Engineered channels enhance cellular density in perfused scaffolds

Elimination of Induced Hypoxic Regions in Depth of 3D Porous Silk Scaffolds by the Introduction of Channel Configuration

Development of large, clinically sized tissue constructs with efficient mass transport is a tremendous need in tissue engineering. One major challenge in large tissue-engineered constructs is to support homogeneous delivery of oxygen and nutrients throughout the tissue scaffold while eliminating induced hypoxic regions in depth. To address this goal, we introduced an especial channeled architecture on porous silk-based tissue scaffolds to improve supplying of oxygen to the cells in central regions of the scaffolds. Oxygen gradients were measured and evaluated in three scaffold prototypes, namely, one unchanneled and two channeled scaffolds with different channel diameters (500 μm and 1000 μm). The channels were introduced into the constructs using stainless-steel rods arranged uniformly in stainless-steel mold, a fabrication method that enables precise control over channel diameter and the distance between channels. During 2-week culture of G292 cells, the 1000 μm channeled scaffolds demonstrated higher oxygen concentration at the center compared to 500 μm channeled prototype; however, the oxygen concentration approached the same level around the last days of culture. Nevertheless, homogenous oxygen distribution throughout the 1000 μm channeled constructs and the consequence of higher cell proliferation at day 14 postseeding corroborate the efficient elimination of induced hypoxic regions; and therefore, it holds promise for clinically relevant sized scaffold especially in bone tissue engineering.

Assessment of properties, applications and limitations of scaffolds based on cellulose and its derivatives for cartilage tissue engineering: A review

Cartilage is a connective tissue, which is made up of ~80% of water. It is alymphatic, aneural and avascular with only one type of cells present, chondrocytes. They constitute about 1-5% of the entire cartilage tissue. It has a very limited capacity for spontaneous repair. Articular cartilage defects are quite common due to trauma, injury or aging and these defects eventually lead to osteoarthritis, affecting the daily activities. Tissue engineering (TE) is a promising strategy for the regeneration of articular cartilage when compared to the existing invasive treatment strategies. Cellulose is the most abundant natural polymer and has desirable properties for the development of a scaffold, which can be used for the regeneration of cartilage. This review discusses about (i) the basic science behind cartilage TE and the study of cellulose properties that can be exploited for the construction of the engineered scaffold with desired properties for cartilage tissue regeneration, (ii) about the requirement of scaffolds properties, fabrication mechanisms and assessment of cellulose based scaffolds, (iii) details about the modification of cellulose surface by employing various chemical approaches for the production of cellulose derivatives with enhanced characteristics and (iv) limitations and future research prospects of cartilage TE.

Engineering of Hydrogel Materials with Perfusable Microchannels for Building Vascularized Tissues

Vascular systems are responsible for various physiological and pathological processes related to all organs in vivo, and the survival of engineered tissues for enough nutrient supply in vitro. Thus, biomimetic vascularization is highly needed for constructing both a biomimetic organ model and a reliable engineered tissue. However, many challenges remain in constructing vascularized tissues, requiring the combination of suitable biomaterials and engineering techniques. In this review, the advantages of hydrogels on building engineered vascularized tissues are discussed and recent engineering techniques for building perfusable microchannels in hydrogels are summarized, including micromolding, 3D printing, and microfluidic spinning. Furthermore, the applications of these perfusable hydrogels in manufacturing organ-on-a-chip devices and transplantable engineered tissues are highlighted. Finally, current challenges in recapitulating the complexity of native vascular systems are discussed and future development of vascularized tissues is prospected.

Development of an infusion bioreactor for the accelerated preparation of decellularized skeletal muscle scaffolds

The implantation of decellularized tissue has shown effectiveness as a strategy for the treatment of volumetric muscle loss (VML) injuries. The preparation of decellularized tissue typically relies on the diffusion driven removal of cellular debris. For bulky tissues like muscle, the process can be lengthy, which introduces opportunities for both tissue contamination and degradation of key ECM molecules. In this study we report on the accelerated preparation of decellularized skeletal muscle (DSM) scaffolds using a infusion system and examine scaffold performance for the repair of VML injuries. The preparation of DSM scaffolds using infusion was dramatically accelerated. As the infusion rate (1% SDS) was increased from 0.1 to 1 and 10ml/hr, the time needed to remove intracellular myoglobin and actin decreased from a maximum of 140 ± 3hrs to 45 ± 3hrs and 10 ± 2hrs respectively. Although infusion appeared to remove cellular debris more aggressively, it did not significantly decrease the collagen or glycosaminoglycan composition of DSM samples when compared to un-infused controls. Infusion prepared DSM samples retained the aligned network structure and mechanical integrity of control samples. Infusion prepared DSM samples supported the attachment and in-vitro proliferation of myoblast cells and was well tolerated by the host when examined in-vivo. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:745-755, 2016.

Controlling the blood glucose of type 1 diabetes mice by co-culturing MIN-6 β cells on 3D scaffold

T1D is an autoimmune disease, which may be caused by lack of insulin-secreting β cells due to damage of autoimmune system. Living with T1D is a challenge for the child and the family; cell transplantation is a treatment option for diabetes in children. To establish a microenvironment suitable for cell growth and proliferation as well as for sustained cellular function, we used MIN-6 β cells as seed cells and SF-IV collagen as a 3D composite scaffold to construct artificial pancreas in this experiment. The cell viabilities were determined by MTT assay, and the response of cells to different glucose concentrations was observed by glucose stimulation test. Artificial pancreas was transplanted into the abdominal cavity of T1D mice, and the changes of blood glucose were monitored. After 10 days, insulin expression was detected by immunohistochemical method, and the claybank stained area showed effectiveness of insulin secretion. A series of experiments showed that implantation of 3D cell scaffold into the abdominal cavity can effectively control the blood glucose level of T1D mice. It also had longer-lasting hypoglycemic effects than simple cell transplantation, which was expected to become a new method for the treatment of T1D.

Dip TIPS as a facile and versatile method for fabrication of polymer foams with controlled shape, size and pore architecture for bioengineering applications

The porous polymer foams act as a template for neotissuegenesis in tissue engineering, and, as a reservoir for cell transplants such as pancreatic islets while simultaneously providing a functional interface with the host body. The fabrication of foams with the controlled shape, size and pore structure is of prime importance in various bioengineering applications. To this end, here we demonstrate a thermally induced phase separation (TIPS) based facile process for the fabrication of polymer foams with a controlled architecture. The setup comprises of a metallic template bar (T), a metallic conducting block (C) and a non-metallic reservoir tube (R), connected in sequence T-C-R. The process hereinafter termed as Dip TIPS, involves the dipping of the T-bar into a polymer solution, followed by filling of the R-tube with a freezing mixture to induce the phase separation of a polymer solution in the immediate vicinity of T-bar; Subsequent free-drying or freeze-extraction steps produced the polymer foams. An easy exchange of the T-bar of a spherical or rectangular shape allowed the fabrication of tubular, open- capsular and flat-sheet shaped foams. A mere change in the quenching time produced the foams with a thickness ranging from hundreds of microns to several millimeters. And, the pore size was conveniently controlled by varying either the polymer concentration or the quenching temperature. Subsequent in vivo studies in brown Norway rats for 4-weeks demonstrated the guided cell infiltration and homogenous cell distribution through the polymer matrix, without any fibrous capsule and necrotic core. In conclusion, the results show the "Dip TIPS" as a facile and adaptable process for the fabrication of anisotropic channeled porous polymer foams of various shapes and sizes for potential applications in tissue engineering, cell transplantation and other related fields.

In vitro mesenchymal trilineage differentiation and extracellular matrix production by adipose and bone marrow derived adult equine multipotent stromal cells on a collagen scaffold

Directed differentiation of adult multipotent stromal cells (MSC) is critical for effective treatment strategies. This study was designed to evaluate the capability of equine MSC from bone marrow (BMSC) and adipose tissue (ASC) on a type I collagen (COLI) scaffold to undergo chondrogenic, osteogenic and adipogenic differentiation and form extracellular matrix (ECM) in vitro. Following determination of surface antigen expression, MSC were loaded into scaffolds in a perfusion bioreactor and loading efficiency was quantified. Cell-scaffold constructs were assessed after loading and 7, 14 and 21 days of culture in stromal or induction medium. Cell number was determined with DNA content, cell viability and spatial uniformity with confocal laser microscopy and cell phenotype and matrix production with light and scanning electron microscopy and mRNA levels. The MSC were positive for CD29 (>90 %), CD44 (>99 %), and CD105 (>60 %). Loading efficiencies were >70 %. The ASC and BMSC cell numbers on scaffolds were affected by culture in induction medium differently. Viable cells remained uniformly distributed in scaffolds for up to 21 days and could be directed to differentiate or to maintain an MSC phenotype. Micro- and ultrastructure showed lineage-specific cell and ECM changes. Lineage-specific mRNA levels differed between ASC and BMSC with induction and changed with time. Based on these results, equine ASC and BMSC differentiate into chondrogenic, osteogenic and adipogenic lineages and form ECM similarly on COLI scaffolds. The collected data supports the potential for equine MSC-COLI constructs to support diverse equine tissue formation for controlled biological studies.

Cell therapy, 3D culture systems and tissue engineering for cardiac regeneration

Ischemic Heart Disease (IHD) still represents the "Number One Killer" worldwide accounting for the death of numerous patients. However the capacity for self-regeneration of the adult heart is very limited and the loss of cardiomyocytes in the infarcted heart leads to continuous adverse cardiac-remodeling which often leads to heart-failure (HF). The concept of regenerative medicine comprising cell-based therapies, bio-engineering technologies and hybrid solutions has been proposed as a promising next-generation approach to address IHD and HF. Numerous strategies are under investigation evaluating the potential of regenerative medicine on the failing myocardium including classical cell-therapy concepts, three-dimensional culture techniques and tissue-engineering approaches. While most of these regenerative strategies have shown great potential in experimental studies, the translation into a clinical setting has either been limited or too rapid leaving many key questions unanswered. This review summarizes the current state-of-the-art, important challenges and future research directions as to regenerative approaches addressing IHD and resulting HF.

Update on vascularization in tissue engineering

Vascularization of engineered tissues is critical for success. Adequate and physiologically regulated blood supply is important for viability of the implanted tissue but even more important for the proper function of parenchymal cells, which is the desired clinical outcome for most applications in regenerative medicine. Several methods are being developed to stimulate revascularization of engineered tissue. Prevascularized scaffolds with a hierarchical vascular pattern, allowing surgical hook-up of the inflow and outflow tracts, that are already preseeded and cultured with primary vascular cells or precursors will be required for larger tissues or tissues with an immediate high metabolism, such as myocardium. The preimplantation presence of a mature vasculature will improve differentiation and maturation of the parenchyma, thus meeting the functional demands of the host. This may also be true for smaller or metabolically less-active tissues, yet for viability and immediate function they may rely on facilitated postimplantation ingrowth of the host vasculature.

Slowly degradable porous silk microfabricated scaffolds for vascularized tissue formation

There is critical clinical demand for tissue-engineered (TE), three-dimensional (3D) constructs for tissue repair and organ replacements. Current efforts toward this goal are prone to necrosis at the core of larger constructs because of limited oxygen and nutrient diffusion. Therefore, critically sized 3D TE constructs demand an immediate vascular system for sustained tissue function upon implantation. To address this challenge the goal of this project was to develop a strategy to incorporate microchannels into a porous silk TE scaffold that could be fabricated reproducibly using microfabrication and soft lithography. Silk is a suitable biopolymer material for this application because it is mechanically robust, biocompatible, slowly degrades in vivo, and has been used in a variety of TE constructs. We report the fabrication of a silk-based TE scaffold that contains an embedded network of porous microchannels. Enclosed porous microchannels support endothelial lumen formation, a critical step toward development of the vascular niche, while the porous scaffold surrounding the microchannels supports tissue formation, demonstrated using human mesenchymal stem cells. This approach for fabricating vascularized TE constructs is advantageous compared to previous systems, which lack porosity and biodegradability or degrade too rapidly to sustain tissue structure and function. The broader impact of this research will enable the systemic study and development of complex, critically-sized engineered tissues, from regenerative medicine to in vitro tissue models of disease states.

Ice-template-induced silk fibroin-chitosan scaffolds with predefined microfluidic channels and fully porous structures

Scaffold-based tissue engineering has made great progress in fabricating relatively simple tissues. One of the major challenges in creating thick complex organs is to achieve sufficient nutrient supply as well as uniform cell distribution in a three-dimensional (3D) scaffold. Here we employed microstructured ice templates to fabricate silk fibroin-chitosan (SF-CS) scaffolds with predefined microfluidic channels, open-pore surface and oriented porous structures. The effects of these structural organizations in ice-template-induced (ITI) scaffolds on nutrient delivery, cell seeding as well as cell growth were well investigated in comparison with that of polydimethylsiloxane-template-induced scaffolds. The ITI scaffolds exhibited better structural properties in promoting mass transport, facilitating uniform cell distribution and growth. The ITI scaffolds uniformly seeded with living cells could be further rolled up to form a thick tissue-engineered construct with predefined microfluidic channels. We envision that our ITI scaffolds can be potentially used to engineer thick prevascularized organs when the oriented porous structures are uniformly seeded with primary cells and the predefined microfluidic channels are incorporated with endothelial cells.

Bone tissue engineering: current strategies and techniques--part I: Scaffolds

Bone repair and regeneration is a dynamic process that involves a complex interplay between the (1) ground substance, (2) cells, and (3) milieu. While each constituent is integral to the final product, it is often helpful to consider each component individually. Therefore, we created a two-part review to examine scaffolds and cells' roles in bone tissue engineering. In Part I, we review the myriad of materials use for in vivo bone engineering. In Part II, we discuss the variety cell types (e.g., osteocytes, osteoblasts, osteoclasts, chondrocytes, mesenchymal stem cells, and vasculogenic cells) that are seeded upon or recruited to these scaffolds. In Part III, we discuss the optimization of the microenvironment. The biochemical processes and sequence of events that guide matrix production, cellular activation, and ossification are vital to developing successful bone tissue engineering strategies and are thus succinctly reviewed herein.