In situ formation of high viscous inverse lyotropic non-lamellar liquid crystalline phases is a promising approach for sustained drug delivery in the joint. The in situ forming process on exposure of two diclofenac-loaded preformulations to aqueous media was characterized with respect to depot size and shape, initial release and structural transitions using UV-Vis imaging and spatially and time-resolved synchrotron small-angle X-ray scattering (SAXS). The preformulations consisted of 10 % (w/w) ethanol, 10 % (w/w) water and a binary lipid mixture of glycerol monooleate (GMO):1,2-dioleoyl-sn-glycero-3-phospho-rac-(1-glycerol) (DOPG) or GMO:medium chain triglycerides (MCT). Upon injection of preformulations into an employed injection-cell containing excess of bio-relevant medium, rapid generation of liquid crystalline depots was observed. UV-Vis images and constructed 2D SAXS maps of the injection-cell showed depots with different shapes and sizes, and features with high nanostructural heterogeneity. More extensive swelling of the GMO:DOPG-based preformulation was observed compared to the GMO:MCT-based preformulation. The UV image analysis found that a higher amount of diclofenac was released in the image area after 20 h from the GMO:MCT depot compared to the GMO:DOPG depot. The injection-cell setup employing UV-Vis imaging and synchrotron SAXS constitutes an attractive approach for evaluating the in situ forming processes of liquid crystalline depots.
Biotherapeutics is the fastest growing class of drugs administered by subcutaneous injection. In vitro release testing mimicking physiological conditions at the injection site may guide formulation development and improve biopredictive capabilities. Here, an in vitro release cartridge (IVR cartridge) comprising a porous agarose matrix emulating subcutaneous tissue was explored. The objective was to assess effects of medium composition and incorporation of human serum albumin into the matrix. Drug disappearance was assessed for solution, suspension and in situ precipitating insulin products (Actrapid, Levemir, Tresiba, Mixtard 30, Insulatard, Lantus) using the flow-based cartridge. UV–Vis imaging and light microscopy visualized dissolution, precipitation and albumin binding phenomena at the injection site. Divalent cations present in the release medium resulted in slower insulin disappearance for suspension-based and in situ precipitating insulins. Albumin-binding acylated insulin analogs exhibited rapid disappearance from the cartridge; however, sustained retention was achieved by coupling albumin to the matrix. An in vitro-in vivo relation was established for the non-albumin-binding insulins. The IVR cartridge is flexible with potential in formulation development as shown by the ability to accommodate solutions, suspensions, and in situ forming formulations while tailoring of the system to probe in vivo relevant medium effects and tissue constituent interactions.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
A UV imaging release-testing setup comprising an agarose gel as a model for tumorous tissue was developed. The setup was optimized with respect to agarose concentration (0.5% (w/v)), injection procedure, and temperature control. A repeatable injection protocol was established allowing injection into cavities with well-defined geometries. The effective resolution of the SDi2 UV imaging system is 30–80 µm. The linear range of the imaging system is less than that of typical spectrophotometers. Consequently, non-linear cAMP calibration curves were applied for quantification at 280 nm. The degree of deviation from Beer’s law was affected by the background absorbance of the gel matrix. MATLAB scripts provided hitherto missing flexibility with respect to definition and utilization of quantification zones, contour lines facilitating visualization, and automated, continuous data analysis. Various release patterns were observed for an aqueous solution and in situ forming Pluronic F127 hydrogel and PLGA implants containing cAMP as a model for STING ligands. The UV imaging and MATLAB data analysis setup constituted a significant technical development in terms of visualizing behavior for injectable formulations intended for intra-tumoral delivery, and, thereby, a step toward establishment of a bio-predictive in vitro release-testing method.
Transport within human tissue matrices, e.g., the subcutaneous tissue, exhibits some resemblance to chromatographic processes. Here, a porous matrix comprising agarose beads compatible with UV–vis imaging was developed for a parallel piped rectangular flow cell (4 mm light path). Introduction of high-molecular weight dextrans (Mr ∼ 200000 and ∼500000) at 10% (w/v) rendered imaging possible by providing optical clearing of the turbid porous matrix, resulting in improved transmittance as well as resolution (from 400 to 180 μm) at 280 nm, as well as 520 nm. The interplay between diffusive and convective transport at 0 < Pe ≤ 28 was visualized at 280 nm upon injection of dexamethasone suspensions. Real-time UV–vis imaging showed in-flow cell the effect of incorporating ion-exchange resins on the retention of infliximab, lysozyme, and α-lactalbumin. The ion-exchange matrix may serve as a surrogate for polyelectrolytes in the subcutaneous tissue, assessing the potential role of electrostatic interactions of biotherapeutics upon injection. UV–vis imaging of size-exclusion chromatographic matrixes may be of interest in its own right and potentially develop into a characterization tool for injectables.
New strategies are continuously sought for the treatment of skin and wound infections due to increased problems with non-healing wounds. Electrospun nanofiber mats with antibacterial agents as drug delivery systems provide opportunities for the eradication of bacterial infections as well as wound healing. Antibacterial activities of such mats are directly linked with their drug release behavior. Traditional pharmacopoeial drug release testing settings are not always suitable for analyzing the release behavior of fiber mats intended for the local drug delivery. We tested and compared different drug release model systems for the previously characterized electrospun chloramphenicol (CAM)-loaded nanofiber (polycaprolactone (PCL)) and microfiber (PCL in combination with polyethylene oxide) mats with different drug release profiles. Drug release into buffer solution and hydrogel was investigated and drug concentration was determined using either high-performance liquid chromatography, ultraviolet-visible spectrophotometry, or ultraviolet (UV) imaging. The CAM release and its antibacterial effects in disc diffusion assay were assessed by bacterial bioreporters. All tested model systems enabled to study the drug release from electrospun mats. It was found that the release into buffer solution showed larger differences in the drug release rate between differently designed mats compared to the hydrogel release tests. The UV imaging method provided an insight into the interactions with an agarose hydrogel mimicking wound tissue, thus giving us information about early drug release from the mat. Bacterial bioreporters showed clear correlations between the drug release into gel and antibacterial activity of the electrospun CAM-loaded mats.
