TABLE 1.

Intervention strategies based on the design and geometry of the electrode.

(i) Design and geometry
Features	Examples	References
Size effect	PEG-DMA hydrogel coatings and deep and spray coating method	Spencer et al., 2017
	PEG-based coatings	Reviewed in Knop et al. (2010) (Wichterle and Lím, 1960; Rao et al., 2011; Gutowski et al., 2015; Heo et al., 2016; Lee et al., 2017)
	PHEMA-based coatings	Reviewed in Ratner (2002) (Campioni et al., 1998; Jhaveri et al., 2009; Zhang et al., 2017)
Surface morphology	FIB technology as machining technique to modify surface morphology	Raffa et al., 2007
Shape	Flexible implants of multifunctional polymeric fibers	Canales et al., 2015
Design and topography	Physical properties, surface micro-/nano-topography and surface chemistry modifications	Reviewed in Ware et al. (2013) (Anderson et al., 1999; Thull, 2002; Fink et al., 2008; Chen et al., 2010; Gamboa et al., 2013; Hulander et al., 2013)
	3D design of spiked ultraflexible substrates	Rubehn and Stieglitz, 2010; Wang M. et al., 2018
	Neural probe with sinusoidal design and a 3D spheroid tip	Sohal et al., 2014
	Microgeometry and implant thickness effect	Ward et al., 2002
Material morphology	Cationic polymer coatings and PLA and electro-spun fiber meshes with plasma-polymer coating	Ma et al., 2011; Lucke et al., 2018
Surface porosity	Channel size control through (pHEMA-co-MAA) hydrogels	Madden et al., 2010
	PU-based porous implants	Ward et al., 2002
Size and spherical geometry	Alginate spheres/capsules	Veiseh et al., 2015
Intervention strategy
Soft robotics	Control over fluid flow and shear stress through milliscale dynamic soft reservoir with actuatable membrane	Dolan, 2019
Microfabrication	Micro-machined neural prosthetic devices: flexible polymer-based microelectrodes with different shape, size and geometry	Reviewed in Szarowski et al. (2003); Lee et al. (2004), Metz et al. (2004); Polikov et al. (2005), Spataro et al. (2005); Ziegler et al. (2006), Winslow and Tresco (2010); Blau et al. (2011), Gerwig et al. (2012); Gao et al. (2013), Minev et al. (2015); Qi et al. (2017), Vitale et al. (2018); Kozai (2018), Fallahi et al. (2019), and Kumar et al. (2020) (Elyahoodayan et al., 2020)
	Encapsulation technologies of flexible microelectrodes	Reviewed in Ahn et al. (2019)
	Electrically-responsive flexible microfibers	Chen et al., 2017
	Microfabrication of a neural probe with sinusoidal design and a 3D spheroid tip	Sohal et al., 2014
	Wireless, flexible, film-based carbon-polymer composite microelectrode system	Lim et al., 2020
	Additive manufacturing of microelectrode arrays and microneedle arrays	Yang et al., 2016; Morrison et al., 2019; Soltanzadeh et al., 2020
Nanofabrication	CNTs	Reviewed in Aregueta-Robles et al. (2014) (Castagnola et al., 2016)
	Parylene-coated flexible CNTf microelectrodes	Vitale et al., 2018
	Conducting-polymer carbon nanotubes	Abidian et al., 2010; Gerwig et al., 2012; Alba et al., 2015; Mandal et al., 2015; Samba et al., 2015; Du et al., 2018; Altun et al., 2019; Kałuża et al., 2019; Zheng et al., 2019
	PPy nanowires	Reviewed in Qi et al. (2017)
	PPy nanoparticles	Hosseini-Nassab et al., 2017
	SWCNT-PPy/PEGDA composite hydrogels	Xiao et al., 2012
	PPy/CNT films	Luo et al., 2011
	Graphene oxide nanocomposite films of PPy	Weaver et al., 2014
	PLGA nanoparticles embedded in alginate hydrogels	Kim and Martin, 2006
	Nanoparticle-coated nanoelectrodes	Bazard et al., 2017
	Nanoscale biomimetic surfaces	Reviewed in Von Der Mark et al. (2010)

PEG, polyethylene glycol; DMA, dimethacrylate; PHEMA, poly(2-hydroxyethyl methacrylate); FIB, focused ion beam; PLA, poly(l-lactide-co-d/l-lactide); pHEMA-co-MAA, poly(2-hydroxyethyl methacrylate-co-methacrylic acid); PU, polyurethane; CNTs, carbon nanotubes; CNTf, carbon nanotube fiber; PPy, polypyrrole; SWCNT-PPy/PEGDA, single-walled carbon nanotubes-polypyrrole/poly(ethylene glycol) diacrylate; PLGA, poly(lactic-co-glycolic acid). References: except were specifically indicated as ‘Reviewed in,’ all others are research articles.