Tissue-engineered Products Research Articles

Robotics-Driven Manufacturing of Cartilaginous Microtissues for Skeletal Tissue Engineering Applications.

Automated technologies are attractive for enhancing the robust manufacturing of tissue-engineered products for clinical translation. In this work, we present an automation strategy using a robotics platform for media changes, and imaging of cartilaginous microtissues cultured in static microwell platforms. We use an automated image analysis pipeline to extract microtissue displacements and morphological features as noninvasive quality attributes. As a result, empty microwells were identified with a 96% accuracy, and dice coefficient of 0.84 for segmentation. Design of experiment are used for the optimization of liquid handling parameters to minimize empty microwells during long-term differentiation protocols. We found no significant effect of aspiration or dispension speeds at and beyond manual speed. Instead, repeated media changes and time in culture were the driving force or microtissue displacements. As the ovine model is the preclinical model of choice for large skeletal defects, we used ovine periosteum-derived cells to form cartilage-intermediate microtissues. Increased expression of COL2A1 confirms chondrogenic differentiation and RUNX2 shows no osteogenic specification. Histological analysis shows an increased secretion of cartilaginous extracellular matrix and glycosaminoglycans in larger microtissues. Furthermore, microtissue-based implants are capable of forming mineralized tissues and bone after 4 weeks of ectopic implantation in nude mice. We demonstrate the development of an integrated bioprocess for culturing and manipulation of cartilaginous microtissues and anticipate the progressive substitution of manual operations with automated solutions for the manufacturing of microtissue-based living implants.

A NEW TISSUE-ENGINEERED PRODUCT INDICATED FOR BONE RECONSTRUCTION: PROOF OF CONCEPT

To design slow resorption patient-specific bone graft whose properties of bone regeneration are increased by its geometry and composition and to assess it in in-vitro and in-vivo models.A graft composed by hydroxyapatite (HA) and β-TCP was designed as a cylinder with 3D gyroid porosities and 7 mm medullary space based on swine's anatomy. It was produced using a stereolithography 3D-printing machine (V6000, Prodways).Sterile bone grafts impregnated with or without a 10µg/mL porcine BMP-2 (pBMP-2) solution were implanted into porcine femurs in a bone loss model. Bone defect was bi-weekly evaluated by X-ray during 3 months. After sacrifice, microscanner and non-decalcified histology analysis were conducted on biopsies.Finally, osteoblasts were cultured inside the bone graft or in monolayer underneath the bone graft. Cell viability, proliferation, and gene expression were assessed after 7 and 14 days of cell culture (n=3 patients).3D scaffolds were successfully manufactured with a composition of 80% HA and 20% β-TCP ±5% with indentation compressive strength of 4.14 MPa and bending strength of 11.8MPa.In vivo study showed that bone regeneration was highly improved in presence of pBMP-2. Micro-CT shows a filling of the gyroid sinuses of the implant (Figure 1).In vitro, the presence of BMP2 did not influence the viability of the osteoblasts and the mortality remained below 3%. After 7 days, the presence of BMP2 in the scaffold significantly increased by 85 and 65% the COL1A1 expression and by 8 and 33-fold the TNAP expression by osteoblasts in the monolayer or in the scaffold, respectively. This BMP2 effect was transient in monolayer and did not modify gene expression at day 14.BMP2-impregnated bone graft is a promising patient-personalized 3D-printed solution for bone defect regeneration, by promoting neighboring host cells recruitment and solid new bone formation.For any figures and tables, please contact the authors directly.

Regulatory Framework, Challenges, and Initial Strategic Planning for Advanced Therapy Products (PTAs) Development in Brazil.

Advanced Therapies are a class of innovative complex biological products used for therapeutic purposes, encompassing cell therapy, tissue engineering, and gene therapy products. These are promising therapeutic strategies for several complex diseases with low or non-existent therapeutic alternatives. The proper transposition of basic research in this area into medicinal products must comply with regulatory requirements. Here we review the main regulatory recommendations, emphasizing on the Brazilian regulation. The critical points are the manufacturing process, challenges in characterizing the product, development of non-clinical trials, lack of adequate animal models representative of the clinical situation, and absence of valid and measurable therapeutic endpoints. Based on that, we propose a framework for strategic planning of pre-clinical studies in this field. The detailed example involves producing a nonviral vector-based gene editing product, but the regulations and methods may be extrapolated for developing different types of advanced therapies.

Funding of research & innovation in the field of medical technologies and biomedical engineering over the different European framework programmes.

To demonstrate the role of the European Framework Programmes for Research & Innovation in supporting the field of Medical Technologies and Biomedical Engineering and to show which types of medical technologies and which funding instruments are the preferred ones. Based on data available in the European Commission data warehouse for the past two Framework Programmes, funded projects addressing a Medical Technology were identified. This enabled to categorize the projects according to the intended use and to classify into different types. Moreover, the main instruments in the Framework Programme acting as funding sources were explored. The increase in R&I support led to 1961 projects and a total financing of € 3.2 bllion under the last Framework Programme. The categorization showed a balanced funding in terms of intended use, the detailed classification revealed that in-vitro-diagnostics and imaging equipment prevail in the diagnostic category, tissue-engineering products, implants and robotics in the therapeutic domain and ICT or software-based technologies in the miscellaneous category. As to funding sources, the classical health-oriented collaborative research scheme was on top, followed by instruments like the European Research Council, the Future and Emerging Technologies activities and the European Innovation Council, and completed by the Public-Private Partnerships. The European Framework Programmes are key on the global landscape for financing Research & Innovation of Medical Technology and the breadth of supported technologies is equally reflected by the different funding instruments involved.

The Relevance of Advanced Therapy Medicinal Products in the Field of Transplantation and the Need for Academic Research Access: Overcoming Bottlenecks and Claiming a New Time.

The field of transplantation has witnessed the emergence of Advanced Therapy Medicinal Products (ATMPs) as highly promising solutions to address the challenges associated with organ and tissue transplantation. ATMPs encompass gene therapy, cell therapy, and tissue-engineered products, hold immense potential for breakthroughs in overcoming the obstacles of rejection and the limited availability of donor organs. However, the development and academic research access to ATMPs face significant bottlenecks that hinder progress. This opinion paper emphasizes the importance of addressing bottlenecks in the development and academic research access to ATMPs by implementing several key strategies. These include the establishment of streamlined regulatory processes, securing increased funding for ATMP research, fostering collaborations and partnerships, setting up centralized ATMP facilities, and actively engaging with patient groups. Advocacy at the policy level is essential to provide support for the development and accessibility of ATMPs, thereby driving advancements in transplantation and enhancing patient outcomes. By adopting these strategies, the field of transplantation can pave the way for the introduction of innovative and efficacious ATMP therapies, while simultaneously fostering a nurturing environment for academic research.

Mechanically enhanced and osteobioactive synthetic periosteum via development of poly(ε-caprolactone)/microtantalum composite

Periosteum, the thin layer covering adjacent to bone containing specific architecture, is important for functional bone regeneration and remodeling. Synthetic periosteum investigated presently lacks the resemblance of natural periosteum, suffering from poor mechanical strength and cell attachment. Here, we report a newly-developed biomimetic film to function as synthetic periosteum. Based on poly(ε-caprolactone) (PCL), where surface wettability of the synthetic periosteum is enhanced by microtantalum (mTa) particle blending and after a cold drawing process, further obtains topographical anisotropy without any involvement of solvent. This new blend shows mechanical enhancement over pure PCL, with yield stress and elastic strain approaching the natural periosteum. A distinct degradation mechanism is proposed for the blend, and by seeding with mouse calvarial preosteoblasts, cell proliferation is promoted on surface of the drawn PCL but delayed on the mTa-blended PCL. However, cell mineralization is accelerated on the mTa-blended surface. This is less on the drawn PCL. The synergistical integration of cellular proliferation, alignment and osteogenic enhancement suggest that the cold drawn PCL/Ta blend has unique potential for developing into a synthetic periosteum and other tissue-engineering products.

Benefits of platelet rich plasma (PRP) treatment on skin autografts and allografts in a burned patient

Wound healing is promoted by a series of growth factors, secreted from the alpha granules of the platelets. Platelet rich plasma (PRP) emerged as a clinical strategy to increase the physiologic concentration of platelets and its clinical use for a large spectrum of disorders is reported, with good results. Extensive burns represent a promising field for PRP use, those patients confronting challenging wound healing and poor long-term results. We present our initial clinical experience represented by a case of a 51-year-old male patient, severely burned, who benefited from sequential surgical treatment of deep burn wound excisions and coverage using autologous and allogenic skin grafts. PRP was added to this patient’s therapy in two stages, being injected and externally applied on the autografts in functional areas of the hands and the right upper arm region where both autografts and allografts were placed, with the exciting result of promoting allograft integration, long-term persistence and healing. Several literature data validate successful clinical applications of PRP in various therapies, including treatment of soft tissue injuries and chronic wounds, orthopedic surgery, burns, maxillo-facial surgery and elaboration of tissue-engineered products. Based on our preliminary experience and favourable reports in the literature, we encourage wider use of platelet rich plasma for immunomodulation and tissue-engineered constructs, due to its effects on local inflammatory response and role in enhancing the integration of various types of tissue grafts.

Conducting osteochondral injury model in rabbit knee: Pearls and pitfalls

Osteochondral damage is a commonly encountered issue in the daily orthopedic practice and has been extensively researched across various areas, including tissue transplantations, tissue engineering products, stem cell applications, and cell culture studies. The absence of a universally accepted treatment as the gold standard for osteochondral damage indicates the necessity for further studies in this field in the future. Although the biomechanical characteristics of the rabbit knee do not perfectly mimic those of the human knee, experimental studies conducted on rabbit knees are considered the most practical experimental model for testing a well-constructed experimental hypothesis. Our article endeavors to impart our practical insights and experiences to researchers without experience whom seeking to design studies utilizing this model. We aim to offer valuable guidance for preoperative, operative, and postoperative considerations.•Rabbits used in osteochondral healing models should be at least 4 months old or older. Inducing damage in the trochlea is a well-established technique and relatively easy to apply.•Do not use pointy ended drills as it might create uneven damage. Do not place applied treatment agent in inappropriate level in relation to the surrounding cartilage surface.

Cell-based medicinal products approved in the European Union: current evidence and perspectives.

Advanced Therapy Medicinal Products (ATMPs) are innovative clinical treatments exploiting the pharmacological, immunological, or metabolic properties of cells and/or gene(s) with the aim to restore, correct, or modify a biological function in the recipient. ATMPs are heterogeneous medicinal products, developed mainly as individualized and patient-specific treatments, and represent new opportunities for diseases characterized by a high-unmet medical need, including rare, genetic and neurodegenerative disorders, haematological malignancies, cancer, autoimmune, inflammatory and orthopaedic conditions. Into the European Union (EU) market, the first ATMP has been launched in 2009 and, to date, a total of 24 ATMPs have been approved. This review aims at reporting on current evidence of cell-based therapies authorized in the EU, including Somatic Cell Therapies, Tissue Engineering Products, and Cell-based Gene Therapy Products as Chimeric Antigen Receptor (CAR) T-cells, focusing on the evaluation of efficacy and safety in clinical trials and real-world settings. Despite cell-based therapy representing a substantial promise for patients with very limited treatment options, some limitations for its widespread use in the clinical setting remain, including restricted indications, highly complex manufacturing processes, elevated production costs, the lability of cellular products over time, and the potential safety concerns related to the intrinsic characteristics of living cells, including the risk of severe or life-threatening toxicities, such as CAR-T induced neurotoxicity and cytokine release syndrome (CRS). Although encouraging findings support the clinical use of ATMPs, additional data, comparative studies with a long-term follow-up, and wider real-world evidences are needed to provide further insights into their efficacy and safety profiles.

Alignment behavior of nerve, vascular, muscle, and intestine cells in two- and three-dimensional strategies.

By harnessing structural hierarchical insights, plausibly simulate better ones imagination to figure out the best choice of methods for reaching out the unprecedented developments of the tissue engineering products as a next level. Constructing a functional tissue that incorporates two-dimensional (2D) or higher dimensions requires overcoming technological or biological limitations in order to orchestrate the structural compilation of one-dimensional and 2D sheets (microstructures) simultaneously (in situ). This approach enables the creation of a layered structure that can be referred to as an ensemble of layers or, after several days of maturation, a direct or indirect joining of layers. Here, we have avoided providing a detailed methodological description of three-dimensional and 2D strategies, except for a few interesting examples that highlight the higher alignment of cells and emphasize rarely remembered facts associated with vascular, peripheral nerve, muscle, and intestine tissues. The effective directionality of cells in conjunction with geometric cues (in the range of micrometers) is well known to affect a variety of cell behaviors. The curvature of a cell's environment is one of the factors that influence the formation of patterns within tissues. The text will cover cell types containing some level of stemness, which will be followed by their consequences for tissue formation. Other important considerations pertain to cytoskeleton traction forces, cell organelle positioning, and cell migration. An overview of cell alignment along with several pivotal molecular and cellular level concepts, such as mechanotransduction, chirality, and curvature of structure effects on cell alignments will be presented. The mechanotransduction term will be used here in the context of the sensing capability that cells show as a result of force-induced changes either at the conformational or the organizational levels, a capability that allows us to modify cell fate by triggering downstream signaling pathways. A discussion of the cells' cytoskeleton and of the stress fibers involvement in altering the cell's circumferential constitution behavior (alignment) based on exposed scaffold radius will be provided. Curvatures with size similarities in the range of cell sizes cause the cell's behavior to act as if it was in an in vivo tissue environment. The revision of the literature, patents, and clinical trials performed for the present study shows that there is a clear need for translational research through the implementation of clinical trial platforms that address the tissue engineering possibilities raised in the current revision. This article is categorized under: Infectious Diseases > Biomedical Engineering Neurological Diseases > Biomedical Engineering Cardiovascular Diseases > Biomedical Engineering.

Hypericum perforatum Oil and Vitamin A Palmitate-Loaded Gelatin Nanofibers Cross-Linked by Tannic Acid as Wound Dressings.

Recent studies in wound dressing applications offer new therapies to promote the wound healing process. The main strategy of this study is to combine the traditional perspective of using medicinal oils with polymeric scaffolds manufactured by an engineering approach to fabricate a potential tissue engineering product that provides both new tissue formation and wound healing. Thus, Hypericum perforatum oil (HPO) and vitamin A palmitate (VAP) incorporated gelatin (Gt) nanofibrous scaffolds were successfully prepared by the electrospinning method. Tannic acid (TA) was used as the cross-linking agent. The amounts of VAP and HPO loaded in the base Gt solution [15% w/v in 4:6 v/v acetic acid/deionized water] were 5 and 50 wt % (based on the weight of Gt), respectively. The obtained scaffolds were studied regarding their microstructure, chemical structure, thermal stability, antibacterial activity, in vitro release study, and cellular proliferation assay. In the light of these studies, it was determined that VAP and HPO were incorporated successfully in Gt nanofibers cross-linked with TA. Release kinetic tests confirmed that the patterns of TA and VAP release were consistent with the Higuchi model, whereas HPO release was consistent with the first-order kinetic model. In addition, this membrane was biocompatible with L929 fibroblast cells and had antibacterial activity and thermal stability. This preliminary study suggests potential applicability of the proposed dressing to treat skin wounds in clinics.

Three-Dimensional Scaffolds for Bone Tissue Engineering.

Immobilization using external or internal splints is a standard and effective procedure to treat minor skeletal fractures. In the case of major skeletal defects caused by extreme trauma, infectious diseases or tumors, the surgical implantation of a bone graft from external sources is required for a complete cure. Practical disadvantages, such as the risk of immune rejection and infection at the implant site, are high in xenografts and allografts. Currently, an autograft from the iliac crest of a patient is considered the "gold standard" method for treating large-scale skeletal defects. However, this method is not an ideal solution due to its limited availability and significant reports of morbidity in the harvest site (30%) as well as the implanted site (5-35%). Tissue-engineered bone grafts aim to create a mechanically strong, biologically viable and degradable bone graft by combining a three-dimensional porous scaffold with osteoblast or progenitor cells. The materials used for such tissue-engineered bone grafts can be broadly divided into ceramic materials (calcium phosphates) and biocompatible/bioactive synthetic polymers. This review summarizes the types of materials used to make scaffolds for cryo-preservable tissue-engineered bone grafts as well as the distinct methods adopted to create the scaffolds, including traditional scaffold fabrication methods (solvent-casting, gas-foaming, electrospinning, thermally induced phase separation) and more recent fabrication methods (fused deposition molding, stereolithography, selective laser sintering, Inkjet 3D printing, laser-assisted bioprinting and 3D bioprinting). This is followed by a short summation of the current osteochondrogenic models along with the required scaffold mechanical properties for in vivo applications. We then present a few results of the effects of freezing and thawing on the structural and mechanical integrity of PLLA scaffolds prepared by the thermally induced phase separation method and conclude this review article by summarizing the current regulatory requirements for tissue-engineered products.

Current and Future Developments in Wound Healing.

Poor wound healing on the face and neck can lead to significant morbidity and dissatisfaction in facial plastic surgery. With current advances in wound healing management and commercially available biologic and tissue-engineered products, there are several options available to optimize acute wound healing and treat delayed or chronic wounds. This article summarizes some of the key principals and recent developments in wound healing research in addition to potential future advancements in the field of soft tissue wound healing.

PLGA: A Wow Smart Biodegradable Polymer in Drug Delivery System

Abstract: Aim: This article describes how biodegradable polymers and their drug delivery mechanisms can be used to monitor and maintain local or targeted drug distribution. Polylactic-co-glycol acid has been one of the most appealing polymeric candidates for creating drug release and tissue engineering products over the last couple of decades. PLGA has a variety of purposes due to its biodegradability and biocompatibility. Materials and Methods: The enclosed medicine is delivered from PLGA microparticles via diffusion bulk erosion of the biopolymer, with the diffusion rate mainly observed by the drug distributing and partition coefficient. Microparticles with customization and time-controlled drug release can be fabricated. Results: Drugs as anticancer agents, anti-inflammatory non-steroidal, and nutraceutical were favorably close in microparticles made by different methods. Advances in nanobiotechnology have led to a wide range of new technologies which could be used to improve drug delivery rates. Manufacturing methods for PLGA Properties associated nanoparticles, as well as their promising pharmacological uses, also including drug carriers Polymers are involved in making safe and effective immunization, drug, and gene delivery mechanisms using well-described, repeatable fabrication procedures. It has a huge variety of erosion times, unsuitable physical properties, and most fundamentally, FDA approval polymer content. Conclusion: The FDA has approved PLGA for use in a variety of drug delivery systems. The appropriate release rates for pharmaceuticals can be accomplished by varying the lactic acid to glycolic acid ratio. Keywords: PLGA, Biodegradable, Polymer, Drug delivery system, Biocompatible.

Natural 3D Extra Cellular Matrix mimicking stem cells seeded decellularized scaffolds as a platform for tendon regeneration.

Achilles tendon, which connects the calf muscles to heel, is the strongest tendon in the body. Despite its strength, it is more prone to injury due to its limited blood supply. Tendon-related injuries are more common in sportspersons, people with labor-intensive work and the aged community. The currently available treatment mode is surgery which is expensive with chances of re-injury. Present study made an attempt to fabricate a tissue-engineered tendon product using decellularized tendon (DT) seeded with stem cells and bioactive components of Tinospora cordifolia extract (TCE). The bare DT tissue scaffold/substitute may also serve as a drug delivery platform for growth factors and cells with a new approach to promote tissue regeneration in clinical applications. DT construct showed good regenerative potential and easily promoted new tissue formation. Decellularization of the tendon was carried out by chemical method using tri (n-butyl) phosphate (TnBP). DT was physicochemically characterized by contact angle measurement, thermal gravimetric analysis (TGA), and mechanical testing. Rabbit adipose derived mesenchymal stem cells (RADMSCs) were isolated and phenotypically characterized by flow cytometry analysis, tri lineage differentiation, and so forth. Further, stem cell seeded DT scaffolds were prepared and found to be non-toxic by cytotoxicity, cell adhesion by scanning electron microscope (SEM) analysis, cell viability by live dead assays, and so forth. The findings of this study yield valid proof for the employability of cell-seeded DT construct as a natural scaffold in repairing injured tendons-the toughest chords of the skeleton. This is a cost effective method for the replacement of injured/damaged tendons for athletes, people in labor-intensive occupations, the elderly population, and so forth-a boon towards the repair of the tendon in damage/injury.

Primary Chondroprogenitors: Standardized & Versatile Allogeneic Cytotherapeutics

Primary chondroprogenitors obtained from standardized cell sources (e.g., FE002 clinical grade cell sources) may be cultured in vitro and may be cytotherapeutically applied in allogeneic musculoskeletal regenerative medicine. Multicentric translational research on FE002 human primary chondroprogenitors under the Swiss progenitor cell transplantation program has notably validated their robustness and high versatility for therapeutic formulation in clinically compatible prototypes, as well as a good safety profile in diverse in vivo preclinical models. Therein, stringently controlled primary cell source establishment and extensive cell manufacturing optimization have technically confirmed the adequation of FE002 primary chondroprogenitors with standard industrial biotechnology workflows for consistent diploid cell biobanking under GMP. Laboratory characterization studies and extensive qualification work on FE002 progenitor cell sources have elucidated the key and critical attributes of the cellular materials of interest for potential and diversified human cytotherapeutic uses. Multiple formulation studies (i.e., hydrogel-based standardized transplants, polymeric-scaffold-based tissue engineering products) have shown the high versatility of FE002 primary chondroprogenitors, for the obtention of functional allogeneic cytotherapeutics. Multiple in vivo preclinical studies (e.g., rodent models, GLP goat model) have robustly documented the safety of FE002 primary chondroprogenitors following implantation. Clinically, FE002 primary chondroprogenitors may potentially be used in various forms for volumetric tissue replacement (e.g., treatment of large chondral/osteochondral defects of the knee) or for the local management of chondral affections and pathologies (i.e., injection use in mild to moderate osteoarthritis cases). Overall, standardized FE002 primary chondroprogenitors as investigated under the Swiss progenitor cell transplantation program were shown to constitute tangible contenders in novel human musculoskeletal regenerative medicine approaches, for versatile and safe allogeneic clinical cytotherapeutic management.

HISTOLOGICAL AND MORPHOMETRIC STUDIES OF BONE TISSUE AUTOGRAFTS FROM INTRAORAL AND EXTRAORAL DONOR ZONES

Major research carried out in modern dentistry and maxillofacial surgery is commonly focused on long-term and stable results for implant rehabilitation of jaw defects and deformities in patients with bone and soft tissue losses at the site of planned implantation. Various osteoplastic materials, donor or the patient’s own bone, tissue-engineering and cellular products are common in clinical medicine, since guided regeneration can help not only recover the volume of bone tissue once lost, yet also ensure an outcome acceptable from both functional and aesthetic view. Guided bone regeneration employs methods of regenerative medicine and tissue engineering, with transplantation of native bone tissue and cell transplants, as well as various osteoplastic materials with osteoinductive and osteoconductive properties. In order to compare the structure of intact bone tissue obtained from intraoral and extraoral donor zones, histological and morphometric studies of bone autografts in 4 certified male cadavers with intact dentition were carried out. The results of histological studies in bone tissue autografts from intraoral and extraoral donor zones revealed that the highest density of bone rods could be observed in biopsies taken from the mandible outer oblique line area and chin symphysis. Whereas the lowest rate of the said factor we observed in the biopsies obtained from the iliac crest area. The highest rate of the inter-rod girder space was found in the area of the iliac crest, and the minimal – in biopsies from the parietal bone. The highest bone vascularization level was identified at the iliac crest and the parietal bone, while its lowest levels were seen in biopsies taken from the area of the mandible outer oblique line. The density of cellular elements was found to be highest at the iliac crest. The lowest density level was registered in biopsies from the area of the mandible outer oblique line. The high rates of cellular elements in autografts from the iliac crest area can be accounted for by the predominance of spongy substance over cortical, while in bone biopsies taken from the mandible outer oblique line, chin symphysis, maxillary tuberosity and parietal bone, the share of cellular elements failed to exceed 27% within the total data set. This points at the predominance of cortical rather than spongy substance. In reconstructive bone plastic surgery for augmentation of the maxillary alveolar process and the mandible alveolar part with significant atrophy, it is reasonable to use autogenous transplants taken from intraoral donor zones. The autogenous transplants have cortical morphology and embryological origin similar to the jaw bones. Bone blocks from the donor zones of the mandible outer oblique line, the chin symphysis and the maxillary tuberosity have the highest density of the bone cortical substance and the duly sufficient amount of spongy substance.

Tissue Engineering - A New Aspect in Periodontal Regeneration

The goal behind periodontal treatment is to accomplish regeneration of tissues affected by periodontal disease. Periodontal regeneration is the restoration of original architecture and function of periodontal tissue. Tissue engineering is a way to repair or restore human tissue. It may provide a promising approach to regenerate complex periodontal tissue. Strategies to tissue engineering are conductive approach, inductive approach and cell transplantation approach. The main aim of this review is to explain the available tissue engineering products, their importance and their advantages in terms of periodontal regeneration reported in the literature. Furthermore, we emphasize on recent advances in tissue engineering, gene therapy and nanotechnology.

Formalin-free fixation and xylene-free tissue processing preserves cell-hydrogel interactions for histological evaluation of 3D calcium alginate tissue engineered constructs

Histological evaluation of tissue-engineered products, including hydrogels for cellular encapsulation, is a critical and invaluable tool for assessing the product across multiple stages of its lifecycle from manufacture to implantation. However, many tissue-engineered products are comprised of polymers and hydrogels which are not optimized for use with conventional methods of tissue fixation and histological processing. Routine histology utilizes a combination of chemical fixatives, such as formaldehyde, and solvents such as xylene which have been optimized for use with native biological tissues due to their high protein and lipid content. Previous work has highlighted the challenges associated with processing hydrogels for routine histology due to their high water content and lack of diverse chemical moieties amenable for tissue fixation with traditional fixatives. Thus, hydrogel-based tissue engineering products are prone to histological artifacts during their validation which can lead to challenges in correctly interpreting results. In addition, chemicals used in conventional histological approaches are associated with significant health and environmental concerns due to their toxicity and there is thus an urgent need to identify suitable replacements. Here we use a multifactorial design of experiments approach to identify processing parameters capable of preserving cell-biomaterial interactions in a prototypical hydrogel system: ionically crosslinked calcium alginate. We identify a formalin free fixative which better retains cell-biomaterial interactions and calcium alginate hydrogel integrity as compared to the state-of-the-art formalin-based approaches. In addition, we demonstrate that this approach is compatible with a diversity of manufacturing techniques used to fabricate calcium alginate-based scaffolds for tissue engineering and cell therapy, including histological evaluation of cellular encapsulation in 3D tubes and thin tissue engineering scaffolds (∼50 μm). Furthermore, we show that formalin-free fixation can be used to retain cell-biomaterial interactions and hydrogel architecture in hybrid alginate-gelatin based scaffolds for use with histology and scanning electron microscopy. Taken together, these findings are a significant step forward towards improving histological evaluation of ionically crosslinked calcium alginate hydrogels and help make their validation less toxic, thus more environmentally friendly and sustainable.

Bioreactor strategies for tissue-engineered osteochondral constructs: Advantages, present situations and future trends

The aim of osteochondral tissue engineering is to achieve the complex, functional and three-dimensional tissue regeneration under well defined, controlled and reproducible conditions in vitro. To achieve tissue-engineered products in vitro that incorporate rapidly in vivo with healthy tissue, it is essential to develop high-performance cell/scaffold culture systems that mimic the dynamics of the in vivo environment. Bioreactors could provide specific physicochemical culture environment, suitable mechanical stimulation and controlled condition for the development of osteochondral constructs in vitro. This review highlighted the multifunction of bioreactor in tissue engineering, and presented microenvironment and biomechanics of native osteochondral tissue, to illustrate the necessity of establishing osteochondral constructs by bioreactor. Then, we especially emphasized the advantages and limitations of various bioreactors. Furthermore, we systematically summarized and discussed the development of bioreactor-based production systems for bone, cartilage and osteochondral tissue engineering in recent years. Finally, we made a simple conclusion and offered perspectives of bioreactor‐based osteochondral tissue engineering. This review aims to serve as a reference for incorporating bioreactor strategies which could provide mechanical stimulation and physicochemical culture environment into the osteochondral construct culture regimens.