An ice-templated, linearly aligned chitosan-alginate scaffold for neural tissue engineering

Comparative analysis of aligned and random amniotic membrane-derived cryogels for neural tissue repair

The ordered arrangement of cells and extracellular matrix facilitates the seamless transmission of electrical signals along axons in the spinal cord and peripheral nerves. Therefore, restoring tissue geometry is crucial for neural regeneration. This study presents a novel method using proteins derived from the human amniotic membrane, which is modified with photoresponsive groups, to produce cryogels with aligned porosity. Freeze-casting was used to produce cryogels with longitudinally aligned pores, while cryogels with randomly distributed porosity were used as the control. The cryogels exhibited remarkable injectability and shape-recovery properties, essential for minimally invasive applications. Different tendencies in proliferation and differentiation were evident between aligned and random cryogels, underscoring the significance of the scaffold's microstructure in directing the behaviour of neural stem cells (NSC). Remarkably, aligned cryogels facilitated extensive cellular infiltration and migration, contrasting with NSC cultured on isotropic cryogels, which predominantly remained on the scaffold's surface throughout the proliferation experiment. Significantly, the proliferation assay demonstrated that on day 7, the aligned cryogels contained eight times more cells compared to the random cryogels. Consistent with the proliferation experiments, NSC exhibited the ability to differentiate into neurons within the aligned scaffolds and extend neurites longitudinally. In addition, differentiation assays showed a four-fold increase in the expression of neural markers in the cross-sections of the aligned cryogels. Conversely, the random cryogels exhibited minimal presence of cell bodies and extensions. The presence of synaptic vesicles on the anisotropic cryogels indicates the formation of functional synaptic connections, emphasizing the importance of the scaffold's microstructure in guiding neuronal reconnection.

Sulfated Alginate for Biomedical Applications

Alginate (Alg) polymers have received much attention due to the mild conditions required for gel formation and their good bio-acceptability. However, due to limited interactions with cells, many drugs, and biomolecules, chemically modified alginates are of great interest. Sulfated alginate (S-Alg) is a promising heparin-mimetic that continues to be investigated both as a drug molecule and as a component of biomaterials. Herein, the S-Alg literature of the past five years (2017-2023) is reviewed. Several methods used to synthesize S-Alg are described, with a focus on new advances in characterization and stereoselectivity. Material fabrication is another focus and spans bulk materials, particles, scaffolds, coatings, and part of multicomponent biomaterials. The new application of S-Alg as an antitumor agent is highlighted together with studies evaluating safety and biodistribution. The high binding affinity of S-Alg for various drugs and heparin-binding proteins is exploited extensively in biomaterial design to tune the encapsulation and release of these agents and this aspect is covered in detail. Recommondations include publishing key material properties to allow reproducibility, careful selection of appropriate sulfation strategies, the use of cross-linking strategies other than ionic cross-linking for material fabrication, and more detailed toxicity and biodistribution studies to inform future work.

Biomaterial strategies for regulating the neuroinflammatory response

Injury and disease in the central nervous system (CNS) can result in a dysregulated inflammatory environment that inhibits the repair of functional tissue. Biomaterials present a promising approach to tackle this complex inhibitory environment and modulate the mechanisms involved in neuroinflammation to halt the progression of secondary injury and promote the repair of functional tissue. In this review, we will cover recent advances in biomaterial strategies, including nanoparticles, hydrogels, implantable scaffolds, and neural probe coatings, that have been used to modulate the innate immune response to injury and disease within the CNS. The stages of inflammation following CNS injury and the main inflammatory contributors involved in common neurodegenerative diseases will be discussed, as understanding the inflammatory response to injury and disease is critical for identifying therapeutic targets and designing effective biomaterial-based treatment strategies. Biomaterials and novel composites will then be discussed with an emphasis on strategies that deliver immunomodulatory agents or utilize cell-material interactions to modulate inflammation and promote functional tissue repair. We will explore the application of these biomaterial-based strategies in the context of nanoparticle- and hydrogel-mediated delivery of small molecule drugs and therapeutic proteins to inflamed nervous tissue, implantation of hydrogels and scaffolds to modulate immune cell behavior and guide axon elongation, and neural probe coatings to mitigate glial scarring and enhance signaling at the tissue-device interface. Finally, we will present a future outlook on the growing role of biomaterial-based strategies for immunomodulation in regenerative medicine and neuroengineering applications in the CNS.

Recent Advances in Alginate-Based Hydrogels for Cell Transplantation Applications

With its exceptional biocompatibility, alginate emerged as a highly promising biomaterial for a large range of applications in regenerative medicine. Whether in the form of microparticles, injectable hydrogels, rigid scaffolds, or bioinks, alginate provides a versatile platform for encapsulating cells and fostering an optimal environment to enhance cell viability. This review aims to highlight recent studies utilizing alginate in diverse formulations for cell transplantation, offering insights into its efficacy in treating various diseases and injuries within the field of regenerative medicine.

Hesperidin guided injured spinal cord neural regeneration with a combination of MWCNT-collagen-hyaluronic acid composite: In-vitro analysis

Restoring the lost bioelectrical signal transmission along with the appropriate microenvironment is one of the major clinical challenges in spinal cord regeneration. In the current research, we developed a polysaccharide-based protein composite Multiwalled Carbon Nanotubes (MWCNTs)/ Collagen (Col)/ Hyaluronic acid (HA) composite with Hesperidin (Hes) natural compound to investigate its combined therapeutic effect along with biocompatibility, antioxidant activity, and electrical conductivity. The multifunctional composites were characterized via FT-IR, XRD, SEM, HR-TEM, BET, C.V, and EIS techniques. The electrical conductivity and modulus of the MWCNT-Col-HA-Hes were 0.06 S/cm and 12.3 kPa, similar to the native spinal cord. The in-vitro Cytotoxicity, cell viability, antioxidant property, and cell migration ability of the prepared composites were investigated with a PC-12 cell line. In-vitro studies revealed that the multifunctional composites show higher cell viability, antioxidant, and cell migration properties than the control cells. Reduction of ROS level indicates that the Hes presence in the composite could reduce the cell stress by protecting it from oxidative damage and promoting cell migration towards the lesion site. The developed multifunctional composite can provide the antioxidant microenvironment with compatibility and mimic the native spinal cord by providing appropriate conductivity and mechanical strength for spinal cord tissue regeneration.

Citrus peel pectin and alginate-based emulgel particles for small intestine-targeted oral delivery of curcumin

Polysaccharides are a prominent choice in the realm of food-grade oral delivery systems due to their resistance to degradation by digestive enzymes in the oral, gastric, and small intestinal environments, as well as their ease of production, cost-effectiveness, and potential health benefits as prebiotics. Furthermore, their ability to respond to pH-induced dissolution, along with their emulsifying properties, can be strategically employed to achieve precise targeting of lipophilic bioactives to the small intestine. In this study, citrus peel pectin and alginate served as stabilizers for emulgel particles without supplementary emulsifiers or gelling agents. Within this system, pectin functioned as an emulsifier, while alginate acted as a gelling agent, facilitated by Ca2+-induced ionic crosslinking. The synergistic interplay between pectin and alginate efficiently protected curcumin in gastric conditions and controlled dissolution in the small intestine, depending on the pectin/alginate ratio. These controlled phenomena facilitated lipolysis, curcumin release, and ultimately enhanced curcumin bioaccessibility. Furthermore, once the emulgel particle released all the entrapped curcumin in the small intestine, residual polysaccharides underwent facile degradation by pectinase and alginate lyase, yielding fermentable monosaccharides. This confirms the potential of the emulgel particles for use as a prebiotic in the colon. These findings offer significant promise for enhancing the systematic design of food-grade delivery systems that encapsulate lipophilic bioactives, achieving controlled release, enhanced stability, and improved bioaccessibility. Importantly, this system can comprise components that undergo complete digestion, absorption, and utilization in the human body, encompassing materials such as oil, nutraceuticals, and prebiotics, all without presenting health risks.

Porous biomaterial scaffolds for skeletal muscle tissue engineering

Volumetric muscle loss is a traumatic injury which overwhelms the innate repair mechanisms of skeletal muscle and results in significant loss of muscle functionality. Tissue engineering seeks to regenerate these injuries through implantation of biomaterial scaffolds to encourage endogenous tissue formation and to restore mechanical function. Many types of scaffolds are currently being researched for this purpose. Scaffolds are typically made from either natural, synthetic, or conductive polymers, or any combination therein. A major criterion for the use of scaffolds for skeletal muscle is their porosity, which is essential for myoblast infiltration and myofiber ingrowth. In this review, we summarize the various methods of fabricating porous biomaterial scaffolds for skeletal muscle regeneration, as well as the various types of materials used to make these scaffolds. We provide guidelines for the fabrication of scaffolds based on functional requirements of skeletal muscle tissue, and discuss the general state of the field for skeletal muscle tissue engineering.

Tensile properties of freeze-cast collagen scaffolds: How processing conditions affect structure and performance in the dry and fully hydrated states

Tensile properties of directionally freeze-cast biopolymer scaffolds are rarely reported, even though they are of interest from a fundamental science perspective and critical in applications such as scaffolds for the regeneration of nerves or when used as ureteral stents. The focus of this study is on collagen scaffolds freeze-cast with two different applied cooling rates (10 °C/min and 1 °C/min) in two freezing directions (longitudinal and radial). Reported are the results of a systematic structural characterization of dry scaffolds by scanning electron microscopy and the mechanical characterization in tension of both dry and fully hydrated scaffolds. Systematic structure-property-processing correlations are obtained for a comparison of the tensile performance of longitudinally and radially freeze-cast collagen scaffolds with their performance in compression. Collated, the correlations, obtained both in tension in this study and in compression for collagen and chitosan in two earlier reports, not only enable the custom-design of freeze-cast biopolymer scaffolds for biomedical applications but also provide new insights into similarities and differences of scaffold and cell-wall structure formation during the directional solidification of "smooth" and "fibrillar" biopolymers.

Enhanced neural differentiation by applying electrical stimulation utilizing conductive and antioxidant alginate-polypyrrole/poly-l-lysine hydrogels

The challenge of restoration from neurodegenerative disorder requires effective solutions. To enhance the healing efficiencies, scaffolds with antioxidant activities, electroconductivity, and versatile features to encourage neuronal differentiation are potentially useful. Herein, polypyrrole-alginate (Alg-PPy) copolymer was used to design antioxidant and electroconductive hydrogels through the chemical oxidation radical polymerization method. The hydrogels have antioxidant effects to combat oxidative stress in nerve damage thanks to the introduction of PPy. Additionally, poly-l-lysine (PLL) provided these hydrogels with a great differentiation ability of stem cells. The morphology, porosity, swelling ratio, antioxidant activity, rheological behavior, and conductive characteristics of these hydrogels were precisely adjusted by altering the amount of PPy. Characterization of hydrogels showed appropriate electrical conductivity and antioxidant activity for neural tissue applications. Cytocompatibility, live/dead assays, and Annexin V/PI staining by flow cytometry using P19 cells confirmed the excellent cytocompatibility and cell protective effect under ROS microenvironment of these hydrogels in both normal and oxidative conditions. The neural marker investigation in the induction of electrical impulses was assessed through RT-PCR and immunofluorescence assay, demonstrating the differentiation of P19 cells to neurons cultured in these scaffolds. In summary, the antioxidant and electroconductive Alg-PPy/PLL hydrogels demonstrated excellent potential as promising scaffolds for treating neurodegenerative disorders.

Applications of chitosan-based biomaterials: From preparation to spinal cord injury neuroprosthetic treatment

Spinal cord injury (SCI)-related disabilities are a serious problem in the modern society. Further, the treatment of SCI is highly challenging and is urgently required in clinical practice. Research on nerve tissue engineering is an emerging approach for improving the treatment outcomes of SCI. Chitosan (CS) is a cationic polysaccharide derived from natural biomaterials. Chitosan has been found to exhibit excellent biological properties, such as nontoxicity, biocompatibility, biodegradation, and antibacterial activity. Recently, chitosan-based biomaterials have attracted significant attention for SCI repair in nerve tissue engineering applications. These studies revealed that chitosan-based biomaterials have various functions and mechanisms to promote SCI repair, such as promoting neural cell growth, guiding nerve tissue regeneration, delivering nerve growth factors, and as a vector for gene therapy. Chitosan-based biomaterials have proven to have excellent potential for the treatment of SCI. This review aims to introduce the recent advances in chitosan-based biomaterials for SCI treatment and to highlight the prospects for further application.

Fabrication of Silk Hydrogel Scaffolds with Aligned Porous Structures and Tunable Mechanical Properties

The effectiveness of cell culture and tissue regeneration largely depends on the structural and physiochemical characteristics of tissue-engineering scaffolds. Hydrogels are frequently employed in tissue engineering because of their high-water content and strong biocompatibility, making them the ideal scaffold materials for simulating tissue structures and properties. However, hydrogels created using traditional methods have low mechanical strength and a non-porous structure, which severely restrict their application. Herein, we successfully developed silk fibroin glycidyl methacrylate (SF-GMA) hydrogels with oriented porous structures and substantial toughness through directional freezing (DF) and in situ photo-crosslinking (DF-SF-GMA). The oriented porous structures in the DF-SF-GMA hydrogels were induced by directional ice templates and maintained after photo-crosslinking. The mechanical properties, particularly the toughness, of these scaffolds were enhanced compared to the traditional bulk hydrogels. Interestingly, the DF-SF-GMA hydrogels exhibit fast stress relaxation and variable viscoelasticity. The remarkable biocompatibility of the DF-SF-GMA hydrogels was further demonstrated in cell culture. Accordingly, this work reports a method to prepare tough SF hydrogels with aligned porous structures, which can be extensively applied to cell culture and tissue engineering.

Circulating Tumor Cells in Cancer Diagnostics and Prognostics by Single-Molecule and Single-Cell Characterization

Circulating tumor cells (CTCs) represent an interesting source of biomarkers for diagnosis, prognosis, and the prediction of cancer recurrence, yet while they are extensively studied in oncobiology research, their diagnostic utility has not yet been demonstrated and validated. Their scarcity in human biological fluids impedes the identification of dangerous CTC subpopulations that may promote metastatic dissemination. In this Perspective, we discuss promising techniques that could be used for the identification of these metastatic cells. We first describe methods for isolating patient-derived CTCs and then the use of 3D biomimetic matrixes in their amplification and analysis, followed by methods for further CTC analyses at the single-cell and single-molecule levels. Finally, we discuss how the elucidation of mechanical and morphological properties using techniques such as atomic force microscopy and molecular biomarker identification using nanopore-based detection could be combined in the future to provide patients and their healthcare providers with a more accurate diagnosis.

Anisotropic 3D scaffolds for spinal cord guided repair: Current concepts

A spinal cord injury (SCI) can be caused by unforeseen events such as a fall, a vehicle accident, a gunshot, or a malignant illness, which has a significant impact on the quality of life of the patient. Due to the limited regenerative potential of the central nervous system (CNS), SCI is one of the most daunting medical challenges of modern medicine. Great advances have been made in tissue engineering and regenerative medicine, which include the transition from two-dimensional (2D) to three-dimensional (3D) biomaterials. Combinatory treatments that use 3D scaffolds may significantly enhance the repair and regeneration of functional neural tissue. In an effort to mimic the chemical and physical properties of neural tissue, scientists are researching the development of the ideal scaffold made of synthetic and/or natural polymers. Moreover, in order to restore the architecture and function of neural networks, 3D scaffolds with anisotropic properties that replicate the native longitudinal orientation of spinal cord nerve fibres are being designed. In an effort to determine if scaffold anisotropy is a crucial property for neural tissue regeneration, this review focuses on the most current technological developments relevant to anisotropic scaffolds for SCI. Special consideration is given to the architectural characteristics of scaffolds containing axially oriented fibres, channels, and pores. By analysing neural cell behaviour in vitro and tissue integration and functional recovery in animal models of SCI, the therapeutic efficacy is evaluated for its successes and limitations.

Preparation, Properties, and Mechanism of Flame-Retardant Poly(vinyl alcohol) Aerogels Based on the Multi-Directional Freezing Method

In this work, exfoliated α-zirconium phosphate (α-ZrP) and phosphated cellulose (PCF) were employed to synthesize poly(vinyl alcohol) composite aerogels (PVA/PCF/α-ZrP) with excellent flame retardancy through the multi-directional freezing method. The peak heat release rate (PHRR), total smoke release (TSR), and CO production (COP) of the (PVA/PCF₁₀/α-ZrP₁₀-3) composite aerogel were considerably decreased by 42.3%, 41.4%, and 34.7%, as compared to the pure PVA aerogel, respectively. Simultaneously, the limiting oxygen index (LOI) value was improved from 18.1% to 28.4%. The mechanistic study of flame retardancy showed evidence that PCF and α-ZrP promoted the crosslinking and carbonization of PVA chains to form a barrier, which not only served as insulation between the material and the air, but also significantly reduced the emissions of combustible toxic gases (CO₂, CO). In addition, the multi-directional freezing method further improved the catalytic carbonization process. This mutually advantageous strategy offers a new strategy for the preparation of composite aerogels with enhanced fire resistance.

Biomimetic Silk Macroporous Materials for Drug Delivery Obtained via Ice-Templating

Silk from Bombyx mori is one of the most exciting materials in nature. The apparently simple arrangement of its two major components─two parallel filaments of silk fibroin (SF) coated by a common sericin (SS) sheath─provides a combination of mechanical and surface properties that can protect the moth during its most vulnerable phase, the pupal stage. Here, we recapitulate the topology of native silk fibers but shape them into three-dimensional porous constructs using an unprecedented design strategy. We demonstrate, for the first time, the potential of these macroporous silk foams as dermal patches for wound protection and for the controlled delivery of Rifamycin (Rif), a model antibiotic. The method implies (i) removing SS from silk fibers; (ii) shaping SF solutions into macroporous foams via ice-templating; (iii) stabilizing the SF macroporous foam in a methanolic solution of Rif; and (iv) coating Rif-loaded SF foams with a SS sheath. The resulting SS@SF foams exhibit water wicking capacity and accommodate up to ∼20% deformation without detaching from a skin model. The antibacterial behavior of Rif-loaded SS@SF foams against Staphylococcus aureus on agar plates outperforms that of SF foams (>1 week and 4 days, respectively). The reassembly of natural materials as macroporous foams─illustrated here for the reconstruction of silk-based materials─can be extended to other multicomponent natural materials and may play an important role in applications where controlled release of molecules and fluid transport are pivotal.

Implantable nerve guidance conduits: Material combinations, multi-functional strategies and advanced engineering innovations

Nerve guidance conduits (NGCs) have attracted much attention due to their great necessity and applicability in clinical use for the peripheral nerve repair. Great efforts in recent years have been devoted to the development of high-performance NGCs using various materials and strategies. The present review provides a comprehensive overview of progress in the material innovation, structural design, advanced engineering technologies and multi functionalization of state-of-the-art nerve guidance conduits NGCs. Abundant advanced engineering technologies including extrusion-based system, laser-based system, and novel textile forming techniques in terms of weaving, knitting, braiding, and electrospinning techniques were also analyzed in detail. Findings arising from this review indicate that the structural mimetic NGCs combined with natural and synthetic materials using advanced manufacturing technologies can make full use of their complementary advantages, acquiring better biomechanical properties, chemical stability and biocompatibility. Finally, the existing challenges and future opportunities of NGCs were put forward aiming for further research and applications of NGCs.

Oscillating field stimulation promotes axon regeneration and locomotor recovery after spinal cord injury

Oscillating field stimulation (OFS) is a potential method for treating spinal cord injury. Although it has been used in spinal cord injury (SCI) therapy in basic and clinical studies, its underlying mechanism and the correlation between its duration and nerve injury repair remain poorly understood. In this study, we established rat models of spinal cord contusion at T10 and then administered 12 weeks of OFS. The results revealed that effectively promotes the recovery of motor function required continuous OFS for more than 6 weeks. The underlying mechanism may be related to the effects of OFS on promoting axon regeneration, inhibiting astrocyte proliferation, and improving the linear arrangement of astrocytes. This study was approved by the Animal Experiments and Experimental Animal Welfare Committee of Capital Medical University (supplemental approval No. AEEI-2021-204) on July 26, 2021.

Activated Graphene Oxide-Calcium Alginate Beads for Adsorption of Methylene Blue and Pharmaceuticals

The remarkable adsorption capacity of graphene-derived materials has prompted their examination in composite materials suitable for deployment in treatment of contaminated waters. In this study, crosslinked calcium alginate–graphene oxide beads were prepared and activated by exposure to pH 4 by using 0.1M HCl. The activated beads were investigated as novel adsorbents for the removal of organic pollutants (methylene blue dye and the pharmaceuticals famotidine and diclofenac) with a range of physicochemical properties. The effects of initial pollutant concentration, temperature, pH, and adsorbent dose were investigated, and kinetic models were examined for fit to the data. The maximum adsorption capacities q_max obtained were 1334, 35.50 and 36.35 mg g⁻¹ for the uptake of methylene blue, famotidine and diclofenac, respectively. The equilibrium adsorption had an alignment with Langmuir isotherms, while the kinetics were most accurately modelled using pseudo- first-order and second order models according to the regression analysis. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated and the adsorption process was determined to be exothermic and spontaneous.

Natural Polymeric Scaffolds for Tissue Engineering Applications

Natural polymeric scaffolds can be used for tissue engineering applications such as cell delivery and cell-free supporting of native tissues. This is because of their desirable properties such as; high biocompatibility, tunable mechanical strength and conductivity, large surface area, porous- and extracellular matrix (ECM)-mimicked structures. Specifically, their less toxicity and biocompatibility makes them suitable for several tissue engineering applications. For these reasons, several biopolymeric scaffolds are currently being explored for numerous tissue engineering applications. To date, research on the nature, chemistry, and properties of nanocomposite biopolymers are been reported, while the need for a comprehensive research note on more tissue engineering application of these biopolymers remains. As a result, this present study comprehensively reviews the development of common natural biopolymers as scaffolds for tissue engineering applications such as cartilage tissue engineering, cornea repairs, osteochondral defect repairs, and nerve regeneration. More so, the implications of research findings for further studies are presented, while the impact of research advances on future research and other specific recommendations are added as well.

Preservation of biomaterials and cells by freeze-drying: Change of paradigm

Freeze-drying is the most widespread method to preserve protein drugs and vaccines in a dry form facilitating their storage and transportation without the laborious and expensive cold chain. Extending this method for the preservation of natural biomaterials and cells in a dry form would provide similar benefits, but most results in the domain are still below expectations. In this review, rather than consider freeze-drying as a traditional black box we "break it" through a detailed process thinking approach. We discuss freeze-drying from process thinking aspects, introduce the chemical, physical, and mechanical environments important in this process, and present advanced biophotonic process analytical technology. In the end, we review the state of the art in the freeze-drying of the biomaterials, extracellular vesicles, and cells. We suggest that the rational design of the experiment and implementation of advanced biophotonic tools are required to successfully preserve the natural biomaterials and cells by freeze-drying. We discuss this change of paradigm with existing literature and elaborate on our perspective based on our new unpublished results.

Structure-property-processing correlations of longitudinal freeze-cast chitosan scaffolds for biomedical applications

Needed for the custom-design of longitudinally freeze-cast chitosan scaffolds for biomedical applications are systematic structure-property-processing correlations. Combining mechanical testing in compression with both scanning electron microscopy and semiautomated confocal microscopy for a quantitative structural characterization of fully hydrated chitosan scaffolds, robust correlations were determined. Decreasing the applied cooling rate from 10 °C/min to 0.1 °C/min, the short and long axes of the pore cross-sections, the pore aspect ratio, and the pore area were found to increase from 68.0 μm to 120.5 μm, from 189.2 μm to 401.2 μm, from 2.64 to 3.52, and from 8,922 μm² to 35,596 μm², respectively. Values for the scaffolds' modulus, yield strength, and toughness range from 1,067 kPa to 3,209 kPa, from 37.7 kPa to 75.5 kPa, and from 20.3 kJ/m³ to 35.3 kJ/m³, respectively. Because of additional structural features, such as cell wall stiffening ridges, affecting the mechanical properties, not linear but more complex correlation with modulus, yield strength, and toughness were observed. Contrasting the results of this study with those obtained in an earlier study of dry and fully hydrated collagen scaffolds, we were able to identify features that are important and peculiar to each material system. Highlighted in this study are newly determined robust structure-property-processing correlations as well as processing conditions and features that are critical for the mechanical performance of chitosan and other biopolymer scaffolds made by freeze casting for biomedical applications.

Colloidal assembly by directional ice templating

We investigate directional ice templating of dilute aqueous colloidal particle dispersions and examine the nature of the assemblies that result. We coat micron-size polystyrene colloids with cross-linkable polymer (polyethyleneimine, PEI), add cross-linker, and subject this dispersion to unidirectional freezing. We work at sufficiently low colloid concentrations, such that the particles do not percolate on freezing. When the aqueous dispersion freezes, ice crystals force polymer-coated particles and cross-linker into close proximity. This results in the formation of cross-linked clusters of particles at ice crystal boundaries. We vary the particle volume fraction from φ ∼ 2.5 × 10-3 to φ ∼ 5.0 × 10-2 and observe that there is a transition from isolated single particles to increasingly large sized clusters. Most of the clusters formed under these conditions are either linear, two-particle wide chains, or sheet-like aggregates. The probability (Pn) of clusters containing n particles (n > 2) obeys a power law Pn ∼ n-η, where η strongly depends on the particle concentration in the dispersion, varying from 2.10 (for φ ∼ 5.0 × 10-2) to 3.03 (for φ ∼ 2.5 × 10-3). This change in η is qualitatively different from the case of isotropic freezing, where η is particle concentration-independent and depends only on the ice nucleation density. To understand the differences between isotropic and directional ice templating, we performed lattice simulations of a highly simplified model, where ice crystals grow at a constant rate to force clustering. We ignore hydrodynamic interactions and ice growth instabilities. Despite ignoring these experimental details, the simulations capture the experimental results, nearly quantitatively. As the ice crystals grow and the space available to the colloids "closes up" so that the particles cluster to form aggregates, crystallization protocol-induced differences in the geometry of these "closed up" spaces determine the scaling behaviour of Pn.

Intralayered Ostwald Ripening-Induced Self-Catalyzed Growth of CNTs on MXene for Robust Lithium-Sulfur Batteries

The distinguishable physicochemical properties of MXenes render them attractive in electrochemical energy storage. However, the strong tendency to self-restack owing to the van der Waals interactions between the MXene layers incurs a massive decrease in surface area and blocking of ions transfer and electrolytes penetration. Here, in situ generated Ti₃ C₂ T_x MXene-carbon nanotubes (Ti₃ C₂ T_x -CNTs) hybrids are reported via low-temperature self-catalyzing growth of CNTs on Ti₃ C₂ T_x nanosheets without the addition of any catalyst precursors. With combined spectroscopic studies and theoretical calculation results, it is certified that the intralayered Ostwald ripening-induced Ti₃ C₂ T_x nanomesh structure contributes to the uniform precipitation of ultrafine metal Ti catalysts on Ti₃ C₂ T_x , thus giving rise to the in situ CNTs formation on the surface of Ti₃ C₂ T_x with high integrity. Taking advantages of intimate electrolyte penetration, unobstructed 3D Li⁺ /e transport, and rich electroactive sites, the Ti₃ C₂ T_x -CNTs hybrids are confirmed to be ideal 3D scaffolds for accommodating sulfur and regulating the polysulfides conversion for high-loaded lithium-sulfur batteries.

Hydrogel-Forming Algae Polysaccharides: From Seaweed to Biomedical Applications

With the increasing growth of the algae industry and the development of algae biorefinery, there is a growing need for high-value applications of algae-extracted biopolymers. The utilization of such biopolymers in the biomedical field can be considered as one of the most attractive applications but is challenging to implement. Historically, polysaccharides extracted from seaweed have been used for a long time in biomedical research, for example, agarose gels for electrophoresis and bacterial culture. To overcome the current challenges in polysaccharides and help further the development of high-added-value applications, an overview of the entire polysaccharide journey from seaweed to biomedical applications is needed. This encompasses algae culture, extraction, chemistry, characterization, processing, and an understanding of the interactions of soft matter with living organisms. In this review, we present algae polysaccharides that intrinsically form hydrogels: alginate, carrageenan, ulvan, starch, agarose, porphyran, and (nano)cellulose and classify these by their gelation mechanisms. The focus of this review further lays on the culture and extraction strategies to obtain pure polysaccharides, their structure-properties relationships, the current advances in chemical backbone modifications, and how these modifications can be used to tune the polysaccharide properties. The available techniques to characterize each organization scale of a polysaccharide hydrogel are presented, and the impact on their interactions with biological systems is discussed. Finally, a perspective of the anticipated development of the whole field and how the further utilization of hydrogel-forming polysaccharides extracted from algae can revolutionize the current algae industry are suggested.

Short communication: The effect of pectin and sodium alginate on labans made from camel milk and bovine milk

Camel milk (CM) is gaining scientific attention due to its potential health and therapeutic benefits. Fermented drinkable yogurts (labans) were prepared from CM and bovine milk (BM) using mixed Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus bacteria supplemented with 1 of 2 hydrocolloids: pectin (0.1-0.3%) or sodium alginate (0.1-0.5%). The different labans were compared by studying their acidity and rheology as well as their structural and sensory properties. The CM and BM labans had titratable acidity values that ranged from 0.85 to 1.27 and 0.61 to 0.93%, respectively. Pectin at 0.2% enhanced the rheological properties of BM labans, but had no effect in CM labans. Sodium alginate at 0.3% and 0.5% increased viscosity, elastic or storage modulus (G'), and viscous or loss modulus (G″) values for both types of laban. Scanning electron microscopy indicated that the CM laban contained lower levels of "spike-like structures" than BM laban, and that the addition of hydrocolloids improved this effect. Quantitative descriptive sensory analysis showed that CM labans fortified with either 0.2% pectin or 0.3% sodium alginate were comparable to commercial BM laban in viscous mouthfeel. Fortified CM labans were more acidic and had stronger flavors than unfortified samples. Overall, this study demonstrated that the addition of sodium alginate or pectin at intermediate levels permits production of palatable CM labans of a satisfactory viscous consistency.

Recent advances in ice templating: from biomimetic composites to cell culture scaffolds and tissue engineering

We review the evolution of ice-templating process from initial inorganic materials to recent developments in shaping increasingly labile biological matter.

Effects of lamellar microstructure of retinoic acid loaded-matrixes on physicochemical properties, migration, and neural differentiation of P19 embryonic carcinoma cells

In this study, retinoic acid loaded-PLGA-gelatin matrixes were prepared with both freeze-casting and freeze-drying techniques. Herein, the effect of unidirectional microstructure with tunable pores on release profile, cellular adhesion, migration, and differentiation was compared. Morphological observation determined that highly interconnected porous structure can be formed, but lamellar pore channels were observed in freeze-casting prepared constructs. The absorption ratio was increased, and the biodegradation rate was decreased as a function of the orientation of microstructure. The in-vitro release study illustrated non-Fickian release mechanism in both methods, so that erosion has predominated over diffusion. Accordingly, PLGA-gelatin scaffolds prepared with freeze-drying technique showed no adequate erosion due to the rigid structure, while freeze-casting one presented more favorable erosion. Microscopic observations of adhered P19 embryonic cells on the scaffolds showed that the freeze-casting matrixes with unidirectional pores provide a more compatible microenvironment for cell attachments and spreading. Besides, it facilitated cell migration and penetration inside the structure and may act as guidance for neuron growth. Improvement in the expression of neural genes in unidirectionally oriented pores proved the decisive role of contact guidance for nerve healing. It seems that the freeze-cast PLGA-gelatin-retinoic acid scaffolds have initial features for nerve tissue regeneration studies.

Application of fibrin-based hydrogels for nerve protection and regeneration after spinal cord injury

Traffic accidents, falls, and many other events may cause traumatic spinal cord injuries (SCIs), resulting in nerve cells and extracellular matrix loss in the spinal cord, along with blood loss, inflammation, oxidative stress (OS), and others. The continuous development of neural tissue engineering has attracted increasing attention on the application of fibrin hydrogels in repairing SCIs. Except for excellent biocompatibility, flexibility, and plasticity, fibrin, a component of extracellular matrix (ECM), can be equipped with cells, ECM protein, and various growth factors to promote damage repair. This review will focus on the advantages and disadvantages of fibrin hydrogels from different sources, as well as the various modifications for internal topographical guidance during the polymerization. From the perspective of further improvement of cell function before and after the delivery of stem cell, cytokine, and drug, this review will also evaluate the application of fibrin hydrogels as a carrier to the therapy of nerve repair and regeneration, to mirror the recent development tendency and challenge.

Quantitative evaluation of the in vivo biocompatibility and performance of freeze-cast tissue scaffolds

Quantitative methods are little used for the in vivo assessment of tissue scaffolds to evaluate biocompatibility. To complement current histological techniques, we introduce as a measure of biocompatibility a straightforward, geometric analysis for the quantitative assessment of encapsulation thickness, cross-sectional area, and biomaterial shape. Advantages of this new technique are that it enables, on the one hand, a more complete and objective comparison of scaffolds with differing compositions, architectures, and mechanical properties, and, on the other, a more objective approach to their selection for a given application. In this contribution, we focus on freeze-cast polymeric scaffolds for tissue regeneration and their subcutaneous implantation in mice for biocompatibility testing. Initially, seven different scaffold types are screened. Of these, three are selected for systematic biocompatibility studies based on histopathological criteria: EDC-NHS-crosslinked bovine collagen, EDC-NHS-crosslinked bovine collagen-nanocellulose, and chitin. Geometric models developed to quantify scaffold size, ovalization, and encapsulation thickness are tested, evaluated, and found to be a powerful and objective metric for the in vivo assessment of biocompatibility and performance of tissue scaffolds.

Hydrogels based on modified pectins capable of modulating neural cell behavior as prospective biomaterials in glioblastoma treatment

Glioblastoma is the most common malignant tumor of the brain, but its treatment outcomes can be improved by new therapeutic techniques using biocompatible materials. Utilizing controllable alkaline de-esterification we obtained pectin preparation with 27.4% esterification degree and used it for bio-artificial matrix production. We discovered optimal gelation conditions in the presence of Ca²⁺ by the analysis of visco-elastic properties of the gels and produced a series of biomaterials in hydrogel forms. Hydrogels based on low-esterified pectin significantly slow down the metabolism of C6 glioma cells and neural stem cells (NSCs) and slightly decrease the viability of the C6 glioma, but not of NSCs. This happens due to a decrease in cell proliferation rate, while apoptosis degrees remain stable or negligibly decrease. We created a set of pectin hydrogels supplemented with different ratios of two ECM proteins-collagens I and IV. We have shown that the formation of cell processes in glioma C6 can be regulated by varying the ratio of two ECM proteins in gels used for 3D cell cultivation. Thus, composite matrix materials obtained can be used for modeling brain tumor invasion. The results presented suggest that modified pectins supplemented with two collagen types may serve as prospective biomaterials for glioblastoma treatment due to their ability to regulate glioma cell dynamics.

Activity and stability of the catalytic hydrogel membrane reactor for treating oxidized contaminants

The catalytic hydrogel membrane reactor (CHMR) is an interfacial membrane process that uses nano-sized catalysts for the hydrogenation of oxidized contaminants in drinking water. In this study, the CHMR was operated as a continuous-flow reactor using nitrite (NO₂^-) as a model contaminant and palladium (Pd) as a model catalyst. Using the overall bulk reaction rate for NO₂^- reduction as a metric for catalytic activity, we evaluated the effect of the hydrogen gas (H₂) delivery method to the CHMR, the initial H₂ and NO₂^- concentrations, Pd density in the hydrogel, and the presence of Pd-deactivating species. The chemical stability of the catalytic hydrogel was evaluated in the presence of aqueous cations (H⁺, Na⁺, Ca²⁺) and a mixture of ions in a hard groundwater. Delivering H₂ to the CHMR lumens using a vented operation mode, where the reactor is sealed and the lumens are periodically flushed to the atmosphere, allowed for a combination of a high H₂ consumption efficiency and catalytic activity. The overall reaction rate of NO₂^- was dependent on relative concentrations of H₂ and NO₂^- at catalytic sites, which was governed by both the chemical reaction and mass transport rates. The intrinsic catalytic reaction rate was combined with a counter-diffusional mass transport component in a 1-D computational model to describe the CHMR. Common Pd-deactivating species [sulfite, bisulfide, natural organic matter] hindered the reaction rate, but the hydrogel afforded some protection from deactivation compared to a batch suspension. No chemical degradation of the hydrogel structure was observed for a model water (pH > 4, Na⁺, Ca²⁺) and a hard groundwater after 21 days of exposure, attesting to its stability under natural water conditions.

Freeze Casting: From Low-Dimensional Building Blocks to Aligned Porous Structures-A Review of Novel Materials, Methods, and Applications

Freeze casting, also known as ice templating, is a particularly versatile technique that has been applied extensively for the fabrication of well-controlled biomimetic porous materials based on ceramics, metals, polymers, biomacromolecules, and carbon nanomaterials, endowing them with novel properties and broadening their applicability. The principles of different directional freeze-casting processes are described and the relationships between processing and structure are examined. Recent progress in freeze-casting assisted assembly of low dimensional building blocks, including graphene and carbon nanotubes, into tailored micro- and macrostructures is then summarized. Emerging trends relating to novel materials as building blocks and novel freeze-cast geometries-beads, fibers, films, complex macrostructures, and nacre-mimetic composites-are presented. Thereafter, the means by which aligned porous structures and nacre mimetic materials obtainable through recently developed freeze-casting techniques and low-dimensional building blocks can facilitate material functionality across multiple fields of application, including energy storage and conversion, environmental remediation, thermal management, and smart materials, are discussed.

Aligned 3D porous polyurethane scaffolds for biological anisotropic tissue regeneration

A green fabrication process (organic solvent-free) of artificial scaffolds is required in tissue engineering field. In this work, a series of aligned three-dimensional (3D) scaffolds are made from biodegradable waterborne polyurethane (PU) emulsion via directional freeze-drying method to ensure no organic byproducts. After optimizing the concentration of polymer in the emulsion and investigating different freezing temperatures, an aligned PUs scaffold (PU14) generated from 14 wt% polymer content and processed at -196°C was selected based on the desired oriented porous structure (pore size of 32.5 ± 9.3 μm, porosity of 92%) and balanced mechanical properties both in the horizontal direction (strength of 41.3 kPa, modulus of 72.3 kPa) and in the vertical direction (strength of 45.5 kPa, modulus of 139.3 kPa). The response of L929 cells and the regeneration of muscle tissue demonstrated that such pure material-based aligned 3D scaffold can facilitate the development of orientated cells and anisotropic tissue regeneration both in vitro and in vivo. Thus, these pure material-based scaffolds with ordered architecture have great potentials in tissue engineering for biological anisotropic tissue regeneration, such as muscle, nerve, spinal cord and so on.

Advancing fabrication and properties of three-dimensional graphene-alginate scaffolds for application in neural tissue engineering

Neural tissue engineering provides enormous potential for restoring and improving the function of diseased/damaged tissues and promising opportunities in regenerative medicine, stem cell technology, and drug discovery. The conventional 2D cell cultures have many limitations to provide informative and realistic neural interactions and network formation. Hence, there is a need to develop three-dimensional (3D) bioscaffolds to facilitate culturing cells with matched microenvironment for cell growth and interconnected pores for penetration and migration of cells. Herein, we report the synthesis and characterization of 3D composite bioscaffolds based on graphene-biopolymer with porous structure and improved performance for tissue engineering. A simple, eco-friendly synthetic method is introduced and optimized for synthesis of this hybrid fibrous scaffold by combining Graphene Oxide (GO) and Sodium Alginate (Na-ALG) which are specifically selected to match the mechanical strength of the central nervous system (CNS) tissue and provide porous structure for connective tissue engineering. Properties of the developed scaffold in terms of the structure, porosity, thermal stability, mechanical properties, and electrical conductivity are presented. These properties were optimised through key synthesis conditions including GO concentrations, reduction process and crosslinking time. In contrast to other studies, the presented structure maintains its stability in aqueous media and uses a bio-friendly reducing agent which enable the structure to enhance neuron cell interactions and act as nerve conduits for neurological diseases.

Plant-Derived Nanocellulose as Structural and Mechanical Reinforcement of Freeze-Cast Chitosan Scaffolds for Biomedical Applications

Despite considerable recent interest in micro- and nanofibrillated cellulose as constituents of lightweight structures and scaffolds for applications that range from thermal insulation to filtration, few systematic studies have been reported to date on structure-property-processing correlations in freeze-cast chitosan-nanocellulose composite scaffolds, in general, and their application in tissue regeneration, in particular. Reported in this study are the effects of the addition of plant-derived nanocellulose fibrils (CNF), crystals (CNCs), or a blend of the two (CNB) to the biopolymer chitosan on the structure and properties of the resulting composites. Chitosan-nanocellulose composite scaffolds were freeze-cast at 10 and 1 °C/min, and their microstructures were quantified in both the dry and fully hydrated states using scanning electron and confocal microscopy, respectively. The modulus, yield strength, and toughness (work to 60% strain) were determined in compression parallel and the modulus also perpendicular to the freezing direction to quantify anisotropy. Observed were the preferential alignments of CNCs and/or fibrils parallel to the freezing direction. Additionally, observed was the self-assembly of the nanocellulose into microstruts and microbridges between adjacent cell walls (lamellae), features that affected the mechanical properties of the scaffolds. When freeze-cast at 1 °C/min, chitosan-CNF scaffolds had the highest modulus, yield strength, toughness, and smallest anisotropy ratio, followed by chitosan and the composites made with the nanocellulose blend, and that with crystalline cellulose. These results illustrate that the nanocellulose additions homogenize the mechanical properties of the scaffold through cell-wall material self-assembly, on the one hand, and add architectural features such as bridges and pillars, on the other. The latter transfer loads and enable the scaffolds to resist deformation also perpendicular to the freezing direction. The observed property profile and the materials' proven biocompatibility highlight the promise of chitosan-nanocellulose composites for a large range of applications, including those for biomedical implants and devices.

Aligned hydrogel tubes guide regeneration following spinal cord injury

Directing the organization of cells into a tissue with defined architectures is one use of biomaterials for regenerative medicine. To this end, hydrogels are widely investigated as they have mechanical properties similar to native soft tissues and can be formed in situ to conform to a defect. Herein, we describe the development of porous hydrogel tubes fabricated through a two-step polymerization process with an intermediate microsphere phase that provides macroscale porosity (66.5%) for cell infiltration. These tubes were investigated in a spinal cord injury model, with the tubes assembled to conform to the injury and to provide an orientation that guides axons through the injury. Implanted tubes had good apposition and were integrated with the host tissue due to cell infiltration, with a transient increase in immune cell infiltration at 1 week that resolved by 2 weeks post injury compared to a gelfoam control. The glial scar was significantly reduced relative to control, which enabled robust axon growth along the inner and outer surface of the tubes. Axon density within the hydrogel tubes (1744 axons/mm²) was significantly increased more than 3-fold compared to the control (456 axons/mm²), with approximately 30% of axons within the tube myelinated. Furthermore, implantation of hydrogel tubes enhanced functional recovery relative to control. This modular assembly of porous tubes to fill a defect and directionally orient tissue growth could be extended beyond spinal cord injury to other tissues, such as vascular or musculoskeletal tissue. STATEMENT OF SIGNIFICANCE: Tissue engineering approaches that mimic the native architecture of healthy tissue are needed following injury. Traditionally, pre-molded scaffolds have been implemented but require a priori knowledge of wound geometries. Conversely, hydrogels can conform to any injury, but do not guide bi-directional regeneration. In this work, we investigate the feasibility of a system of modular hydrogel tubes to promote bi-directional regeneration after spinal cord injury. This system allows for tubes to be cut to size during surgery and implanted one-by-one to fill any injury, while providing bi-directional guidance. Moreover, this system of tubes can be broadly applied to tissue engineering approaches that require a modular guidance system, such as repair to vascular or musculoskeletal tissues.

Anisotropic freeze-cast collagen scaffolds for tissue regeneration: How processing conditions affect structure and properties in the dry and fully hydrated states

Few systematic structure-property-processing correlations for directionally freeze-cast biopolymer scaffolds are reported. Such correlations are critical to enable scaffold design with attractive structural and mechanical cues in vivo. This study focuses on freeze-cast collagen scaffolds with three different applied cooling rates (10, 1, and 0.1 °C/min) and two freezing directions (longitudinal and radial). A semi-automated approach for the structural characterization of fully hydrated scaffolds by confocal microscopy is developed to facilitate an objective quantification and comparison of structural features. Additionally, scanning electron microscopy and compression testing are performed longitudinally and transversely. Structural and mechanical properties are determined on dry and fully hydrated scaffolds. Longitudinally frozen scaffolds have aligned and regular pores while those in radially frozen ones exhibit greater variations in pore geometry and alignment. Lamellar spacing, pore area, and cell wall thickness increase with decreasing cooling rate: in longitudinally frozen scaffolds from 25 µm to 83.5 µm, from 814 µm² to 8452 µm², and from 4.21 µm to 10.4 µm, and in radially frozen ones, from 69 µm to 116 µm, from 7679 µm² to 25,670 µm², and from 6.18 µm to 13.6 µm, respectively. Both longitudinally and radially frozen scaffolds possess higher mechanical property values, when loaded parallel rather than perpendicular to the ice-crystal growth direction. Modulus and yield strength range from 779 kPa to 4700 kPa and from 38 kPa to 137 kPa, respectively, as a function of cooling rate and freezing direction. Collated, the correlations obtained in this study enable the custom-design of freeze-cast collagen scaffolds, which are ideally suited for a large variety of tissue regeneration applications.

Exploiting natural polysaccharides to enhance in vitro bio-constructs of primary neurons and progenitor cells

Current strategies in Central Nervous System (CNS) repair focus on the engineering of artificial scaffolds for guiding and promoting neuronal tissue regrowth. Ideally, one should combine such synthetic structures with stem cell therapies, encapsulating progenitor cells and instructing their differentiation and growth. We used developments in the design, synthesis, and characterization of polysaccharide-based bioactive polymeric materials for testing the ideal composite supporting neuronal network growth, synapse formation and stem cell differentiation into neurons and motor neurons. Moreover, we investigated the feasibility of combining these approaches with engineered mesenchymal stem cells able to release neurotrophic factors. We show here that composite bio-constructs made of Chitlac, a Chitosan derivative, favor hippocampal neuronal growth, synapse formation and the differentiation of progenitors into the proper neuronal lineage, that can be improved by local and continuous delivery of neurotrophins.

STATEMENT OF SIGNIFICANCE

In our work, we characterized polysaccharide-based bioactive platforms as biocompatible materials for nerve tissue engineering. We show that Chitlac-thick substrates are able to promote neuronal growth, differentiation, maturation and formation of active synapses. These observations support this new material as a promising candidate for the development of complex bio-constructs promoting central nervous system regeneration. Our novel findings sustain the exploitation of polysaccharide-based scaffolds able to favour neuronal network reconstruction. Our study shows that Chitlac-thick may be an ideal candidate for the design of biomaterial scaffolds enriched with stem cell therapies as an innovative approach for central nervous system repair.

A compound scaffold with uniform longitudinally oriented guidance cues and a porous sheath promotes peripheral nerve regeneration in vivo

Scaffolds with inner fillers that convey directional guidance cues represent promising candidates for nerve repair. However, incorrect positioning or non-uniform distribution of intraluminal fillers might result in regeneration failure. In addition, proper porosity (to enhance nutrient and oxygen exchange but prevent fibroblast infiltration) and mechanical properties (to ensure fixation and to protect regenerating axons from compression) of the outer sheath are also highly important for constructing advanced nerve scaffolds. In this study, we constructed a compound scaffold using a stage-wise strategy, including directionally freezing orientated collagen-chitosan (O-CCH) filler, electrospinning poly(ε-caprolactone) (PCL) sheaths and assembling O-CCH/PCL scaffolds. Based on scanning electron microscopy (SEM) and mechanical tests, a blend of collagen/chitosan (1:1) was selected for filler fabrication, and a wall thickness of 400 μm was selected for PCL sheath production. SEM and three-dimensional (3D) reconstruction further revealed that the O-CCH filler exhibited a uniform, longitudinally oriented microstructure (over 85% of pores were 20-50 μm in diameter). The electrospun PCL porous sheath with pore sizes of 6.5 ± 3.3 μm prevented fibroblast invasion. The PCL sheath exhibited comparable mechanical properties to commercially available nerve conduits, and the O-CCH filler showed a physiologically relevant substrate stiffness of 2.0 ± 0.4 kPa. The differential degradation time of the filler and sheath allows the O-CCH/PCL scaffold to protect regenerating axons from compression stress while providing enough space for regenerating nerves. In vitro and in vivo studies indicated that the O-CCH/PCL scaffolds could promote axonal regeneration and Schwann cell migration. More importantly, functional results indicated that the CCH/PCL compound scaffold induced comparable functional recovery to that of the autograft group at the end of the study. Our findings demonstrated that the O-CCH/PCL scaffold with uniform longitudinal guidance filler and a porous sheath exhibits favorable properties for clinical use and promotes nerve regeneration and functional recovery. The O-CCH/PCL scaffold provides a promising new path for developing an optimal therapeutic alternative for peripheral nerve reconstruction.

STATEMENT OF SIGNIFICANCE

Scaffolds with inner fillers displaying directional guidance cues represent a promising candidate for nerve repair. However, further clinical translation should pay attention to the problem of non-uniform distribution of inner fillers, the porosity and mechanical properties of the outer sheath and the morphological design facilitating operation. In this study, a stage-wise fabrication strategy was used, which made it possible to develop an O-CCH/PCL compound scaffold with a uniform longitudinally oriented inner filler and a porous outer sheath. The uniform distribution of the pores in the O-CCH/PCL scaffold provides a solution to resolve the problem of non-uniform distribution of inner fillers, which impede the clinical translation of scaffolds with longitudinal microstructured fillers, especially for aligned-fiber-based scaffolds. In vitro and in vivo studies indicated that the O-CCH/PCL scaffolds could provide topographical cues for axonal regeneration and SC migration, which were not found for random scaffolds (with random microstructure resemble sponge-based scaffolds). The electrospun porous PCL sheath of the O-CCH/PCL scaffold not only prevented fibroblast infiltration, but also satisfied the mechanical requirements for clinical use, paving the way for clinical translation. The differential degradation time of the O-CCH filler and the PCL sheath makes O-CCH/PCL scaffold able to provide long protection for regenerating axons from compression stress, but enough space for regenerating nerve. These findings highlight the possibility of developing an optimal therapeutic alternative for nerve defects using the O-CCH/PCL scaffold.

Predicting Ligand-Free Cell Attachment on Next-Generation Cellulose-Chitosan Hydrogels

There is a growing appreciation that engineered biointerfaces can regulate cell behaviors, or functions. Most systems aim to mimic the cell-friendly extracellular matrix environment and incorporate protein ligands; however, the understanding of how a ligand-free system can achieve this is limited. Cell scaffold materials comprised of interfused chitosan-cellulose hydrogels promote cell attachment in ligand-free systems, and we demonstrate the role of cellulose molecular weight, MW, and chitosan content and MW in controlling material properties and thus regulating cell attachment. Semi-interpenetrating network (SIPN) gels, generated from cellulose/ionic liquid/cosolvent solutions, using chitosan solutions as phase inversion solvents, were stable and obviated the need for chemical coupling. Interface properties, including surface zeta-potential, dielectric constant, surface roughness, and shear modulus, were modified by varying the chitosan degree of polymerization and solution concentration, as well as the source of cellulose, creating a family of cellulose-chitosan SIPN materials. These features, in turn, affect cell attachment onto the hydrogels and the utility of this ligand-free approach is extended by forecasting cell attachment using regression modeling to isolate the effects of individual parameters in an initially complex system. We demonstrate that increasing the charge density, and/or shear modulus, of the hydrogel results in increased cell attachment.

Efficacy of chitosan and sodium alginate scaffolds for repair of spinal cord injury in rats

Spinal cord injury results in the loss of motor and sensory pathways and spontaneous regeneration of adult mammalian spinal cord neurons is limited. Chitosan and sodium alginate have good biocompatibility, biodegradability, and are suitable to assist the recovery of damaged tissues, such as skin, bone and nerve. Chitosan scaffolds, sodium alginate scaffolds and chitosan-sodium alginate scaffolds were separately transplanted into rats with spinal cord hemisection. Basso-Beattie-Bresnahan locomotor rating scale scores and electrophysiological results showed that chitosan scaffolds promoted recovery of locomotor capacity and nerve transduction of the experimental rats. Sixty days after surgery, chitosan scaffolds retained the original shape of the spinal cord. Compared with sodium alginate scaffolds- and chitosan-sodium alginate scaffolds-transplanted rats, more neurofilament-H-immunoreactive cells (regenerating nerve fibers) and less glial fibrillary acidic protein-immunoreactive cells (astrocytic scar tissue) were observed at the injury site of experimental rats in chitosan scaffold-transplanted rats. Due to the fast degradation rate of sodium alginate, sodium alginate scaffolds and composite material scaffolds did not have a supporting and bridging effect on the damaged tissue. Above all, compared with sodium alginate and composite material scaffolds, chitosan had better biocompatibility, could promote the regeneration of nerve fibers and prevent the formation of scar tissue, and as such, is more suitable to help the repair of spinal cord injury.

Regeneration of osteochondral defects in vivo by a cell-free cylindrical poly(lactide-co-glycolide) scaffold with a radially oriented microstructure

A scaffold with an oriented porous architecture to facilitate cell infiltration and bioactive interflow between neo-host tissues is of great importance for in situ inductive osteochondral regeneration. In this study, a poly(lactide-co-glycolide) (PLGA) scaffold with oriented pores in its radial direction was fabricated via unidirectional cooling of the PLGA solution in the radial direction, following with lyophilization. Micro-computed tomography evaluation and scanning electron microscopy observation confirmed the radially oriented microtubular pores in the scaffold. The scaffold had porosity larger than 90% and a compressive modulus of 4 MPa in a dry state. Culture of bone marrow stem cells in vitro revealed faster migration and regular distribution of cells in the poly(lactide-co-glycolide) scaffold with oriented pores compared with the random PLGA scaffold. The cell-free oriented macroporous PLGA scaffold was implanted into rabbit articular osteochondral defect in vivo for 12 weeks to evaluate its inductive tissue regeneration function. Histological analysis confirmed obvious tide mark formation and abundant chondrocytes distributed regularly with obvious lacunae in the cartilage layer. Safranin O-fast green staining showed an obvious boundary between the two layers with distinct staining results, indicating the simultaneous regeneration of the cartilage and subchondral bone layers, which is not the case for the random poly(lactide-co-glycolide) scaffold after the same implantation in vivo. The oriented macroporous PLGA scaffold is a promising material for the in situ inductive osteochondral regeneration without the necessity of preseeding cells.

Polymeric scaffolds for three-dimensional culture of nerve cells: a model of peripheral nerve regeneration

Understanding peripheral nerve repair requires the evaluation of 3D structures that serve as platforms for 3D cell culture. Multiple platforms for 3D cell culture have been developed, mimicking peripheral nerve growth and function, in order to study tissue repair or diseases. To recreate an appropriate 3D environment for peripheral nerve cells, key factors are to be considered including: selection of cells, polymeric biomaterials to be used, and fabrication techniques to shape and form the 3D scaffolds for cellular culture. This review focuses on polymeric 3D platforms used for the development of 3D peripheral nerve cell cultures.