Open Access Publications

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Open access publications by faculty, postdocs, and graduate students in the Department of Chemical and Biomolecular Engineering

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Accelerating manufacturing for biomass conversion via integrated process and bench digitalization: a perspective
(Reaction Chemistry and Engineering, 2022-01-25) Batchu, Sai Praneet; Hernandez, Borja; Malhotra, Abhinav; Fang, Hui; Ierapetritou, Marianthi; Vlachos, Dionisios G.
We present a perspective for accelerating biomass manufacturing via digitalization. We summarize the challenges for manufacturing and identify areas where digitalization can help. A profound potential in using lignocellulosic biomass and renewable feedstocks, in general, is to produce new molecules and products with unmatched properties that have no analog in traditional refineries. Discovering such performance-advantaged molecules and the paths and processes to make them rapidly and systematically can transform manufacturing practices. We discuss retrosynthetic approaches, text mining, natural language processing, and modern machine learning methods to enable digitalization. Laboratory and multiscale computation automation via active learning are crucial to complement existing literature and expedite discovery and valuable data collection without a human in the loop. Such data can help process simulation and optimization select the most promising processes and molecules according to economic, environmental, and societal metrics. We propose the close integration between bench and process scale models and data to exploit the low dimensionality of the data and transform the manufacturing for renewable feedstocks.
Activation of Molecular Oxygen for Alcohol Oxidation over Vanadium Carbon Catalysts Synthesized via the Heterogeneous Ligand Strategy
(ACS Catalysis, 2022-12-16) Zhao, Li; Yang, Piaoping; Shi, Song; Zhu, Guozhi; Feng, Xiao; Zheng, Weiqing; Vlachos, Dionisios G.; Xu, Jie
Activation of molecular oxygen to realize selective oxidation is challenging. We employ a heterogeneous ligand method to prepare a vanadium carbon catalyst (V–C catalyst) of high efficiency in alcohol oxidation via oxygen activation. Principal component analysis revealed that the chemisorbed oxygen and pentavalent vanadium oxide are crucial in catalyst performance. Isotopic labeling, electron paramagnetic resonance, and control experiments confirmed that the V–C catalyst activates molecular oxygen to singlet oxygen or its analogue and carries out the reaction. A kinetic study and in situ React-IR spectra illustrated that the main reaction route is the O2 activation to 1O2 or its analogue and oxidizes the substrate through C–H bond activation. We demonstrate the efficiency of the V–C catalyst in selectively oxidizing the hydroxyl group in other substrates, including benzyl alcohols, methyl lactate, and ethyl lactate biomass-based alcohols. This will guide the development of highly active nonprecious metal catalysts for activating O2 for aerobic oxidation.
Anomalous rheological aging of a model thermoreversible colloidal gel following a thermal quench
(The Journal of Chemical Physics, 2022-06-15) Suman, Khushboo; Wagner, Norman J.
We investigate the aging behavior in a well-studied model system comprised of a colloidal suspension of thermoreversible adhesive hard spheres (AHS) but thermally quenched below the gel transition to much larger depths than previously studied. The aging behavior in the model AHS system is monitored by small amplitude oscillatory shear rheology measurements conducted while rapidly quenching from liquid state at 40{degree sign}C to a temperature below the gel temperature and new, anomalous aging behaviors are observed. Shallow quenches lead to monotonic development of the elastic modulus with time consistent with prior reports for the development of a homogeneous gel (Gordon et al., Journal of Rheology 2017). However, for deeper quenches, a unique and new phenomenon is reported - namely after an initial rise in the modulus, a reproducible drop in modulus is observed, followed by a plateau in modulus value. This drop can be gradual or sudden, and the extent of the drop, both depends on quench depth. After this drop in modulus, AHS gel evolves toward a quench-path independent state over the experimental timescale. These effects of the extent of quenching on aging behavior is hypothesized to be a consequence of quenching into different underlying thermodynamic states of colloidal gels and the possible influence of the adhesive glass dynamical arrest for the deepest quenches. The research connects homogeneous gelation with heterogeneous gel formation due to phase separation and shows that the extent of quench can be used as an independent parameter to govern the rheological response of the arrested gel.
Area-based Image Analysis Algorithm for Quantification of Macrophage-fibroblast Cocultures
(Journal of Visualized Experiments, 2022-02-15) Borjigin, Tohn; Boddupalli, Anuraag; Sullivan, Millicent O.
Quantification of cells is necessary for a wide range of biological and biochemical studies. Conventional image analysis of cells typically employs either fluorescence detection approaches, such as immunofluorescent staining or transfection with fluorescent proteins or edge detection techniques, which are often error-prone due to noise and other non-idealities in the image background. We designed a new algorithm that could accurately count and distinguish macrophages and fibroblasts, cells of different phenotypes that often colocalize during tissue regeneration. MATLAB was used to implement the algorithm, which differentiated distinct cell types based on differences in height from the background. A primary algorithm was developed using an area-based method to account for variations in cell size/structure and high-density seeding conditions. Non-idealities in cell structures were accounted for with a secondary, iterative algorithm utilizing internal parameters such as cell coverage computed using experimental data for a given cell type. Finally, an analysis of coculture environments was carried out using an isolation algorithm in which various cell types were selectively excluded based on the evaluation of relative height differences within the image. This approach was found to accurately count cells within a 5% error margin for monocultured cells and within a 10% error margin for cocultured cells.
Best practices for electrochemical reduction of carbon dioxide
(Nature Sustainability, 2023-01-02) Seger, Brian; Robert, Marc; Jiao, Feng
Carbon capture, utilization and storage, a fundamental process to a sustainable future, relies on a suite of technologies among which electrochemical reduction of carbon dioxide is essential. Here, we discuss the issues faced when reporting performance of this technology and recommend how to move forward at both materials and device levels. Electrochemical reduction of CO2 into value-added chemicals has attracted considerable attention recently1,2,3. However, reporting the performance of a new CO2 electrocatalyst or a new reactor design is not trivial because of the complex nature of the CO2 electroreduction reaction. In many cases, the results are presented in a confusing manner, rendering it difficult to assess the true performance of the catalyst and/or device. In this Comment, we first discuss common problems in reporting the performance of a new electrocatalyst (including both heterogeneous and molecular catalysts) in the literature and then extend the discussion to how the products should be properly measured and quantified. Finally, we comment on the issues associated with full-cell level studies and recommend the best practices for electrochemical CO2 reduction.
Biomanufacturing readiness levels—A shared vocabulary for biopharmaceutical technology development and commercialization
(Biotechnology and Bioengineering, 2022-09-07) Kedia, Sandeep B.; Baker, Jeffrey C.; Carbonell, Ruben G.; Lee, Kelvin H.; Roberts, Christopher J.; Erickson, John; Schiel, John E.; Rogers, Kelley; Schaefer, Gene; Pluschkell, Stefanie
The Manufacturing Readiness Levels (MRLs) developed by the Department of Defense are well-established tools for describing the maturity of new technologies resulting from government-sponsored Research and Development programs, from the concept phase to commercial deployment. While MRLs are generally applicable to a wide range of industries and technologies, there is significant value in offering an industry-specific view on how the basic principles may be applied to biomanufacturing. This paper describes Biomanufacturing Readiness Levels (BRLs) developed by the National Institute for Innovation in Manufacturing Biopharmaceuticals (NIIMBL), a public/private partnership that is part of the Manufacturing USA network. NIIMBL brings together private, federal, nonprofit, and academic stakeholders to accelerate the deployment of innovative technologies for biopharmaceutical production and to educate and train a world-leading biomanufacturing workforce. We anticipate that these BRLs will lay the groundwork for a shared vocabulary for assessment of technology maturity and readiness for commercial biomanufacturing that effectively meets the needs of this critical, specialized, and highly regulated industry.
Catalytic Dehydrogenation of Ethane over Mn Oxide Supported on Zeolite Chabazite
(ChemCatChem, 2022-09-04) Pan, Jian; Shi, Song; Yuan, Yong; Lobo, Raul Francisco
A new class of Mn-containing zeolites prepared by incipient wetness impregnation (IWI) have been found to catalyze the ethane dehydrogenation reaction with high selectivity (98%+). Preparation by IWI leads to the formation of Mn 2 O 3 nanoparticles on the external surface of the zeolite crystals and herein is shown that the primary active sites for the reaction are located on the surface of these particles. Propane dehydrogenation is also successfully catalyzed by this catalyst. Other Mn-zeolites (MFI and BEA) also have high reactivity and selectivity towards light alkane dehydrogenation.
Characterization and implications of host-cell protein aggregates in biopharmaceutical processing
(Biotechnology and Bioengineering, 2023-03-14) Oh, Young Hoon; Becker, Matthew L.; Mendola, Kerri M.; Choe, Leila H.; Min, Lie; Lee, Kelvin H.; Yigzaw, Yinges; Seay, Alexander; Bill, Jerome Jr.; Li, Xuanwen; Roush, David J.; Cramer, Steven M.; Menegatti, Stefano; Lenhoff, Abraham M.
In the production of biopharmaceuticals such as monoclonal antibodies (mAbs) and vaccines, the residual amounts of host-cell proteins (HCPs) are among the critical quality attributes. In addition to overall HCP levels, individual HCPs may elude purification, potentially causing issues in product stability or patient safety. Such HCP persistence has been attributed mainly to biophysical interactions between individual HCPs and the product, resin media, or residual chromatin particles. Based on measurements on process streams from seven mAb processes, we have found that HCPs in aggregates, not necessarily chromatin-derived, may play a significant role in the persistence of many HCPs. Such aggregates may also hinder accurate detection of HCPs using existing proteomics methods. The findings also highlight that certain HCPs may be difficult to remove because of their functional complementarity to the product; specifically, chaperones and other proteins involved in the unfolded protein response (UPR) are disproportionately present in the aggregates. The methods and findings described here expand our understanding of the origins and potential behavior of HCPs in cell-based biopharmaceutical processes and may be instrumental in improving existing techniques for HCP detection and clearance.
Comparison of lunar and Martian regolith simulant-based geopolymer cements formed by alkali-activation for in-situ resource utilization
(Advances in Space Research, 2021-12-20) Mills, Jennifer N.; Katzarova, Maria; Wagner, Norman J.
Future human space exploration and habitation on the lunar and Martian surfaces necessitates in-situ resource utilization (ISRU) for the development of construction materials tailored for infrastructure and environmental protection. Here we explore the use of lunar and Martian regoliths to create construction materials with properties suitable for such structures as landing pads. Alkali activation of a spectrum of lunar and Martian regolith simulants generates geopolymer binders under ambient and vacuum curing conditions as well as exposure to extreme high and low temperatures (600 and −80 °C). Compressive strength is reduced for binders prepared from each simulant after curing under vacuum and exposure to sub-zero temperatures. In lunar simulant binders, the compressive strength is increased after heating to 600 °C, but the opposite effect is observed in the Martian simulant binder. Amorphous aluminosilicate content and percentage of small particles in the simulants are hypothesized to have a positive impact on compressive strength under ambient curing. Iron and magnesium content may be responsible for decreased compressive strength of the Martian binder after heating. This study offers a robust framework for comparing performance of different simulants under the same curing protocols and environmental exposures, as well as offering insight as to the effects of vacuum curing, and exposure to high and low temperature environments on cured binder samples. Developing a landing pad by transporting activator to the lunar surface is shown to be conceptually feasible within current payload constraints.
Comprehensive assessment of host cell protein expression after extended culture and bioreactor production of CHO cell lines
(Biotechnology and Bioengineering, 2022-05-04) Hamaker, Nathaniel K.; Min, Lie; Lee, Kelvin H.
The biomanufacturing industry is advancing toward continuous processes that will involve longer culture durations and older cell ages. These upstream trends may bring unforeseen challenges for downstream purification due to fluctuations in host cell protein (HCP) levels. To understand the extent of HCP expression instability exhibited by Chinese hamster ovary (CHO) cells over these time scales, an industry-wide consortium collaborated to develop a study to characterize age-dependent changes in HCP levels across 30, 60, and 90 cell doublings, representing a period of approximately 60 days. A monoclonal antibody (mAb)-producing cell line with bulk productivity up to 3 g/L in a bioreactor was aged in parallel with its parental CHO-K1 host. Subsequently, both cell types at each age were cultivated in an automated bioreactor system to generate harvested cell culture fluid (HCCF) for HCP analysis. More than 1500 HCPs were quantified using complementary proteomic techniques, two-dimensional electrophoresis (2DE) and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). While up to 13% of proteins showed variable expression with age, more changes were observed when comparing between the two cell lines with up to 47% of HCPs differentially expressed. A small subset (50 HCPs) with age-dependent expression were previously reported to be problematic as high-risk and/or difficult-to-remove impurities; however, the vast majority of these were downregulated with age. Our findings suggest that HCP expression changes over this time scale may not be as dramatic and pose as great of a challenge to downstream processing as originally expected but that monitoring of variably expressed problematic HCPs remains critical.
Design and qualification of a bench-scale model for municipal waste-to-energy combustion
(Journal of the Air & Waste Management Association, 2022-04-25) Giraud, Robert J.; Taylor, Philip H.; Diemer, R. Bertrum; Huang, Chin-Pao
This paper reports the design and qualification of the first purpose-built, bench-scale reactor system to model the municipal waste-to-energy combustion of fluorinated polymers. Using the principle of similarity, the gas-phase combustion zone of a typical municipal waste-to-energy plant has been scaled down to the bench with a focus on chemical similarity. Chemical similarity is achieved in large part through the use of methanol as a surrogate for municipal solid waste (MSW). Review of prior research shows that methanol is one of the major volatile products expected during MSW thermal conversion in the fuel bed of waste-to-energy plants. Like full-scale waste-energy plants, the design of the bench-scale model includes a flame zone and a post-flame zone. Maintaining steady methanol vapor flow premixed with air to the model reactor system ensures stable combustion resulting in bench-scale CO emission levels comparable to those of full-scale waste-to-energy plants. Since investigation of fluorinated polymer combustion includes trace analysis of exhaust gas for perfluorooctanoic acid (PFOA), qualification testing focused on PFOA collection efficiency. High PFOA collection efficiency (>90%) demonstrated the capability of the reactor system in transporting and absorbing PFOA that may be generated during high-temperature combustion testing of fluorinated polymers. Overall, the bench-scale system is qualified for its intended use to investigate potential generation of PFOA from combustion of fluorinated polymers under conditions representative of waste-to-energy combustion. Implications: Decision makers depend on environmental researchers to provide reliable predictions of pollutant emissions from waste combustion of polymers at end of product life. Reliable predictions are especially important with regard to questions about potential PFOA emissions from municipal waste combustion of fluorinated polymers. Results from qualification testing confirm that the novel bench-scale model reactor system is capable of representing gas-phase municipal waste combustion behavior upstream of air pollution control and generating representative exhaust gas samples for off-line trace-level analysis of PFOA.
Dynamic modulation of enzyme activity by synthetic CRISPR–Cas6 endonucleases
(Nature Chemical Biology, 2022-04-25) Mitkas, Alexander A.; Valverde, Mauricio; Chen, Wilfred
In nature, dynamic interactions between enzymes play a crucial role in defining cellular metabolism. By controlling the spatial and temporal organization of these supramolecular complexes called metabolons, natural metabolism can be tuned in a highly dynamic manner. Here, we repurpose the CRISPR–Cas6 family proteins as a synthetic strategy to create dynamic metabolons by combining the ease of RNA processing and the predictability of RNA hybridization for protein assembly. By disturbing RNA–RNA networks using toehold-mediated strand displacement reactions, on-demand assembly and disassembly are achieved using both synthetic RNA triggers and mCherry messenger RNA. Both direct and ‘Turn-On’ assembly of the pathway enzymes tryptophan-2-monooxygenase and indoleacetamide hydrolase can enhance indole-3-acetic acid production by up to ninefold. Even multimeric enzymes can be assembled to improve malate production by threefold. By interfacing with endogenous mRNAs, more complex metabolons may be constructed, resulting in a self-responsive metabolic machinery capable of adapting to changing cellular demand.
Effect of scatterer interactions on photon transport in diffusing wave spectroscopy
(Physical Review E, 2022-12-16) Sbalbi, Nicholas; Li, Qi; Furst, Eric M.
We calculate the effect of particle size, concentration, and interactions on the photon transport mean-free path l∗ that characterizes the multiple light scattering in diffusing wave spectroscopy (DWS). For scatterers of sufficient size, such that the first peak of the suspension structure factor S(qmax) remains in the range of accessible scattering vectors, neither repulsive nor attractive interactions between scatterers contribute strongly to l∗; its values are bounded by those for hard spheres and scatterers without interactions. However, for scatterers smaller than the wavelength of light, crowding induced by attraction or repulsion can lead to nonmonotonic behavior in l∗ with increasing scatterer concentration. The effect is strongest for repulsive particles.
Estrogenic activity of lignin-derivable alternatives to bisphenol A assessed via molecular docking simulations
(RSC Advances, 2021-06-23) Amitrano, Alice; Mahajan, Jignesh S.; Korley, LaShanda T. J.; Epps, Thomas H. III
Lignin-derivable bisphenols are potential alternatives to bisphenol A (BPA), a suspected endocrine disruptor; however, a greater understanding of structure–activity relationships (SARs) associated with such lignin-derivable building blocks is necessary to move replacement efforts forward. This study focuses on the prediction of bisphenol estrogenic activity (EA) to inform the design of potentially safer BPA alternatives. To achieve this goal, the binding affinities to estrogen receptor alpha (ERα) of lignin-derivable bisphenols were calculated via molecular docking simulations and correlated to median effective concentration (EC50) values using an empirical correlation curve created from known EC50 values and binding affinities of commercial (bis)phenols. Based on the correlation curve, lignin-derivable bisphenols with binding affinities weaker than ∼−6.0 kcal mol−1 were expected to exhibit no EA, and further analysis suggested that having two methoxy groups on an aromatic ring of the bio-derivable bisphenol was largely responsible for the reduction in binding to ERα. Such dimethoxy aromatics are readily sourced from the depolymerization of hardwood biomass. Additionally, bulkier substituents on the bridging carbon of lignin-bisphenols, like diethyl or dimethoxy, were shown to weaken binding to ERα. And, as the bio-derivable aromatics maintain major structural similarities to BPA, the resultant polymeric materials should possess comparable/equivalent thermal (e.g., glass transition temperatures, thermal decomposition temperatures) and mechanical (e.g., tensile strength, modulus) properties to those of polymers derived from BPA. Hence, the SARs established in this work can facilitate the development of sustainable polymers that maintain the performance of existing BPA-based materials while simultaneously reducing estrogenic potential.
Extracellular vesicles facilitate large-scale dynamic exchange of proteins and RNA among cultured Chinese hamster ovary and human cells
(Biotechnology and Bioengineering, 2022-02-04) Belliveau, Jessica; Papoutsakis, Eleftherios T.
Cells in culture are viewed as unique individuals in a large population communicating through extracellular molecules and, more recently extracellular vesicles (EVs). Our data here paint a different picture: large-scale exchange of cellular material through EVs. To visualize the dynamic production and cellular uptake of EVs, we used correlative confocal microscopy and scanning electron microscopy, as well as flow cytometry to interrogate labeled cells. Using cells expressing fluorescent proteins (GFP, miRFP703) and cells tagged with protein and RNA dyes, we show that Chinese hamster ovary (CHO) cells dynamically produce and uptake EVs to exchange proteins and RNAs at a large scale. Applying a simple model to our data, we estimate, for the first time, the per cell-specific rates of EV production (68 and 203 microparticles and exosomes, respectively, per day). This EV-mediated massive exchange of cellular material observed in CHO cultures was also observed in cultured human CHRF-288-11 and primary hematopoietic stem and progenitor cells. This study demonstrates an underappreciated massive protein and RNA exchange between cells mediated by EVs spanning cell type, suggesting that the proximity of cells in normal and tumor tissues may also result in prolific exchange of cellular material. This exchange would be expected to homogenize the cell-population cytosol and dynamically regulate cell proliferation and the cellular state.
Flowthrough of 239PU and 55FE during RNA extraction
(Journal of Radiological Protection, 2023-01-31) Manglass, Lisa M.; Vogel, Charlotte M.; Wintenberg, Molly; Blenner, Mark A.; Martinez, Nicole E.
Analysis of gene expression has become an important tool in understanding low-dose effect mechanisms of ionizing radiation at the cellular level. Metal binding to nucleic acids needs to be considered when interpreting these results, as some radioactive metals, particularly actinides, may produce free radicals and cause oxidative stress damage via chemical means at rates much higher than free radical formation related to their radiological properties. Bacteria exposed in situ to low dose rates of plutonium-239 (239Pu) and iron-55 (55Fe) were previously analysed for gene expression. The work herein was motivated by an interest in more precisely identifying the distribution of radionuclides in these bacteria as well as the practical need to ensure appropriate transport and handling of the associated ribonucleic acid (RNA) extractions. RNA extractions were performed on bacteria growth media with and without bacteria cells (i.e. with and without RNA) at several different concentrations of 239Pu and 55Fe to inform the level of specificity of the extraction membrane as well as provide insight into internal (uptake) vs external (sorption) accumulation of these radionuclides in bacteria cells. Results of the study suggest that 239Pu and 55Fe detected in RNA extraction samples during long term cell studies is the result of binding to RNA prior to the time of extraction, as opposed to flow through or binding after cell lysis, and it highlights the practical importance of nucleic acid sample characterization to radiation protection more generally.
A hybrid inorganic–biological artificial photosynthesis system for energy-efficient food production
(Nature Food, 2022-06-23) Hann, Elizabeth C.; Overa, Sean; Harland-Dunaway, Marcus; Narvaez, Andrés F.; Le, Dang N.; Orozco-Cárdenas, Martha L.; Jiao, Feng; Jinkerson, Robert E.
Artificial photosynthesis systems are proposed as an efficient alternative route to capture CO2 to produce additional food for growing global demand. Here a two-step CO2 electrolyser system was developed to produce a highly concentrated acetate stream with a 57% carbon selectivity (CO2 to acetate), allowing its direct use for the heterotrophic cultivation of yeast, mushroom-producing fungus and a photosynthetic green alga, in the dark without inputs from biological photosynthesis. An evaluation of nine crop plants found that carbon from exogenously supplied acetate incorporates into biomass through major metabolic pathways. Coupling this approach to existing photovoltaic systems could increase solar-to-food energy conversion efficiency by about fourfold over biological photosynthesis, reducing the solar footprint required. This technology allows for a reimagination of how food can be produced in controlled environments.
Hydrogel nanoparticle degradation influences the activation and survival of primary macrophages
(Journal of Materials Chemistry B, 2021-06-28) Jarai, Bader M.; Stillman, Zachary; Fromen, Catherine A.
The effect of nanoparticle (NP) internalization on cell fate has emerged as an important consideration for nanomedicine design, as macrophages and other phagocytes are the primary clearance mechanisms of administered NP formulations. Pro-survival signaling is thought to be concurrent with phagocytosis and recent work has shown increased macrophage survival following lysosomal processing of internalized NPs. These observations have opened the door to explorations of NP physiochemical properties aimed at tuning the NP-driven macrophage survival at the lysosomal synapse. Here, we report that NP-induced macrophage survival and activation is strongly dependent on NP degradation rate using a series of thiol-containing poly(ethylene glycol) diacrylate-based NPs of equivalent size and zeta potential. Rapidly degrading, high thiol-containing NPs allowed for dramatic enhancement of cell longevity that was concurrent with macrophage stimulation after 2 weeks in ex vivo culture. While equivalent NP internalization resulted in suppressed caspase activity across the NP series, macrophage activation was correlated with increasing thiol content, leading to increased lysosomal activity and a robust pro-survival phenotype. Our results provide insight on tuning NP physiochemical properties as design handles for maximizing ex vivo macrophage longevity, which has implications for improving macrophage-based immune assays, biomanufacturing, and cell therapies.
Hydrogen-powered Electrochemically-driven CO2 Removal from Air Containing 400 to 5000 ppm CO2
(Journal of The Electrochemical Society, 2022-07-07) Matz, Stephanie; Shi, Lin; Zhao, Yun; Gottesfeld, Shimshon; Setzler, Brian P.; Yan, Yushan
The performance of a hydrogen-powered, electrochemically-driven CO2 separator (EDCS) was demonstrated at cathode inlet CO2 concentrations from 400 ppm to 5,000 ppm. The impact of current density and CO2 concentration were evaluated to predict operating windows for various applications. The single-cell data was used to scale a 100 cm2, multi-cell stack using a shorted-membrane design for four applications: direct air capture (DAC), hydroxide exchange membrane fuel cell (HEMFC) air pretreatment, submarine life support, and space habitation. For DAC, a 339-cell EDCS stack (7.7 L, 17 kg) was projected to remove 1 tonne CO2 per year. The addition of the EDCS in HEMFC systems would result in nearly a 30% increase in volume, and therefore further improvements in performance would be necessary. A module containing five 338-cell EDCS stacks (38 L, 85 kg) in parallel can support a 150 person crew at 2.1% of the volume of the liquid amine system employed in submarines. For space habitation, a 109-cell EDCS stack (3.2 L, 10 kg) is adequate for 6 crewmembers, and is less than 1% the size and 5% the weight of the current CO2 removal system installed on the International Space Station.
Impact of collagen-like peptide (CLP) heterotrimeric triple helix design on helical thermal stability and hierarchical assembly: a coarse-grained molecular dynamics simulation study
(Soft Matter, 2022-04-05) Taylor, Phillip A.; Kloxin, April M.; Jayaraman, Arthi
Collagen-like peptides (CLP) are multifunctional materials garnering a lot of recent interest from the biomaterials community due to their hierarchical assembly and tunable physicochemical properties. In this work, we present a computational study that links the design of CLP heterotrimers to the thermal stability of the triple helix and their self-assembly into fibrillar aggregates and percolated networks. Unlike homotrimeric helices, the CLP heterotrimeric triple helices in this study are made of CLP strands of different chain lengths that result in ‘sticky’ ends with available hydrogen bonding groups. These ‘sticky’ ends at one end or both ends of the CLP heterotrimer then facilitate inter-helix hydrogen bonding leading to self-assembly into fibrils (clusters) and percolated networks. We consider the cases of three sticky end lengths – two, four, and six repeat units – present entirely on one end or split between two ends of the CLP heterotrimer. We observe in CLP heterotrimer melting curves generated using coarse grained Langevin dynamics simulations at low CLP concentration that increasing sticky end length results in lower melting temperatures for both one and two sticky ended CLP designs. At higher CLP concentrations, we observe non-monotonic trends in cluster sizes with increasing sticky end length with one sticky end but not for two sticky ends with the same number of available hydrogen bonding groups as the one sticky end; this nonmonotonicity stems from the formation of turn structures stabilized by hydrogen bonds at the single, sticky end for sticky end lengths greater than four repeat units. With increasing CLP concentration, heterotrimers also form percolated networks with increasing sticky end length with a minimum sticky end length of four repeat units required to observe percolation. Overall, this work informs the design of thermoresponsive, peptide-based biomaterials with desired morphologies using strand length and dispersity as a handle for tuning thermal stability and formation of supramolecular structures.

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