Mesenchymal Stem Cell-based Scaffolds in Regenerative Medicine of Dental Diseases

Biomedical engineering breakthroughs and increased patient expectations and requests for more comprehensive care are propelling the field of regenerative dentistry forward at a fast pace. Stem cells (SCs), bioactive compounds, and scaffolds are the mainstays of tissue engineering, the backbone of regenerative dentistry. Repairing damaged teeth and gums is a significant scientific problem at present. Novel therapeutic approaches for tooth and periodontal healing have been inspired by tissue engineering based on mesenchymal stem cells (MSCs). Furthermore, as a component of the MSC secretome, extracellular vesicles (EVs) have been shown to contribute to periodontal tissue repair and regeneration. The scaffold, made of an artificial extracellular matrix (ECM), acts as a supporting structure for new cell development and tissue formation. To effectively promote cell development, a scaffold must be non-toxic, biodegradable, biologically compatible, low in immunogenicity, and safe. Due to its promising biological characteristics for cell regeneration, dental tissue engineering has recently received much attention for its use of natural or synthetic polymer scaffolds with excellent mechanical properties, such as small pore size and a high surface-to-volume ratio, as a matrix. Moreover, as a bioactive material for carrying MSC-EVs, the combined application of scaffolds and MSC-EVs has a better regenerative effect on dental diseases. In this paper, we discuss how MSCs and MSC-derived EV treatment may be used to regenerate damaged teeth, and we highlight the role of various scaffolds in this process.

3D Aligned Nanofiber Scaffold Fabrication with Trench-Guided Electrospinning for Cardiac Tissue Engineering

Constructing three-dimensional (3D) aligned nanofiber scaffolds is significant for the development of cardiac tissue engineering, which is promising in the field of drug discovery and disease mechanism study. However, the current nanofiber scaffold preparation strategy, which mainly includes manual assembly and hybrid 3D printing, faces the challenge of integrated fabrication of morphology-controllable nanofibers due to its cross-scale structural feature. In this research, a trench-guided electrospinning (ES) strategy was proposed to directly fabricate 3D aligned nanofiber scaffolds with alternative ES and a direct ink writing (DIW) process. The electric field effect of DIW poly(dimethylsiloxane) (PDMS) side walls on guiding whipping ES nanofibers was investigated to construct trench design rules. It was found that the width/height ratio of trenches greatly affected the nanofiber alignment, and the trench width/height ratio of 1.5 provided the nanofiber alignment degree over 60%. As a proof of principle, 3D nanofiber scaffolds with controllable porosity (60-80%) and alignment (30-60%) were fabricated. The effect of the scaffolds was verified by culturing human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), which resulted in the uniform 3D distribution of aligned hiPSC-CMs with ∼1000 μm thickness. Therefore, this printing strategy shows great potential for the efficient engineered tissue construction.

Biomimetic alginate-based electroconductive nanofibrous scaffolds for bone tissue engineering application

Novel electrically conductive nanofibrous scaffolds were designed and fabricated through the grafting of aniline monomer onto a phenylamine-functionalized alginate (Alg-NH2) followed by electrospinning with poly(vinyl alcohol) (PVA). Performance of the prepared scaffolds in bone tissue engineering (TE) were studied in terms of physicochemical (e.g., conductivity, electroactivity, morphology, hydrophilicity, water uptake, and mechanical) and biological (cytocompatibility, in vitro biodegradability, cells attachment and proliferation, hemolysis, and protein adsorption) properties. The contact angles of the scaffolds with water drop were obtained about 50 to 60° that confirmed their excellent hydrophilicities for TE applications. Three dimensional (3D), inter-connected and uniform porous structures of the scaffolds without any bead formation was confirmed by scanning electron microscopy (SEM). Electrical conductivities of the fabricated scaffolds were obtained as 1.5 × 10-3 and 2.7 × 10-3 Scm-1. MTT assay results revealed that the scaffolds have acceptable cytocompatibilities and can enhance the cells adhesion as well as proliferation, which approved their potential for TE applications. Hemolysis rate of the developed scaffolds were quantified <2 % even at high concentration (200 μgmL-1) of samples that approved their hemocompatibilities. The scaffolds were also exhibited acceptable protein adsorption capacities (65 and 68 μgmg-1). As numerous experimental results, the developed scaffolds have acceptable potential for bone TE.

3D printed wound constructs for skin tissue engineering: A systematic review in experimental animal models

Wound dressings are one of the most used treatments for chronic wounds. Moreover, 3D printing has been emerging as a promising strategy for printing 3D printed wound constructs, being able of manufacturing multi layers, with a solid 3D structure. Although all these promising effects of 3D printed wound constructs, there is still few studies and limited understanding of the interaction of these dressings with skin tissue and their effect on the process of skin wound healing. In this context, the aim of this work was to perform a systematic review of the literature to examine the effects of 3D printed wound constructs on the process of skin wound healing in animal models. The articles were selected from three databases following Medical Subject Headings (MeSH) descriptors "3D printing," "skin," "wound," and "in vivo." After the selection, exclusion and inclusion criteria, nine articles were analyzed. This review confirms the significant benefits of using 3D printed wound constructs for skin repair and regeneration. All the used inks demonstrated the ability of mimicking the structure of skin tissue and promoting cell adhesion, proliferation, migration, and mobility. Furthermore, in vivo findings showed full wound closure in most of the studies, with well-organized dermal and epidermal layers.

3D-printed hydroxyapatite scaffolds for bone tissue engineering: A systematic review in experimental animal studies

The use of 3D-printed hydroxyapatite (HA) scaffolds for stimulating bone healing has been increasing over the years. Although all the promising effects of these scaffolds, there are still few studies and limited understanding of their interaction with bone tissue and their effects on the process of fracture healing. In this context, this study aimed to perform a systematic literature review examining the effects of different 3D-printed HA scaffolds in bone healing. The search was made according to the preferred reporting items for systematic reviews and meta-analysis (PRISMA) orientations and Medical Subject Headings (MeSH) descriptors "3D printing," "bone," "HA," "repair," and "in vivo." Thirty-six articles were retrieved from PubMed and Scopus databases. After eligibility analyses, 20 papers were included (covering the period of 2016 and 2021). Results demonstrated that all the studies included in this review showed positive outcomes, indicating the efficacy of scaffolds treated groups in the in vivo experiments for promoting bone healing in different animal models. In conclusion, 3D-printed HA scaffolds are excellent candidates as bone grafts due to their bioactivity and good bone interaction.

Rete ridges: Morphogenesis, function, regulation, and reconstruction

Rete ridges (RRs) are distinct undulating microstructures at the junction of the dermis and epidermis in the skin of humans and certain animals. This structure is essential for enhancing the mechanical characteristics of skin and preserving homeostasis. With the development of tissue engineering and regenerative medicine, artificial skin grafts have made great progress in the field of skin healing. However, the restoration of RRs has been often disregarded or absent in artificial skin grafts, which potentially compromise the efficacy of tissue repair and regeneration. Therefore, this review collates recent research advances in understanding the structural features, function, morphogenesis, influencing factors, and reconstruction strategies pertaining to RRs. In addition, the preparation methods and limitations of tissue-engineered skin with RRs are discussed. STATEMENT OF SIGNIFICANCE: The technology for the development of tissue-engineered skin (TES) is widely studied and reported; however, the preparation of TES containing rete ridges (RRs) is often ignored, with no literature reviews on the structural reconstruction of RRs. This review focuses on the progress pertaining to RRs and focuses on the reconstruction methods for RRs. In addition, it discusses the limitations of existing reconstruction methods. Therefore, this review could be a valuable reference for transferring TES with RR structure from the laboratory to clinical applications in skin repair.

Biodegradable and Electrically Conductive Melanin-Poly (3-Hydroxybutyrate) 3D Fibrous Scaffolds for Neural Tissue Engineering Applications

Due to the severity of peripheral nerve injuries (PNI) and spinal cord injuries (SCI), treatment options for patients are limited. In this context, biomaterials designed to promote regeneration and reinstate the lost function are being explored. Such biomaterials should be able to mimic the biological, chemical, and physical cues of the extracellular matrix for maximum effectiveness as therapeutic agents. Development of biomaterials with desirable physical, chemical, and electrical properties, however, has proven challenging. Here a novel biomaterial formulation achieved by blending the pigment melanin and the natural polymer Poly-3-hydroxybutyrate (PHB) is proposed. Physio-chemical measurements of electrospun fibers reveal a feature rich surface nano-topography, a semiconducting-nature, and brain-tissue-like poroviscoelastic properties. Resulting fibers improve cell adhesion and growth of mouse sensory and motor neurons, without any observable toxicity. Further, the presence of polar functional groups positively affect the kinetics of fibers degradation at a pH (≈7.4) comparable to that of body fluids. Thus, melanin-PHB blended scaffolds are found to be physio-chemically, electrically, and biologically compatible with neural tissues and could be used as a regenerative modality for neural tissue injuries. A biomaterial for scaffolds intended to promote regeneration of nerve tissue after injury is developed. This biomaterial, obtained by mixing the pigment melanin and the natural polymer PHB, is biodegradable, electrically conductive, and beneficial to the growth of motor and sensory neurons. Thus, it is believed that this biomaterial can be used in the context of healthcare applications.

Scaffold-based delivery of mesenchymal stromal cells to diabetic wounds

Foot ulceration is a major complication of diabetes mellitus, which results in significant human suffering and a major burden on healthcare systems. The cause of impaired wound healing in diabetic patients is multifactorial with contributions from hyperglycaemia, impaired vascularization and neuropathy. Patients with non-healing diabetic ulcers may require amputation, creating an urgent need for new reparative treatments. Delivery of stem cells may be a promising approach to enhance wound healing because of their paracrine properties, including the secretion of angiogenic, immunomodulatory and anti-inflammatory factors. While a number of different cell types have been studied, the therapeutic use of mesenchymal stromal cells (MSCs) has been widely reported to improve delayed wound healing. However, topical administration of MSCs via direct injection has several disadvantages, including low cell viability and poor cell localization at the wound bed. To this end, various biomaterial conformations have emerged as MSC delivery vehicles to enhance cell viability and persistence at the site of implantation. This paper discusses biomaterial-based MSCs therapies in diabetic wound healing and highlights the low conversion rate to clinical trials and commercially available therapeutic products.

Nano-Structured Ridged Micro-Filaments (≥100 µm Diameter) Produced Using a Single Step Strategy for Improved Bone Cell Adhesion and Proliferation in Textile Scaffolds

Textile scaffolds that are either 2D or 3D with tunable shapes and pore sizes can be made through textile processing (weaving, knitting, braiding, nonwovens) using microfilaments. However, these filaments lack nano-topographical features to improve bone cell adhesion and proliferation. Moreover, the diameter of such filaments should be higher than that used for classical textiles (10−30 µm) to enable adhesion and the efficient spreading of the osteoblast cell (>30 µm diameter). We report, for the first time, the fabrication of biodegradable nanostructured cylindrical PLLA (poly-L-Lactic acid) microfilaments of diameters 100 µm and 230 µm, using a single step melt-spinning process for straightforward integration of nano-scale ridge-like structures oriented in the fiber length direction. Appropriate drawing speed and temperature used during the filament spinning allowed for the creation of instabilities giving rise to nanofibrillar ridges, as observed by AFM (Atomic Force Microscopy). These micro-filaments were hydrophobic, and had reduced crystallinity and mechanical strength, but could still be processed into 2D/3D textile scaffolds of various shapes. Biological tests carried out on the woven scaffolds made from these nano-structured micro filaments showed excellent human bone cell MG 63 adhesion and proliferation, better than on smooth 30 µm- diameter fibers. Elongated filopodia of the osteoblast, intimately anchored to the nano-structured filaments, was observed. The filaments also induced in vitro osteogenic expression, as shown by the expression of osteocalcin and bone sialoprotein after 21 days of culture. This work deals with the fabrication of a new generation of nano-structured micro-filament for use as scaffolds of different shapes suited for bone cell engineering.

Methods to Characterize Electrospun Scaffold Morphology: A Critical Review

Electrospun scaffolds can imitate the hierarchical structures present in the extracellular matrix, representing one of the main concerns of modern tissue engineering. They are characterized in order to evaluate their capability to support cells or to provide guidelines for reproducibility. The issues with widely used methods for morphological characterization are discussed in order to provide insight into a desirable methodology for electrospun scaffold characterization. Reported methods include imaging and physical measurements. Characterization methods harbor inherent limitations and benefits, and these are discussed and presented in a comprehensive selection matrix to provide researchers with the adequate tools and insights required to characterize their electrospun scaffolds. It is shown that imaging methods present the most benefits, with drawbacks being limited to required costs and expertise. By making use of more appropriate characterization, researchers will avoid measurements that do not represent their scaffolds and perhaps might discover that they can extract more characteristics from their scaffold at no further cost.

Osteon-mimetic 3D nanofibrous scaffold enhances stem cell proliferation and osteogenic differentiation for bone regeneration

The scaffold microstructure is important for bone tissue engineering. Failure to synergistically imitate the hierarchical microstructure of the components of bone, such as an osteon with concentric multilayers assembled by nanofibers, hinders the performance for guiding bone regeneration. Here, a 2D bilayer nanofibrous membrane (BLM) containing poly(lactide-co-glycolide) (PLGA)/polycaprolactone (PCL) composite membranes in similar compositions (PCL15 and PCL20), but possessing different degrees of shrinkage, was fabricated via sequential electrospinning. Upon incubation in phosphate buffered saline (PBS) (37 °C), the 2D BLM spontaneously deformed into a 3D shape induced by PCL crystallization within the PLGA matrix, and the PCL15 and PCL20 layer formed a concave and convex surface, respectively. The 3D structure contained curved multilayers with an average diameter of 776 ± 169 μm, and on the concave and convex surface the nanofiber diameters were 792 ± 225 and 881 ± 259 nm, respectively. The initial 2D structure facilitated the even distribution of seeded cells. Adipose-derived stem cells from rats (rADSCs) proliferated faster on a concave surface than on a convex surface. For the 3D BLM, the osteogenic differentiation of rADSCs was significantly higher than that on 2D surfaces, even without osteogenic supplements, which resulted from the stretched cell morphology on the curved sublayer leading to increased expression of lamin-A. After being implanted into cranial defects in Sprague Dawley (SD) rats, 3D BLM significantly accelerated bone formation. In summary, 3D BLM with an osteon-like structure provides a potential strategy to repair bone defects.

Magnetomechanical force: an emerging paradigm for therapeutic applications

Mechanical forces, which play an profound role in cell fate regulation, have prompted the rapid development and popularization of mechanobiology. More recently, magnetic fields in combination with intelligent materials featuring...

Development of 3D culture scaffolds for directional neuronal growth using 2-photon lithography

Conventional applications of transplant technology, applied to severe traumatic injuries of the nervous system, have met limited success in the clinics due to the complexity of restoring function to the damaged tissue. Neural tissue engineering aims to deploy scaffolds mimicking the physiological properties of the extracellular matrix to facilitate the elongation of axons and the repair of damaged nerves. However, the fabrication of ideal scaffolds with precisely controlled thickness, texture, porosity, alignment, and with the required mechanical strength, features needed for effective clinical applications, remains technically challenging. We took advantage of state-of-the-art 2-photon photolithography to fabricate highly ordered and biocompatible 3D nanogrid structures to enhance neuronal directional growth. First, we characterized the physical and chemical properties and proved the biocompatibility of said scaffolds by successfully culturing primary sensory and motor neurons on their surface. Interestingly, axons extended along the fibers with a high degree of alignment to the pattern of the nanogrid, as opposed to the lack of directionality observed on flat glass or polymeric surfaces, and could grow in 3D between different layers of the scaffold. The axonal growth pattern observed is highly desirable for the treatment of traumatic nerve damage occurring during peripheral and spinal cord injuries. Thus, our findings provide a proof of concept and explore the possibility of deploying aligned fibrous 3D scaffold/implants for the directed growth of axons, and could be used in the design of scaffolds targeted towards the restoration and repair of lost neuronal connections.

Cultivation of hierarchical 3D scaffolds inside a perfusion bioreactor: scaffold design and finite-element analysis of fluid flow

The use of porous 3D scaffolds for the repair of bone nonunion and osteoporotic bone is currently an area of great interest. Using a combination of thermally-induced phase separation (TIPS) and 3D-plotting (3DP), we have generated hierarchical 3DP/TIPS scaffolds made of poly(lactic-co-glycolic acid) (PLGA) and nanohydroxyapatite (nHA). A full factorial design of experiments was conducted, in which the PLGA and nHA compositions were varied between 6-12% w/v and 10-40% w/w, respectively, totaling 16 scaffold formulations with an overall porosity ranging between 87%-93%. These formulations included an optimal scaffold design identified in our previous study. The internal structures of the scaffolds were examined using scanning electron microscopy and microcomputed tomography. Our optimal scaffold was seeded with MC3T3-E1 murine preosteoblastic cells and subjected to cell culture inside a tissue culture dish and a perfusion bioreactor. The results were compared to those of a commercial CellCeram™ scaffold with a composition of 40% β-tricalcium phosphate and 60% hydroxyapatite (β-TCP/HA). Media flow within the macrochannels of 3DP/TIPS scaffolds was modeled in COMSOL software in order to fine tune the wall shear stress. CyQUANT DNA assay was performed to assess cell proliferation. The normalized number of cells for the optimal scaffold was more than twofold that of CellCeram™ scaffold after two weeks of culture inside the bioreactor. Despite the substantial variability in the results, the observed improvement in cell proliferation upon culture inside the perfusion bioreactor (vs. static culture) demonstrated the role of macrochannels in making the 3DP/TIPS scaffolds a promising candidate for scaffold-based tissue engineering.

Influence of Bioinspired Lithium-Doped Titanium Implants on Gingival Fibroblast Bioactivity and Biofilm Adhesion

Soft tissue integration (STI) at the transmucosal level around dental implants is crucial for the long-term success of dental implants. Surface modification of titanium dental implants could be an effective way to enhance peri-implant STI. The present study aimed to investigate the effect of bioinspired lithium (Li)-doped Ti surface on the behaviour of human gingival fibroblasts (HGFs) and oral biofilm in vitro. HGFs were cultured on various Ti surfaces—Li-doped Ti (Li_Ti), NaOH_Ti and micro-rough Ti (Control_Ti)—and were evaluated for viability, adhesion, extracellular matrix protein expression and cytokine secretion. Furthermore, single species bacteria (Staphylococcus aureus) and multi-species oral biofilms from saliva were cultured on each surface and assessed for viability and metabolic activity. The results show that both Li_Ti and NaOH_Ti significantly increased the proliferation of HGFs compared to the control. Fibroblast growth factor-2 (FGF-2) mRNA levels were significantly increased on Li_Ti and NaOH_Ti at day 7. Moreover, Li_Ti upregulated COL-I and fibronectin gene expression compared to the NaOH_Ti. A significant decrease in bacterial metabolic activity was detected for both the Li_Ti and NaOH_Ti surfaces. Together, these results suggest that bioinspired Li-doped Ti promotes HGF bioactivity while suppressing bacterial adhesion and growth. This is of clinical importance regarding STI improvement during the maintenance phase of the dental implant treatment.

Applications of scaffold-based advanced materials in biomedical sensing

There have been many efforts to synthesize advanced materials that are capable of real-time specific recognition of a molecular target, and allow the quantification of a variety of biomolecules. Scaffold materials have a porous structure, with a high surface area and their intrinsic nanocavities can accommodate cells and macromolecules. The three-dimensional structure (3D) of scaffolds serves not only as a fibrous structure for cell adhesion and growth in tissue engineering, but can also provide the controlled release of drugs and other molecules for biomedical applications. There has been a limited number of reports on the use of scaffold materials in biomedical sensing applications. This review highlights the potential of scaffold materials in the improvement of sensing platforms and summarizes the progress in the application of novel scaffold-based materials as sensor, and discusses their advantages and limitations. Furthermore, the influence of the scaffold materials on the monitoring of infectious diseases such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and bacterial infections, was reviewed.

Engineered Nanotopography on the Microfibers of 3D-Printed PCL Scaffolds to Modulate Cellular Responses and Establish an In Vitro Tumor Model

Scaffold-based three-dimensional (3D) cell culture systems have gained increased interest in cell biology, tissue engineering, and drug screening fields as a replacement of two-dimensional (2D) monolayer cell culture and as a way to provide biomimetic extracellular matrix environments. In this study, microscale fibrous scaffolds were fabricated via electrohydrodynamic printing, and nanoscale features were created on the fiber surface by simply leaching gliadin of poly(ε-caprolactone) (PCL)/gliadin composites in ethanol solution. The microstructure of the printed scaffolds could be precisely controlled by printing parameters, and the surface nanotopography of the printed fiber could be tuned by varying the PCL/gliadin ratios. By seeding mouse embryonic fibroblast (NIH/3T3) cells and human nonsmall cell lung cancer (A549) cells on the printed scaffolds, the cellular responses showed that the fiber nanotopography on printed scaffolds efficiently favored cell adhesion, migration, proliferation, and tissue formation. Quantitative analysis of the transcript expression levels of A549 cells seeded on nanoporous scaffolds further revealed the upregulation of integrin-β1, focal adhesion kinase, Ki-67, E-cadherin, and epithelial growth factor receptors over what was observed in the cells grown on the pure PCL scaffold. Furthermore, a significant difference was found in the relevant biomarker expression on the developed scaffolds compared with that in the monolayer culture, demonstrating the potential of cancer cell-seeded scaffolds as 3D in vitro tumor models for cancer research and drug screening.

Reduced Graphene Oxide-Encapsulated Microfiber Patterns Enable Controllable Formation of Neuronal-Like Networks

Scaffold-guided formation of neuronal-like networks, especially under electrical stimulation, can be an appealing avenue toward functional restoration of injured nervous systems. Here, 3D conductive scaffolds are fabricated based on printed microfiber constructs using near-field electrostatic printing (NFEP) and graphene oxide (GO) coating. Various microfiber patterns are obtained from poly(l-lactic acid-co-caprolactone) (PLCL) using NFEP and complexity is achieved via modulating the fiber overlay angles (45°, 60°, 75°, 90°), fiber diameters (15 to 148 µm), and fiber spatial organization (spider web and tubular structure). Upon coating GO onto PLCL microfibers via a layer-by-layer (L-b-L) assembly technique and in situ reduction into reduced GO (rGO), the obtained conductive scaffolds, with 25-50 layers of rGO, demonstrate superior conductivity (≈0.95 S cm-1 ) and capability of inducing neuronal-like network formation along the conductive microfibers under electrical stimulation (100-150 mV cm-1 ). Both electric field (0-150 mV cm-1 ) and microfiber diameter (17-150 µm) affect neurite outgrowth (PC-12 cells and primary mouse hippocampal neurons) and the formation of orientated neuronal-like networks. With further demonstration of such guidance to neuronal cells, these conductive scaffolds may see versatile applications in nerve regeneration and neural engineering.

Fabrication of Multilayered Nanofiber Scaffolds with a Highly Aligned Nanofiber Yarn for Anisotropic Tissue Regeneration

Nanofibrous scaffolds were widely studied to construct scaffold for various fields of tissue engineering due to their ability to mimic a native extracellular matrix (ECM). However, generally, an electrospun nanofiber exhibited a two-dimensional (2D) membrane form with a densely packed structure, which inhibited the formation of a bulk tissue in a three-dimensional (3D) structure. The appearance of a nanofiber yarn (NFY) made it possible to further process the electrospun nanofiber into the desired fabric for specific tissue regeneration. Here, poly(l-lactic acid) (PLLA) NFYs composed of a highly aligned nanofiber were prepared via a dual-nozzle electrospinning setup. Afterward, a noobing technique was applied to fabricate multilayered scaffolds with three orthogonal sets of PLLA NFYs, without interlacing them. Thus the constituent NFYs of the fabric were free of any crimp, apart from the binding yarn, which was used to maintain the integrity of the noobing scaffold. Remarkably, the highly aligned PLLA NFY expressed strengthened mechanical properties than that of a random film, which also promoted the cell adhesion on the NFY scaffold with unidirectional topography and less spreading bodies. In vitro experiments indicated that cells cultured on a noobing NFY scaffold showed a higher proliferation rate during long culture period. The controllable pore structure formed by the vertically arrayed NFY could allow the cell to penetrate through the thickness of the 3D scaffold, distributed uniformly in each layer. The topographic clues guided the orientation of H9C2 cells, forming tissues on different layers in two perpendicular directions. With NFY as the building blocks, noobing and/or 3D weaving methods could be applied in the fabrication of more complex 3D scaffolds applied in anisotropic tissues or organs regeneration.

Preparation of PI/PTFE-PAI Composite Nanofiber Aerogels with Hierarchical Structure and High-Filtration Efficiency

Electrospun nanofiber, showing large specific area and high porosity, has attracted much attention across various fields, especially in the field of air filtration. The small diameter contributes to the construction of filters with high-filtration efficiency for fine particulate matter (PM), however, along with an increase in air resistance. Herein, composited nanofiber aerogels (NAs), a truly three-dimensional (3D) derivative of the densely compacted electrospun mat, were constructed with the blocks of polytetrafluoroethylene-polyamideimide (PTFE-PAI) composite nanofiber and polyimide (PI) nanofiber. PI/PTFE-PAI NAs with hierarchically porous architecture and excellent mechanical properties have been obtained by thermally induced crosslink bonding. Results indicated that sintering at 400 °C for 30 min could complete the decomposition of polyethylene (PEO) and imidization of polyamic acid (PAA) into PI, as well as generate sufficient mechanical bonding between adjacent nanofibers in the NAs without extra additive. The well-prepared PI/PTFE-PAI NAs could withstand high temperature up to 500 °C. In addition, the filtration tests illustrated that the composite NAs had an excellent performance in PM filtration. More importantly, the filtration behavior could be adjusted to meet the requirements of various applications. The excellent thermal stability and high-filtration efficiency indicated its great potential in the field of high-temperature air filtration.

Prevention of excessive scar formation using nanofibrous meshes made of biodegradable elastomer poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

To reduce excessive scarring in wound healing, electrospun nanofibrous meshes, composed of haloarchaea-produced biodegradable elastomer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), are fabricated for use as a wound dressing. Three PHBV polymers with different 3HV content are used to prepare either solution-cast films or electrospun nanofibrous meshes. As 3HV content increases, the crystallinity decreases and the scaffolds become more elastic. The nanofibrous meshes exhibit greater elasticity and elongation at break than films. When used to culture human dermal fibroblasts in vitro, PHBV meshes give better cell attachment and proliferation, less differentiation to myofibroblasts, and less substrate contraction. In a full-thickness mouse wound model, treatment with films or meshes enables regeneration of pale thin tissues without scabs, dehydration, or tubercular scar formation. The epidermis of wounds treated with meshes develop small invaginations in the dermis within 2 weeks, indicating hair follicle and sweat gland regeneration. Consistent with the in vitro results, meshes reduce myofibroblast differentiation in vivo through downregulation of α-SMA and TGF-β1, and upregulation of TGF-β3. The regenerated wounds treated with meshes are softer and more elastic than those treated with films. These results demonstrate that electrospun nanofibrous PHBV meshes mitigate excessive scar formation by regulating myofibroblast formation, showing their promise for use as wound dressings.

Microfluidic Technology for the Production of Well-Ordered Porous Polymer Scaffolds

Advances in tissue engineering (TE) have revealed that porosity architectures, such as pore shape, pore size and pore interconnectivity are the key morphological properties of scaffolds. Well-ordered porous polymer scaffolds, which have uniform pore size, regular geometric shape, high porosity and good pore interconnectivity, facilitate the loading and distribution of active biomolecules, as well as cell adhesion, proliferation and migration. However, these are difficult to prepare by traditional methods and the existing well-ordered porous scaffold preparation methods require expensive experimental equipment or cumbersome preparation steps. Generally, droplet-based microfluidics, which generates and manipulates discrete droplets through immiscible multiphase flows inside microchannels, has emerged as a versatile tool for generation of well-ordered porous materials. This short review details this novel method and the latest developments in well-ordered porous scaffold preparation via microfluidic technology. The pore structure and properties of microfluidic scaffolds are discussed in depth, laying the foundation for further research and application in TE. Furthermore, we outline the bottlenecks and future developments in this particular field, and a brief outlook on the future development of microfluidic technique for scaffold fabrication is presented.

Mechanotactic Activation of TGF-β by PEDOT Artificial Microenvironments Triggers Epithelial to Mesenchymal Transition

Epithelial to mesenchymal transition (EMT) is integral for cells to acquire metastatic properties, and ample evidence links it to bioorganic framework of the tumor microenvironment (TME). Hydroxymethyl-functionalized 3,4-ethylenedioxythiophene polymer (PEDOT-OH) enables construction of diverse nanotopography size and morphologies and is therefore exploited to engineer organic artificial microenvironments bearing nanodots from 300 to 1000 nm in diameter to understand spatiotemporal EMT regulation by biophysical components of the TME. MCF-7 breast cancer cells are cultured on these artificial microenvironments, and temporal regulation of cellular morphology and EMT markers is investigated. The results show that upon physical stimulation, cells on 300 nm artificial microenvironments advance to EMT and display a decreased extracellular matrix (ECM) protein secretion. In contrast, cells on 500 nm artificial microenvironments are trapped in EMT-imbalance. Interestingly, cells on 1000 nm artificial microenvironments resemble those on control surfaces. Upon further investigation, it is found that EMT induction is triggered via transforming growth factor β (TGF-β) and ECM cleaving protein, matrix metalloproteinease-9. Immunostaining EMT proteins highlighted that EMT induction is achieved through attenuation of cell-cell and cell-microenvironment adhesions. The physical stimulation-induced TGF-β perturbation can have a profound impact on the understanding of tumor-promoting signaling cascades originated by cellular microenvironment.

Fabrication and characterization of polylactic acid/polycaprolactone composite macroporous micro-nanofiber scaffolds by phase separation

By using incompatible polymers, the preparation of scaffolds with a macroporous structure has overcome the use of porogens and carcinogenic solvents.

Fabrication of 3D plotted scaffold with microporous strands for bone tissue engineering

Scaffold porosity has played a key role in bone tissue engineering aimed at effective tissue regeneration, by promoting cell attachment, proliferation, and osteogenic differentiation for new bone formation.

I-Optimal Design of Hierarchical 3D Scaffolds Produced by Combining Additive Manufacturing and Thermally Induced Phase Separation

The limitations in the transport of oxygen, nutrients, and metabolic waste products pose a challenge to the development of bioengineered bone of clinically relevant size. This paper reports the design and characterization of hierarchical macro/microporous scaffolds made of poly(lactic-co-glycolic) acid and nanohydroxyapatite (PLGA/nHA). These scaffolds were produced by combining additive manufacturing (AM) and thermally induced phase separation (TIPS) techniques. Macrochannels with diameters of ~300 μm, ~380 μm, and ~460 μm were generated by embedding porous 3D-plotted polyethylene glycol (PEG) inside PLGA/nHA/1,4-dioxane or PLGA/1,4-dioxane solutions, followed by PEG extraction using deionized (DI) water. We have used an I-optimal design of experiments (DoE) and the response surface analysis (JMP® software) to relate three responses (scaffold thickness, porosity, and modulus) to the four experimental factors affecting the scaffold macro/microstructures (e.g., PEG strand diameter, PLGA concentration, nHA content, and TIPS temperature). Our results indicated that a PEG strand diameter of ~380 μm, a PLGA concentration of ~10% w/v, a nHA content of ~10% w/w, and a TIPS temperature around -10°C could generate scaffolds with a porosity of ~90% and a modulus exceeding 4 MPa. This paper presents the steps for the I-optimal design of these scaffolds and reports on their macro/microstructures, characterized using scanning electron microscopy (SEM) and micro-computed tomography (micro-CT).

Chitosan based-asymmetric membranes for wound healing: A review

The wound healing process involves highly complex and dynamic events that allow the re-establishment of skin's structural integrity. To further improve or to overcome the drawbacks associated with this process, researchers have been focused on the development of new therapeutics. Among them, asymmetric membranes are currently one of the most promising approaches to be used in wound healing due to its structural similarities with the epidermal and dermal layers of the native skin. The outer layer of asymmetric membranes provides a barrier that protects the wound from external damages (e.g. microorganisms and chemical agents), whereas the interior porous layer acts as template for supporting cell adhesion, migration and proliferation. Among the different materials used to produce these distinct layers, the chitosan arises as one of the preeminent materials due to its inherent biocompatibility, antibacterial, hemostatic, and healing properties. Therefore, in this review, it is provided an overview of the different chitosan-based asymmetric membranes developed for wound dressing applications. Further, the chitosan modifications to enhance its bioactivity as well as the asymmetric membranes general properties and production techniques are also described.

Coaxial Hydro-Nanofibrils for Self-Assembly of Cell Sheets Producing Skin Bilayers

Bilayered cell sheets were fabricated with coaxial hydro-nanofibrils for three-dimensional (3D) cultivation in a biomimetic environment. Polycaprolactone (PCL) was electrospun and hydrolyzed to release fragmented nanofibrils (NF) in an alkaline condition. Methacrylated gelatin (GelMA) was adsorbed and phototethered on the surface of the fibrils to prepare coaxial NF composed of hydrophilic shells and hydrophobic cores. GelMA layers on the NF were characterized by X-ray photoemission spectroscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The GelMA showed higher decoration level on NF compared to that on native gelatin. GelMA-decorated NF significantly enhanced cell proliferation rate and phenotypic expression of human dermal fibroblasts when spontaneous formation of cell sheets was observed for 7 days. HaCaT cells were layered on top of the fibroblast sheets and further cultivated in air-water interfaces to prepare bilayered skin sheets. After 21 days of incubation, the top layers of the bilayered sheets showed higher expression of pan-keratin, and the dermal cells showed higher proliferation in the GelMA-decorated NF.

Porous Three-Dimensional Silk Fibroin Scaffolds for Tracheal Epithelial Regeneration in Vitro and in Vivo

The regeneration of functional epithelial lining is critical for artificial grafts to repair tracheal defects. Although silk fibroin (SF) scaffolds have been widely studied for biomedical application (e.g., artificial skin), its potential for tracheal substitute and epithelial regeneration is still unknown. In this study, we fabricated porous three-dimensional (3D) silk fibroin scaffolds and cocultured them with primary human tracheobronchial epithelial cells (HBECs) for 21 days in vitro. Examined by scanning electronic microscopy (SEM) and calcein-AM staining with inverted phase contrast microscopy, the SF scaffolds showed excellent properties of promoting cell growth and proliferation for at least 21 days with good viability. In vivo, the porous 3D SF scaffolds (n = 18) were applied to repair a rabbit anterior tracheal defect. In the control group (n = 18), rabbit autologous pedicled trachea wall without epithelium, an ideal tracheal substitute, was implanted in situ. Observing by endoscopy and computed tomography (CT) scan, the repaired airway segment showed no wall collapse, granuloma formation, or stenosis during an 8-week interval in both groups. SEM and histological examination confirmed the airway epithelial growth on the surface of porous SF scaffolds. Both the epithelium repair speed and the epithelial cell differentiation degree in the SF scaffold group were comparable to those in the control group. Neither severe inflammation nor excessive fibrosis occurred in both groups. In summary, the porous 3D SF scaffold is a promising biomaterial for tracheal repair by successfully supporting tracheal wall contour and promoting tracheal epithelial regeneration.

Silk Fibroin Acts as a Self-Emulsifier to Prepare Hierarchically Porous Silk Fibroin Scaffolds through Emulsion-Ice Dual Templates

Silk fibroin (SF) has shown enormous potentials in various fields; however, application of SF in emulsion technology is quite limited. Here, we use SF as a self-emulsifier to form an oil-in-water (O/W) emulsion by emulsifying 1-butanol in SF aqueous solution. This showed that SF possessed strong surface activity to stabilize the O/W emulsion without the need for any other surface-active agent until its solidification because of 1-butanol-induced conformational transition of SF to β-sheet. After freezing the preformed emulsions at -20 °C, robust three-dimensional porous SF scaffolds were prepared without the need for any further post-treatment. The evolution from the O/W emulsion to porous scaffold formation under freezing was tracked, and an emulsion-ice dual template mechanism was proposed for scaffold formation, based on which SF scaffolds with controllable hierarchically porous structures were achieved by tuning the dispersed droplet volume fraction. Furthermore, SF scaffolds with hierarchical porosity showed significantly higher bioactivity toward L929 fibroblasts than that of SF scaffolds with mono macroporosity, highlighting the great asset of this hierarchically porous SF scaffold for broad applications in tissue engineering. Therefore, the strong surface-active characteristic of SF presented here, in addition to its distinct advantages, sheds a bright light on the application of SF in the vast range of emulsion technologies, especially in cosmetic-, food-, and biomedical-related areas.

Photodynamic therapy in 3D cancer models and the utilisation of nanodelivery systems

Photodynamic therapy (PDT) is the subject of considerable research in experimental cancer models mainly for the treatment of solid cancerous tumours. Recent studies on the use of nanoparticles as photosensitiser carriers have demonstrated improved PDT efficacy in experimental cancer therapy. Experiments typically employ conventional monolayer cell culture but there is increasing interest in testing PDT using three dimensional (3D) cancer models. 3D cancer models can better mimic in vivo models than 2D cultures by for example enabling cancer cell interactions with a surrounding extracellular matrix which should enable the treatment to be optimised prior to in vivo studies. The aim of this review is to discuss recent research using PDT in different types of 3D cancer models, from spheroids to nano-fibrous scaffolds, using a range of photosensitisers on their own or incorporated in nanoparticles and nanodelivery systems.

Electrospun 3D Scaffolds for Tissue Regeneration

Tissue engineering aims to fabricate and functionalise constructs that mimic the native extracellular matrix (ECM) in the closest way possible to induce cell growth and differentiation in both in vitro and in vivo conditions. Development of scaffolds that can function as tissue substitutes or augment healing of tissues is an essential aspect of tissue regeneration. Although there are many techniques for achieving this biomimicry in 2D structures and 2D cell cultures, translation of successful tissue regeneration in true 3D microenvironments is still in its infancy. Electrospinning, a well known electrohydrodynamic process, is best suited for producing and functionalising, nanofibrous structures to mimic the ECM. A systematic control of the processing parameters coupled with novel process innovations, has recently resulted in novel 3D electrospun structures. This chapter gives a brief account of the various 3D electrospun structures that are being tried as tissue engineering scaffolds. Combining electrospinning with other 3D structure forming technologies, which have shown promising results, has also been discussed. Electrospinning has the potential to bridge the gap between what is known and what is yet to be known in fabricating 3D scaffolds for tissue regeneration.

The effect of ordered and partially ordered surface topography on bone cell responses: a review

Current understanding of the role of ordered and partially ordered surface topography in bone cell responses for bone implant design.

Sacrificial template method for the synthesis of three-dimensional nanofibrous 58S bioglass scaffold and its in vitro bioactivity and cell responses

Three-dimensional nanofibrous scaffolds that morphologically mimic natural extracellular matrices hold great promises in tissue engineering and regenerative medicine due to their increased cell attachment and differentiation compared with block structure. In this work, for the first time, three-dimensional porous nanofibrous 58S bioglass scaffolds have been fabricated using a sacrificial template method. During the process, a natural three-dimensional nanofibrous bacterial cellulose was used as the sacrificial template on which precursor 58S glass was deposited via a sol-gel route. SEM and TEM results verify that the as-prepared 58S scaffolds can inherit the three-dimensional nanofibrous feature of bacterial cellulose. Pore structure characterizations by nitrogen adsorption-desorption and mercury intrusion porosimetry demonstrate that the 58S scaffolds are highly porous with a porosity of 75.1% and contain both mesopores (39.4 nm) and macropores (60 µm) as well as large BET surface area (127.4 m² g^-1). In vitro cell studies suggest that the 58S scaffold is bioactive and biocompatible with primary mouse osteoblast cells, suggesting that the nanofibrous structure of 58S is able to provide an appropriate environment for cellular functioning. These results strongly suggest that the three-dimensional nanofibrous 58S scaffold has great potential for application in bone tissue engineering and regenerative medicine.

Porous Polymeric Films from Microbubbles Generated Using a T-Junction Microfluidic Device

In this work, a simple microfluidic junction with a T geometry and coarse (200 μm diameter) capillaries was used to generate monodisperse microbubbles with an alginate polymer shell. Subsequently, these bubbles were used to prepare porous alginate films with good control over the pore structure. The lack of pore size, shape, and surface control in scalable forming of polymeric films is a major application-limiting drawback at present. Controlling the thinning process of the shell of the bubbles to tune the surface of the resulting structures was also explored. Films were prepared with nanopatterned surfaces by controlling the thinning of the bubble shell, with the aid of surfactants, to induce efficient bursting (fragmentation) of bubbles to generate nanodroplets, which become embedded within the film surface. This novel feature greatly expands and enhances the use of hydrophilic polymers in a wide range of biomedical applications, particularly in drug delivery and tissue engineering, such as studying cellular responses to different morphological surfaces.

Enhanced proliferation of PC12 neural cells on untreated, nanotextured glass coverslips

Traumatic injury to the central nervous system is a significant health problem. There is no effective treatment available partly because of the complexity of the system. Implementation of multifunctional micro- and nano-device based combinatorial therapeutics can provide biocompatible and tunable approaches to perform on-demand release of specific drugs. This can help the damaged cells to improve neuronal survival, regeneration of axons, and their reconnection to appropriate targets. Nano-topological features induced rapid cell growth is especially important towards the design of effective platforms to facilitate damaged neural circuit reconstruction. In this study, for the first time, feasibility of neuron-like PC12 cell growth on untreated and easy to prepare nanotextured surfaces has been carried out. The PC12 neuron-like cells were cultured on micro reactive ion etched  nanotextured glass coverslips. The effect of nanotextured topology as physical cue for the growth of PC12 cells was observed exclusively, eliminating the possible influence(s) of the enhanced concentration of coated materials on the surface. The cell density was observed to increase by almost 200% on nanotextured coverslips compared to plain coverslips. The morphology study indicated that PC12 cell attachment and growth on the nanotextured substrates did not launch any apoptotic machinery of the cell. Less than 5% cells deformed and depicted condensed nuclei with apoptotic bodies on nanotextured surfaces which is typical for the normal cell handling and culture. Enhanced PC12 cell proliferation by such novel and easy to prepare substrates is not only attractive for neurite outgrowth and guidance, but may be used to increase the affinity of similar cancerous cells (ex: B35 neuroblastoma) and rapid proliferation thereafter-towards the development of combinatorial theranostics to diagnose and treat aggressive cancers like neuroblastoma.