The influence of gelatin type and process parameter variation on the robustness of nanoparticle production by coacervation

Abstract

Gelatin, the irreversible hydrolysis product of animal collagen, is an ideal candidate for the production of nanoparticles for drug and gene delivery systems. However, the heterogeneous mixture of different sized proteins composing the native gelatin makes it a particularly challenging biopolymer from which nanoparticles with narrow size distributions can be produced. B75, B225, CWFS, A90-110 and A175 gelatins have been simultaneously studied and the desolvation method of GNP production developed by Farrugia and Groves (1999) was used as basis for this study. Earlier studies had indicated that the desolvation process of gelatin by ethanol is affected by various factors, and hence, the influence of several small, planned modifications in the process factors on the robustness of the nanoparticle production method has been investigated. The experimental conditions modified included the 1° dispersion gelatin concentration, the pH of the gelatin stock solution, glutaraldehyde concentration as the cross-linker and different combinations of ethanol concentration for both the 1° dispersion and cross-linking stages. Contrary to what various researchers have previously suggested, one-step desolvation does not necessarily produce GNPs with inferior characteristics as compared with two-step desolvation methods. GNPs characterized by ZAverage diametric sizes of around or below 200 nm, with narrow size distributions, were obtained from the 5 gelatin types tested. While different gelatins required, as one would expect, different optimized conditions of GNPs production, B225 and CWFS gelatins led to the production of GNPs with the best stability profiles during storage over 15 days at 5 °C, RT and 40 °C as well as in 1X PBS solution. An improved stability was observed when a 0.2% w/w gelatin in the 1° dispersion was employed as opposed to 0.1% w/w, and it has also been shown that the 1° dispersion ethanol concentration plays a more critical role when compared to the cross-linking ethanol concentration in dictating the size and polydispersity of the subsequent cross-linked GNPs. The lower levels of stability observed for GNPs produced from Type-A gelatins serves as evidence that glutaraldehyde cross-linking of proteins occurs preferentially in the presence of unprotonated amino groups. In the absence of the latter, at the acidic pHs used for Type-A gelatins, insufficient cross-linking probably took place. This research was carried out following the award of an ENDEAVOUR Scholarship for 2016.