Bioscaffolds embedded with regulatory modules for cell growth and tissue formation: A review

Silk-Based 3D Porous Scaffolds for Tissue Engineering

Silk fibroin, extracted from the silk of the Bombyx mori silkworm, stands out as a biomaterial due to its nontoxic nature, excellent biocompatibility, and adjustable biodegradability. Porous scaffolds, a type of biomaterial, are crucial for creating an optimal microenvironment that supports cell adhesion and proliferation, thereby playing an essential role in tissue remodeling and repair. Therefore, this review focuses on 3D porous silk fibroin-based scaffolds, first summarizing their preparation methods and then detailing their regenerative effects on bone, cartilage, tendon, vascular, neural, skin, hepatic, and tracheal epithelial tissue engineering in recent years.

Optimization of Cobalt-Chromium (Co-Cr) Scaffolds for Bone Tissue Engineering in Endocrine, Metabolic and Immune Disorders

Approximately 50% of the adult global population is projected to suffer from some form of metabolic disease by 2050, including metabolic syndrome and diabetes mellitus. At the same time, this trend indicates a potential increase in the number of patients who will be in need of implant-supported reconstructions of specific bone regions subjected to inflammatory states. Moreover, physiological conditions associated with dysmetabolic subjects have been suggested to contribute to the severity of bone loss after bone implant insertion. However, there is a perspective evidence strengthening the hypothesis that custom-fabricated bioengineered scaffolds may produce favorable bone healing effects in case of altered endocrine or metabolic conditions. This perspective review aims to share a comprehensive knowledge of the mechanisms implicated in bone resorption and remodelling processes, which have driven researchers to develop metallic implants as the cobalt-chromium (Co-Cr) bioscaffolds, presenting optimized geometries that interact in an effective way with the osteogenetic precursor cells, especially in the cases of perturbed endocrine or metabolic conditions.

The effect of GelMA/alginate interpenetrating polymeric network hydrogel on the performance of porous zirconia matrix for bone regeneration applications

Bone tissue is a natural composite, exhibiting complicated structures and unique mechanical/biological properties. With an attempt of mimicking the bone tissue, a novel inorganic-organic composite scaffolds (ZrO2-GM/SA) was designed and prepared via the vacuum infiltration method and the single/double cross-linking strategy by blending GelMA/alginate (GelMA/SA) interpenetrating polymeric network (IPN) into the porous zirconia (ZrO2) scaffold. The structure, morphology, compressive strength, surface/interface properties, and biocompatibility of the ZrO2-GM/SA composite scaffolds were characterized to evaluate the performance of the composite scaffolds. Results showed that compared to ZrO2 bare scaffolds with well-defined open pores, the composite scaffolds prepared by double cross-linking of GelMA hydrogel and sodium alginate (SA) presented a continuous, tunable and honeycomb-like microstructure. Meanwhile, GelMA/SA showed favorable and controllable water-uptake capacity, swelling property and degradability. After the introduction of IPN components, the mechanical strength of composite scaffolds was further improved. The compressive modulus of composite scaffolds was significantly higher than the bare ZrO2 scaffolds. In addition, ZrO2-GM/SA composite scaffolds had highly biocompatibility and displayed a potent proliferation and osteogenesis of MC3T3-E1 pre-osteoblasts compared to bare ZrO2 scaffolds and ZrO2-GelMA composite scaffolds. At the same time, ZrO2-10GM/1SA composite scaffold regenerated significantly greater bone than other groups in vivo. This study demonstrated that the proposed ZrO2-GM/SA composite scaffolds had great research and application potential in bone tissue engineering.

Viscous Microcapsules as Microbioreactors to Study Mesenchymal Stem/Stromal Cells Osteolineage Commitment

It is essential to design a multifunctional well-controlled platform to transfer mechanical cues to the cells in different magnitudes. This study introduces a platform, a miniaturized bioreactor, which enables to study the effect of shear stress in microsized compartmentalized structures. In this system, the well-established cell encapsulation system of liquefied capsules (LCs) is used as microbioreactors in which the encapsulated cells are exposed to variable core viscosities to experience different mechanical forces under a 3D dynamic culture. The LC technology is joined with electrospraying to produce such microbioreactors at high rates, thus allowing the application of microcapsules for high-throughput screening. Using this platform for osteogenic differentiation as an example, shows that microbioreactors with higher core viscosity which produce higher shear stress lead to significantly higher osteogenic characteristics. Moreover, in this system the forces experienced by cells in each LC are simulated by computational modeling. The maximum wall shear stress applied to the cells inside the bioreactor with low, and high core viscosity environment is estimated to be 297 and 1367 mPa, respectively, for the experimental setup employed. This work outlines the potential of LC microbioreactors as a reliable in vitro customizable platform with a wide range of applications.

Nanoindentation Response of 3D Printed PEGDA Hydrogels in a Hydrated Environment

Hydrogels are commonly used materials in tissue engineering and organ-on-chip devices. This study investigated the nanomechanical properties of monolithic and multilayered poly(ethylene glycol) diacrylate (PEGDA) hydrogels manufactured using bulk polymerization and layer-by-layer projection lithography processes, respectively. An increase in the number of layers (or reduction in layer thickness) from 1 to 8 and further to 60 results in a reduction in the elastic modulus from 5.53 to 1.69 and further to 0.67 MPa, respectively. It was found that a decrease in the number of layers induces a lower creep index (CIT) in three-dimensional (3D) printed PEGDA hydrogels. This reduction is attributed to mesoscale imperfections that appear as pockets of voids at the interfaces of the multilayered hydrogels attributed to localized regions of unreacted prepolymers, resulting in variations in defect density in the samples examined. An increase in the degree of cross-linking introduced by a higher dosage of ultraviolet (UV) exposure leads to a higher elastic modulus. This implies that the elastic modulus and creep behavior of hydrogels are governed and influenced by the degree of cross-linking and defect density of the layers and interfaces. These findings can guide an optimal manufacturing pathway to obtain the desirable nanomechanical properties in 3D printed PEGDA hydrogels, critical for the performance of living cells and tissues, which can be engineered through control of the fabrication parameters.

Fabrication and detection of a novel hybrid conductive scaffold based on alginate/gelatin/carboxylated carbon nanotubes (Alg/Gel/mMWCNTs) for neural tissue engineering

Carbon nanotubes (CNTs), as kinds of conductive carbon nanomaterials, were widely applied in neural tissue engineering due to their excellent electrical conductivity and good biocompatibility. In this study, the carboxyl-modified multi-walled carbon nanotubes (mMWCNTs) were introduced into sodium alginate/gelatin (Alg/Gel) scaffolds to optimize the function of the hybrid scaffolds. The Alg/Gel/mMWCNTs conductive scaffolds with mMWCNTs content of 1%, 3%, and 5% were prepared by freeze-drying, respectively. Following this, the physicochemical properties and biocompatibility of the hybrid scaffolds at different magnetic field intensities were evaluated. The conductive scaffolds were characterized by Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). In general, the mMWCNTs addition improved the hydrophilic, electrical conductivity and mechanical properties of the composite scaffold, and PC12 cells showed a trend of gradual increase over culture time. Particularly, the Alg/Gel-1%C scaffold exhibited the best cell proliferation behavior. Briefly, the surface contact angle decreased from 74 ± 1° to 60 ± 3°, the electrical conductivity and compressive modulus increased to 1.32 × 10^-3 ± 2.1 × 10^-4 S/cm and 1.40 ± 0.076 Mpa, the G1 phase from 55.67 ± 1.86% to 59.77 ± 0.94% and the G2 phase from 10.32 ± 0.35% to 13.93 ± 1.26%，respectively. In the SEM images, PC12 cells were well-shaped and densely distributed. Therefore, the Alg/Gel/mMWCNTs conductive scaffold has potential as a tissue engineering scaffold in nerve regeneration.

Urinary Bladder Patch Made with Decellularized Vein Scaffold Seeded with Adipose-Derived Mesenchymal Stem Cells: Model in Rabbits

BACKGROUND

To evaluate tissue regeneration of the urinary bladder after the implantation of a decellularized vein sown with autologous adipose-derived mesenchymal stem cells (ASC) on luminal surfaces.

METHODS

New Zealand rabbits (n = 10) were distributed in two groups: Group Bioscaffold alone (G1)-decellularized vena cava (1 cm2) was implanted, and Group Bioscaffold plus ACSs (G2)-decellularized vena cava (1 cm2) containing ASCs were implanted. ASCs were expanded, characterized, and maintained for one week in culture with a decellularized vein scaffold. The implants were performed under general anesthesia using a continuous suture pattern. Afterward, 21 d (day) specimens were collected and analyzed by hematoxylin and eosin (HE) histology and scanning electron microscopy (SEM).

RESULTS

The integrity of the urinary bladder was maintained in both groups. A superior regenerative process was observed in the G2 group, compared to the G1 group. We observed a greater urothelial epithelialization and maturity of the mucosa and submucosa fibroblasts. Furthermore, SEM demonstrated a notable amount of urothelial villus in the G2 group.

CONCLUSION

Decellularized vena cava scaffolds were able to maintain the integrity of the urinary bladder in the proposed model. In addition, ASCs accelerated the regenerative process development, observed primarily by the new urothelial epithelization and the maturity of mucosa and submucosa fibroblasts.

Recent advances in 3D-printed polylactide and polycaprolactone-based biomaterials for tissue engineering applications

The three-dimensional printing (3DP) also known as the additive manufacturing (AM), a novel and futuristic technology that facilitates the printing of multiscale, biomimetic, intricate cytoarchitecture, function-structure hierarchy, multi-cellular tissues in the complicated micro-environment, patient-specific scaffolds, and medical devices. There is an increasing demand for developing 3D-printed products that can be utilized for organ transplantations due to the organ shortage. Nowadays, the 3DP has gained considerable interest in the tissue engineering (TE) field. Polylactide (PLA) and polycaprolactone (PCL) are exemplary biomaterials with excellent physicochemical properties and biocompatibility, which have drawn notable attraction in tissue regeneration. Herein, the recent advancements in the PLA and PCL biodegradable polymer-based composites as well as their reinforcement with hydrogels and bio-ceramics scaffolds manufactured through 3DP are systematically summarized and the applications of bone, cardiac, neural, vascularized and skin tissue regeneration are thoroughly elucidated. The interaction between implanted biodegradable polymers, in-vivo and in-vitro testing models for possible evaluation of degradation and biological properties are also illustrated. The final section of this review incorporates the current challenges and future opportunities in the 3DP of PCL- and PLA-based composites that will prove helpful for biomedical engineers to fulfill the demands of the clinical field.

Matrix stiffness regulates the immunomodulatory effects of mesenchymal stem cells on macrophages via AP1/TSG-6 signaling pathways

It is well-recognized that the matrix stiffness as an important stem cell niche can mediate stem cell behavior such as attachment, proliferation and differentiation, but how matrix stiffness affects the immunomodulatory efficacy of stem cells has been little explored, which, however, is of significant importance in determining the outcomes of stem cell-based therapies and engineered tissue mimics. We herein studied the immunomodulatory efficacy of mesenchymal stem cells (MSCs) in response to matrix stiffness by the evaluation of macrophage polarization in vitro and inflammatory response in vivo by subcutaneous implantation of MSC-laden hydrogels. Remarkably, we found that soft matrix enabled MSCs to produce significantly higher levels of immunomodulatory factors compared to stiff matrix, and induced the presence of more anti-inflammatory macrophages in vitro and attenuated macrophages-mediated inflammatory response in vivo. More importantly, we revealed stiffness-mediated immunoregulatory effect of MSCs was mainly attributed to tumor necrosis factor-α-stimulated protein 6 (TSG-6), which was mechanosensitively regulated by the MAPK and Hippo signaling pathway and downstream AP1 complex, and which in turn exerted an effect on macrophages through CD44 receptor to inhibit NF-κB pathway. To conclude, our results for the first time identify TSG-6 as the key factor in regulating immunomodulatory efficacy of MSCs in mechanical response, and can be potentially utilized to empower stem cell-based therapy and tissue engineering strategy in regenerative medicine. STATEMENT OF SIGNIFICANCE: Matrix stiffness as an important stem cell niche can mediate stem cell behavior such as attachment and differentiation, but how matrix stiffness affects the immunomodulatory efficacy of stem cells has been little explored, which, however, is of significant importance in determining the outcomes of stem cell-based therapies and engineered tissue mimics. Our results for the first time identify TSG-6 as the key factor in regulating the immunomodulatory efficacy of MSCs in mechanical response, which was regulated by the MAPK and Hippo signaling pathways and downstream AP1 complex, and which in turn exerted an effect on macrophages through CD44 receptor to inhibit NF-κB pathway, and can be potentially utilized to empower stem cell-based therapy and tissue engineering strategy in regenerative medicine.

Application of microneedle patches for drug delivery; doorstep to novel therapies

In the past decade, microneedle-based drug delivery systems showed promising approaches to become suitable and alternative for hypodermic injections and can control agent delivery without side effects compared to conventional approaches. Despite these advantages, the procedure of microfabrication is facing some difficulties. For instance, drug loading method, stability of drugs, and retention time are subjects of debate. Besides, the application of novel refining fabrication methods, types of materials, and instruments are other issues that need further attention. Herein, we tried to summarize recent achievements in controllable drug delivery systems (microneedle patches) in vitro and in vivo settings. In addition, we discussed the influence of delivered drugs on the cellular mechanism and immunization molecular signaling pathways through the intradermal delivery route. Understanding the putative efficiency of microneedle patches in human medicine can help us develop and design sophisticated therapeutic modalities.

Co-culture of Schwann cells and endothelial cells for synergistically regulating dorsal root ganglion behavior on chitosan-based anisotropic topology for peripheral nerve regeneration

Background

Anisotropic topologies are known to regulate cell-oriented growth and induce cell differentiation, which is conducive to accelerating nerve regeneration, while co-culture of endothelial cells (ECs) and Schwann cells (SCs) can significantly promote the axon growth of dorsal root ganglion (DRG). However, the synergistic regulation of EC and SC co-culture of DRG behavior on anisotropic topologies is still rarely reported. The study aims to investigate the effect of anisotropic topology co-cultured with Schwann cells and endothelial cells on dorsal root ganglion behavior for promoting peripheral nerve regeneration.

Methods

Chitosan/artemisia sphaerocephala (CS/AS) scaffolds with anisotropic topology were first prepared using micro-molding technology, and then the surface was modified with dopamine to facilitate cell adhesion and growth. The physical and chemical properties of the scaffolds were characterized through morphology, wettability, surface roughness and component variation. SCs and ECs were co-cultured with DRG cells on anisotropic topology scaffolds to evaluate the axon growth behavior.

Results

Dopamine-modified topological CS/AS scaffolds had good hydrophilicity and provided an appropriate environment for cell growth. Cellular immunofluorescence showed that in contrast to DRG growth alone, co-culture of SCs and ECs could not only promote the growth of DRG axons, but also offered a stronger guidance for orientation growth of neurons, which could effectively prevent axons from tangling and knotting, and thus may significantly inhibit neurofibroma formation. Moreover, the co-culture of SCs and ECs could promote the release of nerve growth factor and vascular endothelial growth factor, and up-regulate genes relevant to cell proliferation, myelination and skeletal development via the PI3K-Akt, MAPK and cytokine and receptor chemokine pathways.

Conclusions

The co-culture of SCs and ECs significantly improved the growth behavior of DRG on anisotropic topological scaffolds, which may provide an important basis for the development of nerve grafts in peripheral nerve regeneration.

Milestones and current achievements in development of multifunctional bioscaffolds for medical application

Tissue engineering (TE) is a rapidly growing interdisciplinary field, which aims to restore or improve lost tissue function. Despite that TE was introduced more than 20 years ago, innovative and more sophisticated trends and technologies point to new challenges and development. Current challenges involve the demand for multifunctional bioscaffolds which can stimulate tissue regrowth by biochemical curves, biomimetic patterns, active agents and proper cell types. For those purposes especially promising are carefully chosen primary cells or stem cells due to its high proliferative and differentiation potential. This review summarized a variety of recently reported advanced bioscaffolds which present new functions by combining polymers, nanomaterials, bioactive agents and cells depending on its desired application. In particular necessity of study biomaterial-cell interactions with in vitro cell culture models, and studies using animals with in vivo systems were discuss to permit the analysis of full material biocompatibility. Although these bioscaffolds have shown a significant therapeutic effect in nervous, cardiovascular and muscle, tissue engineering, there are still many remaining unsolved challenges for scaffolds improvement.