Accelerated bioethanol fermentation by using a novel yeast immobilization technique: Microtube array membrane

A Review on Opportunities and Limitations of Membrane Bioreactor Configuration in Biofuel Production

Biofuels are a clean and renewable source of energy that has gained more attention in recent years; however, high energy input and processing cost during the production and recovery process restricted its progress. Membrane technology offers a range of energy-saving separation for product recovery and purification in biorefining along with biofuel production processes. Membrane separation techniques in combination with different biological processes increase cell concentration in the bioreactor, reduce product inhibition, decrease chemical consumption, reduce energy requirements, and further increase product concentration and productivity. Certain membrane bioreactors have evolved with the ability to deal with different biological production and separation processes to make them cost-effective, but there are certain limitations. The present review describes the advantages and limitations of membrane bioreactors to produce different biofuels with the ability to simplify upstream and downstream processes in terms of sustainability and economics.

Utilization of Corncob as an Immobilization Matrix for a Xylanolytic Yeast Strain

Immobilization of microbial cells for the production of industrially important enzymes has been reported to offer the advantages of recyclability, higher yields and cost effectiveness. The search for an appropriate matrix that is affordable and easy to prepare is a significant topic in microbial biotechnology. Here, an abundant type of agro-industrial waste-corncob-was utilized as an immobilization matrix for the production of xylanase from an indigenous yeast strain, Saccharomyces cerevisiae MK-157. This is the first report describing xylanase production from immobilized S. cerevisiae. To render the corncob matrix more porous, alkaline pretreatment was undertaken and yeast cells were immobilized on the matrix by cultivating at 30 °C for 48 h in Sabouraud dextrose broth. After incubation, the immobilized matrix was transferred to mineral salt medium containing 1% xylan and incubated at 30 °C for 24 h. Xylanase production was determined in cell-free culture supernatant and the matrix was recycled for up to seven cycles. Moreover, xylanase-mediated saccharification was carried out using sugarcane bagasse as a substrate and the release of reducing sugars was monitored. The results showed that the immobilized yeast produced 4.97 IU mL-1 xylanase in the first production cycle, indicating a >tenfold increase compared to the free cells. Xylanase production further increased to its maximum levels (9.23 IU mL-1) in the fourth production cycle. Nonetheless, the cells retained 100% productivity for up to seven cycles. The volumetric and specific productivity of xylanase were also the highest in the fourth cycle. Scanning electron microscopy images revealed the rough surface of the untreated corncob, which became more porous after alkaline pretreatment. Immobilized yeast cells were also visible on the corncob pieces. The saccharification of a natural resource-sugarcane bagasse-using xylanase preparation yielded 26 mg L-1 of reducing sugars. Therefore, it can be concluded that yeast strains can yield sufficient quantities of xylanase, allowing possible biotechnological applications. Moreover, corncob can serve as a cost-effective matrix for industrially important yeast strains.

Microtube Array Membrane Encapsulated Cell Therapy: A Novel Platform Technology Solution for Treatment of Alzheimer's Disease

Alzheimer's disease is the most frequent form of dementia in aging population and is presently the world's sixth largest cause of mortality. With the advancement of therapies, several solutions have been developed such as passive immunotherapy against these misfolded proteins, thereby resulting in the clearance. Within this segment, encapsulated cell therapy (ECT) solutions that utilize antibody releasing cells have been proposed with a multitude of techniques under development. Hence, in this study, we utilized our novel and patented Microtube Array Membranes (MTAMs) as an encapsulating platform system with anti-pTau antibody-secreting hybridoma cells to study the impact of it on Alzheimer's disease. In vivo results revealed that in the water maze, the mice implanted with hybridoma cell MTAMs intracranially (IN) and subcutaneously (SC) showed improvement in the time spent the goal quadrant and escape latency. In passive avoidance, hybridoma cell loaded MTAMs (IN and SC) performed significantly well in step-through latency. At the end of treatment, animals with hybridoma cell loaded MTAMs had lower phosphorylated tau (pTau) expression than empty MTAMs had. Combining both experimental results unveiled that the clearance of phosphorylated tau might rescue the cognitive impairment associated with AD.

Ultra-High Packing Density Next Generation Microtube Array Membrane for Absorption Based Applications

Previously, we successfully developed an extracorporeal endotoxin removal device (EERD) that is based on the novel next generation alternating microtube array membrane (MTAM-A) that was superior to the commercial equivalent. In this article, we demonstrated multiple different parameter modifications that led to multiple different types of novel new MTAM structures, which ultimately led to the formation of the MTAM-A. Contrary to the single layered MTAM, the MTAM-A series consisted of a superior packing density fiber connected in a double layered, alternating position which allowed for the greater fiber count to be packed per unit area. The respective MTAM variants were electrospun by utilizing our internally developed tri-axial electrospinning set up to produce the novel microstructures as seen in the respective MTAM variants. A key uniqueness of this study is the ability to produce self-arranged fibers into the respective MTAM variants by utilizing a single spinneret, which has not been demonstrated before. Of the MTAM variants, we observed a change in the microstructure from a single layered MTAM to the MTAM-A series when the ratio of surfactant to shell flow rate approaches 1:1.92. MTAM-A registered the greatest surface area of 2.2 times compared to the traditional single layered MTAM, with the greatest tensile strength at 1.02 ± 0.13 MPa and a maximum elongation of 57.70 ± 9.42%. The MTAM-A was selected for downstream immobilization of polymyxin B (PMB) and assembly into our own internally developed and fabricated dialyzer housing. Subsequently, the entire setup was tested with whole blood spiked with endotoxin; and benchmarked against commercial Toraymyxin fibers of the same size. The results demonstrated that the EERD based on the MTAM-A performed superior to that of the commercial equivalent, registering a rapid reduction of 73.18% of endotoxin (vs. Toraymyxin at 38.78%) at time point 15 min and a final total endotoxin removal of 89.43% (vs. Toraymyxin at 65.03%).

Yeast encapsulation in nanofiber via electrospinning: Shape transformation, cell activity and immobilized efficiency

To realize encapsulation of living microbial cells and easily evaluation of cell viability after immobilization, the yeast cells were encapsulated in water soluble PAAm nanofiber by a facile and effective electrospinning technology. Firstly, the conductivity, shear viscosity and surface tension of PAAm/yeast electrospinning solution as a function of mass ratios of yeast/PAAm were investigated to determine the optimum solution condition for electrospinning immobilization. After electrospinning, it is interesting to note that the original ellipsoidal structure of yeast cells turns to oblate spheroid structure. To distinguish immobilization structure from the bead appearing during general electrospinning process, immobilization structure and bead structure were compared and analyzed by FESEM and EDX. Free cell activity, the immediate cell activity after electrospinning and cell activity for seven days storage after immobilization were evaluated by dying methods of CTC and methylene blue, respectively. The results show that encapsulation efficiency maintained at about 40%, and immobilized yeast cells remain active even after seven days storage, which provides a promising application prospect for electrospinning immobilization.

Ultrahigh packing density next generation microtube array membrane: A novel solution for absorption-based extracorporeal endotoxin removal device

Sepsis is a deadly disease that is widely attributed to endotoxin released by gram-negative bacterial infections often plague emergency care facilities. Conventionally antibiotics and vasopressors are used to treat this disease. Recent treatment protocol shifted to a membrane to remove the offending endotoxin monomer. Despite this shift, membrane-based devices are often extremely costly, hindering accessibility to this life saving medical device. In view of this challenges, we adopted the internally developed polysulfone (PSF) microtube array membrane alternating (MTAM-A) for use in blood sepsis treatment. PSF MTAM-A were with polymyxin B (PMB) molecules immobilized were assembled into an internally developed cartridge housing and subjected to endotoxin removal models with water and blood spiked with 100 EU/ml of endotoxin as the feed solution. Samples were derived at 15, 30, 60, and 120 min and endotoxin levels were determined with limulus amebocyte lysate assay and benchmarked against the commercially available Toraymyxin device. The PSF MTAM-A with 2.3 times the surface area was successfully fabricated and with PMB molecules immobilized, and assembled into a hemoperfusion device. Dynamic endotoxin removal test revealed and overall endotoxin removal capacity of 90% and a superior endotoxin removal efficiency that was significantly higher than that of Toraymyxin (internally conducted and reported). The data suggested that PSF MTAM-A PMB membranes could potentially be applied in future hemoperfusion devices which would be significantly more efficient, compact, and affordable; potentially making such a life-saving medical device widely available to the general public.

Microtube Array Membrane (MTAM)-Based Encapsulated Cell Therapy for Cancer Treatment

The treatment of cancer has evolved significantly in recent years with a strong focus on immunotherapy. Encapsulated Cell Therapy (ECT) for immunotherapy-based anti-cancer treatment is a unique niche within this landscape, where molecules such as signaling factors and antibodies produced from cells are encapsulated within a vehicle, with a host amount of benefits in terms of treatment efficacy and reduced side effects. However, traditional ECTs generally lie in two extremes; either a macro scale vehicle is utilized, resulting in a retrievable system but with limited diffusion and surface area, or a micro scale vehicle is utilized, resulting in a system that has excellent diffusion and surface area but is unretrievable in the event of side effects occurring, which greatly compromises the biosafety of patients. In this study we adapted our patented and novel electrospun Polysulfone (PSF) Microtube Array Membranes (MTAMs) as a 'middle' approach to the above dilemma, which possess excellent diffusion and surface area while being retrievable. Hybridoma cells were encapsulated within the PSF MTAMs, where they produced CEACAM6 antibodies to be used in the suppression of cancer cell line A549, MDA-MB-468 and PC 3 (control). In vitro and in vivo studies revealed excellent cell viability of hybridoma cells with continuous secretion of CEACAM6 antibodies which suppressed the MDA-MB-468 throughout the entire 21 days of experiment. Such outcome suggested that the PSF MTAMs were not only an excellent three-dimensional (3D) cell culture substrate but potentially also an excellent vehicle for the application in ECT systems. Future research needs to include a long term in vivo >6 months study before it can be used in clinical applications.

Top-Down Strategy of Implantable Biosensor Using Adaptable, Porous Hollow Fibrous Membrane

Fabrication of an outer membrane is crucial for an implantable biosensor to enhance the long-term stability and accuracy of sensors. Herein, an adaptable, controllable, porous outer membrane for an implantable biosensor was fabricated using a "top-down" method, allowing maximum retention of enzyme activity and fine control over membrane microstructure. Polysulfone hollow fibrous membranes with different pore sizes and porosities were used as a base membrane. Chitosan (CH) and sodium alginate (SA) were self-assembled on the inner surface of PSfHM to construct a biocompatible and conductive interface between PSfHM and the electrode. In vitro and in vivo experiments were used to evaluate the performance of implantable glucose biosensors with PSfHM and CH/SA modified PSfHM (PSfHM-CH/SA). The glucose biosensor with PSfHM-CH/SA exhibited a more stable output current than bare sensors and a quick response time (<50 s). The glucose biosensor with PSfHM-CH/SA linear sensing range was between 0 and 22 mM ( R² = 0.9905), and relative sensitivity remained at >87% within 7 days and >76% within 15 days. Furthermore, response currents recorded by implanted sensors closely followed the blood glucose trend from the tail vein blood during in vivo experiments.

Electrospun Polylactic Acid (PLLA) Microtube Array Membrane (MTAM)-An Advanced Substrate for Anticancer Drug Screening

The advent of personalized cancer treatment resulted in the shift from the administration of cytotoxic drugs with broad activity spectrum to a targeted tumor-specific therapy. Aligned to this development, the focus of this study revolved around the application of our novel and patented microtube array membrane (MTAM) in the US National Cancer Institute (NCI) developed an HFA (hollow fiber assay) assay; hereinafter known as MTAM/HFA. Electrospun poly-L-lactic acid (PLLA) MTAM was sterilized and loaded with cell lines/patient derived tumor cells (PDTC) and subcutaneously implanted into the backs of BALB/C mice. Anticancer drugs were administered at the respective time points and the respective MTAMs were retrieved and the viability tumor cells within were quantified with the MTT assay. Results revealed that the MTAMs were excellent culture substrate for various cancer cell lines and PDTCs (patient derived tumor cells). Compared to traditional HFA systems that utilize traditional hollow fibers, MTAM/HFA revealed superior drug sensitivity for a wide range of anticancer drug classes. Additionally, the duration for each test was <14 days; all this while capable of producing similar trend outcome to the current gold-standard xenograft models. These benefits were observed in both the in vitro and in vivo stages, making it a highly practical phenotypic-based solution that could potentially be applied in personalized medicine.

A Microtube Array Membrane (MTAM) Encapsulated Live Fermenting Staphylococcus epidermidis as a Skin Probiotic Patch against Cutibacterium acnes

Antibiotics without selectivity for acne treatment may destroy the beneficial microbes in the human microbiome that helps to fight Cutibacterium acnes (C. acnes), a bacterium associated with inflammatory acne vulgaris. Probiotic treatment by direct application of live Staphylococcus epidermidis (S. epidermidis) onto the open acne lesions may run the risk of bloodstream infections. Here, we fabricated the polysulfone microtube array membranes (PSF MTAM) to encapsulate probiotic S.epidermidis. We demonstrate that the application of the encapsulation of S. epidermidis in PSF MTAM enhanced the glycerol fermentation activities of S. epidermidis. To mimic the granulomatous type of acne inflammatory acne vulgaris, the ears of mice were injected intradermally with C. acnes to induce the secretion of macrophage inflammatory protein-2 (MIP-2), a murine counterpart of human interleukin (IL)-8. The C. acnes-injected mouse ears were covered with a PST MTAM encapsulated with or without S.epidermidis in the presence of glycerol. The application of S.epidermidis-encapsulated PST MTAM plus glycerol onto the C. acnes-injected mouse ears considerably reduced the growth of C. acnes and the production of MIP-2. Furthermore, no S. epidermidis leaked from PSF MTAM into mouse skin. The S. epidermidis-encapsulated PST MTAM functions as a probiotic acne patch.

Cytocompatible Fabrication of Yeast Cells/Fabrics Composite Sheet for Bioethanol Production

Entrapment of living cells into a polymer network has significant potential in various fields such as biomass conversion and tissue engineering. A crucial challenge for this strategy is to provide a mild enough condition to preserve cell viability. Here, a facile and cytocompatible method to entrap living yeast cells into a poly(ethylene glycol) (PEG) network grafting from polypropylene nonwoven fabrics via visible-light-induced surface living graft crosslinking polymerization is reported. Due to the mild reaction conditions and excellent biocompatibility of PEG, the immobilized yeast cells could maintain their viability and proliferate well. The obtained composite sheet has excellent long-term stability and shows no significant efficiency loss after 25 cycles of repeated batch bioethanol fermentation. The immobilized yeast cells exhibit 18.0% higher bioethanol fermentation efficiency than free cells. This strategy for immobilization of living cells with high viability has significant potential application.

An Effective Cell Coculture Platform Based on the Electrospun Microtube Array Membrane for Nerve Regeneration

Recently, a novel substrate known as an electrospun polylactic acid (PLLA) microtube array membrane (MTAM) was successfully developed as a cell coculture platform. Structurally, this substrate is made up of one-to-one connected, ultrathin, submicron scale fibers that are arranged in an arrayed formation. Its unique structure confers several key advantages which are beneficial in a cell coculture system. In this study, the interaction between rat fetal neural stem cells (NSC) and astrocytes was examined by comparing the outcome of a typical Transwell-based coculture system and that of an electrospun PLLA MTAM-based coculture system. Compared to tissue culture polystyrene (TCP) and Transwell coculture inserts, a superior cell viability of NSC was observed when cultured in lumens of electrospun PLLA MTAM (with supportive immunostaining images). Reverse transcription polymerase chain reaction revealed a strong interaction between astrocytes and NSC through a higher expression of doublecortin and a lower expression of nestin. These data demonstrate that MTAM is clearly a better coculture platform than the traditional Transwell system.