Objectives. Recently, the field of tissue engineering has made numerous advances towards achieving artificial tendon substitutes with excellent mechanical and histological properties, and has had some promising experimental results. The purpose of this systematic review is to assess the efficacy of tissue engineering in the treatment of tendon injuries. Methods. We searched MEDLINE, Embase, and the Cochrane Library for the time period 1999 to 2016 for trials investigating tissue engineering used to improve tendon healing in animal models. The studies were screened for inclusion based on randomization, controls, and reported measurable outcomes. The RevMan software package was used for the meta-analysis. Results. A total of 388 references were retrieved and 35 studies were included in this systematic review. The different biomaterials developed were analyzed and we found that they improve the biomechanical and histological characteristics of the repaired tendon. At meta-analysis, despite a high heterogeneity, it revealed a statistically significant effect in favour of the maximum load, the maximum stress, and the Young’s modulus between experimental and control groups. In the forest plot, the diamond was on the right side of the vertical line and did not intersect with the line, favouring experimental groups. Conclusions. This review of the literature demonstrates the heterogeneity in the tendon tissue engineering literature. Several biomaterials have been developed and have been shown to enhance tendon healing and regeneration with improved outcomes. Cite this article: D. González-Quevedo, I. Martínez-Medina, A. Campos, F. Campos, V. Carriel. Tissue engineering strategies for the treatment of tendon injuries: a systematic review and meta-analysis of animal models. Bone Joint Res 2018;7:318–324. DOI: 10.1302/2046-3758.74.BJR-2017-0326

When transferring tissue regenerative strategies involving skeletal stem cells to human application, consideration needs to be given to factors that may affect the function of the cells that are transferred. Local anaesthetics are frequently used during surgical procedures, either administered directly into the operative site or infiltrated subcutaneously around the wound. The aim of this study was to investigate the effects of commonly used local anaesthetics on the morphology, function and survival of human adult skeletal stem cells.

Cells from three patients who were undergoing elective hip replacement were harvested and incubated for two hours with 1% lidocaine, 0.5% levobupivacaine or 0.5% bupivacaine hydrochloride solutions. Viability was quantified using WST-1 and DNA assays. Viability and morphology were further characterised using CellTracker Green/Ethidium Homodimer-1 immunocytochemistry and function was assessed by an alkaline phosphatase assay. An additional group was cultured for a further seven days to allow potential recovery of the cells after removal of the local anaesthetic.

A statistically significant and dose dependent reduction in cell viability and number was observed in the cell cultures exposed to all three local anaesthetics at concentrations of 25% and 50%, and this was maintained even following culture for a further seven days.

This study indicates that certain local anaesthetic agents in widespread clinical use are deleterious to skeletal progenitor cells when studied in vitro; this might have relevance in clinical applications.

Currently, fibrin glue obtained from fibrinogen and thrombin of human and animal blood are widely investigated to use as injectable hydrogel for tissue engineering which contributes to minimally invasive surgery, superior biodegradability, cell attachment, proliferation and regenerating new tissue. However, most of them fail to achieve to be used for tissue engineering application because of a risk of immune response and poor mechanical properties. To overcome the limitation of fibrin glue and to reduce the usage of products from human and animal blood, the artificial fibrin glue materials were developed. Recently, cellulose nanofiber (CNF) as reinforcing agent has been explored for many tissue engineering applications such as bone and cartilage due to its impressive biological compatibility, biodegradability and mechanical properties. CNF was extracted from cassava pulp. PEO-PPO-PEO diacrylate block copolymer is a biodegradable synthetic polymers which is water insoluble hydrogel after curing by UV light at low intensity. To enhance the cell adhesion abilities, gelatin methacrylate (GelMA), the denature form of collagen was used to incorporate into hydrogel. The aim of this study was to develop the artificial fibrin glue from CNF reinforced PEO-PPO-PEO diacrylate block copolymer/GelMA injectable hydrogel. CNF/PEO-PPO-PEO diacrylate block copolymer/GelMA injectable hydrogels were prepared with 2-hydroxy-1-(4-(hydroxy ethoxy) phenyl)-2-methyl-1-propanone (Irgacure 2959) as a photoinitiator. The physicochemical properties were investigated by measuring various properties such as thickness, gel fraction, mechanical properties and water uptake. At optimal preparation condition, CNF reinforced injectable hydrogel was successful prepared after curing with UV light within 7 minutes. This hydrogel showed gel fraction and water uptake of 81 and 85%, respectively. The cytotoxicity, cell adhesion and proliferation of CNF reinforced injectable hydrogel was presented. Cellulose nanofiber from casava pulp was successfully used to prepare injectable hydrogel as artificial fibrin glue for tissue engineering. The hydrogel showed good physical properties which can be applied to use for tissue engineering application

A major obstacle in biofabrication is replicating the organization of the extracellular matrix and cellular patterns found in anisotropic tissues within bioengineered constructs. While magnetically-assisted 3D bioprinting techniques have the potential to create scaffolds that mimic natural biological structures, they currently lack the ability to accurately control the dispersion of magnetic substances within the bioinks without compromising the fidelity of the intended composite. To overcome this dichotomy, the concepts of magnetically- and matrix-assisted 3D bioprinting are combined here. This method preserves the resolution of printed structures by keeping low viscosity bioinks uncrosslinked during printing, which allows for the arrangement of magnetically-responsive microfibers without compromising the structural integrity of the design. Solidification is induced after the microfibers are arranged in the desired pattern. Furthermore, the precise design of these magnetic microfillers permits the utilization of low levels of inorganic materials and weak magnetic field strengths, which reduces the potential risks that may be associated with their use. The effectiveness of this approach is evaluated in the context of tendon tissue engineering, and the results demonstrate that combining the tendons like anisotropic fibrous microstructure with remote magneto-mechanical stimulation during in vitro maturation provides both biochemical and biophysical cues that effectively guide human adipose-derived stem cells towards a tenogenic phenotype In summary, the developed strategy allows the fabrication of anisotropic high-resolution magnetic composites with remote stimulation functionalities, opening new horizons for tissue engineering applications. Acknowledgments: ERC Grant CoG MagTendon nr 772817, BioChips PoC project nr 10106930, (PD/BD/129403/2017), (CEECIND/01375/2017), (2020.03410.CEECIND), (2022.05526.PTDC), (ED481B2019/025)

Tissue engineering and regenerative medicine are increasingly taking advantage of active materials, allowing to provide specific clues to the cells. In particular, the use of electroactive polymers that deliver electrical signals to the cells upon mechanical solicitation, open new scientific and technological opportunities, as they in fact mimic signals and effects present in living tissues, allowing the development of suitable microenvironments for tissue regeneration. In fact, electrical and electromechanical clues are among the most relevant ones in determining tissue functionality in tissues such as muscle and bone, among others, indicating their requirement for proper tissue regeneration. Piezoelectric polymers have already shown strong potential for novel tissue engineering strategies, once they can account for the existence of piezoelectricity within some specific tissues and also can modulate the electrical signals existing in tissue development and function. In this context, this talk reports on piezoelectric and magnetoelectric materials used for tissue engineering applications. The most used materials and morphologies for tissue engineering strategies are reported, together with the need of novel bioreactor designs allowing to take full advantage of those materials. Further, the main achievements, challenges and future needs for research and actual therapies will be presented and discussed

The key factors in Tissue Engineering are multipotent stem cells, growth factors (necessary to manipulate cell destiny) and scaffolds (3D constructs which support the growing tissue). Mesenchymal stem cells are the most important part of this equation, and it is procurement and manipulation of these that lies at the heart of tissue engineering. Luckily, mensenchymal stem cells can be obtained from many tissues, including synovium, bone marrow and periosteum. The use of bioreactors to optimise culture conditions and improve cell viability provides an opportunity to control stem cell destiny. Various Tissue Engineering strategies exist: manipulating cells in situ with osteogenic growth factors, such as BMP; implanting whole tissue grafts; and the use of Gene therapy. The tissues that concern orthopaedic surgeons are very diverse and no single tissue engineered construct will be able to fulfil all our clinical needs. Tissue engineering of articular cartilage is very difficult technically, but once accomplished will revolutionalise practice. The challenge lies in being able to produce cartilage as similar to native hyaline cartilage as possible. Although promising, ACI, using culture expanded cells, is able at best to produce hyaline-like cartilage but not the real thing. Multipotent mesenchymal stem cells are being used in this field. Even simply injecting these intraarticularly has been shown to retard the progression of OA in animal models. When attempting to regenerate meniscal cartilage, the mechanical properties of the scaffold become crucial, as the biomechanics of the knee are highly hostile. Ligaments and tendons, though the least complex tissues architecturally, have very high tensile properties which will be hard to replicate. The challenging aspects of Orthopaedic Tissue Engineering are manifold, yet the field itself is growing in leaps and bounds. Despite some initial setbacks, the new developments in this discipline are very encouraging

Tissue engineering in reconstructive surgery has many potential attractions, not the least to avoid donor site morbidity and reduce the potential need for allografts and prostheses. Currently there are only two products that have FDA approval in the United States, namely skin and cartilage. Other potential products being trialled are artificial blood vessels and heart valves. The common denominator of these is that they are essentially two dimensional and relatively avascular. Three dimensional tissue engineering has three essential components, (1) cells, (2) scaffold and (3) blood supply. Cells are most easily derived from an autologous source, by conventional tissue culture where they are expanded and implanted into the required site. They are committed cells and usually a large source of donor tissue is required to obtain an adequate source of cells for reconstruction. Stem cells have the potential to grow and differentiate, they may be embryonal which introduces ethical problems or adult stem cells. Cells can be genetically engineered to produce specific growth factors for the purpose of further cell proliferation, such as vascular endothelial growth factor for angiogenesis. The second essential is a scaffold for cells to adhere to and grow. This is particularly important for the development of the vascular network. Fibrin, PTFE (Dexon) Matrigel (a form of Laminen) or collagen are the most popular forms of matrix. The third and most essential component for three-dimensional tissue engineering is vascularization. To date, most tissue engineering research involves invitro studies of cell differentiation and growth but the invivo potential is limited because of inability to transfer a blood supply. At the Bernard O’Brien Institute at St Vincent’s Hospital, Melbourne, we have developed a model of invivo tissue engineering which involves the initial creation of a vascular core inside a plastic chamber which can be moulded to any desired shape. This construct seems to be an ideal environment for seeding of cells, including stem cells which allows them to survive and differentiate into various mesenchymal tissues. To date we have been able to generate skin flaps, fat, tissue and skeletal muscle. Although our prime interest has not been bone or cartilage it is reasonable to assume that this can be relatively simply produced in the same model from either stem cell sources or by the use of differentiating factors

Skeletal muscle tissue engineering has made progress towards production of functional tissues in line with the development in materials science and fabrication techniques. In particular, combining the specificity of 3D printing with smart materials has introduced a new concept called the 4D printing. Inspired by the unique properties of smart/responsive materials, we designed a bioink made of gelatin, a polymer with well-known cell compatibility, to be 3D printed on a magnetically responsive substrate. Gelatin was made photocrosslinkable by the methacrylate reaction (GELMA), and its viscosity was finetuned by blending with alginate which was later removed by alginate lyase treatment, so that the printability of the bioink as well as the cell viability can be finetuned. C2C12 mouse myoblasts-laden bioink was then 3D printed on a magnetic substrate for 4D shape-shifting. The magnetic substrate was produced using silicon rubber (EcoFlex) and carbonyl iron powders. After 3D printing, the bioink was crosslinked on the substrate, and the substrate was rolled with the help of a permanent magnet. Unrolled (Open) samples were used as the control group. The stiffness of the bioink matrix was found to be in the range of 13–45 kPa, which is the appropriate value for the adhesion of C2C12 cells. In the cell viability analysis, it was observed that the cells survived and could proliferate within the 7-day duration of the experiment. As a result of the immunofluorescence test, compared to the Open Group, more cell nuclei were observed overlapping MyoD1 expression in the Rolled Group; this indicated that the cells in these samples had more cell-cell interactions and therefore tended to form more myotubes. Acknowledgements: This research was supported by the TÜBİTAK 2211-A and YÖK 100/2000 scholarship programs

Successful anterior cruciate ligament (ACL) reconstructions strive a firm ligament-bone integration. Therefore, the aim of this study was to address in more detail the enthesis as the thriphasic bone attachment of the ACL using a tissue engineering approach. To establish a tissue-engineered enthesis-like construct, triphasic scaffolds embroidered from poly(L-lactide-co-caprolactone) and polylactic acid functionalized with collagen foam were colonized with osteogenically differentiated human mesenchymal stromal cells (hMSCs) and lapine (L) ACL fibroblasts. These triphasic scaffolds with a bone-, a fibrocartilage transition- and a ligament phase were seeded directly after spheroid assembly or with 14 days precultured LACL fibroblast spheroids and 14 days osteogenically differentiated hMSCs spheroids (=longer preculture) and cultured for further 14 days. Cell survival was tested. Collagen type I and vimentin were immunolabeled and the content of DNA and sulfated glycosaminoglycan (sGAG) was quantified. The relative gene expression of tenascin C, type I and X collagens, Mohawk and Runx2 was analyzed. Compared to the LACL spheroids the hMSC spheroids adhered better to the scaffold surface with faster cell outgrowth on the fibers. Collagen type I and vimentin were mainly detected in the hMSCs colonizing the bone zone. The DNA content was generally higher in the bone (hMSCs) than in the ligament zones and after short spheroid preculture higher than after longer preculture whereas the sGAG content was greater after longer preculture for both cell types. The longer precultivated hMSCs expressed more type I collagen in comparison to those only shortly precultured before scaffold seeding. Type I collagen and tenascin C were higher expressed in scaffolds directly colonized with LACL compared to those seeded after longer spheroid preculture. The gene expression of ECM components and transcription factors depended on cell type and preculturing condition. Zonal colonization of triphasic scaffolds using the spheroid method is possible offering a novel approach for enthesis tissue engineering

Purpose: The purpose of our tissue engineering work was to produce a substitute for the anterior cruciate ligament (ACL) in laboratory cultures for human implantation and to conduct fundamental studies on healing mechanisms. Material: We used cells isolated from ACL biopsies obtained from the host, type I bovine collagen, and two bone blocks to produce ACL in culture. Methods: Several layers of collagen containing host autologous ACL cells were superposed and linked to two bones that were placed on either side, according to a process currently being patented. The cells, or fibroblasts, enter into contact with the collagen matrix and start remodelling it, in the laboratory, before implantation. This ACL produced by tissue engineering can be ready for implantation 10–12 days after isolating the autologous cells from a ruptured ACL. Results: Implantation of autologous ACL reconstructs was successful in eight goats. Histological analysis of the implanted grafts showed permanent integration into the tissues after 1–13 months. Th synovial membrane was reformed and rapidly vascularised, about one month after the graft. Thereafter, remodelling of the collagen matrix led to the formation of a very dense network of fibres, organised in bundles, very comparable to the normal histological aspect of the ACL. The bone blocks were also integrated by incorporation into the femur and tibia of the host. Sharpey fibres were present at the bone-ligament surface and a well structured fibro-cartilage was observed. In addition, the synovial membrane around the graft was innervated five months after implantation, suggesting that propioception could be recovered over time. Finally, progressive gain in force reached 20 – 36% of the normal ACL, 9 to 13 months after implantation;. Discussion: These promising data demonstrate that an autologous ACL with an interesting potential for regeneration can be produced in the laboratory, avoiding the risk of rejection and sparing healthy knee structures, thus favouring more rapid functional rehabilitation. Conclusion: Tissue engineering is a new avenue of research with potential applications in orthopaedic surgery, particularly for reconstruction of the ACL

Background. Auxetic materials have a negative poisons ratio, and a number of native biological tissues are proposed to possess auxetic properties. One such tissue is annulus fibrosus (AF), the fibrous outer layers of the intervertebral disc (IVD). However, few studies to date have investigated the potential of these materials as tissue engineering scaffolds. Here we describe the potential of manually converted polyurethane (PU) foams as three dimensional cellular scaffolds for AF repair. Methods. Rat MSCs were seeded onto fibronectin coated auxetic foams at a cell density of 6.4 × 10. 3. cells/mm. 3. , and cultured for up to 3 weeks. Cell viability was assessed throughout culture and following culture scanning electron microscopy (SEM) was used to assess morphological characteristics. Histological assessment was performed to assess production of matrix proteins. Results. Cells adhered to the surface auxetic foams and remained viable for the 3 weeks investigated. Histology and SEM demonstrated cells within the full thickness of the auxetic foams, where extracellular matrix was starting to be produced following 3 weeks, including collagens suggesting differentiation of the MSCs. Conclusion. Auxetic PU foams have a significant potential for use in tissue engineering applications, potentially mimicking the multiaxial strains of annulus fibrous tissue. MSCs were shown to adhere, survive and produce matrix within the foams after 3 weeks, future work will focus on longer term studies and in depth analysis of the phenotype of the cells. No conflicts of interest. Funding provided by a grant from Sheffield Children's Hospital NHS trust

Introduction. In tissue engineering, the establishment of sufficient vascularization is essential for tissue viability and functionality. Inadequate vascularization disrupts nutrients and oxygen supply. Nonetheless, regenerating intricate vascular networks represents a significant challenge. Consequently, research efforts devoted to preserving and regenerating functional vascular networks in engineered tissues are of paramount importance. The present work aims to validate a decellularisation process with preservation of the vascular network and extracellular matrix (ECM) components in fasciocutaneous flaps. Method. Five vascularized fasciocutaneous flaps from cadaveric donors were carefully harvested from the anterolateral thigh (ALT), preserving the main perforator of the fascia lata. The entire ALT flap underwent decellularization by perfusion using a clinically validated chemical protocol. Fluoroscopy and computed tomography (CT) were used to analyze the persistence of the vascular network within the flap, pre- and post-decellularization. Histological analysis, including hematoxylin and eosin staining, and quantitative DNA assessment evaluated decellularization efficacy. Further qualitative (immunohistochemistry, IHC) and quantitative analyses were conducted to assess the preservation of ECM components, such as collagen, glycosaminoglycans, and elastin. Result. On average, the ALT flap maintains 82% of the perfusion area (p = 0.094) post-treatment. Histological analysis confirmed decellularization efficacy and revealed structural rearrangement. Paired analysis revealed a significant decrease in DNA levels (<14.8 ng/mg of dry weight, p****< 0.0001) and well-maintained ECM. IHC indicated the persistence of elastine, collagen IV and laminin. Quantitative analysis confirmed elastin (p = 0.44) and collagen persistence (+74%, p*** = 0.001, albeit with a decrease in matrix glycosaminoglycans (-41%, p*** = 0.01). Conclusion. Decellularization effectively removed cells, while preserving the ECM overall and maintaining some vascular network integrity. Yet, further study is needed to validate these findings, involving microCT examination of the vascular network and its ability to support cell colonization and viability

Bottom-up tissue engineering (TE) strategies employing microscale living materials as building blocks provide a promising avenue for generating intricate 3D constructs resembling native tissues. These microtissue units exhibit high cell densities and a diverse extracellular matrix (ECM) composition, enhancing their biological relevance. By thoughtfully integrating different cell types, the establishment of vital cell-cell and cell-matrix interactions can be promoted, enabling the recreation of biomimetic micro-niches and the replication of complex morphogenetic processes. Notably, by co-assembling blood vessel-forming endothelial cells with supportive stromal cells, microtissues with stable capillary beds, referred to as vascular units (VUs), can be generated. Through a modular TE approach, these VUs can be further combined with other microtissues and biomaterials to construct large-scale vascularized tissues from the bottom up. Integration of VUs with technologies such as 3D bioprinting and microfluidics allows for the creation of structurally intricate and perfusable constructs. In this presentation, we will showcase examples of VUs and explore their applications in regenerative medicine and tissue modeling. Acknowledgements: This work was supported by project EndoSWITCH (PTDC/BTM-ORG/5154/2020) funded by FCT (Portuguese Foundation for Science and Technology)

Organ and tissue decellularisation are promising approaches for the generation of scaffolds for tissue regeneration since these materials provides the accurate composition and architecture for the specific tissues. Repopulation of the devitalized matrixes is the most critical step and a challenge, especially in dense tissues such as cartilage. To overcome this difficulty, several chemical and mechanical strategies have been developed. Chemical extraction targeting specific matrix components such as elastin, makes auricular cartilage accessible for cells via channels originating from the elastic fiber network. However, chemical treatment for glycosaminoglycan removal is not sufficient to allow cell ingrowth in articular cartilage. As alternative, laser perforation has been developed allowing to engrave fine structures with controlled size, distance and depth, with reproducibility and high throughput. Two of the most commonly used laser technologies used in the medical field, the CO. 2. and femtosecond laser, were applied to hyaline cartilage with very different structural effect. Within this talk, the structuralizing possibilities of laser and enzymatic treatments, the effect on the matrix and the general advantages and disadvantages for tissue engineering are discussed. We believe that the optimal combination of chemical and laser treatment has high potential for a new generation of biomaterials for tissue engineering

By definition, a smart biomaterial is a material, such as a ceramic, alloy, gel or polymer, that can convert energy from one form into another by responding to a change in a stimulus in its environment. These stimuli may involve temperature, pH, moisture, or electric and magnetic fields. In particular, thermoresponsive biomaterials have been successfully employed to host mammalian cells with a view to musculoskeletal tissue engineering. The presentation provides an overview of the use of thermosensitive polymers for the non-enzymatic stem cell harvesting, cell sheet engineering, three-dimensional scaffolds fabrications and organ-printing materials

Current issues being debated in ACL reconstruction include injury prevention, graft choice, graft positioning, graft fixation, graft remodelling and rehabilitation. Tissue engineering, the alteration of biological mechanisms by application of novel proteins, enzymes and hormones, is rapidly changing the way we approach all aspects of surgery. Tissue engineering techniques in ACL/PCL reconstruction focus on new biosynthetic ACL material, fixation of soft tissue grafts to bony tunnels and graft remodelling. OP-1 is recombinant human Osteogenic Protein 1 (BMP-7). It is a member of the Transforming Growth Factor β (TGFβ) super family. OP-1 promotes the recruitment, attachment, proliferation and differentiation of pluripotential mesenchymal stem cells. It promotes both osteogenesis and chondrogenesis. The carrier is highly purified bovine bone type 1 collagen, which provides an osteoconductive matrix. We have completed a study assessing the use of OP-1 as a means of enhancing early biological fixation of soft tissue grafts within bone tunnels in a sheep ACL model. We have commenced a clinical trial using OP-1 in adult ACL reconstruction, believing that OP-1 will enhance early biological graft fixation, and hence, improve clinical results, speed up rehabilitation and prevent tunnel widening. Other studies have shown the beneficial effects of BMP-2 on an extraarticular bone tendon fixation model, the use of TGF-B to enhance graft remodelling and the application of gene therapy to deliver BMP’s for enhanced graft fixation. Several projects are underway looking at creating biosynthetic ACL grafts using tissue engineering techniques. As opposed to purely synthhetic grafts, bioACL grafts are made of a collagen scaffold, allowing for remodelling and revascularisation. ACL reconstructive surgery is constantly evolving. Tissue engineering may provide us with a means of minimising morbidity, accelerating rehabilitation and improving the clinical outcome following this common surgery

Tissue engineering is a promising approach to regenerate damaged skeletal tissues. In particular, the use of injectable hydrogels alleviates common issues of poor cell viability and engraftment. However, uncontrolled cell fate, resulting from unphysiological environments and degradation rates, still remain a hurdle and impedes tissue healing. We thus aim at developing a new platform of injectable hyaluronic acid (HA) hydrogels with a large panel of properties (stiffness, degradation…) matching those of skeletal tissues. Hence, HA with different molecular weights were functionalized with silylated moieties. Upon injection, these hydrogels formed through a sol-gel chemistry within 5 to 20 minutes in physiological conditions, as demonstrated by rheological characterization. By varying the crosslinking density and concentration, we obtained hydrogels spanning a large range of elastic moduli (E = 0.1–20 kPa), similar to those of native ECMs, with tunable biodegradation rates (from 24 hours to > 50 days) and swelling ratios (500 to 5000% (w/w)). Cell viability was confirmed by Live/Dead assays and will be completed by in vivo subcutaneous implantations in mice to study the foreign body reaction and degradation rate. We further developed hybrid HA/biphasic calcium phosphate granules hydrogels and demonstrated a strong mechanical reinforcement (E = 0.1 MPa) and a faster relaxation behaviour (τ. 1/2. < 400s), with similar degradation rates. Ongoing in vitro differentiation assays and in vivo implantations in a rabbit femur model will further assess their ability to drive bone regeneration. Collectively, these results suggest that this hydrogel platform offers promising outcomes for improved strategies in skeletal tissue engineering

Biodegradable porous scaffolds play an important role in tissue engineering as the temporary templates for transplanted cells to guide the formation of the new organs. The most commonly used porous scaffolds are constructed from two classes of biomaterials. One class consists of synthetic biodegradable polymers such as poly (α-hydroxy acids), poly(glycolic acid), poly(lactic acid), and their copolymer of poly(DL-lactic-co-glycolic acid) (PLGA). The other class consists of naturally derived polymers such as collagen. These biomaterials have their respective advantages and drawbacks. Therefore, hybridization of these biomaterials has been expected to combine their advantages to provide excellent three-dimensional porous biomaterials for tissue engineering. Our group developed one such kind of hybrid biodegradable porous scaffolds by hybridizing synthetic poly (α-hydroxy acids) with collagen. Collagen microsponges were nested in the pores of poly (α-hydroxy acids) sponge to construct the poly (α-hydroxy acids)-collagen hybrid sponge. Observation by scanning electron microscopy (SEM) showed that microsponges of collagen with interconnected pore structures were formed in the pores of poly (α-hydroxy acids) sponge. The mechanical strength of the hybrid sponge was higher than those of either poly (α-hydroxy acids) or collagen sponges both in dry and wet states. The wettability with water was improved by hybridization with collagen, which facilitated cell seeding in the hybrid sponge. Use of the poly (α-hydroxy acids) sponge as a skeleton facilitated formation of the hybrid sponge into the desired shapes with high mechanical strength, while collagen microsponges contributed good cell interaction and hydrophilicity. One of such kind of hybrids. Additionally, our group developed a hydrostatic pressure bioreactor for chondrocyte culture. And our study showed that hydrostatic pressure (0–3 MPa) had promotional effects on the production of proteoglycan and type II collagen by cultured chondrocytes. Therefore, it would be a promising pathway for reconstructing cartilage-like tissue to culture chondrocytes in this three-dimensional hybrid sponge under physiological hydrostatic pressure

Tissue engineering regards the generation, regeneration, augmentation or limitation of the structure and function of living tissues by the application of scientific and engineering principles. Skeletal defects resulting from tumor resection, congenital abnormalities or trauma often require surgical intervention to restore the function. Current option for bone replacement include autografts,allografts,metals,ceramic and polymers.However, all these materials have drawbacks, and their selection usually require some compromises. Skeletal tissues are under extensive investigation in tissue engineering research and beside the biological issues, the scaffolds design plays an important role. A number of biodegradable and bioabsorbable materials as well as scaffold designs, have been experimentally and, in some cases clinically studied. An appropriate scaffold should posses highly porous with interconnected pore network for cell growth and flow transport of nutrient and metabolic waste; biocompatible and bioresorbable with a controlled degradation and resorption rate to match cell/ tissue growth, suitable surface chemistry for cell attachment, proliferation and differentiation, and mechanical properties to match those of the implanted tissue. Synthetic biodegradable polymers and inorganic materials are promising as extracellular matrix analogue to facilitated tissue development and growth; these include: polyglycolic acid, poly-l-lactic acid, copolymers, poly-caprolactones, hydroxyapatite, tricalcium phosphates. All these scaffolds are well performing from biological and chemical-physical but they have some limitations from mechanical point of view. To overcome this problem a composite structure made by Polycaprolactone and Hydroxyapatite is studied by mechanical and biological analysis. To obtain a porous structure, the casting and salt leaching technique is implemented. The composite shows mechanical properties in the range of the spongy bone and interesting biological properties with regards to osteoblasts. Injectable gels made of collagen are analysed to carry cells, a preliminary results of collagen gel loaded with MSC cells have been performed and rheological and proliferation study are showing the feasibility to obtain a bioactive materials/cells to be inject in the defined body site defects avoiding massive surgery

Hyaline cartilage and immature nucleus pulposus possess similar macromolecules in their extracellular matrix, and there is no unique molecular marker to distinguish the two tissues. We show that in normal disc (fifteen to twenty-five years old), the GAG to hydroxyproline ratio (proteoglycan to collagen ratio) within the nucleus pulposus is approximately 28:1. However, the GAG to hydroxyproline ratio within hyaline cartilage of the same group is 2.5:1. This information is important in identifying stem cell conversion to a nucleus pulposus cell phenotype rather than a chondrocyte phenotype for tissue engineering of intervertebral disc. Tissue engineering of intervertebral discs (IVDs) using mesenchymal stem cells (MSCs) induced to differentiate into a disc-cell phenotype has been considered as an alternative treatment for disc degeneration. Since there is no unique marker for disc tissue, and because cartilage and immature nucleus pulposus (NP) possess similar macromolecules in their extracellular matrix, it is currently difficult to recognize MSC conversion to a disc cell. In this study, we compare the proteoglycan to collagen ratio in the NP of normal disc to that of the hyaline cartilage of the endplate within the same group of individuals. To distinguish between a normal NP and hyaline cartilage phenotype for tissue engineering of IVDs. Human lumbar spine specimens were harvested from fresh cadavers, aged twelve week to seventy-nine year. Discs and endplates were examined for total collagen using the hydroxyproline assay and glycosaminoglycan (GAG) content using a standard assay. In a mature disc with no degeneration (fifteen to twentyfive years), the GAG to hydroxyproline ratio within the NP is approximately 28:1. However, the ratio within the hyaline cartilage endplate of the same group is 2.5:1. A high proteoglycan to collagen ratio can be used to distinguish NP cells from chondrocytes. The lower NP collagen content is probably responsible for its gelatinous nature rather than the firm texture of hyaline cartilage, and this is essential for normal disc function. This information is crucial in identifying a NP-like phenotype when MSCs are induced to differentiate into a disc cell as opposed to a chondrocyte, for tissue engineering of IVDs