Table 3.

Summary of surface modification strategies.

Surface Modification	Author (Year)	Materials	Animal	Experiments
Biocompatible Coating	Cui [111] (2003)	PEDOT a/DCDPGYIGSR	Guinea pig	Decrease in impedance Increase in SNR
	Ludwig [64] (2006)	PEDOT	Rat	Decrease in impedance 17% increase in number of recorded units
	Rao [108] (2012)	PEG b-PU c hydrogel	Rat	Increase in neuronal density Decrease in glial density
Bioactive Coating	He [109] (2006)	Laminin	Rat	Reduction in glial density in 2 weeks No change in neuronal density
	Kim [110] (2007)	PPy d/PSS e/NGF f PEDOT/PBS g/NGF	in vitro	22% increase in neuronal density
	Kolarcik [112] (2012)	L1	in vitro Rat	Decrease in the size of kill zone
Drug Release	Kato [113] (2006)	NGF (in microsphere)	Rat	Extension of neuritis observed
	Zhong [119] (2007)	DEX h (in nitrocellulose coating)	Rat	60% decrease in immunoreactivity 50% decrease in glial density
	Mercanzini [37] (2010)	DEX (in nanoparticles)	Rat	Decrease in impedance
	Tien [33] (2013)	chABC i (in silk film)	in vitro	Reduced glial scar
	Potter [120] (2014)	Curcumin (in poly(vinyl alcohol))	Rats	Increase in neuronal survival in 4 weeks Lost benefit of drug in 12 weeks
	Huang [40] (2015)	PMSC j-OPC k (in nanogels)	Rat	Decrease in impedance Increase in SNR 40%–80% reduction in immunoreactivity 100%–1100% increase in neuronal density

^a PEDOT: poly(3,4-ethylenedioxythiophen); ^b PEG: polyethyleneglycol; ^c PU: polyurethane; ^d PPy: polypyrrole; ^e PSS: poly(styrenesulfonate); ^f NGF: nerve growth factor; ^g PBS: phosphate-buffered saline; ^h DEX: dexamethasone; ⁱ chABC: chondroitinase ABC; ^j PMSC: polydimethylsiloxane (PDMS) modified N,O-carboxylic chitosan; ^k OPC: oligo-proanthocyanidin.