In VitroandIn VivoCartilage Engineering Using a Combination of Chondrocyte-Seeded Long-Term Stable Fibrin Gels and Polycaprolactone-Based Polyurethane Scaffolds

In-Vitro Evaluation of Novel Polycaprolactone/ Chitosan/ Carbon Nano Tube Scaffold for Tissue Regeneration

BACKGROUND

Many patients lose their organs or tissues due to disease, trauma, or a variety of genetic disorders. Tissue engineering is a multidisciplinary science to regenerate or restore tissue or organ function and an appropriate scaffold is the first and certainly a crucial step in tissue engineering strategies.

OBJECTIVE

The purpose of this study is to fabricate and evaluate the in-vitro response of porous nano Polycaprolactone (PCL)/ chitosan/ multi-wall carbon nanotube (MWCNTs) scaffold for tissue regeneration.

MATERIAL AND METHODS

In this experimental research, a novel scaffold containing MWCNTs in polycaprolactone/chitosan nanofibrous scaffold was synthesized by electrospinning technique.

RESULTS

According to scanning electron microscopy SEM images, by increasing the number of MWCNT in the scaffold by 2%, the average diameter decreased significantly for fabricated scaffolds with 5% MWCNTs. Based on the results, the scaffolds plunged from submicron to nanoscale fibers at about 80 nm. In addition, by adding more MWCNT to the nanofibrous scaffold, the biodegradation rate was decreased by 32%. However, mechanical characterization demonstrates that the higher level of MWCNT increases young modulus by 96%, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay illustrated that MWCNTs could enhance bioactivity and cell- scaffold relationship in addition to alkaline phosphatase (ALP).

CONCLUSION

MWCNT significantly improves the physical and mechanical properties of fabricated scaffolds and in-vitro assessment demonstrated that the prepared nanofibrous scaffold containing 4% MWCNT could be a very useful biocompatible material for tissue engineering.

A Fibrin Coating Method of Polypropylene Meshes Enables the Adhesion of Menstrual Blood-Derived Mesenchymal Stromal Cells: A New Delivery Strategy for Stem Cell-Based Therapies

Polypropylene (PP) mesh is well-known as a gold standard of all prosthetic materials of choice for the reinforcement of soft tissues in case of hernia, organ prolapse, and urinary incontinence. The adverse effects that follow surgical mesh implantation remain an unmet medical challenge. Herein, it is outlined a new approach to allow viability and adhesion of human menstrual blood-derived mesenchymal stromal cells (MenSCs) on PP surgical meshes. A multilayered fibrin coating, based on fibrinogen and thrombin from a commercial fibrin sealant, was optimized to guarantee a homogeneous and stratified film on PP mesh. MenSCs were seeded on the optimized fibrin-coated meshes and their adhesion, viability, phenotype, gene expression, and immunomodulatory capacity were fully evaluated. This coating guaranteed MenSC viability, adhesion and did not trigger any change in their stemness and inflammatory profile. Additionally, MenSCs seeded on fibrin-coated meshes significantly decreased CD4+ and CD8+ T cell proliferation, compared to in vitro stimulated lymphocytes (p < 0.0001). Hence, the proposed fibrin coating for PP surgical meshes may allow the local administration of stromal cells and the reduction of the exacerbated inflammatory response following mesh implantation surgery. Reproducible and easy to adapt to other cell types, this method undoubtedly requires a multidisciplinary and translational approach to be improved for future clinical uses.

Differentiation Behaviour of Adipose-Derived Stromal Cells (ASCs) Seeded on Polyurethane-Fibrin Scaffolds In Vitro and In Vivo

Adipose-derived stromal cells (ASCs) are a promising cell source for tissue engineering and regenerative medicine approaches for cartilage replacement. For chondrogenic differentiation, human (h)ASCs were seeded on three-dimensional polyurethane (PU) fibrin composites and induced with a chondrogenic differentiation medium containing TGF-ß3, BMP-6, and IGF-1 in various combinations. In addition, in vitro predifferentiated cell-seeded constructs were implanted into auricular cartilage defects of New Zealand White Rabbits for 4 and 12 weeks. Histological, immunohistochemical, and RT-PCR analyses were performed on the constructs maintained in vitro to determine extracellular matrix (ECM) deposition and expression of specific cartilage markers. Chondrogenic differentiated constructs showed a uniform distribution of cells and ECM proteins. RT-PCR showed increased gene expression of collagen II, collagen X, and aggrecan and nearly stable expression of SOX-9 and collagen I. Rabbit (r)ASC-seeded PU-fibrin composites implanted in ear cartilage defects of New Zealand White Rabbits showed deposition of ECM with structures resembling cartilage lacunae by Alcian blue staining. However, extracellular calcium deposition became detectable over the course of 12 weeks. RT-PCR showed evidence of endochondral ossification during the time course with the expression of specific marker genes (collagen X and RUNX-2). In conclusion, hASCs show chondrogenic differentiation capacity in vitro with the expression of specific marker genes and deposition of cartilage-specific ECM proteins. After implantation of predifferentiated rASC-seeded PU-fibrin scaffolds into a cartilage defect, the constructs undergo the route of endochondral ossification.

Evaluation of Fibrin-Agarose Tissue-Like Hydrogels Biocompatibility for Tissue Engineering Applications

Generation of biocompatible and biomimetic tissue-like biomaterials is crucial to ensure the success of engineered substitutes in tissue repair. Natural biomaterials able to mimic the structure and composition of native extracellular matrices typically show better results than synthetic biomaterials. The aim of this study was to perform an in vivo time-course biocompatibility analysis of fibrin-agarose tissue-like hydrogels at the histological, imagenological, hematological, and biochemical levels. Tissue-like hydrogels were produced by a controlled biofabrication process allowing the generation of biomechanically and structurally stable hydrogels. The hydrogels were implanted subcutaneously in 25 male Wistar rats and evaluated after 1, 5, 9, and 12 weeks of in vivo follow-up. At each period of time, animals were analyzed using magnetic resonance imaging (MRI), hematological analyses, and histology of the local area in which the biomaterials were implanted, along with major vital organs (liver, kidney, spleen, and regional lymph nodes). MRI results showed no local or distal alterations during the whole study period. Hematology and biochemistry showed some fluctuation in blood cells values and in some biochemical markers over the time. However, these parameters were progressively normalized in the framework of the homeostasis process. Histological, histochemical, and ultrastructural analyses showed that implantation of fibrin-agarose scaffolds was followed by a progressive process of cell invasion, synthesis of components of the extracellular matrix (mainly, collagen) and neovascularization. Implanted biomaterials were successfully biodegraded and biointegrated at 12 weeks without any associated histopathological alteration in the implanted zone or distal vital organs. In summary, our in vivo study suggests that fibrin-agarose tissue-like hydrogels could have potential clinical usefulness in engineering applications in terms of biosafety and biocompatibility.

Cell-Free Scaffolds as a Monotherapy for Focal Chondral Knee Defects

Chondral knee defects have a limited ability to be repaired. Current surgical interventions have been unable to regenerate articular cartilage with the mechanical properties of native hyaline cartilage. The use of a scaffold-based approach is a potential solution. Scaffolds are often implanted with cells to stimulate cartilage regeneration, but cell-based therapies are associated with additional regulatory restrictions, an additional surgical procedure for cell harvest, time for cell expansion, and the associated costs. To overcome these disadvantages, cell-free scaffolds can be used in isolation allowing native cells to attach over time. This review discusses the optimal properties of scaffolds used for chondral defects, and the evidence for the use of hydrogel scaffolds and hydrogel-synthetic polymer hybrid scaffolds. Preclinical and clinical studies have shown that cell-free scaffolds can support articular cartilage regeneration and have the potential to treat chondral defects. However, there are very few studies in this area and, despite the many biomaterials tested in cell-based scaffolds, most cell-free studies focused on a specific type I collagen scaffold. Future studies on cell-free scaffolds should adopt the modifications made to cell-based scaffolds and replicate them in the clinical setting. More studies are also needed to understand the underlying mechanism of cell-free scaffolds.

Controlled curcumin release from nanofibers based on amphiphilic-block segmented polyurethanes

A series of biodegradable amphiphilic-block segmented polyurethanes (SPUs) are designed and synthesized based on di-block and tri-block macrodiols of polycaprolactone (PCL) and polyethylene glycol (PEG). Curcumin, as a model herbal antibacterial agent, is used due to its effective inhibitory action against Gram-positive and Gram-negative bacteria. Curcumin-loaded nanofibers, with 400-900 nm diameter range, have been prepared by electrospinning of SPUs. The synthesized SPUs can be used for wound dressing applications due to their excellent mechanical properties and higher hydrophilicity in comparison to PCL-based polyurethane. The elongation-at-break of tri-block SPU with PEG-PCL-PEG soft segments is 350% when produced as an electrospun mat and that for film is 1500%. In vitro release of curcumin, examined by UV-Vis spectroscopy, shows a steady release during 18 days. The inclusion of PEG chains in the soft segment increases the hydrophilicity and biodegradation rate of the electrospun mats compared to a PCL-based polyurethane, which eventually results in a higher curcumin release rate. The antibacterial activity of 50 mg of 10% curcumin-loaded SPU nanofibers is about 100% and 93% against Escherichia coli (E. coli ATCC: 25922) and Staphylococcus aureus (S. aureus ATCC: 6538), respectively. Nontoxic behavior of the scaffolds is evaluated through MTT assay against L929 mouse fibroblast cells. The results show that the synthesized SPUs can be used as a nanoscale sustained release carrier. The SPU with PEG-PCL-PEG soft segments is an excellent candidate for wound dressing in tissues undergoing large deformations during normal activities.

Using Chitosan Besides Nano Hydroxyapatite and Fluorohydroxyapatite Boost Dental Pulp Stem Cell Proliferation

The dental tissue scaffold must provide a favorable surface for dental pulp stem cell attachment and proliferation. Employing nanohydroxyapatite (HA) and nanofluorohydroxyapatite (FHA) beside synthetic and organic polymer in favor of scaffolds would be used in bone and dental tissue engineering. In this research, nanoHA and FHA/chitosan scaffolds were synthesized by freeze-drying technique. Surface morphology, chemical composition and hydrophilicity have a great impact on initial cell attachment which will further affect the cell viability and proliferation which evaluated by SEM, XRD and contact angle measurement. Bioactivity of scaffolds was investigated by immersion in simulated body fluid (SBF) and cell proliferation assay. In freeze-drying technique percentage usage of hydroxyapatite could be risen up to 40% and shown better macro-mechanical and physical properties and bioactivity. According to obtained results by adding chitosan, contact angle was decreased by %54 and %37 for polycaprolactone (PCL)/HA and PCL/FHA scaffolds. In addition, addition of chitosan causes significant increase in the cell proliferation for PCL/HA and PCL/FHA up to 81% and 164%, respectively. These results indicate that PCL/FHA/chitosan scaffold represent a big potential for dental tissue engineering.

Anisotropic magnetic hydrogels: design, structure and mechanical properties

Anisotropy is an intrinsic feature of most of the human tissues (e.g. muscle, skin or cartilage). Because of this, there has been an intense effort in the search of methods for the induction of permanent anisotropy in hydrogels intended for biomedical applications. The dispersion of magnetic particles or beads in the hydrogel precursor solution prior to cross-linking, in combination with applied magnetic fields, which gives rise to columnar structures, is one of the most recently proposed approaches for this goal. We have gone even further and, in this paper, we show that it is possible to use magnetic particles as actuators for the alignment of the polymer chains in order to obtain anisotropic hydrogels. Furthermore, we characterize the microstructural arrangement and mechanical properties of the resulting hydrogels. This article is part of a theme issue 'Heterogeneous materials: metastable and non-ergodic internal structures'.

Nondegradable magnetic poly (carbonate urethane) microspheres with good shape memory as a proposed material for vascular embolization

In this study, nondegradable poly (carbonate urethane) (PCU) and poly (carbonate urethane) incorporated variable Fe₃O₄ content microspheres (PCU/Fe₃O₄) were synthesized using pre-polymerization and suspension polymerization. Synthesis was confirmed through Fourier transform infrared spectroscopy (FTIR). The effect of Fe₃O₄ incorporation was investigated on crystalline, thermal, shape memory and degradation properties by X-Ray diffraction (XRD), Differential scanning calorimetery (DSC), compression test and degradation in vitro, respectively. Otherwise, the assessment of magnetic characteristics by vibrational sample magnetometry (VSM) disclosed superparamagnetic behavior. The tunable superparamagnetic behavior depends on the amount of magnetic particles incorporated within the networks. The biological study results of as-synthesized polymers from the platelet adhesion test and the cell proliferation inhibition test indicated they were biocompatible in vitro. Fe₃O₄ incorporation was conductive to reducing platelet adhesion in blood contacting test and promotion of rat vascular smooth muscle cell proliferation and growth. These nondegradable, superparamagnetic, biocompatible polymers, combined with their good shape memory properties may allow for their future exploitation in the biomedical field, such as, in cardiovascular implants, targeted tumor treatment, tissue engineering and artificial organ's engineering.

Amniotic membrane-derived stem cells help repair osteochondral defect in a weight-bearing area in rabbits

Our study evaluated the use of amniotic membrane-derived stem cells for repairing osteochondral defects in a weight-bearing area in rabbits. Twenty-four 3-month-old male or female New Zealand white rabbits were selected. The rabbits were randomly divided into 3 groups of eight, according to the treatment received for an experimentally inflicted femoral medial malleolus lesion, group I received a human acellular amniotic membrane seeded with bone marrow-derived mesenchymal stem cells (HAAM-BMSCs) implant; group II received a simple HAAM implant and the control group received no experimental lesion or treatment. The rabbits were sacrificed at 12 and 24 weeks after the procedures (4 rabbits in each time-point) and the cartilage repair status in each animal was evaluated under the microscope. The tissue of the HAAM-BMSCs group grew well covering an area in the visual field that was significantly larger than that of the HAAM group (p<0.05). The percentage of collagen II-positive area in the HAAM-BMSC group was significantly higher than that in HAAM group (p<0.05). The number of chondrocytes determined by toluidine blue staining was higher in the HAAM-BMSC group than that in the HAAM group (p<0.05). The Wakitani scores of the HAAM and HAAM-BMSC groups were significantly higher (worse) than those of the normal control group (p<0.05), but the score in the HAAM-BMSC group was significantly lower than that in the HAAM group (p<0.05). The Wakitani scores in the HAAM-BMSC group were not different between the two time-points taken. Based on our findings, the amniotic membrane-derived stem cells had a good therapeutic effect in repairing the osteochondral defects in the weight-bearing area, and the number of chondrocytes in the injured area was increased significantly, which accelerated the repair of the damaged tissue in rabbits.

Polymers in Cartilage Defect Repair of the Knee: Current Status and Future Prospects

Cartilage defects in the knee are often seen in young and active patients. There is a need for effective joint preserving treatments in patients suffering from cartilage defects, as untreated defects often lead to osteoarthritis. Within the last two decades, tissue engineering based techniques using a wide variety of polymers, cell sources, and signaling molecules have been evaluated. We start this review with basic background information on cartilage structure, its intrinsic repair, and an overview of the cartilage repair treatments from a historical perspective. Next, we thoroughly discuss polymer construct components and their current use in commercially available constructs. Finally, we provide an in-depth discussion about construct considerations such as degradation rates, cell sources, mechanical properties, joint homeostasis, and non-degradable/hybrid resurfacing techniques. As future prospects in cartilage repair, we foresee developments in three areas: first, further optimization of degradable scaffolds towards more biomimetic grafts and improved joint environment. Second, we predict that patient-specific non-degradable resurfacing implants will become increasingly applied and will provide a feasible treatment for older patients or failed regenerative treatments. Third, we foresee an increase of interest in hybrid construct, which combines degradable with non-degradable materials.

Platelet-rich plasma gel composited with nondegradable porous polyurethane scaffolds as a potential auricular cartilage alternative

Total auricular reconstruction is still a challenge, and autologous cartilage transplant is the main therapy so far. Tissue engineering provides a promising method for auricular cartilage reconstruction. However, although degradable framework demonstrated excellent initial cosmetic details, it is difficult to maintain the auricular contour over time and the metabolites tended to be harmful to human body. In this study, biocompatible and safe nondegradable elastic polyurethane was used to make porous scaffold in specific details by rapid prototyping technology. Platelet-rich plasma contains fibrin and abundant autologous growth factors, which was used as cell carriers for in vitro expanded cells. When crosslinking polyurethane framework, platelet-rich plasma and cells together, we successfully made polyurethane/platelet-rich plasma/cell composites, and implanted them into dorsal subcutaneous space of nude mice. The results showed that this method resulted in more even cell distribution and higher cell density, promoted chondrocyte proliferation, induced higher level expressions of aggrecan and type II collagen gene, increased content of newly developed glycosaminoglycans, and produced high-quality cartilaginous tissue. This kind of cartilage tissue engineering approach may be a potential promising alternative for external ear reconstruction.

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.

Combined use of crushed cartilage and fibrin sealant for radix augmentation in Asian rhinoplasty

BACKGROUND

Crushed cartilage grafts are used to conceal irregularities and achieve a smoother nasal surface. They can potentially be stabilized by a fibrin sealant acting as a carrier. The primary purpose of this study was to assess the clinical outcome of crushed cartilage-fibrin sealant combination grafts for radix augmentation performed in Asian patients.

METHODS

This study included 51 patients (38 men and 13 women) who underwent rhinoplasty with radix augmentation using crushed cartilage grafts. The malleable construct used for radix augmentation contained autologous crushed cartilage grafts stabilized with a fibrin sealant. Preoperative and postoperative photographs were reviewed for objective and subjective assessment of aesthetic outcomes. The mean follow-up period was 18.5 months (range, 12 to 25 months).

RESULTS

Preoperative and postoperative objective measurements indicated that the mean increment of the radix projection was 28.5 ± 7.9 percent and that of the nasofrontal angle was 11.5 ± 3.8 degrees. Most patients showed prominent radix augmentation and good cosmetic results. Postoperative aesthetic outcomes were graded as excellent in 41.2 percent of cases, good in 37.3 percent, fair in 15.7 percent, and unchanged/poor in 5.9 percent. Complications included one case (2.0 percent) of partial graft resorption and two cases (3.9 percent) of graft visibility.

CONCLUSIONS

The results show that the use of a crushed cartilage-fibrin sealant graft is a reliable and effective technique of stabilizing grafts for radix augmentation in Asian patients.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Vascularization of engineered cartilage constructs in a mouse model

Tissue engineering of cartilage tissue offers a promising method for reconstructing ear, nose, larynx and trachea defects. However, a lack of sufficient nutrient supply to cartilage constructs limits this procedure. Only a few animal models exist to vascularize the seeded scaffolds. In this study, polycaprolactone (PCL)-based polyurethane scaffolds are seeded with 1 × 10(6) human cartilage cells and implanted in the right hind leg of a nude mouse using an arteriovenous flow-through vessel loop for angiogenesis for the first 3 weeks. Equally seeded scaffolds but without access to a vessel loop served as controls. After 3 weeks, a transposition of the vascularized scaffolds into the groin of the nude mouse was performed. Constructs (verum and controls) were explanted 1 and 6 weeks after transposition. Constructs with implanted vessels were well vascularized. The amount of cells increased in vascularized constructs compared to the controls but at the same time noticeably less extracellular matrix was produced. This mouse model provides critical answers to important questions concerning the vascularization of engineered tissue, which offers a viable option for repairing defects, especially when the desired amount of autologous cartilage or other tissues is not available and the nutritive situation at the implantation site is poor.

Updates in biological therapies for knee injuries: full thickness cartilage defect

Full thickness cartilage defect might occur at different ages, but a focal defect is a major concern in the knee of young athletes. It causes impairment and does not heal by itself. Several techniques were described to treat symptomatic full thickness cartilage defect. Recently, several advances were described on the known techniques of microfracture, osteochondral allograft, cell therapy, and others. This article brings an update of current literature on these well-described techniques for full thickness cartilage defect.

Novel nano-rough polymers for cartilage tissue engineering

This study presents an innovative method for creating a highly porous surface with nanoscale roughness on biologically relevant polymers, specifically polyurethane (PU) and polycaprolactone (PCL). Nanoembossed polyurethane (NPU) and nanoembossed polycaprolactone (NPCL) were produced by the casting of PU and PCL over a plasma-deposited, spiky nanofeatured crystalline titanium (Ti) surface. The variables used in the process of making the spiky Ti surface can be altered to change the physical properties of the spiky particles, and thus, the cast polymer substrate surface can be altered. The spiky Ti surface is reusable to produce additional nanopolymer castings. In this study, control plain PU and PCL polymers were produced by casting the polymers over a plain Ti surface (without spikes). All polymer surface morphologies were characterized using both scanning electron microscopy and atomic force microscopy, and their surface energies were measured using liquid contact angle measurements. The results revealed that both NPU and NPCL possessed a higher degree of nanometer surface roughness and higher surface energy compared with their respective unaltered polymers. Further, an in vitro study was carried out to determine chondrocyte (cartilage-producing cells) functions on NPU and NPCL compared with on control plain polymers. Results of this study provided evidence of increased chondrocyte numbers on NPU and NPCL compared with their respective plain polymers after periods of up to 7 days. Moreover, the results provide evidence of greater intracellular protein production and collagen secretion by chondrocytes cultured on NPU and NPCL compared with control plain polymers. In summary, the present in vitro results of increased chondrocyte functions on NPU and NPCL suggest these materials may be suitable for numerous polymer-based cartilage tissue-engineering applications and, thus, deserve further investigation.

Morphology, mechanical properties, and shape memory effects of poly(lactic acid)/ thermoplastic polyurethane blend scaffolds prepared by thermally induced phase separation

Novel blended scaffolds combining biobased polylactic acid (PLA) and thermoplastic polyurethane (TPU) were fabricated by thermally induced phase separation (TIPS) using two different solvents. Pure PLA and TPU polymer scaffolds using 1,4-dioxane as the sole solvent exhibited typical ladder-like structures, while blended PLA/TPU scaffolds using the same solvent showed a more uniform microstructure. When de-ionized water was added to the solution as a non-solvent, scaffolds with the mixed solvent showed more open cells and greater interconnectivity. In compression tests, it was found that specimens, including pure PLA, TPU, and blended scaffolds with the mixed solvent, showed a higher compressive modulus than their counterparts that used dioxane as the single solvent. Dynamic mechanical analysis (DMA) was employed to characterize the shape memory properties of the scaffolds. DMA indicated that the shape fixing ratio was highest in the PLA scaffolds, while the shape recovery ratio of the TPU scaffolds was the greatest among the specimens. More interestingly, when the mixed solvent was used, the shape memory property of the blended scaffolds displayed a similar deformation curve to the TPU scaffold. This was due to the presence of the TPU phase and similarity in structure between PLA/TPU and TPU scaffolds when mixed solvent was used. In the degradation test, the blended scaffolds showed a balanced degradation behavior in-between the more easily degraded PLA and the more stable TPU in the phosphate-buffered saline (PBS), and the addition of water to the systems accelerated the degradation process of the specimens. Cell culture results showed that all of the scaffolds had good biocompatibility.

Biomimetic polyurethanes in nano and regenerative medicine

Nature's inspiration is a promising tool to design new biomaterials especially for frontier technological areas such as tissue engineering and nanomedicine.

A synthetic oxygen carrier-olfactory ensheathing cell composition system for the promotion of sciatic nerve regeneration

The treatment of lengthy peripheral nerve defects is challenging in the field of the regenerative medicine. Thus far, many nerve scaffolds with seeded cells have been developed, which hold great potential to replace nerve autograft in bridging lengthy nerve defects by providing guiding and bioactive cues. However, low oxygen status has been found within nerve scaffolds after their implantation in vivo, which has been shown to result in death or loss of function of supportive cells, and significantly limit nerve regeneration and functional recovery after nerve injury. In the present study, perfluorotributylamine (PFTBA) was introduced into a collagen-chitosan conduit within which olfactory ensheathing cells (OECs) were seeded to increase oxygen supply to OECs, as well as regenerating axons. The "PFTBA-OECs" enriched scaffolds were then used to bridge a 15-mm-long sciatic nerve defect in rats. Both nerve regeneration and functional recovery were examined at pre-defined time points after surgery. We found that the number of GFP-labeled OECs was significantly higher in the "PFTBA-OECs" scaffold than that in the single OECs scaffold. In addition, PFTBA was found to enhance the beneficial effect of OECs-enriched scaffold on axonal regeneration and functional recovery. All these findings indicate that the "PFTBA-OECs" enriched scaffolds are capable of promoting nerve regeneration and functional recovery, which might be attributable, at least in part, to their beneficial effect on the survival of OECs after their implantation in vivo.

Enhanced adenovirus transduction of hMSCs using 3D hydrogel cell carriers

Hydrogels are increasingly being investigated as a means to implant cells for tissue engineering. One way to further enhance the repair response would be to combine the hydrogel cell carrier with gene transfer. Gene therapy, using adenoviral vectors, is an effective way to provide transient delivery of bioactive factors. However, current protocols require further optimization, especially if they are to be transferred into the clinic. This study opted to compare the efficiency of protocols for standard two-dimensional (2D) versus three-dimensional (3D), adenoviral-mediated, transduction of human mesenchymal stem cells. Two different multiplicities of infection were tested. After encapsulation in fibrin, alginate or agarose, cells were cultured for 28 days. Transduction in 3D showed a much higher efficiency, compared to standard 2D transduction protocols. In 3D, the amount of transgene produced was significantly higher, for every condition investigated. Furthermore, transduction in 3D does not require a cell culture step and can be conducted within the operating theatre. In conclusion, it was demonstrated that 3D transduction, using adenoviral vectors, is superior to standard transduction protocols in 2D. It therefore, might help increasing its administration in tissue engineering and clinical applications.

Prefabrication of 3D cartilage contructs: towards a tissue engineered auricle--a model tested in rabbits

The reconstruction of an auricle for congenital deformity or following trauma remains one of the greatest challenges in reconstructive surgery. Tissue-engineered (TE) three-dimensional (3D) cartilage constructs have proven to be a promising option, but problems remain with regard to cell vitality in large cell constructs. The supply of nutrients and oxygen is limited because cultured cartilage is not vascular integrated due to missing perichondrium. The consequence is necrosis and thus a loss of form stability. The micro-surgical implantation of an arteriovenous loop represents a reliable technology for neovascularization, and thus vascular integration, of three-dimensional (3D) cultivated cell constructs. Auricular cartilage biopsies were obtained from 15 rabbits and seeded in 3D scaffolds made from polycaprolactone-based polyurethane in the shape and size of a human auricle. These cartilage cell constructs were implanted subcutaneously into a skin flap (15×8 cm) and neovascularized by means of vascular loops implanted micro-surgically. They were then totally enhanced as 3D tissue and freely re-implanted in-situ through microsurgery. Neovascularization in the prefabricated flap and cultured cartilage construct was analyzed by microangiography. After explantation, the specimens were examined by histological and immunohistochemical methods. Cultivated 3D cartilage cell constructs with implanted vascular pedicle promoted the formation of engineered cartilaginous tissue within the scaffold in vivo. The auricles contained cartilage-specific extracellular matrix (ECM) components, such as GAGs and collagen even in the center oft the constructs. In contrast, in cultivated 3D cartilage cell constructs without vascular pedicle, ECM distribution was only detectable on the surface compared to constructs with vascular pedicle. We demonstrated, that the 3D flaps could be freely transplanted. On a microangiographic level it was evident that all the skin flaps and the implanted cultivated constructs were well neovascularized. The presented method is suggested as a promising alternative towards clinical application of engineered cartilaginous tissue for plastic and reconstructive surgery.

A synthetic oxygen carrier in fibrin matrices promotes sciatic nerve regeneration in rats

Tissue-engineering nerve conduits have been studied for a long time in bridging large nerve defects. However, the low oxygen availability within the nerve conduits, which results in death of migratory Schwann cells (SC) or loss of the newly formed tissue's function, is still an obstacle for axonal regeneration. Thus, it was hypothesized that an oxygen-enriched conduit would enhance axonal regeneration and functional recovery in vivo. To address this issue, perfluorotributylamine (PFTBA) enriched fibrin hydrogel was prepared and injected into collagen-chitosan conduits. The conduit containing PFTBA-enriched fibrin hydrogel was then used to bridge a 12-mm sciatic nerve defect in rats. The control rats were bridged with collagen-chitosan conduits filled with fibrin matrices without PFTBA. It was found that axonal regeneration and functional recovery in the combined PFTBA group were significantly higher than those in the control group without PFTBA. Further investigations showed that the mRNA and protein levels of S-100, brain-derived neurotrophic factor and nerve growth factor were enhanced by PFTBA at 1 and 3weeks after surgery. However, the mRNA and protein levels of vascular endothelial growth factor were in a similar range between the combined PFTBA group and the control group without PFTBA. In addition, immunohistochemical results showed that the morphological appearances of regenerated nerve and survival of SC were enhanced by PFTBA at 4 and 12weeks after surgery. In conclusion, PFTBA-enriched nerve conduit is capable of enhancing axonal regeneration, which provides a new avenue for achieving better functional recovery in the treatment of nerve defect.

Influence of Different Growth Factors on Chondrogenic Differentiation of Adipose-Derived Stem Cells in Polyurethane-Fibrin Composites

Introduction

Chondrogenic differentiation of adipose-derived stem cells (ASCs) has proven to be feasible. To compensate for laryngeal palsy or cartilage defects after surgery or trauma using tissue engineering, a formable and stable scaffold material is mandatory.

Methods

ASCs were seeded in fibrin-polyurethane scaffolds and cultured in chondrogenic differentiation medium adding the growth factors TGF-□1, TGF-□3, and BMP-2 for up to 35 days.

Results

Histological examination showed acid glycosaminoglycans in the extracellular matrix in all groups. Immunofluorescence presented positive staining for collagen II, aggrecan, and SOX-9 in the TGF-□1–, TGF-□3–, and BMP-2-group. With Real-time PCR analyses, chondrogenic differentiation became apparent by the expression of the specific genes COL2A1 (collagen II), AGC 1 (aggrecan), and SOX-9, whereas collagen II expression was low in all groups compared to bone marrow-derived stem cells (BMSC) due to reduced chondrogenic ability.

Conclusions

These findings demonstrate the general ability of ASCs to differentiate into matrix-producing chondrocytes in fibrin-polyurethane scaffolds. However, further experiments are necessary to enhance this chondrogenic potential of ASCs seeded in fibrin-polyurethane scaffolds in order to produce a suitable regeneration method for treating cartilage defects or an implantable medialization material for vocal cord palsy.

Synovium-derived mesenchymal stem cells encapsulated in a novel injectable gel can repair osteochondral defects in a rabbit model

We developed a novel injectable type I collagen/hyaluronic acid/fibrinogen (COL/HA/FG) composite gel that encapsulated synovium-derived mesenchymal stem cells (SDSCs) for the repair of damaged articular cartilage. We first analyzed the suitability of the composite gel as a three-dimensional injectable cell carrier in vitro. In an in vivo rabbit model, the COL/HA/FG composite gel displayed the potential to regenerate and repair osteochondral defects in the knee. Culture of the SDSCs encapsulated COL/HA/FG composite gel in a chondrogenic medium resulted in high viability of the SDSCs and high expressions of type II collagen, aggrecan, and sox 9 mRNA. Moreover, glycosaminoglycans and type II collagen were accumulated within the extracellular matrix. In the animal model, the SDSCs encapsulated COL/HA/FG composite gel produced a hyaline-like cartilage construct. Twenty-four weeks after transplantation, the defects had been repaired with hyaline cartilage-like tissue that was densely stained by safranin-O and immunostained by a type II collagen antibody. This data suggest that the SDSC-encapsulated COL/HA/FG composite gel can be a good therapeutic candidate/strategy for repairing of damaged articular cartilage.

Foamed oligo(poly(ethylene glycol)fumarate) hydrogels as versatile prefabricated scaffolds for tissue engineering

Radically cross-linked hydrogels are frequently used as cell carriers due to their excellent biocompatibility and their tissue-like mechanical properties. Through frequent investigation, PEG-based polymers such as oligo(poly(ethylene glycol)fumarate [OPF] have proven to be especially suitable as cell carriers by encapsulating cells during hydrogel formation. In some cases, NaCl or biodegradable gelatin microparticles were added prior to cross-linking in order to provide space for the proliferating cells, which would otherwise stay embedded in the hydrogel matrix. However, all of these immediate cross-linking procedures involve time consuming sample preparation and sterilization directly before cell culture and often show notable swelling after their preparation. In this study, ready to use OPF-hydrogel scaffolds were prepared by gas foaming, freeze drying, individual packing into bags and subsequent γ-sterilization. The scaffolds could be stored and used "off-the-shelf" without any need for further processing prior to cell culture. Thus the handling was simplified and the sterility of the cell carrier was assured. Further improvement of the gel system was achieved using a two component injectable system, which may be used for homogenous injection molding in order to create individually shaped three dimensional scaffolds. In order to evaluate the suitability of the scaffolds for tissue engineering, constructs were seeded with juvenile bovine chondrocytes and cultured for 28 days. Cross-sections of the respective constructs showed an intense and homogenous red staining of GAG with safranin O, indicating a homogenous cell distribution within the scaffolds and the production of substantial amounts of GAG-rich matrix.

Controlled release of triamcinolone acetonide from polyurethane implantable devices: application for inhibition of inflammatory-angiogenesis

The purpose of this study was to develop triamcinolone acetonide-loaded polyurethane implants (TA PU implants) for the local treatment of different pathologies including arthritis, ocular and neuroinflammatory disorders. The TA PU implants were characterized by FTIR, SAXS and WAXS. The in vitro and in vivo release of TA from the PU implants was evaluated. The efficacy of TA PU implants in suppressing inflammatory-angiogenesis in a murine sponge model was demonstrated. FTIR results revealed no chemical interactions between polymer and drug. SAXS results indicated that the incorporation of the drug did not disturb the polymer morphology. WAXS showed that the crystalline nature of the TA was preserved after incorporation into the PU. The TA released from the PU implants efficiently inhibited the inflammatory-angiogenesis induced by sponge discs in an experimental animal model. Finally, TA PU implants could be used as local drug delivery systems because of their controlled delivery of TA.

Interplay between local versus soluble transforming growth factor-beta and fibrin scaffolds: role of cells and impact on human mesenchymal stem cell chondrogenesis

Structural extracellular matrix molecules gain increasing attention as scaffolds for cartilage tissue engineering owing to their natural role as a growth factor repository. We recently observed that a collagen-type I/III (Col-I/III) matrix, human recombinant transforming growth factor-beta (TGF-β) protein, and fibrin hydrogel (FG) combined to a biphasic construct provided sufficient long-term TGF-β support to drive in vitro chondrogenesis of human mesenchymal stem cells (hMSC). Here we ask whether FG and Col-I/III can both retain TGF-β, describe the influence of cell seeding on TGF-β release, and compare the molecular path of hMSC chondrogenic differentiation under soluble versus local TGF-β supply. Release of growth factor from scaffolds augmented with increasing amounts of TGF-β was analyzed over 7 days and chondrogenesis was assessed over 42 days. Low TGF-β release rates from Col-I/III as opposed to higher release from FG indicated that both molecules retained TGF-β, with Col-I/III being the superior storage component. Cell seeding enhanced TGF-β retention in FG by about threefold and almost stopped release beyond 24 h. TGF-β remained bioactive and supported MSC chondrogenesis without impairing the amount of proteoglycan and collagen-type II deposition per cell and per construct compared to standard scaffold-free MSC pellets supplied with soluble TGF-β. Local TGF-β, however, mediated lower cell content, less collagen-type X relative to collagen-type II deposition and no matrix metalloproteinase-13 up-regulation. In conclusion, cells quickly halted release of local TGF-β from FG, turning FG and Col-I/III into attractive TGF-β repositories capable to drive full hMSC chondrogenesis, but via a modulated differentiation pathway. Since only part of the changes was reproduced by transient soluble TGF-β supply, release kinetics alone could not explain the molecular differences, suggesting that local TGF-β acts distinct from its soluble counterpart.

Physiological cartilage tissue engineering effect of oxygen and biomechanics

In vitro engineering of cartilaginous tissues has been studied for many years, and tissue-engineered constructs are sought to be used clinically for treating articular cartilage defects. Even though there is a plethora of studies and data available, no breakthroughs have been achieved yet that allow for implanting in vivo cultured articular cartilaginous tissues in patients. A review of contributions to cartilage tissue engineering over the past decades emphasizes that most of the studies were performed under environmental conditions neglecting the physiological situation. This is specifically pronounced in the use of bioreactor systems which neither allow for application of near physiomechanical stimulations nor for controlling a hypoxic environment as it is experienced in synovial joints. It is suspected that the negligence of these important parameters has slowed down progress and prevented major breakthroughs in the field. This review focuses on the main aspects of cartilage tissue engineering with emphasis on the relation and understanding of employing physiological conditions.

Incorporation of exudates of human platelet-rich fibrin gel in biodegradable fibrin scaffolds for tissue engineering of cartilage

The goal of this study was to assess the incorporation of exudates of human platelet-rich fibrin (hPRF) that is abundant in platelet cytokines and growth factors into biodegradable fibrin (FB) scaffolds as a regeneration matrix for promoting chondrocyte proliferation and re-differentiation. hPRF was obtained from human blood by centrifugation without an anticoagulant, and the exudate of hPRF was collected and mixed with bovine fibrinogen, and then thrombin was added to form the FB scaffold. Proliferation and differentiation of human primary chondrocytes and a human chondrosarcoma cell line, the SW-1353, embedded in the three-dimensional (3D) scaffolds and on the two-dimensional (2D) surface of the FB scaffolds so produced were evaluated in comparison with an agarose (AG) scaffold serving as the control. Results demonstrated that the amounts of these cytokines and growth factors in hPRF exudates were higher than those in the blood-derived products except for TGF-β1. Chondrocytes and SW1353 cells on the 2D and 3D FB scaffolds with the addition of the exudates of PRF exhibited more-available proliferation and differentiation than cells on 2D and 3D FB and AG scaffolds. It was concluded that FB scaffolds can provide an appropriate environment for chondrocyte proliferation and re-differentiation, and it could be improved by adding exudates of hPRF. These 3D scaffolds have great promise for cartilage tissue engineering.

Reliability, reproducibility, and validation of five major histological scoring systems for experimental articular cartilage repair in the rabbit model

Histological evaluation of the repair tissue is a main pillar in the advancing field of experimental articular cartilage repair. Despite their widespread use, the major histological scoring systems for cartilage repair have seldom been validated. We tested the hypotheses (1) that elementary scores have a better reproducibility compared with more complex systems and (2) that the data from these different histological scores correlate with the DNA and proteoglycan contents of the repair tissue. A total of 1,165 observations of cartilage repair based on histological sections (n=233) from an experimental investigation on the repair of standardized osteochondral defects in vivo were made by three investigators with different levels of experience in cartilage research to determine the inter- and intra-observer reproducibility of elementary (Pineda and Wakitani score) and complex (O'Driscoll, Sellers, Fortier score) histological grading systems. DNA and proteoglycan contents of the repair tissues from simultaneously created defects were determined and correlated with histological (a) overall score values, (b) matrix staining, and (c) cellular characteristics of the five scores. Finally, applying the proteoglycan content as validating test, sensitivity, and specificity of the grading systems were assessed. All histological scores provided high intra- (Pearson r=0.92-0.99) and inter-observer reliability (intra-class correlation=0.94-0.99), low numerical intra- and inter-observer differences, and high internal correlations (Spearman's ρ=0.63-0.91). No disparity in reliability and reproducibility was detected between elementary and complex scores or between investigators with different levels of experience (all p>0.05). Individual histological overall score values did not correlate with proteoglycan contents but with DNA contents of the repair tissue (O'Driscoll, Wakitani, Sellers score). In all systems, proteoglycan contents did not correlate with matrix staining (all p>0.05), but histological cellular characteristics correlated with total cell numbers (p<0.001). These data indicate that both elementary and comprehensive histological scores are suited to quantify cartilage repair. Histological and biochemical evaluations may serve as complementary tools to assess articular cartilage repair in vivo.

Hydrogels for biomedical applications

Hydrogels are swollen, crosslinked networks that have great potential for use in biomedicine. Their softness, biocompatibility and ability for rapid diffusion of molecules make them useful for drug delivery, cell culture, wound healing and sensing applications. The chemical functionality of the gels can be easily modified to provide signalling and growth factors for cell proliferation. To allow the ingress of large cells, either porosity of the substrate can be controlled, or the gel can be made biodegradable. One ultimate goal is the growth of entire organs in the laboratory for eventual transplantation. Gels can be used as drug-delivery vehicles, either as implantable depots, or as microgels in blood-based delivery systems. One expanding area is the use of gels as surgical aides to prevent bleeding, infection and post-operative complications.

Tissue engineering of functional articular cartilage: the current status

Osteoarthritis is a degenerative joint disease characterized by pain and disability. It involves all ages and 70% of people aged >65 have some degree of osteoarthritis. Natural cartilage repair is limited because chondrocyte density and metabolism are low and cartilage has no blood supply. The results of joint-preserving treatment protocols such as debridement, mosaicplasty, perichondrium transplantation and autologous chondrocyte implantation vary largely and the average long-term result is unsatisfactory. One reason for limited clinical success is that most treatments require new cartilage to be formed at the site of a defect. However, the mechanical conditions at such sites are unfavorable for repair of the original damaged cartilage. Therefore, it is unlikely that healthy cartilage would form at these locations. The most promising method to circumvent this problem is to engineer mechanically stable cartilage ex vivo and to implant that into the damaged tissue area. This review outlines the issues related to the composition and functionality of tissue-engineered cartilage. In particular, the focus will be on the parameters cell source, signaling molecules, scaffolds and mechanical stimulation. In addition, the current status of tissue engineering of cartilage will be discussed, with the focus on extracellular matrix content, structure and its functionality.

In vivo implantation of tissue-engineered human nasal septal neocartilage constructs: a pilot study

OBJECTIVE

To determine the in vivo biocompatibility of septal neocartilage constructs developed in vitro by an alginate intermediate step.

STUDY DESIGN

Prospective, animal model.

SETTING

Research laboratory.

SUBJECTS AND METHODS

A murine model was used to examine the maturation of neocartilage constructs in vivo. Chondrocytes collected from patients undergoing septoplasty were expanded in monolayer and suspended in alginate beads for 3-dimensional culture in media containing human serum and growth factors. After in vitro incubation for 5 weeks, the constructs were implanted in the dorsum of athymic mice for 30 and 60 days (n = 9). After the mice were sacrificed, the constructs were recovered for assessment of their morphological, histochemical, biochemical, and biomechanical properties.

RESULTS

The mice survived and tolerated the implants well. Infection and extrusion were not observed. Neocartilage constructs maintained their general shape and size and demonstrated cell viability after implantation. The implanted constructs were firm and opaque, sharing closer semblance to native septal tissue relative to the gelatinous, translucent preimplant constructs. Histochemical staining with hematoxylin and eosin (H&E) revealed that the constructs exhibited distinct morphologies characteristic of native tissue, which were not observed in preimplant constructs. DNA and type II collagen increased with duration of implantation, whereas type I collagen and glycoaminoglycans (GAG) decreased. Mechanical testing of a 60-day implanted construct demonstrated characteristics similar to native human septal cartilage.

CONCLUSIONS

Neocartilage constructs are viable in an in vivo murine model. The histologic, biochemical, and biomechanical features of implanted constructs closely resemble native septal tissue when compared with preimplant constructs.

Fibrin coating on poly (L-lactide) scaffolds for tissue engineering

A hybrid scaffold was obtained by the deposition of a thin network of submicron fibrin fibrils on the microporous walls of a macroporous poly(L-lactide) (PLLA) three-dimensional structure. The fibrin coating is homogeneous across the entire substrate and allowed the pore structure remain open in the hybrid scaffold. The elastic modulus of the hybrid scaffold (0.65 MPa) was increased up to twofold compared to the pure PLLA scaffold (0.29 MPa). Mouse pre-osteoblastic cells, MC3T3, were seeded on both pure PLLA and hybrid scaffolds, and cultured for 3, 6, and 24 h. The coating enhanced the cell colonization and proliferation and provided a more homogeneous distribution of cells within the scaffolds. In addition, the coating improved the scaffold adhesion properties by supplying new binding sites to the cells that modify the transmembrane receptors involved in initial cell adhesion mechanism. The expression of the β3 integrin was observed in cells cultured on fibrin-coated scaffolds instead of the α5 integrin, which was expressed in the uncoated scaffold. These hybrid PLLA/fibrin scaffolds have cell culture features suitable to promote early tissue regeneration.

Chondrocytes suspended in modified fibrin glue for vocal fold augmentation: An in vitro study in a porcine larynx model

BACKGROUND

Injection laryngoplasty is an option for treatment of dysphonia following vocal fold paralysis. Modified fibrin glue with suspended chondrocytes might be a favorable cell-based material for permanent vocal fold medialization.

METHODS

We compared fibrin glue with suspended chondrocytes to collagen and hyaluronic acid gels concerning alteration of vocal fold vibration and correct intralaryngeal placement after intralaryngeal injection into porcine larynges. Viscoelastic properties of the materials were analyzed by means of a parallel plate rheometer.

RESULTS

Fibrin glue with cells was comparable to collagen and hyaluronic acid with respect to amplitudes, symmetry, and periodicity of vocal fold vibration. Application and positioning of fibrin glue with suspended chondrocytes were technically undemanding and comparable with controls. Complex stress modulus of fibrin glue with suspended cells was comparable to that of collagen gel.

CONCLUSIONS

Fibrin glue with suspended chondrocytes seems suitable for the indication of injection laryngoplasty and holds promise for permanent vocal fold medialization.

Bioprinting of hybrid tissue constructs with tailorable mechanical properties

Tissue/organ printing aims to recapitulate the intrinsic complexity of native tissues. For a number of tissues, in particular those of musculoskeletal origin, adequate mechanical characteristics are an important prerequisite for their initial handling and stability, as well as long-lasting functioning. Hence, organized implants, possessing mechanical characteristics similar to the native tissue, may result in improved clinical outcomes of regenerative approaches. Using a bioprinter, grafts were constructed by alternate deposition of thermoplastic fibers and (cell-laden) hydrogels. Constructs of different shapes and sizes were manufactured and mechanical properties, as well as cell viability, were assessed. This approach yields novel organized viable hybrid constructs, which possess favorable mechanical characteristics, within the same range as those of native tissues. Moreover, the approach allows the use of multiple hydrogels and can thus produce constructs containing multiple cell types or bioactive factors. Furthermore, since the hydrogel is supported by the thermoplastic material, a broader range of hydrogel types can be used compared to bioprinting of hydrogels alone. In conclusion, we present an innovative and versatile approach for bioprinting, yielding constructs of which the mechanical stiffness provided by thermoplastic polymers can potentially be tailored, and combined specific cell placement patterns of multiple cell types embedded in a wide range of hydrogels.