Micro-scaffolds as synthetic cell niches: recent advances and challenges

Bioactive Glass Microscaffolds Fabricated by Two-Photon Lithography

Porous scaffolds made of bioactive glass (BG) are of great interest for tissue engineering as they can bond to bone rapidly and promote new bone formation. Pores and channels between 100 and 500 µm provide space for cell intrusion and nutrient supply, facilitating bone ingrowth and vascularization. Furthermore, smaller pores and structural features of a few microns in size influence cell behavior, such as adhesion and osteogenic differentiation. Additive manufacturing (AM) is well suited to fabricate such geometries. However, microstructuring BG is demanding and common AM techniques are unable to achieve features below 100 µm. In this work, two-photon lithography (TPL) is used for the first time to structure BG with single-micron features. A composite containing BG nanoparticles is structured using TPL and thermally processed to receive glass scaffolds. The glass used in this study demonstrates in vitro bioactivity in simulated body fluid (SBF) and cytocompatibility toward human mesenchymal stromal cells (MSCs), making it a suitable material for tissue engineering. This process will open a toolbox for a variety of existing BG particles to be shaped with features as small as 6 µm and will broaden the understanding of the influence of scaffold design on cell behavior.

Site-Selective Biofunctionalization of 3D Microstructures Via Direct Ink Writing

Two-photon lithography has revolutionized multi-photon 3D laser printing, enabling precise fabrication of micro- and nanoscale structures. Despite many advancements, challenges still persist, particularly in biofunctionalization of 3D microstructures. This study introduces a novel approach combining two-photon lithography with scanning probe lithography for post-functionalization of 3D microstructures overcoming limitations in achieving spatially controlled biomolecule distribution. The method utilizes a diverse range of biomolecule inks, including phospholipids, and two different proteins, introducing high spatial resolution and distinct functionalization on separate areas of the same microstructure. The surfaces of 3D microstructures are treated using bovine serum albumin and/or 3-(Glycidyloxypropyl)trimethoxysilane (GPTMS) to enhance ink retention. The study further demonstrates different strategies to create binding sites for cells by integrating different biomolecules, showcasing the potential for customized 3D cell microenvironments. Specific cell adhesion onto functionalized 3D microscaffolds is demonstrated, which paves the way for diverse applications in tissue engineering, biointerfacing with electronic devices and biomimetic modeling.

Impact of Composition and Autoclave Sterilization on the Mechanical and Biological Properties of ECM-Mimicking Cryogels

Cryogels represent a valid strategy as scaffolds for tissue engineering. In order to adequately support adhesion and proliferation of anchorage-dependent cells, different polymers need to be combined within the same scaffold trying to mimic the complex features of a natural extracellular matrix (ECM). For this reason, in this work, gelatin (Gel) and chondroitin sulfate (CS), both functionalized with methacrylic groups to produce CSMA and GelMA derivatives, were selected to prepare cryogel networks. Both homopolymer and heteropolymer cryogels were produced, via radical crosslinking reactions carried out at -12 °C for 2 h. All the scaffolds were characterized for their mechanical, swelling and morphological properties, before and after autoclave sterilization. Moreover, they were evaluated for their biocompatibility and ability to support the adhesion of human gingival fibroblasts and tenocytes. GelMA-based homopolymer networks better withstood the autoclave sterilization process, compared to CSMA cryogels. Indeed, GelMA cryogels showed a decrease in stiffness of approximately 30%, whereas CSMA cryogels of approximately 80%. When GelMA and CSMA were blended in the same network, an intermediate outcome was observed. However, the hybrid scaffolds showed a general worsening of the biological performance. Indeed, despite their ability to withstand autoclave sterilization with limited modification of the mechanical and morphological properties, the hybrid cryogels exhibited poor cell adhesion and high LDH leakage. Therefore, not only do network components need to be properly selected, but also their combination and ability to withstand effective sterilization process should be carefully evaluated for the development of efficient scaffolds designed for tissue engineering purposes.

Deer antler stem cell niche: An interesting perspective

In recent years, there has been considerable exploration into methods aimed at enhancing the regenerative capacity of transplanted and/or tissue-resident cells. Biomaterials, in particular, have garnered significant interest for their potential to serve as natural scaffolds for cells. In this editorial, we provide commentary on the study by Wang et al, in a recently published issue of World J Stem Cells, which investigates the use of a decellularized xenogeneic extracellular matrix (ECM) derived from antler stem cells for repairing osteochondral defects in rat knee joints. Our focus lies specifically on the crucial role of biological scaffolds as a strategy for augmenting stem cell potential and regenerative capabilities, thanks to the establishment of a favorable microenvironment (niche). Stem cell differentiation heavily depends on exposure to intrinsic properties of the ECM, including its chemical and protein composition, as well as the mechanical forces it can generate. Collectively, these physicochemical cues contribute to a bio-instructive signaling environment that offers tissue-specific guidance for achieving effective repair and regeneration. The interest in mechanobiology, often conceptualized as a form of "structural memory", is steadily gaining more validation and momentum, especially in light of findings such as these.

Bilateral Crosslinking with Glutaraldehyde and 1-Ethyl-3-(3-Dimethylaminopropyl) Carbodiimide: An Optimization Strategy for the Application of Decellularized Human Amniotic Membrane in Tissue Engineering

Introduction

The decellularized human amniotic membrane (dHAM) emerges as a viable 3D scaffold for organ repair and replacement using a tissue engineering strategy. Glutaraldehyde (GTA) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) can increase the biomechanical properties of dHAM. However, the crosslinking process is associated with biochemical changes and residual toxic materials, dampening the biocompatibility of the dHAM. From a histologic point of view, each side of the amniotic membrane is biologically different. While the dHAM basement membrane side is rich in growth factors, the stromal side of the dHAM contains more connective tissue matrix (e.g., collagen fibers) which supports its biomechanical properties. Biocompatibility and biomechanical properties are two important challenges in the field of materials science. In this study, for the first time, the stromal and basement membrane side are cross-linked with GTA and EDC, respectively, to optimize the biocompatibility of the treated dHAM while sparing the GTA-mediated biomechanical improvements.

Methods

Crosslinking was carried out on dHAM in three groups: EDC, GTA and bilateral treatment with EDC>A. Mechanical resistance, degradability, and crosslinking measurements were performed on treated dHAM. The viability of mesenchymal stem cells (MSCs) on the scaffolds was evaluated by the MTT assay. The expression levels of surface markers and images of the MSCs were thoroughly studied.

Results

The results obtained showed that bilateral treatment of dHAM with EDC and GTA increased mechanical resistance. Similarly, the evaluation of surface markers revealed that bilaterally treated dHAM sustains the stemness and viability of MSCs at a level equal to that achieved with EDC alone. The SEM images indicated that the MSCs maintained adhesion on EDC>A-cross-linked dHAM.

Conclusion

The current study explores a pioneering treatment of dHAM, a material long recognized for its regenerative properties, in a novel context. This research delves into the utilization of dHAM cross-linked with EDC>A, demonstrating its optimized efficacy in tissue engineering. The enhanced crosslinking technique significantly alters the membrane's properties, amplifying its durability and therapeutic potential. In this novel bilateral treatment strategy (EDC and GTA), improving mechanical properties by GTA on the stromal surface and maintaining the biocompatibility of EDC on the side of the basement membrane of dHAM had been attained together. By investigating the handling and impact of this cross-linked membrane, this study unveils a new approach in leveraging a well-known material through an innovative process, revolutionizing its application in wound care.

Selective Positioning of Different Cell Types on 3D Scaffolds via DNA Hybridization

Three-dimensional (3D) microscaffolds for cell biology have shown their potential in mimicking physiological environments and simulating complex multicellular constructs. However, controlling the localization of cells precisely on microfabricated structures is still complex and usually limited to two-dimensional assays. Indeed, the implementation of an efficient method to selectively target different cell types to specific regions of a 3D microscaffold would represent a decisive step toward cell-by-cell assembly of complex cellular arrangements. Here, we use two-photon lithography (2PL) to fabricate 3D microarchitectures with functional photoresists. UV-mediated click reactions are used to functionalize their surfaces with single-stranded DNA oligonucleotides, using sequential repetition to decorate different scaffold regions with individual DNA addresses. Various immortalized cell lines and stem cells modified by grafting complementary oligonucleotides onto the phospholipid membranes can then be immobilized onto complementary regions of the 3D structures by selective hybridization. This allows controlled cocultures to be established with spatially separated arrays of eukaryotic cells in 3D.

Review on Bioinspired Design of ECM-Mimicking Scaffolds by Computer-Aided Assembly of Cell-Free and Cell Laden Micro-Modules

Tissue engineering needs bioactive drug delivery scaffolds capable of guiding cell biosynthesis and tissue morphogenesis in three dimensions. Several strategies have been developed to design and fabricate ECM-mimicking scaffolds suitable for directing in vitro cell/scaffold interaction, and controlling tissue morphogenesis in vivo. Among these strategies, emerging computer aided design and manufacturing processes, such as modular tissue unit patterning, promise to provide unprecedented control over the generation of biologically and biomechanically competent tissue analogues. This review discusses recent studies and highlights the role of scaffold microstructural properties and their drug release capability in cell fate control and tissue morphogenesis. Furthermore, the work highlights recent advances in the bottom-up fabrication of porous scaffolds and hybrid constructs through the computer-aided assembly of cell-free and/or cell-laden micro-modules. The advantages, current limitations, and future challenges of these strategies are described and discussed.

The emerging role of cancer nanotechnology in the panorama of sarcoma

In the field of nanomedicine a multitude of nanovectors have been developed for cancer application. In this regard, a less exploited target is represented by connective tissue. Sarcoma lesions encompass a wide range of rare entities of mesenchymal origin affecting connective tissues. The extraordinary diversity and rarity of these mesenchymal tumors is reflected in their classification, grading and management which are still challenging. Although they include more than 70 histologic subtypes, the first line-treatment for advanced and metastatic sarcoma has remained unchanged in the last fifty years, excluding specific histotypes in which targeted therapy has emerged. The role of chemotherapy has not been completely elucidated and the outcomes are still very limited. At the beginning of the century, nano-sized particles clinically approved for other solid lesions were tested in these neoplasms but the results were anecdotal and the clinical benefit was not substantial. Recently, a new nanosystem formulation NBTXR3 for the treatment of sarcoma has landed in a phase 2-3 trial. The preliminary results are encouraging and could open new avenues for research in nanotechnology. This review provides an update on the recent advancements in the field of nanomedicine for sarcoma. In this regard, preclinical evidence especially focusing on the development of smart materials and drug delivery systems will be summarized. Moreover, the sarcoma patient management exploiting nanotechnology products will be summed up. Finally, an overlook on future perspectives will be provided.

Fractone Stem Cell Niche Components Provide Intuitive Clues in the Design of New Therapeutic Procedures/Biomatrices for Neural Repair

The aim of this study was to illustrate recent developments in neural repair utilizing hyaluronan as a carrier of olfactory bulb stem cells and in new bioscaffolds to promote neural repair. Hyaluronan interacts with brain hyalectan proteoglycans in protective structures around neurons in perineuronal nets, which also have roles in the synaptic plasticity and development of neuronal cognitive properties. Specialist stem cell niches termed fractones located in the sub-ventricular and sub-granular regions of the dentate gyrus of the hippocampus migrate to the olfactory bulb, which acts as a reserve of neuroprogenitor cells in the adult brain. The extracellular matrix associated with the fractone stem cell niche contains hyaluronan, perlecan and laminin α5, which regulate the quiescent recycling of stem cells and also provide a means of escaping to undergo the proliferation and differentiation to a pluripotent migratory progenitor cell type that can participate in repair processes in neural tissues. Significant improvement in the repair of spinal cord injury and brain trauma has been reported using this approach. FGF-2 sequestered by perlecan in the neuroprogenitor niche environment aids in these processes. Therapeutic procedures have been developed using olfactory ensheathing stem cells and hyaluronan as a carrier to promote neural repair processes. Now that recombinant perlecan domain I and domain V are available, strategies may also be expected in the near future using these to further promote neural repair strategies.

Construction of multifunctional cell aggregates in angiogenesis and osteogenesis through incorporating hVE-cad-Fc-modified PLGA/β-TCP microparticles for enhancing bone regeneration

Multicellular aggregates have been widely utilized for regenerative medicine; however, the heterogeneous structure and undesired bioactivity of cell-only aggregates hinder their clinical translation. In this study, we fabricated an innovative kind of microparticle-integrated cellular aggregate with multifunctional activities in angiogenesis and osteogenesis, by combining stem cells from human exfoliated deciduous teeth (SHEDs) and bioactive composite microparticles. The poly(lactide-co-glycolide) (PLGA)-based bioactive microparticles (PTV microparticles) were ∼15 μm in diameter, with dispersed β-tricalcium phosphate (β-TCP) nanoparticles and surface-modified vascular endothelialcadherin fusion protein (hVE-cad-Fc). After co-culturing with microparticles in U-bottomed culture plates, SHEDs could firmly attach to the microparticles with a homogeneous distribution. The PTV microparticle-integrated SHED aggregates (PTV/SHED aggregates) showed significant positive CD31 and ALP expression, as well as the significantly upregulated osteogenesis makers (Runx2, ALP, and OCN) and angiogenesis makers (Ang-1 and CD31), compared with PLGA, PLGA/β-TCP (PT) and PLGA/hVE-cad-Fc (PV) microparticle-integrated SHED aggregates. Finally, in mice, 3 mm calvarial defects filled with the PTV microparticle-integrated SHED aggregates achieved abundant vascularized neo-bone regeneration within 4 weeks. Overall, we believe that these multifunctional PTV/SHED aggregates could be used as modules for bottom-up regenerative medicine, and provide a promising method for vascularized bone regeneration.