Fiber-reinforced scaffolds in soft tissue engineering

Gelatin/EGDE Ultrafine Composite Fibers Reinforced with 3D Spacer Fabric as Bicomponent Scaffolds for Tissue Engineering

Protein-based ultrafine fibrous scaffolds can mimic the native extracellular matrices (ECMs) with regard to the morphology and chemical composition but suffer from poor mechanical and wet stability. As a result, cells cannot get a true three-dimensional (3D) environment as they find in native ECMs. In this study, an epoxide, ethylene glycol diglycidylether (EGDE), with high reactivity to active hydrogen is introduced to gelatin solution, serving as an effective cross-linker. The gelatin/EGDE 3D-ultrafine (∼500 nm in diameter) fibrous composite scaffolds are made by an ultralow-concentration phase separation technique (ULCPS). The effects of the polymer content and modification conditions on the morphology and wet stability of the constructs are investigated. It is revealed that ultrafine fibers with 3D random orientation could be formed at low concentrations (0.01, 0.05, and 0.1 wt %, respectively). The wet stability of the constructs could be effectively improved by introducing EGDE into the gelatin system. The shrinkage is reduced to merely 2.14% after the modification at 120 °C for 2 h and could be maintained for up to 3 days. In order to improve the compression properties, the same technique is utilized with the presence of a poly(lactic acid) (PLA) spacer fabric to produce a bicomponent scaffold. The mechanical property and cell viability of the bicomponent scaffolds are investigated, and it is found that cells could enter deep inside and orient themselves randomly at the central area of the bicomponent scaffold. The modification and design approach presented in this study has the potential to provide various protein-based ultrafine fibrous biomaterials for a variety of biomedical applications.

Developing strategies to optimize the anchorage between electrospun nanofibers and hydrogels for multi-layered plasmonic biomaterials

Polycaprolactone (PCL), a recognized biopolymer, has emerged as a prominent choice for diverse biomedical endeavors due to its good mechanical properties, exceptional biocompatibility, and tunable properties. These attributes render PCL a suitable alternative biomaterial to use in biofabrication, especially the electrospinning technique, facilitating the production of nanofibers with varied dimensions and functionalities. However, the inherent hydrophobicity of PCL nanofibers can pose limitations. Conversely, acrylamide-based hydrogels, characterized by their interconnected porosity, significant water retention, and responsive behavior, present an ideal matrix for numerous biomedical applications. By merging these two materials, one can harness their collective strengths while potentially mitigating individual limitations. A robust interface and effective anchorage during the composite fabrication are pivotal for the optimal performance of the nanoplatforms. Nanoplatforms are subject to varying degrees of tension and physical alterations depending on their specific applications. This is particularly pertinent in the case of layered nanostructures, which require careful consideration to maintain structural stability and functional integrity in their intended applications. In this study, we delve into the influence of the fiber dimensions, orientation and surface modifications of the nanofibrous layer and the hydrogel layer's crosslinking density on their intralayer interface to determine the optimal approach. Comprehensive mechanical pull-out tests offer insights into the interfacial adhesion and anchorage between the layers. Notably, plasma treatment of the hydrophobic nanofibers and the stiffness of the hydrogel layer significantly enhance the mechanical effort required for fiber extraction from the hydrogels, indicating improved anchorage. Furthermore, biocompatibility assessments confirm the potential biomedical applications of the proposed nanoplatforms.

Tissue engineering studies in male infertility disorder

Infertility is an important issue among couples worldwide which is caused by a variety of complex diseases. Male infertility is a problem in 7% of all men. In vitro spermatogenesis (IVS) is the experimental approach that has been developed for mimicking seminiferous tubules-like functional structures in vitro. Currently, various researchers are interested in finding and developing a microenvironmental condition or a bioartificial testis applied for fertility restoration via gamete production in vitro. The tissue engineering (TE) has developed new approaches to treat male fertility preservation through development of functional male germ cells. This makes TE a possible future strategy for restoration of male fertility. Although 3D culture systems supply the perception of the effect of cellular interactions in the process of spermatogenesis, formation of a native gradient of autocrine/paracrine factors in 3D culture systems have not been considered. These results collectively suggest that maintaining the microenvironment of testicular cells even in the form of a 3D-culture system is crucial in achieving spermatogenesis ex vivo. It is also possible to engineer the testicular structures using biomaterials to provide a supporting scaffold for somatic and stem cells. The insemination of these cells with GFs is possible for temporally and spatially adjusted release to mimic the microenvironment of the in situ seminiferous epithelium. This review focuses on recent studies and advances in the application of TE strategies to cell-tissue culture on synthetic or natural scaffolds supplemented with growth factors.

Exploring the biointerfaces: ab initio investigation of nano-montmorillonite clay, and its interaction with unnatural amino acids

We investigated the interaction between biomimetic Fe and Mg co-doped montmorillonite nanoclay and eleven unnatural amino acids. Employing three different functionals (PBE-GGA, PBE-GGA + U, and HSE06), we examined the clay's structural, electronic, and magnetic properties. Our results revealed the necessity of using PBE-GGA + U with U ≥ 4 eV to accurately describe key clay properties. We identified amino acids that strongly interacted with the clay surface, with steric orientation playing a crucial role in facilitating binding. Our DFT calculations highlighted significant electrostatic interactions between the amino acids and the clay slab, with the amino group's predominant role in this interaction. These findings hold promise for designing amino acids for clay-amino acid systems, leading to innovative bio-material composites for various applications. Additionally, our ab-initio molecular dynamics simulations confirmed the stability of clay-amino acid systems under ambient conditions, and the introduction of an implicit water solvent enhanced the binding energy of amino acids on the clay surface.

Poly(ε-caprolactone)/bioactive glass composite electrospun fibers for tissue engineering applications

In this work, composite electrospun fibers containing innovative bioactive glass nanoparticles were produced and characterized. Poly(ε-caprolactone), benign solvents, and sol-gel B- and Cu-doped bioactive glass powders were used to fabricate fibrous scaffolds. The retention of bioactive glass nanoparticles in the polymer matrix, the electrospinnability of this novel solution and the obtained electrospun composites were extensively characterized. As a result, composite electrospun fibers characterized by biocompatibility, bioactivity, and exhibiting overall properties adequate for both hard and soft tissue engineering applications, have been produced. The addition of these bioactive glass nanoparticles was, indeed, able to impart bioactive properties to the fibers. Cell culture studies show promising results, demonstrating proliferation and growth of cells on the composite fibers. Wettability, degradation rate, and mechanical performance were also tested and are in line with previous results.

Lifelike Transformative Materials for Biohybrid Implants: Inspired by Nature, Driven by Technology

Today's living world is enriched with a myriad of natural biological designs, shaped by billions of years of evolution. Unraveling the construction rules of living organisms offers the potential to create new materials and systems for biomedicine. From the close examination of living organisms, several concepts emerge: hierarchy, pattern repetition, adaptation, and irreducible complexity. All these aspects must be tackled to develop transformative materials with lifelike behavior. This perspective article highlights recent progress in the development of transformative biohybrid systems for applications in the fields of tissue regeneration and biomedicine. Advances in computational simulations and data-driven predictions are also discussed. These tools enable the virtual high-throughput screening of implant design and performance before committing to fabrication, thus reducing the development time and cost of biomimetic and biohybrid constructs. The ongoing progress of imaging methods also constitutes an essential part of this matter in order to validate the computation models and enable longitudinal monitoring. Finally, the current challenges of lifelike biohybrid materials, including reproducibility, ethical considerations, and translation, are discussed. Advances in the development of lifelike materials will open new biomedical horizons, where perhaps what is currently envisioned as science fiction will become a science-driven reality in the future.

Hydrogels for Oral Tissue Engineering: Challenges and Opportunities

Oral health is crucial to daily life, yet many people worldwide suffer from oral diseases. With the development of oral tissue engineering, there is a growing demand for dental biomaterials. Addressing oral diseases often requires a two-fold approach: fighting bacterial infections and promoting tissue growth. Hydrogels are promising tissue engineering biomaterials that show great potential for oral tissue regeneration and drug delivery. In this review, we present a classification of hydrogels commonly used in dental research, including natural and synthetic hydrogels. Furthermore, recent applications of these hydrogels in endodontic restorations, periodontal tissues, mandibular and oral soft tissue restorations, and related clinical studies are also discussed, including various antimicrobial and tissue growth promotion strategies used in the dental applications of hydrogels. While hydrogels have been increasingly studied in oral tissue engineering, there are still some challenges that need to be addressed for satisfactory clinical outcomes. This paper summarizes the current issues in the abovementioned application areas and discusses possible future developments.

Three-dimensional biomimetic reinforced chitosan/gelatin composite scaffolds containing PLA nano/microfibers for soft tissue engineering application

In the current study, we successfully prepared chitosan/gelatin composite scaffolds reinforced by centrifugally spun polylactic acid (PLA) chopped nano/microfibers (PLA-CFs). Herein, different amounts of PLA-CFs (0 %, 1 %, 2 %, 3 %, and 4 % w/v) dispersed in chitosan/gelatin solution were used. Morphological characterization of prepared scaffolds revealed that at the initial stage of adding PLA-CFs, the chopped fibers were localized at the wall of the pores; however, as the fiber load increased, aggregations of chopped-fibers could be seen. Also, mechanical evaluation of scaffolds in terms of compression and tensile mode showed that samples reinforced with 2 % PLA-CFs had enhanced mechanical properties. Indeed, its tensile strength increased from 123.8 to 247.2 kPa for dry and 18.9 to 48.6 kPa for wet conditions. Furthermore, the tensile modulus associated with both conditions increased from 2.99 MPa and 44.5 kPa to 6.43 MPa and 158.4 kPa, respectively. The results of cell culture studies also confirmed that the prepared composite scaffold exhibited appropriate biocompatibility, cell proliferation and migration. The cell infiltration study of the samples revealed that scaffolds reinforced with 2 % PLA-CFs had significantly better cell penetration and distribution compared with the control ones on both days (7 and 14).

Fiber diameters and parallel patterns: proliferation and osteogenesis of stem cells

Due to the innate extracellular matrix mimicking features, fibrous materials exhibited great application potential in biomedicine. In developing excellent fibrous biomaterial, it is essential to reveal the corresponding inherent fiber features' effects on cell behaviors. Due to the inevitable 'interference' cell adhesions to the background or between adjacent fibers, it is difficult to precisely reveal the inherent fiber diameter effect on cell behaviors by using a traditional fiber mat. A single-layer and parallel-arranged polycaprolactone fiber pattern platform with an excellent non-fouling background is designed and constructed herein. In this unique material platform, the 'interference' cell adhesions through interspace between fibers to the environment could be effectively ruled out by the non-fouling background. The 'interference' cell adhesions between adjacent fibers could also be excluded from the sparsely arranged (SA) fiber patterns. The influence of fiber diameter on stem cell behaviors is precisely and comprehensively investigated based on eliminating the undesired 'interference' cell adhesions in a controllable way. On the SA fiber patterns, small diameter fiber (SA-D1, D1 means 1 μm in diameter) may seriously restrict cell proliferation and osteogenesis when compared to the middle (SA-D8) and large (SA-D56) ones and SA-D8 shows the optimal osteogenesis enhancement effect. At the same time, the cells present similar proliferation ability and even the highest osteogenic ability on the densely arranged (DA) fiber patterns with small diameter fiber (DA-D1) when compared to the middle (DA-D8) and large (DA-D56) ones. The 'interference' cell adhesion between adjacent fibers under dense fiber arrangement may be the main reason for inducing these different cell behavior trends along with fiber diameters. Related results and comparisons have illustrated the effects of fiber diameter on stem cell behaviors more precisely and objectively, thus providing valuable reference and guidance for developing effective fibrous biomaterials.

Fabrication and Evaluation of Electrospun Silk Fibroin/Halloysite Nanotube Biomaterials for Soft Tissue Regeneration

The production of nanofibrous materials for soft tissue repair that resemble extracellular matrices (ECMs) is challenging. Electrospinning uniquely produces scaffolds resembling the ultrastructure of natural ECMs. Herein, electrospinning was used to fabricate Bombyx mori silk fibroin (SF) and SF/halloysite nanotube (HNT) composite scaffolds. Different HNT loadings were examined, but 1 wt% HNTs enhanced scaffold hydrophilicity and water uptake capacity without loss of mechanical strength. The inclusion of 1 wt% HNTs in SF scaffolds also increased the scaffold’s thermal stability without altering the molecular structure of the SF, as revealed by thermogravimetric analyses and Fourier transform infrared spectroscopy (FTIR), respectively. SF/HNT 1 wt% composite scaffolds better supported the viability and spreading of 3T3 fibroblasts and the differentiation of C2C12 myoblasts into aligned myotubes. These scaffolds coated with decellularised ECM from 3T3 cells or primary human dermal fibroblasts (HDFs) supported the growth of primary human keratinocytes. However, SF/HNT 1 wt% composite scaffolds with HDF-derived ECM provided the best microenvironment, as on these, keratinocytes formed intact monolayers with an undifferentiated, basal cell phenotype. Our data indicate the merits of SF/HNT 1 wt% composite scaffolds for applications in soft tissue repair and the expansion of primary human keratinocytes for skin regeneration.

The Construction of Biologically Relevant Fiber-Reinforced Hydrogel Geometries Using Air-Assisted Dual-Polarity Electrospinning

Fiber-reinforced hydrogels are a class of soft composite materials that has seen increased use across a wide variety of biomedical applications. However, existing fabrication techniques for these hydrogels are unable to realize biologically relevant macro/meso-scale geometries. To address this limitation, this paper presents a novel air-assisted, dual-polarity electrospinning printhead that converges high-strength electric fields, with low velocity air flow to remove the collector dependency seen with traditional far-field electrospinning setups. The use of this printhead, in conjunction with different configurations of deformable collection templates has resulted in the production of three classes of fiber-reinforced hydrogel prototype geometries, viz. (i) tubular geometries with bifurcations and meso-scale texturing; (ii) hollow, non-tubular geometries with single and dual-entrances; and (iii) 3D printed flat geometries with varying fiber density. All three classes of prototype geometries were mechanically characterized to have properties that were in line with those observed in living soft tissues. With the realization of this printhead, biologically relevant macro/meso-scale geometries can be realized using fiber-reinforced hydrogels to aid a wide array of biomedical applications.

An overview on electrospinning and its advancement toward hard and soft tissue engineering applications

One of the emerging technologies of the recent times harboring nanotechnology to fabricate nanofibers for various biomedical and environmental applications are electrospinning (nanofiber technology). Their relative ease in use, simplicity, functionality and diversity has surpassed the pitfalls encountered with the conventional method of generating fibers. This review aims to provide an overview of electrospinning, principle, methods, feed materials, and applications toward tissue engineering. To begin with, evolution of electrospinning and its typical apparatus have been briefed. Simultaneously, discussion on the production of nanofibers with diversified feed materials such as polymers, small molecules, colloids, and nanoparticles and its transformation into a powerful technology has been dealt with. Further, highlights on the application of nanofibers in tissue engineering and the commercialized products developed using nanofiber technology have been summed up. With this rapidly emerging technology, there would be a great demand pertaining to scalability and environmental challenge toward tissue engineering applications.

Progress in the Development of Graphene-Based Biomaterials for Tissue Engineering and Regeneration

Over the last few decades, tissue engineering has become an important technology for repairing and rebuilding damaged tissues and organs. The scaffold plays an important role and has become a hot pot in the field of tissue engineering. It has sufficient mechanical and biochemical properties and simulates the structure and function of natural tissue to promote the growth of cells inward. Therefore, graphene-based nanomaterials (GBNs), such as graphene and graphene oxide (GO), have attracted wide attention in the field of biomedical tissue engineering because of their unique structure, large specific surface area, good photo-thermal effect, pH response and broad-spectrum antibacterial properties. In this review, the structure and properties of typical GBNs are summarized, the progress made in the development of GBNs in soft tissue engineering (including skin, muscle, nerve and blood vessel) are highlighted, the challenges and prospects of the application of GBNs in soft tissue engineering have prospected.

Poly (vinyl alcohol)-alginate as potential matrix for various applications: A focused review

Advances in polymers have made significant contribution in diverse application oriented fields. Multidisciplinary applicability of polymers generates a range of strategies, which is pertinent in a wide range of fields. Blends of natural and synthetic polymers have spawned a different class of materials with synergistic effects. Specifically, poly (vinyl alcohol) (PVA) and alginate (AG) blends (PVAG) have demonstrated some promising results in almost every segment, ranging from biomedical to industrial sector. Combination of PVAG with other materials, immobilization with specific moieties and physical and chemical crosslinking could result in amendments in the structure and properties of the PVAG matrices. Here, we provide an overview of the recent developments in designing PVAG based matrix and complexes with their structural and functional properties. The article also provides a comprehensive outline on the applicability of PVAG matrix in wastewater treatment, biomedical, photocatalysis, food packaging, and fuel cells and sheds light on the challenges that need to be addressed. Finally, the review elaborates the future prospective of PVAG matrices in other unexplored fields like aircraft industry, nuclear science and space exploration.

Low methacrylated poly (glycerol sebacate) for soft tissue engineering

Tissue engineering for soft tissue has made great advances in recent years, though there are still challenges to overcome. The main problem is that autologous tissue implants have not given...

Multifarious applications of bioactive glasses in soft tissue engineering

Tissue engineering (TE), a new paradigm in regenerative medicine, repairs and restores the diseased or damaged tissues and eliminates drawbacks associated with autografts and allografts. In this context, many biomaterials have been developed for regenerating tissues and are considered revolutionary in TE due to their flexibility, biocompatibility, and biodegradability. One such well-documented biomaterial is bioactive glasses (BGs), known for their osteoconductive and osteogenic potential and their abundant orthopedic and dental clinical applications. However, in the last few decades, the soft tissue regenerative potential of BGs has demonstrated great promise. Therefore, this review comprehensively covers the biological application of BGs in the repair and regeneration of tissues outside the skeleton system. BGs promote neovascularization, which is crucial to encourage host tissue integration with the implanted construct, making them suitable biomaterial scaffolds for TE. Moreover, they heal acute and chronic wounds and also have been reported to restore the injured superficial intestinal mucosa, aiding in gastroduodenal regeneration. In addition, BGs promote regeneration of the tissues with minimal renewal capacity like the heart and lungs. Besides, the peripheral nerve and musculoskeletal reparative properties of BGs are also reported. These results show promising soft tissue regenerative potential of BGs under preclinical settings without posing significant adverse effects. Albeit, there is limited bench-to-bedside clinical translation of elucidative research on BGs as they require rigorous pharmacological evaluations using standardized animal models for assessing biomolecular downstream pathways.

3D-Printed Reinforcement Scaffolds with Targeted Biodegradation Properties for the Tissue Engineering of Articular Cartilage

Achieving regeneration of articular cartilage is challenging due to the low healing capacity of the tissue. Appropriate selection of cell source, hydrogel, and scaffold materials are critical to obtain good integration and long-term stability of implants in native tissues. Specifically, biomechanical stability and in vivo integration can be improved if the rate of degradation of the scaffold material matches the stiffening of the sample by extracellular matrix secretion of the encapsulated cells. To this end, a novel 3D-printed lactide copolymer is presented as a reinforcement scaffold for an enzymatically crosslinked hyaluronic acid hydrogel. In this system, the biodegradable properties of the reinforced scaffold are matched to the matrix deposition of articular chondrocytes embedded in the hydrogel. The lactide reinforcement provides stability to the soft hydrogel in the early stages, allowing the composite to be directly implanted in vivo with no need for a preculture period. Compared to pure cellular hydrogels, maturation and matrix secretion remain unaffected by the reinforced scaffold. Furthermore, excellent biocompatibility and production of glycosaminoglycans and collagens are observed at all timepoints. Finally, in vivo subcutaneous implantation in nude mice shows cartilage-like tissue maturation, indicating the possibility for the use of these composite materials in one-step surgical procedures.

Bacterial cellulose-based composites for biomedical and cosmetic applications: Research progress and existing products

Bacterial cellulose (BC) is a promising unique material for various biomedical and cosmetic applications due to its morphology, mechanical strength, high purity, high water uptake, non-toxicity, chemical controllability, and biocompatibility. Today, extensive investigation is into the manufacturing of BC-based composites with other components such as nanoparticles, synthetic polymers, natural polymers, carbon materials, and biomolecules, which will allow the development of a wide range of biomedical and cosmetic products. Moreover, the addition of different reinforcement substances into BC and the organized arrangement of BC nano-fibers have proven a promising improvement in their properties for biomedical applications. This review paper highlights the progress in synthesizing BC-based composites and their applications in biomedical fields, such as wound healing, drug delivery, tissue engineering, and cancer treatment. It emphasizes high-performance BC-based materials and cosmetic applications. Furthermore, it presents challenges yet to be defeated and future possibilities for BC-based composites for biomedical and cosmetic applications.

Improvement of mechanical properties of zein porous scaffold by quenching/electrospun fiber reinforcement

As a novel bone substitute material, zein-based scaffolds (ZS) should have suitable mechanical properties and porosity. ZS has shown good compressive properties matching cancellous bone, but there is still a demand to improve its mechanical properties, especially tensile and bending properties without adding plasticizers. The present study explored two simple and environment-friendly factors for this purpose: fiber reinforcement and quenching. Addition of electrospun zein fibers enhanced all mechanical properties significantly including compressive, tensile, and bending moduli; compressive and bending strengths of ZS with both higher (70-80%) and lower (50-60%) porosities, no matter whether heating treated or not treated. Especially, all these parameters were further enhanced significantly by addition of heating treated fibers. AFM provided evidence that high temperature modification could significantly alter the micro-elastic properties of zein electrospun fibers, i.e., increased stiffness of fibers. Quenching treatment also enhanced compressive, tensile, and bending strengths significantly. Finally, quenching treated ZS were implanted into critical-sized bone defects (15 mm) of the rabbit model to compare the repair efficacy with a commercial β-tricalcium phosphate product. The results demonstrated that there were no remarkable differences in bone reconstructions between these two materials.

3D Printed Composite Scaffolds in Bone Tissue Engineering: A systematic review

OBJECTIVE

This study aimed to analyze the effect of fabrication factors on both biological and physico-chemical features of 3-dimensional (3D) printed composite scaffolds.

METHOD

Electronic search was done according to the PRISMA guideline in PubMed and Scopus databases limited to English articles published until May 2021.Studies in which composite scaffolds were fabricated through computer-aided design and computer-aided manufacturing (CAD-CAM)-based methods were included.Articles regarding the features of the scaffolds fabricated through indirect techniques were excluded.

RESULTS

Full text of 121 studies were reviewed, and 69 met the inclusion criteria. According to analyzed studies, PCL and HA were the most commonly used polymer and ceramic,respectively. Besides,the Solvent-based technique was the most commonly used composition technique, which enabled preparing blends with high concentrations of ceramic materials. The most common fabrication method used in the included studies was Fused deposition modeling (FDM).The addition of bio-ceramics enhanced the mechanical features and the biological behaviors of the printed scaffolds in a ratio-dependent manner. However,studies that analyzed the effect of ceramic weight ratio showed that scaffolds with the highest ceramic content did not necessarily possess the optimal biological and non-biological features.

CONCLUSION

The biological and physico-chemical behaviors of the scaffold can be affected by pre-printing factors, including utilized materials, composition techniques, and fabrication methods. Fabricating scaffolds with high mineral content as of the natural bone may not provide the optimal condition for bone formation. Therefore, it is recommended that future studies compare the efficiency of different kinds of biomaterials rather than different weight ratios of one type.

Engineering Fiber-Based Nervous Tissue Constructs for Axon Regeneration

Biomaterial-based scaffolds used in nerve conduits including channels for confining regenerating axons and 3-dimensional (3D) gels as substrates for growth have made improvements in models of nerve repair. Many biomaterial strategies, however, continue to fall short of autologous nerve grafts, which remain the current gold standard in repairing severe nerve lesions (<20 mm). Intraluminal nerve conduit fibers have also shown considerable promise in directing regenerating axons in vitro and in vivo and have gained increasing interest for nerve repair. It is unknown, however, how growing axons respond to a fiber when encountered in a 3D environment. In this study, we considered a construct consisting of a compliant collagen hydrogel matrix and a fiber component to assess contact-guided axon growth. We investigated preferential axon outgrowth on synthetic and natural polymer fibers by utilizing small-diameter microfibers of poly-L-lactic acid and type I collagen representing 2 different fiber stiffnesses. We found that axons growing freely in a 3D hydrogel culture preferentially attach, turn and follow fibers with outgrowth rates and distances that far exceed outgrowth in a hydrogel alone. Wet-spun type I collagen from rat tail tendon performed the best, associated with highly aligned and accelerated outgrowth. This study also evaluated the response of dorsal root ganglion neurons from adult rats to provide data more relevant to axon regenerative potential in nerve repair. We found that ECM treatments on fibers enhanced the regeneration of adult axons indicating that both the physical and biochemical presentation of the fibers are essential for enhancing axon guidance and growth.

Carbon fiber/microlattice 3D hybrid architecture as multi-scale scaffold for tissue engineering

Multiscale 3D carbon architectures are of particular interest in tissue engineering applications, as these structures may allow for three-dimensional cell colonization essential for tissue growth. In this work, carbon fiber/microlattice hybrid architectures are introduced as innovative multi-scale scaffolds for tissue engineering. The microlattice provides the design freedom and structural integrity, whereas the fibrous component creates a cellular microenvironment for cell colonization. The hybrid structures are fabricated by carbonization of stereolithographically 3D printed epoxy microlattice architectures which are pre-filled with cotton fibers within the empty space of the architectures. The cotton filling result in less shrinkage of the architecture during carbonization, as the tight confinement of the fibrous material prevents the free-shrinkage of the microlattices. The hybrid architecture exhibits a compressive strength of 156.9±25.6 kPa, which is significantly higher than an empty carbon microlattice architecture. Furthermore, the hybrid architecture exhibits a flexible behavior up to 30% compressive strain, which is also promising towards soft-tissue regeneration. Osteoblast-like murine MC3T3-E1 cells are cultured within the 3D hybrid structures. Results show that the cells are able to not only proliferate on the carbon microlattice elements as well as along the carbon fibers, but also make connections with each other across the inner pores created by the fibers, leading to a three-dimensional cell colonization. These carbon fiber/microlattice hybrid structures are promising for future fabrication of functionally graded scaffolds for tissue repair applications.

A comprehensive review summarizing the recent biomedical applications of functionalized carbon nanofibers

Since the discovery and fabrication of carbon nanofibers (CNFs) over a decade ago, scientists foster to discover novel myriad potential applications for this material in both biomedicine and industry. The unique economic viability, mechanical, electrical, optical, thermal, and structural properties of CNFs led to their rapid emergence. CNFs become an artificial intelligence platform for different uses, including a wide range of biomedical applications. Furthermore, CNFs have exceptionally large surface areas that make them flexible for tailoring and functionalization on demand. This review highlights the recent progress and achievements of CNFs in a wide range of biomedical fields, including cancer therapy, biosensing, tissue engineering, and wound dressing. Besides the synthetic techniques of CNFs, their potential toxicity and limitations, as biomaterials in real clinical settings, will be presented. This review discusses CNF's future investigations in other biomedical fields, including gene delivery and bioimaging and CNFs risk assessment.

Magnetic Nanocomposite Hydrogels for Tissue Engineering: Design Concepts and Remote Actuation Strategies to Control Cell Fate

Most tissues of the human body are characterized by highly anisotropic physical properties and biological organization. Hydrogels have been proposed as scaffolding materials to construct artificial tissues due to their water-rich composition, biocompatibility, and tunable properties. However, unmodified hydrogels are typically composed of randomly oriented polymer networks, resulting in homogeneous structures with isotropic properties different from those observed in biological systems. Magnetic materials have been proposed as potential agents to provide hydrogels with the anisotropy required for their use on tissue engineering. Moreover, the intrinsic properties of magnetic nanoparticles enable their use as magnetomechanic remote actuators to control the behavior of the cells encapsulated within the hydrogels under the application of external magnetic fields. In this review, we combine a detailed summary of the main strategies to prepare magnetic nanoparticles showing controlled properties with an analysis of the different approaches available to their incorporation into hydrogels. The application of magnetically responsive nanocomposite hydrogels in the engineering of different tissues is also reviewed.

Long-Term Evaluation of Allogenic Chondrocyte-Loaded PVA-PCL IPN Scaffolds for Articular Cartilage Repair in Rabbits

OBJECTIVE

This study tested the long-term efficacy of two synthetic scaffolds for osteochondral defects and compare the outcomes with that of an established technique that uses monolayer cultured chondrocytes in a rabbit model.

METHODS

Articular cartilage defect was created in both knees of 18 rabbits and divided into three groups of six in each. The defects in first group receiving cells loaded on Scaffold A (polyvinyl alcohol-polycaprolactone semi-interpenetrating polymer network (Monophasic, PVA-PCL semi-IPN), the second on Scaffold B (biphasic, PVA-PCL incorporated with bioglass as the lower layer), and the third group received chondrocytes alone. One animal from each group was sacrificed at 2 months and the rest at 1 year. O'Driscoll's score measured the quality of cartilage repair.

RESULTS

The histological outcome had good scores (22, 20, and 19) for all three groups at 2 months. At 1-year follow-up, the chondrocyte alone group had the best scores (mean 20.0 ± 1.4), while the group treated by PVA-PCL semi-IPN scaffolds fared better (mean 15 ± 4.2) than the group that received biphasic scaffolds (mean 11.8 ± 5.9). In all three groups, defects treated without cells scored less than the transplant.

CONCLUSION

These results indicate that while these scaffolds with chondrocytes perform well initially, their late outcome is disappointing. We propose that for all scaffold-based tissue repairs, a long-term evaluation should be mandatory. The slow degrading scaffolds need further modifications to improve the milieu for long-term growth of chondrocytes and their hyaline phenotype for the better incorporation of tissue-engineered constructs.

Multifunctional hydrogels for wound healing: Special focus on biomacromolecular based hydrogels

Hydrogels are widely used for wound healing applications due to their similarity to the native extracellular matrix (ECM) and ability to provide a moist environment. However, lack of multifunctionality and low mechanical properties of previously developed hydrogels may limit their ability to support skin tissue regeneration. Incorporating various biomaterials and nanostructures into the hydrogels is an emerging approach to develop multifunctional hydrogels with new functions that are beneficial for wound healing. These multifunctional hydrogels can be fabricated with a wide range of functions and properties, including antibacterial, antioxidant, bioadhesive, and appropriate mechanical properties. Two approaches can be used for development of multifunctional hydrogel-based dressings; taking the advantages of the chemical composition of biomaterials and addition of nanomaterials or nanostructures. A large number of synthetic and natural polymers, bioactive molecules, or nanomaterials have been used to obtain hydrogel-based dressings with multifunctionality for wound healing applications. In the present review paper, advances in the development of multifunctional hydrogel-based dressings for wound healing have been highlighted.

Paramagnetic Functionalization of Biocompatible Scaffolds for Biomedical Applications: A Perspective

The burst of research papers focused on the tissue engineering and regeneration recorded in the last years is justified by the increased skills in the synthesis of nanostructures able to confer peculiar biological and mechanical features to the matrix where they are dispersed. Inorganic, organic and hybrid nanostructures are proposed in the literature depending on the characteristic that has to be tuned and on the effect that has to be induced. In the field of the inorganic nanoparticles used for decorating the bio-scaffolds, the most recent contributions about the paramagnetic and superparamagnetic nanoparticles use was evaluated in the present contribution. The intrinsic properties of the paramagnetic nanoparticles, the possibility to be triggered by the simple application of an external magnetic field, their biocompatibility and the easiness of the synthetic procedures for obtaining them proposed these nanostructures as ideal candidates for positively enhancing the tissue regeneration. Herein, we divided the discussion into two macro-topics: the use of magnetic nanoparticles in scaffolds used for hard tissue engineering for soft tissue regeneration.

Anisotropic Fiber-Reinforced Glycosaminoglycan Hydrogels for Heart Valve Tissue Engineering

This study investigates polymer fiber-reinforced protein-polysaccharide-based hydrogels for heart valve tissue engineering applications. Polycaprolactone and gelatin (3:1) blends were jet-spun to fabricate aligned fibers that possessed fiber diameters in the range found in the native heart valve. These fibers were embedded in methacrylated hydrogels made from gelatin, sodium hyaluronate, and chondroitin sulfate to create fiber-reinforced hydrogel composites (HCs). The fiber-reinforced gelatin glycosaminoglycan (GAG)-based HC possessed interconnected porous structures and porosity higher than fiber-only conditions. These fiber-reinforced HCs exhibited compressive modulus and biaxial mechanical behavior comparable to that of native porcine aortic valves. The fiber-reinforced HCs were able to swell higher and degraded less than the hydrogels. Elution studies revealed that less than 20% of incorporated gelatin methacrylate and GAGs were released over 2 weeks, with a steady-state release after the first day. When cultured with porcine valve interstitial cells (VICs), the fiber-reinforced composites were able to maintain higher cell viability compared with fiber-only samples. Quiescent VICs expressed alpha smooth muscle actin and calponin showing an activated phenotype, along with a few cells expressing the proliferation marker Ki67 and negative expression for RUNX2, an osteogenic marker. Our study demonstrated that compared with the hydrogels and fibers alone, combining both components can yield durable, reinforced composites that mimic heart valve mechanical behavior, while maintaining high cell viability and expressing positive activation as well as proliferation markers.

Design and development of a reinforced tubular electrospun construct for the repair of ruptures of deep flexor tendons

This research aims at developing a more potent solution for deep flexor tendon repair by combining a mechanical and biological approach. A reinforced, multi-layered electrospun tubular construct is developed, composed of three layers: an inner electrospun layer containing an anti-inflammatory component (Naproxen), a middle layer of braided monofilament as reinforcement and an outer electrospun layer containing an anti-adhesion component (hyaluronic acid, HA). In a first step, a novel acrylate endcapped urethane-based precursor (AUP) is developed and characterized by measuring molar mass, acrylate content and thermo-stability. The AUP material is benchmarked against commercially available poly(ε-caprolactone) (PCL). Next, the materials are processed into multi-layered, tubular constructs with bio-active components (Naproxen and HA) using electrospinning. In vitro assays using human fibroblasts show that incorporation of the bio-active components is successful and not-cytotoxic. Moreover, tensile testing using ex vivo sheep tendons prove that the developed multi-layered constructs fulfill the required strength for tendon repair (i.e. 2.79-3.98 MPa), with an ultimate strength of 8.56 ± 1.92 MPa and 8.36 ± 0.57 MPa for PCL and AUP/PCL constructs respectively. In conclusion, by combining a mechanical approach (improved mechanical properties) with the incorporation of bio-active compounds (biological approach), this solution shows its potential for application in deep flexor tendon repair.

Construction and application of textile-based tissue engineering scaffolds: a review

Tissue engineering (TE) provides a practicable method for tissue and organ repair or substitution. As the most important component of TE, a scaffold plays a critical role in providing a growing environment for cell proliferation and functional differentiation as well as good mechanical support. And the restorative effects are greatly dependent upon the nature of the scaffold including the composition, morphology, structure, and mechanical performance. Medical textiles have been widely employed in the clinic for a long time and are being extensively investigated as TE scaffolds. However, unfortunately, the advantages of textile technology cannot be fully exploited in tissue regeneration due to the ignoring of the diversity of fabric structures. Therefore, this review focuses on textile-based scaffolds, emphasizing the significance of the fabric design and the resultant characteristics of cell behavior and extracellular matrix reconstruction. The structure and mechanical behavior of the fabrics constructed by various textile techniques for different tissue repairs are summarized. Furthermore, the prospect of structural design in the TE scaffold preparation was anticipated, including profiled fibers and some unique and complex textile structures. Hopefully, the readers of this review would appreciate the importance of structural design of the scaffold and the usefulness of textile-based TE scaffolds in tissue regeneration.

The Role of Two-Step Blending in the Properties of Starch/Chitin/Polylactic Acid Biodegradable Composites for Biomedical Applications

The current research trend for excellent miscibility in polymer mixing is the use of plasticizers. The use of most plasticizers usually has some negative effects on the mechanical properties of the resulting composite and can sometimes make it toxic, which makes such polymers unsuitable for biomedical applications. This research focuses on the improvement of the miscibility of polymer composites using two-step mixing with a rheomixer and a mix extruder. Polylactic acid (PLA), chitin, and starch were produced after two-step mixing, using a compression molding method with decreasing composition variation (between 8% to 2%) of chitin and increasing starch content. A dynamic mechanical analysis (DMA) was used to study the mechanical behavior of the composite at various temperatures. The tensile strength, yield, elastic modulus, impact, morphology, and compatibility properties were also studied. The DMA results showed a glass transition temperature range of 50 °C to 100 °C for all samples, with a distinct peak value for the loss modulus and factor. The single distinct peak value meant the polymer blend was compatible. The storage and loss modulus increased with an increase in blending, while the loss factor decreased, indicating excellent compatibility and miscibility of the composite components. The mechanical properties of the samples improved compared to neat PLA. Small voids and immiscibility were noticed in the scanning electron microscopy images, and this was corroborated by X-ray diffraction graphs that showed an improvement in the crystalline nature of PLA with starch. Bioabsorption and toxicity tests showed compatibility with the rat system, which is similar to the human system.

In vitro comparison of 3D printed polylactic acid/hydroxyapatite and polylactic acid/bioglass composite scaffolds: Insights into materials for bone regeneration

3D printing of polylactic acid (PLA) and hydroxyapatite (HA) or bioglass (BG) bioceramics composites is the most promising technique for artificial bone construction. However, HA and BG have different chemical composition as well as different bone regeneration inducing mechanisms. Thus, it is important to compare differentiation processes induced by 3D printed PLA + HA and PLA + BG scaffolds in order to evaluate the strongest osteoconductive and osteoinductive properties possessing bioceramics. In this study, we analysed porous PLA + HA (10%) and PLA + BG (10%) composites' effect on rat's dental pulp stem cells fate in vitro. Obtained results indicated, that PLA + BG scaffolds lead to weaker cell adhesion and proliferation than PLA + HA. Nevertheless, osteoinductive and other biofriendly properties were more pronounced by PLA + BG composites. Overall, the results showed a strong advantage of bioceramic BG against HA, thus, 3D printed PLA + BG composite scaffolds could be a perspective component for patient-specific, cheaper and faster artificial bone tissue production.

Recent advances in biomaterials for 3D scaffolds: A review

Considering the advantages and disadvantages of biomaterials used for the production of 3D scaffolds for tissue engineering, new strategies for designing advanced functional biomimetic structures have been reviewed. We offer a comprehensive summary of recent trends in development of single- (metal, ceramics and polymers), composite-type and cell-laden scaffolds that in addition to mechanical support, promote simultaneous tissue growth, and deliver different molecules (growth factors, cytokines, bioactive ions, genes, drugs, antibiotics, etc.) or cells with therapeutic or facilitating regeneration effect. The paper briefly focuses on divers 3D bioprinting constructs and the challenges they face. Based on their application in hard and soft tissue engineering, in vitro and in vivo effects triggered by the structural and biological functionalized biomaterials are underlined. The authors discuss the future outlook for the development of bioactive scaffolds that could pave the way for their successful imposing in clinical therapy.

Functionalization of Carbon Nanomaterials for Biomedical Applications

Over the past decade, carbon nanostructures (CNSs) have been widely used in a variety of biomedical applications. Examples are the use of CNSs for drug and protein delivery or in tools to locally dispense nucleic acids to fight tumor affections. CNSs were successfully utilized in diagnostics and in noninvasive and highly sensitive imaging devices thanks to their optical properties in the near infrared region. However, biomedical applications require a complete biocompatibility to avoid adverse reactions of the immune system and CNSs potentials for biodegradability. Water is one of the main constituents of the living matter. Unfortunately, one of the disadvantages of CNSs is their poor solubility. Surface functionalization of CNSs is commonly utilized as an efficient solution to both tune the surface wettability of CNSs and impart biocompatible properties. Grafting functional groups onto the CNSs surface consists in bonding the desired chemical species on the carbon nanoparticles via wet or dry processes leading to the formation of a stable interaction. This latter may be of different nature as the van Der Waals, the electrostatic or the covalent, the π-π interaction, the hydrogen bond etc. depending on the process and on the functional molecule at play. Grafting is utilized for multiple purposes including bonding mimetic agents such as polyethylene glycol, drug/protein adsorption, attaching nanostructures to increase the CNSs opacity to selected wavelengths or provide magnetic properties. This makes the CNSs a very versatile tool for a broad selection of applications as medicinal biochips, new high-performance platforms for magnetic resonance (MR), photothermal therapy, molecular imaging, tissue engineering, and neuroscience. The scope of this work is to highlight up-to-date using of the functionalized carbon materials such as graphene, carbon fibers, carbon nanotubes, fullerene and nanodiamonds in biomedical applications.

Synthetic polymer scaffolds for soft tissue engineering

Tissue engineering (TE) and regenerative medicine are progressively developed areas due to many novel tissue replacements and implementation strategies. Increasing knowledge involving the fabrication of biomaterials with advanced physicochemical and biological characteristics, successful isolation and preparation of stem cells, incorporation of growth and differentiation factors, and biomimetic environments gives us a unique opportunity to develop various types of scaffolds for TE. The current strategies for soft tissue reconstitution or regeneration highlight the importance of novel regenerative therapies in cases of significant soft tissue loss and in cases of congenital defects, disease, trauma and ageing. Various types of biomaterials and scaffolds have been tested for soft tissue regeneration. The synthetic types of materials have gained great attention due to high versatility, tunability and easy functionalization for better biocompatibility. This article reviews the current materials that are usually the most used for the fabrication of scaffolds for soft TE; in addition, the types of scaffolds together with examples of their applications for the regenerative purposes of soft tissue, as well as their major physicochemical characteristics regarding the increased applicability of these materials in medicine, are reviewed.

Polysaccharide Based Scaffolds for Soft Tissue Engineering Applications

Soft tissue reconstructs require materials that form three-dimensional (3-D) structures supportive to cell proliferation and regenerative processes. Polysaccharides, due to their hydrophilicity, biocompatibility, biodegradability, abundance, and presence of derivatizable functional groups, are distinctive scaffold materials. Superior mechanical properties, physiological signaling, and tunable tissue response have been achieved through chemical modification of polysaccharides. Moreover, an appropriate formulation strategy enables spatial placement of the scaffold to a targeted site. With the advent of newer technologies, these preparations can be tailor-made for responding to alterations in temperature, pH, or other physiological stimuli. In this review, we discuss the developmental and biological aspects of scaffolds prepared from four polysaccharides, viz. alginic acid (ALG), chitosan (CHI), hyaluronic acid (HA), and dextran (DEX). Clinical studies on these scaffolds are also discussed.

3D printing of nanocellulose hydrogel scaffolds with tunable mechanical strength towards wound healing application

We present for the first time approaches to 3D-printing of nanocellulose hydrogel scaffolds based on double crosslinking, first by in situ Ca²⁺ crosslinking and post-printing by chemical crosslinking with 1,4-butanediol diglycidyl ether (BDDE). Scaffolds were successfully printed from 1% nanocellulose hydrogels, with their mechanical strength being tunable in the range of 3 to 8 kPa. Cell tests suggest that the 3D-printed and BDDE-crosslinked nanocellulose hydrogel scaffolds supported fibroblast cells' proliferation, which was improving with increasing rigidity. These 3D-printed scaffolds render nanocellulose a new member of the family of promising support structures for crucial cellular processes during wound healing, regeneration and tissue repair.

Fabrication and characterization of collagen-based injectable and self-crosslinkable hydrogels for cell encapsulation

Injectable and self-crosslinkable hydrogels have drawn much attention for their potential application as cell delivery carriers to deliver cells to the injury site of arbitrary shape. In this study, injectable and self-crosslinkable hydrogels were designed and fabricated based on collagen type I (Col I) and activated chondroitin sulfate (CS-sNHS) by physical and chemical crosslinking without the addition of any catalysts. The physical properties of hydrogels, including mechanical properties, swelling and degradation properties, were investigated. The results demonstrated that the physical properties of hydrogels, especially the stiffness of hydrogels, were readily tuned by varying the degree of substitution (DS) of CS-sNHS without changing the concentration of collagen-based precursor. Chondrocytes were encapsulated into hydrogels to investigate the effects of hydrogels on the survival, proliferation and extracellular matrix (ECM) secretion of cells by FDA/PI staining, CCK-8 test and histological staining. The results suggested that all of these hydrogels supported the survival and ECM secretion of chondrocytes, while there was more ECM secretion around chondrocytes encapsulated in hydrogel Col I/CS-sNHS56% in which the DS of CS-sNHS was 56%. When the neutral precursor solution for hydrogel of Col I or Col I/CS-sNHS56% was subcutaneously injected into SD rats, hydrogels both displayed acceptable biocompatibility in vivo. These results imply that these injectable and self-crosslinkable hydrogels are suitable candidates for applications in the fields of cell delivery and tissue engineering.