TGF-beta1 immobilized tri-co-polymer for articular cartilage tissue engineering

Strategies to Control or Mimic Growth Factor Activity for Bone, Cartilage, and Osteochondral Tissue Engineering

Growth factors play a critical role in tissue repair and regeneration. However, their clinical success is limited by their low stability, short half-life, and rapid diffusion from the delivery site. Supraphysiological growth factor concentrations are often required to demonstrate efficacy but can lead to adverse reactions, such as inflammatory complications and increased cancer risk. These issues have motivated the development of delivery systems that enable sustained release and controlled presentation of growth factors. This review specifically focuses on bioconjugation strategies to enhance growth factor activity for bone, cartilage, and osteochondral applications. We describe approaches to localize growth factors using noncovalent and covalent methods, bind growth factors via peptides, and mimic growth factor function with mimetic peptide sequences. We also discuss emerging and future directions to control spatiotemporal growth factor delivery to improve functional tissue repair and regeneration.

Concise Review: Mesenchymal Stem Cells for Functional Cartilage Tissue Engineering: Taking Cues from Chondrocyte-Based Constructs

Osteoarthritis, the most prevalent form of joint disease, afflicts 9% of the U.S. population over the age of 30 and costs the economy nearly $100 billion annually in healthcare and socioeconomic costs. It is characterized by joint pain and dysfunction, though the pathophysiology remains largely unknown. Due to its avascular nature and limited cellularity, articular cartilage exhibits a poor intrinsic healing response following injury. As such, significant research efforts are aimed at producing engineered cartilage as a cell-based approach for articular cartilage repair. However, the knee joint is mechanically demanding, and during injury, also a milieu of harsh inflammatory agents. The unforgiving mechano-chemical environment requires tissue replacements that are capable of bearing such burdens. The use of mesenchymal stem cells (MSCs) for cartilage tissue engineering has emerged as a promising cell source due to their ease of isolation, capacity to readily expand in culture, and ability to undergo lineage-specific differentiation into chondrocytes. However, to date, very few studies utilizing MSCs have successfully recapitulated the structural and functional properties of native cartilage, exposing the difficult process of uniformly differentiating stem cells into desired cell fates and maintaining the phenotype during in vitro culture and after in vivo implantation. To address these shortcomings, here, we present a concise review on modulating stem cell behavior, tissue development and function using well-developed techniques from chondrocyte-based cartilage tissue engineering. Stem Cells Translational Medicine 2017;6:1295-1303.

Synthesis of and in vitro and in vivo evaluation of a novel TGF-β1-SF-CS three-dimensional scaffold for bone tissue engineering

The role of transforming growth factor-β1 (TGF-β1) in normal human fracture healing has been previously demonstrated. The objective of the present study was to examine the biocompatibility of TGF-β1-silk fibroin-chitosan (TGF-β1-SF-CS) three-dimensional (3D) scaffolds in order to construct an ideal scaffold for bone tissue engineering. We added TGF-β1 directly to the SF-CS scaffold to construct a 3D scaffold for the first time, to the best of our knowledge, and performed evaluations to determine whether it may have potential applications as a growth factor delivery device. Bone marrow-derived mesenchymal stem cells (BMSCs) were seeded on the TGF-β1-SF-CS scaffolds and the silk fibroin-chitosan (SF-CS) scaffolds. On the TGF-β1‑SF-CS and the SF-CS scaffolds, the cell adhesion rate increased in a time‑dependent manner. Using a Cell Counting Kit-8 (CCK-8) assay and analyzing the alkaline phosphatase (ALP) expression proved that TGF-β1 significantly enhanced the growth and proliferation of BMSCs on the SF-CS scaffolds in a time-dependent manner. To examine the in vivo biocompatibility and osteogenesis of the TGF-β1‑SF-CS scaffolds, the TGF-β1-SF-CS scaffolds and the SF-CS scaffolds were implanted in rabbit mandibles and studied histologically and microradiographically. The 3D computed tomography (CT) scan and histological examinations of the samples showed that the TGF-β1-SF-CS scaffolds exhibited good biocompatibility and extensive osteoconductivity with the host bone after 8 weeks. Moreover, the introduction of TGF-β1 to the SF-CS scaffolds markedly enhanced the efficiency of new bone formation, and this was confirmed using bone mineral density (BMD) and biomechanical evaluation, particularly at 8 weeks after implantation. We demonstrated that the TGF-β1‑SF-CS scaffolds possessed as good biocompatibility and osteogenesis as the hybrid ones. Taken together, these findings indicate that the TGF-β1-SF-CS scaffolds fulfilled the basic requirements of bone tissue engineering, and have the potential to be applied in orthopedic, reconstructive and maxillofacial surgery. Thus, TGF-β1-SF-CS composite scaffolds represent a promising, novel type of scaffold for use in bone tissue engineering.

Histochemical and functional improvement of adipose-derived stem cell-based tissue-engineered cartilage by hyperbaric oxygen/air treatment in a rabbit articular defect model

Cartilage is exposed to compression forces during joint loading. Therefore, exogenous stimuli are frequently used in cartilage tissue engineering strategies to enhance chondrocyte differentiation and extracellular matrix (ECM) secretion. In this study, human adipose-derived stem cells were seeded on a gelatin/polycaprolactone scaffold to evaluate the histochemical and functional improvement of tissue-engineered cartilage after hyperbaric oxygen/air treatment in a rabbit articular defect model. Behavior tests showed beneficial effects on weight-bearing and rear leg-supporting capacities after treatment of tissue-engineered cartilage with 2.5 ATA oxygen or air. Moreover, positron emission tomography images and immunohistochemistry staining demonstrated hydroxyapatite formation and increased ECM synthesis, respectively, at the tissue-engineered cartilage graft site after high pressure oxygen/air treatment. Based on these results, we concluded that hyperbaric oxygen and air treatment can improve the quality of tissue-engineered cartilage in vivo by increasing the synthesis of ECM.

Transforming growth factor-beta 1 delivery from microporous scaffolds decreases inflammation post-implant and enhances function of transplanted islets

Biomaterial scaffolds are central to many regenerative strategies as they create a space for infiltration of host tissue and provide a platform to deliver growth factors and progenitor cells. However, biomaterial implantation results in an unavoidable inflammatory response, which can impair tissue regeneration and promote loss or dysfunction of transplanted cells. We investigated localized TGF-β1 delivery to modulate this immunological environment around scaffolds and transplanted cells. TGF-β1 was delivered from layered scaffolds, with protein entrapped within an inner layer and outer layers designed for cell seeding and host tissue integration. Scaffolds were implanted into the epididymal fat pad, a site frequently used for cell transplantation. Expression of cytokines TNF-α, IL-12, and MCP-1 were decreased by at least 40% for scaffolds releasing TGF-β1 relative to control scaffolds. This decrease in inflammatory cytokine production corresponded to a 60% decrease in leukocyte infiltration. Transplantation of islets into diabetic mice on TGF-β1 scaffolds significantly improved the ability of syngeneic islets to control blood glucose levels within the first week of transplant and delayed rejection of allogeneic islets. Together, these studies emphasize the ability of localized TGF-β1 delivery to modulate the immune response to biomaterial implants and enhance cell function in cell-based therapies.

Improved immobilization of gelatin on a modified polyurethane urea

In this study, polyurethane urea was surface-modified to elevate cell recognition through immobilization of bioactive gelatin. The poly(urethane urea) was synthesized using poly(ε-caprolactone) diol in the absence of a chain extender. The synthesized polyurethane urea was then functionalized with gelatin (gelatin-grafted poly(urethane urea)) via aminolysis. Chemical changes at the polyurethane urea surface were monitored using titration, water contact angle. Fourier transform infrared, and zeta potential measurements. Significantly larger amounts of gelatin were grafted on the polyurethane urea surface compared to those previously reported for poly(ε-caprolactone) diol (three times more) and polyurethanes (two times more), while the mechanical properties were not compromised. Proliferation of human adipose–derived mesenchymal stem cells on the polyurethane urea and the gelatin-grafted polyurethane urea was evaluated through MTT assay. Although both samples enhanced human adipose–derived mesenchymal stem cells’ proliferation, gelatin-grafted polyurethane urea supported human adipose–derived mesenchymal stem cells’ proliferation at a remarkably higher rate.

Nanotechnology biomimetic cartilage regenerative scaffolds

Cartilage has a limited regenerative capacity. Faced with the clinical challenge of reconstruction of cartilage defects, the field of cartilage engineering has evolved. This article reviews current concepts and strategies in cartilage engineering with an emphasis on the application of nanotechnology in the production of biomimetic cartilage regenerative scaffolds. The structural architecture and composition of the cartilage extracellular matrix and the evolution of tissue engineering concepts and scaffold technology over the last two decades are outlined. Current advances in biomimetic techniques to produce nanoscaled fibrous scaffolds, together with innovative methods to improve scaffold biofunctionality with bioactive cues are highlighted. To date, the majority of research into cartilage regeneration has been focused on articular cartilage due to the high prevalence of large joint osteoarthritis in an increasingly aging population. Nevertheless, the principles and advances are applicable to cartilage engineering for plastic and reconstructive surgery.

Growth factor conjugation: strategies and applications

Growth factors, first known for their essential role in the initiation of mitosis, are required for a variety of cellular processes and their localized delivery is considered as a rational approach in their therapeutic application to assure a safe and effective treatment while avoiding unwanted adverse effects. Noncovalent immobilization of growth factors as well as their covalent conjugation is amongst the most common strategies for localized delivery of growth factors. Today, immobilized and covalently conjugated growth factors are considered as a promising drug design and are widely used for protein reformulation and material design to cover the unwanted characteristics of growth factors as well as improving their functions. Selection of a suitable conjugation technique depends on the substrate chemistry and the availability of functional reactive groups in the structure of growth factor, the position of reactive groups in growth factor molecules and its relation with the receptor binding area, and the intention of creating either patterned or unpatterned conjugation. Various approaches for growth factor reformulation have been reported. This review provides an overview on chemical conjugation of growth factors and covers the relevant studies accomplished for bioconjugation of growth factors and their related application.

Latent Transforming Growth Factor-beta1 Functionalised Electrospun Scaffolds Promote Human Cartilage Differentiation: Towards an Engineered Cartilage Construct

Background

To overcome the potential drawbacks of a short half-life and dose-related adverse effects of using active transforming growth factor-beta 1 for cartilage engineering, a cell-mediated latent growth factor activation strategy was developed incorporating latent transforming growth factor-β1 (LTGF) into an electrospun poly(L-lactide) scaffold.

Methods

The electrospun scaffold was surface modified with NH₃ plasma and biofunctionalised with LTGF to produce both random and orientated biofunctionalised electrospun scaffolds. Scaffold surface chemical analysis and growth factor bioavailability assays were performed. In vitro biocompatibility and human nasal chondrocyte gene expression with these biofunctionalised electrospun scaffold templates were assessed. In vivo chondrogenic activity and chondrocyte gene expression were evaluated in athymic rats.

Results

Chemical analysis demonstrated that LTGF anchored to the scaffolds was available for enzymatic, chemical and cell activation. The biofunctionalised scaffolds were non-toxic. Gene expression suggested chondrocyte re-differentiation after 14 days in culture. By 6 weeks, the implanted biofunctionalised scaffolds had induced highly passaged chondrocytes to re-express Col2A1 and produce type II collagen.

Conclusions

We have demonstrated a proof of concept for cell-mediated activation of anchored growth factors using a novel biofunctionalised scaffold in cartilage engineering. This presents a platform for development of protein delivery systems and for tissue engineering.

Tissue engineering and regenerative medicine: history, progress, and challenges

The past three decades have seen the emergence of an endeavor called tissue engineering and regenerative medicine in which scientists, engineers, and physicians apply tools from a variety of fields to construct biological substitutes that can mimic tissues for diagnostic and research purposes and can replace (or help regenerate) diseased and injured tissues. A significant portion of this effort has been translated to actual therapies, especially in the areas of skin replacement and, to a lesser extent, cartilage repair. A good amount of thoughtful work has also yielded prototypes of other tissue substitutes such as nerve conduits, blood vessels, liver, and even heart. Forward movement to clinical product, however, has been slow. Another offshoot of these efforts has been the incorporation of some new exciting technologies (e.g., microfabrication, 3D printing) that may enable future breakthroughs. In this review we highlight the modest beginnings of the field and then describe three application examples that are in various stages of development, ranging from relatively mature (skin) to ongoing proof-of-concept (cartilage) to early stage (liver). We then discuss some of the major issues that limit the development of complex tissues, some of which are fundamentals-based, whereas others stem from the needs of the end users.

Natural and Genetically Engineered Proteins for Tissue Engineering

To overcome the limitations of traditionally used autografts, allografts and, to a lesser extent, synthetic materials, there is the need to develop a new generation of scaffolds with adequate mechanical and structural support, control of cell attachment, migration, proliferation and differentiation and with bio-resorbable features. This suite of properties would allow the body to heal itself at the same rate as implant degradation. Genetic engineering offers a route to this level of control of biomaterial systems. The possibility of expressing biological components in nature and to modify or bioengineer them further, offers a path towards multifunctional biomaterial systems. This includes opportunities to generate new protein sequences, new self-assembling peptides or fusions of different bioactive domains or protein motifs. New protein sequences with tunable properties can be generated that can be used as new biomaterials. In this review we address some of the most frequently used proteins for tissue engineering and biomedical applications and describe the techniques most commonly used to functionalize protein-based biomaterials by combining them with bioactive molecules to enhance biological performance. We also highlight the use of genetic engineering, for protein heterologous expression and the synthesis of new protein-based biopolymers, focusing the advantages of these functionalized biopolymers when compared with their counterparts extracted directly from nature and modified by techniques such as physical adsorption or chemical modification.

Biological hydrogel synthesized from hyaluronic acid, gelatin and chondroitin sulfate by click chemistry

In order to mimic the natural cartilage extracellular matrix, which is composed of core proteins and glycosaminoglycans, a biological hydrogel was synthesized from the biopolymers hyaluronic acid (HA), chondroitin sulfate (CS) and gelatin via click chemistry. HA and CS were modified with 11-azido-3,6,9-trioxaundecan-1-amine (AA) and gelatin was modified with propiolic acid (PA). The molecular structures were verified by (1)H nuclear magnetic resonance, infrared spectroscopy and elemental analysis, giving substitution degrees of 29%, 89% and 44% for HA-AA, CS-AA and gelatin-PA (G-PA), respectively. The -N(3) groups of HA-AA and CS-AA were reacted with the acetylene groups of G-PA, catalyzed by Cu(I), to form triazole rings, thereby forming a cross-linked hydrogel. The gelation time was decreased monotonically with increasing Cu(I) concentration up to 0.95 mg ml(-1). The hydrogel obtained was in a highly swollen state and showed the characteristics of an elastomer. Incubation in phosphate-buffered saline for 4 weeks resulted in a weight loss of up to 45%. Moreover, about 20% gelatin and 10% CS were released from the hydrogel in 2 weeks. In vitro cell culture showed that the hydrogel could support the adhesion and proliferation of chondrocytes.

Potential applications of natural origin polymer-based systems in soft tissue regeneration

Despite the many advances in tissue engineering approaches, scientists still face significant challenges in trying to repair and replace soft tissues. Nature-inspired routes involving the creation of polymer-based systems of natural origins constitute an interesting alternative route to produce novel materials. The interest in these materials comes from the possibility of constructing multi-component systems that can be manipulated by composition allowing one to mimic the tissue environment required for the cellular regeneration of soft tissues. For this purpose, factors such as the design, choice, and compatibility of the polymers are considered to be key factors for successful strategies in soft tissue regeneration. More recently, polysaccharide-protein based systems have being increasingly studied and proposed for the treatment of soft tissues. The characteristics, properties, and compatibility of the resulting materials investigated in the last 10 years, as well as commercially available matrices or those currently under investigation are the subject matter of this review.

TGF-β3 immobilized PLGA-gelatin/chondroitin sulfate/hyaluronic acid hybrid scaffold for cartilage regeneration

Although most in vitro studies indicate that transforming growth factor β3 (TGF-β3) immobilized scaffold is suitable for cartilage tissue engineering, in vivo studies of implanting immobilized scaffold for chondral defect repair are still lacking. This study is to evaluate the potentials of TGF-β3 immobilized poly-(lactic-co-glycolic acid)-gelatin/chondroitin sulfate/hyaluronic acid (PLGA-GCH) hybrid scaffold for cartilage regeneration. The scaffold was fabricated by incorporating GCH micro-sponges into PLGA frameworks and then crosslinked with TGF-β3 to mimic natural cartilaginous extra cellular matrix (ECM). In vitro study demonstrated that MSCs proliferated vigorously and produced abundant ECM on scaffold. The immunohistochemistry staining and alcian blue staining confirmed the cartilaginous ECM production. The chondrogenic differentiation of MSCs on scaffold was proved by the expression of collagen II gene in mRNA and protein level. Then MSCs/TGF-β3 immobilized scaffolds were implanted in rabbits for chondral defects repair. After eight weeks, histological observation showed that differentiated MSCs were located in lacunae within the metachromatic staining matrix and exhibited typical chondrocyte morphology. Histological grading scores also indicated the congruent cartilage was regenerated. In conclusion, the TGF-β3 immobilized PLGA-GCH hybrid scaffold has great potential in constructing the tissue-engineered cartilage.

Engineering nanoassemblies of polysaccharides

Polysaccharides offer a wealth of biochemical and biomechanical functionality that can be used to develop new biomaterials. In mammalian tissues, polysaccharides often exhibit a hierarchy of structure, which includes assembly at the nanometer length scale. Furthermore, their biochemical function is determined by their nanoscale organization. These biological nanostructures provide the inspiration for developing techniques to tune the assembly of polysaccharides at the nanoscale. These new polysaccharide nanostructures are being used for the stabilization and delivery of drugs, proteins, and genes, the engineering of cells and tissues, and as new platforms on which to study biochemistry. In biological systems polysaccharide nanostructures are assembled via bottom-up processes. Many biologically derived polysaccharides behave as polyelectrolytes, and their polyelectrolyte nature can be used to tune their bottom-up assembly. New techniques designed to tune the structure and composition of polysaccharides at the nanoscale are enabling researchers to study in detail the emergent biological properties that arise from the nanoassembly of these important biological macromolecules.

Controlling stem cell fate with material design

Advances in our understanding of stem cell interactions with their environment are leading to the development of new materials-based approaches to control stem cell behavior toward cellular culture and tissue regeneration applications. Materials can provide cues based on chemistry, mechanics, structure, and molecule delivery that control stem cell fate decisions and matrix formation. These approaches are helping to advance clinical translation of a range of stem cell types through better expansion techniques and scaffolding for use in tissue engineering approaches for the regeneration of many tissues. With this in mind, this progress report covers basic concepts and recent advances in the use of materials for manipulating stem cells.

Cartilage repair: current and emerging options in treatment

Currently, there are many options in cartilage repair. These cartilage repair techniques can generally be categorized into 3 groups: marrow stimulation-based techniques, osteochondral transfer techniques, and cell-based cartilage repair techniques. This review article presents an overview of these techniques, indications for usage, advantages and disadvantages of each, and a current review of applications in foot and ankle surgery.

Novel composite hyaluronan/type I collagen/fibrin scaffold enhances repair of osteochondral defect in rabbit knee

A new composite scaffold containing type I collagen, hyaluronan, and fibrin was prepared with and without autologous chondrocytes and implanted into a rabbit femoral trochlea. The biophysical properties of the composite scaffold were similar to native cartilage. The macroscopic, histological, and immunohistochemical analysis of the regenerated tissue from cell-seeded scaffolds was performed 6 weeks after the implantation and predominantly showed formation of hyaline cartilage accompanied by production of glycosaminoglycans and type II collagen with minor fibro-cartilage production. Implanted scaffolds without cells healed predominantly as fibro-cartilage, although glycosaminoglycans and type II collagen, which form hyaline cartilage, were also observed. On the other hand, fibro-cartilage or fibrous tissue or both were only formed in the defects without scaffold. The new composite scaffold containing collagen type I, hyaluronan, and fibrin, seeded with autologous chondrocytes and implanted into rabbit femoral trochlea, was found to be highly effective in cartilage repair after only 6 weeks. The new composite scaffold can therefore enhance cartilage regeneration of osteochondral defects, by the supporting of the hyaline cartilage formation.

The use of scaffolds in the management of articular cartilage injury

Managing articular cartilage injury continues to be a difficult challenge for the clinician. Although the short- and intermediate-term results of autologous chondrocyte implantation appear to be favorable, resources are being directed toward research to improve the technology. One promising area of investigation is the combination of cultured chondrocytes with scaffolds. Clinicians desire techniques that may be implanted easily, reduce surgical morbidity, do not require harvesting of other tissues, exhibit enhanced cell proliferation and maturation, have easier phenotype maintenance, and allow for efficient and complete integration with surrounding articular cartilage. The characteristics that make scaffolds optimal for clinical use are that they be biocompatible, biodegradable, permeable, reproducible, mechanically stable, noncytotoxic, and capable of serving as a temporary support for the cells while allowing for eventual replacement by matrix components synthesized by the implanted cells. Clinical experience is growing with three scaffold-based cartilage repair techniques, each using a different type of scaffold material: matrix-induced autologous chondrocyte implantation, a hyaluronic acid-based scaffold, and a composite polylactic/polyglycolic acid polymer fleece. Clinical results are encouraging. Future directions in scaffold-based cartilage repair include bioactive and spatially oriented scaffolds.

Characterization of collagen II fibrils containing biglycan and their effect as a coating on osteoblast adhesion and proliferation

Collagen has been used as a coating material for titanium-based implants for bone contact and as a component of scaffolds for bone tissue engineering. In general collagen type I has been used, however very little attention has been focussed on collagen type II. Collagen-based coatings and scaffolds have been enhanced by the incorporation of the glycosaminoglycan chondroitin sulphate (CS), however the proteglycan biglycan, which is found in bone and contains glycosaminoglycan chains consisting of CS, has not been used as a biomaterial component. The study had the following aims: firstly, five different collagen II preparations were compared with regard to their ability to bind CS and biglycan and the changes in fibril morphology thereby induced. Secondly, the effects of biglycan on the adhesion of primary rat osteoblasts (rO) as well as the proliferation of rO, primary human osteoblasts (hO) and the osteoblast-like cell line 7F2 were studied by culturing the cells on surfaces coated with collagen II fibrils containing biglycan. Fibrils of the collagen II preparation which bound the most biglycan were used to coat titanium surfaces. Bare titanium, titanium coated with collagen II fibrils and titanium coated with collagen II fibrils containing biglycan were compared. It was found that different collagen II preparations showed different affinities for CS and biglycan. In four of the five preparations tested, biglycan reduced fibril diameter, however the ability of a preparation to bind more biglycan did not appear to lead to a greater reduction in fibril diameter. Fibrils containing biglycan promoted the formation of focal adhesions by rO and significantly enhanced the proliferation of hO but not of rO or 7F2 cells. These results should encourage further investigation of biglycan as a component of collagen-based scaffolds and/or coatings.

Influence of collagen-fibril-based coatings containing decorin and biglycan on osteoblast behavior

Collagen is used as a scaffold material for tissue engineering as well as a coating material for implants with a view to enhancing osseointegration by mimicry of the bone extracellular matrix in vivo. The biomimicry strategy can be taken further by incorporating the small leucine-rich proteoglycans (SLRPs) decorin and biglycan, which are expressed in bone. Both bind to fibrils during fibrillogenesis in vitro. In this study, the ability of collagen types I, II, and III to bind decorin and biglycan was compared. Collagen type II bound significantly more SLRPs in fibrils than collagen I and III, with more biglycan than decorin bound by all three collagen types. Therefore, type II fibrils with bound decorin or biglycan or neither were used to coat titanium surfaces. Bioavailability of SLRPs was confirmed by direct ELISA after SLRP biotinilation. The in vitro behavior of osteoblasts from rat calvaria (rOs) and human knee (hOs) cultured on different surfaces was compared. Proliferation and collagen synthesis were determined. Also, the influence of SLRPs on the formation of focal adhesions by rO was investigated. Biglycan enhanced the formation of focal adhesions after 2 and 24 h. Decorin and biglycan affected rO and hO proliferation and collagen synthesis differently. Biglycan stimulated hO proliferation significantly but had no effect on rO proliferation, and also inhibited rO collagen synthesis significantly while not affecting hO collagen synthesis. Decorin promoted hO proliferation slightly but did not influence rO proliferation. The results could be relevant when designing implant coatings or tissue engineering scaffolds.

Covalently immobilized biosignal molecule materials for tissue engineering

Immobilization of biosignal molecules including growth factors and cytokines is important for developing biologically active materials which can contribute to tissue engineering as a component. The immobilization has more meanings than only immobilization of the enzyme in a bioreactor or ligand-receptor interactions, because the immobilized biosignal molecules work on cells which have very complex structures and functions. This review discusses recent progress in immobilization of biosignal molecules, including the mechanisms and design concepts.

Matrices and scaffolds for drug delivery in dental, oral and craniofacial tissue engineering

Current treatments for diseases and trauma of dental, oral and craniofacial (DOC) structures rely on durable materials such as amalgam and synthetic materials, or autologous tissue grafts. A paradigm shift has taken place to utilize tissue engineering and drug delivery approaches towards the regeneration of these structures. Several prototypes of DOC structures have been regenerated such as temporomandibular joint (TMJ) condyle, cranial sutures, tooth structures and periodontium components. However, many challenges remain when taking in consideration the high demand for esthetics of DOC structures, the complex environment and yet minimal scar formation in the oral cavity, and the need for accommodating multiple tissue phenotypes. This review highlights recent advances in the regeneration of DOC structures, including the tooth, periodontium, TMJ, cranial sutures and implant dentistry, with specific emphasis on controlled release of signaling cues for stem cells, biomaterial matrices and scaffolds, and integrated tissue engineering approaches.

Fibrin glue mixed with gelatin/hyaluronic acid/chondroitin-6-sulfate tri-copolymer for articular cartilage tissue engineering: The results of real-time polymerase chain reaction

Autologous fibrin glue has been demonstrated as a potential scaffold with very good biocompatibility for neocartilage formation. However, fibrin glue has been reported not to provide enough mechanical strength, but with many growth factors to interfere the tissue growth. Gelatin/hyaluronic acid/chondroitin-6-sulfate (GHC6S) tri-copolymer sponge has been prepared as scaffold for cartilage tissue engineering and showed very good results, but problems of cell seeding and cell distribution troubled the researchers. In this study, GHC6S particles would be added into the fibrin glue to provide better mechanical strength, better cell distribution, and easier cell seeding, which would be expected to improve cartilage regeneration in vitro. Porcine cryo-precipitated fibrinogen and thrombin prepared from prothrombin activated by 10% CaCl(2) solution were used in two groups. One is the fibrin glue group in which porcine chondrocytes were mixed with thrombin-fibrinogen solution, which was then converted into fibrin glue. The other is GHC6S-fibrin glue in which GHC6S particles were added into the thrombin-fibrinogen solution with porcine chondrocytes. After culturing for 1-2 weeks, the chondrocytes cultured in GHC6S-fibrin glue showed a round shape with distinct lacuna structure and showed positive in S-100 protein immunohistochemical stain. The related gene expressions of tissue inhibitor of metalloproteinases-1, matrix metalloproteinase-2, MT1-MMP, aggrecan, decorin, type I, II, X collagen, interleukin-1 beta, transforming growth factor-beta 1 (TGF-beta1), and Fas-associating death domain were checked by real-time PCR. The results indicated that the chondrocytes cultured in GHC6S-fibrin glue would effectively promote extracellular matrix (ECM) secretion and inhibit ECM degradation. The evidence could support that GHC6S-fibrin glue would be a promising scaffold for articular cartilage tissue engineering.