Preconditioning Human Adipose-Derived Stromal Cells on Decellularized Adipose Tissue Scaffolds Within a Perfusion Bioreactor Modulates Cell Phenotype and Promotes a Pro-regenerative Host Response

Human tendon stem/progenitor cell-derived extracellular vesicle production promoted by dynamic culture

Tendon injuries significantly impact quality of life, prompting the exploration of innovative solutions beyond conventional surgery. Extracellular Vesicles (EVs) have emerged as a promising strategy to enhance tendon regeneration. In this study, human Tendon Stem/Progenitor Cells (TSPCs) were isolated from surgical biopsies and cultured in a Growth-Differentiation Factor-5-supplemented medium to promote tenogenic differentiation under static and dynamic conditions using a custom-made perfusion bioreactor. Once at 80% confluence, cells were transitioned to a serum-free medium for conditioned media collection. Ultracentrifugation revealed the presence of vesicles with a 106 particles/mL concentration and sub-200nm diameter size. Dynamic culture yielded a 3-fold increase in EV protein content compared to static culture, as confirmed by Western-blot analysis. Differences in surface marker expression were also shown by flow cytometric analysis. Data suggest that we efficiently developed a protocol for extracting EVs from human TSPCs, particularly under dynamic conditions. This approach enhances EV protein content, offering potential therapeutic benefits for tendon regeneration. However, further research is needed to fully understand the role of EVs in tendon regeneration.

A Simple, Cost-Effective Microfluidic Device Using a 3D Cross-Flow T-Junction for Producing Decellularized Extracellular Matrix-Derived Microcarriers

Cell therapies using human mesenchymal stromal cells (MSCs) are promising for a wide variety of clinical applications. However, broad-scale clinical translation is limited by conventional culture methods for MSC expansion within 2D tissue-culture flasks. MSC expansion on ECM-derived microcarriers within stirred bioreactor systems offers a promising approach to support MSC growth. Previously, our team established methods for fabricating ECM-derived microcarriers from a variety of decellularized tissue sources using electrospraying techniques. However, these microcarriers are relatively large and have a broad size distribution, which may limit their utility. Smaller and more uniform microcarriers may be favorable for MSC growth within bioreactors and have greater potential to serve as a minimally invasive injectable cell delivery platform. To address these limitations, the current project focused on the development of a new microfluidic-based approach enabling both uniform and small microcarrier production. Using a novel, modified 3D T-junction design, we successfully generated microcarriers using human decellularized adipose tissue (DAT) as the ECM source. Our new cost-effective device produced microbeads that were small and monodisperse, at a range of flow rate combinations and with high production rates. Photo-crosslinking using rose bengal allowed for the generation of microcarriers that retained their shape and could withstand rehydration, with a mean diameter of 196 ± 47 μm. Following methods optimization and microcarrier characterization, in vitro studies confirmed that the new microcarriers supported human adipose-derived stromal cell (hASC) attachment and growth, as well as ECM production, across 14 days within spinner flask bioreactors. Overall, this study demonstrates the feasibility of using our novel, cost-effective, and reusable microfluidics device to generate cell-supportive microcarriers comprised exclusively of ECM that show promise as an MSC expansion platform.

T-PRP-DAT Gel: A Novel Material Promotes Adipose Tissue Regeneration

BACKGROUND

Decellularized adipose tissue (DAT) has emerged as a promising tissue-specific regenerative platform for soft tissue augmentation and reconstruction. Hydrogels are a widely used DAT scaffold format for their injectability and porous structure. While unstable structure and poor vascularization limit the adipose tissue regeneration of DAT gels, this yields significant clinical necessity for solutions to this problem.

METHODS

Based on collagen-fibrin interpenetrating, we developed an injectable thermosensitive DAT/PRP interpenetrating polymer network (t-DP gel/t-DPI) with the composition of DAT and temperature-controlled platelet-rich plasma (t-PRP). The same volume of t-DP gel and DAT gel were transplanted in a mouse model, and graft volume, weight, adipose tissue regeneration rate, and vascularization were compared.

RESULTS

The t-DPI showed reinforced stability for the interpenetrating polymer network (IPN) of collagen-fibrin and sustained release of growth factors from the t-PRP, resulting in improved graft volume, weight, adipose tissue regeneration, and vascularization.

CONCLUSIONS

Compared with traditional DAT gel, t-DP gel promotes adipose tissue regeneration by promoting angiogenesis and stability, and t-DP gel has great potential for future applications in the field of plastic surgery for its simple preparation and regeneration ability.

Manipulating immune activity of macrophages: a materials and mechanics perspective

Macrophage immune cells exist on a plastic spectrum of phenotypes governed by their physical and biochemical environment. Controlling macrophage function to facilitate immunological regeneration or fighting pathology has emerged as a therapeutic possibility. The rate-limiting step in translating macrophage immunomodulation therapies has been the absence of fundamental knowledge of how physics and biochemistry in the macrophage microenvironment converge to inform phenotype. In this review we explore recent trends in bioengineered model systems that integrate physical and biochemical variables applied to macrophage mechanosensing and plasticity. We focus on how tuning of mechanical forces and biomaterial composition orchestrate macrophage function in physiological and pathological contexts. Ultimately, a broader understanding of stimuli-responsiveness in macrophages leads to informed design for future modulatory therapies.

Stimuli-Mediated Macrophage Switching, Unraveling the Dynamics at the Nanoplatforms-Macrophage Interface

Macrophages play an essential role in immunotherapy and tissue regeneration owing to their remarkable plasticity and diverse functions. Recent bioengineering developments have focused on using external physical stimuli such as electric and magnetic fields, temperature, and compressive stress, among others, on micro/nanostructures to induce macrophage polarization, thereby increasing their therapeutic potential. However, it is difficult to find a concise review of the interaction between physical stimuli, advanced micro/nanostructures, and macrophage polarization. This review examines the present research on physical stimuli-induced macrophage polarization on micro/nanoplatforms, emphasizing the synergistic role of fabricated structure and stimulation for advanced immunotherapy and tissue regeneration. A concise overview of the research advancements investigating the impact of physical stimuli, including electric fields, magnetic fields, compressive forces, fluid shear stress, photothermal stimuli, and multiple stimulations on the polarization of macrophages within complex engineered structures, is provided. The prospective implications of these strategies in regenerative medicine and immunotherapeutic approaches are highlighted. This review will aid in creating stimuli-responsive platforms for immunomodulation and tissue regeneration.

Combining Allograft Adipose and Fascia Matrix as an Off-the-Shelf Scaffold for Adipose Tissue Engineering Stimulates Angiogenic Responses and Activates a Proregenerative Macrophage Profile in a Rodent Model

OBJECTIVE

Bioscaffolds for treating soft tissue defects have limitations. As a bioscaffold, allograft adipose matrix (AAM) is a promising approach to treat soft tissue defects. Previously, we revealed that combining superficial adipose fascia matrix with AAM, components of the hypodermis layer of adipose tissue, improved volume retention, adipogenesis, and angiogenesis in rats 8 weeks after it was implanted compared with AAM alone. Here, we modified the fascia matrix and AAM preparation, examined the tissue over 18 weeks, and conducted a deeper molecular investigation. We hypothesized that the combined matrices created a better scaffold by triggering angiogenesis and proregenerative signals.

METHODS

Human AAM and fascia matrix were implanted (4 [1 mL] implants/animal) into the dorsum of male Fischer rats (6-8 weeks old; ~140 g) randomly as follows: AAM, fascia, 75/25 (AAM/fascia), 50/50, and 50/50 + hyaluronic acid (HA; to improve extrudability) (n = 4/group/time point). After 72 hours, as well as 1, 3, 6, 9, 12, and 18 weeks, graft retention was assessed by a gas pycnometer. Adipogenesis (HE), angiogenesis (CD31), and macrophage infiltration (CD80 and CD163) were evaluated histologically at all time points. The adipose area and M1/M2 macrophage ratio were determined using ImageJ. RNA sequencing (RNA-seq) and bioinformatics were conducted to evaluate pathway enrichments.

RESULTS

By 18 weeks, the adipose area was 2365% greater for 50/50 HA (281.6 ± 21.6) than AAM (11.4 ± 0.9) (P < 0.001). The M1/M2 macrophage ratio was significantly lower for 50/50 HA (0.8 ± 0.1) than AAM (0.9 ± 0.1) at 6 weeks (16%; P < 0.05). This inversely correlated with adipose area (r = -0.6; P > 0.05). The RNA-seq data revealed that upregulated adipogenesis, angiogenesis, and macrophage-induced tissue regeneration genes were temporally different between the groups.

CONCLUSIONS

Combining the fascia matrix with AAM creates a bioscaffold with an improved retention volume that supports M2 macrophage-mediated angiogenesis and adipogenesis. This bioscaffold is worthy of further investigation.

Recent Advances in Decellularized Matrix-Derived Materials for Bioink and 3D Bioprinting

As an emerging 3D printing technology, 3D bioprinting has shown great potential in tissue engineering and regenerative medicine. Decellularized extracellular matrices (dECM) have recently made significant research strides and have been used to create unique tissue-specific bioink that can mimic biomimetic microenvironments. Combining dECMs with 3D bioprinting may provide a new strategy to prepare biomimetic hydrogels for bioinks and hold the potential to construct tissue analogs in vitro, similar to native tissues. Currently, the dECM has been proven to be one of the fastest growing bioactive printing materials and plays an essential role in cell-based 3D bioprinting. This review introduces the methods of preparing and identifying dECMs and the characteristic requirements of bioink for use in 3D bioprinting. The most recent advances in dECM-derived bioactive printing materials are then thoroughly reviewed by examining their application in the bioprinting of different tissues, such as bone, cartilage, muscle, the heart, the nervous system, and other tissues. Finally, the potential of bioactive printing materials generated from dECM is discussed.

Angiogenesis and Re-endothelialization in decellularized scaffolds: Recent advances and current challenges in tissue engineering

Decellularization of tissues and organs has recently become a promising approach in tissue engineering and regenerative medicine to circumvent the challenges of organ donation and complications of transplantations. However, one main obstacle to reaching this goal is acellular vasculature angiogenesis and endothelialization. Achieving an intact and functional vascular structure as a vital pathway for supplying oxygen and nutrients remains the decisive challenge in the decellularization/re-endothelialization procedure. In order to better understand and overcome this issue, complete and appropriate knowledge of endothelialization and its determining variables is required. Decellularization methods and their effectiveness, biological and mechanical characteristics of acellular scaffolds, artificial and biological bioreactors, and their possible applications, extracellular matrix surface modification, and different types of utilized cells are factors affecting endothelialization consequences. This review focuses on the characteristics of endothelialization and how to optimize them, as well as discussing recent developments in the process of re-endothelialization.

Myogenic commitment of human stem cells by myoblasts Co-culture: a static vs. a dynamic approach

An in-vitro model of human bone marrow mesenchymal stem cells (hBM-MSCs) myogenic commitment by synergic effect of a differentiation media coupled with human primary skeletal myoblasts (hSkMs) co-culture was developed adopting both conventional static co-seeding and perfused culture systems. Static co-seeding provided a notable outcome in terms of gene expression with a significant increase of Desmin (141-fold) and Myosin heavy chain II (MYH2, 32-fold) at day 21, clearly detected also by semi-quantitative immunofluorescence. Under perfusion conditions, myogenic induction ability of hSkMs on hBM-MSCs was exerted by paracrine effect with an excellent gene overexpression and immunofluorescence detection of MYH2 protein; furthermore, due to the dynamic cell culture in separate wells, western blot data were acquired confirming a successful cell commitment at day 14. A significant increase of anti-inflammatory cytokine gene expression, including IL-10 and IL-4 (15-fold and 11-fold, respectively) at day 14, with respect to the pro-inflammatory cytokines IL-12A (7-fold at day 21) and IL-1β (1.4-fold at day 7) was also detected during dynamic culture, confirming the immunomodulatory activity of hBM-MSCs along with commitment events. The present study opens interesting perspectives on the use of dynamic culture based on perfusion as a versatile tool to study myogenic events and paracrine cross-talk compared to the simple co-seeding static culture.

Construction of adipose tissue using a silica expander capsule and cell sheet-assembled of decellularized adipose tissue

Delayed neovascularization and unstable adipose formation are major confounding factors in adipose tissue engineering. A system using decellularized adipose tissue (DAT), adipose-derived stem cells (ADSCs), and human umbilical vein endothelial cells (HUVECs) has been preliminarily studied, but it requires optimization, as adipogenic and angiogenic capabilities for maintaining a stable construct shape are limited. The current study aimed to address these limitations. Our initial modification involved the addition of exogenous chemokine (C-C motif) ligand 2 (CCL2), which resulted in enhanced adipogenesis and angiogenesis. However, further improvement was required due to delayed blood recanalization. To further optimize the system, a vascularized fibrous capsule derived from an implanted silica expander was utilized as a second modification. We hypothesized this would function as both a microbioreactor to fix the seed cells and exogenous CCL2 locally and as a vascular bed to promote neovascularization. Compared with that of the CCL2 loaded ADSC-HUVECs cell sheet assembled DAT system, adding the silica expander capsule resulted in significantly increased construct stability, new vessel intensity, a greater number of Oil Red O-positive lipid droplets, more enhanced tissue remodeling, and upregulated peroxisome proliferator-activated receptor gamma (PPARγ) & leptin expression. Thus, these two modifications helped optimize the currently available ADSC-HUVEC cell sheet assembled DAT system, providing an adipose tissue construction strategy with enhanced adipogenesis and angiogenesis to reconstruct soft tissue defects. Moreover, close-to-normal leptin expression provided the engineered adipose tissue with a glucometabolic function, in addition to remodeling capabilities. STATEMENT OF SIGNIFICANCE: Delayed neovascularization and unstable adipose formation are the two major problems in tissue engineering adipose. Here, we introduced an adipose tissue engineering construction strategy using a silica expander capsule along with hADSCs-HUVECs cell sheet-assembled DAT in a CCL2-rich microenvironment. Our data suggested that CCL2 could improve angiogenesis and adipogenesis in vitro and in vivo. The addition of tissue expander capsule could further improve the stability of construction and fabricated adipose tissue with increased new vessel intensity, greater numbers of Oil Red O-positive lipid droplets, more enhanced tissue remodeling, and upregulated leptin expression. CCL2 and expander capsule can have clinical utility for soft tissue defects repair, and these two factors can be useful in other tissue engineering.

Modular cell-assembled adipose matrix-derived bead foams as a mesenchymal stromal cell delivery platform for soft tissue regeneration

With the goal of establishing a new clinically-relevant bioscaffold format to enable the delivery of high densities of human adipose-derived stromal cells (ASCs) for applications in soft tissue regeneration, a novel "cell-assembly" method was developed to generate robust 3-D scaffolds comprised of fused networks of decellularized adipose tissue (DAT)-derived beads. In vitro studies confirmed that the assembly process was mediated by remodelling of the extracellular matrix by the seeded ASCs, which were well distributed throughout the scaffolds and remained highly viable after 8 days in culture. The ASC density, sulphated glycosaminoglycan content and scaffold stability were enhanced under culture conditions that included growth factor preconditioning. In vivo testing was performed to compare ASCs delivered within the cell-assembled DAT bead foams to an equivalent number of ASCs delivered on a previously-established pre-assembled DAT bead foam platform in a subcutaneous implant model in athymic nude mice. Scaffolds were fabricated with human ASCs engineered to stably co-express firefly luciferase and tdTomato to enable long-term cell tracking. Longitudinal bioluminescence imaging showed a significantly stronger signal associated with viable human ASCs at timepoints up to 7 days in the cell-assembled scaffolds, although both implant groups were found to retain similar densities of human ASCs at 28 days. Notably, the infiltration of CD31⁺ murine endothelial cells was enhanced in the cell-assembled implants at 28 days. Moreover, microcomputed tomography angiography revealed that there was a marked reduction in vascular permeability in the cell-assembled group, indicating that the developing vascular network was more stable in the new scaffold format. Overall, the novel cell-assembled DAT bead foams represent a promising platform to harness the pro-regenerative paracrine functionality of human ASCs and warrant further investigation as a clinically-translational approach for volume augmentation.