**5. One-step supercritical foaming + impregnation process: a particular case**

In our facilities PCL scaffolds impregnated with quercetin were prepared using supercritical CO2. PCL is a semicrystalline polyester with a melting point (Tm) of 329–334 K and a glass transition temperature (Tg) of 213 K [52]. Quercetin (Q ) is a flavonoid present in many fruits and vegetables [53]. This flavonoid highlights its antioxidant action, but it has different benefits as antibacterial, cardiovascular health, anti-inflammatory, and anticancer effects [54, 55]. The study was supported by an experimental design to elucidate the influence of pressure (15–30 MPa), temperature (308–333 K), and depressurization rate (0.1–20) on foaming, melting temperature, melting heat, and amount of released quercetin.

The experiments were carried out in a plant RESS250 developed by Thar Technologies [56]. PCL and quercetin were mixed physically into an aluminum foil support (ratio 50:1 PCL/Q ), and it was introduced into a stainless steel vessel. Then, CO2 was pumped to the vessel till the desired operating pressure at the same time that the temperature was adjusted is reached. A determined impregnation time was awaited, and once finished, the output valve was opened to vent the CO2 in a range of depressurization rate of 0.1–20 MPa min<sup>−</sup><sup>1</sup> . In the SEM image in **Figure 2**, it can be seen that PCL/quercetin foamed in our facilities [56].

The generated PCL/quercetin scaffold with higher pore density and smaller pore size was achieved for higher pressure and depressurization rate and lower

temperatures (300 bar, 308 K, and 20 MPa min<sup>−</sup><sup>1</sup> ). In general according to our results, the high level of temperature is recommended to obtain a pronounced effect of foaming to produce scaffold.

It was also observed that experiments done at lower pressure and temperature together with a higher depressurization rate led to a higher melting temperature. An increase of pressure and temperature leads to composite which released a higher amount of quercetin. However, depressurization rate has the opposite trend, so an increase of depressurization rate leads to a lower amount of released quercetin. These facts can be observed in the contour surface plots (**Figures 3** and **4**).

Release profiles showed that quercetin took five times longer to dissolve the same amount of quercetin into the first 8 h, demonstrating the efficacy of using PCL to control quercetin release and its possible use with other medical or pharmaceutical compounds (**Figure 5**).

**Figure 2.** *SEM image of PCL/quercetin scaffold.*

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**6. Conclusions**

**Figure 5.**

**Figure 4.**

Impregnated scaffolds are an interesting alternative to be used in pharmacology and biomedicine because scaffolds act not only as a physical support but also as a carrier of a bioactive substance with a controllable release. The possibility of regulating the rate of the scaffold degradation and the kinetics of drug release make it easy to fabricate particular drug release systems. Bone regeneration, implants, hormonal treatment, and tissue engineering applications are fields where scaffolds could be used. The way to create the porosity in the polymer originated a multiple scaffold fabrication methods based most of them in molding and removing the used organic solvent in a posterior step. Supercritical CO2 has been used as dryer in many conventional methods as sol-gel where the solvent must be evaporated. However, in these methods supercritical CO2 is able to remove almost the totality of used organic solvent, which requires several process steps. Another way to use supercritical CO2 is in the gas foaming process. In this sense the porosity is created at the same time that the bioactive substance is incorporated, avoiding the use of organic solvent. Moreover these processes do not use high temperature, so the activity of the bioactive molecule would hold unaltered. Foaming process changes not only the polymer porosity but also other properties as melting, crystallization or glass transition

*Foaming + Impregnation One-Step Process Using Supercritical CO2*

*DOI: http://dx.doi.org/10.5772/intechopen.91304*

*Contour plot of release quercetin of PCL/quercetin scaffold.*

*Release profile from raw quercetin and PCL/quercetin scaffold.*

**Figure 3.** *Contour plot of melting temperature of PCL/quercetin scaffold.*

*Foaming + Impregnation One-Step Process Using Supercritical CO2 DOI: http://dx.doi.org/10.5772/intechopen.91304*

*Advanced Supercritical Fluids Technologies*

of foaming to produce scaffold.

(**Figures 3** and **4**).

compounds (**Figure 5**).

temperatures (300 bar, 308 K, and 20 MPa min<sup>−</sup><sup>1</sup>

results, the high level of temperature is recommended to obtain a pronounced effect

Release profiles showed that quercetin took five times longer to dissolve the same amount of quercetin into the first 8 h, demonstrating the efficacy of using PCL to control quercetin release and its possible use with other medical or pharmaceutical

It was also observed that experiments done at lower pressure and temperature together with a higher depressurization rate led to a higher melting temperature. An increase of pressure and temperature leads to composite which released a higher amount of quercetin. However, depressurization rate has the opposite trend, so an increase of depressurization rate leads to a lower amount of released quercetin. These facts can be observed in the contour surface plots

). In general according to our

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**Figure 3.**

**Figure 2.**

*SEM image of PCL/quercetin scaffold.*

*Contour plot of melting temperature of PCL/quercetin scaffold.*

**Figure 4.** *Contour plot of release quercetin of PCL/quercetin scaffold.*

**Figure 5.** *Release profile from raw quercetin and PCL/quercetin scaffold.*
