is shown to enhance system performance.
Conversely, reducing the porosity of the transmitting spheroid can adversely
affect system performance.
