3D-Printed Microfluidic Perfusion System for Parallel Monitoring of Hydrogel-Embedded Cell Cultures

The use of three-dimensional (3D) cell cultures has become increasingly popular in the contexts of drug discovery, disease modelling, and tissue engineering, as they aim to replicate in vivo-like conditions. To achieve this, new hydrogels are being developed to mimic the extracellular matrix. Testing the ability of these hydrogels is crucial, and the presented 3D-printed microfluidic perfusion system offers a novel solution for the parallel cultivation and evaluation of four separate 3D cell cultures. This system enables easy microscopic monitoring of the hydrogel-embedded cells and significantly reduces the required volumes of hydrogel and cell suspension. This cultivation device is comprised of two 3D-printed parts, which provide four cell-containing hydrogel chambers and the associated perfusion medium chambers. An interfacing porous membrane ensures a defined hydrogel thickness and prevents flow-induced hydrogel detachment. Integrated microfluidic channels connect the perfusion chambers to the overall perfusion system, which can be operated in a standard CO₂-incubator. A 3D-printed adapter ensures the compatibility of the cultivation device with standard imaging systems. Cultivation and cell staining experiments with hydrogel-embedded murine fibroblasts confirmed that cell morphology, viability, and growth inside this cultivation device are comparable with those observed within standard 96-well plates. Due to the high degree of customization offered by additive manufacturing, this system has great potential to be used as a customizable platform for 3D cell culture applications.

Employing QbD strategies to assess the impact of cell viability and density on the primary recovery of monoclonal antibodies

Quality by Design (QbD) is one of the most important tools for the implementation of Process Analytical Technology (PAT) in biopharmaceutical production. For optimal characterization of a monoclonal antibody (mAb) upstream process a stepwise approach was implemented. The upstream was divided into three process stages, namely inoculum expansion, production, and primary recovery, which were investigated individually. This approach enables analysis of process parameters and associated intermediate quality attributes as well as systematic knowledge transfer to subsequent process steps. Following previous research, this study focuses on the primary recovery of the mAb and thereby marks the final step toward a holistic characterization of the upstream process. Based on gained knowledge during the production process evaluation, the cell viability and density were determined as critical parameters for the primary recovery. Directed cell viability adjustment was achieved using cytotoxic camptothecin in a novel protocol. Additionally, the cell separation method was added to the Design of Experiments (DoE) as a qualitative factor and varied between filtration and centrifugation. To assess the quality attributes after cell separation, the bioactivity of the mAb was analyzed using a cell-based assay and the purity of the supernatant was evaluated by measurement of process related impurities (host cell protein proportion, residual DNA). Multivariate data analysis of the compiled data confirmed the hypothesis that the upstream process has no significant influence on the bioactivity of the mAb. Therefore, process control must be tuned towards high mAb titers and purity after the primary recovery, enabling optimal downstream processing of the product. To minimize amounts of host cell proteins and residual DNA the cell viability should be maintained above 85% and the cell density should be controlled around 15 × 10⁶ cells/ml during the cell removal. Thereby, this study shows the importance of QbD for the characterization of the primary recovery of mAbs and highlights the useful implementation of the stepwise approach over subsequent process stages.

Automation of cell culture assays using a 3D-printed servomotor-controlled microfluidic valve system

Microfluidic valve systems show great potential to automate mixing, dilution, and time-resolved reagent supply within biochemical assays and novel on-chip cell culture systems. However, most of these systems require a complex and cost-intensive fabrication in clean room facilities, and the valve control element itself also requires vacuum or pressure sources (including external valves, tubing, ports and pneumatic control channels). Addressing these bottlenecks, the herein presented biocompatible and heat steam sterilizable microfluidic valve system was fabricated via high-resolution 3D printing in a one-step process - including inlets, micromixer, microvalves, and outlets. The 3D-printed valve membrane is deflected via miniature on-chip servomotors that are controlled using a Raspberry Pi and a customized Python script (resulting in a device that is comparatively low-cost, portable, and fully automated). While a high mixing accuracy and long-term robustness is established, as described herein the system is further applied in a proof-of-concept assay for automated IC₅₀ determination of camptothecin with mouse fibroblasts (L929) monitored by a live-cell-imaging system. Measurements of cell growth and IC₅₀ values revealed no difference in performance between the microfluidic valve system and traditional pipetting. This novel design and the accompanying automatization scripts provide the scientific community with direct access to customizable full-time reagent control of 2D cell culture, or even novel organ-on-a-chip systems.

Optimization of a mAb production process with regard to robustness and product quality using quality by design principles

Quality by Design principles are well described and widely used in biopharmaceutical industry. The characterization of a monoclonal antibody (mAb) production process is crucial for novel process development and control. Yet, the application throughout the entire upstream process was rarely demonstrated. Following previously published research, this study marks the second step toward a complete process characterization and is focused on the effect of critical process parameters on the antibody production efficiency and quality of the process. In order to conduct the complex Design of Experiments approach with optimal control and comparability, the ambr®15 micro bioreactor platform was used. Investigated parameters included the pH and dissolved oxygen set points, the initial viable cell density (iVCD) as well as the N‐1 duration. Various quality attributes (e.g., growth rate, viability, mAb titer, and peak proportion) were monitored and analyzed using multivariate data analysis to evaluate the parameter effects. The pH set point and the initial VCD were identified as key process parameters with strong influence on the cell growth as well as the mAb production and its proportion to the total protein concentration. For optimization and improvement in robustness of these quality attributes the pH must be increased to 7.2, while the iVCD must be lowered to 0.2 × 10⁶ cells/mL. Based on the defined design space, additional experiments verified the results and confirmed the intact bioactivity of the antibody. Thereby, process control strategies could be tuned toward high cell maintenance and mAb production, which enable optimal downstream processing.

In vitro biocompatibility evaluation of a heat‐resistant 3D printing material for use in customized cell culture devices

Additive manufacturing (3D printing) enables the fabrication of highly customized and complex devices and is therefore increasingly used in the field of life sciences and biotechnology. However, the application of 3D‐printed parts in these fields requires not only their biocompatibility but also their sterility. The most common method for sterilizing 3D‐printed parts is heat steam sterilization—but most commercially available 3D printing materials cannot withstand high temperatures. In this study, a novel heat‐resistant polyacrylate material for high‐resolution 3D Multijet printing was evaluated for the first time for its resistance to heat steam sterilization and in vitro biocompatibility with mouse fibroblasts (L929), human embryonic kidney cells (HEK 293E), and yeast (Saccharomyces cerevisiae (S. cerevisiae)). Analysis of the growth and viability of L929 cells and the growth of S. cerevisiae confirmed that the extraction media obtained from 3D‐printed parts had no negative effect on the aforementioned cell types, while, in contrast, viability and growth of HEK 293E cells were affected. No different effects of the material on the cells were found when comparing heat steam sterilization and disinfection with ethanol (70%, v/v). In principle, the investigated material shows great potential for high‐resolution 3D printing of novel cell culture systems that are highly complex in design, customized and easily sterilizable—however, the biocompatibility of the material for other cell types needs to be re‐evaluated.

Monitoring cell productivity for the production of recombinant proteins by flow cytometry: An effective application using the cold capture assay

Due to the increasing economic and social relevance of biotherapeutics, their production processes are continually being reconsidered and reoptimized in an effort to secure higher product concentrations and qualities. Monitoring the productivity of cultured cells is therefore a critically important part of the cultivation process. Traditionally, this is achieved by determining the overall product titer by high performance liquid chromatography (HPLC), and then calculating the specific cell productivity based on this titer and an associated viable cell density. Unfortunately, this process is typically time-consuming and laborious. In this study, the productivity of Chinese Hamster Ovary (CHO) cells expressing a monoclonal antibody was analyzed over the course of the cultivation process. In addition to calculating the specific cell productivity based on the traditional product titer determined by HPLC analysis, culture productivity of single cells was also analyzed via flow cytometry using a cold capture assay. The cold capture assay is a cell surface labelling technique described by Brezinsky et al., which allows for the visualization of a product on the surface of the producing cell. The cell productivity results obtained via HPLC and the results of cold capture assay remained in great accordance over the whole cultivation process. Accordingly, our study demonstrates that the cold capture assay offers an interesting, comparatively time-effective, and potentially cheaper alternative for monitoring the productivity of a cell culture.

Furosemide inhibits 11 beta-hydroxysteroid dehydrogenase in vitro and in vivo

11 beta-hydroxysteroid dehydrogenase (11 beta-OHSD) protects the non-selective renal mineralocorticoid receptor from the endogeneous glucocorticoid cortisol. Thus, drugs inhibiting 11 beta-OHSD might enhance urinary loss of potassium. In an attempt to find drugs inhibiting 11 beta-OHSD, 23 commonly used agents known to interfere with the potassium metabolism have been screened for inhibitory effect on 11 beta-OHSD. Furosemide appeared as the only inhibitor. Its inhibition constant (Ki) was 19.5 microM when kidney and 21.3 microM when liver microsomes were used as a source of 11 beta-OHSD. The type of inhibition was competitive. For confirmation that furosemide specifically inhibits 11 beta-OHSD, the complementary DNA (cDNA) of 11 beta-OHSD was transfected into COS-1 cells devoid of spontaneous expression of 11 beta-OHSD. In these cells, oxidation of corticosterone (Ki = 17.4 microM) and reduction of dehydrocorticosterone (Ki = 12.5 microM) was inhibited by furosemide. To establish whether this inhibition also occurs in vivo, the 11 beta-hydroxysteroid prednisolone was administered with and without furosemide to rats. The concentration ratio of prednisolone to its 11-ketometabolite prednisone increased in kidney and liver tissue after furosemide administration, indicating inhibition of 11 beta-OHSD. These data suggest that furosemide modulates in vivo the access of 11 beta-OH glucocorticoids to their target organs.