The effects of cross-linking of collagen-glycosaminoglycan scaffolds on compressive stiffness, chondrocyte-mediated contraction, proliferation and biosynthesis

A Comparison of Guided Bone Regeneration vs. the Shell Technique Using Xenogeneic Bone Blocks in Horizontal Bone Defects: A Randomized Clinical Trial

In cases of severe horizontal atrophy, implant placement requires bone reconstruction procedures. The aim of this randomized controlled trial is to compare the outcomes of bone augmentation with simultaneous implant placement using the shell technique to the outcomes of guided bone regeneration (GBR) in cases of severely horizontal bone atrophy. This study was designed as a monocentric, parallel-group, randomized controlled trial with a six-month follow-up. Among the primary outcomes of this study, peri-implant bone regeneration and peri-implant bone defect closure were selected. Forty-four patients were recruited and equally divided between two groups. In the GRB group, a horizontal regeneration of 2.31 ± 0.23 mm was observed opposed to a horizontal regeneration of 2.36 ± 0.17 mm in the shell group (p = 0.87). A volumetric increase was observed in both groups, with an increase of 0.30 ± 0.12 cm3 in the GBR group and an increase of 0.39 ± 0.09 cm3 in the shell group, highlighting a significant difference between the two groups (p = 0.02). In conclusion, bone augmentation with simultaneous implant placement using the shell technique or guided bone regeneration in horizontal bone atrophy are both predictable therapeutic options.

Facilitate the preparation of naturally modified and self-healing superhydrophobic/superoleophilic biochar-based foams for efficient oil-water separation

Oil spills are sudden, complex, and long-term hazardous, and the existing adsorption materials still have the disadvantages of small selective adsorption capacity, easy secondary contamination, and difficult to repair after breakage in practical applications. Herein, melamine foam (MF) coated by ball milled biochar (BMBC) and natural beeswax (Wax@BMBC@MF) was prepared by a bio-inspired functionalization method and further added with self-healing function (SH-Wax@BMBC@MF) to cope with complex environments, and applied to oil-water separation for oil adsorption. SEM and FTIR results showed that BMBC and natural beeswax nanoparticles successfully encapsulated the smooth surface of the melamine foam skeleton. The loading of natural beeswax increased the foam's ability to absorb oil and organic solvents from 0.6108-1.134 g to 0.850-1.391 g, and the oil-absorbing capacity of the foam remained at 0. 758-1.263 g after being cut by a knife and self-healing. The oil-absorbing capacity of SH-Wax@BMBC@MF remained in the range of 0.936-1.336 g under acid/alkali environment (pH =1-13). The surface functional groups of BMBC improved the surface roughness of the material and strengthen the MF skeleton to adsorb oils and organic solvents by capillary action. The generation of the di-coordinated structure by Fe3+ and catechol group contributed the restoration of SH-Wax@BMBC@MF structure and oil absorption capacity. SH-Wax@BMBC@MF has superiority of superhydrophobic, superoleophilic, self-healing after damage, and environmental friendliness, which provides a promising solution for the treatment of oil spills at sea.

Collagen-Based Medical Devices for Regenerative Medicine and Tissue Engineering

Assisted reproductive technologies are key to solving the problems of aging and organ defects. Collagen is compatible with living tissues and has many different chemical properties; it has great potential for use in reproductive medicine and the engineering of reproductive tissues. It is a natural substance that has been used a lot in science and medicine. Collagen is a substance that can be obtained from many different animals. It can be made naturally or created using scientific methods. Using pure collagen has some drawbacks regarding its physical and chemical characteristics. Because of this, when collagen is processed in various ways, it can better meet the specific needs as a material for repairing tissues. In simpler terms, collagen can be used to help regenerate bones, cartilage, and skin. It can also be used in cardiovascular repair and other areas. There are different ways to process collagen, such as cross-linking it, making it more structured, adding minerals to it, or using it as a carrier for other substances. All of these methods help advance the field of tissue engineering. This review summarizes and discusses the current progress of collagen-based materials for reproductive medicine.

Cell-Tissue Interaction: The Biomimetic Approach to Design Tissue Engineered Biomaterials

The advancement achieved in Tissue Engineering is based on a careful and in-depth study of cell-tissue interactions. The choice of a specific biomaterial in Tissue Engineering is fundamental, as it represents an interface for adherent cells in the creation of a microenvironment suitable for cell growth and differentiation. The knowledge of the biochemical and biophysical properties of the extracellular matrix is a useful tool for the optimization of polymeric scaffolds. This review aims to analyse the chemical, physical, and biological parameters on which are possible to act in Tissue Engineering for the optimization of polymeric scaffolds and the most recent progress presented in this field, including the novelty in the modification of the scaffolds' bulk and surface from a chemical and physical point of view to improve cell-biomaterial interaction. Moreover, we underline how understanding the impact of scaffolds on cell fate is of paramount importance for the successful advancement of Tissue Engineering. Finally, we conclude by reporting the future perspectives in this field in continuous development.

Recent development in multizonal scaffolds for osteochondral regeneration

Osteochondral (OC) repair is an extremely challenging topic due to the complex biphasic structure and poor intrinsic regenerative capability of natural osteochondral tissue. In contrast to the current surgical approaches which yield only short-term relief of symptoms, tissue engineering strategy has been shown more promising outcomes in treating OC defects since its emergence in the 1990s. In particular, the use of multizonal scaffolds (MZSs) that mimic the gradient transitions, from cartilage surface to the subchondral bone with either continuous or discontinuous compositions, structures, and properties of natural OC tissue, has been gaining momentum in recent years. Scrutinizing the latest developments in the field, this review offers a comprehensive summary of recent advances, current hurdles, and future perspectives of OC repair, particularly the use of MZSs including bilayered, trilayered, multilayered, and gradient scaffolds, by bringing together onerous demands of architecture designs, material selections, manufacturing techniques as well as the choices of growth factors and cells, each of which possesses its unique challenges and opportunities.

Ultraviolet light induces mechanical and structural changes in full thickness human skin

While the detrimental health effects of prolonged ultraviolet (UV) irradiation on skin health have been widely accepted, the biomechanical process by which photoaging occurs and the relative effects of irradiation with different UV ranges on skin biomechanics have remained relatively unexplored. In this study, the effects of UV-induced photoageing are explored by quantifying the changes in the mechanical properties of full-thickness human skin irradiated with UVA and UVB light for incident dosages up to 1600 J/cm2. Mechanical testing of skin samples excised parallel and perpendicular to the predominant collagen fiber orientation show a rise in the fractional relative difference of elastic modulus, fracture stress, and toughness with increased UV irradiation. These changes become significant with UVA incident dosages of 1200 J/cm2 for samples excised both parallel and perpendicular to the dominant collagen fiber orientation. However, while mechanical changes occur in samples aligned with the collagen orientation at UVB dosages of 1200 J/cm2, statistical differences in samples perpendicular to the collagen orientation emerge only for UVB dosages of 1600 J/cm2. No notable or consistent trend is observed for the fracture strain. Analyses of toughness changes with maximum absorbed dosage reveals that no one UV range is more impactful in inducing mechanical property changes, but rather these changes scale with maximum absorbed energy. Evaluation of the structural characteristics of collagen further reveals an increase in collagen fiber bundle density with UV irradiation, but not collagen tortuosity, potentially linking mechanical changes to altered microstructure.

3D Bioprinting of Hyaline Articular Cartilage: Biopolymers, Hydrogels, and Bioinks

The musculoskeletal system, consisting of bones and cartilage of various types, muscles, ligaments, and tendons, is the basis of the human body. However, many pathological conditions caused by aging, lifestyle, disease, or trauma can damage its elements and lead to severe disfunction and significant worsening in the quality of life. Due to its structure and function, articular (hyaline) cartilage is the most susceptible to damage. Articular cartilage is a non-vascular tissue with constrained self-regeneration capabilities. Additionally, treatment methods, which have proven efficacy in stopping its degradation and promoting regeneration, still do not exist. Conservative treatment and physical therapy only relieve the symptoms associated with cartilage destruction, and traditional surgical interventions to repair defects or endoprosthetics are not without serious drawbacks. Thus, articular cartilage damage remains an urgent and actual problem requiring the development of new treatment approaches. The emergence of biofabrication technologies, including three-dimensional (3D) bioprinting, at the end of the 20th century, allowed reconstructive interventions to get a second wind. Three-dimensional bioprinting creates volume constraints that mimic the structure and function of natural tissue due to the combinations of biomaterials, living cells, and signal molecules to create. In our case-hyaline cartilage. Several approaches to articular cartilage biofabrication have been developed to date, including the promising technology of 3D bioprinting. This review represents the main achievements of such research direction and describes the technological processes and the necessary biomaterials, cell cultures, and signal molecules. Special attention is given to the basic materials for 3D bioprinting-hydrogels and bioinks, as well as the biopolymers underlying the indicated products.

Cutting Edge Aquatic-Based Collagens in Tissue Engineering

Aquatic-based collagens have attracted much interest due to their great potential application for biomedical sectors, including the tissue engineering sector, as a major component of the extracellular matrix in humans. Their physical and biochemical characteristics offer advantages over mammalian-based collagen; for example, they have excellent biocompatibility and biodegradability, are easy to extract, and pose a relatively low immunological risk to mammalian products. The utilization of aquatic-based collagen also has fewer religious restrictions and lower production costs. Aquatic-based collagen also creates high-added value and good environmental sustainability by aquatic waste utilization. Thus, this study aims to overview aquatic collagen's characteristics, extraction, and fabrication. It also highlights its potential application for tissue engineering and the regeneration of bone, cartilage, dental, skin, and vascular tissue. Moreover, this review highlights the recent research in aquatic collagen, future prospects, and challenges for it as an alternative biomaterial for tissue engineering and regenerative medicines.

Understanding the Influence of Local Physical Stimuli on Chondrocyte Behavior

Investigating the mechanobiology of chondrocytes is challenging due to the complex micromechanical environment of cartilage tissue. The innate zonal differences and poroelastic properties of the tissue combined with its heterogeneous composition create spatial- and temporal-dependent cell behavior, which further complicates the investigation. Despite the numerous challenges, understanding the mechanobiology of chondrocytes is crucial for developing strategies for treating cartilage related diseases as chondrocytes are the only cell type within the tissue. The effort to understand chondrocyte behavior under various mechanical stimuli has been ongoing over the last 50 years. Early studies examined global biosynthetic behavior under unidirectional mechanical stimulus. With the technological development in high-speed confocal imaging techniques, recent studies have focused on investigating real-time individual and collective cell responses to multiple / combined modes of mechanical stimuli. Such efforts have led to tremendous advances in understanding the influence of local physical stimuli on chondrocyte behavior. In addition, we highlight the wide variety of experimental techniques, spanning from static to impact loading, and analysis techniques, from biochemical assays to machine learning, that have been utilized to study chondrocyte behavior. Finally, we review the progression of hypotheses about chondrocyte mechanobiology and provide a perspective on the future outlook of chondrocyte mechanobiology.

Optimization of Freeze-FRESH Methodology for 3D Printing of Microporous Collagen Constructs

Freeform reversible embedding of suspended hydrogels (FRESH) is a layer-by-layer extrusion-based technique to enable three-dimensional (3D) printing of soft tissue constructs by using a thermo-reversible gelatin support bath. Suboptimal resolution of extrusion-based printing limits its use for the creation of microscopic features in the 3D construct. These microscopic features (e.g., pore size) are known to have a profound effect on cell migration, cell-cell interaction, proliferation, and differentiation. In a recent study, FRESH-based 3D printing was combined with freeze-casting in the Freeze-FRESH (FF) method, which yielded alginate constructs with hierarchical porosity. However, use of the FF approach allowed little control of micropore size in the printed alginate constructs. Herein, the FF methodology was optimized for 3D printing of collagen constructs with greater control of microporosity. Modifications to the FF method entailed melting of the FRESH bath before freezing to allow more efficient heat transport, achieve greater control on microporosity, and permit polymerization of collagen molecules to enable 3D printing of stable microporous collagen constructs. The effects of different freezing temperatures on microporosity and physical properties of the 3D-printed collagen constructs were assessed. In addition, finite element (FE) models were generated to predict the mechanical properties of the microporous constructs. Further, the impact of different micropore sizes on cellular response was evaluated. Results showed that the microporosity of 3D-printed collagen constructs can be tailored by customizing the FF approach. Compressive modulus of microporous constructs was significantly lower than the non-porous control, and the FE model verified these findings. Constructs with larger micropore size were more stable and showed significantly greater cell infiltration and metabolic activity. Together, these results suggest that the FF method can be customized to guide the design of 3D-printed microporous collagen constructs.

Challenges and tissue engineering strategies of periodontal guided tissue regeneration

Periodontitis is a chronic infectious oral disease with a high prevalence rate in the world, and is a major cause of tooth loss. Nowadays, people have realized that the local microenvironment that includes proteins, cytokines, and extracellular matrix has a key influence on the functions of host immune cells and periodontal ligament stem cells during a chronic infectious disease such as periodontitis. The above pathological process of periodontitis will lead to a defect of periodontal tissues. Through the application of biomaterials, biological agents, and stem cells therapy, guided tissue regeneration (GTR) makes it possible to reconstruct healthy periodontal ligament tissue after local inflammation control. To date, substantial advances have been made in periodontal guided tissue regeneration. However, the process of periodontal remodeling experiences complex microenvironment changes, and currently periodontium regeneration still remains to be a challenging feat. In this review, we summarized the main challenges in each stage of periodontal regeneration, and try to put forward appropriate biomaterial treatment mechanisms or potential tissue engineering strategies that provide a theoretical basis for periodontal tissue engineering regeneration research.

Hydrogels for Exosome Delivery in Biomedical Applications

Hydrogels, which are hydrophilic polymer networks, have attracted great attention, and significant advances in their biological and biomedical applications, such as for drug delivery, tissue engineering, and models for medical studies, have been made. Due to their similarity in physiological structure, hydrogels are highly compatible with extracellular matrices and biological tissues and can be used as both carriers and matrices to encapsulate cellular secretions. As small extracellular vesicles secreted by nearly all mammalian cells to mediate cell–cell interactions, exosomes play very important roles in therapeutic approaches and disease diagnosis. To maintain their biological activity and achieve controlled release, a strategy that embeds exosomes in hydrogels as a composite system has been focused on in recent studies. Therefore, this review aims to provide a thorough overview of the use of composite hydrogels for embedding exosomes in medical applications, including the resources for making hydrogels and the properties of hydrogels, and strategies for their combination with exosomes.

A two-stage in vivo approach for implanting a 3D printed tissue-engineered tracheal replacement graft: A proof of concept

OBJECTIVES

To optimize a 3D printed tissue-engineered tracheal construct using a combined in vitro and a two-stage in vivo technique.

METHODS

A 3D-CAD (Computer-aided Design) template was created; rabbit chondrocytes were harvested and cultured. A Makerbot Replicator™ 2x was used to print a polycaprolactone (PCL) scaffold which was then combined with a bio-ink and the previously harvested chondrocytes. In vitro: Cell viability was performed by live/dead assay using Calcein A/Ethidium. Gene expression was performed using quantitative real-time PCR for the following genes: Collagen Type I and type II, Sox-9, and Aggrecan. In vivo: Surgical implantation occurred in two stages: 1) Index procedure: construct was implanted within a pocket in the strap muscles for 21 days and, 2) Final surgery: construct with vascularized pedicle was rotated into a segmental tracheal defect for 3 or 6 weeks. Following euthanasia, the construct and native trachea were explanted and evaluated.

RESULTS

In vitro: After 14 days in culture the constructs showed >80% viable cells. Collagen type II and sox-9 were overexpressed in the construct from day 2 and by day 14 all genes were overexpressed when compared to chondrocytes in monolayer.

IN VIVO

By day 21 (immediately before the rotation), cartilage formation could be seen surrounding all the constructs. Mature cartilage was observed in the grafts after 6 or 9 weeks in vivo.

CONCLUSION

This two-stage approach for implanting a 3D printed tissue-engineered tracheal replacement construct has been optimized to yield a high-quality, printable segment with cellular growth and viability both in vitro and in vivo.

P, Arora V, Sachdeva K, Sharma H, Dinda AK, Agrawal AK, Jassal M, Mohanty S. Promoting in-vivo bone regeneration using facile engineered load-bearing 3D bioactive scaffold

The worldwide incidence of bone disorders has trended steeply upward and is expected to get doubled by 2030. Biological mechanism of bone repair involves both osteo-conductivity and osteo-inductivity. In spite of the self-healing functionality after injury, bone tissue faces multitude of pathological challenges. Several innovative approaches have been developed to prepare biomaterial-based bone grafts. To design a suitable bone material, the freeze-drying technique has achieved significant importance among the other conventional methods. However, the functionality of the polymeric freeze-dried scaffold in in-vivo osteogenesis is in nascent stage. In this study facile, freeze dried, biomaterial-based load bearing 3D porous composite scaffolds have been prepared. The biocompatible scaffolds have been made by using chitosan (C), polycaprolactone (P), hydroxyapatite (H), glass ionomer (G), and graphene (gr). Scaffolds of eight different groups (C, P, CP, CPH, CPHG, CPHGgr1, CPHGgr2, CPHGgr3) have been designed and characterized to evaluate their applicability in orthopaedics. To evaluate the efficacy of the scaffolds a series of physio-chemical, morphological, and in-vitro & in-vivo biological experiments have been performed. From the obtained results it was observed that the CPHGgr1 is the ideal compatible material for Wharton’s Jelly derived mesenchymal stem cells and the blood cells. The in-vitro bone specific gene expression study revealed that, the scaffold assists MSCs osteogenic differentiation. Additionally, the in-vivo study on mice model was also performed for a period of 4 weeks and 8 weeks. The sub-cutaneous implantation of the designed scaffolds didn’t show any altered physiological condition in the animals, which indicated the in-vivo biocompatibility of the designed material. The histopathological study revealed that after 8 weeks of implantation, the CPHGgr1 scaffold supported significantly better collagen deposition and calcification. The facile designing of CPHGgr1 multicomponent nanocomposite provided an osteo-regenerative biomaterial with desired mechanical strength as an ideal regenerative material for cancellous bone tissue regeneration.

Suture Fiber Reinforcement of a 3D Printed Gelatin Scaffold for Its Potential Application in Soft Tissue Engineering

Gelatin has excellent biological properties, but its poor physical properties are a major obstacle to its use as a biomaterial ink. These disadvantages not only worsen the printability of gelatin biomaterial ink, but also reduce the dimensional stability of its 3D scaffolds and limit its application in the tissue engineering field. Herein, biodegradable suture fibers were added into a gelatin biomaterial ink to improve the printability, mechanical strength, and dimensional stability of the 3D printed scaffolds. The suture fiber reinforced gelatin 3D scaffolds were fabricated using the thermo-responsive properties of gelatin under optimized 3D printing conditions (-10 °C cryogenic plate, 40-80 kPa pneumatic pressure, and 9 mm/s printing speed), and were crosslinked using EDC/NHS to maintain their 3D structures. Scanning electron microscopy images revealed that the morphologies of the 3D printed scaffolds maintained their 3D structure after crosslinking. The addition of 0.5% (w/v) of suture fibers increased the printing accuracy of the 3D printed scaffolds to 97%. The suture fibers also increased the mechanical strength of the 3D printed scaffolds by up to 6-fold, and the degradation rate could be controlled by the suture fiber content. In in vitro cell studies, DNA assay results showed that human dermal fibroblasts' proliferation rate of a 3D printed scaffold containing 0.5% suture fiber was 10% higher than that of a 3D printed scaffold without suture fibers after 14 days of culture. Interestingly, the supplement of suture fibers into gelatin biomaterial ink was able to minimize the cell-mediated contraction of the cell cultured 3D scaffolds over the cell culture period. These results show that advanced biomaterial inks can be developed by supplementing biodegradable fibers to improve the poor physical properties of natural polymer-based biomaterial inks.

Investigation of an injectable gold nanoparticle extracellular matrix

Post-traumatic osteoarthritis (PTOA) is a progressive articular degenerative disease that degrades articular cartilage and stimulates apoptosis in chondrocyte cells. An injectable decellularized, extracellular matrix (ECM) scaffold, that might be able to combat the effects of PTOA, was developed where the ECM was conjugated with 20 nm gold nanoparticles (AuNP) and supplemented with curcumin and hyaluronic acid (HA). Porcine diaphragm ECM was decellularized and homogenized; AuNPs were conjugated using chemical crosslinking followed by mixing with curcumin and/or HA. Injection force testing and scanning electron microscopy with energy-dispersive X-ray spectroscopy were utilized to characterize the ECM scaffolds. In vitro testing with L929 murine fibroblasts, equine synovial fibroblasts, and Human Chondrocytes were used to determine biocompatibility, reactive oxygen species (ROS) reduction, and chondroprotective ability. The results demonstrated that conjugation of 20 nm AuNPs to the ECM was successful without significantly altering the physical properties as noted in the low injection force. In vitro work provided evidence of biocompatibility with a propensity to reduce intracellular ROS and an ability to mitigate apoptosis of chondrocyte cells stimulated with IL-1β, a known apoptosis inducing cytokine. It was concluded that an injectable AuNP-ECM may have the ability to mitigate inflammation and apoptosis.

The effect of collagen hydrogels on chondrocyte behaviors through restricting the contraction of cell/hydrogel constructs

Collagen is a promising material for tissue engineering, but the poor mechanical properties of collagen hydrogels, which tend to cause contraction under the action of cellular activity, make its application challengeable. In this study, the amino group of type I collagen (Col I) was modified with methacrylic anhydride (MA) and the photo-crosslinkable methacrylate anhydride modified type I collagen (CM) with three different degrees of substitution (DS) was prepared. The physical properties of CM and Col I hydrogels were tested, including micromorphology, mechanical properties and degradation properties. The results showed that the storage modulus and degradation rate of hydrogels could be adjusted by changing the DS of CM. In vitro, chondrocytes were seeded into these four groups of hydrogels and subjected to fluorescein diacetate/propidium iodide (FDA/PI) staining, cell counting kit-8 (CCK-8) test, histological staining and cartilage-related gene expression analysis. In vivo, these hydrogels encapsulating chondrocytes were implanted subcutaneously into nude mice, then histological staining and sulfated glycosaminoglycan (sGAG)/DNA assays were performed. The results demonstrated that contraction of hydrogels affected behaviors of chondrocytes, and CM hydrogels with suitable DS could resist contraction of hydrogels and promote the secretion of cartilage-specific matrix in vitro and in vivo.

The role of synovial fluid constituents in the lubrication of collagen-glycosaminoglycan scaffolds for cartilage repair

Extracellular matrix (ECM)-derived scaffolds have shown promise as tissue-engineered grafts for promoting cartilage repair. However, there has been a lack of focus on fine-tuning the frictional properties of scaffolds for cartilage tissue engineering as well as understanding their interactions with synovial fluid constituents. Proteoglycan-4 (PRG4) and hyaluronan (HA) are macromolecules within synovial fluid that play key roles as boundary mode lubricants during cartilage surface interactions. The overall objective of this study was to characterize the role PRG4 and HA play in the lubricating function of collagen-glycosaminoglycan (GAG) scaffolds for cartilage repair. As a first step towards this goal, we aimed to develop a suitable in vitro friction test to establish the boundary mode lubrication parameters for collagen-GAG scaffolds articulated against glass in a phosphate buffered saline (PBS) bath. Subsequently, we sought to leverage this system to determine the effect of physiological synovial fluid lubricants, PRG4 and HA, on the frictional properties of collagen-GAG scaffolds, with scaffolds hydrated in PBS and bovine synovial fluid (bSF) serving as negative and positive controls, respectively. At all compressive strains examined (ε = 0.1-0.5), fluid depressurization within hydrated collagen-GAG scaffolds was >99% complete at ½ minute. The coefficient of friction was stable at all compressive strains (ranging from a low 0.103 ± 0.010 at ε = 0.3 up to 0.121 ± 0.015 at ε = 0.4) and indicative of boundary-mode conditions. Immunohistochemistry demonstrated that PRG4 from recombinant human (rh) and bovine sources adsorbed to collagen-GAG scaffolds and the coefficient of friction for scaffolds immersed in rhPRG4 (0.067 ± 0.027) and normal bSF (0.056 ± 0.020) solution decreased compared to PBS (0.118 ± 0.21, both p < 0.05, at ε = 0.2). The ability of the adsorbed rhPRG4 to reduce friction on the scaffolds indicates that its incorporation within collagen-GAG biomaterials may enhance their lubricating ability as potential tissue-engineered cartilage replacements. To conclude, this study reports the development of an in vitro friction test capable of characterizing the coefficient of friction of ECM-derived scaffolds tested in a range of synovial fluid lubricants and demonstrates frictional properties as a potential design parameter for implants and materials for soft tissue replacement.

A Graded, Porous Composite of Natural Biopolymers and Octacalcium Phosphate Guides Osteochondral Differentiation of Stem Cells

Lesions involving the osteochondral unit are difficult to treat. Biomimetic scaffolds are previously shown as promising alternative. Such devices often lack multiple functional layers that mimic bone, cartilage, and the interface. In this study, multilayered scaffolds are developed based on the use of natural extracellular matrix (ECM)-like biopolymers. Particular attention is paid to obtain a complex matrix that mimics the native osteochondral transition. Porous, sponge-like chitosan-collagen-octacalcium phosphate (OCP) scaffolds are obtained. Collagen content increases while the amount of OCP particles decreases toward the cartilage layer. The scaffolds are bioactive as a mineral layer is deposited containing hydroxyapatite at the bony side. The scaffolds stimulate proliferation of human adipose-derived mesenchymal stem cells, but the degree of proliferation depends on the cell seeding density. The scaffolds give rise to a zone-specific gene expression. RUNX2, COL1A1, BGLAP, and SPP1 are upregulated in the bony layer of the scaffold. SOX9 is upregulated concomitant with COL2A1 expression in the cartilage zone. Mineralization in presence of the cells is prominent in the bone area with Ca and P steadily increasing over time. These results are encouraging for the fabrication of biomimetic scaffolds using ECM-like materials and featuring gradients that mimic native tissues and their interface.

Advances in biofabrication techniques for collagen-based 3D in vitro culture models for breast cancer research

Collagen is the most abundant component of the extracellular matrix (ECM), therefore it represents an ideal biomaterial for the culture of a variety of cell types. Recently, collagen-based scaffolds have shown promise as 3D culture platforms for breast cancer-based research. Two-dimensional (2D) in vitro culture models, while useful for gaining preliminary insights, are ultimately flawed as they do not adequately replicate the tumour microenvironment. As a result, they do not facilitate proper 3D cell-cell/cell-matrix interactions and often an exaggerated response to therapeutic agents occurs. The ECM plays a crucial role in the development and spread of cancer. Alterations within the ECM have a significant impact on the pathogenesis of cancer, the initiation of metastasis and ultimate progression of the disease. 3D in vitro culture models that aim to replicate the tumour microenvironment have the potential to offer a new frontier for cancer research with cell growth, morphology and genetic properties that more closely match in vivo cancers. While initial 3D in vitro culture models used in breast cancer research consisted of simple hydrogel platforms, recent advances in biofabrication techniques, including freeze-drying, electrospinning and 3D bioprinting, have enabled the fabrication of biomimetic collagen-based platforms that more closely replicate the breast cancer ECM. This review highlights the current application of collagen-based scaffolds as 3D in vitro culture models for breast cancer research, specifically for adherence-based scaffolds (i.e. matrix-assisted). Finally, the future perspectives of 3D in vitro breast cancer models and their potential to lead to an improved understanding of breast cancer diagnosis and treatment are discussed.

Engineering Functional Rat Ovarian Spheroids Using Granulosa and Theca Cells

Although menopausal hormone therapy (MHT) is the most effective approach to managing the loss of ovarian activity, serious side effects have been reported. Cell-based therapy is a promising alternative for MHT. This study constructed engineered ovarian cell spheroids and investigated their endocrine function. Theca and granulosa cells were isolated from ovaries of 10-week-old rats. Two types of engineered ovarian cell spheroids were fabricated through forced aggregation in microwells, multilayered spheroids with centralized granulosa aggregates surrounded by an outer layer of theca cells and mixed ovarian spheroids lacking spatial rearrangement. The ovarian cell spheroids were encapsulated into a collagen gel. Non-aggregated ovarian cells served as controls. The endocrine function of the engineered ovarian spheroids was assessed over 30 days. The structure of the spheroids was well maintained during culture. The secretion of 17β-estradiol from both types of engineered ovarian cell spheroids was higher than in the control group and increased continuously in a time-dependent manner. Secretion of 17β-estradiol in the multi-layered ovarian cell spheroids was higher than in the non-layered constructs. Increased secretion of progesterone was detected in the multi-layered ovarian cell spheroids at day 5 of culture and was sustained during the culture period. The initial secretion level of progesterone in the non-layered ovarian cell spheroids was similar to those from the controls and increased significantly from days 21 to 30. An in vitro rat model of engineered ovarian cell spheroids was developed that was capable of secreting sex steroid hormones, indicating that the hormone secreting function of ovaries can be recapitulated ex vivo and potentially adapted for MHT.

Collagen and chondroitin sulfate functionalized bioinspired fibers for tendon tissue engineering application

Functional tendon tissue engineering depends on harnessing the biochemical and biophysical cues of the native tendon extracellular matrix. In this study, we fabricated highly-aligned poly(L-lactic acid) (PLLA) fibers with surfaces decorated by two of the crucial tendon ECM components, type 1 collagen (COL1) and chondroitin sulfate (CS), through a coaxial stable jet electrospinning approach. Effects of the biomimetic COL1-CS (shell)/PLLA (core) fibers on the tenogenic differentiation of human mesenchymal stem cells (hMSCs) in vitro were investigated. Higher rates of cell spreading and proliferation are observed on the aligned COL1-CS/PLLA fibers compared to that on the plain PLLA fibers. Expression of the tendon-associated genes scleraxis (SCX) and COL1 as well as protein tenomodulin (TNMD) are significantly increased. Introduction of mechanical stimulation gives rise to synergistic effect on tenogenic differentiation of hMSCs. Higher expression of TGF-β2, TGFβR-II, and Smad3 by the cells on the COL1-CS/PLLA fiber substrates are observed, which indicates that COL1-CS/PLLA ultrafine fibers dictate the hMSC tenogenic differentiation through activating the TGF-β signaling pathway. Animal study in rat Achilles tendon repair model corroborated the promoting role of COL1-CS/PLLA in regenerating a tendon-like tissue. Thus, our highly aligned biomimicking fibers may serve as an efficient scaffolding system for functional tendon regeneration.

Bone formation potential of collagen type I-based recombinant peptide particles in rat calvaria defects

Introduction

This study aimed to examine the bone-forming ability of medium-cross-linked recombinant collagen peptide (mRCP) particles developedbased on human collagen type I, contains an arginyl-glycyl-aspartic acid-rich motif, fabricated as bone filling material, compared to that of the autologous bone graft.

Methods

Calvarial bone defects were created in immunodeficient rats though a surgical procedure. The rats were divided into 2 groups: mRCP graft and tibia bone graft (bone graft). The bone formation potential of mRCP was evaluated by micro-computed tomography and hematoxylin-eosin staining at 1, 2, 3, and 4 weeks after surgery, and the data were analyzed and compared to those of the bone graft.

Results

The axial volume-rendered images demonstrated considerable bony bridging with the mRCP graft, but there was no significant difference in the bone volume and bone mineral density between the mRCP graft and bone graft at 4 weeks. The peripheral new bone density was significantly higher than the central new bone density and the bottom side score was significantly higher than the top side score at early stage in the regenerated bone within the bone defects.

Conclusion

These results indicate that mRCP has a high potential of recruiting osteogenic cells, comparable to that of autologous bone chips.

•

Bone formation potential of mRCP were comparable to that of autogenous bone.

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mRCP particles exhibit high new bone formation potential in the calvaria defect.

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Bone bridging was observed over the entire defect in mRCP graft at 4 weeks.

•

mRCP has a high potential of recruiting osteogenic cells comparable to bone graft.

Bioprinting of Collagen: Considerations, Potentials, and Applications

Collagen is the most abundant extracellular matrix protein that is widely used in tissue engineering (TE). There is little research done on printing pure collagen. To understand the bottlenecks in printing pure collagen, it is imperative to understand collagen from a bottom-up approach. Here it is aimed to provide a comprehensive overview of collagen printing, where collagen assembly in vivo and the various sources of collagen available for TE application are first understood. Next, the current printing technologies and strategy for printing collagen-based materials are highlighted. Considerations and key challenges faced in collagen printing are identified. Finally, the key research areas that would enhance the functionality of printed collagen are presented.

3D printing of fibre-reinforced cartilaginous templates for the regeneration of osteochondral defects

Successful osteochondral defect repair requires regenerating the subchondral bone whilst simultaneously promoting the development of an overlying layer of articular cartilage that is resistant to vascularization and endochondral ossification. During skeletal development articular cartilage also functions as a surface growth plate, which postnatally is replaced by a more spatially complex bone-cartilage interface. Motivated by this developmental process, the hypothesis of this study is that bi-phasic, fibre-reinforced cartilaginous templates can regenerate both the articular cartilage and subchondral bone within osteochondral defects created in caprine joints. To engineer mechanically competent implants, we first compared a range of 3D printed fibre networks (PCL, PLA and PLGA) for their capacity to mechanically reinforce alginate hydrogels whilst simultaneously supporting mesenchymal stem cell (MSC) chondrogenesis in vitro. These mechanically reinforced, MSC-laden alginate hydrogels were then used to engineer the endochondral bone forming phase of bi-phasic osteochondral constructs, with the overlying chondral phase consisting of cartilage tissue engineered using a co-culture of infrapatellar fat pad derived stem/stromal cells (FPSCs) and chondrocytes. Following chondrogenic priming and subcutaneous implantation in nude mice, these bi-phasic cartilaginous constructs were found to support the development of vascularised endochondral bone overlaid by phenotypically stable cartilage. These fibre-reinforced, bi-phasic cartilaginous templates were then evaluated in clinically relevant, large animal (caprine) model of osteochondral defect repair. Although the quality of repair was variable from animal-to-animal, in general more hyaline-like cartilage repair was observed after 6 months in animals treated with bi-phasic constructs compared to animals treated with commercial control scaffolds. This variability in the quality of repair points to the need for further improvements in the design of 3D bioprinted implants for joint regeneration. STATEMENT OF SIGNIFICANCE: Successful osteochondral defect repair requires regenerating the subchondral bone whilst simultaneously promoting the development of an overlying layer of articular cartilage. In this study, we hypothesised that bi-phasic, fibre-reinforced cartilaginous templates could be leveraged to regenerate both the articular cartilage and subchondral bone within osteochondral defects. To this end we used 3D printed fibre networks to mechanically reinforce engineered transient cartilage, which also contained an overlying layer of phenotypically stable cartilage engineered using a co-culture of chondrocytes and stem cells. When chondrogenically primed and implanted into caprine osteochondral defects, these fibre-reinforced bi-phasic cartilaginous grafts were shown to spatially direct tissue development during joint repair. Such developmentally inspired tissue engineering strategies, enabled by advances in biofabrication and 3D printing, could form the basis of new classes of regenerative implants in orthopaedic medicine.

Biomaterial Based Strategies for Engineering New Lymphatic Vasculature

The lymphatic system is essential for tissue regeneration and repair due to its pivotal role in resolving inflammation, immune cell surveillance, lipid transport, and maintaining tissue homeostasis. Loss of functional lymphatic vasculature is directly implicated in a variety of diseases, including lymphedema, obesity, and the progression of cardiovascular diseases. Strategies that stimulate the formation of new lymphatic vessels (lymphangiogenesis) could provide an appealing new approach to reverse the progression of these diseases. However, lymphangiogenesis is relatively understudied and stimulating therapeutic lymphangiogenesis faces challenges in precise control of lymphatic vessel formation. Biomaterial delivery systems could be used to unleash the therapeutic potential of lymphangiogenesis for a variety of tissue regenerative applications due to their ability to achieve precise spatial and temporal control of multiple therapeutics, direct tissue regeneration, and improve the survival of delivered cells. In this review, the authors begin by introducing therapeutic lymphangiogenesis as a target for tissue regeneration, then an overview of lymphatic vasculature will be presented followed by a description of the mechanisms responsible for promoting new lymphatic vessels. Importantly, this work will review and discuss current biomaterial applications for stimulating lymphangiogenesis. Finally, challenges and future directions for utilizing biomaterials for lymphangiogenic based treatments are considered.

Resveratrol and Celastrol Loaded Collagen Dental Implants Regulate Periodontal Ligament Fibroblast Growth and Osteoclastogenesis of Bone Marrow Macrophages

Collagen is widely used for dental therapy in several ways such as films, 3D matrix, and composites, besides traditional Chinese medicine (TCM), has been used in tissue regeneration and wound healing application for centuries. Hence, the present study was targeted for the first time to fabricate collagen film with TCM such as resveratrol and celastrol in order to investigate the human periodontal ligament fibroblasts (HPLF) growth and bone marrow macrophages (BMM) derived osteoclastogenesis. Further, the physicochemical, mechanical and biological activities of collagen-TCM films crosslinked by glycerol and EDC-NHS (1-ethyl-3-(3-dimethylaminopropyl)carbodiimide-N-hydroxysulfosuccinimide) were investigated. Collagen film characterization was significantly regulated by the nature of plasticizers like hydrophobic and degree of polarity. Interestingly, the collagen film's denaturation temperature was increased by EDC-NHS than glycerol. FT-IR data confirmed the functional group changes due to chemical interaction of collagen with TCM. Morphological changes of HPLF cells cultured in control and collagen films were observed by SEM. Importantly, the addition of resveratrol upregulated the proliferation of HPLF cells, while osteoclastogenesis of BMM cells treated with mCSF-RANKL was significantly downregulated by celastrol. Accordingly, the collagen-TCM film could be an interesting material for dental regeneration, and especially it is a therapeutic target to restrain the elevated bone resorption during osteoporosis.

Ionically and Enzymatically Dual Cross-Linked Oxidized Alginate Gelatin Hydrogels with Tunable Stiffness and Degradation Behavior for Tissue Engineering

Hydrogels that allow for the successful long-term in vitro culture of cell-biomaterial systems to enable the maturation of tissue engineering constructs are highly relevant in regenerative medicine. Naturally derived polysaccharide-based hydrogels promise to be one material group with enough versatility and chemical functionalization capability to tackle the challenges associated with long-term cell culture. We report a marine derived oxidized alginate, alginate dialdehyde (ADA), and gelatin (GEL) system (ADA-GEL), which is cross-linked via ionic (Ca²⁺) and enzymatic (microbial transglutaminase, mTG) interaction to form dually cross-linked hydrogels. The cross-linking approach allowed us to tailor the stiffness of the hydrogels in a wide range (from <5 to 120 kPa), without altering the initial ADA and GEL hydrogel chemistry. It was possible to control the degradation behavior of the hydrogels to be stable for up to 30 days of incubation. Increasing concentrations of mTG cross-linker solutions allowed us to tune the degradation behavior of the ADA-GEL hydrogels from fast (<7 days) to moderate (14 days) and slow (>30 days) degradation kinetics. The cytocompatibility of mTG cross-linked ADA-GEL was assessed using NIH-3T3 fibroblasts and ATDC-5 mouse teratocarcinoma cells. Both cell types showed highly increased cellular attachment on mTG cross-linked ADA-GEL in comparison to Ca²⁺ cross-linked hydrogels. In addition, ATDC-5 cells showed a higher proliferation on mTG cross-linked ADA-GEL hydrogels in comparison to tissue culture polystyrene control substrates. Further, the attachment of human umbilical vein endothelial cells (HUVEC) on ADA-GEL (+) mTG was confirmed, proving the suitability of mTG+Ca²⁺ cross-linked ADA-GEL for several cell types. Summarizing, a promising platform to control the properties of ADA-GEL hydrogels is presented, with the potential to be applied in long-term cell culture investigations such as cartilage, bone, and blood-vessel engineering, as well as for biofabrication.

Collagen Type I and II Blend Hydrogel with Autologous Mesenchymal Stem Cells as a Scaffold for Articular Cartilage Defect Repair

Collagen type II is a promising material to repair cartilage defects since it is a major component of articular cartilage and plays a key role in chondrocyte function. This study investigated the chondrogenic differentiation of bone marrow-derived mesenchymal stem cells (MSCs) embedded within a 3:1 collagen type I to II blend (Col I/II) hydrogel or an all collagen type I (Col I) hydrogel. Glycosaminoglycan (GAG) production in Col I/II hydrogels was statistically higher than that in Col I hydrogels or pellet culture, and these results suggested that adding collagen type II promoted GAG production. Col I/II hydrogels had statistically lower alkaline phosphatase (AP) activity than pellets cultured in a chondrogenic medium. The ability of MSCs encapsulated in Col I/II hydrogels to repair cartilage defects was investigated by creating two cartilage defects in the femurs of rabbits. After 13 weeks, histochemical staining suggested that Col I/II blend hydrogels provided favorable conditions for cartilage repair. Histological scoring revealed a statistically higher cartilage repair score for the Col I/II hydrogels compared to either the Col I hydrogels or empty defect controls. Results from this study suggest that there is clinical value in the cartilage repair capabilities of our Col I/II hydrogel with encapsulated MSCs.

Enhanced chondrogenesis of human umbilical cord mesenchymal stem cells in a gelatin honeycomb scaffold

Transplantation of chondrogenic stem cells is a promising strategy for cartilage repair, but requires improvements in cell sourcing, maintenance, and chondrogenic differentiation efficiency. We examined whether gelatin honeycomb scaffolds can enhance the proliferation, viability, and chondrogenic capability of human umbilical cord mesenchymal stem cells (HUCMSCs) compared to standard plate cultures. In addition, the survival and phenotypic stability of HUCMSC-derived chondrocytes in a scaffold were evaluated in mice over 6 weeks post-transplantation. Survival and proliferation rates of HUCMSCs were comparable between scaffold and plate culture. Scaffold culture in a chondrogenic differentiation medium induced more stable expression of the key hyaline cartilage genes COL2A1 and ACAN and the production of the respective proteins Type II collagen and aggrecan as well as glycosaminoglycan. These HUCMSC-differentiated chondrocytes also stably expressed cartilage genes and proteins in the scaffold 6 weeks after transplantation into nonobese diabetic/severe combined immunodeficient mice. These findings indicate that honeycomb-like gelatin scaffolds can promote the survival and chondrogenic differentiation of HUCMSCs to form hyaline-like cartilage.

Selection of Collagen Membranes for Bone Regeneration: A Literature Review

Several treatment modalities have been proposed to regenerate bone, including guided bone regeneration (GBR) where barrier membranes play an important role by isolating soft tissue and allowing bone to grow. Not all membranes biologically behave the same way, as they differ from their origin and structure, with reflections on their mechanical properties and on their clinical performance. Collagen membranes have been widely used in medicine and dentistry, because of their high biocompatibility and capability of promoting wound healing. Recently, collagen membranes have been applied in guided bone regeneration with comparable outcomes to non-resorbable membranes. Aim of this work is to provide a review on the main features, application, outcomes, and clinical employment of the different types of collagen membranes. Comparisons with non-resorbable membranes are clarified, characteristics of cross-linked collagen versus native collagen, use of different grafting materials and need for membrane fixation are explored in order to gain awareness of the indications and limits and to be able to choose the right membrane required by the clinical condition.

Applications of decellularized materials in tissue engineering: advantages, drawbacks and current improvements, and future perspectives

Decellularized materials (DMs) are attracting more and more attention in tissue engineering because of their many unique advantages, and they could be further improved in some aspects through various means.

Adhesion, proliferation and differentiation of human mesenchymal stem cell on chitosan/collagen composite scaffold

In vitro tissue engineering requires a progenitor cell source and a porous scaffold providing three dimensional (3D) supports for growth and differentiation to attain tissue architectures. This research focused on fabrication and characterization of 3D porous scaffolds using chitosan (CS), collagen (CG) and chitosan-collagen (CS-CG) composite to investigate their influence on human mesenchymal stem cell (hMSC) adhesion, proliferation and differentiation. Material dependent variations in porous morphology and mechanical behavior of the fabricated CS, CG and CS-CG scaffold showed significant impact on hMSC adhesion, proliferation and differentiation. The maximum hMSC adhesion and proliferation was reported on CS-CG scaffold among all fabricated scaffold groups. Interconnectivity of pores structure in CS-CG scaffold was considered as preferable attribute for such enhanced growth and distribution throughout the scaffold. Besides, CS scaffold with well interconnected pores showed poor adhesion and proliferation because of inadequate adhesion motifs. In case of CG scaffold, optimum growth and distribution of hMSC occurs only at the surface because of the absence of interconnectivity in their pore structures. Likewise, osteogenic differentiation of hMSC occurs most preferably in CS-CG composite scaffold among all scaffold groups. Such enhanced hMSC proliferation and differentiation in CS-CG scaffold significantly influenced on mechanical behavior of scaffold which is essential for in vivo application of a bone tissue implant. Thus CS-CG composite scaffold holds promise to be a suitable platform for in vitro engineering of bone tissue implant.

Current progress in hepatic tissue regeneration by tissue engineering

Liver, as a vital organ, is responsible for a wide range of biological functions to maintain homeostasis and any type of damages to hepatic tissue contributes to disease progression and death. Viral infection, trauma, carcinoma, alcohol misuse and inborn errors of metabolism are common causes of liver diseases are a severe known reason for leading to end-stage liver disease or liver failure. In either way, liver transplantation is the only treatment option which is, however, hampered by the increasing scarcity of organ donor. Over the past years, considerable efforts have been directed toward liver regeneration aiming at developing new approaches and methodologies to enhance the transplantation process. These approaches include producing decellularized scaffolds from the liver organ, 3D bio-printing system, and nano-based 3D scaffolds to simulate the native liver microenvironment. The application of small molecules and micro-RNAs and genetic manipulation in favor of hepatic differentiation of distinct stem cells could also be exploited. All of these strategies will help to facilitate the application of stem cells in human medicine. This article reviews the most recent strategies to generate a high amount of mature hepatocyte-like cells and updates current knowledge on liver regenerative medicine.

Ultraviolet light (365 nm) transmission properties of articular cartilage as a function of depth, extracellular matrix, and swelling

Current tissue engineering approaches for treatment of injured or diseased articular cartilage use ultraviolet light (UV) for in situ photopolymerization of biomaterials to fill chondral and osteochondral defects as well as resurfacing, stiffening and bonding the extracellular matrix and tissue interfaces. The most commonly used UV light wavelength is UVA 365 nm, the least cytotoxic and deepest penetrating. However, little information is available on the transmission of UVA 365 nm light through the cartilage matrix. In the present study, 365 nm UV light transmission was measured as a function of depth through 100 μm thick slices of healthy articular cartilage removed from mature bovine knees. Transmission properties were measured in normal (Native) cartilage and after swelling equilibration in phosphate-buffered saline (Swollen). Single-factor and multiple linear regression analyses were performed to determine depth-dependencies between the effective attenuation coefficients and proteoglycan, collagen and water contents. For both cartilages, a significant depth-dependency was found for the effective attenuation coefficients, being highest at the articular surface (superficial zone) and decreasing with depth. The effective attenuation coefficients for full-thickness cartilages were approximately a third lower than the total attenuation coefficients calculated from the individual slices. Analysis of absorption and scattering effects due to the ECM and chondrocytes found that UV light scatter coefficients were ∼10 times greater than absorption coefficients. The greater transmittance of UV light through the thicker cartilage was attributed to the collagen within the ECM causing significant backscatter forward reflectance.

Marine Collagen as A Promising Biomaterial for Biomedical Applications

This review focuses on the expanding role of marine collagen (MC)-based scaffolds for biomedical applications. A scaffold-a three-dimensional (3D) structure fabricated from biomaterials-is a key supporting element for cell attachment, growth, and maintenance in 3D cell culture and tissue engineering. The mechanical and biological properties of the scaffolds influence cell morphology, behavior, and function. MC, collagen derived from marine organisms, offers advantages over mammalian collagen due to its biocompatibility, biodegradability, easy extractability, water solubility, safety, low immunogenicity, and low production costs. In recent years, the use of MC as an increasingly valuable scaffold biomaterial has drawn considerable attention from biomedical researchers. The characteristics, isolation, physical, and biochemical properties of MC are discussed as an understanding of MC in optimizing the subsequent modification and the chemistries behind important tissue engineering applications. The latest technologies behind scaffold processing are assessed and the biomedical applications of MC and MC-based scaffolds, including tissue engineering and regeneration, wound dressing, drug delivery, and therapeutic approach for diseases, especially those associated with metabolic disturbances such as obesity and diabetes, are discussed. Despite all the challenges, MC holds great promise as a biomaterial for developing medical products and therapeutics.

Conductive collagen/polypyrrole-b-polycaprolactone hydrogel for bioprinting of neural tissue constructs

Bioprinting is increasingly being used for fabrication of engineered tissues for regenerative medicine, drug testing, and other biomedical applications. The success of this technology lies with the development of suitable bioinks and hydrogels that are specific to the intended tissue application. For applications such as neural tissue engineering, conductivity plays an important role in determining the neural differentiation and neural tissue regeneration. Although several conductive hydrogels based on metal nanoparticles (NPs) such as gold and silver, carbon-based materials such as graphene and carbon nanotubes and conducting polymers such as polypyrrole (PPy) and polyaniline were used, they possess several disadvantages. The long-term cytotoxicity of metal nanoparticles (NPs) and carbon-based materials restricts their use in regenerative medicine. The conductive polymers, on the other hand, are non-biodegradable and possess weak mechanical properties limiting their printability into three-dimensional constructs. The aim of this study is to develop a biodegradable, conductive, and printable hydrogel based on collagen and a block copolymer of PPy and polycaprolactone (PCL) (PPy-block-poly(caprolactone) [PPy-b-PCL]) for bioprinting of neural tissue constructs. The printability, including the influence of the printing speed and material flow rate on the printed fiber width; rheological properties; and cytotoxicity of these hydrogels were studied. The results prove that the collagen/PPy-b-PCL hydrogels possessed better printability and biocompatibility. Thus, the collagen/PPy-b-PCL hydrogels reported this study has the potential to be used in the bioprinting of neural tissue constructs for the repair of damaged neural tissues and drug testing or precision medicine applications.

Meniscus-Derived Matrix Scaffolds Promote the Integrative Repair of Meniscal Defects

Meniscal tears have a poor healing capacity, and damage to the meniscus is associated with significant pain, disability, and progressive degenerative changes in the knee joint that lead to osteoarthritis. Therefore, strategies to promote meniscus repair and improve meniscus function are needed. The objective of this study was to generate porcine meniscus-derived matrix (MDM) scaffolds and test their effectiveness in promoting meniscus repair via migration of endogenous meniscus cells from the surrounding meniscus or exogenously seeded human bone marrow-derived mesenchymal stem cells (MSCs). Both endogenous meniscal cells and MSCs infiltrated the MDM scaffolds. In the absence of exogenous cells, the 8% MDM scaffolds promoted the integrative repair of an in vitro meniscal defect. Dehydrothermal crosslinking and concentration of the MDM influenced the biochemical content and shear strength of repair, demonstrating that the MDM can be tailored to promote tissue repair. These findings indicate that native meniscus cells can enhance meniscus healing if a scaffold is provided that promotes cellular infiltration and tissue growth. The high affinity of cells for the MDM and the ability to remodel the scaffold reveals the potential of MDM to integrate with native meniscal tissue to promote long-term repair without necessarily requiring exogenous cells.

Modular, tissue-specific, and biodegradable hydrogel cross-linkers for tissue engineering

Synthetic hydrogels are investigated extensively in tissue engineering for their tunable physicochemical properties but are bioinert and lack the tissue-specific cues to produce appropriate biological responses. To introduce tissue-specific biochemical cues to these hydrogels, we have developed a modular hydrogel cross-linker, poly(glycolic acid)-poly(ethylene glycol)-poly(glycolic acid)-di(but-2-yne-1,4-dithiol) (PdBT), that can be functionalized with small peptide-based cues and large macromolecular cues simply by mixing PdBT in water with the appropriate biomolecules at room temperature. Cartilage- and bone-specific PdBT macromers were generated by functionalization with a cartilage-associated hydrophobic N-cadherin peptide, a hydrophilic bone morphogenetic protein peptide, and a cartilage-derived glycosaminoglycan, chondroitin sulfate. These biofunctionalized PdBT macromers can spontaneously cross-link polymers such as poly(N-isopropylacrylamide) to produce rapidly cross-linking, highly swollen, cytocompatible, and hydrolytically degradable hydrogels suitable for mesenchymal stem cell encapsulation. These favorable properties, combined with PdBT's modular design and ease of functionalization, establish strong potential for its usage in tissue engineering applications.

Decellularized biological scaffold and stem cells from autologous human adipose tissue for cartilage tissue engineering

Here, the in vitro engineering of a cartilage-like tissue by using decellularized extracellular matrix scaffold (hECM) seeded with human adipose stem cells (hASCs) which can both be isolated from the human waste adipose tissue is described. Cell-free, highly fibrous and porous hECM was produced using a protocol containing physical (homogenization, centrifugation, molding) and chemical (crosslinking) treatments, characterized by SEM, histochemistry, immunohistochemistry and in vitro cell interaction study. A construct of hECM seeded with hASCs was cultured in chondrogenic medium (with TGF-β3 and BMP-6) for 42 days. SEM and histology showed that the biological scaffold was highly porous and had a compact structure suitable for handling and subsequent cell culture stages. Cells successfully integrated into the scaffold and had good cellular viability and continuity to proliferate. Constructs showed the formation of cartilage-like tissue with the synthesis of cartilage-specific proteins, Collagen type II and Aggrecan. Dimethylmethylene blue dye binding assay demonstrated that the GAG content of the constructs was in tendency to increase with time confirming chondrogenic differentiation of hASCs. The results support that human waste adipose tissue is an important source for decellularized hECM as well as stem cells, and adipose hECM scaffold provides a suitable environment for chondrogenic differentiation of hASCs.

Tissue Engineering in Pediatric Bladder Reconstruction-The Road to Success

Several congenital disorders can cause end stage bladder disease and possibly renal damage in children. The current gold standard therapy is enterocystoplasty, a bladder augmentation using an intestinal segment. However, the use of bowel tissue is associated with numerous complications such as metabolic disturbance, stone formation, urine leakage, chronic infections, and malignancy. Urinary diversions using engineered bladder tissue would obviate the need for bowel for bladder reconstruction. Despite impressive progress in the field of bladder tissue engineering over the past decades, the successful transfer of the approach into clinical routine still represents a major challenge. In this review, we discuss major achievements and challenges in bladder tissue regeneration with a focus on different strategies to overcome the obstacles and to meet the need for living functional tissue replacements with a good growth potential and a long life span matching the pediatric population.