Development of 3D-Printed Hydrogel Disks as Standardized Platform for Evaluating Excipient Impact on Metronidazole's Antimicrobial Activity

Abstract

Background/Objectives: Effective drug delivery systems require precise formulation and understanding of excipient impact on active pharmaceutical ingredient (API) stability and efficacy, as uncontrolled interactions can compromise outcomes. This study developed and validated a semi-solid extrusion (SSE) 3D printing method for polyvinyl alcohol (PVA)-based hydrogel disks with metronidazole (MET). These disks served as a standardized platform to assess excipient influence on MET's antimicrobial activity, focusing on plasticizers (polyethylene glycol 400, glycerol, propylene glycol, and diethylene glycol monoethyl ether)-excipients that modify hydrogel properties for their application in printing dressing matrices-with the platform's capabilities demonstrated using in vitro antimicrobial susceptibility testing against Bacteroides fragilis. Methods: Hydrogel inks based on PVA with added plasticizers and MET were prepared. These inks were used to 3D-print standardized disks. The MET content in the disks was precisely determined. The antimicrobial activity of all formulation variants was evaluated using the disk diffusion method against B. fragilis. Results: The incorporated plasticizers did not negatively affect the antimicrobial efficacy of MET against B. fragilis. All printed hydrogel matrices exhibited clear antimicrobial activity. The 3D-printed disks showed high repeatability and precision regarding MET content. Conclusions: SSE 3D printing is viable for manufacturing precise, reproducible MET-loaded PVA hydrogel disks. It provides a standardized platform to evaluate diverse excipient impacts, like plasticizers, on API antimicrobial performance. The tested plasticizers were compatible with MET. This platform aids rational formulation design and screening for optimal excipients in designed formulations and for various pharmaceutical applications.

Keywords: 3D printing (extrusion-based); Bacteroides fragilis; antibacterial wound dressings; drug delivery; hydrogels; metronidazole; personalized therapy; plasticizers; polyvinyl alcohol.

Figure 1

Microbiological disks design.

Figure 2

Arrangement of the designed disks on the printer table.

Figure 3

Printer configuration.

Figure 4

Printed microbiological disks before and after water evaporation from the hydrogel.

Figure 5

Relationship between the diameter of the inhibition zone and the metronidazole content in the standard microbiological and hydrogel disks.

Figure 6

Calibration curve illustrating the correlation between MET concentration in the hydrogel ink and the resulting MET content in the 3D-printed microbiological disks. Each point represents the mean ± standard deviation (n = 6).

Figure 7

Influence of hydrogel formulation composition on metronidazole activity against B. fragilis ATCC^® 25285™ (n = 3); DEGEE—diethylene glycol monoethyl ether; GL—glycerol; PEG—polyethylene glycol 400; PG—propylene glycol.

Figure 8

Antimicrobial activity of placebo hydrogel matrices (without API) and individual components against B. fragilis ATCC^® 25285™ (n = 3). The asterisk (P*) indicates a placebo formulation. An inhibition zone diameter of 6 mm corresponds to the disk diameter, indicating no antimicrobial effect on bacterial growth.

Figure 9

Inhibition zones of B. fragilis ATCC^® 25285™ growth for: (a,b)—seven disks containing 5 µg MET and two placebo disks; (c)—cellulose disks impregnated with 10 µL of plasticizers; (d)—cellulose disks impregnated with 50 µL of plasticizers: (d1)—PEG 400; (d2)—GC; (d3)—DEGEE.