Anti-Inflammatory Peptide-Conjugated Silk Fibroin/Cryogel Hybrid Dual Fiber Scaffold with Hierarchical Structure Promotes Healing of Chronic Wounds

Chronic wounds resulting from diabetes, pressure, radiation therapy, and other factors continue to pose significant challenges in wound healing. To address this, this study introduces a novel hybrid fibroin fibrous scaffold (FFS) comprising randomly arranged fibroin fibers and vertically aligned cryogel fibers (CFs). The fibroin scaffold is efficiently degummed at room temperature and simultaneously formed a porous structure. The aligned CFs are produced via directional freeze-drying, achieved by controlling solution concentration and freezing polymerization temperature. The incorporation of aligned CFs into the expanded fibroin fiber scaffold leads to enhanced cell infiltration both in vitro and in vivo, further elevating the hybrid scaffold's tissue compatibility. The anti-inflammatory peptide 1 (AP-1) is also conjugated to the hybrid fibrous scaffold, effectively transforming the inflammatory status of chronic wounds from pro-inflammatory to pro-reparative. Consequently, the FFS-AP1+CF group demonstrates superior granulation tissue formation, angiogenesis, collagen deposition, and re-epithelialization during the proliferative phase compared to the commercial product PELNAC. Moreover, the FFS-AP1+CF group displays epidermis thickness, number of regenerated hair follicles, and collagen density closer to normal skin tissue. These findings highlight the potential of random fibroin fibers/aligned CFs hybrid fibrous scaffold as a promising approach for skin tissue filling and tissue regeneration.

Development of bioactive short fiber-reinforced printable hydrogels with tunable mechanical and osteogenic properties for bone repair

Personalized bone-regenerative materials have attracted substantial interest in recent years. Modern clinical settings demand the use of engineered materials incorporating patient-derived cells, cytokines, antibodies, and biomarkers to enhance the process of regeneration. In this work, we formulated short microfiber-reinforced hydrogels with platelet-rich fibrin (PRF) to engineer implantable multi-material core-shell bone grafts. By employing 3D bioprinting technology, we fabricated a core-shell bone graft from a hybrid composite hydroxyapatite-coated poly(lactic acid) (PLA) fiber-reinforced methacryolyl gelatin (GelMA)/alginate hydrogel. The overall concept involves 3D bioprinting of long bone mimic microstructures that resemble a core-shell cancellous-cortical structure, with a stiffer shell and a softer core with our engineered biomaterial. We observed a significantly enhanced stiffness in the hydrogel scaffold incorporated with hydroxyapatite (HA)-coated PLA microfibers compared to the pristine hydrogel construct. Furthermore, HA non-coated PLA microfibers were mixed with PRF and GelMA/alginate hydrogel to introduce a slow release of growth factors which can further enhance cell maturation and differentiation. These patient-specific bone grafts deliver cytokines and growth factors with distinct spatiotemporal release profiles to enhance tissue regeneration. The biocompatible and bio-responsive bone mimetic core-shell multi-material structures enhance osteogenesis and can be customized to have materials at a specific location, geometry, and material combination.

Copper-Cystine Biohybrid-Embedded Nanofiber Aerogels Show Antibacterial and Angiogenic Properties

Copper-cystine-based high aspect ratio structures (CuHARS) possess exceptional physical and chemical properties and exhibit remarkable biodegradability in human physiological conditions. Extensive testing has confirmed the biocompatibility and biodegradability of CuHARS under diverse biological conditions, making them a viable source of essential Cu2+. These ions are vital for catalyzing the production of nitric oxide (NO) from the decomposition of S-nitrosothiols (RSNOs) found in human blood. The ability of CuHARS to act as a Cu2+ donor under specific concentrations has been demonstrated in this study, resulting in the generation of elevated levels of NO. Consequently, this dual function makes CuHARS effective as both a bactericidal agent and a promoter of angiogenesis. In vitro experiments have shown that CuHARS actively promotes the migration and formation of complete lumens by redirecting microvascular endothelial cells. To maximize the benefits of CuHARS, they have been incorporated into biomimetic electrospun poly(ε-caprolactone)/gelatin nanofiber aerogels. Through the regulated release of Cu2+ and NO production, these channeled aerogels not only provide antibacterial support but also promote angiogenesis. Taken together, the inclusion of CuHARS in biomimetic scaffolds could hold great promise in revolutionizing tissue regeneration and wound healing.

Mechanically resilient hybrid aerogels containing fibers of dual-scale sizes and knotty networks for tissue regeneration

The structure and design flexibility of aerogels make them promising for soft tissue engineering, though they tend to come with brittleness and low elasticity. While increasing crosslinking density may improve mechanics, it also imparts brittleness. In soft tissue engineering, resilience against mechanical loads from mobile tissues is paramount. We report a hybrid aerogel that consists of self-reinforcing networks of micro- and nanofibers. Nanofiber segments physically entangle microfiber pillars, allowing efficient stress distribution through the intertwined fiber networks. We show that optimized hybrid aerogels have high specific tensile moduli (~1961.3 MPa cm3 g-1) and fracture energies (~7448.8 J m-2), while exhibiting super-elastic properties with rapid shape recovery (~1.8 s). We demonstrate that these aerogels induce rapid tissue ingrowth, extracellular matrix deposition, and neovascularization after subcutaneous implants in rats. Furthermore, we can apply them for engineering soft tissues via minimally invasive procedures, and hybrid aerogels can extend their versatility to become magnetically responsive or electrically conductive, enabling pressure sensing and actuation.

New dimensions of electrospun nanofiber material designs for biotechnological uses

Electrospinning technology has garnered wide attention over the past few decades in various biomedical applications including drug delivery, cell therapy, and tissue engineering. This technology can create nanofibers with tunable fiber diameters and functionalities. However, the 2D membrane nature of the nanofibers, as well as the rigidity and low porosity of electrospun fibers, lower their efficacy in tissue repair and regeneration. Recently, new avenues have been explored to resolve the challenges associated with 2D electrospun nanofiber membranes. This review discusses recent trends in creating different electrospun nanofiber microstructures from 2D nanofiber membranes by using various post-processing methods, as well as their biotechnological applications.

Biomimetic natural biomaterials for tissue engineering and regenerative medicine: new biosynthesis methods, recent advances, and emerging applications

Biomimetic materials have emerged as attractive and competitive alternatives for tissue engineering (TE) and regenerative medicine. In contrast to conventional biomaterials or synthetic materials, biomimetic scaffolds based on natural biomaterial can offer cells a broad spectrum of biochemical and biophysical cues that mimic the in vivo extracellular matrix (ECM). Additionally, such materials have mechanical adaptability, microstructure interconnectivity, and inherent bioactivity, making them ideal for the design of living implants for specific applications in TE and regenerative medicine. This paper provides an overview for recent progress of biomimetic natural biomaterials (BNBMs), including advances in their preparation, functionality, potential applications and future challenges. We highlight recent advances in the fabrication of BNBMs and outline general strategies for functionalizing and tailoring the BNBMs with various biological and physicochemical characteristics of native ECM. Moreover, we offer an overview of recent key advances in the functionalization and applications of versatile BNBMs for TE applications. Finally, we conclude by offering our perspective on open challenges and future developments in this rapidly-evolving field.

Cellulose-based composite scaffolds for bone tissue engineering and localized drug delivery

Natural bone constitutes a complex and organized structure of organic and inorganic components with limited ability to regenerate and restore injured tissues, especially in large bone defects. To improve the reconstruction of the damaged bones, tissue engineering has been introduced as a promising alternative approach to the conventional therapeutic methods including surgical interventions using allograft and autograft implants. Bioengineered composite scaffolds consisting of multifunctional biomaterials in combination with the cells and bioactive therapeutic agents have great promise for bone repair and regeneration. Cellulose and its derivatives are renewable and biodegradable natural polymers that have shown promising potential in bone tissue engineering applications. Cellulose-based scaffolds possess numerous advantages attributed to their excellent properties of non-toxicity, biocompatibility, biodegradability, availability through renewable resources, and the low cost of preparation and processing. Furthermore, cellulose and its derivatives have been extensively used for delivering growth factors and antibiotics directly to the site of the impaired bone tissue to promote tissue repair. This review focuses on the various classifications of cellulose-based composite scaffolds utilized in localized bone drug delivery systems and bone regeneration, including cellulose-organic composites, cellulose-inorganic composites, cellulose-organic/inorganic composites. We will also highlight the physicochemical, mechanical, and biological properties of the different cellulose-based scaffolds for bone tissue engineering applications.

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Cellulose and its derivatives are renewable and biodegradable natural polymers that with great potential for bone tissue engineering.

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Cellulose-based materials can be used various therapeutics directly to the bone to achieve bone regeneration.

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Bioinks made of cellulose-based materials hold great promise to develop patient specific solutions for bone repair using 3D printing.

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Challenges associated with inaccuracies in existing preclinical models, sterilization regulatory barriers still need to be addressed before clinical translation.

Extracellular Matrix Secretion Mechanically Reinforces Interlocking Interfaces

Drawing inspiration for biomaterials from biological systems has led to many biomedical innovations. One notable bioinspired device, Velcro, consists of two substrates with interlocking ability. Generating reversibly interlocking biomaterials is an area of investigation, as such devices can allow for modular tissue engineering, reversibly interlocking biomaterial interfaces, or friction-based coupling devices. Here, a biaxially interlocking interface generated using electrostatic flocking is reported. Two electrostatically flocked substrates are mechanically and reversibly interlocked with the ability to resist shearing and compression forces. An initial high-throughput screen of polyamide flock fibers with varying diameters and fiber lengths is conducted to elucidate the roles of different fiber parameters on scaffold mechanical properties. After determining the most desirable parameters via weight scoring, polylactic acid (PLA) fibers are used to emulate the ideal scaffold for in vitro use. PLA flocked scaffolds are populated with osteoblasts and interlocked. Interlocked flocked scaffolds improved cell survivorship under mechanical compression and sustained cell viability and proliferation. Additionally, the compression and shearing resistance of cell-seeded interlocking interfaces increased with increasing extracellular matrix deposition. The introduction of extracellular matrix-reinforced interlocking interfaces may serve as binders for modular tissue engineering, act as scaffolds for engineering tissue interfaces, or enable friction-based couplers for biomedical applications.

Thermoresponsive shear-thinning hydrogel (T-STH) hemostats for minimally invasive treatment of external hemorrhages

Hemorrhage is the leading cause of death following battlefield injuries. Although several hemostats are commercially available, they do not meet all the necessary requirements to stop bleeding in combat injuries. Here, we engineer thermoresponsive shear-thinning hydrogels (T-STH) composed of a thermoresponsive polymer, poly(N-isopropyl acrylamide) (p(NIPAM)), and hemostatic silicate nanodisks, LAPONITE®, as minimally invasive injectable hemostatic agents. Our T-STH is a physiologically stable hydrogel that can be easily injected through a syringe and needle and exhibits rapid mechanical recovery. Additionally, it demonstrates temperature-dependent blood coagulation owing to the phase transition of p(NIPAM). It decreases in vitro blood clotting times over 50% at physiological temperatures compared to room temperature. Furthermore, it significantly prevents blood loss in an ex vivo bleeding model at different blood flow rates (1 mL min^-1 and 5 mL min^-1) by forming a wound plug. More importantly, our T-STH is comparable to a commercially available hemostat, Floseal, in terms of blood loss and blood clotting time in an in vivo rat liver bleeding model. Furthermore, once the hemorrhage is stabilized, our T-STH can be easily removed using a cold saline wash without any rebleeding or leaving any residues. Taken together, our T-STH can be used as a first aid hemostat to treat external hemorrhages in emergency situations.

Nanofiber Aerogels with Precision Macrochannels and LL-37-Mimic Peptides Synergistically Promote Diabetic Wound Healing

Fast healing of diabetic wounds remains a major clinical challenge. Herein, this work reports a strategy to combine nanofiber aerogels containing precision macrochannels and the LL-37-mimic peptide W379 for rapid diabetic wound healing. Nanofiber aerogels consisting of poly(glycolide-co-lactide) (PGLA 90:10)/gelatin and poly-p-dioxanone (PDO)/gelatin short electrospun fiber segments were prepared by partially anisotropic freeze-drying, crosslinking, and sacrificial templating with three-dimensional (3D)-printed meshes, exhibiting nanofibrous architecture and precision micro-/macrochannels. Like human cathelicidin LL-37, W379 peptide at a concentration of 3 μg/mL enhanced the migration and proliferation of keratinocytes and dermal fibroblasts in a cell scratch assay and a proliferation assay. In vivo studies show that nanofiber aerogels with precision macrochannels can greatly promote cell penetration compared to aerogels without macrochannels. Relative to control and aerogels with and without macrochannels, adding W379 peptides to aerogels with precision macrochannels shows the best efficacy in healing diabetic wounds in mice in terms of cell infiltration, neovascularization, and re-epithelialization. The fast re-epithelization could be due to upregulation of phospho-extracellular signal-regulated kinase (p38 MAPK) after treatment with W379. Together, the approach developed in this work could be promising for the treatment of diabetic wounds and other chronic wounds.

Engineered Exosomes Containing Cathelicidin/LL-37 Exhibit Multiple Biological Functions

Exosomes show great potential in diagnostic and therapeutic applications. Inspired by the human innate immune defense, herein, we report engineered exosomes derived from monocytic cells treated with immunomodulating compounds 1α,25-dihydroxyvitamin D3, and CYP24A1 inhibitor VID400 which are slowly released from electrospun nanofiber matrices. These engineered exosomes contain significantly more cathelicidin/LL-37 when compared with exosomes derived from either untreated cells or Cathelicidin Human Tagged ORF Clone transfected cells. In addition, such exosomes exhibit multiple biological functions evidenced by killing bacteria, facilitating human umbilical vein endothelial cell tube formation, and enhancing skin cell proliferation and migration. Taken together, the engineered exosomes developed in this study can be used as therapeutics alone or in combination with other biomaterials for effective infection management, wound healing, and tissue regeneration.

Recent advances in biopolymer-based hemostatic materials

Hemorrhage is the leading cause of trauma-related deaths, in hospital and pre-hospital settings. Hemostasis is a complex mechanism that involves a cascade of clotting factors and proteins that result in the formation of a strong clot. In certain surgical and emergency situations, hemostatic agents are needed to achieve faster blood coagulation to prevent the patient from experiencing a severe hemorrhagic shock. Therefore, it is critical to consider appropriate materials and designs for hemostatic agents. Many materials have been fabricated as hemostatic agents, including synthetic and naturally derived polymers. However, compared to synthetic polymers, natural polymers or biopolymers, which include polysaccharides and polypeptides, have greater biocompatibility, biodegradability, and processibility. Thus, in this review, we focus on biopolymer-based hemostatic agents of different forms, such as powder, particles, sponges, and hydrogels. Finally, we discuss biopolymer-based hemostats currently in clinical trials and offer insight into next-generation hemostats for clinical translation.

Electrospun Nanofibers for Wound Management

Electrospun nanofibers show great potential in biomedical applications. This mini review article traces the recent advances in electrospun nanofibers for wound management via various approaches. Initially, we provide a short note on the four phases of wound healing, including hemostasis, inflammation, proliferation, and remodeling. Then, we state how the nanofiber dressings can stop bleeding and reduce the pain. Following that, we discuss the delivery of therapeutics and cells using different types of nanofibers for enhancing cell migration, angiogenesis, and re-epithelialization, resulting in the promotion of wound healing. Finally, we present the conclusions and future perspectives regarding the use of electrospun nanofibers for wound management.

Nanofiber capsules for minimally invasive sampling of biological specimens from gastrointestinal tract

Accurate and rapid point-of-care tissue and microbiome sampling is critical for early detection of cancers and infectious diseases and often result in effective early intervention and prevention of disease spread. In particular, the low prevalence of Barrett's and gastric premalignancy in the Western world makes population-based endoscopic screening unfeasible and cost-ineffective. Herein, we report a method that may be useful for prescreening the general population in a minimally invasive way using a swallowable, re-expandable, ultra-absorbable, and retrievable nanofiber cuboid and sphere produced by electrospinning, gas-foaming, coating, and crosslinking. The water absorption capacity of the cuboid- and sphere-shaped nanofiber objects is shown ∼6000% and ∼2000% of their dry mass. In contrast, unexpanded semicircular and square nanofiber membranes showed <500% of their dry mass. Moreover, the swallowable sphere and cuboid were able to collect and release more bacteria, viruses, and cells/tissues from solutions as compared with unexpanded scaffolds. In addition to that, an expanded sphere shows higher cell collection capacity from the esophagus inner wall as compared with the unexpanded nanofiber membrane. Taken together, the nanofiber capsules developed in this study could provide a minimally invasive method of collecting biological samples from the duodenal, gastric, esophagus, and oropharyngeal sites, potentially leading to timely and accurate diagnosis of many diseases. STATEMENT OF SIGNIFICANCE: Recently, minimally invasive technologies have gained much attention in tissue engineering and disease diagnosis. In this study, we engineered a swallowable and retrievable electrospun nanofiber capsule serving as collection device to collect specimens from internal organs in a minimally invasive manner. The sample collection device could be an alternative endoscopy to collect the samples from internal organs like jejunum, stomach, esophagus, and oropharynx without any sedation. The newly engineered nanofiber capsule could be used to collect, bacteria, virus, fluids, and cells from the abovementioned internal organs. In addition, the biocompatible and biodegradable nanofiber capsule on a string could exhibit a great sample collection capacity for the primary screening of Barret Esophagus, acid reflux, SARS-COVID-19, Helicobacter pylori, and gastric cancer.

Electrostatic flocking of salt-treated microfibers and nanofiber yarns for regenerative engineering

Electrostatic flocking is a textile technology that employs a Coulombic driving force to launch short fibers from a charging source towards an adhesive-covered substrate, resulting in a dense array of aligned fibers perpendicular to the substrate. However, electrostatic flocking of insulative polymeric fibers remains a challenge due to their insufficient charge accumulation. We report a facile method to flock electrostatically insulative poly(ε-caprolactone) (PCL) microfibers (MFs) and electrospun PCL nanofiber yarns (NFYs) by incorporating NaCl during pre-flock processing. Both MF and NFY were evaluated for flock functionality, mechanical properties, and biological responses. To demonstrate this platform's diverse applications, standalone flocked NFY and MF scaffolds were synthesized and evaluated as scaffold for cell growth. Employing the same methodology, scaffolds made from poly(glycolide-co-_l-lactide) (PGLA) (90:10) MFs were evaluated for their wound healing capacity in a diabetic mouse model. Further, a flock-reinforced polydimethylsiloxane (PDMS) disc was fabricated to create an anisotropic artificial vertebral disc (AVD) replacement potentially used as a treatment for lumbar degenerative disc disease. Overall, a salt-based flocking method is described with MFs and NFYs, with wound healing and AVD repair applications presented.

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NaCl coatings enable sufficient charge accumulation on electrically insulative polymer fibers during electrostatic flocking.

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Flocked nanofiber yarns allow further functionalization of flocked scaffolds.

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Flocked fiber scaffolds sustain cell proliferation.

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Flocked PGLA (90:10) fiber scaffolds promote modest fiber-density dependent wound healing and angiogenesis.

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Flock fibers-reinforced elastomeric artificial vertebral discs are mechanically robust.

Understanding and utilizing textile-based electrostatic flocking for biomedical applications

Electrostatic flocking immobilizes electrical charges to the surface of microfibers from a high voltage-connected electrode and utilizes Coulombic forces to propel microfibers toward an adhesive-coated substrate, leaving a forest of aligned fibers. This traditional textile engineering technique has been used to modify surfaces or to create standalone anisotropic structures. Notably, a small body of evidence validating the use of electrostatic flocking for biomedical applications has emerged over the past several years. Noting the growing interest in utilizing electrostatic flocking in biomedical research, we aim to provide an overview of electrostatic flocking, including the principle, setups, and general and biomedical considerations, and propose a variety of biomedical applications. We begin with an introduction to the development and general applications of electrostatic flocking. Additionally, we introduce and review some of the flocking physics and mathematical considerations. We then discuss how to select, synthesize, and tune the main components (flocking fibers, adhesives, substrates) of electrostatic flocking for biomedical applications. After reviewing the considerations necessary for applying flocking toward biomedical research, we introduce a variety of proposed use cases including bone and skin tissue engineering, wound healing and wound management, and specimen swabbing. Finally, we presented the industrial comments followed by conclusions and future directions. We hope this review article inspires a broad audience of biomedical, material, and physics researchers to apply electrostatic flocking technology to solve a variety of biomedical and materials science problems.

Electrostatic Flocking of Insulative and Biodegradable Polymer Microfibers for Biomedical Applications

Electrostatic flocking, a textile engineering technique, uses Coulombic driving forces to propel conductive microfibers toward an adhesive-coated substrate, leaving a forest of aligned fibers. Though an easy way to induce anisotropy along a surface, this technique is limited to microfibers capable of accumulating charge. This study reports a novel method, utilizing principles from the percolation theory to make electrically insulative polymeric microfibers flockable. A variety of well-mixed, conductive materials are added to multiple insulative and biodegradable polymer microfibers during wet spinning, which enables nearly all types of polymer microfibers to accumulate sufficient charges required for flocking. Biphasic, biodegradable scaffolds are fabricated by flocking silver nanoparticle (AgNP)-filled poly(ε-caprolactone) (PCL) microfibers onto substrates made from 3D printing, electrospinning, and thin-film casting. The incorporation of AgNP into PCL fibers and use of chitosan-based adhesive enables antimicrobial activity against methicillin-resistant Staphylococcus aureus. The fabricated scaffolds demonstrate both favorable in vitro cell response and new tissue formation after subcutaneous implantation in rats, as evident by newly formed blood vessels and infiltrated cells. This technology opens the door for using previously unflockable polymer microfibers as surface modifiers or standalone structures in various engineering fields.

Biomaterials with structural hierarchy and controlled 3D nanotopography guide endogenous bone regeneration

Biomaterials without exogenous cells or therapeutic agents often fail to achieve rapid endogenous bone regeneration with high quality. Here, we reported a class of three-dimensional (3D) nanofiber scaffolds with hierarchical structure and controlled alignment for effective endogenous cranial bone regeneration. 3D scaffolds consisting of radially aligned nanofibers guided and promoted the migration of bone marrow stem cells from the surrounding region to the center in vitro. These scaffolds showed the highest new bone volume, surface coverage, and mineral density among the tested groups in vivo. The regenerated bone exhibited a radially aligned fashion, closely recapitulating the scaffold's architecture. The organic phase in regenerated bone showed an aligned, layered, and densely packed structure, while the inorganic mineral phase showed a uniform distribution with smaller pore size and an even distribution of stress upon the simulated compression. We expect that this study will inspire the design of next-generation biomaterials for effective endogenous bone regeneration with desired quality.

Freeze-Casting with 3D-Printed Templates Creates Anisotropic Microchannels and Patterned Macrochannels within Biomimetic Nanofiber Aerogels for Rapid Cellular Infiltration

A new approach is described for fabricating 3D poly(ε-caprolactone) (PCL)/gelatin (1:1) nanofiber aerogels with patterned macrochannels and anisotropic microchannels by freeze-casting with 3D-printed sacrificial templates. Single layer or multiple layers of macrochannels are formed through an inverse replica of 3D-printed templates. Aligned microchannels formed by partially anisotropic freezing act as interconnected pores between templated macrochannels. The resulting macro-/microchannels within nanofiber aerogels significantly increase preosteoblast infiltration in vitro. The conjugation of vascular endothelial growth factor (VEGF)-mimicking QK peptide to PCL/gelatin/gelatin methacryloyl (1:0.5:0.5) nanofiber aerogels with patterned macrochannels promotes the formation of a microvascular network of seeded human microvascular endothelial cells. Moreover, nanofiber aerogels with patterned macrochannels and anisotropic microchannels show significantly enhanced cellular infiltration rates and host tissue integration compared to aerogels without macrochannels following subcutaneous implantation in rats. Taken together, this novel class of nanofiber aerogels holds great potential in biomedical applications including tissue repair and regeneration, wound healing, and 3D tissue/disease modeling.

Ultra-absorptive Nanofiber Swabs for Improved Collection and Test Sensitivity of SARS-CoV-2 and other Biological Specimens

Following the COVID-19 outbreak, swabs for biological specimen collection were thrust to the forefront of healthcare materials. Swab sample collection and recovery are vital for reducing false negative diagnostic tests, early detection of pathogens, and harvesting DNA from limited biological samples. In this study, we report a new class of nanofiber swabs tipped with hierarchical 3D nanofiber objects produced by expanding electrospun membranes with a solids-of-revolution-inspired gas foaming technique. Nanofiber swabs significantly improve absorption and release of proteins, cells, bacteria, DNA, and viruses from solutions and surfaces. Implementation of nanofiber swabs in SARS-CoV-2 detection reduces the false negative rates at two viral concentrations and identifies SARS-CoV-2 at a 10× lower viral concentration compared to flocked and cotton swabs. The nanofiber swabs show great promise in improving test sensitivity, potentially leading to timely and accurate diagnosis of many diseases.

3D Hybrid Nanofiber Aerogels Combining with Nanoparticles Made of a Biocleavable and Targeting Polycation and MiR-26a for Bone Repair

The healing of large bone defects represents a clinical challenge, often requiring some form of grafting. Three-dimensional (3D) nanofiber aerogels could be a promising bone graft due to their biomimetic morphology and controlled porous structures and composition. miR-26a has been reported to induce the differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) and facilitate bone formation. Introducing miR-26a with a suitable polymeric vector targeting BMSCs could improve and enhance the functions of 3D nanofiber aerogels for bone regeneration. Herein, we first developed the comb-shaped polycation (HA-SS-PGEA) carrying a targeting component, biocleavable groups and short ethanolamine (EA)-decorated poly(glycidyl methacrylate) (PGMA) (abbreviated as PGEA) arms as miR-26a delivery vector. We then assessed the cytotoxicity and transfection efficiency of this polycation and cellular response to miR-26a-incorporated nanoparticles (NPs) in vitro. HA-SS-PGEA exhibited a stronger ability to transport miR-26a and exert its functions than the gold standard polyethyleneimine (PEI) and low-molecular-weight linear PGEA. We finally examined the efficacy of HA-SS-PGEA/miR-26a NPs loaded 3D hybrid nanofiber aerogels showing a positive effect on the cranial bone defect healing. Together, the combination of 3D nanofiber aerogels and functional NPs consisting of a biodegradable and targeting polycation and therapeutic miRNA could be a promising approach for bone regeneration.

Periosteum Mimetic Coating on Structural Bone Allografts via Electrospray Deposition Enhances Repair and Reconstruction of Segmental Defects

Structural bone allograft transplantation remains one of the common strategies for repair and reconstruction of large bone defects. Due to the loss of periosteum that covers the outer surface of the cortical bone, the healing and incorporation of allografts is extremely slow and limited. To enhance the biological performance of allografts, herein, we report a novel and simple approach for engineering a periosteum mimetic coating on the surface of structural bone allografts via polymer-mediated electrospray deposition. This approach enables the coating on allografts with precisely controlled composition and thickness. In addition, the periosteum mimetic coating can be tailored to achieve desired drug release profiles by making use of an appropriate biodegradable polymer or polymer blend. The efficacy study in a murine segmental femoral bone defect model demonstrates that the allograft coating composed of poly(lactic-co-glycolic acid) and bone morphogenetic protein-2 mimicking peptide significantly improves allograft healing as evidenced by decreased fibrotic tissue formation, increased periosteal bone formation, and enhanced osseointegration. Taken together, this study provides a platform technology for engineering a periosteum mimetic coating which can greatly promote bone allograft healing. This technology could eventually result in an off-the-shelf and multifunctional structural bone allograft for highly effective repair and reconstruction of large segmental bone defects. The technology can also be used to ameliorate the performance of other medical implants by modifying their surfaces.

Converting 2D Nanofiber Membranes to 3D Hierarchical Assemblies with Structural and Compositional Gradients Regulates Cell Behavior

New methods are described for converting 2D electrospun nanofiber membranes to 3D hierarchical assemblies with structural and compositional gradients. Pore-size gradients are generated by tuning the expansion of 2D membranes in different layers with incorporation of various amounts of a surfactant during the gas-foaming process. The gradient in fiber organizations is formed by expanding 2D nanofiber membranes composed of multiple regions collected by varying rotating speeds of mandrel. A compositional gradient on 3D assemblies consisting of radially aligned nanofibers is prepared by dripping, diffusion, and crosslinking. Bone mesenchymal stem cells (BMSCs) on the 3D nanofiber assemblies with smaller pore size show significantly higher expression of hypoxia-related markers and enhanced chondrogenic differentiation compared to BMSCs cultured on the assemblies with larger pore size. The basic fibroblast growth factor gradient can accelerate fibroblast migration from the surrounding area to the center in an in vitro wound healing model. Taken together, 3D nanofiber assemblies with gradients in pore sizes, fiber organizations, and contents of signaling molecules can be used to engineer tissue constructs for tissue repair and build biomimetic disease models for studying disease biology and screening drugs, in particular, for interface tissue engineering and modeling.

Dissolvable Microneedles Coupled with Nanofiber Dressings Eradicate Biofilms via Effectively Delivering a Database-Designed Antimicrobial Peptide

Biofilms in chronic wounds, including diabetic foot ulcers, pressure ulcers, and venous leg ulcers, pose a major challenge to wound management. Herein, we report a Janus-type antimicrobial dressing for eradication of biofilms in chronic wounds. The dressing consists of electrospun nanofiber membranes coupled with dissolvable microneedle arrays to enable effective delivery of a database-designed antimicrobial peptide to both inside and outside biofilms. This antimicrobial dressing exhibited high efficacy against a broad spectrum of resistant pathogens in vitro. Importantly, such a dressing was able to eradicate methicillin-resistant Staphylococcus aureus (MRSA) biofilms in both an ex vivo human skin wound infection model and a type II diabetic mouse wound infection model after daily treatment without applying surgical debridement. Most importantly, the dressing can also completely remove the Pseudomonas aeruginosa and MRSA, dual-species biofilm in an ex vivo human skin infection model. In addition, our computational simulations also suggested that microneedles were more effective in the delivery of peptides to the biofilms than free drugs. Our results indicate that the Janus-type antimicrobial dressings may provide an effective treatment and management of chronic wound polymicrobial infections.

Fast transformation of 2D nanofiber membranes into pre-molded 3D scaffolds with biomimetic and oriented porous structure for biomedical applications

The ability to transform two-dimensional (2D) structures into three-dimensional (3D) structures leads to a variety of applications in fields such as soft electronics, soft robotics, and other biomedical-related fields. Previous reports have focused on using electrospun nanofibers due to their ability to mimic the extracellular matrix. These studies often lead to poor results due to the dense structures and small poor sizes of 2D nanofiber membranes. Using a unique method of combining innovative gas-foaming and molding technologies, we report the rapid transformation of 2D nanofiber membranes into predesigned 3D scaffolds with biomimetic and oriented porous structure. By adding a surfactant (pluronic F-127) to poly(ε-caprolactone) (PCL) nanofibers, the rate of expansion is dramatically enhanced due to the increase in hydrophilicity and subsequent gas bubble stability. Using this novel method together with molding, 3D objects with cylindrical, hollow cylindrical, cuboid, spherical, and irregular shapes are created. Interestingly, these 3D shapes exhibit anisotropy and consistent pore sizes throughout entire object. Through further treatment with gelatin, the scaffolds become superelastic and shape-recoverable. Additionally, gelatin-coated, cube-shaped scaffolds were further functionalized with polypyrrole coatings and exhibited dynamic electrical conductivity during cyclic compression. Cuboid-shaped scaffolds have been demonstrated to be effective for compressible hemorrhage in a porcine liver injury model. In addition, human neural progenitor cells can be uniformly distributed and differentiated into neurons throughout the cylinder-shaped nanofiber scaffolds, forming ordered 3D neural tissue constructs. Taken together, the approach presented in this study is very promising in the production of pre-molded 3D nanofiber scaffolds for many biomedical applications.

New forms of electrospun nanofiber materials for biomedical applications

Over the past two decades, electrospinning has emerged as an enabling nanotechnology to produce nanofiber materials for various biomedical applications. In particular, therapeutic/cellloaded nanofiber scaffolds have been widely examined in drug delivery, wound healing, and tissue repair and regeneration. However, due to the insufficient porosity, small pore size, noninjectability, and inaccurate spatial control in nanofibers of scaffolds, many efforts have been devoted to exploring new forms of nanofiber materials including expanded nanofiber scaffolds, nanofiber aerogels, short nanofibers, and nanofiber microspheres. This short review discusses the preparation and potential biomedical applications of new forms of nanofiber materials.

Engineering Biomimetic Nanofiber Microspheres with Tailored Size, Predesigned Structure, and Desired Composition via Gas Bubble-Mediated Coaxial Electrospray

Minimally invasive therapies avoiding surgical complexities evoke great interest in developing injectable biomedical devices. Herein, a versatile approach is reported for engineering injectable and biomimetic nanofiber microspheres (NMs) with tunable sizes, predesigned structures, and desired compositions via gas bubble-mediated coaxial electrospraying. The sizes and structures of NMs are controlled by adjusting processing parameters including air flow rate, applied voltage, distance, and spinneret configuration in the coaxial setup. Importantly, unlike the self-assembly method, this technique can be used to fabricate NMs from any material feasible for electrospinning or other nanofiber fabrication techniques. To demonstrate the versatility, open porous NMs are successfully fabricated that consist of various short nanofibers made of poly(ε-caprolactone), poly(lactic-co-glycolic acid), gelatin, methacrylated gelatin, bioglass, and magneto-responsive polymer composites. Open porous NMs support human neural progenitor cell growth in 3D with a larger number and more neurites than nonporous NMs. Additionally, highly open porous NMs show faster cell infiltration and host tissue integration than nonporous NMs after subcutaneous injection to rats. Such a novel class of NMs holds great potential for many biomedical applications such as tissue filling, cell and drug delivery, and minimally invasive tissue regeneration.

Mesenchymal stem cell-laden, personalized 3D scaffolds with controlled structure and fiber alignment promote diabetic wound healing

The management of diabetic wounds remains a major therapeutic challenge in clinics. Herein, we report a personalized treatment using 3D scaffolds consisting of radially or vertically aligned nanofibers in combination with bone marrow mesenchymal stem cells (BMSCs). The 3D scaffolds have customizable sizes, depths, and shapes, enabling them to fit a variety of type 2 diabetic wounds. In addition, the 3D scaffolds are shape-recoverable in atmosphere and water following compression. The BMSCs-laden 3D scaffolds are capable of enhancing the formation of granulation tissue, promoting angiogenesis, and facilitating collagen deposition. Further, such scaffolds inhibit the formation of M1-type macrophages and the expression of pro-inflammatory cytokines IL-6 and TNF-α and promote the formation of M2-type macrophages and the expression of anti-inflammatory cytokines IL-4 and IL-10. Taken together, BMSCs-laden, 3D nanofiber scaffolds with controlled structure and alignment hold great promise for the treatment of diabetic wounds. STATEMENT OF SIGNIFICANCE: In this study, we developed 3D radially and vertically aligned nanofiber scaffolds to transplant bone marrow mesenchymal stem cells (BMSCs). We personalized 3D scaffolds that could completely match the size, depth, and shape of diabetic wounds. Moreover, both the radially and vertically aligned nanofiber scaffolds could completely recover their shape and maintain structural integrity after repeated loads with compressive stresses. Furthermore, the BMSCs-laden 3D scaffolds are able to promote granulation tissue formation, angiogenesis, and collagen deposition, and switch the immune responses to the pro-regenerative direction. These 3D scaffolds consisting of radially or vertically aligned nanofibers in combination with BMSCs offer a robust, customizable platform potentially for a significant improvement of managing diabetic wounds.

Dual Delivery of Alendronate and E7-BMP-2 Peptide via Calcium Chelation to Mineralized Nanofiber Fragments for Alveolar Bone Regeneration

The fixation and stability of dental implants is governed by the quality of the underlying alveolar bone. The current study investigates if the dual delivery of calcium chelating bone therapeutics from mineralized nanofiber fragments can help regenerate alveolar bone in vivo. Alendronate (ALN) or/and bone morphogenetic protein-2-mimicking peptide conjugated to a heptaglutamate moiety (E7-BMP-2) were incorporated onto mineralized nanofiber fragments of polylactide-co-glycolide-collagen-gelatin (PCG in 2:1:1 weight ratios) via calcium coupling/chelation. Two mg of the single-loaded (ALN) and coloaded (ALN + E7-BMP-2) mineralized nanofiber PCG grafts was filled into critical-sized (2 mm diameter × 2 mm depth) alveolar bone defects in rat maxillae and let heal for 4 weeks. X-ray microcomputed tomography analysis of the retrieved maxillae revealed significantly elevated new bone formation parameters for the ALN and ALN + E7-BMP-2 groups compared with the unfilled defect controls. However, no significant differences between the single and coloaded nanofiber grafts were noted. Furthermore, the histopathological analysis of the tissue sections divulged islands of new bone tissue in the ALN and ALN + E7-BMP-2 groups, whereas the control defect was covered with gingival tissue. Together, the presented strategy using mineralized nanofiber fragments in the sustained delivery of dual calcium chelating therapeutics could have potential applications in enhancing bone regeneration.

Tethering peptides onto biomimetic and injectable nanofiber microspheres to direct cellular response

Biomimetic and injectable nanofiber microspheres (NMs) could be ideal candidate for minimally invasive tissue repair. Herein, we report a facile approach to fabricate peptide-tethered NMs by combining electrospinning, electrospraying, and surface conjugation techniques. The composition and size of NMs can be tuned by varying the processing parameters during the fabrication. Further, bone morphogenic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF) mimicking peptides have been successfully tethered onto poly(ε-caprolactone) (PCL):gelatin:(gelatin-methacryloyl) (GelMA)(1:0.5:0.5) NMs through photocrosslinking of the methacrylic group in GelMA and octenyl alanine (OCTAL) in the modified peptides. The BMP-2-OCTAL peptide-tethered NMs significantly promote osteogenic differentiation of bone marrow-derived stem cells (BMSCs). Moreover, human umbilical vein endothelial cells (HUVECs) seeded on VEGF mimicking peptide QK-OCTAL-tethered NMs significantly up-regulated vascular-specific proteins, leading to microvascularization. The strategy developed in this work holds great potential in developing a biomimetic and injectable carrier to efficiently direct cellular response (Osteogenesis and Angiogenesis) for tissue repair.

pH/redox dual stimuli-responsive sheddable nanodaisies for efficient intracellular tumour-triggered drug delivery

A series of dual stimuli-responsive poly(l-histidine)_n-S-S-polyurethane-S-S-poly(l-histidine)_n [p(His)_n-SS-PU-SS-p(His)_n; n = 25, 35, 50, and 75] triblock copolymers that bear two pH-responsive p(His)_n end-blocks and PU middle-blocks tethered by a redox-responsive disulphide linker have been synthesized. The resulting triblock copolymers self-assemble to form micelles, nanodaisies (NDs), of uniform size (∼100 nm) and efficiently encapsulate the anticancer drug doxorubicin (Dox) with a high drug loading content (∼19%). The in vitro release profile shows an enhanced release of Dox in an acidic environment in the presence of 10 mM glutathione. The in vitro cell viability assays performed in various cell lines show that the NDs have no acute or intrinsic toxicity. Confocal microscopy images and flow cytometry results show the pH-responsive cellular uptake of Dox-loaded NDs, accelerated at pH ≤ 5.0. The tumour accumulation and in vivo bio-distribution studies of near-infrared dye (IR-820)-labeled NDs show higher tumour accumulation in CT26 tumour-bearing mice within 72 h. Furthermore, the Dox-loaded NDs effectively inhibit the CT26 tumours, suggesting that they are promising nanocarriers for cancer therapy.

Phospholipid End-Capped Acid-Degradable Polyurethane Micelles for Intracellular Delivery of Cancer Therapeutics

Nanoscale drug carriers fabricated by phospholipid end-capped polyurethane bearing acetal backbones that degrade in acidic conditions are fabricated. These micelles effectively allow drugs to enter the blood circulation, and then disintegrate in acidic endosomes and lysosomes for intelligent delivery of payloads.

Tumor homing indocyanine green encapsulated micelles for near infrared and photoacoustic imaging of tumors

Photoacoustic imaging (PAI) is an emerging analytical modality that is under intense preclinical development for the early diagnosis of various medical conditions, including cancer. However, the lack of specific tumor targeting by various contrast agents used in PAI obstructs its clinical applications. In this study, we developed indocyanine green (ICG)-encapsulated micelles specific for the CD 44 receptor and used in near infrared and photoacoustic imaging of tumors. ICG was hydrophobically modified prior to loading into hyaluronic acid (HA)-based micelles utilized for CD 44 based-targeting. We investigated the physicochemical characteristics of prepared HA only and ICG-encapsulated HA micelles (HA-ICG micelles). After intravenous injection of tumor-bearing mice, the bio-distribution and in vivo photoacoustic images of ICG-encapsulated HA micelles accumulating in tumors were also investigated. Our study further encourages the application of this HA-ICG-based nano-platform as a tumor-specific contrast agent for PAI.

Dual Stimuli-Responsive Vesicular Nanospheres Fabricated by Lipopolymer Hybrids for Tumor-Targeted Photodynamic Therapy

Smart delivery system of photosensitizer chlorin e6 (Ce6) has been developed for targeted photodynamic therapy (PDT). Simple self-assemblies of the mixtures comprising soybean lecithin derived phosphatidylcholine (PC), phosphatidylethanolamine-poly(L-histidine)40 (PE-p(His)40), and folic acid (FA) conjugated phosphatidylethanolamine-poly(N-isopropylacrylamide)40 (PE-p(NIPAM)40-FA) in different ratios yield smart nanospheres characterized by (i) stable and uniform particle size (∼100 nm), (ii) positive surface charge, (iii) high hydrophobic drug (Ce6) loading efficiency up to 45%, (iv) covalently linked targeting moiety, (v) low cytotoxicity, and (vi) smartness showing p(His) block oriented pH and p(NIPAM) oriented temperature responsiveness. The Ce6-encapsulated vesicular nanospheres (Ce6@VNS) were used to confirm the efficiency of cellular uptake, intracellular distribution, and phototoxicity against KB tumor cells compared to free Ce6 at different temperature and pH conditions. The Ce6@VNS system showed significant photodynamic therapeutic efficiency on KB cells than free Ce6. A receptor-mediated inhibition study proved the site-specific delivery of Ce6 in targeted tumor cells.

Poly(PEGA)-b-poly(L-lysine)-b-poly(L-histidine) Hybrid Vesicles for Tumoral pH-Triggered Intracellular Delivery of Doxorubicin Hydrochloride

A series of poly(ethylene glycol) methyl ether acrylate-block-poly(L-lysine)-block-poly(L-histidine) [p(PEGA)30-b-p(Lys)25-b-p(His)n] (n = 25, 50, 75, 100) triblock copolypeptides were designed and synthesized for tumoral pH-responsive intracellular release of anticancer drug doxorubicin hydrochloride (Dox). The tumoral acidic pH-responsive hybrid vesicles fabricated were stable at physiological pH 7.4 and could gradually destabilize in acidic pH as a result of pH-induced swelling of the p(His) block. The blank vesicles were nontoxic over a wide concentration range (0.01-100 μg/mL) in normal cell lines. The tumor acidic pH responsiveness of these vesicles was exploited for intracellular delivery of Dox. Vesicles efficiently encapsulated Dox, and pH-induced destabilization resulted in the controlled and sustained release of Dox in CT26 murine cancer cells, and dose-dependent cytotoxicity. The tumor-specific controlled release Dox from vesicles demonstrates this system represents a promising theranostic agent for tumor-targeted delivery.

Polymer-Block-Polypeptides and Polymer-Conjugated Hybrid Materials as Stimuli-Responsive Nanocarriers for Biomedical Applications

Stimuli-responsive nanocarriers are a class of soft materials that includes natural polymers, synthetic polymers, and polypeptides. Recently, modern synthesis tools such as atom transfer radical polymerization, reversible addition-fragmentation chain transfer polymerization, nitroxide-mediated radical polymerization, ring-opening polymerization of α-amino acid N-carboxyanhydrides, and various "click" chemistry strategies were simultaneously employed for the design and synthesis of nanosized drug delivery vehicles. Importantly, the research focused on the improvement of the nanocarrier targetability and the site-specific, triggered release of therapeutics with high drug loading efficiency and minimal drug leakage during the delivery to specific targets. In this context, nanocarriers responsive to common stimuli such as pH, temperature, redox potential, light, etc. have been widely used for the controlled delivery of therapeutics to pathological sites. Currently, different synthesis and self-assembly strategies improved the drug loading efficacy and targeted delivery of therapeutic agents to the desired site. In particular, polypeptide-containing hybrid materials have been developed for the controlled delivery of therapeutic agents. Therefore, stimuli-sensitive synthetic polypeptide-based materials have been extensively investigated in recent years. This review focuses on recent advances in the development of polymer-block-polypeptides and polymer-conjugated hybrid materials that have been designed and evaluated for various stimuli-responsive drug and gene delivery applications.

Folic acid-tethered poly(N-isopropylacrylamide)–phospholipid hybrid nanocarriers for targeted drug delivery

Folic acid-tethered poly(N-isopropylacrylamide)–phospholipid nanocarriers exhibit tumour targetability and temperature responsive Doxorubicin releasing behaviour under physiological conditions.