Table 3.

Bio-hybrid tactile sensing: biological component, transduction mechanism and main features.

Bio-Hybrid Tactile Sensing
Method	Biological component	Transduction mechanism	Main features
Silicon-based bio-hybrid tactile sensor with integrated microfluidics and conductivity sensors	Polycarbonate nanoporous membrane (100 μm thick) forming a layer upon which cells (tissue engineered alginate encapsulated fibroblasts) are cultured	Three local conductivity sensors, consisting of a pair of thin film metallic electrodes deposited on the membrane	The system is capable of monitoring the response of cells when normal and tangential loads are applied
Silicon-based MEMS sensors with tissue engineered skin	Keratinocytes tissue engineered skin; keratinocytes are obtained from neonatal rat sacrificed by cervical dislocation, isolated and cultured for 2 weeks to obtain keratinocytes stratification	4 × 1 linear sensor array fabricated by means of MEMS microfabrication technologies, mounted on a chip carrier, wire bonded and connected to the electronics	The system is capable of measuring the contact force distribution when the device comes into contact with stimuli by means of load-unload indentation cycles
Polymeric substrate with bio-hybrid skin like electrode	3t3 fibroblasts are seeded, incubated and attached to a PDMS substrate	Electrode composed of a PDMS bottom layer, an interlayer and a PDMS upper layer with a central hole in which cells are seeded and housed	3t3 fibroblasts attach sufficiently to the PDMS substrate after one week of culture. When a load is applied, a Ca2+ influx is observed
Polymeric and elastomeric materials in MEMS devices	Polymeric and elastomeric materials used as substrates for cell adhesion and proliferation (e.g., mammalian cells, liver cells, stem cells)	The transduction mechanisms are mainly based on synthetic principles	The systems show an improved biocompatibility and biodegradability