The Efficacy of Prevascularization by Basic FGF for Hepatocyte Transplantation Using Polymer Devices in Rats

Three Dimensional Bioprinting for Hepatic Tissue Engineering: From In Vitro Models to Clinical Applications

Fabrication of functional organs is the holy grail of tissue engineering and the possibilities of repairing a partial or complete liver to treat chronic liver disorders are discussed in this review. Liver is the largest gland in the human body and plays a responsible role in majority of metabolic function and processes. Chronic liver disease is one of the leading causes of death globally and the current treatment strategy of organ transplantation holds its own demerits. Hence there is a need to develop an in vitro liver model that mimics the native microenvironment. The developed model should be a reliable to understand the pathogenesis, screen drugs and assist to repair and replace the damaged liver. The three-dimensional bioprinting is a promising technology that recreates in vivo alike in vitro model for transplantation, which is the goal of tissue engineers. The technology has great potential due to its precise control and its ability to homogeneously distribute cells on all layers in a complex structure. This review gives an overview of liver tissue engineering with a special focus on 3D bioprinting and bioinks for liver disease modelling and drug screening.

Bioengineering a pre-vascularized pouch for subsequent islet transplantation using VEGF-loaded polylactide capsules

The effectiveness of cell transplantation can be improved by optimization of the transplantation site. For some types of cells that form highly oxygen-demanding tissue, e.g., pancreatic islets, a successful engraftment depends on immediate and sufficient blood supply. This critical point can be avoided when cells are transplanted into a bioengineered pre-vascularized cavity which can be formed using a polymer scaffold. In our study, we tested surface-modified poly(lactide-co-caprolactone) (PLCL) capsular scaffolds containing the pro-angiogenic factor VEGF. After each modification step (i.e., amination and heparinization), the surface properties and morphology of scaffolds were characterized by ATR-FTIR and XPS spectroscopy, and by SEM and AFM. All modifications preserved the gross capsule morphology and maintained the open pore structure. Optimized aminolysis conditions decreased the Mw of PLCL only up to 10% while generating a sufficient number of NH2 groups required for the covalent immobilization of heparin. The heparin layer served as a VEGF reservoir with an in vitro VEGF release for at least four weeks. In vivo studies revealed that to obtain highly vascularized PLCL capsules (a) the optimal VEGF dose for the capsule was 50 μg and (b) the implantation time was four weeks when implanted into the greater omentum of Lewis rats; dense fibrous tissue accompanied by vessels completely infiltrated the scaffold and created sparse granulation tissue within the internal cavity of the capsule. The prepared pre-vascularized pouch enabled the islet graft survival and functioning for at least 50 days after islet transplantation. The proposed construct can be used to create a reliable pre-vascularized pouch for cell transplantation.

Tissue Engineering of the Microvasculature

The ability to generate new microvessels in desired numbers and at desired locations has been a long-sought goal in vascular medicine, engineering, and biology. Historically, the need to revascularize ischemic tissues nonsurgically (so-called therapeutic vascularization) served as the main driving force for the development of new methods of vascular growth. More recently, vascularization of engineered tissues and the generation of vascularized microphysiological systems have provided additional targets for these methods, and have required adaptation of therapeutic vascularization to biomaterial scaffolds and to microscale devices. Three complementary strategies have been investigated to engineer microvasculature: angiogenesis (the sprouting of existing vessels), vasculogenesis (the coalescence of adult or progenitor cells into vessels), and microfluidics (the vascularization of scaffolds that possess the open geometry of microvascular networks). Over the past several decades, vascularization techniques have grown tremendously in sophistication, from the crude implantation of arteries into myocardial tunnels by Vineberg in the 1940s, to the current use of micropatterning techniques to control the exact shape and placement of vessels within a scaffold. This review provides a broad historical view of methods to engineer the microvasculature, and offers a common framework for organizing and analyzing the numerous studies in this area of tissue engineering and regenerative medicine. © 2019 American Physiological Society. Compr Physiol 9:1155-1212, 2019.

Whole liver engineering: A promising approach to develop functional liver surrogates

Liver donor shortage remains the biggest challenge for patients with end-stage liver failures. While bioartificial liver devices have been developed as temporary supports for patients waiting for transplantation, their applications have been limited clinically. Whole liver engineering is a biological scaffold based regenerative medicine approach that holds promise for developing functional liver surrogates. Significant advancements have been made since the first report in 2010. This review focuses on the recent achievements of whole liver engineering studies.

The Protective Effect of Transplanting Liver Cells Into the Mesentery on the Rescue of Acute Liver Failure After Massive Hepatectomy

Postoperative liver failure is one of the most critical complications following extensive hepatectomy. Although transplantation of allogeneic hepatocytes is an attractive therapy for posthepatectomy liver failure, transplanting cells via the portal veins typically causes portal vein embolization. The embolization by transplanted cells would be lethal in patients who have undergone massive hepatectomy. Thus, transplant surgeons need to select extrahepatic sites as transplant sites to prevent portal vein embolization. We aimed to investigate the mechanism of how liver cells transplanted into the mesentery protect recipient rats from acute liver failure after massive hepatectomy. We induced posthepatectomy liver failure by 90% hepatectomy in rats. Liver cells harvested from rat livers were transplanted into the mesenteries of hepatectomized rats. Twenty percent of the harvested cells, which consisted of hepatocytes and nonparenchymal cells, were transplanted into each recipient. The survival rate improved significantly in the liver cell transplantation group compared to the control group 7 days after hepatectomy (69 vs. 7%). Histological findings of the transplantation site, in vivo imaging system study findings, quantitative polymerase chain reaction assays of the transplanted cells, and serum albumin measurements of transplanted Nagase analbuminemic rats showed rapid deterioration of viable transplanted cells. Although viable transplanted cells deteriorated in the transplanted site, histological findings and an adenosine-5'-triphosphate (ATP) assay showed that the transplanted cells had a protective effect on the remaining livers. These results indicated that the paracrine effects of transplanted liver cells had therapeutic effects. The same protective effects were observed in the hepatocyte transplantation group, but not in the liver nonparenchymal cell transplantation group. Therefore, this effect on the remnant liver was mainly due to the hepatocytes among the transplanted liver cells. We demonstrated that transplanted liver cells protect the remnant liver from severe damage after massive hepatectomy.

Cellular therapy and bioartificial approaches to liver replacement

PURPOSE OF REVIEW

The success of liver transplantation has increased over the past 20 years due to improved immunosuppressive medications, surgical technique and donor-recipient selection. To date, the number of patients waiting for a liver transplant exceeds the number of transplants performed yearly by over a 2 : 1 ratio. Despite efforts to expand the donor pool, mortality of patients waiting for a liver remains high due to the shortage of donor organs. Herein, we discuss options for liver replacement that are currently under development.

RECENT FINDINGS

Extracorporeal bioactive liver perfusion devices were investigated in the late 1990s and preliminarily demonstrated safety but failed to show clinical efficacy. Current research is ongoing, but the focus has shifted to xenotransplantation of whole organs, organ engineering and cell transplantation. These new modalities are limited to small and large animal studies and each present unique advantages and limitations.

SUMMARY

Discovery of new sources of organs or cells to replace a damaged liver may be the only long-term solution to provide definitive therapy to all patients who require transplantation. The past 2 years have seen notable achievements in xenotransplantation, tissue engineering and cell transplantation. Though challenges remain, now identified, they may be readily solved.

Scaffolds containing growth factors and extracellular matrix induce hepatocyte proliferation and cell migration in normal and regenerating rat liver

BACKGROUND & AIMS

Intrahepatic drug delivery from implantable scaffolds is being developed as a strategy to modulate growth and enhance regeneration at the time of liver resection. In this study we examine the effects of scaffolds containing hepatocyte growth factor, epidermal growth factor, fibroblast growth factor 1, fibroblast growth factor 2, and liver-derived extracellular matrix (L-ECM) when implanted into normal and partially hepatectomized rat livers.

METHODS

Scaffolds loaded with combinations of growth factors and L-ECM were implanted into normal livers (controls=L-ECM, polymer or sham) and livers following partial hepatectomy (controls=partial hepatectomy or sham). The primary end points were hepatocyte DNA synthesis and liver tissue penetration into scaffolds. Secondary end points included non-parenchymal cell DNA synthesis, liver weight analysis, liver function, and histological characterisation of the peri-implant parenchyma.

RESULTS

Four days after implantation in normal livers, there was significantly more hepatocyte proliferation around growth factor scaffolds than controls. Seven days after implantation, there was significantly more tissue penetration into growth factor scaffolds than control scaffolds. ED-1 and desmin positive cells were present in the pores of scaffolds. Two days after partial hepatectomy, there was significantly more hepatocyte proliferation around scaffold implanted livers than after partial hepatectomy alone.

CONCLUSIONS

Growth factors and L-ECM accelerated non-parenchymal cell migration into scaffolds and increased hepatocyte and non-parenchymal cell proliferation around them. These results demonstrate the potential for intrahepatic implantation of scaffolds containing growth factors and L-ECM to modulate growth in the normal and regenerating liver.

Neovascularization by bFGF releasing hyaluronic acid-gelatin microspheres: in vitro and in vivo studies

Therapeutic angiogenesis with angiogenic growth factors has been described as a promising approach for tissue engineering, wound healing, and for treating ischemic tissues. Here, we assessed the merit of heparin-entrapped hyaluronic acid-gelatin (HA-G) microspheres for the sustained release of recombinant basic fibroblast growth factor (rbFGF) to promote localized neovascularization. HA-G microspheres were prepared by a water-in-oil emulsion method, and the in vitro release kinetics were first examined using three model proteins. Then, bFGF was incorporated into microspheres, and the bioactivity of the in vitro-released rbFGF was tested on human umbilical vein endothelial cell cultures. The ability to promote microvessel growth was assessed in vivo, at the subcutaneous groin fascia of Wistar rats after 3, 7, 14, and 21 days. Histological and morphometrical analysis indicated that heparin-entrapped HA-G microspheres have the capacity to release bioactive rbFGF, leading to localized neovascularization in the rat subcutaneous tissue.

Effects of basic fibroblast growth factor on rat vocal fold fibroblasts

OBJECTIVES

The overarching goal of this line of research is to translate basic fibroblast growth factor (bFGF) treatment for vocal fold scarring into practical clinical use. In a previous canine investigation, we demonstrated that bFGF improves phonation threshold pressure, mucosal wave amplitude, and histologic measures in vocal folds treated after injury. In the present study, we studied the effects of bFGF on gene expression of the extracellular matrix and growth factors in rat vocal fold fibroblasts.

METHODS

Fibroblasts harvested from the vocal folds of 5 rats were treated with 3 concentrations of bFGF (0, 10, and 100 ng/mL). The fibroblasts were collected at 24 hours and 72 hours after bFGF administration. Quantitative polymerase chain reaction was then used to investigate the gene expression of the investigated growth factors and extracellular matrices.

RESULTS

The results revealed significantly down-regulated expression of procollagen I and significantly up-regulated expression of hyaluronic acid synthase (HAS) 2 and fibronectin in fibroblasts treated with bFGF. The administration of bFGF also resulted in the up-regulation of bFGF and hepatocyte growth factor (HGF). No changes in the expression of HAS-1, tropoelastin, or procollagen III were observed between the treatment and control conditions.

CONCLUSIONS

Treatment with bFGF induces the down-regulation of procollagen I and the up-regulation of HAS-2 in vocal fold fibroblast cell cultures. These gene expression alterations to key mediators of the wound healing process may translate into potential benefits in the remediation of vocal fold injury. The up-regulation of HGF, an antifibrotic effector molecule, may demonstrate additional benefits by optimizing the wound healing environment and by accelerating the wound repair cascade. These findings may provide fuel for additional discoveries into the development of growth factor therapy for the treatment of vocal fold scar.

Treatment of acute vocal fold scar with local injection of basic fibroblast growth factor: a canine study

CONCLUSIONS

Results of the current study revealed improved phonation threshold pressure (PTP), normalized mucosal wave amplitude (NMWA), and less contraction of the lamina propria in injured larynges treated with basic fibroblast growth factor (bFGF).

OBJECTIVES

We investigated the effects of local injection of bFGF for treatment of acute vocal fold injury in a canine model.

METHODS

Vocal folds of eight beagles were unilaterally injured by removal of the mucosa under direct laryngoscopy. Four beagles received local injections of bFGF delivered to the scarred vocal fold at 1 month after injury. The remaining four beagles received local injections of saline and served as a sham-treatment group. Larynges were harvested 5 months after treatment and excised larynx experiments were performed to measure PTP, NMWA, and normalized glottal gap (NGG). Histologic staining was performed to evaluate structural changes of the extracellular matrix.

RESULTS

Excised larynx measurements revealed significantly lower PTP and increased NMWA in bFGF-treated vocal fold. Elastica Van Gieson staining revealed less contraction of the bFGF-treated vocal fold. Histologic measurements revealed that the thickness of the lamina propria was significantly greater in the bFGF-treated vocal fold. Alcian blue staining revealed improved restoration of hyaluronic acid in the bFGF-treated vocal fold.

Biomaterial technology for tissue engineering applications

Tissue engineering is a newly emerging biomedical technology and methodology to assist and accelerate the regeneration and repairing of defective and damaged tissues based on the natural healing potentials of patients themselves. For the new therapeutic strategy, it is indispensable to provide cells with a local environment that enhances and regulates their proliferation and differentiation for cell-based tissue regeneration. Biomaterial technology plays an important role in the creation of this cell environment. For example, the biomaterial scaffolds and the drug delivery system (DDS) of biosignalling molecules have been investigated to enhance the proliferation and differentiation of cell potential for tissue regeneration. In addition, the scaffold and DDS technologies contribute to develop the basic research of stem cell biology and medicine as well as obtain a large number of cells with a high quality for cell transplantation therapy. A technology to genetically engineer cells for their functional manipulation is also useful for cell research and therapy. Several examples of tissue engineering applications with the cell scaffold and DDS of growth factors and genes are introduced to emphasize the significance of biomaterial technology in new therapeutic and research fields.

Experimental tissue regeneration by DDS technology of bio-signaling molecules

The medical therapy of tissue regeneration achieved by biomaterial-based tissue engineering has been currently expected as the third option following reconstructive surgery and organ transplantation. The basic idea of this regenerative therapy is to assist the self-healing potentials of body to induce the natural regeneration and repairing of defective or injured tissue. To this end, it is practically important to create a local environment which enables cells to promote their proliferation and differentiation, resulting in the induction of cell-based tissue regeneration. Tissue engineering is a biomedical technology or methodology to build up this regeneration environment by making use of biomaterials. Drug delivery system (DDS) is a biomaterial technology to enhance the in vivo biological functions of bio-signaling molecules (growth factors and genes) for promoted tissue regeneration. This paper overviews the recent status of tissue regeneration therapy based on the DDS technology of bio-signaling molecules.

Biodegradable elastomeric scaffolds with basic fibroblast growth factor release

Scaffolds that better approximate the mechanical properties of cardiovascular and other soft tissues might provide a more appropriate mechanical environment for tissue development or healing in vivo. An ability to induce local angiogenesis by controlled release of an angiogenic factor, such as basic fibroblast growth factor (bFGF), from a biodegradable scaffold with mechanical properties more closely approximating soft tissue could find application in a variety of settings. Toward this end biodegradable poly(ester urethane)urea (PEUU) scaffolds loaded with bFGF were fabricated by thermally induced phase separation. Scaffold morphology, mechanical properties, release kinetics, hydrolytic degradation and bioactivity of the released bFGF were assessed. The scaffolds had inter-connected pores with porosities of 90% or greater and pore sizes ranging from 34-173 microm. Scaffolds had tensile strengths of 0.25-2.8 MPa and elongations at break of 81-443%. Incorporation of heparin into the scaffold increased the initial burst release of bFGF, while the initial bFGF loading content did not change release kinetics significantly. The released bFGF remained bioactive over 21 days as assessed by smooth muscle mitogenicity. Scaffolds loaded with bFGF showed slightly higher degradation rates than unloaded control scaffolds. Smooth muscle cells seeded into the scaffolds with bFGF showed higher cell densities than for control scaffolds after 7 days of culture. The bFGF-releasing PEUU scaffolds thus exhibited a combination of mechanical properties and bioactivity that might be attractive for use in cardiovascular and other soft tissue applications.

Regenerative inductive therapy based on DDS technology of protein and gene

Recent development of biomedical engineering including biomaterials and drug delivery system (DDS) as well as basic biology and medicine has enabled cells to induce regeneration repairing of defective tissues as well as substitute the biological functions of damaged organs. For successful tissue regeneration, it is undoubtedly indispensable to give cells a local environment which allows cells to efficiently promote their proliferation and differentiation and consequently induce cell-based tissue regeneration. Tissue engineering is one of the biomedical forms to create this regeneration environment of cells. The tissue and organ repairing based on their regeneration induction has been realized by combining cells with the tissue engineering technology or methodology in a surgical or internally medical manner. This paper overviews the present status and future direction of tissue engineering for regenerative inductive therapy, briefly explaining the key technology of tissue engineering, especially DDS of growth factor and gene.

Vascular endothelial growth factor-releasing scaffolds enhance vascularization and engraftment of hepatocytes transplanted on liver lobes

Hepatocyte transplantation within porous scaffolds (HT) is being explored as a treatment strategy for end-stage liver diseases and enzyme deficiencies. One of the main issues in this approach is the limited viability of transplanted cells because vascularization of the scaffold site is either too slow or insufficient. We now address this by enhancing scaffold vascularization before cell transplantation via sustained delivery of vascular endothelial growth factor (VEGF), and by examining the liver lobes as a platform for transplanting donor hepatocytes in close proximity to the host liver. The vascularization kinetics of unseeded VEGF-releasing scaffolds on rat liver lobes were evaluated by analyzing the microvascular density and tissue ingrowth in implants harvested on days 3, 7, and 14 postimplantation. Capillary density was greater at all times in VEGF-releasing scaffolds than in the control scaffold without VEGF supplementation; on day 14, it was 220 +/- 33 versus 139 +/- 23 capillaries/mm2 (p < 0.05). Furthermore, 35% of the newly formed capillaries in VEGF-releasing scaffolds were larger than 16 microm in diameter, whereas in control scaffolds only 10% exceeded this size. VEGF had no effect on tissue ingrowth into the scaffolds. HT onto the implanted VEGF-releasing or control scaffolds was performed after 1 week of prevascularization on the liver lobe in Lewis rats. Fifty implants were harvested on days 1, 3, 7, and 12 and the area of viable hepatocytes was evaluated. The enhanced vascularization improved hepatocyte engraftment; 12 days after HT, the intact hepatocyte area (136,910 microm2/cross-section) in VEGF-releasing scaffolds was 4.6 higher than in the control group. This study shows that sustained local delivery of VEGF induced vascularization of porous scaffolds implanted on liver lobes and improved hepatocyte engraftment.

Significance of release technology in tissue engineering

Regenerative medical therapy has been expected to compensate for the therapeutic disadvantages of reconstructive surgery and organ transplantation, as well as offering a new therapeutic strategy. The objective of regenerative medical therapy is to induce the repair of defective tissues based on the natural healing potential of patients. For successful tissue regeneration, it is indispensable to provide cells with a local environment of artificial extracellular matrix where they can proliferate and differentiate efficiently. Tissue engineering is the key to this regeneration environment; release technology often enhances the in vivo stability of growth factors and related genes and prolongs the maintenance of biological functions for tissue regeneration.

Tissue regeneration based on tissue engineering technology

Recent development of biomedical engineering as well as basic biology and medicine has enabled us to induce cell-based regeneration of body tissue to self-repair defective tissue or substitute biological functions of damaged organs. For successful tissue regeneration, it is indispensable to give cells an environment suitable for regeneration induction. Tissue engineering is a newly emerging biomedical technology for creating an environment for tissue regeneration with various biomaterials. The paper presented here overviews recent research data on tissue regeneration based on tissue engineering, and briefly explains the key technology of tissue engineering.

Tissue regeneration based on growth factor release

Tissue engineering is an emerging biomedical field intended to assist the regeneration of body tissue defects too large to self-repair as well as to substitute for the biological functions of damaged and injured organs by using cells with proliferative and differentiative potential. In addition to basic research on such cells, it is undoubtedly indispensable for successful tissue engineering to create an artificial environment enabling cells to induce tissue regeneration. Such an environment can be achieved by making use of a scaffold for cell proliferation and differentiation and for growth factors, as well as their combination. Growth factors are often required to promote tissue regeneration, as they can induce angiogenesis, which supplies oxygen and nutrients to cells transplanted for organ substitution to maintain their biological functions. However, the biological effects of growth factors cannot always be expected because of their poor in vivo stability, unless a drug delivery system is contrived. In this article, tissue regeneration based on the release of growth factors is reviewed to emphasize the significance of drug delivery systems in tissue engineering.