Orthotopic Bone Formation by Streamlined Engineering and Devitalization of Human Hypertrophic Cartilage

Advances in abiotic tissue-based biomaterials: A focus on decellularization and devitalization techniques

This Review explores the growing and diversifying field of tissue-derived abiotic constructs for tissue engineering applications, with main focus on decellularization and devitalization techniques and principles. Acellular fractions derived from biological tissues, such as the extracellular matrix (ECM), have long been considered a valuable approach for the generation of numerous scaffolds and more complex constructs. The removal of the cellular content has been considered essential to prevent the development of adverse immunological reactions. Nevertheless, the discovery of promising features of certain cellular components has sparked interest in the use of inactivated or devitalized cellular fractions for several applications, particularly in regenerative medicine and inflammation control. Devitalization has been described for several clinical applications, but remains poorly explored in terms of in vitro constructs compared to decellularization methods currently available. In this review, we present and critically evaluate a spectrum of approaches for the decellularization of whole-organs and in vitro constructs, and the most prevalent devitalization techniques, with a discussion on their implications on scaffolds composition, structure, and potentially therapeutic properties. Processing methodologies to achieve optimal cell-based abiotic materials and approaches for their effective characterization are described and discussed. The application of these materials in healthcare, with most focus on regenerative approaches and including examples of commercially available products, is also addressed.

Application of Adipose Extracellular Matrix and Reduced Graphene Oxide Nanocomposites for Spinal Cord Injury Repair

Graphene-based materials (GBMs) hold strong promise to restore the spinal cord microenvironment and promote functional recovery after spinal cord injury (SCI). Nanocomposites consisting of reduced graphene oxide (rGO) and adipose tissue-derived extracellular matrix (adECM) are known to promote neuronal growth in vitro and to evoke a biocompatible response in vivo when implanted on top of the intact spinal cord. In this study, pristine adECM and adECM-rGO nanocomposites are implanted directly after hemisection SCI in rats. Scaffolds composed of collagen type I (COL) are applied as negative control, based on evidence that COL triggers integrin-mediated astrogliosis. However, COL scaffolds induce orthotopic bone formation in the lesion site and are therefore excluded from further analyses. Compared to pristine adECM, adECM-rGO nanocomposites completely restore spinal cord integrity. Macrophage-mediated uptake and clearance of rGO remnants is observed as early as 3 weeks post-implantation. Nanocomposites show an elevated presence of βIII-tubulin-positive axons in the host-material interface after 8 weeks, yet scaffold penetration by axons is only occasionally observed. This is partially due to an increased expression of chondroitin sulfate proteoglycans (CSPGs) within the nanocomposites, even though reactive astrogliosis is unaltered. Despite the complete restoration of tissue architecture, adECM-rGO treatment does not significantly improve functional recovery.

Exploring calcium-free alternatives in endochondral bone repair tested on In vivo trials - A review

Bone repair via endochondral ossification is a complex process for the critical size reparation of bone defects. Tissue engineering strategies are being developed as alternative treatments to autografts or allografts. Most approaches to bone regeneration involve the use of calcium composites. However, exploring calcium-free alternatives in endochondral bone repair has emerged as a promising way to contribute to bone healing. By analyzing researches from the last ten years, this review identifies the potential benefits of such alternatives compared to traditional calcium-based approaches. Understanding the impact of calcium-free alternatives on endochondral bone repair can have profound implications for orthopedic and regenerative medicine. This review evaluates the efficacy of calcium-free alternatives in endochondral bone repair through in vivo trials. The findings may guide future research to develop innovative strategies to improve endochondral bone repair without relying on calcium. Exploring alternative approaches may lead to the discovery of novel therapies that improve bone healing outcomes.

Engineered phalangeal grafts for children with symbrachydactyly: A proof of concept

Tissue engineering approaches hold great promise in the field of regenerative medicine, especially in the context of pediatric applications, where ideal grafts need to restore the function of the targeted tissue and consider growth. In the present study, we aimed to develop a protocol to engineer autologous phalangeal grafts of relevant size for children suffering from symbrachydactyly. This condition results in hands with short fingers and missing bones. A previously-described, developmentally-inspired strategy based on endochondral ossification (ECO)-the main pathway leading to bone and bone marrow development-and adipose derived-stromal cells (ASCs) as the source of chondroprogenitor was used. First, we demonstrated that pediatric ASCs associated with collagen sponges can generate hypertrophic cartilage tissues (HCTs) in vitro that remodel into bone tissue in vivo via ECO. Second, we developed and optimized an in vitro protocol to generate HCTs in the shape of small phalangeal bones (108-390 mm3) using freshly isolated adult cells from the stromal vascular fraction (SVF) of adipose tissue, associated with two commercially available large collagen scaffolds (Zimmer Plug® and Optimaix 3D®). We showed that after 12 weeks of in vivo implantation in an immunocompromised mouse model such upscaled grafts remodeled into bone organs (including bone marrow tissues) retaining the defined shape and size. Finally, we replicated similar outcome (albeit with a slight reduction in cartilage and bone formation) by using minimally expanded pediatric ASCs (3 × 106 cells per grafts) in the same in vitro and in vivo settings, thereby validating the compatibility of our pediatric phalanx engineering strategy with a clinically relevant scenario. Taken together, these results represent a proof of concept of an autologous approach to generate osteogenic phalangeal grafts of pertinent clinical size, using ASCs in children born with symbrachydactyly, despite a limited amount of tissue available from pediatric patients.

Translation of biophysical environment in bone into dynamic cell culture under flow for bone tissue engineering

Bone is a dynamic environment where osteocytes, osteoblasts, and mesenchymal stem/progenitor cells perceive mechanical cues and regulate bone metabolism accordingly. In particular, interstitial fluid flow in bone and bone marrow serves as a primary biophysical stimulus, which regulates the growth and fate of the cellular components of bone. The processes of mechano-sensory and -transduction towards bone formation have been well studied mainly in vivo as well as in two-dimensional (2D) dynamic cell culture platforms, which elucidated mechanically induced osteogenesis starting with anabolic responses, such as production of nitrogen oxide and prostaglandins followed by the activation of canonical Wnt signaling, upon mechanosensation. The knowledge has been now translated into regenerative medicine, particularly into the field of bone tissue engineering, where multipotent stem cells are combined with three-dimensional (3D) scaffolding biomaterials to produce transplantable constructs for bone regeneration. In the presence of 3D scaffolds, the importance of suitable dynamic cell culture platforms increases further not only to improve mass transfer inside the scaffolds but to provide appropriate biophysical cues to guide cell fate. In principle, the concept of dynamic cell culture platforms is rooted to bone mechanobiology. Therefore, this review primarily focuses on biophysical environment in bone and its translation into dynamic cell culture platforms commonly used for 2D and 3D cell expansion, including their advancement, challenges, and future perspectives. Additionally, it provides the literature review of recent empirical studies using 2D and 3D flow-based dynamic cell culture systems for bone tissue engineering.

Fabricating the cartilage: recent achievements

This review aims to describe the most recent achievements and provide an insight into cartilage engineering and strategies to restore the cartilage defects. Here, we discuss cell types, biomaterials, and biochemical factors applied to form cartilage tissue equivalents and update the status of fabrication techniques, which are used at all stages of engineering the cartilage. The actualized concept to improve the cartilage tissue restoration is based on applying personalized products fabricated using a full cycle platform: a bioprinter, a bioink consisted of ECM-embedded autologous cell aggregates, and a bioreactor. Moreover, in situ platforms can help to skip some steps and enable adjusting the newly formed tissue in the place during the operation. Only some achievements described have passed first stages of clinical translation; nevertheless, the number of their preclinical and clinical trials is expected to grow in the nearest future.

Immunogenicity of decellularized extracellular matrix scaffolds: a bottleneck in tissue engineering and regenerative medicine

Tissue-engineered decellularized extracellular matrix (ECM) scaffolds hold great potential to address the donor shortage as well as immunologic rejection attributed to cells in conventional tissue/organ transplantation. Decellularization, as the key process in manufacturing ECM scaffolds, removes immunogen cell materials and significantly alleviates the immunogenicity and biocompatibility of derived scaffolds. However, the application of these bioscaffolds still confronts major immunologic challenges. This review discusses the interplay between damage-associated molecular patterns (DAMPs) and antigens as the main inducers of innate and adaptive immunity to aid in manufacturing biocompatible grafts with desirable immunogenicity. It also appraises the impact of various decellularization methodologies (i.e., apoptosis-assisted techniques) on provoking immune responses that participate in rejecting allogenic and xenogeneic decellularized scaffolds. In addition, the key research findings regarding the contribution of ECM alterations, cytotoxicity issues, graft sourcing, and implantation site to the immunogenicity of decellularized tissues/organs are comprehensively considered. Finally, it discusses practical solutions to overcome immunogenicity, including antigen masking by crosslinking, sterilization optimization, and antigen removal techniques such as selective antigen removal and sequential antigen solubilization.

Repair of a Rat Mandibular Bone Defect by Hypertrophic Cartilage Grafts Engineered From Human Fractionated Adipose Tissue

Background: Devitalized bone matrix (DBM) is currently the gold standard alternative to autologous bone grafting in maxillofacial surgery. However, it fully relies on its osteoconductive properties and therefore requires defects with healthy bone surrounding. Fractionated human adipose tissue, when differentiated into hypertrophic cartilage in vitro, was proven reproducibly osteogenic in vivo, by recapitulating endochondral ossification (ECO). Both types of bone substitutes were thus compared in an orthotopic, preclinical mandibular defect model in rat.

Methods: Human adipose tissue samples were collected and cultured in vitro to generate disks of hypertrophic cartilage. After hypertrophic induction, eight samples from two donors were implanted into a mandible defect in rats, in parallel to Bio-Oss® DBM granules. After 12 weeks, the mandible samples were harvested and evaluated by Micro-CT and histology.

Results: Micro-CT demonstrated reproducible ECO and complete restoration of the mandibular geometry with adipose-based disks, with continuous bone inside and around the defect, part of which was of human (donor) origin. In the Bio-Oss® group, instead, osteoconduction from the border of the defect was observed but no direct connection of the granules with the surrounding bone was evidenced. Adipose-based grafts generated significantly higher mineralized tissue volume (0.57 ± 0.10 vs. 0.38 ± 0.07, n = 4, p = 0.03) and newly formed bone (18.9 ± 3.4% of surface area with bone tissue vs. 3 ± 0.7%, p < 0.01) than Bio-Oss^®.

Conclusion: Our results provide a proof-of-concept that adipose-based hypertrophic cartilage grafts outperform clinical standard biomaterials in maxillofacial surgery.

Recent approaches towards bone tissue engineering

Bone tissue engineering approaches have evolved towards addressing the challenges of tissue mimetic requirements over the years. Different strategies have been combining scaffolds, cells, and biologically active cues using a wide range of fabrication techniques, envisioning the mimicry of bone tissue. On the one hand, biomimetic scaffold-based strategies have been pursuing different biomaterials to produce scaffolds, combining with diverse and innovative fabrication strategies to mimic bone tissue better, surpassing bone grafts. On the other hand, biomimetic scaffold-free approaches mainly foresee replicating endochondral ossification, replacing hyaline cartilage with new bone. Finally, since bone tissue is highly vascularized, new strategies focused on developing pre-vascularized scaffolds or pre-vascularized cellular aggregates have been a motif of study. The recent biomimetic scaffold-based and scaffold-free approaches in bone tissue engineering, focusing on materials and fabrication methods used, are overviewed herein. The biomimetic vascularized approaches are also discussed, namely the development of pre-vascularized scaffolds and pre-vascularized cellular aggregates.

The therapeutic effects of X-ray devitalization and replantation and alcoholic devitalization and replantation in adolescent patients with lower limb osteosarcoma

OBJECTIVE

To compare and analyze the therapeutic effects of X-ray devitalization and replantation and alcoholic devitalization and replantation in adolescent patients with lower limb osteosarcoma.

METHODS

We collected clinical data for 43 osteosarcoma patients with limb salvage treatment treated in our hospital from February 2014 to February 2018. The patients were divided into x-ray devitalization and replantation group (n=23) and alcoholic devitalization and replantation group (n=20) based on the treatment methods. The two groups were compared in operation duration, intraoperative blood loss, postoperative fracture healing time, length of tumor bones, MSTS score and ISOLS score, postoperative complications, postoperative follow-ups and postoperative recurrence and metastases.

RESULTS

Operation duration and intraoperative blood loss of the alcoholic group were less than that of the X-ray group, while postoperative fracture healing time of the alcoholic group was longer than that of the X-ray group (P<0.05). For the X-ray group, MSTS score and ISOLO score of the final follow-up were 26.13±2.65 and 32.53±3.73 respectively. For the alcoholic group, MSTS score and ISOLO score of the final follow-up were 23.69±3.27 and 30.98±3.56 respectively. MSTS score of the X-ray group was higher than that of the alcoholic group (P<0.05). There were 2 cases of internal fixation failure and 2 cases of adhesive knee joints stiffness in the X-ray group. As for the alcoholic group, there were 2 cases of internal fixation failure and 2 cases of incision soft tissue infection. There were no statistically significant differences in postoperative complications, recurrence, and metastases between the two groups (P>0.05).

CONCLUSION

Both methods are convenient, inexpensive, and effective for adolescent patients with lower limb osteosarcoma. Alcoholic devitalization and replantation results in shorter operation duration and less intraoperative blood loss, while X-ray devitalization and replantation results in better postoperative limb function restoration.

The Application of Bioreactors for Cartilage Tissue Engineering: Advances, Limitations, and Future Perspectives

Tissue engineering (TE) has brought new hope for articular cartilage regeneration, as TE can provide structural and functional substitutes for native tissues. The basic elements of TE involve scaffolds, seeded cells, and biochemical and biomechanical stimuli. However, there are some limitations of TE; what most important is that static cell culture on scaffolds cannot simulate the physiological environment required for the development of natural cartilage. Recently, bioreactors have been used to simulate the physical and mechanical environment during the development of articular cartilage. This review aims to provide an overview of the concepts, categories, and applications of bioreactors for cartilage TE with emphasis on the design of various bioreactor systems.