Materials for Dentoalveolar Bioprinting: Current State of the Art

Although current treatments can successfully address a wide range of complications in the dentoalveolar region, they often still suffer from drawbacks and limitations, resulting in sub-optimal treatments for specific problems. In recent decades, significant progress has been made in the field of tissue engineering, aiming at restoring damaged tissues via a regenerative approach. Yet, the translation into a clinical product is still challenging. Novel technologies such as bioprinting have been developed to solve some of the shortcomings faced in traditional tissue engineering approaches. Using automated bioprinting techniques allows for precise placement of cells and biological molecules and for geometrical patient-specific design of produced biological scaffolds. Recently, bioprinting has also been introduced into the field of dentoalveolar tissue engineering. However, the choice of a suitable material to encapsulate cells in the development of so-called bioinks for bioprinting dentoalveolar tissues is still a challenge, considering the heterogeneity of these tissues and the range of properties they possess. This review, therefore, aims to provide an overview of the current state of the art by discussing the progress of the research on materials used for dentoalveolar bioprinting, highlighting the advantages and shortcomings of current approaches and considering opportunities for further research.

Effect of Amniotic Membrane/Collagen-Based Scaffolds on the Chondrogenic Differentiation of Adipose-Derived Stem Cells and Cartilage Repair

Objectives: Repairing articular cartilage damage is challenging. Clinically, tissue engineering technology is used to induce stem cell differentiation and proliferation on biological scaffolds to repair defective joints. However, no ideal biological scaffolds have been identified. This study investigated the effects of amniotic membrane/collagen scaffolds on the differentiation of adipose-derived stem cells (ADSCs) and articular cartilage repair.Methods: Adipose tissue of New Zealand rabbits was excised, and ADSCs were isolated and induced for differentiation. An articular cartilage defect model was constructed to identify the effect of amniotic membrane/collagen scaffolds on cartilage repair. Cartilage formation was analyzed by imaging and toluene blue staining. Knee joint recovery in rabbits was examined using hematoxylin and eosin, toluidine, safranine, and immunohistochemistry at 12 weeks post-operation. Gene expression was examined using ELISA, RT-PCR, Western blotting, and immunofluorescence.Results: The adipose tissue was effectively differentiated into ADSCs, which further differentiated into chondrogenic, osteogenic, and lipogenic lineages after 3 weeks’ culture in vitro. Compared with platelet-rich plasmon (PRP) scaffolds, the amniotic membrane scaffolds better promoted the growth and differentiation of ADSCs. Additionally, scaffolds containing the PRP and amniotic membrane efficiently enhanced the osteogenic differentiation of ADSCs. The levels of COL1A1, COL2A1, COL10A1, SOX9, and ACAN in ADSCs + amniotic membrane + PRP group were significantly higher than the other groups both in vitro and in vivo. The Wakitani scores of the ADSC + amniotic membrane + PRP group were lower than that in ADSC + PRP (4.4 ± 0.44**), ADSC + amniotic membrane (2.63 ± 0.38**), and control groups (6.733 ± 0.21) at week 12 post-operation. Osteogenesis in rabbits of the ADSC + amniotic membrane + PRP group was significantly upregulated when compared with other groups. Amniotic membranes significantly promoted the expression of cartilage regeneration-related factors (SOX6, SOX9, RUNX2, NKX3-2, MEF2C, and GATA4). The ADSC + PRP + amniotic membrane group exhibited the highest levels of TGF-β, PDGF, and FGF while exhibiting the lowest level of IL-1β, IL6, and TNF-α in articular cavity.Conclusion: Amniotic membrane/collagen combination-based scaffolds promoted the proliferation and cartilage differentiation of ADSCs, and may provide a new treatment paradigm for patients with cartilage injury.

Physical Cues of Matrices Reeducate Nerve Cells

The behavior of nerve cells plays a crucial role in nerve regeneration. The mechanical, topographical, and electrical microenvironment surrounding nerve cells can activate cellular signaling pathways of mechanical transduction to affect the behavior of nerve cells. Recently, biological scaffolds with various physical properties have been developed as extracellular matrix to regulate the behavior conversion of nerve cell, such as neuronal neurite growth and directional differentiation of neural stem cells, providing a robust driving force for nerve regeneration. This review mainly focused on the biological basis of nerve cells in mechanical transduction. In addition, we also highlighted the effect of the physical cues, including stiffness, mechanical tension, two-dimensional terrain, and electrical conductivity, on neurite outgrowth and differentiation of neural stem cells and predicted their potential application in clinical nerve tissue engineering.

Decellularization Strategies to Engineer Fibrocartilage Bioscaffolds: A Review

Fibrocartilage or known as meniscus tissues located in between the tibia and femur always subjected to extreme forces that can lead to injury especially for the sportsperson. The meniscal injury mean incidence in the general population is 66 per 100,000. The principal methods for the surgical management of fibrocartilage injury have been improvised from meniscectomy to meniscal repair and meniscal reconstruction that portrays different advantages and disadvantages in the short and long-term results. The inability to treat meniscus injury without osteoarthritis development in long-term results also motivates to find new treatment strategies. In this current era, the development of the multidisciplinary fields of tissue engineering and regenerative medicine provides new alternatives for the treatment approaches. This field involves the regeneration of the required tissue using scaffolds such as synthetic, natural, and biological scaffolds to restore the damaged one. Biological scaffolds are preferable because it tremendously mimics the native anatomical structure and has similar ratios and concentration of the proteins and growth factors that influence tissue repair and remodeling. The development of biological scaffolds with low immunogenic levels involves the decellularization process that eliminates all the cellular components while preserved the extracellular matrix (ECM) integrity and mechanics. In this review, the pros and cons of the recent decellularization strategies to engineer fibrocartilage scaffolds have been discussed. We believed that the ideal decellularization methods still need to be explored to develop suitable biological scaffolds that structurally and functionally mimic native tissue as a replacement for new tissue regeneration.

Preparing Sheep Bladder Scaffold and Examining the Differentiation of Mesenchymal Stem Cell into Myocytes on Scaffolds

Background: Tissue engineering may be used to repair, preserve, or improve tissues and organs. In this regard, acellular biological scaffolds are mainly used to reconstruct damaged tissues in regenerative medicine. Objectives: The present study examined the in vitro process of myocytes differentiated from bone marrow mesenchymal stem cells (BM‐MSCs) on the sheep bladder scaffold induced by 5-azacytidine. Methods: Decellularization was performed using a mixed method (physical and chemical) to prepare scaffolds kept at -20°C. The 5-azacytidine was used to induce BM‐MSCs to myocytes. Moreover, the muscle-specific gene expression (Desmin, α-Actinin, Myo D) was evaluated using the RT-PCR method. Results: It was revealed that BM‐MSCs on the scaffold had high proliferation and differentiation potentials. Desmin and α-Actinin gene expression marked the differentiation at the end of the fourth week. Moreover, the results of Masson’s trichrome staining at the end of the second, third and, fourth weeks also indicated that the first differentiation signs emerged at the end of the second week. Furthermore, differentiation reached its maximum level during the fourth week. Conclusions: According to the findings, combining physical and chemical methods was the best technique to prepare the bladder scaffold so that the bone marrow mesenchymal stem cells can be differentiated into myocytes on the bladder scaffold affected by 5-azacytidine (5 µmol), and As the induction time increases to day 28, myocyte cells become more developed.

FGF2 and EGF for the Regeneration of Tympanic Membrane: A Systematic Review

Objective. A systematic review was conducted to compare the effectiveness and safety of fibroblast growth factor-2 (FGF2) and epidermal growth factor (EGF) for regeneration of the tympanic membrane (TM). Methods. The PubMed database was searched for relevant studies. Experimental and clinical studies reporting acute and chronic TM perforations in relation to two healing outcomes (success rate and closure time) and complications were selected. Results. A total of 47 studies were included. Five experimental studies showed closure rates of 55%–100% with FGF2 compared with 10%–62.5% in controls for acute perforations. Five experimental studies showed closure rates of 30.3%–100% with EGF and 3.6%–41% in controls for chronic perforations. Two experimental studies showed closure rates of 31.6% or 85.7% with FGF2 and 15.8% or 100% with EGF. Nine clinical studies of acute large perforations showed closure rates of 91.4%–100% with FGF2 or EGF. Two clinical studies showed similar closure rates between groups treated with FGF2 and EGF. Seven clinical studies showed closure rates of 88.9%–100% within 3 months and 58%–66% within 12 months using FGF2 in repair of chronic perforations, but only one study showed a significantly higher closure rate in the saline group compared with the FGF2 group (71.4% vs. 57.5%, respectively, P = 0.547 ). In addition, three experimental studies showed no ototoxicity associated with FGF2 or EGF. No middle ear cholesteatoma or epithelial pearls were reported, except in one experimental study and one clinical study, respectively. Conclusions. FGF2 and EGF showed good effects and reliable safety for the regeneration of TM. In addition, EGF was better for the regeneration of acute perforations, while FGF2 combined with biological scaffolds was superior to EGF for chronic perforations, but was associated with high rates of reperforation over time. Further studies are required to determine whether EGF or FGF2 is better for TM regeneration.