Balancing sterilization and functional properties in Poloxamer 407 hydrogels: comparing heat and radiation techniques

Abstract

Poloxamer 407, also known as Pluronic^® F127, is gaining interest in the cosmetic, biomedical and pharmaceutical fields for its biocompatibility, safety and thermo-sensitive properties. Ensuring sterility is critical in clinical applications, and sterilization is often preferred over aseptic processing. However, sterilization can impact the functional properties of the hydrogel. In this study, we investigate the effects of steam heat (121°C, 20 min), dry heat (160°C, 1 h), gamma irradiation (25 kGy) and electron beam (e-beam) irradiation (15 and 25 kGy) on a 30% w/v Poloxamer 407 hydrogel formulation. Our analysis encompasses gelling properties, pH, Fourier-transform infrared spectroscopy, gel permeation chromatography, small-angle X-ray scattering, rheology, swelling, degradation by-products and lactate dehydrogenase release of the sterilized hydrogels, comparing them to a non-sterile counterpart. We demonstrated that heat sterilization alters the hydrogel's gelling and structural properties due to water evaporation and oxidation under harsh temperature conditions, especially when applying the dry heat method. Gamma irradiation proved unsuitable, resulting in an acidic and cytotoxic hydrogel due to oxidative degradation. In contrast, e-beam irradiation preserves the hydrogel's elasticity, gelling and structural properties while enhancing mechanical resilience and moderating swelling. Therefore, e-beam irradiation within the 15-25 kGy range appears to be the most suitable method for sterilizing a 30% w/v Poloxamer 407 hydrogel.

Keywords: Poloxamer 407; functional properties; hydrogels; sterilization.

Graphical abstract

Figure 1.

30%w/v Poloxamer 407 hydrogel formulation and sterilization processes.

Figure 2.

FTIR Spectra of non-sterile and sterilized 30% w/v Poloxamer 407 hydrogels in the 4000–650 cm⁻¹ range.

Figure 3.

Swelling study of non-sterile and sterilized 30% w/v Poloxamer 407 hydrogels. Mean ± SD, n = 5. *Statistically significance difference (P < 0.05) compared to the non-sterile sample (one-way ANOVA). (A) Non-sterile, (B) steam heat, (C) dry heat, (D) gamma 25 kGy, (E) e-beam 15 kGy, and (F) e-beam 25 kGy.

Figure 4.

Amplitude sweeps of non-sterile and sterilized 30%w/v Poloxamer 407 hydrogels at 37°C. ■ storage modulus, ▼ loss modulus. (A) Non-sterile, (B) steam heat, (C) dry heat, (D) gamma 25 kGy, (E) e-beam 15 kGy and (F) e-beam 25 kGy.

Figure 5.

Frequency sweeps of non-sterile and sterilized 30%w/v Poloxamer 407 hydrogels at 37°C. ■ storage modulus, ▼ loss modulus. (A) Non-sterile, (B) steam heat, (C) dry heat, (D) gamma 25 kGy, (E) e-beam 15 kGy and (F) e-beam 25 kGy.

Figure 6.

GPC of non-sterile and sterilized 30% w/v Poloxamer 407 hydrogels.

Figure 7.

SAXS spectra of non-sterile and sterilized 30% w/v Poloxamer 407 hydrogels.

Figure 8.

Relative LDH release from non-sterile and sterilized 30% w/v Poloxamer 407 hydrogels. Mean ± SD, n = 3; *Statistical significance (P < 0.05) compared to the initial time point (t-test). (A) control, (B) non-sterile, (C) steam heat, (D) dry heat, (E) gamma 25 kGy, (F) e-beam 15 kGy and (G) e-beam 25 kGy.

Figure 9.

Cells morphology in non-sterile and sterilized 30% w/v Poloxamer 407 hydrogels. Upper panel: 24-h time point. Lower panel: 48-h time point. (A) control, (B) non-sterile, (C) steam heat, (D) dry heat, (E) gamma 25 kGy, (F) e-beam 15 kGy and (G) e-beam 25 kGy.

Figure 10.

(A) Peroxide groups concentration in sterilized 30% w/v Poloxamer 407 hydrogels, with non-sterile values subtracted, mean ± SD, n = 3. (B) Carbonyl groups concentration in sterilized 30% w/v Poloxamer 407 hydrogels, with non-sterile values subtracted, mean ± SD, n = 3. *A statistically significant difference (P < 0.05) compared to the non-sterile sample (one-way ANOVA).