The Host Response in Tissue Engineering: Crosstalk Between Immune cells and Cell-laden Scaffolds

Navigating the Immunological Crossroads: Mesenchymal Stem/Stromal Cells as Architects of Inflammatory Harmony in Tissue-Engineered Constructs

In the dynamic landscape of tissue engineering, the integration of tissue-engineered constructs (TECs) faces a dual challenge-initiating beneficial inflammation for regeneration while avoiding the perils of prolonged immune activation. As TECs encounter the immediate reaction of the immune system upon implantation, the unique immunomodulatory properties of mesenchymal stem/stromal cells (MSCs) emerge as key navigators. Harnessing the paracrine effects of MSCs, researchers aim to craft a localized microenvironment that not only enhances TEC integration but also holds therapeutic promise for inflammatory-driven pathologies. This review unravels the latest advancements, applications, obstacles, and future prospects surrounding the strategic alliance between MSCs and TECs, shedding light on the immunological symphony that guides the course of regenerative medicine.

Immunomodulatory Strategies for Cartilage Regeneration in Osteoarthritis

Osteoarthritis (OA) is the most prevalent musculoskeletal disorder and a leading cause of disability globally. Although many efforts have been made to treat this condition, current tissue engineering (TE) and regenerative medicine strategies fail to address the inflammatory tissue environment that leads to the rapid progression of the disease and prevents cartilage tissue formation. First, this review addresses in detail the current anti-inflammatory therapies for OA with a special emphasis on pharmacological approaches, gene therapy, and mesenchymal stromal cell (MSC) intra-articular administration, and discusses the reasons behind the limited clinical success of these approaches at enabling cartilage regeneration. Then, we analyze the state-of-the-art TE strategies and how they can be improved by incorporating immunomodulatory capabilities such as the optimization of biomaterial composition, porosity and geometry, and the loading of anti-inflammatory molecules within an engineered structure. Finally, the review discusses the future directions for the new generation of TE strategies for OA treatment, specifically focusing on the spatiotemporal modulation of anti-inflammatory agent presentation to allow for tailored patient-specific therapies. Impact statement Osteoarthritis (OA) is a prevalent and debilitating musculoskeletal disorder affecting millions worldwide. Despite significant advancements in regenerative medicine and tissue engineering (TE), mitigating inflammation while simultaneously promoting cartilage tissue regeneration in OA remains elusive. In this review article, we discuss current anti-inflammatory therapies and explore their potential synergy with cutting-edge cartilage TE strategies, with a special focus on novel spatiotemporal and patient-specific anti-inflammatory strategies.

Efficient Decellularization of the Full-Thickness Rat-Derived Abdominal Wall to Produce Acellular Biologic Scaffolds for Tissue Reconstruction: Promising Evidence Acquired from In Vitro Results

BACKGROUND

Functional restoration of abdominal wall defects represents one of the fundamental challenges of reconstructive surgery. Synthetic grafts or crosslinked animal-derived biological grafts are characterized by significant adverse reactions, which are mostly observed after their implantation. The aim of this study was to evaluate the efficacy of the decellularization protocol to produce a completely acellular full-thickness abdominal wall scaffold.

METHODS

Full-thickness abdominal wall samples were harvested from Wistar rats and submitted to a three-cycle decellularization process. Histological, biochemical, and DNA quantification analyses were applied to evaluate the effect of the decellularization protocol. Mechanical testing and immunogenicity assessment were also performed.

RESULTS

Histological, biochemical, and DNA analysis results showed efficient decellularization of the abdominal wall samples after the third cycle. Decellularized abdominal wall scaffolds were characterized by good biochemical and mechanical properties.

CONCLUSION

The data presented herein confirm the effective production of a rat-derived full-thickness abdominal wall scaffold. Expanding this approach will allow the exploitation of the capacity of the proposed decellularization protocol in producing acellular abdominal wall scaffolds from larger animal models or human cadaveric donors. In this way, the utility of biological scaffolds with preserved in vivo remodeling properties may be one step closer to its application in clinical studies.

Resorbable Biomaterials Used for 3D Scaffolds in Tissue Engineering: A Review

This article provides a thorough overview of the available resorbable biomaterials appropriate for producing replacements for damaged tissues. In addition, their various properties and application possibilities are discussed as well. Biomaterials are fundamental components in tissue engineering (TE) of scaffolds and play a critical role. They need to exhibit biocompatibility, bioactivity, biodegradability, and non-toxicity, to ensure their ability to function effectively with an appropriate host response. With ongoing research and advancements in biomaterials for medical implants, the objective of this review is to explore recently developed implantable scaffold materials for various tissues. The categorization of biomaterials in this paper includes fossil-based materials (e.g., PCL, PVA, PU, PEG, and PPF), natural or bio-based materials (e.g., HA, PLA, PHB, PHBV, chitosan, fibrin, collagen, starch, and hydrogels), and hybrid biomaterials (e.g., PCL/PLA, PCL/PEG, PLA/PEG, PLA/PHB PCL/collagen, PCL/chitosan, PCL/starch, and PLA/bioceramics). The application of these biomaterials in both hard and soft TE is considered, with a particular focus on their physicochemical, mechanical, and biological properties. Furthermore, the interactions between scaffolds and the host immune system in the context of scaffold-driven tissue regeneration are discussed. Additionally, the article briefly mentions the concept of in situ TE, which leverages the self-renewal capacities of affected tissues and highlights the crucial role played by biopolymer-based scaffolds in this strategy.

3D Printed Hierarchical Porous Poly(ε-caprolactone) Scaffolds from Pickering High Internal Phase Emulsion Templating

In the realm of biomaterials, particularly bone tissue engineering, there has been a great increase in interest in scaffolds with hierarchical porosity and customizable multifunctionality. Recently, the three-dimensional (3D) printing of biopolymer-based inks (solutions or emulsions) has gained high popularity for fabricating tissue engineering scaffolds, which optimally satisfies the desired properties and performances. Herein, therefore, we explore the fabrication of 3D printed hierarchical porous scaffolds of poly(ε-caprolactone) (PCL) using the water-in-oil (w/o) Pickering PCL high internal phase emulsions (HIPEs) as the ink in 3D printer. The Pickering PCL HIPEs stabilized using hydrophobically modified nanoclay comprised of aqueous poly(vinyl alcohol) (PVA) as the dispersed phase. Rheological measurements suggested the shear thinning behavior of Pickering HIPEs having a dispersed droplet diameter of 3-25 μm. The pore morphology resembling the natural extracellular matrix and the mechanical properties of scaffolds were customized by tuning the emulsion composition and 3D printing parameters. In vitro biomineralization and drug release studies proved the scaffolds' potential in developing the apatite-rich bioactive interphase and controlled drug delivery, respectively. During in vitro osteoblast (MG63) growth experiments for up to 7 days, good adhesion and proliferation on PCL scaffolds confirmed their cytocompatibility, assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) analysis. This study suggests that the assembly of HIPE templates and 3D printing is a promising approach to creating hierarchical porous scaffolds potentially suitable for bone tissue engineering and can be stretched to other biopolymers as well.

Immune microenvironment: novel perspectives on bone regeneration disorder in osteoradionecrosis of the jaws

Osteoradionecrosis of the jaws (ORNJ) is a severe complication that occurs after radiotherapy of head and neck malignancies. Clinically, conservative treatments and surgeries for ORNJ exhibited certain therapeutic effects, whereas the regenerative disorder of the post-radiation jaw remains a pending problem to be solved. In recent years, the recognition of the role of the immune microenvironment has led to a shift from an osteoblasts (OBs) or bone marrow mesenchymal stromal cells (BMSCs)-centered view of bone regeneration to the concept of a complicated microecosystem that supports bone regeneration. Current advances in osteoimmunology have uncovered novel targets within the immune microenvironment to help improve various regeneration therapies, notably therapies potentiating the interaction between BMSCs and immune cells. However, these researches lack a thorough understanding of the immune microenvironment and the interaction network of immune cells in the course of bone regeneration, especially for the post-operative defect of ORNJ. This review summarized the composition of the immune microenvironment during bone regeneration, how the immune microenvironment interacts with the skeletal system, and discussed existing and potential strategies aimed at targeting cellular and molecular immune microenvironment components.

Implanted Tissue-Engineered Vascular Graft Cell Isolation with Single-Cell RNA Sequencing Analysis

The advent of single-cell RNA sequencing (scRNA-Seq) has brought with it the ability to gain greater insights into the cellular composition of tissues and heterogeneity in gene expression within specific cell types. For tissue-engineered blood vessels, this is particularly impactful to better understand how neotissue forms and remodels into tissue resembling a native vessel. A notable challenge, however, is the ability to separate cells from synthetic biomaterials to generate high-quality single-cell suspensions to interrogate the cellular composition of our tissue-engineered vascular grafts (TEVGs) during active remodeling in situ. We present here a simple, commercially available approach to separate cells within our TEVG from the residual scaffold for downstream use in a scRNA-Seq workflow. Utilizing this method, we identified the cell populations comprising explanted TEVGs and compared these with results from immunohistochemical analysis. The process began with explanted TEVGs undergoing traditional mechanical and enzymatic dissociation to separate cells from scaffold and extracellular matrix proteins. Magnetically labeled antibodies targeting murine origin cells were incubated with enzymatic digests of TEVGs containing cells and scaffold debris in suspension allowing for separation by utilizing a magnetic separator column. Single-cell suspensions were processed through 10 × Genomics and data were analyzed utilizing R to generate cell clusters. Expression data provided new insights into a diverse composition of phenotypically unique subclusters within the fibroblast, macrophage, smooth muscle cell, and endothelial cell populations contributing to the early neotissue remodeling stages of TEVGs. These populations were correlated qualitatively and quantitatively with immunohistochemistry highlighting for the first time the potential of scRNA-Seq to provide exquisite detail into the host cellular response to an implanted TEVG. These results additionally demonstrate magnetic cell isolation is an effective method for generating high-quality cell suspensions for scRNA-Seq. While this method was utilized for our group's TEVGs, it has broader applications to other implantable materials that use biodegradable synthetic materials as part of scaffold composition. Impact statement Single-cell RNA sequencing is an evolving technology with the ability to provide detailed information on the cellular composition of remodeling biomaterials in vivo. This present work details an effective approach for separating nondegraded biomaterials from cells for downstream RNA-sequencing analysis. We applied this method to implanted tissue-engineered vascular grafts and for the first time describe the cellular composition of the remodeling graft at a single-cell gene expression level. While this method was effective in our scaffold, it has broad applicability to other implanted biomaterials that necessitate separation of cell from residual scaffold materials for single-cell RNA sequencing.

[Research of diclofenac sodium-loaded gelatin scaffold with anti-inflammatory activity for promoting in vivo cartilage regeneration]

Objective

To develop a diclofenac sodium-loaded gelatin scaffold with anti-inflammatory activity and provide a new avenue for alleviating the inflammatory response and enhancing cartilage regeneration in vivo.

Methods

Diclofenac sodium was homogeneously mixed with gelatin to prepare a diclofenac sodium-loaded porous gelatin scaffold by freeze-drying method as the experimental group, and a pristine porous gelatin scaffold was served as a control group. The general morphology of the scaffold was observed, the pore size of the scaffold was measured by scanning electron microscopy, the porosity of the scaffold was calculated by drainage method, the loading of diclofenac sodium into the gelatin scaffold was detected by fourier transform infrared spectrometer and X-ray diffraction examinations, and the release kinetics of diclofenac sodium from gelatin scaffold was tested using an in vitro release assay. The two scaffolds were co-cultured with lipopolysaccharide-predisposed RAW264.7 in vitro, and the expressions of interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α) were detected by reverse transcription polymerase chain reaction (RT-PCR), enzyme-linked immuno sorbent assay, and Western blot, to detect the in vitro anti-inflammatory effect of the drug-loaded scaffold. Thereafter, the second generation chondrocytes of New Zealand white rabbits were inoculated on the two groups of scaffolds for in vitro culture, and the cytocompatibility of the scaffold was tested by live/dead staining and cell counting kit 8 assay, the feasibility of in vitro cartilage regeneration of the scaffold was evaluated via gross observation, HE staining, Safranin-O staining, and immunohistochemical collagen type Ⅱ staining, as well as biochemical quantitative analyses. Finally, the two groups of chondrocyte-scaffolds were implanted subcutaneously into New Zealand white rabbits, and after 4 weeks, the general observation, HE staining, safranin O staining, immunohistochemical collagen type Ⅱ staining, and biochemical quantitative analyses were performed to verify the cartilage regeneration in vivo, and the expression of inflammation-related genes CD3 and CD68 was detected by RT-PCR to comprehensively evaluate the anti-inflammatory performance of the scaffolds in vivo.

Results

The two scaffolds exhibited similar gross, microporous structure, pore size, and porosity, showing no significant difference (P>0.05). Diclofenac sodium was successfully loaded into gelatin scaffold. Data from in vitro anti-inflammatory assay suggested that diclofenac sodium-loaded gelatin scaffold showed alleviated gene and protein expressions of IL-1β and TNF-α when compared with gelatin scaffold (P<0.05). The evaluation of cartilage regeneration in vitro showed that the number of living cells increased significantly with the extension of culture time, and there was no significant difference between the two groups at each time point (P>0.05). White cartilage-like tissue was regenerated from the scaffolds in both groups, histological observation showed typical cartilage lacuna structure and specific cartilage extracellular matrix secretion. There was no significant difference in the content of cartilage-specific glycosaminoglycan (GAG) and collagen type Ⅱ between the two groups (P>0.05). In vivo experiments showed that the samples in the experimental group had porcelain white cartilage like morphology, histologic staining showed obvious cartilage lacuna structure and cartilage specific extracellular matrix, the contents of GAG and collagen type Ⅱ were significantly higher than those in the control group, and the protein and mRNA expressions of CD3 and CD68 were significantly lower than those in the control group, with significant differences (P<0.05).

Conclusion

The diclofenac sodium-loaded gelatin scaffold presents suitable pore size, porosity, and cytocompatibility, as well as exhibited satisfactory anti-inflammatory ability, providing a reliable scheme for alleviating the inflammatory reaction of regenerated cartilage tissue after in vivo implantation and promoting cartilage regeneration in vivo.

VEGF-Loaded Heparinised Gelatine-Hydroxyapatite-Tricalcium Phosphate Scaffold Accelerates Bone Regeneration via Enhancing Osteogenesis-Angiogenesis Coupling

Background: Bone tissue defect, one of the common orthopaedicdiseases, is traumatizing and affects patient’s lifestyle. Although autologous and xenograft bone transplantations are performed in bone tissue engineering, clinical development of bone transplantation is limited because ofvarious factors, such as varying degrees of immune rejection, lack of bone sources, and secondary damage to bone harvesting.

Methods: We synthesised a heparinised gelatine-hydroxyapatite-tricalcium phosphate (HG-HA-TCP) scaffold loaded with sustained-release vascular endothelial growth factor (VEGF) analysed their structure, mechanical properties, and biocompatibility. Additionally, the effects of HG-HA-TCP (VEGF) scaffolds on osteogenic differentiation and vascularisation of stem cells from human exfoliated deciduous teeth (SHED) in vitro and bone regeneration in vivo were investigated.

Results: HG-HA-TCP scaffold possessed good pore structure, mechanical properties, and biocompatibility. HG-HA-TCP scaffold loaded with VEGF could effectively promote SHED proliferation, migration, and adhesion. Moreover, HG-HA-TCP (VEGF) scaffold increased the expression of osteogenesis- and angiogenesis-related genes and promoted osteogenic differentiation and vascularisation in cells. In vivo results demonstrated that VEGF-loaded HG-HA-TCP scaffold improved new bone regeneration and enhanced bone mineral density, revealed byhistological, micro-CT and histochemical straining analyses. Osteogenic and angiogenic abilities of the three biological scaffolds wereranked as follows: HG-HA-TCP (VEGF) > G-HA-TCP (VEGF) > G-HA-TCP.

Conclusion: HG-HA-TCP (VEGF) scaffold with good biocompatibility could create an encouraging osteogenic microenvironment that could accelerate vessel formation and osteogenesis, providing an effective scaffold for bone tissue engineering and developing new clinical treatment strategies for bone tissue defects.

Resident Macrophages and Their Potential in Cardiac Tissue Engineering

Many facets of tissue engineered models aim at understanding cellular mechanisms to recapitulate in vivo behavior, to study and mimic diseases for drug interventions, and to provide a better understanding toward improving regenerative medicine. Recent and rapid advances in stem cell biology, material science and engineering, have made the generation of complex engineered tissues much more attainable. One such tissue, human myocardium, is extremely intricate, with a number of different cell types. Recent studies have unraveled cardiac resident macrophages as a critical mediator for normal cardiac function. Macrophages within the heart exert phagocytosis and efferocytosis, facilitate electrical conduction, promote regeneration, and remove cardiac exophers to maintain homeostasis. These findings underpin the rationale of introducing macrophages to engineered heart tissue (EHT), to more aptly capitulate in vivo physiology. Despite the lack of studies using cardiac macrophages in vitro, there is enough evidence to accept that they will be key to making EHTs more physiologically relevant. In this review, we explore the rationale and feasibility of using macrophages as an additional cell source in engineered cardiac tissues. Impact statement Macrophages play a critical role in cardiac homeostasis and in disease. Over the past decade, we have come to understand the many vital roles played by cardiac resident macrophages in the heart, including immunosurveillance, regeneration, electrical conduction, and elimination of exophers. There is a need to improve our understanding of the resident macrophage population in the heart in vitro, to better recapitulate the myocardium through tissue engineered models. However, obtaining them in vitro remains a challenge. Here, we discuss the importance of cardiac resident macrophages and potential ways to obtain cardiac resident macrophages in vitro. Finally, we critically discuss their potential in realizing impactful in vitro models of cardiac tissue and their impact in the field.

Biomaterials as a Vital Frontier for Stem Cell-Based Tissue Regeneration

Biomaterials and tissue regeneration represent two fields of intense research and rapid advancement. Their combination allowed the utilization of the different characteristics of biomaterials to enhance the expansion of stem cells or their differentiation into various lineages. Furthermore, the use of biomaterials in tissue regeneration would help in the creation of larger tissue constructs that can allow for significant clinical application. Several studies investigated the role of one or more biomaterial on stem cell characteristics or their differentiation potential into a certain target. In order to achieve real advancement in the field of stem cell-based tissue regeneration, a careful analysis of the currently published information is critically needed. This review describes the fundamental description of biomaterials as well as their classification according to their source, bioactivity and different biological effects. The effect of different biomaterials on stem cell expansion and differentiation into the primarily studied lineages was further discussed. In conclusion, biomaterials should be considered as an essential component of stem cell differentiation strategies. An intense investigation is still required. Establishing a consortium of stem cell biologists and biomaterial developers would help in a systematic development of this field.

Protein Based Biomaterials for Therapeutic and Diagnostic Applications

Proteins are some of the most versatile and studied macromolecules with extensive biomedical applications. The natural and biological origin of proteins offer such materials several advantages over their synthetic counterparts, such as innate bioactivity, recognition by cells and reduced immunogenic potential. Furthermore, proteins can be easily functionalized by altering their primary amino acid sequence and can often be further self-assembled into higher order structures either spontaneously or under specific environmental conditions. This review will feature the recent advances in protein-based biomaterials in the delivery of therapeutic cargo such as small molecules, genetic material, proteins, and cells. First, we will discuss the ways in which secondary structural motifs, the building blocks of more complex proteins, have unique properties that enable them to be useful for therapeutic delivery. Next, supramolecular assemblies, such as fibers, nanoparticles, and hydrogels, made from these building blocks that are engineered to behave in a cohesive manner, are discussed. Finally, we will cover additional modifications to protein materials that impart environmental responsiveness to materials. This includes the emerging field of protein molecular robots, and relatedly, protein-based theranostic materials that combine therapeutic potential with modern imaging modalities, including near-infrared fluorescence spectroscopy (NIRF), single-photo emission computed tomography/computed tomography (SPECT/CT), positron emission tomography (PET), magnetic resonance imaging (MRI), and ultrasound/photoacoustic imaging (US/PAI).

Macrophage M1/M2 polarization dynamically adapts to changes in microenvironment and modulates alveolar bone remodeling after dental implantation

As one of the first arriving immune cells after dental implantation, Mϕs own the abilities to polarize into to a spectrum of diverse phenotypes, from "classically activated" M1 Mϕs to "alternatively activated" M2 Mϕs. Herein, it was hypothesized that Mϕ phenotypes dynamically adapt after dental implantation, and the changes ensue a cascade of coordinated interplay with the bone-forming osteoblast and the bone-resorbing osteoclast. Results showed that the remodelling process after dental implantation was similar with the standard response to tissue injury (exampled by tooth extraction models), only with the delay of bone regeneration phases. Additionally, Mϕ activation in both groups underwent a transition from M1 Mϕs dominated to M2-type dominated stage, but the persistence of M1 Mϕs occurred in rat model of dental implantation. Further research in vitro showed that M1 Mϕs are involved in osteoclast activities via secreting the highest levels of TNF-α and IL-1β, as well as being the potential precursor of osteoclasts. Besides, they also recruited BMSCs by secreting the highest levels of chemoattractants, CCL2 and VEGF. M2 Mϕs accelerated osteogenesis in the subsequent stage via their capability to secrete osteogenesis-related proteins, BMP-2 and TGF-β1. However, the osteogenic differentiation of BMSCs was inhibited when cultured in a high concentration of conditioned media from each Mϕ phenotype, meaning that the immune strategies should be controlled within the proper ranges. These results suggest that coordinated efforts by both M1 and M2 Mϕs for bone remodelling, which may highlight an optimization strategy for tissue engineering implants.

Engineering Musculoskeletal Grafts for Multi-Tissue Unit Repair: Lessons From Developmental Biology and Wound Healing

In the musculoskeletal system, bone, tendon, and skeletal muscle integrate and act coordinately as a single multi-tissue unit to facilitate body movement. The development, integration, and maturation of these essential components and their response to injury are vital for conferring efficient locomotion. The highly integrated nature of these components is evident under disease conditions, where rotator cuff tears at the bone-tendon interface have been reported to be associated with distal pathological alterations such as skeletal muscle degeneration and bone loss. To successfully treat musculoskeletal injuries and diseases, it is important to gain deep understanding of the development, integration and maturation of these musculoskeletal tissues along with their interfaces as well as the impact of inflammation on musculoskeletal healing and graft integration. This review highlights the current knowledge of developmental biology and wound healing in the bone-tendon-muscle multi-tissue unit and perspectives of what can be learnt from these biological and pathological processes within the context of musculoskeletal tissue engineering and regenerative medicine. Integrating these knowledge and perspectives can serve as guiding principles to inform the development and engineering of musculoskeletal grafts and other tissue engineering strategies to address challenging musculoskeletal injuries and diseases.

Chemokine-Induced PBMC and Subsequent MSC Migration Toward Decellularized Heart Valve Tissue

PURPOSE

Enhancing the recellularization of a decellularized heart valve in situ may lead to an improved or ideal heart valve replacement. A promising approach is leveraging the immune response for inflammation-mediated recellularization. However, this mechanism has not been previously demonstrated in vitro.

METHODS

This study investigated loading the chemokine MCP-1 into decellularized porcine heart valve tissue and measured the migration of human peripheral blood mononuclear cells (PBMCs) and mesenchymal stem cells (MSCs) toward the chemokine loaded valve tissue.

RESULTS

The results of this study demonstrate that MCP-1-loaded tissues increase PBMC migration compared to non-loaded tissues. Additionally, we demonstrate MCP-1-loaded tissues that have recruited PBMCs lead to increased migration of MSCs compared to decellularized tissue alone.

CONCLUSION

The results of this study provide evidence for the inflammation-mediated recellularization mechanism. Furthermore, the results support the use of such an approach for enhancing the recellularization of a decellularized heart valve.

Mesenchymal stem cell-inspired microgel scaffolds to control macrophage polarization

There is a desire in regenerative medicine to create biofunctional materials that can control and direct cell function in a precise manner. One particular stem cell of interest, human mesenchymal stem cells (hMSCs), can function as regulators of the immunogenic response and aid in tissue regeneration and wound repair. Here, a porous hydrogel scaffold assembled from microgel subunits was used to recapitulate part of this immunomodulatory behavior. The scaffolds were used to culture a macrophage cell line, while cytokines were delivered exogenously to polarize the macrophages to either a pro-inflammatory (M1) or alternatively activated (M2a) phenotypes. Using a cytokine array, interleukin 10 (IL-10) was identified as one key anti-inflammatory factor secreted by hMSCs in pro-inflammatory conditions; it was elevated (125 ± 25 pg/ml) in pro-inflammatory conditions compared to standard medium (6 ± 10 pg/ml). The ability of hMSC laden scaffolds to reverse the M1 phenotype was then examined, even in the presence of exogenous pro-inflammatory cytokines. Co-culture of M1 and M2 macrophages with hMSCs reduced the secretion of TNFα, a pro-inflammatory cytokine even in the presence of pro-inflammatory stimulatory factors. Next, IL-10 was supplemented in the medium or tethered directly to the microgel subunits; both methods limited the secretion of pro-inflammatory cytokines of encapsulated macrophages even in pro-inflammatory conditions. Cumulatively, these results reveal the potential of biofunctional microgel-based scaffolds as acellular therapies to present anti-inflammatory cytokines and control the immunogenic cascade.

The Future of Neuroscience: Flexible and Wireless Implantable Neural Electronics

Neurological diseases are a prevalent cause of global mortality and are of growing concern when considering an ageing global population. Traditional treatments are accompanied by serious side effects including repeated treatment sessions, invasive surgeries, or infections. For example, in the case of deep brain stimulation, large, stiff, and battery powered neural probes recruit thousands of neurons with each pulse, and can invoke a vigorous immune response. This paper presents challenges in engineering and neuroscience in developing miniaturized and biointegrated alternatives, in the form of microelectrode probes. Progress in design and topology of neural implants has shifted the goal post toward highly specific recording and stimulation, targeting small groups of neurons and reducing the foreign body response with biomimetic design principles. Implantable device design recommendations, fabrication techniques, and clinical evaluation of the impact flexible, integrated probes will have on the treatment of neurological disorders are provided in this report. The choice of biocompatible material dictates fabrication techniques as novel methods reduce the complexity of manufacture. Wireless power, the final hurdle to truly implantable neural interfaces, is discussed. These aspects are the driving force behind continued research: significant breakthroughs in any one of these areas will revolutionize the treatment of neurological disorders.

VE-cadherin-based matrix promoting the self-reconstruction of pro-vascularization microenvironments and endothelial differentiation of human mesenchymal stem cells

Regulating the secretion and endothelial differentiation of human mesenchymal stem cells (hMSCs) plays an important role in the vascularization in tissue engineering and regenerative medicine. In this study, a recombinant cadherin fusion protein consisting of a human vascular endothelial-cadherin extracellular domain and immunoglobulin IgG Fc region (hVE-cad-Fc) was developed as a bioartificial matrix for modulating hMSCs. The hVE-cad-Fc matrix significantly enhanced the secretion of angiogenic factors, activated the VE-cadherin-VEGFR2/FAK-AKT/PI3K signaling pathway in hMSCs, and promoted the endothelial differentiation of hMSCs even without extra VEGF. Furthermore, the hVE-cad-Fc matrix was applied for the surface modification of a poly (lactic-co-glycolic acid) (PLGA) porous scaffold, which significantly improved the hemocompatibility and vascularization of the PLGA scaffold in vivo. These results revealed that the hVE-cad-Fc matrix should be a superior bioartificial ECM for remodeling the pro-vascularization extracellular microenvironment by regulating the secretion of hMSCs, and showed great potential for the vascularization in tissue engineering.

Three-dimensional endothelial cell incorporation within bioactive nanofibrous scaffolds through concurrent emulsion electrospinning and coaxial cell electrospraying

Nanofibrous scaffolds hold great promise in tissue engineering owing to their extracellular matrix (ECM)-mimicking architectures. Electrospinning, with its ease for producing nanofibrous scaffolds, has therefore been widely employed for various tissue engineering applications. However, electrospun nanofibrous scaffolds have faced the inherent challenge of three-dimensional (3D) cell distribution due to the small sizes of interconnected pores in these scaffolds when conventional approach of scaffold fabrication with subsequent cell seeding is adopted, which severely limits their applications in repairing/regenerating human body tissues with thick and vascularized structures. In this study, we demonstrate a method to directly place living endothelial cells within bioactive nanofibrous scaffolds in 3D through concurrent emulsion electrospinning and coaxial cell electrospraying. Using this concurrent manufacturing method, endothelial cells are encapsulated in hydrogel microspheres and deposited along with vascular endothelial growth factor (VEGF)-containing nanofibers in the scaffold fabrication process, resulting in nanofibrous scaffolds with 3D embedded cell-encapsulated microspheres. After selective disruption of the hydrogel microspheres, the encapsulated endothelial cells are released, yielding bioactive nanofibrous scaffolds with tissue-like 3D cell-incorporated nanofibrous structures. It is shown that cell viability is well preserved (>98%) during the concurrent manufacturing process and that a deep cell distribution (~100 μm) through the scaffold thickness has been achieved. With combined structural and biochemical cues via the 3D cell-incorporated architectures, endothelial cells can freely stretch, display enhanced intercellular connections, and maintain the phenotype in the bioactive nanofibrous scaffolds. Our investigations offer a promising platform technology for creating bioactive nanofibrous scaffolds with 3D cell incorporation and for overcoming inherent problems of electrospun nanofibrous scaffolds, which should open new avenues for biomanufacturing tissue-mimicking constructs with vascularized structures and complex anatomy. STATEMENT OF SIGNIFICANCE: Electrospun nanofibrous scaffolds face challenges in three-dimensional (3D) cell incorporation and vascularization. Enhancing cell penetration via enlarged interconnected pores is a common strategy to address that. However, there are conflicts between cell penetration and structural integrity for scaffolds formed using such strategy, as deep cell penetration, if possible, can only achieve in highly loose architectures. In this investigation, we demonstrate a concurrent emulsion electrospinning and coaxial cell electrospraying technique, realizing 3D endothelial cell incorporation in electrospun nanofibrous scaffolds independent of cell penetration. Our technology appropriately addresses the conflict between deep 3D cell incorporation and structural integrity. In the scaffolds, the 3D incorporated endothelial cells show well-preserved viability, phenotype and functions, implying improved vascularization potential.

A 3D Printed Composite Scaffold Loaded with Clodronate to Regenerate Osteoporotic Bone: In Vitro Characterization

Additive manufacturing (AM) is changing our current approach to the clinical treatment of bone diseases, providing new opportunities to fabricate customized, complex 3D structures with bioactive materials. Among several AM techniques, the BioCell Printing is an advanced, integrated system for material manufacture, sterilization, direct cell seeding and growth, which allows for the production of high-resolution micro-architectures. This work proposes the use of the BioCell Printing to fabricate polymer-based scaffolds reinforced with ceramics and loaded with bisphosphonates for the treatment of osteoporotic bone fractures. In particular, biodegradable poly(ε-caprolactone) was blended with hydroxyapatite particles and clodronate, a bisphosphonate with known efficacy against several bone diseases. The scaffolds' morphology was investigated by means of Scanning Electron Microscopy (SEM) and micro-Computed Tomography (micro-CT) while Energy Dispersive X-ray Spectroscopy (EDX) and X-ray Photoelectron Spectroscopy (XPS) revealed the scaffolds' elemental composition. A thermal characterization of the composites was accomplished by Thermogravimetric analyses (TGA). The mechanical performance of printed scaffolds was investigated under static compression and compared against that of native human bone. The designed 3D scaffolds promoted the attachment and proliferation of human MSCs. In addition, the presence of clodronate supported cell differentiation, as demonstrated by the normalized alkaline phosphatase activity. The obtained results show that the BioCell Printing can easily be employed to generate 3D constructs with pre-defined internal/external shapes capable of acting as a temporary physical template for regeneration of cancellous bone tissues.

Advances on Bone Substitutes through 3D Bioprinting

Reconstruction of bony defects is challenging when conventional grafting methods are used because of their intrinsic limitations (biological cost and/or biological properties). Bone regeneration techniques are rapidly evolving since the introduction of three-dimensional (3D) bioprinting. Bone tissue engineering is a branch of regenerative medicine that aims to find new solutions to treat bone defects, which can be repaired by 3D printed living tissues. Its aim is to overcome the limitations of conventional treatment options by improving osteoinduction and osteoconduction. Several techniques of bone bioprinting have been developed: inkjet, extrusion, and light-based 3D printers are nowadays available. Bioinks, i.e., the printing materials, also presented an evolution over the years. It seems that these new technologies might be extremely promising for bone regeneration. The purpose of the present review is to give a comprehensive summary of the past, the present, and future developments of bone bioprinting and bioinks, focusing the attention on crucial aspects of bone bioprinting such as selecting cell sources and attaining a viable vascularization within the newly printed bone. The main bioprinters currently available on the market and their characteristics have been taken into consideration, as well.

Improved Immunoregulation of Ultra-Low-Dose Silver Nanoparticle-Loaded TiO2 Nanotubes via M2 Macrophage Polarization by Regulating GLUT1 and Autophagy

Introduction

The bone regeneration of endosseous implanted biomaterials is often impaired by the host immune response, especially macrophage-related inflammation which plays an important role in the bone healing process. Thus, it is a promising strategy to design an osteo-immunomodulatory biomaterial to take advantage of the macrophage-related immune response and improve the osseointegration performance of the implant.

Methods

In this study, we developed an antibacterial silver nanoparticle-loaded TiO₂ nanotubes (Ag@TiO₂-NTs) using an electrochemical anodization method to make the surface modification and investigated the influences of Ag@TiO₂-NTs on the macrophage polarization, osteo-immune microenvironment as well as its potential molecular mechanisms in vitro and in vivo.

Results

The results showed that Ag@TiO₂-NTs with controlled releasing of ultra-low-dose Ag⁺ ions had the excellent ability to induce the macrophage polarization towards the M2 phenotype and create a suitable osteo-immune microenvironment in vitro, via inhibiting PI3K/Akt, suppressing the downstream effector GLUT1, and activating autophagy. Moreover, Ag@TiO₂-NTs surface could improve bone formation, suppress inflammation, and promote osteo-immune microenvironment compared to the TiO₂-NTs and polished Ti surfaces in vivo. These findings suggested that Ag@TiO₂-NTs with controlled releasing of ultra-low-dose Ag⁺ ions could not only inhibit the inflammation process but also promote the bone healing by inducing healing-associated M2 polarization.

Discussion

Using this surface modification strategy to modulate the macrophage-related immune response, rather than prevent the host response, maybe a promising strategy for implant surgeries in the future.

Recent advances toward understanding the role of transplanted stem cells in tissue-engineered regeneration of musculoskeletal tissues

Stem cell-based tissue engineering is poised to revolutionize the treatment of musculoskeletal injuries. However, in order to overcome scientific, practical, and regulatory obstacles and optimize therapeutic strategies, it is essential to better understand the mechanisms underlying the pro-regenerative effects of stem cells. There has been an attempted paradigm shift within the last decade to think of transplanted stem cells as "medicinal" therapies that orchestrate healing on the basis of their secretome and immunomodulatory profiles rather than acting as bona fide stem cells that proliferate, differentiate, and directly produce matrix to form de novo tissues. Yet the majority of current bone and skeletal muscle tissue engineering strategies are still premised on a direct contribution of stem cells as building blocks to tissue regeneration. Our review of the recent literature finds that researchers continue to focus on the quantification of de novo bone/skeletal muscle tissue following treatment and few studies aim to address this mechanistic conundrum directly. The dichotomy of thought is reflected in the diversity of new advances ranging from in situ three-dimensional bioprinting to a focus on exosomes and extracellular vesicles. However, recent findings elucidating the role of the immune system in tissue regeneration combined with novel imaging platform technologies will have a profound impact on our future understanding of how stem cells promote healing following biomaterial-mediated delivery to defect sites.

Inflammation via myeloid differentiation primary response gene 88 signaling mediates the fibrotic response to implantable synthetic poly(ethylene glycol) hydrogels

Synthetic hydrogels, such as poly(ethylene glycol) (PEG), are promising for a range of in vivo applications. However, like all non-biological biomaterials, synthetic hydrogels including PEG elicit a foreign body response (FBR). The FBR is thought to be initiated by adsorbed protein that is recognized by and subsequently activates inflammatory cells, notably macrophages, and culminates with fibrotic encapsulation. However, the molecular mechanisms that drive the FBR are not well understood. Toll-like receptors (TLRs) are key receptors that recognize pathogens, but also recognize altered host proteins that display damage-associated molecular patterns (DAMPs). Thus TLRs may play a role in the FBR. Here, we investigated myeloid differentiation primary response gene 88 (MyD88), a signaling adaptor protein that mediates inflammatory cytokine production induced by most TLRs. An in vitro model was used consisting of macrophages cultured on the surface of synthetic hydrogels, specifically PEG, with pre-adsorbed serum proteins. Our in vitro findings demonstrate that MyD88-dependent signaling is the predominant inflammatory pathway in macrophage activation to synthetic hydrogels. When stimulated with TLR agonists to mimic additional DAMPs present in vivo, MyD88-dependent signaling was also the predominant pathway in macrophage activation. An in vivo model of PEG hydrogels implanted subcutaneously in wild-type and MyD88^-/- mice also demonstrated that MyD88 is the key contributor to the recruitment of inflammatory cells and formation of the fibrous capsule surrounding the implanted hydrogel. Taken together, findings from this study identify MyD88-mediated inflammation as being a critical pathway involved not only in the inflammatory response, but in formation of the fibrous capsule to PEG hydrogels. STATEMENT OF SIGNIFICANCE: Synthetic hydrogels are promising for in vivo applications but, like all non-biological biomaterials, synthetic hydrogels elicit a foreign body response (FBR). The molecular mechanisms that drive the FBR are not well understood. This work identifies the myeloid differentiation primary response gene 88 (MyD88) as a central mediator to macrophage activation in response to a poly(ethylene glycol) hydrogel with pre-adsorbed proteins in vitro. Moreover, MyD88 was also central to the recruitment of inflammatory cells, which included neutrophils, monocytes, and macrophages, to implanted PEG hydrogels and to fibrous encapsulation. These findings demonstrate that MyD88-mediated inflammation is responsible in part for the formation of the fibrous capsule of the FBR.