I. INTRODUCTION

Section:

ChooseTop of pageABSTRACTI. INTRODUCTION <<II. MATERIALS AND METHODSIII. RESULTSIV. DISCUSSIONV. CONCLUSIONSREFERENCESDiabetes mellitus is defined as a group of metabolic disorders characterized by high blood glucose levels (hyperglycemia).1–31. M. Fralick, A. J. Jenkins, K. Khunti, J. C. Mbanya, V. Mohan, and M. I. Schmidt, Nat. Rev. Endocrinol. 18, 199 (2022). https://doi.org/10.1038/s41574-021-00621-y2. C. Lamina and N. C. Ward, Atherosclerosis 349, 63 (2022). https://doi.org/10.1016/j.atherosclerosis.2022.04.0163. G. Targher, K. E. Corey, C. D. Byrne, and M. Roden, Nat. Rev. Gastroenterol. Hepatol. 18, 599 (2021). https://doi.org/10.1038/s41575-021-00448-y Type 1 diabetes, also known as juvenile diabetes, accounts for 10% of all diabetes mellitus cases. It results from a deficiency in insulin, a 51-amino-acid peptide produced by the ß-cells of islets of Langerhans in the pancreas, which regulates blood glucose levels by stimulating liver and muscle cells to take up glucose from the blood.44. N. D. Rios-Arce, D. K. Murugesh, N. R. Hum, A. Sebastian, E. H. Jbeily, B. A. Christiansen, and G. G. Loots, JBMR Plus 6, e10625 (2022). https://doi.org/10.1002/jbm4.10625This deficiency stems from an autoimmune response in affected individuals that leads to the T-cell-mediated destruction of ß-cells and subsequent hypoinsulinemia and hyperglycemia.55. A. M. Mitchell et al., Proc. Natl. Acad. Sci. U.S.A. 118, e2019129118 (2021). https://doi.org/10.1073/pnas.2019129118 Therefore, since patients with type 1 diabetes lack these vital cells, they are unable to generate insulin, and, consequently, glucose utilization is substantially impaired. Diabetes mellitus is a chronic medical condition, meaning that although there is a treatment for it, there is currently no cure.66. A. Helman and D. A. Melton, Cold Spring Harbor Perspect. Biol. 13, a035741 (2021). https://doi.org/10.1101/cshperspect.a035741Currently, the most widespread treatment for type 1 diabetes is exogenous insulin treatment, either by manual injection or by an insulin pump, both of which are unable to provide tight physiological control of the blood glucose level, leading to complications such as diabetic retinopathy, nephropathy, and neuropathy.77. A. L. Mahoney, N. T. Nassif, B. A. O’Brien, and A. M. Simpson, Cells 11, 2145 (2022). https://doi.org/10.3390/cells11142145The allogeneic transplantation of the islets of Langerhans has been studied for nearly 20 years.88. S. Liu et al., Am. J. Hematol. 96, 671 (2021). https://doi.org/10.1002/ajh.26160 Membranes have been extensively implemented in the medical field since the introduction of the first hemodialyzer.99. X. Yao, Y. Liu, Z. Chu, and W. Jin, Chin. J. Chem. Eng. 49, 1 (2022). https://doi.org/10.1016/j.cjche.2022.04.027The enactment of membranes is enormously appealing in systems where biocatalysts in the form of mammalian cells, enzymes, or tissue fragments (a part of tissue) are implemented. In fact, allograft and xenograft implants can be conserved against the attack of the host immune system by applying a membrane with the appropriate molecular cutoff.1010. D. W. Scharp, N. S. Mason, and R. E. Sparks, World J. Surg. 8, 221 (1984). https://doi.org/10.1007/BF01655139 Culturing mammalian cells in the shell side of a hollow fiber membrane module was experimentally indicated by Gullino et al..1111. R. A. Knazek, P. M. Gullino, P. O. Kohler, and R. L. Dedrick, Science 178, 65 (1972). https://doi.org/10.1126/science.178.4056.65Nowadays, the bioartificial pancreas has received dramatic attention. A bioartificial pancreas uses a semipermeable membrane to conserve the transplanted islets from recipient immune responses.12–1412. N. Sakata, Y. Gu, M. Qi, C. Yamamoto, A. Hiura, S. Sumi, M. Sunamura, S. Matsuno, and K. Inoue, Pancreas 32, 249 (2006). https://doi.org/10.1097/01.mpa.0000203959.31877.8c13. M. Qi, Y. Gu, N. Sakata, D. Kim, Y. Shirouzu, C. Yamamoto, A. Hiura, S. Sumi, and K. Inoue, Biomaterials 25, 5885 (2004). https://doi.org/10.1016/j.biomaterials.2004.01.05014. Z. Qi et al., Cell Transplant. 21, 525 (2012). https://doi.org/10.3727/096368911X605448 The membrane acts as an obstruction to restrict the elements of the immune system from touching the implant while supporting nutrients and catabolites to infiltrate the viable implant. Although forming blood clots at the interface between blood and the synthetic material is the main problem in these devices, they are enormously appealing because of their flexibility in design and use. In addition, the overall response time of the prosthesis/host system following a growth in blood glucose concentration is decreased because the implant site can be selected.1515. G. Catapano, G. Iorio, E. Drioli, C. Lombardi, F. Crucitti, G. Doglietto, and M. Bellantone, J. Membr. Sci. 52, 351 (1990). https://doi.org/10.1016/S0376-7388(00)85137-6 Several studies have been performed to optimize the bioartificial pancreas. Polydimethylsiloxane (PDMS) has been blended with polyurethane into tubular membranes, demonstrating high diffusion rates for glucose and oxygen.1616. C. K. Colton and E. S. Avgoustiniatos, J. Biomech. Eng. 113, 152 (1991). https://doi.org/10.1115/1.2891229The protective function of the membrane in a bioartificial pancreas is of primary importance. Based on extensive literature reviews, polyethersulphone (PES) was used as the main polymer for manufacturing the membranes. Superior mechanical and film formation properties, as well as impressive thermal, oxidative, and hydrolytic stability, are the marked features of PES. PES membranes are extensively applied in leading-edge separation technology and biomedical fields including artificial organs and medical devices implemented for blood purification (hemodialysis, hemodiafiltration, plasmapheresis, and plasma collection).17–2017. C. S. Zhao, T. Liu, Z. P. Lu, L. P. Cheng, and J. Huang, Artif. Organs 25, 60 (2001). https://doi.org/10.1046/j.1525-1594.2001.06655-2.x18. R. H. Tullis, D. O. Scamurra, and J. L. Ambrus, J Theor. Med. 4, 157 (2002). https://doi.org/10.1080/102736602100004139519. W. Samtleben, C. Dengler, B. Reinhardt, A. Nothdurft, and H. D. Lemke, Nephrol. Dial. Transplant. 18, 2382 (2003). https://doi.org/10.1093/ndt/gfg41020. C. Werner, H. J. Jacobasch, and G. Reichelt, J. Biomater. Sci. Polym. Ed. 7, 61 (1996). https://doi.org/10.1163/156856295x00832However, when blood comes into contact with PES, platelets are activated, which, in turn, leads to clot formation. Consequently, the PES membrane does not possess acceptable blood compatibility. Therefore, it is imperative to modify the PES membrane surface to improve both hemocompatibility and cytocompatibility. A large number of surveys have addressed the possible use of the modified PES membrane in biomedical fields. In these studies, the membrane surface was coated with either bovine serum albumin (BSA)2121. M. Ulbricht and M. Riedel, Biomaterials 19, 1229 (1998). https://doi.org/10.1016/S0142-9612(98)00029-5 or heparin.22,2322. L. Wang, B. Su, C. Cheng, L. Ma, S. Li, S. Nie, and C. Zhao, J. Mater. Chem. B 3, 1391 (2015). https://doi.org/10.1039/C4TB01865F23. M. Tang, J. Xue, K. Yan, T. Xiang, S. Sun, and C. Zhao, J. Colloid Interface Sci. 386, 428 (2012). https://doi.org/10.1016/j.jcis.2012.07.076In another work, pyrolytic carbon (PyC) was reported as a hemocompatible substance widely used for artificial heart valve coating.2424. S. Forti et al., Diamond Relat. Mater. 20, 762 (2011). https://doi.org/10.1016/j.diamond.2011.03.026 Pyrolytic carbon is a hydrophobic material.2525. A. Idris, N. Mat Zain, and M. Y. Noordin, Desalination 207, 324 (2007). https://doi.org/10.1016/j.desal.2006.08.008 As is known, 55% of blood is plasma, which contains 91% water.2626. A. L. Mescher, Junqueira’s Basic Histology: Text and Atlas (McGraw-Hill, New York, 2013). In addition, pyrolytic carbon has very flat and smooth molecules.2727. B. D. Ratner, A. S. Hoffman, F. J. Schoen, and J. E. Lemons, Biomaterials Science: An Introduction to Materials in Medicine (Elsevier, New York, 2004). In addition to other structural properties, high hydrophobicity and flat structure contribute to the acceptable biocompatibility, especially hemocompatibility, of PyC.Therefore, it has been speculated that PyC can be used instead of BSA or fibronectin (FN) to enhance the biocompatibility of PES membranes by coating the surface of the membranes and inside the pores. Therefore, it was used as an additive in the casting solution. This biomaterial is manmade and not found in nature. The PyC biomaterial was developed at General Atomic in the late 1960s using a fluidized-bed reactor. In the original terminology, this material was considered a low-temperature isotropic carbon (LTI carbon). Since the first clinical implant of a PyC component in the DeBakey-Surgitool mechanical valve in 1968, 95% of the mechanical heart valves implanted worldwide have at least one structural element made of PyC. On an annual basis, this translates into approximately 500 000 components. PyC is widely used as a coating for artificial heart valves.2424. S. Forti et al., Diamond Relat. Mater. 20, 762 (2011). https://doi.org/10.1016/j.diamond.2011.03.026

There have been no studies on the biocompatibility (especially hemocompatibility) of membrane composites in which PyC has been used as an additive. The aim of this work was to compare the biocompatibility of PES/PyC and pure PES membranes. The blood compatibility aspects including peripheral blood mononuclear cells (PBMCs) activation, platelet activation, and platelet adhesion and the cytocompatibility aspects including ß-cell viability, proliferation, and response to hyperglycemia were explored.

II. MATERIALS AND METHODS

Section:

ChooseTop of pageABSTRACTI. INTRODUCTIONII. MATERIALS AND METHODS <<III. RESULTSIV. DISCUSSIONV. CONCLUSIONSREFERENCES

A. Membrane preparation and permeability characterizations

The phase inversion method via the immersion precipitation technique was used for preparing PES–PyC membranes. Solutions contained polyethersulphone (PES Ultrason, nominal granule size of 3 mm, 58 kDa, BASF Company), N-methyl-2-pyrrolidone (NMP, Merchmillipore, Germany), and pyrolytic carbon (PyC, Iran Polymer and Petrochemicals Institute). PES–PyC membranes were made in the following manner: different compositions of the materials mentioned in Table I were stirred by a magnetic stirrer at a speed of 2000 rpm for 48 h. The stirring process continued until homogeneous casting solutions were prepared. For further homogenizing and degassing, the solutions were immersed in an ultrasonic bath for 15 min. After being cooled and degassed at the room temperature, the solutions were poured on a glass using a device called “filmograph” with a gap thickness of 200 μm. Then, in order for coagulation and membrane formation, the casted solutions were immediately immersed in a double-distilled water bath at 25 °C. The formed membranes were left for 30 min in the coagulation bath. Then, the removal of the remained NMP completed.2828. A. Idris, N. M. Zain, and M. Noordin, Desalination 207, 324 (2007). https://doi.org/10.1016/j.desal.2006.08.008 The schematics of the membrane preparation process are summarized in Fig. 1.

TABLE I. Compositions of membrane casting solutions.

Membrane numberMembrane nameCasting solution composition (PES–PyC–NMP wt. %)1PES–PyC (0 wt. %)20–0–802PES–PyC (0.05 wt. %)20–0.05–79.953PES–PyC (0.1 wt. %)20–0.1–79.9The synthesized membranes were also characterized in the permeability point of view. In immune-barrier devices, the membrane is a significant part of the device. For a membrane, in order to have its best performance with specified structural characteristics, desired permeability and good biocompatibility are essential. The membrane allows nutrients and metabolites (mainly glucose and insulin) to pass through the membrane and prevent immune cells and molecules from passing. From this point of view, the membrane permeability plays a specific role in the device performance. Both biocompatibility and permeability are affected by the membrane structure. A detailed study of the structure and permeability of PES–PyC membranes is provided by the authors elsewhere,2929. R. Peighami, M. Mehrnia, F. Yazdian, M. Sheikhpour, and H. Esmaeili, J. Polym. Res. 24, 1 (2017). https://doi.org/10.1007/s10965-016-1180-5 but the results of permeability studies are discussed here.As mentioned in the literature, the membrane molecular cutoff necessary for an immuno-barrier or immunoisolation device to have the best performance is 50 kDa.30,3130. C. K. Colton, Cell Transplant. 4, 415 (1995). https://doi.org/10.1177/09636897950040041331. F. T. Gentile, E. J. Doherty, D. H. Rein, M. S. Shoichet, and S. R. Winn, React. Polym. 25, 207 (1995). https://doi.org/10.1016/0923-1137(94)00097-O Therefore, if the prepared membranes are not able to reject components with a molecular weight of above 50 kDa, they will induce the immune rejection in the patient's body. In order for rejection studies, the insulin rejection and PEG50000 studies were developed for the prepared membranes. The results indicated 91.8%, 87.6%, and 83% of PEG5000 rejection rates for the PES–PyC (0 wt. %), PES–PyC (0.05 wt. %), and PES–PyC (0.1 wt. %) membranes, respectively, and 12%, 10.8%, and 9.3% of insulin rejection for the PES–PyC (0 wt. %), PES–PyC (0.05 wt. %), and PES–PyC (0.1 wt. %) membranes, respectively. Details are given elsewhere.2929. R. Peighami, M. Mehrnia, F. Yazdian, M. Sheikhpour, and H. Esmaeili, J. Polym. Res. 24, 1 (2017). https://doi.org/10.1007/s10965-016-1180-5

B. Hemocompatibility assessment

Peripheral blood as the source of lymphoid cells has been used for the examination of immune responses in humans. A straightforward and rapid method for the isolation and purification of PBMCs is the density gradient centrifugation with Ficoll (Histopaque, H 8889, Sigma, Germany and Hypaque, Lymphoprep TM, OsLo, Norway). This method is based on the difference in the densities of leukocytes and other blood elements.3232. A. Bøyum, Tissue Antigens 4, 269 (1974). https://doi.org/10.1111/j.1399-0039.1974.tb00252.xFicoll sucrose polymer aggregates erythrocytes in the bottom, while low-density PBMCs and platelets form a layer on the top of the gradient. Platelets are eliminated by washing with phosphate-buffered saline (PBS). PBMCs were freshly isolated from a healthy male donor aged around 28 years. Then, 4 ml of PBS was added to 4 ml of peripheral blood. The PBS–blood mixture was taken by a sterile pipette and gently layered onto 4 ml of Ficoll solution, which eliminates the disruption of the layer in a conical-bottom falcon tube. The tube was centrifuged at 2500 rpm at room temperature for 20 min. At the end of the centrifugation, a buffy coat layer of PBMC was achieved. The layer between plasma and Ficoll was carefully removed into a new tube, and 10 ml of PBS was added. The cells were centrifuged at 1500 rpm for 10 min. This washing was repeated one more time to remove thrombocytes and platelets. The pellet was resuspended in RPMI containing 5% fetal bovine serum (FBS).3333. R. Nazarpour, E. Zabihi, E. Alijanpour, Z. Abedian, H. Mehdizadeh, and F. Rahimi, Int. J. Mol. Cell. Med. 1, 88 (2012).

C. PBMC activation

As mentioned previously, a bioartificial pancreas is an immunoisolation device that is in contact with bloodstream on the lumen side. Mononuclear blood cells contain immune cells that play a role in immune reactions and rejections. Therefore, the activation of PBMCs was studied for all the three membranes. The effect of biomaterials on the activation of PBMCs was determined. After cell culturing for three days, PBMCs were seeded onto the membranes at a density of approximately 104 cells/cm2. After various time intervals, 10 μl of the 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide solution (MTT, Sigma, USA) was added to each well and incubated for 4 h at 37 °C. Blue/purple formazan crystals were generated because the mitochondrial dehydrogenases of viable cells adhered selectively to the tetrazolium ring. Next, to dissolve the produced formazan crystals, 50 μl of dimethyl sulfoxide (DMSO) was added. Then, the level of cell metabolism was evaluated by the number of formazan crystals dissolved in DMSO. The dissolvable solution was shaken homogeneously for about 15 min by a shaker. The solution of each sample was extracted into a microtiter, and the optical density of the formazan solution was read on a microplate reader (ELIZA Reader, ELX800TM, USA) at 540 nm.3434. S. Todisco, V. Calabro, and G. Iorio, J. Membr. Sci. 106, 221 (1995). https://doi.org/10.1016/0376-7388(95)00087-S

D. Platelet activation

The PES–PyC (0 wt. %), PES–PyC (0.05 wt. %), and PES–PyC (0.1 wt. %) membranes (2 × 2 cm2 each piece) were immersed in the PBS solution and then 99% alcohol five times and then equilibrated at 37 °C for 1 h. The PBS solution was removed, and then, 500 μl of fresh platelet-rich plasma (PRP, Shariati and Masih Daneshvari Hospital, Tehran, Iran) was added. Cells cultured in wells without membranes were considered the control group. After 8 h, the platelet activation was analyzed by studying the released CD62p via flow cytometry.3535. C. H. Gemmell, J. Biomater. Sci. Polym. Ed. 12, 933 (2001). https://doi.org/10.1163/156856201753113114

E. Platelet adhesion (or morphology adhered cells)

Membranes in the platelet activation test were used to study the adhered platelets. A scanning electron microscope (JOEL SEM 6510LV) was used to observe the platelet adhesion. The number of the adhered platelets on the membranes was counted from the SEM pictures of each membrane using an image analyzing software.3636. Z. Liu, X. Deng, M. Wang, J. Chen, A. Zhang, Z. Gu, and C. Zhao, J. Biomater. Sci. Polym. Ed. 20, 377 (2009). https://doi.org/10.1163/156856209X412227

It is worth noting that the mentioned tests are preliminary tests for evaluation hemocompatibility that could help investigate the behavior of the biomaterial. For more investigation, further tests should be replenished such as blood routine examination, hemolysis test, and blood clotting time test.

F. Cytocompatibility

The islets were isolated from an anesthetized mouse obtained from the Anatomy Laboratory of Tarbiat Modares University, Tehran, Iran. The typical procedure was as follows: the pancreas was isolated and placed in a falcon tube containing 5 ml of Roswell Park Memorial Institute medium (RPMI, Gibco USA, containing 2 mg/dl collagenase enzyme) and incubated for 15 min at 37 °C. Then, 10 ml of cold RPMI (5 °C, containing 10% FBS) was added to the falcon tube. After shaking the falcon tube for 2 min, the content was filtered by a 100-μm filter. The filtrate was centrifuged at 1000 rpm for 1 min to eliminate collagenase. This step was repeated three times, and after each centrifugation, the medium was changed. Next, the islets were immersed in 20 ml of Ficoll Histopaque, followed by slowly adding 10 ml of RPMI (containing 5% FBS). The tube was centrifuged at 2000 rpm and 4 °C for 10 min. After centrifugation, the layer between RPMI and Ficoll was carefully removed into a new tube, and 5 ml of RPMI was added. The islets were centrifuged at 1000 rpm and 4 °C for 1 min. Finally, the islets were cultured in the RPMI medium.3434. S. Todisco, V. Calabro, and G. Iorio, J. Membr. Sci. 106, 221 (1995). https://doi.org/10.1016/0376-7388(95)00087-S

G. Cell culture

Before cell culture, the membranes were cut into 0.3 × 1 cm2 pieces, which were situated in 12 wells of a 96-well tissue culture plate and sterilized by 70% ethanol and PBS. Then, the membranes were incubated overnight with RPMI supplemented with 10% FBS, penicillin, streptomycin, and amphotericin B to prevent from the yeast growth, ensure the sterilization, and enhance the cell attachment after seeding. An initial density of 4 × 104 cells per well was suspended in 400 μl of RPMI supplemented with 10% FBS and seeded onto the membranes. Three groups were chosen for three membranes with different compositions. A positive control was chosen from the cells cultured in wells without any membranes.3434. S. Todisco, V. Calabro, and G. Iorio, J. Membr. Sci. 106, 221 (1995). https://doi.org/10.1016/0376-7388(95)00087-S

H. ß-cell viability and proliferation test

ß-cells were cultured on the membranes for 72 h to evaluate the membranes' cytotoxicity. The increased rate of ß-cells was evaluated by the MTT assay. The procedure of the MTT assay is described in .3737. E. Pedraza, “Engineering an optimal bioartificial pancreas for islet transplantation using bioactive scaffolds,” Ph.D. dissertation (University of Miami, 2011).

I. ß-cell functionality test

In this trial, the islet response to glycemic stimuli was investigated. The typical procedure was as follows: the PES, PES–PyC (0.05 wt. %), and PES–PyC (0.1 wt. %) membranes (2 × 2 cm2 each piece) were placed in wells containing an appropriate number of islets and a reaction medium. A well deprived of membranes that contained the cultured cells was considered the positive control. Then, a glucose stimulus (16 μM) was introduced. The solution was incubated for 15 min at 37 °C. The samples were collected, and insulin release was halted in a thermostatic bath at 0 °C. The solution was filtered by an 8-μm filter. At the end of filtration, the solutions were accumulated into Eppendorf tubes at −20 °C. Finally, the insulin assay was carried out.

IV. DISCUSSION

Section:

ChooseTop of pageABSTRACTI. INTRODUCTIONII. MATERIALS AND METHODSIII. RESULTSIV. DISCUSSION <<V. CONCLUSIONSREFERENCESSeveral studies in recent years reported different methods for improving the biocompatibility and separation performance of polyethersulfone in various organs such as graphene oxide-doping for bioartificial kidney and pinning conditions on the properties of the hollow fiber membrane for hemodialysis application. Also, the BSA-modified polyethersulfone membrane and modification of the polyethersulfone hemodialysis membrane by blending citric acid grafted polyurethane and its anticoagulant are the other studies that have been conducted in this area.36,39–4136. Z. Liu, X. Deng, M. Wang, J. Chen, A. Zhang, Z. Gu, and C. Zhao, J. Biomater. Sci. Polym. Ed. 20, 377 (2009). https://doi.org/10.1163/156856209X41222739. A. Modi, S. K. Verma, and J. Bellare, J. Colloid Interface Sci. 514, 750 (2018). https://doi.org/10.1016/j.jcis.2017.12.04440. S. Mansur, M. H. D. Othman, A. F. Ismail, S. H. Sheikh Abdul Kadir, F. Kamal, P. S. Goh, H. Hasbullah, B. C. Ng, and M. S. Abdullah, J. Appl. Polym. Sci. 133, 43633 (2016). https://doi.org/10.1002/app.4363341. L. Li, C. Cheng, T. Xiang, M. Tang, W. Zhao, S. Sun, and C. Zhao, J. Membr. Sci. 405–406, 261 (2012). https://doi.org/10.1016/j.memsci.2012.03.015 In addition, investigations show that other biomaterials as sings carboxylic multiwall carbon nanotubes, low molecular weight polyvinylpyrrolidone based nanocomposites and polyethersulfone ultrafiltration membranes with mussel-inspired polydopamine coatings could upgrade the biocompatibility properties.42,4342. M. Irfan et al., J. Biomed. Mater. Res. Part A 107, 513 (2019). https://doi.org/10.1002/jbm.a.3656643. C. Cheng, S. Li, W. Zhao, Q. Wei, S. Nie, S. Sun, and C. Zhao, J. Membr. Sci. 417–418, 228 (2012). https://doi.org/10.1016/j.memsci.2012.06.045

Current work is the first study that evaluates the biocompatibility of the polyethersulfone–pyrolytic carbon composite membrane in an artificial pancreas. According to the achieved results of PBMC viability and proliferation, it can be concluded that the cells cultured on PES–PyC (0.1) had the maximum viability and proliferation relative to the other membranes. In general, increasing PyC in the casting solution of membranes induces a better adaptation with PBMCs, which stands as one of the important parameters in blood compatibility and immune response of blood to membranes.

According to Fig. 3, PES–PyC (0) induces the maximum platelet activation, while PES–PyC (0.1) causes the minimum platelet activation. It can be clearly noticed that platelets cultured on the PES–PyC (0.1) membrane behave close to the control group. Therefore, it can be concluded that the addition of PyC to the casting solution can positively affect the hemocompatibility of the membrane. The reduction in activated platelets is a major factor in biocompatibility studies because one of the main complications existing in the blood contacting devices such as the bioartificial pancreas is blood clotting, and the central and the most important factor that causes blood clotting is platelet activation. The structural characteristics of PES–PyC (0.1) induce the minimum platelet activation. A high hydrophobicity compared to the other membranes, the low surface roughness (both because of the presence of more PyC particles on the surface), and structural characteristics can cause platelets not to recognize PES–PyC (0.1) as an extraneous object.Figure 4 depicts a plethora of sticking platelets, and the aggregates were inspected on the surface of the pure PES membrane. Platelet adhesion was prevented on the PES–PyC (0.05) and PES–PyC (0.1) membranes. With increasing PyC concentration in the casting solution, the quantity of adhered platelets decreased. Moreover, the platelets on the PES–PyC (0.1) membrane adhered separately and in a less aggregated form compared to the platelets on the pure PES membrane. It shows that the platelets were less activated on the PES–PyC (0.1) membrane because when platelets become activated, the activated platelet adheres to the surface of the foreign body (i.e., membranes in the current work), and then, the degranulation phenomenon occurs. Degranulation causes other platelets to aggregate on the surface of the foreign body. The platelet aggregation is the first step of blood clotting. Therefore, it should be noted that the PES–PyC (0.1) membrane induces a less platelet-inducing effect.According to Fig. 5, it can be clearly viewed that the quantity of the platelets that adhered to the PES–PyC (0.1) membrane significantly decreased. These results prove that using PyC as an additive in the casting solution plays a remarkable role in reducing adhesion, aggregation, and activation of the platelets.

The results of ß-cells viability and functionality clearly indicate that after 24 h, the modified membranes had a slightly better cell viability than the pure PES membrane at all the time intervals.

As illustrated in Fig. 5, after 72 h, the modified membranes showed acceptable proliferation rates; however, the proliferation rates of all the cultured groups were low. It could be stated that ß-cells cultured on the PES–PyC (0.1) membrane have a slightly higher proliferation rate. In other words, increasing PyC in the casting solution enhanced ß-cell viability and proliferation, particularly in the PES–PyC (0.1) membrane. However, it was shown that the proliferation rates of all the four groups were very slow.Regarding Table II, it is evident that insulin secretion increases as time passes, but after 4 min, the insulin secretion rate decreased slowly. It is interesting to note that the insulin secretions of the cells seeded onto all the membranes and the control group were not considerably different. It can be concluded that the pure PES membrane and modified membranes induced no positive or negative impacts on ß-cell functionality. In addition, the kinetics of insulin secretion was close to the relations reported in the literature.4444. G. Catapano, G. Iorio, E. Drioli, C. P. Lombardi, F. Crucitti, G. B. Doglietto, and M. Bellantone, J. Membr. Sci. 52, 351 (1990). https://doi.org/10.1016/S0376-7388(00)85137-6

V. CONCLUSIONS

Section:

ChooseTop of pageABSTRACTI. INTRODUCTIONII. MATERIALS AND METHODSIII. RESULTSIV. DISCUSSIONV. CONCLUSIONS <<REFERENCES

In conclusion, our study showed that PyC could be applied to modify PES membranes. It was accomplished by mixing different concentrations of PyC with PES in the casting solution. The cytocompatibility and hemocompatibility of the membranes were investigated. In the hemocompatibility test, PBMC viability and proliferation, platelet activation, and platelet adhesion were evaluated. Notably, PES–PyC (0.1 wt. %) displayed the highest cell viability and proliferation. In addition, the number of attached platelets and platelet activation decreased. In the cytocompatibility test, ß-cell viability, proliferation, and response to hyperglycemia were evaluated. The results indicated that ß-cells cultured on the PES–PyC (0.1 wt. %) membrane displayed a higher viability and proliferation and better response to hyperglycemia than those on the pure PES and PES–PyC (0.05 wt. %) membranes. Therefore, the PES–PyC (0.1 wt. %) membrane, which has both superior blood compatibility and cytocompatibility, is an auspicious biomaterial that can be incorporated in blood contacting devices and other artificial organs. It is expected that higher concentrations of PyC have a positive biocompatibility effect and also influence mechanical characteristics of the membrane. As a further investigation, membranes with higher concentrations of PyC (more than 0.1%) could be synthesized to investigate its influence on membrane's mechanical characteristics.