Bioreactors For Tissue Engineering Research Articles

Analysis of the role of perfusion, mechanical, and electrical stimulation in bioreactors for cardiac tissue engineering.

Since cardiovascular diseases (CVDs) are globally one of the leading causes of death, of which myocardial infarction (MI) can cause irreversible damage and decrease survivors' quality of life, novel therapeutics are needed. Current approaches such as organ transplantation do not fully restore cardiac function or are limited. As a valuable strategy, tissue engineering seeks to obtain constructs that resemble myocardial tissue, vessels, and heart valves using cells, biomaterials as scaffolds, biochemical and physical stimuli. The latter can be induced using a bioreactor mimicking the heart's physiological environment. An extensive review of bioreactors providing perfusion, mechanical and electrical stimulation, as well as the combination of them is provided. An analysis of the stimulations' mechanisms and modes that best suit cardiac construct culture is developed. Finally, we provide insights into bioreactor configuration and culture assessment properties that need to be elucidated for its clinical translation.

Shear Stress Quantification in Tissue Engineering Bioreactor Heart Valves: A Computational Approach.

Tissue-engineered heart valves can grow, repair, and remodel after implantation, presenting a more favorable long-term solution compared to mechanical and porcine valves. Achieving functional engineered valve tissue requires the maturation of human cells seeded onto valve scaffolds under favorable growth conditions in bioreactors. The mechanical stress and strain on developing valve tissue caused by different pressure and flow conditions in bioreactors are currently unknown. The aim of this study is to quantify the wall shear stress (WSS) magnitude in heart valve prostheses under different valve geometries and bioreactor flow rates. To achieve this, this study used fluid-structure interaction simulations to obtain the valve's opening geometries during the systolic phase. These geometries were then used in computational fluid dynamics simulations with refined near-wall mesh elements and ranges of prescribed inlet flow rates. The data obtained included histograms and regression curves that characterized the distribution, peak, and median WSS for various flow rates and valve opening configurations. This study also found that the upper region of the valve near the commissures experienced higher WSS magnitudes than the rest of the valve.

JANUS: an open-source 3D printable perfusion bioreactor and numerical model-based design strategy for tissue engineering.

Bioreactors have been employed in tissue engineering to sustain longer and larger cell cultures, managing nutrient transfer and waste removal. Multiple designs have been developed, integrating sensor and stimulation technologies to improve cellular responses, such as proliferation and differentiation. The variability in bioreactor design, stimulation protocols, and cell culture conditions hampered comparison and replicability, possibly hiding biological evidence. This work proposes an open-source 3D printable design for a perfusion bioreactor and a numerical model-driven protocol development strategy for improved cell culture control. This bioreactor can simultaneously deliver capacitive-coupled electric field and fluid-induced shear stress stimulation, both stimulation systems were validated experimentally and in agreement with numerical predictions. A preliminary in vitro validation confirmed the suitability of the developed bioreactor to sustain viable cell cultures. The outputs from this strategy, physical and virtual, are openly available and can be used to improve comparison, replicability, and control in tissue engineering applications.

Computer-aided engineering and additive manufacturing for bioreactors in tissue engineering: State of the art and perspectives.

Two main challenges are currently present in the healthcare world, i.e., the limitations given by transplantation and the need to have available 3D in vitro models. In this context, bioreactors are devices that have been introduced in tissue engineering as a support for facing the mentioned challenges by mimicking the cellular native microenvironment through the application of physical stimuli. Bioreactors can be divided into two groups based on their final application: macro- and micro-bioreactors, which address the first and second challenge, respectively. The bioreactor design is a crucial step as it determines the way in which physical stimuli are provided to cells. It strongly depends on the manufacturing techniques chosen for the realization. In particular, in bioreactor prototyping, additive manufacturing techniques are widely used nowadays as they allow the fabrication of customized shapes, guaranteeing more degrees of freedom. To support the bioreactor design, a powerful tool is represented by computational simulations that allow to avoid useless approaches of trial-and-error. In the present review, we aim to discuss the general workflow that must be carried out to develop an optimal macro- and micro-bioreactor. Accordingly, we organize the discussion by addressing the following topics: general and stimulus-specific (i.e., perfusion, mechanical, and electrical) requirements that must be considered during the design phase based on the tissue target; computational models as support in designing bioreactors based on the provided stimulus; manufacturing techniques, with a special focus on additive manufacturing techniques; and finally, current applications and new trends in which bioreactors are involved.

Development of a bioreactor for in-vitro compression cycling of tissue engineered meniscal implants

Injuries to the meniscus are common and can impair physical activities. Bioprinted meniscal tissue offers an attractive alternative to donor tissue for meniscal repair but achieving the strength of native tissue is a challenge. Here we report the development of a tissue engineering bioreactor designed to apply repetitive force which may lead to an increase in the compressive modulus and durability of bioprinted meniscal tissues. The modular bioreactor system is composed of a sterilizable tissue culture vessel together with a dock that applies and measures mechanical force. The culture vessel allows for simultaneous compression cycling of two anatomically sized menisci. Using a hybrid linear actuator with a stepper motor, the dock can apply up to 300 N of force at speeds up to 20 mm/s, corresponding to the upper limits of anatomical force and motion in the knee. An interchangeable 22 N load cell was mated between the culture vessel and the dock to log changes in force. Both the culture vessel and dock are maintained in a standard cell culture incubator to provide heat and CO2, while the dock is powered and controlled externally using a step motor drive and customized software.

Bioreactors for engineering patient-specific tissue grafts

Bioreactors have the potential to advance the clinical application of cell-based therapies. Cell expansion bioreactors have been used commercially for therapeutic applications; however, bioreactor-based engineering of 3D tissue grafts remains challenging owing to the complexity of tissue architectures, cellular heterogeneity and the lack of non-invasive, tissue-specific biomarkers with which to assess graft viability and maturation. Consequently, only a few bioreactor-based start-up companies that engineer patient-specific tissue grafts have emerged. In this Review, we discuss patient-specific bioreactors that can be used to engineer skin, small-diameter arteries and musculoskeletal tissues. We evaluate the impact of precision manufacturing, including 3D bioprinting, automation and non-invasive sensing, on optimizing the biological, chemical and physical parameters of the bioreactors that are required for specific tissue regeneration. We discuss the commercially available tissue-engineering bioreactors and the potential of digital twins and automation, and we outline the scientific and regulatory pathways that must be followed to enable the translation of tissue-specificbioreactors to the clinic. Bioreactors enable the cultivation of mammalian cells in a closely monitored and controlled microenvironment. This Review discusses bioreactor technologies and closed-loop set-ups for producing patient-specific engineered-tissue grafts, including skin, small-diameter arteries and musculoskeletal tissues, with a particular focus on commercialization and regulatory considerations.

In Vitro Differentiation of Myoblast Cell Lines on Spider Silk Scaffolds in a Rotating Bioreactor for Vascular Tissue Engineering.

Functional construction of tissue-engineered vessels as an alternative to autologous vascular grafts has been shown to be feasible, however the proliferation of seeded smooth-muscle cells remains a limiting factor. We employed a rotating bioreactor system to improve myoblast cell differentiation on a spider silk scaffold for tissue-engineered vessel construction. C2C12 myofibroblast cells were seeded on the surface of spider silk scaffold constructs and cultivated in a rotating bioreactor system with a continuous rotation speed (1 rpm). Cell function, cell growth and morphological structure and expression of biomarkers were analyzed using scanning electron microscopy, the LIVE/DEAD® assay, Western blot and quantitative real-time PCR analyses. A dense myofibroblast cell sheet could be developed which resembled native blood vessel muscular tissue in morphological structure and in function. Bioreactor perfusion positively affected cell morphology, and increased cell viability and cell differentiation. The expression of desmin, MYF5 and MEF2D surged as an indication of myoblast differentiation. Cell-seeded scaffolds showed a tear-down at 18 N when strained at a set speed (20 mm min-1). Spider silk scaffolds appear to offer a reliable basis for engineered vascular constructs and rotating bioreactor cultivation may be considered an effective alternative to complex bioreactor setups to improve cell viability and biology.

Perfuse and Reuse: A Low-Cost Three-Dimensional-Printed Perfusion Bioreactor for Tissue Engineering.

This article describes fabrication of a customizable bioreactor, which comprises a perfusion system and coverslip-based tissue culture chamber that allow centimeter-scale vascularized or otherwise canalized tissue constructs to be maintained in weeks long static and/or perfusion culture at an exceptionally low cost, with intermittent live imaging and media sampling capabilities. The perfusion system includes a reusable polydimethylsiloxane (PDMS) lid generated from a three-dimensional (3D)-printed poly-lactic acid (PLA) mold and several lengths of perfusion tubing. The coverslip tissue culture chamber includes PDMS components built with 3D-printed PLA molds, as well as 3D-printed PLA frames and glass coverslips that house perfusable hydrogel constructs. As proof of concept, we fabricated a vascularized hydrogel construct, which was subjected to static and perfusion tissue culture, as well as flow studies using fluorescent beads and widefield fluorescent microscopy. This system can be readily reproduced, promoting the advancement of tissue engineering and regenerative medicine research.

Pneumatic piston hydrostatic bioreactor for cartilage tissue engineering

During exercise, mechanical loads from the body are transduced into interstitial fluid pressure changes which are sensed as dynamic hydrostatic forces by cells in cartilage. The effects of these loading forces in health and disease are of interest to biologists, but the availability of affordable equipment for in vitro experimentation is an obstacle to research progress. Here, we report the development of a cost-effective hydropneumatic bioreactor system for research in mechanobiology. The bioreactor was assembled from readily available components (a closed-loop stepped motor and pneumatic actuator) and a minimal number of easily-machined crankshaft parts, whilst the cell culture chambers were custom designed by the biologists using CAD and entirely 3 D printed in PLA. The bioreactor system was shown to be capable of providing cyclic pulsed pressure waves at a user-defined amplitude and frequency ranging from 0 to 400 kPa and up to 3.5 Hz, which are physiologically relevant for cartilage. Tissue engineered cartilage was created from primary human chondrocytes and cultured in the bioreactor for five days with three hours/day cyclic pressure (300 kPa at 1 Hz), simulating moderate physical exercise. Bioreactor-stimulated chondrocytes significantly increased their metabolic activity (by 21%) and glycosaminoglycan synthesis (by 24%), demonstrating effective cellular transduction of mechanosensing. Our Open Design approach focused on using ‘off-the-shelf’ pneumatic hardware and connectors, open source software and in-house 3 D printing of bespoke cell culture containers to resolve long-standing problems in the availability of affordable bioreactors for laboratory research.

Fluid dynamics characterisation of a rotating bioreactor for tissue engineering.

Biological scaffolds composed of extracellular matrix (ECM) derived from decellularised tissue are increasingly used in regenerative medicine. In this project, a flow perfusion bioreactor (the rotary cell culture system (RCCS), commercially available from Synthecon (Houston, TX)) is used in order to obtain some esophageal extracellular matrix. A theoretical mechanical characterisation of this experimental set-up is provided. Due to the combination of rotation and perfusion, some spiral Poiseuille flow is created inside the tubular esophagus. In a transverse section, a particle (or cell) experiences simultaneously gravitational, Archimedes, centrifugal, Coriolis, and drag forces. In a frame of reference rotating with angular velocity ω, the particle follows a periodic nearly circular path in the clockwise direction, associated with a very slow centrifugal drift towards the esophagus wall. It appears that moderate perfusion rate and rotation speed (ω < 20 rpm and Q < 30 ml/min) are appropriate experimental conditions for esophagus tissue engineering using the RCCS Synthecon bioreactor.

Spinner Flask Bioreactor in Tissue Engineering

Spinner Flask Bioreactors are usually made up of glass or plastic vessel which have been widely used in Tissue Engineering from production of articular cartilage to production of osteoblast cells that help in bone regeneration. Cartilage grown in spinner flask bioreactors had more cells and less GAG than the other types of bioreactors in tissue engineering. In recent years, these bioreactors have also been used for the invitro cultivation of human tenocytes and MSCs. In this type of bioreactor, the cell/scaffold constructs are connected to vertical needles striking from pinnacle of the vessel and immersed inside the culture medium. The pinnacle or the top part of this bioreactor is used for gas exchange and medium oxygenation. Mixing of the medium is maintained with a stir bar at the lowest of the vessel or different blending mechanisms. Spinner Flask Bioreactors have grabbed increased attention in recent years due to its wide range of Tissue Engineering applications. In this review, we have tried to explore the different domains where these bioreactors have found enhanced applications. Keywords: Spin Flask Bioreactor Tissue Engineering, Cell Seeding, Bone Tissue Engineering, Articular Cartilage

Abstract 6041: Perfusion-based bioreactor preserves microenvironment of hepatocellular carcinoma ex vivo

Abstract Background: Hepatocellular carcinoma (HCC) accounts for 75-85% of all primary liver malignancies. HCC represents an attractive target for immune checkpoint inhibitors (ICI) and tumor microenvironment (TME) agents. The development and success of ICI therapies requires a comprehensive model to study interactions of immune networks in the TME. Patient-derived organoids (PDO) have emerged as promising individualized models for ex vivo drug testing. While PDO are superior to previous models, due to their inherent heterogeneity and their enhanced capacity to capture tumor characteristics, the lack of mesenchymal and immune components limit their use for testing drug classes such as ICI or study tumor-TME interaction. Here, we developed and characterized a perfusion-based cultivated ex vivo HCC tissue model that preserves the tumor tissue architecture and maintains the pathophysiological microenvironment of human tissue for testing of TME-related treatments. Materials and methods: Fresh tumor tissue was obtained from surgical specimens of six patients undergoing liver resection for HCC. Tissue fragments of 2x2x2 mm were installed between two discs of collagen type 1 porous scaffold and placed in a perfusion-based bioreactor (U-shaped Culture Under Perfusion; U-CUP) for tissue engineering or cultured in static condition. At different time points, cultured tissue fragments were formalin-fixed and paraffin-embedded for downstream analysis. Cell viability and morphology was monitored on day 0, 5 and 7 by using hematoxylin and eosin staining. The changes in TME composition were monitored by immunohistochemistry using cell-type specific antibodies like CD34 for endothelial cells, CD3 for T-cells, alpha-smooth muscle actin (a-SMA) for fibroblasts and arginase-L for urea cycle. Results: Microscopic analysis revealed that, compare to static culture, the morphology and the viability of the cells were preserved during the culture period in the U-CUP. Tissue histology as well as the immunophenotypic pattern observed in the original tissue was maintained. Similarly, the presence of endothelial cells (CD34+) and fibroblasts (a-SMA+) were detected in the U-CUP cultured samples in a similar proportion to the original tumor samples. The presence of T-cells (CD3+) was stable at all time points. Compared to the samples cultured under static conditions, the U-CUP tended to show less necrosis during the seven-day course. Conclusion: Compared to PDO, U-CUP bioreactor tumor culture seems to preserve mesenchymal and immune components. This enables further investigation and assessment of TME-related treatments, such as ICI. Citation Format: Gabriel Fridolin Hess, Manuele Giuseppe Muraro, Mairene Coto-Llerena, Silvio Däster, Caner Ercan, Simone Muenst, Otto Kollmar, Salvatore Piscuoglio, Savas Deniz Soysal. Perfusion-based bioreactor preserves microenvironment of hepatocellular carcinoma ex vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6041.

Mesenchymal stem cell culture in aligned porous hydroxyapatite scaffolds using a multiwell plate bioreactor for bone tissue engineering

Regeneration of bone lost by trauma, diseases and aging, and restoration of its load-bearing function are major clinical challenges. Hydroxyapatite (HA) is a clinically proven scaffold material for bone grafting, but the random-pore structure limits the homing of the cells inside the graft and the bone regeneration progresses with the resorption of the graft material. This work is based on the hypothesis that aligned through pores in the graft will lead to a faster healing by homing the local cells inside and provide a better environment for new bone formation through the graft structure. The investigation was done using aligned porous HA scaffolds seeded with human Wharton's jelly-derived mesenchymal stem cells (hWJ-MSCs) and cultured in a multiwell format bioreactor setup. The cell adhesion was studied by microscopy, cell proliferation was evaluated by Alamar blue assay and osteogenic differentiation was confirmed by biochemical and molecular assays. The results indicate that the hWJ-MSCs infiltrated through the aligned porous network of the scaffold, proliferated well when cultured in the expansion medium, and differentiated into osteogenic lineage when cultured in the differentiation medium.

Towards the biomimetic design of hollow fiber membrane bioreactors for bioartificial organs and tissue engineering: A micro-computed tomography (μCT) approach

Hollow fiber membrane bioreactors (HFMBs) with cells cultured in the extracapillary space (ECS) have been proposed for bioartificial organs, to assist patients with failing organs, or to produce in vitro engineered biological substitutes of tissues and organs. They have not gained clinical acceptance yet. One factor limiting therapeutic application is the irregular membrane distribution in the HFMB shell, often considered a typical feature of clinical-scale HFMBs. Such distribution does not permit good control of shell spaces, prevents from offering cells a template structure mimicking the tissue-specific extracellular matrix (ECM) and an adequate supply of oxygen and nutrients, and limits control over cell migration, organization, and differentiation in the ECS. In this study, micro-computed tomography and image analysis techniques were used to characterize the space distribution in the shell of HFMBs varying for membrane packing density and bundling technique, and to investigate whether and how it is possible to manufacture HFMBs in which the distribution of intermembrane spaces in the ECS is uniform and biomimetic. Results suggest that the arrangement in HFMBs of hollow fiber membranes bundled in rolled cross-woven mats at high packing density permits to obtain a uniform shell-side membrane distribution with pore size distribution favoring cells migration around the membranes, and mimicking the ECM structure of bone tissue. • HFMBs were equipped with membranes in loose bundles or in cross-woven mats at varying packing density in the ECS. • Voids distribution in ECS was characterized by μCT and image analysis and was compared to natural bone and a synthetic bone substitute. • Results show that in HFMBs with densely packed membranes in cross-woven mats voids distribution is uniform and mimics bone ECM.

Design, fabrication, and characterization of a multimodal reconfigurable bioreactor for bone tissue engineering.

In the past decades, bone tissue engineering developed and exploited many typologies of bioreactors, which, besides providing proper culture conditions, aimed at integrating those bio‐physical stimulations that cells experience in vivo, to promote osteogenic differentiation. Nevertheless, the highly challenging combination and deployment of many stimulation systems into a single bioreactor led to the generation of several unimodal bioreactors, investigating one or at mostly two of the required biophysical stimuli. These systems miss the physiological mimicry of bone cells environment, and often produced contrasting results, thus making the knowledge of bone mechanotransduction fragmented and often inconsistent. To overcome this issue, in this study we developed a perfusion and electroactive‐vibrational reconfigurable stimulation bioreactor to investigate the differentiation of SaOS‐2 bone‐derived cells, hosting a piezoelectric nanocomposite membrane as cell culture substrate. This multimodal perfusion bioreactor is designed based on a numerical (finite element) model aimed at assessing the possibility to induce membrane nano‐scaled vibrations (with ~12 nm amplitude at a frequency of 939 kHz) during perfusion (featuring 1.46 dyn cm−2 wall shear stress), large enough for inducing a physiologically‐relevant electric output (in the order of 10 mV on average) on the membrane surface. This study explored the effects of different stimuli individually, enabling to switch on one stimulation at a time, and then to combine them to induce a faster bone matrix deposition rate. Biological results demonstrate that the multimodal configuration is the most effective in inducing SaOS‐2 cell differentiation, leading to 20‐fold higher collagen deposition compared to static cultures, and to 1.6‐ and 1.2‐fold higher deposition than the perfused‐ or vibrated‐only cultures. These promising results can provide tissue engineering scientists with a comprehensive and biomimetic stimulation platform for a better understanding of mechanotransduction phenomena beyond cells differentiation.

Optimization and Validation of a Custom-Designed Perfusion Bioreactor for Bone Tissue Engineering: Flow Assessment and Optimal Culture Environmental Conditions.

Various perfusion bioreactor systems have been designed to improve cell culture with three-dimensional porous scaffolds, and there is some evidence that fluid force improves the osteogenic commitment of the progenitors. However, because of the unique design concept and operational configuration of each study, the experimental setups of perfusion bioreactor systems are not always compatible with other systems. To reconcile results from different systems, the thorough optimization and validation of experimental configuration are required in each system. In this study, optimal experimental conditions for a perfusion bioreactor were explored in three steps. First, an in silico modeling was performed using a scaffold geometry obtained by microCT and an expedient geometry parameterized with porosity and permeability to assess the accuracy of calculated fluid shear stress and computational time. Then, environmental factors for cell culture were optimized, including the volume of the medium, bubble suppression, and medium evaporation. Further, by combining the findings, it was possible to determine the optimal flow rate at which cell growth was supported while osteogenic differentiation was triggered. Here, we demonstrated that fluid shear stress up to 15 mPa was sufficient to induce osteogenesis, but cell growth was severely impacted by the volume of perfused medium, the presence of air bubbles, and medium evaporation, all of which are common concerns in perfusion bioreactor systems. This study emphasizes the necessity of optimization of experimental variables, which may often be underreported or overlooked, and indicates steps which can be taken to address issues common to perfusion bioreactors for bone tissue engineering.

QS2: DIY Bioreactors for Tissue Engineering - An Ultra-low-cost Platform for Perfusion Cell Culture and Live Imaging

Purpose:While tissue engineering offers the promise of revolutionary innovation, scalable three-dimensional tissue culture is limited by the diffusion of nutrients and oxygen making media perfusion obligatory. Unfortunately, the cost of bioreactors for large construct tissue culture can be prohibitive, with a typical perfusion chamber costing several thousand dollars, and even small petri-dish-sized devices costing hundreds of dollars each. We have developed a low-cost perfusion setup that seals collagen-based perfusable cellular constructs within a sterile PDMS well between coverslips, allowing for repeated live-imaging of perfused 3D engineered tissues. Herein we describe fabrication of this novel system and validate its utility.Methods:Molds and frames were designed on 3D-modeling software (Fusion 360) and printed on a Prusa i3 MK3S 3D printer in poly(lactic acid) (PLA). Molds were filled with poly(dimethyl siloxane) (PDMS), which was cured to form chambers, bubble traps, mason jar lid chambers, and media reservoir lid adapters. In total, the tissue culture chamber device, mason jar lid inset, media reservoir lid, and bubble trap require 4, 1, 2, and 4 unique printed components, respectively.Results:Each perfusion chamber can be assembled for under 8 USD per device and reused repeatedly. The current model has a tissue chamber custom-built with 18x10x4 (LxWxH)mm3 dimensions, but this chamber can be readily customized to experiment-specific dimensions. These devices allow cellular hydrogel constructs to be maintained in a sterile environment after assembly, perfused at varying rates to expose cells to different levels of shear stress, and the cells can be intermittently imaged with light, fluorescent or confocal microscopy - an unparalleled benefit for monitoring of experiments and collection of timepoint imaging data. The perfusion circuit consists of autoclavable glass and PDMS components, including a bubble trap, a crucial component of the circuit for preventing air bubbles that can damage cells and block microchannels, and a lid adapter, which allows 50 mL conical tubes to serve as self-oxygenating media reservoirs. Media changes can be performed via peristaltic pump perfusion or with syringe-based cell culture techniques for static culture. Constructs have been perfused within standard incubators for up to 14 days demonstrating normal cell viability without contamination or evidence of infection, with longer perfusion culture intervals (>1 month) currently being tested.Conclusion:The increasing accessibility of 3D-modeling and 3D-printing has enabled rapid prototyping of devices to address the problems that we face as surgeon-scientists. We have developed a low-cost tissue-engineering perfusion circuit that facilitates 3D-tissue-culture while allowing for repeated live-imaging as the cultured tissue develops. The instructions for our setup can be utilized to replicate our devices in other labs, and these designs can be readily customized to meet the needs of specific experimental aims.

A CRITICAL STEP FOR THE COSMETIC INDUSTRY: SCALE-UP

The perception of aesthetics directs the daily life of people from ancient times to the present. While the desire to be beautiful turns into a passion for some, it can also become a medical necessity for some people, such as war veterans. The historical documents examined show that both men and women use different materials to change their appearance and/or protect their skin. These materials still lead the way in the development of today's cosmetic products. The cosmetics industry is an important business line developed based on this aesthetic perception of societies.Starting from the research and development (R&amp;D) process of a cosmetic formulation and becoming a final product, health authorities control the industry by various regulations. In this process, where each step must be meticulously fulfilled, perhaps the most critical step is the scale-up process. In this review, cosmetic products, scale-up and critical parameters in scale-up process are discussed.&#x0D;                    &#x0D; Peer Review History: &#x0D; Received: 7 May 2021; Revised: 16 June; Accepted: 23 June, Available online: 15 July 2021&#x0D; Academic Editor: Dr. Ali Abdullah Al-yahawi, Al-Razi university, Department of Pharmacy, Yemen, alyahawipharm@yahoo.com&#x0D; UJPR follows the most transparent and toughest ‘Advanced OPEN peer review’ system. The identity of the authors and, reviewers will be known to each other. This transparent process will help to eradicate any possible malicious/purposeful interference by any person (publishing staff, reviewer, editor, author, etc) during peer review. As a result of this unique system, all reviewers will get their due recognition and respect, once their names are published in the papers. We expect that, by publishing peer review reports with published papers, will be helpful to many authors for drafting their article according to the specifications. Auhors will remove any error of their article and they will improve their article(s) according to the previous reports displayed with published article(s). The main purpose of it is ‘to improve the quality of a candidate manuscript’. Our reviewers check the ‘strength and weakness of a manuscript honestly’. There will increase in the perfection, and transparency. &#x0D; Received file:                Reviewer's Comments:&#x0D; Average Peer review marks at initial stage: 6.5/10&#x0D; Average Peer review marks at publication stage: 7.5/10&#x0D; Reviewer(s) detail:&#x0D; Dr. Salfarina Ramli,  salfarina2892@uitm.edu.my    Department of Pharmacology and Pharmaceutical Chemistry, Faculty of Pharmacy, Universiti Teknologi MARA, 42300 Puncak Alam, Selangor, Malaysia.  &#x0D; Dr. Govind Vyas, Compliance &amp; Regulatory Officer Inva-Tech Pharmaceuticals LLC, New-Jersey, USA, govindvyas03@gmail.com&#x0D;  &#x0D; Similar Articles:&#x0D; TISSUE ENGINEERING BIOREACTORS: POTENTIAL APPLICATIONS AND SCALE UP STRATEGY

[Research progress of in vivo bioreactor for bone tissue engineering].

To review the research progress of in vivo bioreactor (IVB) for bone tissue engineering in order to provide reference for its future research direction. The literature related to IVB used in bone tissue engineering in recent years was reviewed, and the principles of IVB construction, tissue types, sites, and methods of IVB construction, as well as the advantages of IVB used in bone tissue engineering were summarized. IVB takes advantage of the body's ability to regenerate itself, using the body as a bioreactor to regenerate new tissues or organs at injured sites or at ectopic sites that can support the regeneration of new tissues. IVB can be constructed by tissue flap (subcutaneous pocket, muscle flap/pocket, fascia flap, periosteum flap, omentum flap/abdominal cavity) and axial vascular pedicle (axial vascular bundle, arteriovenous loop) alone or jointly. IVB is used to prefabricate vascularized tissue engineered bone that matched the shape and size of the defect. The prefabricated vascularized tissue engineered bone can be used as bone graft, pedicled bone flap, or free bone flap to repair bone defect. IVB solves the problem of insufficient vascularization in traditional bone tissue engineering to a certain extent. IVB is a promising method for vascularized tissue engineered bone prefabrication and subsequent bone defect reconstruction, with unique advantages in the repair of large complex bone defects. However, the complexity of IVB construction and surgical complications hinder the clinical application of IVB. Researchers should aim to develop a simple, safe, and efficient IVB.

Effects of Scaffold Pore Morphologies on Glucose Transport Limitations in Hollow Fibre Membrane Bioreactor for Bone Tissue Engineering: Experiments and Numerical Modelling.

In the current research, three electrospun polycaprolactone (PCL) scaffolds with different pore morphology induced by changing the electrospinning parameters, spinning time and rate, have been prepared in order to provide a fundamental understanding on the effects pore morphology have on nutrient transport behaviour in hollow fibre membrane bioreactor (HFMB). After determining the porosity of the scaffolds, they were investigated for glucose diffusivity using cell culture media (CCM) and distilled water in a diffusion cell at 37 °C. The scanning electron microscope (SEM) images of the microstructure of the scaffolds were analysed further using ImageJ software to determine the porosity and glucose diffusivity. A Krogh cylinder model was used to determine the glucose transport profile with dimensionless variables within the HFMB. The paper discusses the roles of various dimensionless numbers (e.g., Péclet and Damköhler numbers) and non-dimensional groups of variables (e.g., non-dimensional fibre radius) on determining glucose concentration profiles, especially in the scaffold region. A negative linear relationship between glucose diffusivities across PCL scaffolds and the minimum glucose concentrations (i.e., concentration on the outer fibre edge on the outlet side (at z = 1 and r = 3.2) was also found. It was shown that the efficiency of glucose consumption improves with scaffolds of higher diffusivities. The results of this study are expected to help in optimizing designs of HFMB as well as carry out more accurate up scaling analyses for the bioreactor.