Collagen scaffolds for tissue engineering

Surface Modification of Nerve Guide Conduits with ECM Coatings and Investigating Their Impact on Schwann Cell Response

In this study, layer-by-layer coatings composed of heparin and collagen are proposed as an extracellular mimetic environment on nerve guide conduits (NGC) to modulate the behavior of Schwann cells (hSCs). The authors evaluated the stability, degradation over time, and bioactivity of six bilayers of heparin/collagen layer-by-layer coatings, denoted as (HEP/COL)6. The stability study reveals that (HEP/COL)6 is stable after incubating the coatings in cell media for up to 21 days. The impact of (HEP/COL)6 on hSCs viability, protein expression, and migration is evaluated. These assays show that hSCs cultured in (HEP/COL)6 have enhanced protein expression and migration. This condition increases the expression of neurotrophic and immunomodulatory factors up to 1.5-fold compared to controls, and hSCs migrated 1.34 times faster than in the uncoated surfaces. Finally, (HEP/COL)6 is also applied to a commercial collagen-based NGC, NeuraGen, and hSC viability and adhesion are studied after 6 days of culture. The morphology of NeuraGen is not altered by the presence of (HEP/COL)6 and a nearly 170% increase of the cell viability is observed in the condition where NeuraGen is used with (HEP/COL)6. Additionally, cell adhesion on the coated samples is successfully demonstrated. This work demonstrates the reparative enhancing potential of extracellular mimetic coatings.

A Comparative Study of the Effects of Different Crosslinking Methods on the Physicochemical Properties of Collagen Multifilament Bundles

Crosslinking is usually required to improve the mechanical properties and stability of collagen-based scaffolds. Introducing exogenous crosslinks into collagen may however affect the collagen structure. Since the architecture of collagen is tied to its functionality, it is important to study the effect of crosslinking and to select a crosslinking method that preserves both the collagen structure and mechanical properties. The objective of this study is to compare the effect of various crosslinking methods on the structure and mechanical properties of bioartificial tendon-like materials (collagen multifilament bundles) fabricated by contact drawing. We examine both physical (ultraviolet light, UVC) and chemical (genipin, carbodiimide (EDC), and glutaraldehyde) crosslinking methods. The presence of collagen and the formation of well-ordered collagen structures are confirmed by attenuated total reflectance Fourier-transform infrared spectromicroscopy and wide-angle X-ray scattering for all crosslinking methods. The morphology of the collagen multifilament bundles is similar across crosslinking methods. Swelling of the multifilament bundles is dramatically reduced following crosslinking and varies by crosslinking method, with genipin- and carbodiimide-crosslinked specimens swelling the least. Ultimate tensile strength (UTS) and Young's modulus significantly improve for all crosslinked specimens compared to non-crosslinked specimens. Glutaraldehyde crosslinked collagen multifilament bundles display the highest UTS values ranging from 33.82±0.0 MPa to 45.59±0.76 MPa.

Three-Dimensional Cultivation a Valuable Tool for Modelling Canine Mammary Gland Tumour Behaviour In Vitro

Cell cultivation has been one of the most popular methods in research for decades. Currently, scientists routinely use two-dimensional (2D) and three-dimensional (3D) cell cultures of commercially available cell lines and primary cultures to study cellular behaviour, responses to stimuli, and interactions with their environment in a controlled laboratory setting. In recent years, 3D cultivation has gained more attention in modern biomedical research, mainly due to its numerous advantages compared to 2D cultures. One of the main goals where 3D culture models are used is the investigation of tumour diseases, in both animals and humans. The ability to simulate the tumour microenvironment and design 3D masses allows us to monitor all the processes that take place in tumour tissue created not only from cell lines but directly from the patient's tumour cells. One of the tumour types for which 3D culture methods are often used in research is the canine mammary gland tumour (CMT). The clinically similar profile of the CMT and breast tumours in humans makes the CMT a suitable model for studying the issue not only in animals but also in women.

Investigation of Liquid Collagen Ink for Three-Dimensional Printing

Three-dimensional printing provides more versatility in the fabrication of scaffold materials for hard and soft tissue replacement, but a critical component is the ink. The ink solution should be biocompatible, stable, and able to maintain scaffold shape, size, and function once printed. This paper describes the development of a collagen ink that remains in a liquid pre-fibrillized state prior to printing. The liquid stability occurs due to the incorporation of ethylenediaminetetraacetic acid (EDTA) during dialysis of the collagen. Collagen inks were 3D-printed using two different printers. The resulting scaffolds were further processed using two different chemical crosslinkers, 1-Ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride)/N-hydroxysuccinimide (EDC/NHS) and genipin; gold nanoparticles were conjugated to the scaffolds. The 3D-printed scaffolds were characterized to determine their extrudability, stability, amount of AuNP conjugated, and overall biocompatibility via cell culture studies using fibroblast cells and stroma cells. The results demonstrated that the liquid collagen ink was amendable to 3D printing and was able to maintain its 3D shape. The scaffolds could be conjugated with gold nanoparticles and demonstrated enhanced biocompatibility. It was concluded that the liquid collagen ink is a good candidate material for the 3D printing of tissue scaffolds.

Collagen-decorated electrospun scaffolds of unsaturated copolyesters for bone tissue regeneration

Many efforts have been devoted to bone tissue to regenerate damaged tissues, and the development of new biocompatible materials that match the biological, mechanical, and chemical features required for this application is crucial. Herein, a collagen-decorated scaffold was prepared via electrospinning using a synthesized unsaturated copolyester (poly(globalide-co-pentadecalactone)), followed by two coupling reactions: thiol-ene functionalization with cysteine and further conjugation via EDC/NHS chemistry with collagen, aiming to design a bone tissue regeneration device with improved hydrophilicity and cell viability. Comonomer ratios were varied, affecting the copolymer's thermal and chemical properties and highlighting the tunable features of this copolyester. Functionalization with cysteine created new carboxyl and amine groups needed for bioconjugation with collagen, which is responsible for providing biological and structural integrity to the extra-cellular matrix. Bioconjugation with collagen turned the scaffold highly hydrophilic, decreasing its contact angle from 107 ± 2° to 0°, decreasing the copolymer crystallinity by 71%, and improving cell viability by 85% compared with the raw scaffold, thus promoting cell growth and proliferation. The highly efficient and biosafe strategy to conjugate polymers and proteins created a promising device for bone repair in tissue engineering.

Evaluation of adipogenesis over time using a novel bioabsorbable implant without the addition of exogenous cells or growth factors

Background

Breast reconstruction is crucial for patients who have undergone mastectomy for breast cancer. Our bioabsorbable implants comprising an outer poly-l-lactic acid mesh and an inner component filled with collagen sponge promote and retain adipogenesis in vivo without the addition of exogenous cells or growth factors. In this study, we evaluated adipogenesis over time histologically and at the gene expression level using this implant in a rodent model.

Methods

The implants were inserted in the inguinal and dorsal regions of the animals. At 1, 3, 6, and 12 months post-operation, the weight, volume, and histological assessment of all newly formed tissue were performed. We analyzed the formation of new adipose tissue using multiphoton microscopy and RNA sequencing.

Results

Both in the inguinal and dorsal regions, adipose tissue began to form 1 month post-operation in the peripheral area. Angiogenesis into implants was observed until 3 months. At 6 months, microvessels matured and the amount of newly generated adipose tissue peaked and was uniformly distributed inside implants. The amount of newly generated adipose tissue decreased from 6 to 12 months but at 12 months, adipose tissue was equivalent to the native tissue histologically and in terms of gene expression.

Conclusions

Our bioabsorbable implants could induce normal adipogenesis into the implants after subcutaneous implantation. Our implants can serve as a novel and safe material for breast reconstruction without requiring exogenous cells or growth factors.

Vaginal reconstruction by collagen scaffolds loaded with vaginal epithelial and smooth muscle cells in pigs

In women, a healthy and functional vagina is important for the maintenance of a good quality of life. Various factors, including congenital anomalies, cancer, trauma, infections, inflammation, or iatrogenic injuries, can lead to damage or loss of the vaginal structure, necessitating repair or replacement. Often, such reconstruction procedures involve the use of nonvaginal tissue substitutes, like segments of the large intestine or skin, which are less than ideal both anatomically and functionally. Therefore, there is an urgent need to develop new methods of vaginal reconstruction. In this study, we established a new method for isolation and expansion of vaginal epithelial and smooth muscle cells. Subsequently, collagen scaffolds designed for vaginal reconstruction were loaded with vaginal epithelial and smooth muscle cells in vitro and tested in vivo using the vaginal excision pig model. The results showed that the collagen scaffold loaded with vaginal epithelial and smooth muscle cells significantly promotes the reconstruction of the vagina compared with small intestinal submucosa (SIS) membrane or bare collagen scaffold. Notably, the reconstructed vaginal tissues exhibit remarkable similarity to their normal counterparts, encompassing not only the vaginal epithelium and smooth muscle but also the intricate networks of blood vessels and nerves. These compelling results underscore the feasibility of a tissue engineering approach in vaginal reconstruction, offering promising prospects for improving the quality of life in affected individuals.

Collagen Matrix to Restore the Tympanic Membrane: Developing a Novel Platform to Treat Perforations

Modern otology faces challenges in treating tympanic membrane (TM) perforations. Instead of surgical intervention, alternative treatments using biomaterials are emerging. Recently, we developed a robust collagen membrane using semipermeable barrier-assisted electrophoretic deposition (SBA-EPD). In this study, a collagen graft shaped like a sponge through SBA-EPD was used to treat acute and chronic TM perforations in a chinchilla model. A total of 24 ears from 12 adult male chinchillas were used in the study. They were organized into four groups. The first two groups had acute TM perforations and the last two had chronic TM perforations. We used the first and third groups as controls, meaning they did not receive the implant treatment. The second and fourth groups, however, were treated with the collagen graft implant. Otoscopic assessments were conducted on days 14 and 35, with histological evaluations and TM vibrational studies performed on day 35. The groups treated with the collagen graft showed fewer inflammatory changes, improved structural recovery, and nearly normal TM vibrational properties compared to the controls. The porous collagen scaffold successfully enhanced TM regeneration, showing high biocompatibility and biodegradation potential. These findings could pave the way for clinical trials and present a new approach for treating TM perforations.

Comparison of the differentiation of ovine fetal bone-marrow mesenchymal stem cells towards osteocytes on chitosan/alginate/CuO-NPs and chitosan/alginate/FeO-NPs scaffolds

In the current study, the creation of a chitosan/alginate scaffold hydrogel with and without FeO-NPs or CuO-NPs was studied. From fetal ovine bone marrow mesenchymal stem cells (BM-MSCs) were isolated and cultivated. Their differentiation into osteocyte and adipose cells was investigated. Also, on the scaffolds, cytotoxicity and apoptosis were studied. To investigate the differentiation, treatment groups include: (1) BM-MSCs were plated in DMEM culture medium with high glucose containing 10% FBS and antibiotics (negative control); (2) BM-MSCs were plated in osteogenic differentiation medium (positive control); (3) positive control group + FeO-NPs, (4) positive control group + CuO-NPs; (5) BM-MSCs were plated in osteogenic differentiation medium on chitosan/alginate scaffold; (6) BM-MSCs were plated in osteogenic differentiation medium on chitosan/alginate/FeO-NPs scaffold; and (7) BM-MSCs were plated in osteogenic differentiation medium on chitosan/alginate/CuO-NPs scaffold. Alkaline phosphatase enzyme concentrations, mineralization rate using a calcium kit, and mineralization measurement by alizarin staining quantification were evaluated after 21 days of culture. In addition, qRT-PCR was used to assess the expression of the ALP, ColA, and Runx2 genes. When compared to other treatment groups, the addition of CuO-NPs in the chitosan/alginate hydrogel significantly increased the expression of the ColA and Runx2 genes (p < 0.05). However, there was no significant difference between the chitosan/alginate hydrogel groups containing FeO-NPs and CuO-NPs in the expression of the ALP gene. It appears that the addition of nanoparticles, in particular CuO-NPs, has made the chitosan/alginate scaffold more effective in supporting osteocyte differentiation.

Construction and characterisation of a structured, tuneable, and transparent 3D culture platform for soil bacteria

We have developed a tuneable workflow for the study of soil microbes in an imitative 3D soil environment that is compatible with routine and advanced optical imaging, is chemically customisable, and is reliably refractive index matched based on the carbon catabolism of the study organism. We demonstrate our transparent soil pipeline with two representative soil organisms, Bacillus subtilis and Streptomyces coelicolor, and visualise their colonisation behaviours using fluorescence microscopy and mesoscopy. This spatially structured, 3D approach to microbial culture has the potential to further study the behaviour of bacteria in conditions matching their native environment and could be expanded to study microbial interactions, such as competition and warfare.

Vascular persistence following precision micropuncture

OBJECTIVE

The success of engineered tissues continues to be limited by time to vascularization and perfusion. Recently, we described a simple microsurgical approach, termed micropuncture (MP), which could be used to rapidly vascularize an adjacently placed scaffold from the recipient macrovasculature. Here we studied the long-term persistence of the MP-induced microvasculature.

METHODS

Segmental 60 μm diameter MPs were created in the recipient rat femoral artery and vein followed by coverage with a simple Type 1 collagen scaffold. The recipient vasculature and scaffold were then wrapped en bloc with a silicone sheet to isolate intrinsic vascularization. Scaffolds were harvested at 28 days post-implantation for detailed analysis, including using a novel artificial intelligence (AI) approach.

RESULTS

MP scaffolds demonstrated a sustained increase of vascular density compared to internal non-MP control scaffolds (p < 0.05) secondary to increases in both vessel diameters (p < 0.05) and branch counts (p < 0.05). MP scaffolds also demonstrated statistically significant increases in red blood cell (RBC) perfused lumens.

CONCLUSIONS

This study further highlights that the intrinsic MP-induced vasculature continues to persist long-term. Its combination of rapid and stable angiogenesis represents a novel surgical platform for engineered scaffold and graft perfusion.

[Experimental evaluation of the efficacy of tissue-engineered constructs in the treatment of limbal stem cell deficiency]

Limbal stem cell deficiency (LSCD) is one of the leading factors negatively affecting the success of keratoplasty, and its treatment remains an urgent problem in ophthalmology. With the development of regenerative medicine, one of the promising approaches is the transplantation of tissue-engineered constructs from cultured limbal stem cells (LSCs) in biopolymer carriers.

PURPOSE

This study was conducted to develop an experimental model of LSCD and evaluate the effectiveness of transplantation of a tissue-engineered construct consisting of cultured cells containing a population of LSCs and a collagen carrier.

MATERIAL AND METHODS

The study was performed on 12 rabbits and included several stages. At the first stage, the physiological effects of collagen matrix implantation into the limbal zone were studied. At the second stage, tissue-engineered constructs consisting of LSCs on a collagen matrix were formed and their effect on the regeneration processes in the experimental LSCD model was analyzed. The animals were divided into 2 groups: surgical treatment (transplantation of the tissue-engineered construct) was used in the experimental group, and conservative treatment was used in the control group. Slit-lamp biomicroscopy with photo-registration, fluorescein corneal staining, optical coherence tomography of the anterior segment of the eye, and impression cytology were used to assess the results.

RESULTS

No side reactions were observed after implantation of the collagen matrix into the limbal zone. One month after surgical treatment of the LSCD model in the experimental group, complete epithelization with minor manifestations of epitheliopathy was observed. In the control group, erosion of the corneal epithelium was noted. The time of corneal epithelization in the experimental and control groups was 9.2±2.95 and 46.20±12.07 days, respectively (p=0.139). According to the data of impression cytology, in the experimental group there were no goblet cells in the central part of the cornea, which indicates the restoration of corneal type epithelial cells, in contrast to the control group.

CONCLUSION

Transplantation of a tissue-engineered construct from cultured limbal cells on a collagen membrane should be considered as a promising method for the treatment of limbal stem cell deficiency.

Advances in Stem Cell-Based Therapies in the Treatment of Osteoarthritis

Osteoarthritis (OA) is a chronic, degenerative joint disease presenting a significant global health threat. While current therapeutic approaches primarily target symptom relief, their efficacy in repairing joint damage remains limited. Recent research has highlighted mesenchymal stem cells (MSCs) as potential contributors to cartilage repair, anti-inflammatory modulation, and immune regulation in OA patients. Notably, MSCs from different sources and their derivatives exhibit variations in their effectiveness in treating OA. Moreover, pretreatment and gene editing techniques of MSCs can enhance their therapeutic outcomes in OA. Additionally, the combination of novel biomaterials with MSCs has shown promise in facilitating the repair of damaged cartilage. This review summarizes recent studies on the role of MSCs in the treatment of OA, delving into their advantages and exploring potential directions for development, with the aim of providing fresh insights for future research in this critical field.

Neural regeneration ability of Polypyrrole-Collagen-Quercetin composite in the spinal cord injury

Spinal cord injury (SCI) is a major clinical problem in young patients. The major hurdle in SCI regeneration is the replacement of lost nerve communication signals due to injury. Here we have prepared a biocompatible electrical conductive composite such as Collagen-Polypyrrole combined with Quercetin (Col-PPy-Qur) composite. The prepared composites are characterized for their chemical functionality and morphology by the FTIR and SEM & TEM analysis, respectively. The Col-PPy-Qur composite observed electrical conductivity at 0.0653 s/cm due to the conductive Polypyrrole polymer present in the composite. The Col-PPy-Qur composite exhibits a mechanical strength of 0.1281 mPa, similar to the native human spinal cord's mechanical strength. In order to explore the regeneration potential, the viability of the composite has been tested with human astrocyte cells (HACs). The Tuj1 and GFAF marker expression was quantized by RT-PCR analysis. Increased Tuj1 and decreased GFAF expression by the Col-PPy-Qur composite indicated the potential differentiation ability of the HACs into neuron cells. The results indicated that the Col-PPy-Qur composite could have good regeneration and differentiation ability, better biocompatibility, and suitable mechanical and conductivity properties. It can act as an excellent strategy for spinal cord regeneration in the nearer future.

Nanomaterials-incorporated hydrogels for 3D bioprinting technology

In the field of tissue engineering and regenerative medicine, various hydrogels derived from the extracellular matrix have been utilized for creating engineered tissues and implantable scaffolds. While these hydrogels hold immense promise in the healthcare landscape, conventional bioinks based on ECM hydrogels face several challenges, particularly in terms of lacking the necessary mechanical properties required for 3D bioprinting process. To address these limitations, researchers are actively exploring novel nanomaterial-reinforced ECM hydrogels for both mechanical and functional aspects. In this review, we focused on discussing recent advancements in the fabrication of engineered tissues and monitoring systems using nanobioinks and nanomaterials via 3D bioprinting technology. We highlighted the synergistic benefits of combining numerous nanomaterials into ECM hydrogels and imposing geometrical effects by 3D bioprinting technology. Furthermore, we also elaborated on critical issues remaining at the moment, such as the inhomogeneous dispersion of nanomaterials and consequent technical and practical issues, in the fabrication of complex 3D structures with nanobioinks and nanomaterials. Finally, we elaborated on plausible outlooks for facilitating the use of nanomaterials in biofabrication and advancing the function of engineered tissues.

Anti-Adhesive Resorbable Indomethacin/Bupivacaine-Eluting Nanofibers for Tendon Rupture Repair: In Vitro and In Vivo Studies

The treatment and surgical repair of torn Achilles tendons seldom return the wounded tendon to its original elasticity and stiffness. This study explored the in vitro and in vivo simultaneous release of indomethacin and bupivacaine from electrospun polylactide-polyglycolide composite membranes for their capacity to repair torn Achilles tendons. These membranes were fabricated by mixing polylactide-polyglycolide/indomethacin, polylactide-polyglycolide/collagen, and polylactide-polyglycolide/bupivacaine with 1,1,1,3,3,3-hexafluoro-2-propanol into sandwich-structured composites. Subsequently, the in vitro pharmaceutic release rates over 30 days were determined, and the in vivo release behavior and effectiveness of the loaded drugs were assessed using an animal surgical model. High concentrations of indomethacin and bupivacaine were released for over four weeks. The released pharmaceutics resulted in complete recovery of rat tendons, and the nanofibrous composite membranes exhibited exceptional mechanical strength. Additionally, the anti-adhesion capacity of the developed membrane was confirmed. Using the electrospinning technique developed in this study, we plan on manufacturing degradable composite membranes for tendon healing, which can deliver sustained pharmaceutical release and provide a collagenous habitat.

Advances in tissue engineering and biofabrication for in vitro skin modeling

The global prevalence of skin disease and injury is continually increasing, yet conventional cell-based models used to study these conditions do not accurately reflect the complexity of human skin. The lack of inadequate in vitro modeling has resulted in reliance on animal-based models to test pharmaceuticals, biomedical devices, and industrial and environmental toxins to address clinical needs. These in vivo models are monetarily and morally expensive and are poor predictors of human tissue responses and clinical trial outcomes. The onset of three-dimensional (3D) culture techniques, such as cell-embedded and decellularized approaches, has offered accessible in vitro alternatives, using innovative scaffolds to improve cell-based models' structural and histological authenticity. However, these models lack adequate organizational control and complexity, resulting in variations between structures and the exclusion of physiologically relevant vascular and immunological features. Recently, biofabrication strategies, which combine biology, engineering, and manufacturing capabilities, have emerged as instrumental tools to recreate the heterogeneity of human skin precisely. Bioprinting uses computer-aided design (CAD) to yield robust and reproducible skin prototypes with unprecedented control over tissue design and assembly. As the interdisciplinary nature of biofabrication grows, we look to the promise of next-generation biofabrication technologies, such as organ-on-a-chip (OOAC) and 4D modeling, to simulate human tissue behaviors more reliably for research, pharmaceutical, and regenerative medicine purposes. This review aims to discuss the barriers to developing clinically relevant skin models, describe the evolution of skin-inspired in vitro structures, analyze the current approaches to biofabricating 3D human skin mimetics, and define the opportunities and challenges in biofabricating skin tissue for preclinical and clinical uses.

Hydrogels as Scaffolds in Bone-Related Tissue Engineering and Regeneration

Several years have passed since the medical and scientific communities leaned toward tissue engineering as the most promising field to aid bone diseases and defects resulting from degenerative conditions or trauma. Owing to their histocompatibility and non-immunogenicity, bone grafts, precisely autografts, have long been the gold standard in bone tissue therapies. However, due to issues associated with grafting, especially the surgical risks and soaring prices of the procedures, alternatives are being extensively sought and researched. Fibrous and non-fibrous materials, synthetic substitutes, or cell-based products are just a few examples of research directions explored as potential solutions. A very promising subgroup of these replacements involves hydrogels. Biomaterials resembling the bone extracellular matrix and therefore acting as 3D scaffolds, providing the appropriate mechanical support and basis for cell growth and tissue regeneration. Additional possibility of using various stimuli in the form of growth factors, cells, etc., within the hydrogel structure, extends their use as bioactive agent delivery platforms and acts in favor of their further directed development. The aim of this review is to bring the reader closer to the fascinating subject of hydrogel scaffolds and present the potential of these materials, applied in bone and cartilage tissue engineering and regeneration.

Microenvironment-targeted strategy steers advanced bone regeneration

Treatment of large bone defects represents a great challenge in orthopedic and craniomaxillofacial surgery. Traditional strategies in bone tissue engineering have focused primarily on mimicking the extracellular matrix (ECM) of bone in terms of structure and composition. However, the synergistic effects of other cues from the microenvironment during bone regeneration are often neglected. The bone microenvironment is a sophisticated system that includes physiological (e.g., neighboring cells such as macrophages), chemical (e.g., oxygen, pH), and physical factors (e.g., mechanics, acoustics) that dynamically interact with each other. Microenvironment-targeted strategies are increasingly recognized as crucial for successful bone regeneration and offer promising solutions for advancing bone tissue engineering. This review provides a comprehensive overview of current microenvironment-targeted strategies and challenges for bone regeneration and further outlines prospective directions of the approaches in construction of bone organoids.

Effect of Nitrogen Arc Discharge Plasma Treatment on Physicochemical Properties and Biocompatibility of PLA-Based Scaffolds

The effect of low-temperature arc discharge plasma treatment in a nitrogen atmosphere on the modification of the physicochemical properties of PLA-based scaffolds was studied. In addition, the cellular-mediated immune response when macrophages of three donors interact with the modified surfaces of PLA-based scaffolds was investigated. PLA surface carbonization, accompanied by a carbon atomic concentration increase, was revealed to occur because of plasma treatment. Nitrogen plasma significantly influenced the PLA wettability characteristics, namely, the hydrophilicity and lipophilicity were improved, as well as the surface energy being raised. The viability of cells in the presence of the plasma-modified PLA scaffolds was evaluated to be higher than that of the initial cells.

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.

3D Bioprinting for Vascularization

In the world of clinic treatments, 3D-printed tissue constructs have emerged as a less invasive treatment method for various ailments. Printing processes, scaffold and scaffold free materials, cells used, and imaging for analysis are all factors that must be observed in order to develop successful 3D tissue constructs for clinical applications. However, current research in 3D bioprinting model development lacks diverse methods of successful vascularization as a result of issues with scaling, size, and variations in printing method. This study analyzes the methods of printing, bioinks used, and analysis techniques in 3D bioprinting for vascularization. These methods are discussed and evaluated to determine the most optimal strategies of 3D bioprinting for successful vascularization. Integrating stem and endothelial cells in prints, selecting the type of bioink according to its physical properties, and choosing a printing method according to physical properties of the desired printed tissue are steps that will aid in the successful development of a bioprinted tissue and its vascularization.

A Systematic Review on Polyester Scaffolds in Dental Three-dimensional Cell Printing: Transferring Art from the Laboratories to the Clinics

Objective

The purpose of this systematic review is to describe developments in three-dimensional (3D) cell printing in the formation of dental pulp tissue using polyester as a scaffold to revitalize the damaged dental pulp tissue.

Materials and methods

A literature search for all the data published in PubMed and Google Scholar from January 2000 to April 2022 was conducted. Articles with the keywords 3D cell printing, scaffolds, polyester, dental pulp, and dentistry were used. Inclusion criteria consisted of any publication in electronic or print media directly studying or commenting on the use of polyester scaffolds in 3D cell printing technology in the regeneration of dental pulp. A total of 528 articles were selected, of which 27 duplicates and 286 irrelevant articles were discarded. A total of 215 articles were finally included in the systematic review.

Result and conclusion

For dental pulp regeneration, several scaffolds have been discovered to be appealing. Polylactic acid (PLA), polyglycolic acid (PGA), and their copolymers are nontoxic and biocompatible synthetic polyesters that degrade by hydrolysis and have received Food and Drug Administration (FDA) approval for a variety of applications. This review paper is intended to spark new ideas for using a certain scaffold in a specific regenerative approach to produce the desired pulp-dentin complex.

Scaffold Using Chitosan, Agarose, Cellulose, Dextran and Protein for Tissue Engineering-A Review

Biological macromolecules like polysaccharides/proteins/glycoproteins have been widely used in the field of tissue engineering due to their ability to mimic the extracellular matrix of tissue. In addition to this, these macromolecules are found to have higher biocompatibility and no/lesser toxicity when compared to synthetic polymers. In recent years, scaffolds made up of proteins, polysaccharides, or glycoproteins have been highly used due to their tensile strength, biodegradability, and flexibility. This review is about the fabrication methods and applications of scaffolds made using various biological macromolecules, including polysaccharides like chitosan, agarose, cellulose, and dextran and proteins like soy proteins, zein proteins, etc. Biopolymer-based nanocomposite production and its application and limitations are also discussed in this review. This review also emphasizes the importance of using natural polymers rather than synthetic ones for developing scaffolds, as natural polymers have unique properties, like high biocompatibility, biodegradability, accessibility, stability, absence of toxicity, and low cost.

Microfabrication approaches for oral research and clinical dentistry

Currently, there is a variety of laboratory tools and strategies that have been developed to investigate in-vivo processes using in-vitro models. Amongst these, microfabrication represents a disruptive technology that is currently enabling next-generation biomedical research through the development of complex laboratory approaches (e.g., microfluidics), engineering of micrometer scale sensors and actuators (micropillars for traction force microscopy), and the creation of environments mimicking cell, tissue, and organ-specific contexts. Although microfabrication has been around for some time, its application in dental and oral research is still incipient. Nevertheless, in recent years multiple lines of research have emerged that use microfabrication-based approaches for the study of oral diseases and conditions with micro- and nano-scale sensitivities. Furthermore, many investigations are aiming to develop clinically relevant microfabrication-based applications for diagnostics, screening, and oral biomaterial manufacturing. Therefore, the objective of this review is to summarize the current application of microfabrication techniques in oral sciences, both in research and clinics, and to discuss possible future applications of these technologies for in-vitro studies and practical patient care. Initially, this review provides an overview of the most employed microfabrication methods utilized in biomedicine and dentistry. Subsequently, the use of micro- and nano-fabrication approaches in relevant fields of dental research such as endodontic and periodontal regeneration, biomaterials research, dental implantology, oral pathology, and biofilms was discussed. Finally, the current and future uses of microfabrication technology for clinical dentistry and how these approaches may soon be widely available in clinics for the diagnosis, prevention, and treatment of relevant pathologies are presented.

Injectable TG-linked recombinant human collagen hydrogel loaded with bFGF for rat cranial defect repair

The basic fibroblast growth factor (bFGF) plays a significant role in promoting the process of bone repair, but bFGF cannot keep its biological activity stable under normal physiological conditions. Therefore, the development of better biomaterials to carry bFGF remains a challenge for bone repair and regeneration. Here we designed a novel recombinant human collagen (rhCol), which could be cross-linked by transglutaminase (TG) and loaded bFGF to prepare rhCol/bFGF hydrogels. The rhCol hydrogel possessed a porous structure and good mechanical properties. The assays, including cell proliferation, migration, and adhesion assay, were performed to evaluate the biocompatibility of rhCol/bFGF and the results demonstrated that the rhCol/bFGF promoted cell proliferation, migration and adhesion. The rhCol/bFGF hydrogel degraded and released bFGF controllably, enhancing utilization rate of bFGF and allowing osteoinductive activity. The results of RT-qPCR and immunofluorescence staining also proved that rhCol/bFGF promoted expression of bone-related proteins. The rhCol/bFGF hydrogels were applied in the cranial defect in rats and the results confirmed that it accelerates bone defect repair. In conclusion, rhCol/bFGF hydrogel has excellent biomechanical properties and can continuously release bFGF to promote bone regeneration, suggesting that rhCol/bFGF hydrogel is a potential scaffold in clinic application.

Denuded Descemet's membrane supports human embryonic stem cell-derived retinal pigment epithelial cell culture

Recent clinical studies suggest that retinal pigment epithelial (RPE) cell replacement therapy may preserve vision in retinal degenerative diseases. Scaffold-based methods are being tested in ongoing clinical trials for delivering pluripotent-derived RPE cells to the back of the eye. The aim of this study was to investigate human embryonic stem cell-derived retinal pigment epithelial (hESC-RPE) cells survival and behaviour on a decellularized Descemet's Membrane (DM), which may be of clinical relevance in retinal transplantation. DMs were isolated from human donor corneas and treated with thermolysin. The DM surface topology and the efficiency of the denudation method were evaluated by atomic force microscope, scanning electron microscopy and histology. hESC-RPE cells were seeded onto the endothelial-side surface of decellularized DM in order to determine the potential of the membrane to support hESC-RPE cell culture, alongside maintaining their viability. Integrity of the hESC-RPE monolayer was assessed by measuring transepithelial resistance. RPE-specific gene expression and growth factors secretion were assessed to confirm maturation and functionality of the cells over the new substrate. Thermolysin treatment did not affect the integrity of the tissue, thus ensuring a reliable method to standardize the preparation of decellularized DM. 24 hours post-seeding, hESC-RPE cell attachment and initial proliferation rate over the denuded DM were higher than hESC-RPE cells cultured on tissue culture inserts. On the new matrix, hESC-RPE cells succeeded in forming an intact monolayer with mature tight junctions. The resulting cell culture showed characteristic RPE cell morphology and proper protein localization. Gene expression analysis and VEGF secretion demonstrate DM provides supportive scaffolding and inductive properties to enhance hESC-RPE cells maturation. Decellularized DM was shown to be capable of sustaining hESC-RPE cells culture, thus confirming to be potentially a suitable candidate for retinal cell therapy.

Characterization of a bioscaffold containing polysaccharide acemannan and native collagen for pulp tissue regeneration

Dental pulp regeneration exploits tissue engineering concepts using stem cells/scaffolds/growth-factors. Extracted collagen is commonly used as a biomaterial-scaffold due to its biocompatibility/biodegradability and mimics the natural extracellular matrix. Adding biomolecules into a collagen-scaffold enhanced pulp regeneration. Acemannan, β-(1-4)-acetylated-polymannose, is a polysaccharide extracted from aloe vera. Acemannan is a regenerative biomaterial. Therefore, acemannan could be a biomolecule in a collagen-scaffold. Here, acemannan and native collagen were obtained and characterized. The AceCol-scaffold's physical properties were investigated using FTIR, SEM, contact angle, swelling, pore size, porosity, compressive modulus, and degradation assays. The AceCol-scaffold's biocompatibility, growth factor secretion, osteogenic protein expression, and calcification were evaluated in vitro. The AceCol-scaffolds demonstrated higher hydrophilicity, swelling, porosity, and larger pore size than the collagen scaffolds (p < 0.05). Better cell-cell and cell-scaffold adhesion, and dentin extracellular matrix protein (BSP/OPN/DSPP) expression were observed in the AceCol-scaffold, however, DSPP expression was not detected in the collagen group. Significantly increased cellular proliferation, VEGF and BMP2 expression, and mineralization were detected in the AceCol-scaffold compared with the collagen-scaffold (p < 0.05). Computer simulation revealed that acemannan's 3D structure changes to bind with collagen. In conclusion, the AceCol-scaffold synergistically provides better physical and biological properties than collagen. The AceCol-scaffold is a promising material for tissue regeneration.

Concise Review: Bioengineering of Limbal Stem Cell Niche

The corneal epithelium is composed of nonkeratinized stratified squamous cells and has a significant turnover rate. Limbal integrity is vital to maintain the clarity and avascularity of the cornea as well as regeneration of the corneal epithelium. Limbal epithelial stem cells (LESCs) are located in the basal epithelial layer of the limbus and preserve this homeostasis. Proper functioning of LESCs is dependent on a specific microenvironment, known as the limbal stem cell niche (LSCN). This structure is made up of various cells, an extracellular matrix (ECM), and signaling molecules. Different etiologies may damage the LSCN, leading to limbal stem cell deficiency (LSCD), which is characterized by conjunctivalization of the cornea. In this review, we first summarize the basics of the LSCN and then focus on current and emerging bioengineering strategies for LSCN restoration to combat LSCD.

Elastin Barrier Membranes for Guided Tissue Regeneration Technologies

This article discusses the prospects for the use of new elastin barrier membranes manufactured using adapted technologies for the selective isolation of the elastin component from the extracellular xenogenic matrix of the pericardium ligamentous apparatus: (1) by high-temperature extraction under pressure; (2) cyanogen bromide method. A commercial material, Geistlich Bio–Gide® membrane (BG), was used as a control comparison group. It is shown that the materials of group (1) have a high degree of biocompatibility, exceeding the indicators of the control group BG. Based on the results of an study in a model of subcutaneous heterotopic implantation in rats, it was shown that elastin BM has a chemoattractant effect on the mesenchymal recipient cells and, unlike the control, is able to integrate to a high degree into the surrounding recipient tissues. At the same time, the materials of group (1) had a pronounced proangiogenic effect. Thus, it has been shown that elastin BM groups (1) have a medium-term barrier function and are able to induce full-fledged cellular repopulation and local neoangiogenesis, which can be useful in clinical practice, primarily in GTR technologies (with gingival flap augmentation) or when used together with other BM as an angiogenesis inducer to ensure formation of the vascular bed in GBR technologies of bone tissue.

The progress in techniques for culturing human limbal epithelial stem cells

In vitro culture of human limbal epithelial stem cells (hLESCs) is crucial to cell therapy in the treatment of limbal stem cell deficiency, a potentially vision-threatening disease that is characterized by persistent corneal epithelial defects and corneal epithelium conjunctivalization. Traditionally, hLESCs are cultivated based on either limbal tissue explants or single-cell suspensions in culture media containing xenogenous components, such as fetal bovine serum and murine 3T3 feeder cells. Plastic culture dishes and human amniotic membranes are classical growth substrates used in conventional hLESC culture systems. The past few decades have witnessed considerable progress and innovations in hLESC culture techniques to ensure a higher level of biosafety and lower immunogenicity for further cell treatment, including complete removal of xenogenous components from culture media, the application of human-derived feeder cells, and the development of novel scaffolds. Three-dimensional artificial niches and three-dimensional culture techniques have also been established to simulate the real microenvironment of limbal crypts for better cell outgrowth and proliferation. All these progresses ensure that in vitro cultured hLESCs are more adaptable to translational stem cell therapy for limbal stem cell deficiency.

Polymeric Gel Scaffolds and Biomimetic Environments for Wound Healing

Infected wounds that do not heal are a worldwide problem that is worsening, with more people dying and more money being spent on care. For any disease to be managed effectively, its root cause must be addressed. Effective wound care becomes a bigger problem when various traditional wound healing methods and products may not only fail to promote good healing. Still, it may also hinder the healing process, causing wounds to stay open longer. Progress in tissue regeneration has led to developing three-dimensional scaffolds (3D) or constructs that can be leveraged to facilitate cell growth and regeneration while preventing infection and accelerating wound healing. Tissue regeneration uses natural and fabricated biomaterials that encourage the growth of tissues or organs. Even though the clinical need is urgent, the demand for polymer-based therapeutic techniques for skin tissue abnormalities has grown quickly. Hydrogel scaffolds have become one of the most imperative 3D cross-linked scaffolds for tissue regeneration because they can hold water perfectly and are porous, biocompatible, biodegradable, and biomimetic. For damaged organs or tissues to heal well, the porosity topography of the natural extracellular matrix (ECM) should be imitated. This review details the scaffolds that heal wounds and helps skin tissue to develop. After a brief overview of the bioactive and drug-loaded polymeric hydrogels, the discussion moves on to how the scaffolds are made and what they are made of. It highlights the present uses of in vitro and in-vivo employed biomimetic scaffolds. The prospects of how well bioactiveloaded hydrogels heal wounds and how nanotechnology assists in healing and regeneration have been discussed.

In vitro biodegradation, cytotoxicity, and biocompatibility of polylactic acid/napier cellulose nanofiber scaffold composites

This study aimed to evaluate the bioactivities and biocompatibilities of porous polylactic acid (PLA) reinforced with cellulose nanofiber (CNF) scaffolds. The in vitro degradation behaviors of the porous PLA/CNF scaffolds were systematically measured for up to 8 weeks in a phosphate-buffered saline medium at 37 °C. The reinforcement of CNF resisted the biodegradation of the scaffolds. The in vitro cytotoxicity and biocompatibility of the scaffolds were determined using the Beas2B American Type Culture Collection cells. The 3-(4,5-cimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide cytotoxicity and proliferation tests showed that the scaffolds were non-toxic, and epithelial cells grew well on the scaffold after 7 days of culture, whereas the percentage of cell proliferation on the PLA/CNF₁₅ scaffold was the largest, 130 %. A scratch wound-healing assay was performed to evaluate the suitability of the scaffolds for cell migration. The results demonstrated that the scaffolds exhibited good cell migration towards nearly complete wound closure.

Regenerative Efficacy of Supercritical Carbon Dioxide-Derived Bone Graft Putty in Rabbit Bone Defect Model

Bone defects can arise from numerous reasons, such as aging, tumor, trauma, infection, surgery, and congenital diseases. Bone grafts are commonly used as a substitute to fill the void and regenerate the defect. Due to its clean and green technology, the supercritical carbon dioxide (SCCO2) extraction aided the production of bone grafts is a recent trend. The SCCO2-derived bone graft has osteoconductive and osteoinductive properties along with excellent biocompatible, nontoxic, bioabsorbable, osteoconductive, and good mechanical properties; however, clinical usage during surgery is time-consuming. Therefore, we produced a putty material combining bone graft powder and acellular dermal matrix (ADM) powder and tested its regenerative efficacy in the critical defect in the rabbit model. The putty was found to retain the tubular structure. In addition, the putty depicted excellent stickiness and cohesiveness in both saline and blood medium. The bone regeneration of bone graft and putty was similar; both had excellent bone healing and regeneration of critical defects as evaluated by the X-ray, microtomography, hematoxylin-eosin, Masson trichrome, and alizarin red staining. Putty contains a less washout rate, good mechanical strength, and biocompatibility. In conclusion, the SCCO2-derived moldable putty could be a promising easy-to-use alternative for bone grafts at present which might have real-world usage in orthopedics as a potential bone void filler and dental socket preservation.

High-Axial-Aspect Tannic Acid Microparticles Facilitate Gelation and Injectability of Collagen-Based Hydrogels

Injectable collagen-based hydrogels offer great promise for tissue engineering and regeneration, but their use is limited by poor mechanical strength. Herein, we incorporate tannic acid (TA) to tailor the rheology of the corresponding hydrogels while simultaneously adding the therapeutic benefits inherent to this polyphenolic component. TA in the solution form and needle-shaped TA microparticles are combined with collagen and the respective systems studied for their time-dependent sol-gel transitions (from storage to body temperatures, 4-37 °C) as a function of TA concentration. Compared to systems incorporating TA microparticles, those with dissolved TA, applied at a similar concentration, generate a less significant enhancement of the elastic modulus. Premature gelation at a low temperature and associated colloidal arrest of the system are proposed as a main factor explaining this limited performance. A higher yield stress (elastic stress method) is determined for systems loaded with TA microparticles compared to the system with dissolved TA. These results are interpreted in terms of the underlying interactions of TA with collagen, as probed by spectroscopy and isothermal titration calorimetry. Importantly, hydrogels containing TA microparticles show high cell viability (human dermal fibroblasts) and comparative cellular activity relative to the collagen-only hydrogel. Overall, composite hydrogels incorporating TA microparticles demonstrate a new, simple, and better-performance alternative to cell culturing and difficult implantation scenarios.

Investigation into self-assembled collagen arrays guided by the surface properties of polyimide films

The mechanism of highly-oriented collagen (Col) fibril arrays on rubbed polyimide (PI) films was investigated in order to understand the interfacial Col-PI interactions. It was found that the orientation of the surface functional groups of the rubbed PI films was most effectively controlled and optimized by the rubbing conditions. In particular, nano-grooves with a width of 100-600 nm and a depth of 2-10 nm were formed on the rubbed PI films at a rubbing strength of 2.4 m, leading to the formation of the highest density of the Col fibril array. Moreover, highly-oriented Col fibrils were formed inside the nano-grooves by the formation of hydrogen bonds between the CO of the imide groups (@ rubbed PI films) and the N-H of the amino groups (@ β-Sheets of Col molecules), resulting in the orientation of the Col molecules and subsequent assembly to the fibrils. Thus, the orientation and density of the fibril arrays on the rubbed PI films were successfully controlled by the interfacial interactions between the β-Sheet component of Col and the nano-groove surfaces of the rubbed PI films. Therefore, the novel technology of this study will provide an effective method to fabricate the one-directional fibrous nanostructures and to understand how to control the orientation of biomolecules in vitro.

Evaluation of Polysaccharide-Peptide Conjugates Containing the RGD Motif for Potential Use in Muscle Tissue Regeneration

New scaffold materials composed of biodegradable components are of great interest in regenerative medicine. These materials should be: stable, nontoxic, and biodegrade slowly and steadily, allowing the stable release of biodegradable and biologically active substances. We analyzed peptide-polysaccharide conjugates derived from peptides containing RGD motif (H-RGDS-OH (1), H-GRGDS-NH₂ (2), and cyclo(RGDfC) (3)) and polysaccharides as scaffolds to select the most appropriate biomaterials for application in regenerative medicine. Based on the results of MTT and Ki-67 assays, we can state that the conjugates containing calcium alginate and the ternary nonwoven material were the most supportive of muscle tissue regeneration. Scanning electron microscopy imaging and light microscopy studies with hematoxylin-eosin staining showed that C2C12 cells were able to interact with the tested peptide-polysaccharide conjugates. The release factor (Q) varied depending on both the peptide and the structure of the polysaccharide matrix. LDH, Alamarblue^®, Ki-67, and cell cycle assays indicated that peptides 1 and 2 were characterized by the best biological properties. Conjugates containing chitosan and the ternary polysaccharide nonwoven with peptide 1 exhibited very high antibacterial activity against Staphylococcus aureus and Klebsiella pneumoniae. Overall, the results of the study suggested that polysaccharide conjugates with peptides 1 and 2 can be potentially used in regenerative medicine.

Efficient co-expression of recombinant human fusion collagen with prolyl 4-hydroxylase from Bacillus anthracis in Escherichia coli

Collagen family members, the most abundant proteins in the human body, are widely used in biomedical fields and tissue engineering industries. However, the applications of collagen remain mostly relying on material derived from native tissues due to its extremely complex post-translational modifications like proline hydroxylation, which hinder the large-scale exogenous production of collagen. In the current study, we propose a novel prolyl hydroxylated recombinant human fusion collagen containing multiple native cell-interaction sites derived from human type Ⅰ and Ⅲ collagen with good biocompatibility and thermal stability. To obtain prolyl hydroxylated collagen, prolyl 4-hydroxylases from Bacillus anthracis, Arabidopsis thaliana, and Dactylosporangium sp. RH1 were co-expressed with collagen in Escherichia coli (E. coli), respectively. Among of which, prolyl 4-hydroxylase (P4H) from Bacillus anthracis showed the highest hydroxyl rate with 63.6%. Furthermore, a yield of hydroxylated collagen at 0.8 g/L was achieved by fed-batch fermentation in a 5 L fermenter with the productivity of 0.0267 g·L^-1 ·h^-1 . Compared with non-hydroxylated recombinant collagen, hydroxylated recombinant collagen showed significant improvements in thermal stability and biocompatibility. Taken this together, our studies provide a promising method for further development of collagen application in biomaterials engineering. A novel recombinant human fusion collagen with multiple motifs derived from both human type I and Ⅲ collagen exhibits good biocompatibility and thermal stability as higher molecular weight of ∼120kDa. By co-expression recombinant collagen and P4H genes in Escherichia coli, the maximum hyp in the recombinant collagen reached 63.6%, and a yield of hydroxylated collagen at 0.8 g/L was achieved by fed-batch fermentation in a 5 L fermenter. This article is protected by copyright. All rights reserved.

In Vivo Bone Tissue Engineering Strategies: Advances and Prospects

Reconstruction of critical-sized bone defects remains a tremendous challenge for surgeons worldwide. Despite the variety of surgical techniques, current clinical strategies for bone defect repair demonstrate significant limitations and drawbacks, including donor-site morbidity, poor anatomical match, insufficient bone volume, bone graft resorption, and rejection. Bone tissue engineering (BTE) has emerged as a novel approach to guided bone tissue regeneration. BTE focuses on in vitro manipulations with seed cells, growth factors and bioactive scaffolds using bioreactors. The successful clinical translation of BTE requires overcoming a number of significant challenges. Currently, insufficient vascularization is the critical limitation for viability of the bone tissue-engineered construct. Furthermore, efficacy and safety of the scaffolds cell-seeding and exogenous growth factors administration are still controversial. The in vivo bioreactor principle (IVB) is an exceptionally promising concept for the in vivo bone tissue regeneration in a predictable patient-specific manner. This concept is based on the self-regenerative capacity of the human body, and combines flap prefabrication and axial vascularization strategies. Multiple experimental studies on in vivo BTE strategies presented in this review demonstrate the efficacy of this approach. Routine clinical application of the in vivo bioreactor principle is the future direction of BTE; however, it requires further investigation for overcoming some significant limitations.

Recent Advances in Microgels: From Biomolecules to Functionality

The emerging applications of hydrogel materials at different length scales, in areas ranging from sustainability to health, have driven the progress in the design and manufacturing of microgels. Microgels can provide miniaturized, monodisperse, and regulatable compartments, which can be spatially separated or interconnected. These microscopic materials provide novel opportunities for generating biomimetic cell culture environments and are thus key to the advances of modern biomedical research. The evolution of the physical and chemical properties has, furthermore, highlighted the potentials of microgels in the context of materials science and bioengineering. This review describes the recent research progress in the fabrication, characterization, and applications of microgels generated from biomolecular building blocks. A key enabling technology allowing the tailoring of the properties of microgels is their synthesis through microfluidic technologies, and this paper highlights recent advances in these areas and their impact on expanding the physicochemical parameter space accessible using microgels. This review finally discusses the emerging roles that microgels play in liquid-liquid phase separation, micromechanics, biosensors, and regenerative medicine.

Research progress in the use of mesenchymal stem cells and their derived exosomes in the treatment of osteoarthritis

Osteoarthritis (OA), as a common orthopedic disease with cartilage injury as its main pathological feature, has a complex pathogenesis and existing medical technology remains unable to reverse the progress of cartilage degeneration caused thereby. In recent years, mesenchymal stem cells (MSCs) and their secreted exosomes have become a focus of research into cartilage regeneration. MSCs have the potential to differentiate into a variety of cells. Under specific conditions, they can be promoted to differentiate into chondrocytes and maintain the function and stability of chondrocytes. Exosomes secreted by MSCs, as an intercellular messenger, can treat OA in a variety of ways through bioactive factors carried therewith, such as protein, lipid, mRNA, and miRNA. This study reviewed the application of MSCs and their exosomes from different sources in the prevention of OA, which provides a new idea for the treatment of OA.

Tri-Layered Doxycycline-, Collagen- and Bupivacaine-Loaded Poly(lactic-co-glycolic acid) Nanofibrous Scaffolds for Tendon Rupture Repair

Achilles tendon rupture is a severe injury, and its optimal therapy remains controversial. Tissue engineering scaffolds play a significant role in tendon healing and tissue regeneration. In this study, we developed tri-layered doxycycline/collagen/bupivacaine (DCB)-composite nanofibrous scaffolds to repair injured Achilles tendons. Doxycycline, collagen, and bupivacaine were integrated into poly(lactic-co-glycolic acid) (PLGA) nanofibrous membranes, layer by layer, using an electrospinning technique as healing promoters, a 3D scaffold, and painkillers, respectively. After spinning, the properties of the nanofibrous scaffolds were characterized. In vitro drug discharge behavior was also evaluated. Furthermore, the effectiveness of the DCB–PLGA-composite nanofibers in repairing ruptured Achilles tendons was investigated in an animal tendon model with histological analyses. The experimental results show that, compared to the pristine PLGA nanofibers, the biomolecule-loaded nanofibers exhibited smaller fiber size distribution and an enhanced hydrophilicity. The DCB-composite nanofibers provided a sustained release of doxycycline and bupivacaine for over 28 days in vivo. Additionally, Achilles tendons repaired using DCB-composite nanofibers exhibited a significantly higher maximum load-to-failure than normal tendons, suggesting that the biomolecule-incorporated nanofibers are promising scaffolds for repairing Achilles tendons.

Characterization of an Innovative Biomaterial Derived From Human Wharton’s Jelly as a New Promising Coating for Tissue Engineering Applications

The extracellular matrix (ECM) offers the opportunity to create a biomaterial consisting of a microenvironment with interesting biological and biophysical properties for improving and regulating cell functions. Animal-derived ECM are the most widely used as an alternative to human tissues that are of very limited availability. However, incomplete decellularization of these tissues presents a high risk of immune rejection and disease transmission. In this study, we present an innovative method to extract human ECM derived from the Wharton’s jelly (WJ-ECMaa) of umbilical cords as a novel biomaterial to be used in tissue engineering. WJ-ECMaa was very efficiently decellularized, suggesting its possible use in allogeneic conditions. Characterization of its content allowed the identification of type I collagen as its main component. Various other matrix proteins, playing an important role in cell adhesion and proliferation, were also detected. WJ-ECMaa applied as a surface coating was analyzed by fluorescent labeling and atomic force microscopy. The results revealed a particular arrangement of collagen fibers not previously described in the literature. This biomaterial also presented better cytocompatibility compared to the conventional collagen coating. Moreover, it showed adequate hemocompatibility, allowing its use as a surface with direct contact with blood. Application of WJ-ECMaa as a coating of the luminal surface of umbilical arteries for a use in vascular tissue engineering, has improved significantly the cellularization of this surface by allowing a full and homogeneous cell coverage. Taking these results together, our novel extraction method of human ECM offers a very promising biomaterial with many potential applications in tissue engineering such as the one presented direct in vascular tissue engineering. Further characterization of the composition and functionality will help explore the ways it can be used in tissue engineering applications, especially as a scaffold or a surface coating.

A three-dimensional (3D), serum-free, Collagen Type I system for chondrogenesis of canine bone marrow-derived multipotent stromal cells (cMSCs)

The dog is an underrepresented large animal translational model for orthopedic cell-based tissue engineering. While chondrogenic differentiation of canine multipotent stromal cells (cMSCs) has been reported using the classic micromass technique, cMSCs respond inconsistently to this method. The objectives of this study were to develop a three-dimensional (3D), serum-free, Collagen Type I system to facilitate cMSC chondrogenesis and, once established, to determine the effect of chondrogenic growth factors on cMSC chondrogenesis. Canine MSCs were polymerized in 100 μL Collagen Type I gels (5 mg/mL) at 1 x 10⁶ cells/construct. Constructs were assessed using morphometry, live/dead staining, and histology in 10 various chondrogenic media. Four media were selected for additional in-depth analyses via lactate dehydrogenase release, total glycosaminoglycan content, qPCR (COL1A1, COL2A, SOX9, ACAN, BGLAP and SP7), immunofluorescence, and TUNEL staining. In the presence of dexamethasone and transforming growth factor-β3 (TGF-β3), both bone morphogenic protein-2 (BMP-2) and basic fibroblast growth factor (bFGF) generated larger chondrogenic constructs, although BMP-2 was required to achieve histologic characteristics of chondrocytes. Chondrogenic medium containing dexamethasone, TGF-β3, BMP-2 and bFGF led to a significant decrease in lactate dehydrogenase release at day 3 and glycosaminoglycan content was significantly increased in these constructs at day 3, 10, and 21. Both osteogenic and chondrogenic transcripts were induced in response to dexamethasone, TGF-β3, BMP-2 and bFGF. Collagen Type II and X were detected in all groups via immunofluorescence. Finally, TUNEL staining was positive in constructs lacking BMP-2 or bFGF. In conclusion, the 3D, serum-free, Collagen Type-I assay described herein proved useful in assessing cMSC differentiation and will serve as a productive system to characterize cMSCs or to fabricate tissue engineering constructs for clinical use.

Application of Hexanoyl Glycol Chitosan as a Non-cell Adhesive Polymer in Three-Dimensional Cell Culture

Cell culture technology has evolved into three-dimensional (3D) artificial tissue models for better reproduction of human native tissues. However, there are some unresolved limitations that arise due to the adhesive properties of cells. In this study, we developed a hexanoyl glycol chitosan (HGC) as a non-cell adhesive polymer for scaffold-based and -free 3D culture. The uniform cell distribution in a porous scaffold was well maintained during the long culutre period on the HGC-coated substrate by preventing ectopic adhesion and migration of cells on the substrate. In addition, when culturing many spheroids in one dish, supplementation of the culture medium with HGC prevented the aggregation of spheroids and maintained the shape and size of spheroids for a long culture duration. Collectively, the use of HGC in 3D culture systems is expected to contribute greatly to creating excellent regenerative therapeutics and screening models of bioproducts.

Suitability of Marine- and Porcine-Derived Collagen Type I Hydrogels for Bioprinting and Tissue Engineering Scaffolds

Collagens from a wide array of animals have been explored for use in tissue engineering in an effort to replicate the native extracellular environment of the body. Marine-derived biomaterials offer promise over their conventional mammalian counterparts due to lower risk of disease transfer as well as being compatible with more religious and ethical groups within society. Here, collagen type I derived from a marine source (Macruronus novaezelandiae, Blue Grenadier) is compared with the more established porcine collagen type I and its potential in tissue engineering examined. Both collagens were methacrylated, to allow for UV crosslinking during extrusion 3D printing. The materials were shown to be highly cytocompatible with L929 fibroblasts. The mechanical properties of the marine-derived collagen were generally lower than those of the porcine-derived collagen; however, the Young’s modulus for both collagens was shown to be tunable over a wide range. The marine-derived collagen was seen to be a potential biomaterial in tissue engineering; however, this may be limited due to its lower thermal stability at which point it degrades to gelatin.

In Vitro Biocompatibility and Degradation Analysis of Mass-Produced Collagen Fibers

Automation and mass-production are two of the many limitations in the tissue engineering industry. Textile fabrication methods such as electrospinning are used extensively in this field because of the resemblance of the extracellular matrix to the fiber structure. However, electrospinning has many limitations, including the ability to mass-produce, automate, and reproduce products. For this reason, this study evaluates the potential use of a traditional textile method such as spinning. Apart from mass production, these methods are also easy, efficient, and cost-effective. This study uses bovine-derived collagen fibers to create yarns using the traditional ring spinning method. The collagen yarns are proven to be biocompatible. Enzymatic biodegradability was also confirmed for its potential use in vivo. The results of this study prove the safety and efficacy of the material and the fabrication method. The material encourages higher cell proliferation and migration compared to tissue culture-treated plastic plates. The process is not only simple but is also streamlined and replicable, resulting in standardized products that can be reproduced.

Engineering Extracellular Microenvironment for Tissue Regeneration

The extracellular microenvironment is a highly dynamic network of biophysical and biochemical elements, which surrounds cells and transmits molecular signals. Extracellular microenvironment controls are of crucial importance for the ability to direct cell behavior and tissue regeneration. In this review, we focus on the different components of the extracellular microenvironment, such as extracellular matrix (ECM), extracellular vesicles (EVs) and growth factors (GFs), and introduce engineering approaches for these components, which can be used to achieve a higher degree of control over cellular activities and behaviors for tissue regeneration. Furthermore, we review the technologies established to engineer native-mimicking artificial components of the extracellular microenvironment for improved regenerative applications. This review presents a thorough analysis of the current research in extracellular microenvironment engineering and monitoring, which will facilitate the development of innovative tissue engineering strategies by utilizing different components of the extracellular microenvironment for regenerative medicine in the future.

2D Polymer Nanonets: Controllable Constructions and Functional Applications

Two-dimensional (2D) polymer nanonets have demonstrated great potential in various application fields due to their integrated advantages of ultrafine diameter, small pore size, high porosity, excellent interconnectivity, and large specific surface area. Here, a comprehensive overview of the controlled constructions of the polymer nanonets derived from electrospinning/netting, direct electronetting, self-assembly of cellulose nanofibers, and nonsolvent-induced phase separation is provided. Then, the widely researched multifunctional applications of polymer nanonets in filtration, sensor, tissue engineering, and electricity are also given. Finally, the challenges and possible directions for further developing the polymer nanonets are also intensively highlighted. This article is protected by copyright. All rights reserved.