(W1130-03-13) Powerful Tools for Precise Engineering of Viatel^TM Diblock Nanoparticle Size: Polymer and Solvent Structure

Purpose: Nanomedicine has immense potential to reduce the burden of disease nanoparticle (NP)-based delivery vehicles for vaccines or APIs, etc . Polymeric NPs have been widely researched and utilized as drug delivery vehicles due to their biocompatibility, biodegradability and potential to provide customized properties and performance by means of tailoring polymer chemistry. NP diameter or size is a critical parameter that directly impacts their circulation time, in vivo biodistribution as well as their uptake by the target cells[1-3]. NP size is also important from a manufacturing point of view. For instance, NPs that are smaller than 200 nm can be sterile filtered. Therefore, it is important to be able to precisely control NP size. In this work, we attempted to determine the most effective operational parameters to control the size of polymeric NPs [4].

Methods: Polymeric NPs were prepared using a nanoprecipitation method, in which the polymer solution is added into an excess amount of nonsolvent. Two compositions of an amphiphilic bioresorbable di-block copolymer marketed by Ashland Inc., viatel™ DL 03 PEG5K, methoxy poly(ethylene glycol)-b-poly(D,L-lactide) were used to form the NPs. Each composition had a PEG length of 5000 Da but varying PLA:PEG contents (60:40, 75:25 wt%). 20 mg/mL of the polymer solution was made in one or mixture of the following solvents: Acetone, Acetonitrile (ACN), dimethyl sulfoxide (DMSO), N-methyl pyrrolidone Pharmasolve^TM (NMP) marketed by Ashland Inc.10 volumes Ultrapure water was used as the nonsolvent. Polymer solution contained 2 mg/mL Atorvastatin when making API loaded NP. NPs were dialyzed using a 14 kDa MWCO membrane to remove organic solvent as well as unloaded API. Dynamic light scattering was used to measure NP diameter size. Morphology of NPs were determined by transmission electron microscopy (TEM). Samples were stained with 2% uranyl acetate, deposited, and dried on a TEM grid (Cu, 400 mesh). API loaded NPs were lyophilized. API was then dissolved in pure ACN and assayed with HPLC to determine API loading.

Results: As the hydrophobic PLA portion of the polymer increases, the diameter of NPs increase consistently regardless of the type of solvent and other operational parameters. The average size of NPs with viatel™ PDLLA-PEG (75:25) was 48.24±0.48 (PDI= 0.089) when pure 100% acetone was used as the solvent whereas viatel™ PDLLA-PEG (75:25) ratio resulted in NPs with average size of 37.87±1.72 (PDI=0.177). Incorporation of 10% atorvastatin within the viatel™ PDLLA-PEG (75:25) NPs was successful and resulted in 45.49 ± 0.46 nm NPs with 91% encapsulation efficiency. Figure 1 shows the size distribution results for both polymers using 100% acetone as solvent. TEM images showed spherical monodisperse morphology for these NPs. The second most influential parameter that impacts NP size was solvent choice. To test the effect of the solvent, we made NPs where polymer was dissolved in three additional solvents other than acetone as well as their mixture with acetone at various fractions. Results are shown in figure 2. Figure 2.A. shows that ACN exhibits similar behavior as acetone, i.e., by increasing ACN content of the solvent NP size does not increase. As Figure 2.B. illustrates, increasing NMP content led to formation of larger NPs when using viatel™ PDLLA-PEG (75:25). The strongest effect was observed for DMSO (figure 2.C) which increases NP size to 192.95 nm with viatel™ PDLLA-PEG (75:25). Figure 2. D compares the effect of all solvents on size of NPs with viatel™ PDLLA-PEG (75:25).

Conclusion: PLA-PEG NP size can be adjusted with two main parameters: polymer structure and solvent choice. Increasing the hydrophobic fraction of the polymer results in formation of larger NPs. Introducing DMSO and NMP into the polymer solution has a significant effect on NP size. As the content of the second solvent increases NP size increases too. Combination of these two parameters allows to precisely design and produce NP with a wide range of diameters.

References: 1- Davis, Mark E., Zhuo Chen, and Dong M. Shin. "Nanoparticle therapeutics: an emerging treatment modality for cancer." Nature reviews Drug discovery 7.9 (2008): 771-782.
2- Wu, Meiyu, et al. "Size-dependent cellular uptake and localization profiles of silver nanoparticles." International journal of nanomedicine (2019): 4247-4259.
3-Aghda, Niloofar Heshmati, et al. "Design of smart nanomedicines for effective cancer treatment." International Journal of Pharmaceutics 621 (2022): 121791.
4- Bernal-Chávez, Sergio A., et al. "Insights into terminal sterilization processes of nanoparticles for biomedical applications." Molecules 26.7 (2021): 2068.


Size distribution and morphology of blank and API (Active Pharmaceutical Ingredient) loaded NPs made with PDLLA-PEG5000