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Recently, a mixture of hemoglobin (Hb) and bovine serum albumin (BSA) was separated into two highly purified fractions with high recovery via internally staged ultrafiltration (ISUF) having a stack of three identical flat 100 kDa ultrafiltration (UF) membranes in a stirred cell. Selectivities as high as 1000–4000+, and high recoveries of individual species were achieved. Successful separation and purification of IgG from a BSA-IgG mixture was also achieved in a stirred cell using a modified ISUF technique with two 100 kDa membranes on a 70 kDa membrane; here BSA was a model for host cell proteins (HCPs) in post-protein A eluate. We explored here separation and purification of the Hb-BSA system in a developmental cassette of 88 cm2 membrane surface area, having a stack of three 100 kDa membranes on each side of the channel. The channel gap was smaller than that in regular cassettes resulting in higher flow pressure drops. The Hb-BSA separation was studied over a diavolume (DV) range of ~0–6. The Hb-BSA selectivity was as high as 1600 and remained above 300 till 6 DV. Lower feed pressure and a particular permeate collection mode leading to reduced transmembrane pressure drop were crucial for higher performance. Species recoveries were lower for the DV range used especially compared to those in a stirred cell. Successful separation and purification of BSA-IgG system was also demonstrated with similar limitations. Increased flow pressure drop due to flow channel height reduction in existing cassette frames and lower flow rates leading to higher concentration polarization suggest modification of the cassette frame for high performance ISUF for difficult-to-separate protein mixtures in biopharmaceutical separation processes. 

Purification of IgG from residual host cell proteins (HCPs) in post-Protein A chromatography is important since some HCPs bind with Protein A and elute with the monoclonal antibody (mAb); removal of HCPs from CHO cell lines is essential. To that end, an advanced separation and purification technique in biopharmaceutical manufacturing, namely, internally staged ultrafiltration (ISUF), is investigated here. Choosing BSA as a model for HCPs in post-protein A eluate, separation of a binary mixture of IgG and BSA containing 1.0 mg/ml IgG and 0.1 mg/ml BSA is successfully demonstrated here using a modified ISUF technique: two Omega 100 kDa membranes on top followed by one Omega 70 kDa membrane at the bottom. This modified configuration demonstrated exceptional performance with almost complete rejection, 99 % purity, and 99.5 % retention of IgG, along with 96.5 % recovery of BSA over 10 diavolumes. This modified membrane stacking resulted from strategic considerations of membrane stacking and careful selection of molecular weight cutoffs and materials, and performance analysis of different membranes and stacking configurations using rejection behaviors, purity levels, and recovery rates under varying diavolume and pressure differential. The approach adopted here enhances flexibility in membrane choices in ISUF and provides valuable insights for optimizing membrane-based biopharmaceutical separation techniques. 

The conventional real-time screening in organs-on-chips is limited to optical tracking of pre-tagged cells and biological agents. This work introduces an efficient biofabrication protocol to integrate tunable hydrogel electrodes into 3D bioprinted-on-chips. We established our method of fabricating cell-laden hydrogel-based microfluidic chips through digital light processing-based 3D bioprinting. Our conductive ink includes poly-(3,4-ethylene-dioxythiophene)-polystyrene sulfonate (PEDOT: PSS) microparticles doped in polyethylene glycol diacrylate (PEGDA). We optimized the manufacturing process of PEDOT: PSS microparticles characterized our conductive ink for different 3D bioprinting parameters, geometries, and materials conditions. While the literature is limited to 0.5% w/v for PEDOT: PSS microparticle concentration, we increased their concentration to 5% w/v with superior biological responses. We measured the conductivity in the 3–15 m/m for a range of 0.5%–5% w/v microparticles, and we showed the effectiveness of 3D-printed electrodes for predicting cell responses when encapsulated in gelatin-methacryloyl (GelMA). Interestingly, a higher cellular activity was observed in the case of 5% w/v microparticles compared to 0.5% w/v microparticles. Electrochemical impedance spectroscopy measurements indicated significant differences in cell densities and spheroid sizes embedded in GelMA microtissues. 

Critical review of point of care devices in oral care. 

The most well-known criterion for POC devices is ASSURED, and affordability, i.e., using low-cost instrumentation, is the most challenging one. This manuscript provides a pathway for transitioning ESSENCE, an impedance-based biosensor platform, from using an expensive benchtop analyzer—KeySight 4294A (~$50k)—to using a significantly portable and cheaper USB oscilloscope—Analog Discovery 2 (~$200) —with similar sensitivity (around 100 times price difference). To achieve this, we carried out a fundamental study of the interplay between an electrolyte like potassium chloride (KCl), and an electrolyte buffer like phosphate buffered saline (PBS) in the presence and absence of a redox buffer like ferro/ferricyanide system and ([Ru(bpy)3]2+). Redox molecules in the electrolyte caused a significant change in the Nyquist curve of the impedance depending on the redox molecule type. The redox species and the background electrolyte have their own RC semicircles in the Nyquist curve, whose overlap depends on the redox concentration and electrolyte ionic strength. We found that by increasing the electrolyte ionic strength or the redox concentration, the RC semicircle moves to higher frequencies and vice versa. Importantly, the use of the buffer electrolyte, instead of KCl, led to a lower standard deviation and overall signal (lesser sensitivity). However, to achieve the best results from the biorecognition signal, we chose a buffered electrolyte like PBS with high ionic strength and lowered the redox probe concentrations to minimize the standard deviation and reduce any noise from migrating to the low-cost analyzer. Comparing the two analyzers shows similar results, with a lowered detection limit from the low-cost analyzer.