Modeling the impact of fluid flow on resveratrol release from electrospun fibers.

Using electrospun fibers to deliver therapeutic agents has gained significant attention in various applications including cancer treatment and tissue regeneration. However, the effect of fluid flow and uptake by cells on the concentration profile is not well understood. In this study, we evaluated the release of lipophilic resveratrol from poly(ε-caprolactone) (PCL)-gelatin (GT) electrospun fibers experimentally and by using computational fluid dynamics (CFD). Resveratrol containing PCL-GT electrospun fibers were formed and used in a custom-built tubular bioreactor, to assess flow effect on concentration profile over 5 days. CFD model was developed to simulate release in both static cultures and under fluid flow conditions. Resveratrol stability in the culture medium and uptake by human umbilical vein endothelial cells and K562 cells over 3 days were used in the model. The concentration profile as a function of time was simulated and validated by experiments. The effects of inlet velocity, cellular uptake rate, bioreactor's length, and surrounding tissue porosity were assessed. The release profile was mainly affected by cellular uptake and the presence of porous media. The model suggests that the perfusion velocity might not have a significant effect relative to the cellular uptake rate and porosity of the surrounding tissue.

Recent advances in the combination delivery of drug for leukemia and other cancers.

Introduction: Combination therapy has been explored for its potential to reduce or eliminate multidrug resistance in treating different types of cancer including leukemia. Nutraceutical, small molecular drugs, and small interfering ribonucleic acid (siRNA) are some of the effective drugs. In order to avoid off-site targeting, reduce the dosage required, and increase the half-life of the drug in the circulation system, drug delivery vehicles, such as nanoparticles and microfibers have been explored.Areas covered: This review summarizes various therapies utilized in treating leukemia based on their effectiveness in inducing protein inhibition and/or apoptosis. In particular, treatment effectiveness using combination therapy using various devices is addressed. Recently explored drug delivery methods are reviewed, providing examples and their applications in cancer treatment. The drug listing, delivery systems classifications, along with the general modeling approach in this review, provide, to a full extent, a basis for cancer drug delivery future studies.Expert opinion: The reviewer's opinion tackles the potential of using a multi-delivery system to deliver multiple drugs, providing better control upon drug release and targeting. Both local and systemic delivery are considered and explored for their potential targets. Researchers are advised to pre-consider all aspects associated with their desired delivery method.

Targeted cancer treatment using a combination of siRNA-liposomes and resveratrol-electrospun fibers in co-cultures.

In this study, we evaluated a novel combination of drug delivery devices composed of holo-transferrin conjugated liposomes for siRNA (36 nM) delivery, and electrospun polycaprolactone (PCL)-gelatin (GT) microfibers for resveratrol (40 µM) release. Single- and co-cultures of cancerous K562 cells and human umbilical vein endothelial cells (HUVECs) were used to test the efficacy and targeting over eight days. BCR-ABL siRNA-encapsulated (36 nM) holo-transferrin-conjugated PEG-liposomes were characterized using dynamic light scattering, and transmission electron microscopy. RT-qPCR was performed to assess the silencing BCR-ABL gene. Two treatment protocols were explored: i) simultaneous administration ii) delayed liposomes addition by three days based on resveratrol release profile. Formed liposomes were 123 (±6.65) nm in diameter, holo-transferrin conjugation efficiency was 85.9 (±7.30)%, and siRNA loading efficiency was 92.3 (±2.57)%. Sphingosine-1-phosphate (S1P) content was analyzed by ELISA. Targeted siRNA release in combination with resveratrol release was more potent and has long-term effects compared to bolus doses. Delayed addition of liposomes increased non-viability of K562 cells to 92.7 (±2.00)% and 94.32 (±1.70)%, in the absence and presence of HUVECs, respectively. HUVECs non-viability level was significantly lower. Using two different delivery devices approach has a broader impact on cancer treatment.

Formation of Stem Cell Aggregates and Their Differentiation on Surface-Patterned Hydrogels Based on Poly(2-hydroxyethyl Methacrylate).

Micropillar patterns were fabricated and used to study cell adhesion, morphology, and function. Micropillars were produced in poly(2-hydroxyethyl methacrylate (HEMA)/N,N-(dimethylaminoethyl)methacrylate (DMAEMA)/tetraethylene glycol dimethacrylate (TEGDMA)) hydrogels using soft lithography, had dimensions of 1 µm diameter, and were either 2.05 or 4.91 µm tall. The patterned hydrogel substrates increased adhesion and induced the formation of cellular aggregates. Digital micrographs were used to quantify aggregate size and number. Differentiation of hMSCs toward adipocytes and chondrocytes was performed using the respective complete culture and differentiation medium for 2 weeks. Cells were stained for Oil red O, Alcian blue, and Type II collagen. Hydrogel substrates supported the differentiation of hMSCs to adipocytes and chondrocytes. The taller micropillar patterns supported the attachment and growth of larger aggregates and were more amenable to aid chondrogenic differentiation.

Type of endothelial cells affects HepaRG cell acetaminophen metabolism in both 2D and 3D porous scaffold cultures.

Recent advances in developing in vitro tissue models show that function of hepatocytes is altered in when cultured in 3D configuration and co-culturing with various non-parenchymal cells. However, tissue source for such non-parenchymal cells on viability and metabolic products of hepatocytes have not been explored. In this study, we evaluated the effect of 2D and 3D cultures either with HepaRG cells alone or in combination with liver sinusoidal endothelial cells (LSECs) and human umbilical vein ECs (HUVECs). For 3D cultures, we used chitosan-gelatin porous structures formed by freeze-drying. We cultured cells for 8 days before challenging with 1 mm acetaminophen (APAP) and assessed APAP, APAP-sulfate and APAP-glucuronide for 24 hours at 6-hour time intervals using high-performance liquid chromatography. We used multiple methods (phase contrast, confocal and scanning electron microscopy and histology via hematoxylin and eosin staining) to ensure cell distribution. We also measured total protein content and albumin secretion and viability. HUVEC 3D co-cultures showed the lowest HepaRG cell viability, while both 2D and 3D LSEC co-cultures had highest HepaRG cell viability. In addition, 3D cultures had significantly higher EC viability relative to 2D cultures. Further, HUVEC co-cultures showed reduced total protein content and albumin expression as early as day 4. However, urea production on a total protein content basis did not change. In addition, LSEC 3D co-cultures had the highest APAP conversion with reduced APAP-sulfate and APAP-glucuronide formation. CYP3A4 was higher in co-culture with HUVEC for 2D and 3D cultures. In conclusion, HepaRG cells with EC co-cultures demonstrated sensitivity to the EC line used.

Immunomodulatory response of layered small intestinal submucosa in a rat bladder regeneration model.

Based on the hypothesis that bioscaffold permeability is a major factor in determining the outcome of histologically complete and functional bladder regeneration, we evaluated regeneration processes of four-layer porcine small intestinal submucosa (SIS) construct; and compared results between rat bladders augmented with single-layer SIS bioscaffolds. Sprague-Dawley female rats were subjected to hemi-cystectomy followed by anastomosis of a patch of either single- or four-layer porcine SIS. Permeability was analyzed in situ using magnetic resonance imaging (MRI) at post-operative days 7 and 14. Bladder sections excised at days 7, 14, 28, and 56 post-operation Samples were assessed by H&E and Masson's trichrome stains. Urothelial differentiation was analyzed using cytokeratin AE1/AE3, and uroplakin III (UPIII). In addition, quantitative and qualitative evaluations of neutrophils, mast cells, eosinophils, and macrophages were performed using anti-myeloperoxidase, Alcian blue, Giemsa stain, and anti-CD68 staining methods, respectively. Four-layer SIS was consistently impermeable as evidenced by the absence of intravesical administered gadolinium with diethylenetriaminepentacetate (Gd-DTPA) contrast signal in peripheral regions of augmented bladders compared with single-layer SIS bioscaffold. Elevated and sustained eosinophil and neutrophil infiltrations were prominent in four-layered SIS-augmented bladders compared with single-layer SIS with comparable impermeability. Delayed but consistent urothelial regeneration and differentiation were observed in four-layer SIS-augmented bladders; and urothelial differentiation was observed at day 56 post-augmentation. In conclusion, four-layer SIS enacts an elevated inflammatory response along with extended urothelial regeneration. Four-layer SIS may activate a different but yet to be identified mechanism for inflammatory responses. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1960-1969, 2019.

Investigation of the Roles of Plasma Species Generated by Surface Dielectric Barrier Discharge.

As an emerging sterilization technology, cold atmospheric plasma offers a dry, non-thermal, rapid process that is minimally damaging to a majority of substrates. However, the mechanisms by which plasma interacts with living cells are poorly understood and the plasma generation apparatuses are complex and resource-intensive. In this study, the roles of reactive oxygen species (ROS), nitric oxide (NO), and charged particles (ions) produced by surface dielectric barrier discharge (SDBD) plasma on prokaryotic (Listeria monocytogenes (Gram-positive)) and eukaryotic (human umbilical vein endothelial cells (HUVEC)) cellular function were evaluated. HUVEC and bacterial oxidative stress responses, the accumulation of nitrite in aqueous media, air ion density, and bacterial inactivation at various distances from SDBD actuators were measured. SDBD actuator designs were also varied in terms of electrode number and length to evaluate the cellular effects of plasma volume and power distribution. NO and ions were found to contribute minimally to the observed cellular effects, whereas ROS were found to cause rapid bacterial inactivation, induce eukaryotic and prokaryotic oxidative stress, and result in rapid oxidation of bovine muscle tissue. The results of this study underscore the dominance of ROS as the major plasma generated species responsible for cellular effects, with ions and RNS having a secondary, complimentary role.

Influence of controlled release of resveratrol from electrospun fibers in combination with siRNA on leukemia cells.

In this study, we evaluated the possibility of i) local release of resveratrol from poly(ε-caprolactone) (PCL) and gelatin (GT) electrospun fibers and ii) combining (i) with siRNA designed to downregulate BCR-ABL pathway on K562 cancer cells. Initially, K562 cell culture experiments were performed using various bolus doses of resveratrol in combination with siRNA for 3 days using a factorial design of experiments approach. Resveratrol content was analyzed using HPLC and cell viability was assessed using Annexin V (Non-viable), and Propidium Iodide (PI) (Necrotic) based flow cytometry. Coaxial electrospun fibers with resveratrol were made using 1:1 PCL-GT blends in different configurations: single fibers and coaxial fibers with same polymer blends, or with PCL inner core. Loading efficiency and release profile over five days were analyzed. Based on release profile, K562 cell viability with fibers was analyzed over eight days. Dose dependent cell death was observed with bolus resveratrol and siRNA in the culture. However, resveratrol content depleted significantly when added directly to solution. The combination therapy was additive in solution. SEM analysis showed no phase separation of components and resveratrol loading efficiency varied from 77% to 88% in different configurations; 95% of resveratrol was released by day five. Permeability of resveratrol showed no significant dependency on fiber configuration. After 8 days, non-viable cell percentages with controlled release were similar to that at three-day bolus dose of resveratrol. However, siRNA interacted with the fibers, resulting in reduced effect on cells. Loading resveratrol into electrospun fibers provides a localized delivery at therapeutic level, and increased resveratrol's apoptotic effect. Using single fibers is sufficient for controlled release.

Reduced urothelial regeneration in rat bladders augmented with permeable porcine small intestinal submucosa assessed by magnetic resonance imaging.

Augmentation enterocystoplasty remains the gold standard surgical bladder reconstruction procedure to increase the capacity and compliance of dysfunctional bladders. Since the use of the patient's intestine has severe risks of complications, alternative biodegradable matrices have been explored. Porcine small intestinal submucosa (SIS) has gained immense interests in bladder reconstruction due to its favorable properties. However, trials have shown inconsistent regeneration with SIS, attributed to the heterogeneity in microstructures and mechanical properties. We hypothesize that uneven SIS permeability to urine is a factor responsible for the inconsistency. We measured permeability to urine in situ using a contrast enhanced-magnetic resonance imaging (MRI), and evaluated urothelium regeneration using immunohistochemical staining of urothelial cell markers in SIS-augmented rat bladders. Results showed significant differences in permeability among SIS-augmented rat bladders. Commercial SIS scaffolds were then categorized into nonleaky and leaky groups based on MRI results. Hematoxylin and eosin staining showed higher numbers of inflammatory cells in leaky SIS on day 14 relative to nonleaky SIS. In addition, trichrome staining showed major changes in the distribution of collagen on day 28 between SIS-augmented bladder groups. Furthermore, expressions of urothelium-associated markers (cytokeratins AE1/AE3, claudin 4, and uroplakin III) were completed in bladders augmented with nonleaky SIS, whereas limited urothelial differentiation was noticed in leaky SIS-augmented bladders at post-augmentative day 14. These results show that scaffold permeability to urine may be responsible for variations in regenerative capacity of porcine SIS. Applications of MRI technique will be helpful to understand a relationship between biomaterial property and regenerative capacity. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1778-1787, 2018.

Bioprinted chitosan-gelatin thermosensitive hydrogels using an inexpensive 3D printer.

The primary bottleneck in bioprinting cell-laden structures with carefully controlled spatial relation is a lack of biocompatible inks and printing conditions. In this regard, we explored using thermogelling chitosan-gelatin (CG) hydrogel as a novel bioprinting ink; CG hydrogels are unique in that it undergoes a spontaneous phase change at physiological temperature, and does not need post-processing. In addition, we used a low cost (<$800) compact 3D printer, and modified with a new extruder to print using disposable syringes and hypodermic needles. We investigated (i) the effect of concentration of CG on gelation characteristics, (ii) solution preparation steps (centrifugation, mixing, and degassing) on printability and fiber formation, (iii) the print bed temperature profiles via IR imaging and grid-based assessment using thermocouples, (iv) the effect of feed rate (10-480 cm min-1), flow rate (15-60 µl min-1) and needle height (70-280 µm) on fiber size and characteristics, and (v) the distribution of neuroblastoma cells in printed fibers, and the viability after five days in culture. We used agarose gel to create uniform print surfaces to maintain a constant gap with the needle tip. These results showed that degassing the solution, and precooling the solution was necessary for obtaining continuous fibers. Fiber size decreased from 760, to 243 µm as the feed rate increased from 10 to 100 cm min-1. Bed temperature played the greatest role in fiber size, followed by feed rate. Increased needle height initially decreased fiber size but then increased showing an optimum. Cells were well distributed within the fibers and exhibited excellent viability and no contamination after 5 d. Overall we printed 3D, sterile, cell-laden structures with an inexpensive bioprinter and a novel ink, without post-processing. The bioprinter described here and the novel CG hydrogels have significant potential as an ink for bioprinitng various cell-laden structures.

Modeling the permeability of multiaxial electrospun poly(ε-caprolactone)-gelatin hybrid fibers for controlled doxycycline release.

Recent advances in electrospinning allow the formation of multiple layers of micro and nanosize fibers to regulate drug/therapeutic agent release. Although there has been significant progress in fiber formation techniques and drug loading, fundamental models providing insights into controlling individual permeabilities is lacking. In this regard, we first explored forming coaxial hybrid fibers from hydrophobic poly(ε-caprolactone) (PCL) and hydrophilic gelatin (GT) in three different configurations, and the release of hydrophilic doxycycline (Dox) at 37°C over five days. Triaxial fibers were also formed with a GT layer between PCL/GT layers. Fibers were analyzed for fiber thickness, matrix porosity and thickness, surface morphologies, internal structures, stability in hydrated condition, viability and attachment of human adipocyte stem cells (hASC). Formed fibers were 10-30µm in diameter. hASC were viable, and showed attachment. Various release profiles were obtained from these fibers based on the combination of the core and shell polymers over five days. Using fiber characteristics and release profiles from each configuration, we obtained the overall permeability using Fick's first law and then individual layer permeability using resistance in series model. Calculated overall permeability showed dependency on fiber thickness and partition coefficient of the drug in the region where it was loaded. Our modeling approach helps in optimizing the electrospinning process, drug loading, and polymer solution configuration in regulating controlled release of a drug.

Recent advances in multiaxial electrospinning for drug delivery.

Electrospun fibers have seen an insurgence in biomedical applications due to their unique characteristics. Coaxial and triaxial electrospinning techniques have added new impetus via fabrication of multilayered nano and micro-size fibers. These techniques offer the possibility of forming fibers with features such as blending, reinforced core, porous and hollow structure. The unique fabrication process can be used to tailor the mechanical properties, biological properties and release of various factors, which can potentially be useful in various controlled drug delivery applications. Harvesting these advantages, various polymers and their combinations have been explored in a number of drug delivery and tissue regeneration applications. New advances have shown the requirement of drug-polymer compatibility in addition to drug-solvent compatibility. We summarize recent findings using both hydrophilic and hydrophobic (or lipophilic) drugs in hydrophobic or hydrophilic polymers on release behavior. We also describe the fundamental forces involved during the electrospinning process providing insight to the factors to be considered to form fibers. Also, various modeling efforts on the drug release profiles are summarized. In addition new developments in the immune response to the electrospun fibers, and advances in scale-up issues needed for industrial size manufacturing.

In vitro characterization of acelluar porcine adipose tissue matrix for use as a tissue regenerative scaffold.

This study evaluated a novel approach to decellularizing porcine adipose tissue while preserving its 3-D architecture. An ethanol-water mixture was used as a solvent to remove lipids and the number of freeze-thaw cycles (1-7), ethanol concentration, and tissue thickness were tested. Trypsin incubation time (1-3 h) and xylene immersion time were investigated separately. Processed sample microarchitecture was analyzed via scanning electron microscope, cellular content was analyzed via hematoxylin and eosin (H&E) staining, and DNA content was analyzed using gel electrophoresis. Tensile testing and five-stage incremental stress-relaxation testing was performed in phosphate-buffered saline at 37°C. Human neuroblasts were seeded and evaluated for infiltration and attachment over 8 days. Four cycles of freeze-thaw in 50% ethanol-water mixture removed one-third of the lipids. Microarchitecture showed the presence of pores, capillary channels, and lack of sidedness; H&E micrographs confirmed unaltered morphology and absence of cells. Incubation for 1.5 h in trypsin removed 99.5% DNA from delipidized samples. An average of 40% rehydration swelling, an elastic modulus of 324(±141) kPa, and an ultimate tensile strength of 87.4(±23.1) kPa were observed. The matrix exhibited strain hardening behavior similar to small intestinal submucosa. Cells successfully infiltrated and spread in the decellularized scaffold. Removal of lipids significantly reduced incubation in trypsin EDTA. In summary, the acellular matrix shows significant potential as a new template for tissue regeneration. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 3127-3136, 2016.

Improving the stability of chitosan-gelatin-based hydrogels for cell delivery using transglutaminase and controlled release of doxycycline.

Although local cell delivery is an option to repair tissues, particularly using chitosan-based hydrogels, significant attrition of injected cells prior to engraftment has been a problem. To address this problem, we explored the possibility of stabilizing the chitosan-gelatin (CG) injectable hydrogels using (1) controlled release of doxycycline (DOX) to prevent premature degradation due to increased gelatinase activity (MMP-2 and MMP-9), and (2) transglutaminase (TG) to in situ cross-link gelatin to improve the mechanical stability. We prepared DOX-loaded PLGA nanoparticles, loaded into the CG hydrogels, measured DOX release for 5 days, and modeled using a single-compartmental assumption. Next, we assessed the influence of TG and DOX on hydrogel compression properties by incubating hydrogels for 7 days in PBS. We evaluated the effect of these changes on retention of fibroblasts and alterations in MMP-2/MMP-9 activity by seeding 500,000 fibroblasts for 5 days. These results showed that 90 % of DOX released from cross-linked CG hydrogels after 4 days, unlike CG hydrogels where 90 % of DOX was released within the first day. Addition of TG enhanced the CG hydrogel stability significantly. More than 60 % of seeded fibroblasts were recovered from the CG-TG hydrogels at day 5, unlike 40 % recovered from CG-hydrogels. Inhibition of MMP-2/MMP-9 were observed. In summary, controlled release of DOX from CG hydrogels cross-linked with TG shows a significant potential as a carrier for cell delivery.

Anisotropic temperature sensitive chitosan-based injectable hydrogels mimicking cartilage matrix.

In this study, chitosan-based hydrogels were formulated with material similarities to three of the four zones of articular cartilage. Gelatin, hyaluronic acid (HA), and ß-tricalcium phosphate for the superficial, radial, and calcified zones, were blended in different amounts and tested for formation of uniform solution, gelability, and rheological characteristics. Confined compression in two configurations (series and parallel to anisotropy), and cyclical tests were performed at the physiological conditions. In vivo gelation and systemic effects were evaluated in male BALB/c mice subcutaneous model. At day 5, hydrogels were harvested along with the adjoining skin and analyzed by histology. Formulations that produced solutions after pH adjustments were selected for each zone. Anisotropic hydrogels were formed by mixing solutions from each zone, which showed uniform gradation. Addition of HA improved structural integrity relative to other formulations. When hydrogels were in series, combined hydrogel modulus was the average of all zones while that in parallel orientation was half of that series orientation. Cyclical tests demonstrated repeatable strength and durability. All formulations were injectable into the subcutaneous region. H/E stained tissues showed minimal invasion of inflammatory cells in radial and calcified zones. Structural integrity of the hydrogel is suggested to be the resultant of the presence of HA.

Multiple approaches to predicting oxygen and glucose consumptions by HepG2 cells on porous scaffolds in an axial-flow bioreactor.

In this study, the distribution of oxygen and glucose was evaluated along with consumption by hepatocytes using three different approaches. The methods include (i) Computational Fluid Dynamics (CFD) simulation, (ii) residence time distribution (RTD) analysis using a step-input coupled with segregation model or dispersion model, and (iii) experimentally determined consumption by HepG2 cells in an open-loop. Chitosan-gelatin (CG) scaffolds prepared by freeze-drying and polycaprolactone (PCL) scaffolds prepared by salt leaching technique were utilized for RTD analyses. The scaffold characteristics were used in CFD simulations i.e. Brinkman's equation for flow through porous medium, structural mechanics for fluid induced scaffold deformation, and advection-diffusion equation coupled with Michaelis-Menten rate equations for nutrient consumption. With the assumption that each hepatocyte behaves like a micro-batch reactor within the scaffold, segregation model was combined with RTD to determine exit concentration. A flow rate of 1 mL/min was used in the bioreactor seeded with 0.6 × 10(6) HepG2 cells/cm(3) on CG scaffolds and oxygen consumption was measured using two flow-through electrodes located at the inlet and outlet. Glucose in the spent growth medium was also analyzed. RTD results showed distribution of nutrients to depend on the surface characteristics of scaffolds. Comparisons of outlet oxygen concentrations between the simulation results, and experimental results showed good agreement with the dispersion model. Outlet oxygen concentrations from segregation model predictions were lower. Doubling the cell density showed a need for increasing the flow rate in CFD simulations. This integrated approach provide a useful strategy in designing bioreactors and monitoring tissue regeneration.

Modeling pressure drop using generalized scaffold characteristics in an axial-flow bioreactor for soft tissue regeneration.

The goal of this study was to better understand how analytical permeability models based on scaffold architecture can facilitate a non-invasive technique to real time monitoring of pressure drop in bioreactors. In particular, we evaluated the permeability equations for electrospun and freeze dried scaffolds via pressure drop comparison in an axial-flow bioreactor using computational fluid dynamic (CFD) and experimentation. The polycaprolactone-cellulose acetate fibers obtained by co-axial electrospinning technique and Chitosan-Gelatin scaffolds prepared using freeze-drying techniques were utilized. Initially, the structural properties (fiber size, pore size and porosity) and mechanical properties (elastic modulus and Poisson's ratio) of scaffolds in phosphate buffered saline at 37 °C were evaluated. The CFD simulations were performed by coupling fluid flow, described by Brinkman equation, with structural mechanics using a moving mesh. The experimentally obtained pressure drop values for both 1 mm thick and 2 mm thick scaffolds agreed with simulation results. To evaluate the effect of permeability and elastic modulus on pressure drop, CFD predictions were extended to a broad range of permeabilities spanning synthetic scaffolds and tissues, elastic moduli, and Poisson's ratio. Results indicated an increase in pressure drop with increase in permeability. Scaffolds with higher elastic modulus performed better and the effect of Poisson's ratio was insignificant. Flow induced deformation was negligible in axial-flow bioreactor. In summary, scaffold permeabilities can be calculated using scaffold microarchitecture and can be used in non-invasive monitoring of tissue regeneration.

Modeling of porous scaffold deformation induced by medium perfusion.

In this study, we tested the possibility of calculating permeability of porous scaffolds utilized in soft tissue engineering using pore size and shape. We validated the results using experimental measured pressure drop and simulations with the inclusion of structural deformation. We prepared Polycaprolactone (PCL) and Chitosan-Gelatin (CG) scaffolds by salt leaching and freeze drying technique, respectively. Micrographs were assessed for pore characteristics and mechanical properties. Porosity for both scaffolds was nearly same but the permeability varied 10-fold. Elastic moduli were 600 and 9 kPa for PCL and CG scaffolds, respectively, while Poisson's ratio was 0.3 for PCL scaffolds and ∼1.0 for CG scaffolds. A flow-through bioreactor accommodating a 10 cm diameter and 0.2 cm thick scaffold was used to determine the pressure-drop at various flow rates. Additionally, computational fluid dynamic (CFD) simulations were performed by coupling fluid flow, described by Brinkman equation, with structural mechanics using a dynamic mesh. The experimentally obtained pressure drop matched the simulation results of PCL scaffolds. Simulations were extended to a broad range of permeabilities (10(-10) m(2) to 10(-14) m(2) ), elastic moduli (10-100,000 kPa) and Poisson's ratio (0.1-0.49). The results showed significant deviation in pressure drop due to scaffold deformation compared to rigid scaffold at permeabilities near healthy tissues. Also, considering the scaffold as a nonrigid structure altered the shear stress profile. In summary, scaffold permeability can be calculated using scaffold pore characteristics and deformation could be predicted using CFD simulation. These relationships could potentially be used in monitoring tissue regeneration noninvasively via pressure drop.

In vitro electrochemical corrosion and cell viability studies on nickel-free stainless steel orthopedic implants.

The corrosion and cell viability behaviors of nanostructured, nickel-free stainless steel implants were studied and compared with AISI 316L. The electrochemical studies were conducted by potentiodynamic polarization and electrochemical impedance spectroscopic measurements in a simulated body fluid. Cytocompatibility was also evaluated by the adhesion behavior of adult human stem cells on the surface of the samples. According to the results, the electrochemical behavior is affected by a compromise among the specimen's structural characteristics, comprising composition, density, and grain size. The cell viability is interpreted by considering the results of the electrochemical impedance spectroscopic experiments.

Computational simulation modelling of bioreactor configurations for regenerating human bladder.

The objective of this study was to investigate a bioreactor suitable for human bladder regeneration. Simulations were performed using the computational fluid dynamic tools. The thickness of the bladder scaffold was 3 mm, similar to the human bladder, and overall hold-up volume within the spherical shape scaffold was 755 ml. All simulations were performed using (i) Brinkman equation on porous regions using the properties of 1% chitosan-1% gelatin structures, (ii) Michaelis-Menten type rate law nutrient consumption for smooth muscle cells (SMCs) and (iii) Mackie-Meares relationship for determining effective diffusivities. Steady state simulations were performed using flow rates from 0.5 to 5 ml/min. Two different inlet shapes: (i) straight entry at the centre (Design 1) and (ii) entry with an expansion (Design 2) were simulated to evaluate shear stress distribution. Also, mimicking bladder shape of two inlets (Design 3) was tested. Design 2 provided the uniform shear stress at the inlet and nutrient distribution, which was further investigated for the effect of scaffold locations within the reactor: (i) attached with a 3-mm open channel (Design 2-A), (ii) flow through with no open channel (Design 2-B) and (iii) porous structure suspended in the middle with 1.5-mm open channel on either side (Design 2-C). In Design 2-A and 2-C, fluid flow occurred by diffusion dominant mechanisms. Furthermore, the designed bioreactor is suitable for increased cell density of SMCs. These results showed that increasing the flow rate is necessary due to the decreased permeability at cell densities similar to the human bladder.