# Engineering Biomimetic Gelatin Based Nanostructures as Synthetic Substrates for Cell Culture
## 1 Introduction
Electrospinning involves the use of a high voltage that repels the surface tension of the polymer solution droplet pumped through a needle [22]. Once the electric charge on the surface of the droplet overcomes the surface tension, a jet of nanofibers is formed and collected [23]. Different synthetic and natural polymers can be used to produce the nanofibers [23]. The physical and chemical properties of these polymers, along with the nanoscale nature of the electrospun fibers are considered to have a profound influence on the cell-scaffold interaction and cell behavior [24]. For instance, previous studies have demonstrated an increase in cell adhesion, cell differentiation with an increase in polymer hydrophilicity, charge density, roughness at the nanoscale, and stiffness with variation in the scaffold porosity [25; 26; 27; 28; 29; 30; 31]. As there is no ideal polymer that possesses all the desired characteristics for use as a scaffold, a mixture of polymers or additives, such as cell growth promoters, can be used to tailor the characteristics to the desired scaffold [32]. In this study, two polymers (polycaprolactone (PCL), gelatin) and a non-ionic surfactant (poloxamer 188) were combined to produce an electrospun composite scaffold as a substrate for intestinal epithelial cells that could mimic the BM. Polycaprolactone (PCL) is a non-toxic synthetic polymer with desirable mechanical characteristics, such as a slow degradation rate and higher elastic modulus, which can efficiently replicate the nanofibrous nature of the ECM when electrospun [33; 34; 35; 36]. However, its hydrophobic nature and lack of cell recognition sites can restrict cell adhesion and overall growth [33; 34; 35; 36]. Gelatin is a biocompatible, biodegradable, non-immunogenic natural polymer with low mechanical strength, which has inbuilt signals (arginine-glycine-aspartic acid sequence) to promote efficient cell adhesion and growth [37]. When combined with PCL, gelatin composite nanofibrous scaffolds exhibit good cell adhesion property along with good mechanical strength enabling improved cell growth [32; 37]. Poloxamer 188 (P188) is a non-ionic surfactant of 8400 Da molecular weight, which has the ability to revive mammalian cells exposed to mechanical and chemical stress [38]. P188 is composed of one unit of hydrophobic poly(oxypropylene) (POP) and two units of hydrophilic poly(oxyethylene) (POE) arranged as a triblock structure POE-POP-POE [38]. The use of P188 in culture media has shown to increase the viability and proliferation of Caco-2 cells [38]. It was reported that P188 has the capability to reseal damaged cell membranes and increase its stiffness, in turn supporting the cell to efficiently adhere to a growth support, resulting in an increase in cell adhesion and proliferation [38]. However, no cell viability studies have been conducted to understand the significance of P188 in polymer blend nanofibers and influence on cell viability [39; 40]. In this study, polycaprolactone (PCL), gelatin, and poloxamer 188 composite nanofibrous scaffolds were generated using electrospinning to produce a scaffold that could act as a substrate, possibly by efficiently mimicking the epithelial BM, and have the desired mechanical and chemical properties for effective cell growth. In a previous work, [PERSON] et al. successfully co-electrospun PCL with gelatin using low toxicity and cost-effective solvents, formic acid and acetic acid [41]. In this experiment, poloxamer 188 was incorporated into the PCL/gelatin blend scaffold to enhance the viability and proliferation of cells.