Differentiation of a fibrin gel encapsulated chondrogenic cell line

Hydrogel: A Potential Material for Bone Tissue Engineering Repairing the Segmental Mandibular Defect

Free flap surgery is currently the only successful method used by surgeons to reconstruct critical-sized defects of the jaw, and is commonly used in patients who have had bony lesions excised due to oral cancer, trauma, infection or necrosis. However, donor site morbidity remains a significant flaw of this strategy. Various biomaterials have been under investigation in search of a suitable alternative for segmental mandibular defect reconstruction. Hydrogels are group of biomaterials that have shown their potential in various tissue engineering applications, including bone regeneration, both through in vitro and in vivo pre-clinical animal trials. This review discusses different types of hydrogels, their fabrication techniques, 3D printing, their potential for bone regeneration, outcomes, and the limitations of various hydrogels in preclinical models for bone tissue engineering. This review also proposes a modified technique utilizing the potential of hydrogels combined with scaffolds and cells for efficient reconstruction of mandibular segmental defects.

Evaluation of Autologously Derived Biomaterials and Stem Cells for Bone Tissue Engineering

Despite progress, clinical translation of tissue engineering (TE) products/technologies is limited. A significant effort is underway to develop biomaterials and cells through a minimally modified process for clinical translation of TE products. Recently, bone marrow aspirate (BMA) was identified as an autologous source of cells for TE applications and is currently being tested in clinical therapies, but the isolation methods need improvement to avoid potential for contamination and increase progenitor cell yield. To address these issues, we reproducibly processed human peripheral blood (PB) and BMA to develop autologously derived biomaterials and cells. We demonstrated PB-derived biomaterial/gel cross-linking and fibrin gel formation with varied gelation times as well as biocompatibility through support of human bone marrow-derived stem cell survival and growth in vitro. Next, we established a plastic culture-free process that concentrates and increases the yield of CD146+/CD271+ early mesenchymal progenitor cells in BMA (concentrated BMA [cBMA]). cBMA exhibited increased colony formation and multipotency (including chondrogenic differentiation) in vitro compared with standard BMA. PB-derived gels encapsulated with cBMA also demonstrated increased cell proliferation and enhanced mineralization when assessed for bone TE in vitro. This strategy can potentially be developed for use in any tissue regeneration application; however, bone regeneration was used as a test bed for this study.

Fibrin matrices: The versatile therapeutic delivery systems

Fibrin sealants, that have been employed for over a century by surgeons to stop post surgery bleeding, are finding novel applications in the controlled delivery of antibiotics and several other therapeutics. Fibrinogen can be easily purified from blood plasma and converted by thrombolysis to fibrin that undergoes spontaneous aggregation to form insoluble clot. During the gelling, fibrin can be formulated into films, clots, threads, microbeads, nanoconstructs and nanoparticles. Whole plasma clots in the form of beads and microparticles can also be prepared by activating endogenous thrombin, for possible drug delivery. Fibrin formulations offer remarkable scope for controlling the porosity as well as in vivo degradability and hence the release of the associated therapeutics. Binding/covalent-linking of therapeutics to the fibrin matrix, crosslinking of the matrix with bifunctional reagents and coentrapment of protease inhibitors have been successful in regulating both in vitro and in vivo release of the therapeutics. The release rates can also be remarkably lowered by preentrapment of therapeutics in insoluble particles like liposomes or by anchoring them to the matrix via molecules that bind them as well as fibrin.

Effect of chitosan incorporation and scaffold geometry on chondrocyte function in dense collagen type I hydrogels

Tissue engineering approaches for articular cartilage (AC) repair using collagen type I (Coll)-based hydrogels are limited by their low collagen fibril density (CFD; <0.5 wt%) and their poor capacity to support chondrocyte differentiation. Chitosan (CTS) is a well-characterized polysaccharide that mimics the glycosaminoglycans (GAGs) present in native AC extracellular matrix and exhibits chondroprotective properties. Here dense Coll/CTS hydrogel discs (16 mm diameter, 140-250 μm thickness) with CFD (∼6 wt%) approaching that of AC were developed to investigate the effect of CTS content on the growth and differentiation of three-dimensionally seeded RCJ3.1C5.18 chondroprogenitor cells. Compared to dense Coll alone, cells seeded within Coll/CTS showed increased viability and metabolic activity, as well as a decrease in cell-mediated gel contraction. Immunohistochemistry for collagen type II, in combination with Safranin O staining and GAG quantification, indicated greater chondroprogenitor differentiation within Coll/CTS, compared to cells seeded within Coll alone. The complex interplay between scaffold geometry, microstructure, composition, mechanical properties and cell function was further evaluated by rolling dense planar sheets to prepare cylindrically shaped constructs having clinically relevant diameters (3-5 mm diameter, 9 mm height). The compressive modulus of the cylindrically shaped constructs decreased significantly after 7 days in culture, and remained unchanged up to 21 days for each scaffold composition. Unlike Coll, cells seeded within Coll/CTS showed greater viability along the entire radial extent of the cylindrical rolls and increased GAG production at each time point. While GAG content decreased over time and reduced cell viability was observed within the core region of all cylindrical rolls, the incorporation of CTS diminished both these effects. In summary, these findings provide insight into the challenges involved when scaling up scaffolds designed and optimised in vitro for tissue repair.

Hydrogel scaffolds for tissue engineering: Progress and challenges

Designing of biologically active scaffolds with optimal characteristics is one of the key factors for successful tissue engineering. Recently, hydrogels have received a considerable interest as leading candidates for engineered tissue scaffolds due to their unique compositional and structural similarities to the natural extracellular matrix, in addition to their desirable framework for cellular proliferation and survival. More recently, the ability to control the shape, porosity, surface morphology, and size of hydrogel scaffolds has created new opportunities to overcome various challenges in tissue engineering such as vascularization, tissue architecture and simultaneous seeding of multiple cells. This review provides an overview of the different types of hydrogels, the approaches that can be used to fabricate hydrogel matrices with specific features and the recent applications of hydrogels in tissue engineering. Special attention was given to the various design considerations for an efficient hydrogel scaffold in tissue engineering. Also, the challenges associated with the use of hydrogel scaffolds were described.

Lead induces an osteoarthritis-like phenotype in articular chondrocytes through disruption of TGF-β signaling

Lead remains a significant environmental toxin, and we believe we may have identified a novel target of lead toxicity in articular chondrocytes. These cells are responsible for the maintenance of joint matrix, and do so under the regulation of TGF-β signaling. As lead is concentrated in articular cartilage, we hypothesize that it can disrupt normal chondrocyte phenotype through suppression of TGF-β signaling. These experiments examine the effects of lead exposure in vivo and in vitro at biologically relevant levels, from 1 nM to 10 µM on viability, collagen levels, matrix degrading enzyme activity, TGF-β signaling, and articular surface morphology. Our results indicate that viability was unchanged at levels ≤100 µM Pb, but low and high level lead in vivo exposure resulted in fibrillation and degeneration of the articular surface. Lead treatment also decreased levels of type II collagen and increased type X collagen, in vivo and in vitro. Additionally, MMP13 activity increased in a dose-dependent manner. Active caspase 3 and 8 were dose-dependently elevated, and treatment with 10 µM Pb resulted in increases of 30% and 500%, respectively. Increasing lead treatment resulted in a corresponding reduction in TGF-β reporter activity, with a 95% reduction at 10µM. Levels of phosphoSmad2 and 3 were suppressed in vitro and in vivo and lead dose-dependently increased Smurf2. These changes closely parallel those seen in osteoarthritis. Over time this phenotypic shift could compromise maintenance of the joint matrix.

New perspectives in cell delivery systems for tissue regeneration: natural-derived injectable hydrogels

Natural polymers, because of their biocompatibility, availability, and physico-chemical properties have been the materials of choice for the fabrication of injectable hydrogels for regenerative medicine. In particular, they are appealing materials for delivery systems and provide sustained and controlled release of drugs, proteins, gene, cells, and other active biomolecules immobilized.In this work, the use of hydrogels obtained from natural source polymers as cell delivery systems is discussed. These materials were investigated for the repair of cartilage, bone, adipose tissue, intervertebral disc, neural, and cardiac tissue. Papers from the last ten years were considered, with a particular focus on the advances of the last five years. A critical discussion is centered on new perspectives and challenges in the regeneration of specific tissues, with the aim of highlighting the limits of current systems and possible future advancements.

Cell-Seeded Collagen Matrix-Supported Autologous Chondrocyte Transplantation (ACT-CS): A Consensus Statement on Surgical Technique

OBJECTIVE

Autologous chondrocyte transplantation has become an established therapy for full-thickness cartilage defects. Cell-seeded collagen matrix-supported autologous chondrocyte transplantation (ACT-CS) has been introduced as a modification of conventional ACT, which allows easier handling and is intended to combine the advantages of using a cell suspension (i.e., cell viability and mitotic activity) with the stability and self-containment provided by a matrix of biomaterials. Unlike other techniques and products, this seeding step can be easily applied using a porcine collagen type I/III membrane and autologous chondrocytes in an operating room setting. Although some suturing is required, this technique provides the distinct advantage of not requiring a water-tight seal of the bilayer membrane, as is required using the classic cell suspension technique. Comparable to other modifications of ACT, the ACT-CS procedure requires a specific surgical technique that focuses on the following important details: (1) accurate debridement of the cartilage defect; (2) preparation of the cells, and seeding and containment of the cells within the transplantation site; and (3) sealing and suturing around the defect.

DESIGN

A consensus meeting of leading European orthopedic surgeons specializing in cartilage repair was convened to discuss and standardize the surgical aspects of this technique.

RESULTS & CONCLUSIONS

The present article describes and discusses the adoption of these best surgical practices for implementing the ACT-CS technique, including more detailed descriptions of each phase of the surgery in order to standardize and optimize patient outcomes.

Fabrication and repair of cartilage defects with a novel acellular cartilage matrix scaffold

The objectives of this study were to develop a three-dimensional acellular cartilage matrix (ACM) and investigate its possibility for use as a scaffold in cartilage tissue engineering. Bovine articular cartilage was decellularized sequentially with trypsin, nuclease solution, hypotonic buffer, and Triton x 100 solution; molded with freeze-drying process; and cross-linked by ultraviolet irradiation. Histological and biochemical analysis showed that the ACM was devoid of cells and still maintained the collagen and glycosaminoglycan components of cartilage. Scanning electronic microscopy and mercury intrusion porosimetry showed that the ACM had a sponge-like structure of high porosity. The ACM scaffold had good biocompatibility with cultured rabbit bone marrow mesenchymal stem cells with no indication of cytotoxicity both in contact and in extraction assays. The cartilage defects repair in rabbit knees with the mesenchymal stem cell-ACM constructs had a significant improvement of histological scores when compared to the control groups at 6 and 12 weeks. In summary, the ACM possessed the characteristics that afford it as a potential scaffold for cartilage tissue engineering.

Fibrin as a delivery system for therapeutic drugs and biomolecules

Fibrin is a natural biopolymer involved in the coagulation cascade. It acts as a reservoir for growth factors, cells, and enzymes during wound healing and provides a scaffold for the synthesis of extracellular matrix. Thus, the use of fibrin has expanded in recent years from traditional use as a sealant for surgical applications, to a tissue engineering scaffold capable of providing nature's cues for tissue regeneration. This paper reviews the advantageous biological aspects of fibrin, the history of the scaffold material, and its present role in the delivery of drugs, growth factors, cells, and gene vectors. Examples are given of studies where the structure and form of the scaffold have been manipulated for optimal release of the therapeutic agent, optimal cellular activity, and investigation into stem cell differentiation. It is evident from the body of literature presented that the benefits of fibrin are being exploited for a vast range of tissue engineering applications and that fibrin remains a key scaffold material for the delivery of drugs and biomolecules.

Hydrogels in regenerative medicine

Hydrogels, due to their unique biocompatibility, flexible methods of synthesis, range of constituents, and desirable physical characteristics, have been the material of choice for many applications in regenerative medicine. They can serve as scaffolds that provide structural integrity to tissue constructs, control drug and protein delivery to tissues and cultures, and serve as adhesives or barriers between tissue and material surfaces. In this work, the properties of hydrogels that are important for tissue engineering applications and the inherent material design constraints and challenges are discussed. Recent research involving several different hydrogels polymerized from a variety of synthetic and natural monomers using typical and novel synthetic methods are highlighted. Finally, special attention is given to the microfabrication techniques that are currently resulting in important advances in the field.

Fibrin: a versatile scaffold for tissue engineering applications

Tissue engineering combines cell and molecular biology with materials and mechanical engineering to replace damaged or diseased organs and tissues. Fibrin is a critical blood component responsible for hemostasis, which has been used extensively as a biopolymer scaffold in tissue engineering. In this review we summarize the latest developments in organ and tissue regeneration using fibrin as the scaffold material. Commercially available fibrinogen and thrombin are combined to form a fibrin hydrogel. The incorporation of bioactive peptides and growth factors via a heparin-binding delivery system improves the functionality of fibrin as a scaffold. New technologies such as inkjet printing and magnetically influenced self-assembly can alter the geometry of the fibrin structure into appropriate and predictable forms. Fibrin can be prepared from autologous plasma, and is available as glue or as engineered microbeads. Fibrin alone or in combination with other materials has been used as a biological scaffold for stem or primary cells to regenerate adipose tissue, bone, cardiac tissue, cartilage, liver, nervous tissue, ocular tissue, skin, tendons, and ligaments. Thus, fibrin is a versatile biopolymer, which shows a great potential in tissue regeneration and wound healing.

Cell-based regeneration of intervertebral disc defects: review and concepts

During the last century low back pain has emerged as a widespread disease often caused by intervertebral disc degeneration (IDD). IDD is a complex problem in which a variety of causes play a role. As IDD causes high costs, corporate interest has led to a number of therapies being developed. Today, these therapies focus not only on minimizing the pain caused by this disease but also on restoring intervertebral disc function. These approaches are often biological and aim to stimulate the regeneration of the intervertebral disc by injection of activator proteins, biomaterials, different cell types or complex cell matrix composites. Genetic engineering of disc cells and in vitro tissue engineering also offer a possibility for curing IDD. This article gives an overview of these concepts.