The use of hyaluronan to regulate protein adsorption and cell infiltration in nanofibrous scaffolds

A multifunctional scaffold that promotes the scaffold-tissue interface integration and rescues the ROS microenvironment for repair of annulus fibrosus defects

Due to the limited self-repair ability of the annulus fibrosus (AF), current tissue engineering strategies tend to use structurally biomimetic scaffolds for AF defect repair. However, the poor integration between implanted scaffolds and tissue severely affects their therapeutic effects. To solve this issue, we prepared a multifunctional scaffold containing loaded lysyl oxidase (LOX) plasmid DNA exosomes and manganese dioxide nanoparticles (MnO2 NPs). LOX facilitates extracellular matrix (ECM) cross-linking, while MnO2 NPs inhibit excessive reactive oxygen species (ROS)-induced ECM degradation at the injury site, enhancing the crosslinking effect of LOX. Our results revealed that this multifunctional scaffold significantly facilitated the integration between the scaffold and AF tissue. Cells were able to migrate into the scaffold, indicating that the scaffold was not encapsulated as a foreign body by fibrous tissue. The functional scaffold was closely integrated with the tissue, effectively enhancing the mechanical properties, and preventing vascular invasion, which emphasized the importance of scaffold-tissue integration in AF repair.

Silk films with distinct surface topography modulate plasma membrane curvature to polarize macrophages

The physical properties of a biomaterial play a vital role in modulating macrophage polarization. However, discerning the specific effects of individual parameters can be intricate due to their interdependencies, limiting the mechanism underlying a specific parameter on the polarization of macrophages. Here, we engineered silk fibroin (SF) films with tunable surface roughness while maintaining similar physical properties by combining casting and salting out techniques. We demonstrate that increased surface roughness in SF films promotes M2-like macrophage polarization, characterized by enhanced secretion of anti-inflammatory cytokines. Transcriptomic analysis unveils the modulation of genes associated with extracellular matrix-cell interactions, highlighting the role of surface topography in regulating cellular processes. Mechanistically, we show that surface roughness induces macrophage membrane curvature, facilitating integrin αv endocytosis and thereby inhibiting the integrin-NF-kB signaling pathway. In vivo implantation assays corroborate that rough SF films substantially mitigate early inflammatory responses. This work establishes a direct link between surface roughness and intracellular signaling in macrophages, adding to our understanding of the biomaterial surface effect at the material-cell interface and bringing insights into material design.

The mechanism of low molecular weight fucoidan-incorporated nanofiber scaffolds inhibiting oral leukoplakia via SR-A/Wnt signal axis

Oral leukoplakia (OLK) is the most common oral precancerous lesion, and 3%-17% of OLK patients progress to oral squamous cell carcinoma. OLK is susceptible to recurrence and has no effective treatment. However, conventional drugs have significant side effects and limitations. Therefore, it is important to identify drugs that target OLK. In this study, scavenger receptor A (SR-A) was found to be abnormally highly expressed in the oral mucosal epithelial cells of OLK patients, whereas molecular biology studies revealed that low molecular weight fucoidan (LMWF) promoted apoptosis of dysplastic oral keratinocytes (DOK) and inhibited the growth and migration of DOK, and the inhibitory effect of LMWF on OLK was achieved by regulating the SR-A/Wnt signaling axis and related genes. Based on the above results and the special situation of the oral environment, we constructed LMWF/poly(caprolactone-co-lactide) nanofiber membranes with different structures for the in-situ treatment of OLK using electrospinning technology. The results showed that the nanofiber membranes with a shell-core structure had the best physicochemical properties, biocompatibility, and therapeutic effect, which optimized the LMWF drug delivery and ensured the effective concentration of the drug at the target point, thus achieving precise treatment of local lesions in the oral cavity. This has potential application value in inhibiting the development of OLK.

Kartogenin delivery systems for biomedical therapeutics and regenerative medicine

Kartogenin, a small and heterocyclic molecule, has emerged as a promising therapeutic agent for incorporation into biomaterials, owing to its unique physicochemical and biological properties. It holds potential for the regeneration of cartilage-related tissues in various common conditions and injuries. Achieving sustained release of kartogenin through appropriate formulation and efficient delivery systems is crucial for modulating cell behavior and tissue function. This review provides an overview of cutting-edge kartogenin-functionalized biomaterials, with a primarily focus on their design, structure, functions, and applications in regenerative medicine. Initially, we discuss the physicochemical properties and biological functions of kartogenin, summarizing the underlying molecular mechanisms. Subsequently, we delve into recent advancements in nanoscale and macroscopic materials for the carriage and delivery of kartogenin. Lastly, we address the opportunities and challenges presented by current biomaterial developments and explore the prospects for their application in tissue regeneration. We aim to enhance the generation of insightful ideas for the development of kartogenin delivery materials in the field of biomedical therapeutics and regenerative medicine by providing a comprehensive understanding of common preparation methods.

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.

Biological properties of polycaprolactone and barium titanate composite in biomedical applications

The ceramic-polymer composite materials are widely known for their exceptional mechanical and biological properties. Polycaprolactone (PCL) is a biodegradable polymer material extensively used in various biomedical applications. At the same time, barium titanate (BT), a ceramic material, exhibits piezoelectric properties similar to bone, which is essential for osseointegration. Furthermore, a composite material that combines the benefits of PCL and BT results in an innovative composite material with enhanced properties for biomedical applications. Thus, this review is organised into three sections. Firstly, it aims to provide an overview of the current research on evaluating biological properties, including antibacterial activity, cytotoxicity and osseointegration, of PCL polymeric matrices in its pure form and reinforced structures with ceramics, polymers and natural extracts. The second section investigates the biological properties of BT, both in its pure form and in combination with other supporting materials. Finally, the third section provides a summary of the biological properties of the PCLBT composite material. Furthermore, the existing challenges of PCL, BT and their composites, along with future research directions, have been presented. Therefore, this review will provide a state-of-the-art understanding of the biological properties of PCL and BT composites as potential futuristic materials in biomedical applications.

Unraveling the potential of 3D bioprinted immunomodulatory materials for regulating macrophage polarization: State-of-the-art in bone and associated tissue regeneration

Macrophage-assisted immunomodulation is an alternative strategy in tissue engineering, wherein the interplay between pro-inflammatory and anti-inflammatory macrophage cells and body cells determines the fate of healing or inflammation. Although several reports have demonstrated that tissue regeneration depends on spatial and temporal regulation of the biophysical or biochemical microenvironment of the biomaterial, the underlying molecular mechanism behind immunomodulation is still under consideration for developing immunomodulatory scaffolds. Currently, most fabricated immunomodulatory platforms reported in the literature show regenerative capabilities of a particular tissue, for example, endogenous tissue (e.g., bone, muscle, heart, kidney, and lungs) or exogenous tissue (e.g., skin and eye). In this review, we briefly introduced the necessity of the 3D immunomodulatory scaffolds and nanomaterials, focusing on material properties and their interaction with macrophages for general readers. This review also provides a comprehensive summary of macrophage origin and taxonomy, their diverse functions, and various signal transduction pathways during biomaterial-macrophage interaction, which is particularly helpful for material scientists and clinicians for developing next-generation immunomodulatory scaffolds. From a clinical standpoint, we briefly discussed the role of 3D biomaterial scaffolds and/or nanomaterial composites for macrophage-assisted tissue engineering with a special focus on bone and associated tissues. Finally, a summary with expert opinion is presented to address the challenges and future necessity of 3D bioprinted immunomodulatory materials for tissue engineering.

Platinum based theranostics nanoplatforms for antitumor applications

Platinum (Pt) based nanoplatforms are biocompatible nanoagents with photothermal antitumor performance, while exhibiting excellent radiotherapy sensitization properties. Pt-nanoplatforms have extensive research prospects in the realm of cancer treatment due to their highly selective and minimally invasive treatment mode with low damage, and integrated diagnosis and treatment with image monitoring and collaborative drug delivery. Platinum based anticancer chemotherapeutic drugs can kill tumor cells by damaging DNA through chemotherapy. Meanwhile, Pt-nanoplatforms also have good electrocatalytic activity, which can mediate novel electrodynamic therapy. Simultaneously, Pt(II) based compounds also have potential as photosensitizers in photodynamic therapy for malignant tumors. Pt-nanoplatforms can also modulate the immunosuppressive environment and synergistically ablate tumor cells in combination with immune checkpoint inhibitors. This article reviews the research progress of platinum based nanoplatforms in new technologies for cancer therapy, starting from widely representative examples of platinum based nanoplatforms in chemotherapy, electrodynamic therapy, photodynamic therapy, photothermal therapy, and immunotherapy. Finally, multimodal imaging techniques of platinum based nanoplatforms for biomedical diagnosis are briefly discussed.

Perspectives of nanofibrous wound dressings based on glucans and galactans - A review

Wound healing is a complex and dynamic process that needs an appropriate environment to overcome infection and inflammation to progress well. Wounds lead to morbidity, mortality, and a significant economic burden, often due to the non-availability of suitable treatments. Hence, this field has lured the attention of researchers and pharmaceutical industries for decades. As a result, the global wound care market is expected to be 27.8 billion USD by 2026 from 19.3 billion USD in 2021, at a compound annual growth rate (CAGR) of 7.6 %. Wound dressings have emerged as an effective treatment to maintain moisture, protect from pathogens, and impede wound healing. However, synthetic polymer-based dressings fail to comprehensively address optimal and quick regeneration requirements. Natural polymers like glucan and galactan-based carbohydrate dressings have received much attention due to their inherent biocompatibility, biodegradability, inexpensiveness, and natural abundance. Also, nanofibrous mesh supports better proliferation and migration of fibroblasts because of their large surface area and similarity to the extracellular matrix (ECM). Thus, nanostructured dressings derived from glucans and galactans (i.e., chitosan, agar/agarose, pullulan, curdlan, carrageenan, etc.) can overcome the limitations associated with traditional wound dressings. However, they require further development pertaining to the wireless determination of wound bed status and its clinical assessment. The present review intends to provide insight into such carbohydrate-based nanofibrous dressings and their prospects, along with some clinical case studies.

Unique Fiber Morphologies from Emulsion Electrospinning—A Case Study of Poly(ε-caprolactone) and Its Applications

The importance of electrospinning to produce biomimicking micro- and nano-fibrous matrices is realized by many who work in the area of fibers. Based on the solubility of the materials to be spun, organic solvents are typically utilized. The toxicity of the utilized organic solvent could be extremely important for various applications, including tissue engineering, biomedical, agricultural, etc. In addition, the high viscosities of such polymer solutions limit the use of high polymer concentrations and lower down productivity along with the limitations of obtaining desired fiber morphology. This emphasizes the need for a method that would allay worries about safety, toxicity, and environmental issues along with the limitations of using concentrated polymer solutions. To mitigate these issues, the use of emulsions as precursors for electrospinning has recently gained significant attention. Presence of dispersed and continuous phase in emulsion provides an easy route to incorporate sensitive bioactive functional moieties within the core-sheath fibers which otherwise could only be hardly achieved using cumbersome coaxial electrospinning process in solution or melt based approaches. This review presents a detailed understanding of emulsion behavior during electrospinning along with the role of various constituents and process parameters during fiber formation. Though many polymers have been studied for emulsion electrospinning, poly(ε-caprolactone) (PCL) is one of the most studied polymers for this technique. Therefore, electrospinning of PCL based emulsions is highlighted as unique case-study, to provide a detailed theoretical understanding, discussion of experimental results along with their suitable biomedical applications.

PEEK and Hyaluronan-Based 3D Printed Structures: Promising Combination to Improve Bone Regeneration

Hybrid bone substitute made up of a 3D printed polyetheretherketone (PEEK) scaffold coated with methacrylated hyaluronic acid (MeHA)-hydroxyapatite (HAp) hydrogel is the objective of the present work. Development and characterization of the scaffold and of the MeHA-HAp after its infiltration and UV photocrosslinking have been followed by analyses of its biological properties using human mesenchymal stem cells (MSCs). Interconnected porous PEEK matrices were produced by fused deposition modeling (FDM) characterized by a reticular pattern with 0°/90° raster orientation and square pores. In parallel, a MeHA-HAp slurry has been synthesized and infiltrated in the PEEK scaffolds. The mechanical properties of the coated and pure PEEK scaffold have been evaluated, showing that the inclusion of MeHA-HAp into the lattice geometry did not significantly change the strength of the PEEK structure with Young's modulus of 1034.9 ± 126.1 MPa and 1020.0 ± 63.7 MPa for PEEK and PEEK-MeHA-HAp scaffolds, respectively. Human MSCs were seeded on bare and coated scaffolds and cultured for up to 28 days to determine the adhesion, proliferation, migration and osteogenic differentiation. In vitro results showed that the MeHA-HAp coating promotes MSCs adhesion and proliferation and contributes to osteogenic differentiation and extracellular matrix mineralization. This study provides an efficient solution for the development of a scaffold combining the great mechanical performances of PEEK with the bioactive properties of MeHA and HAp, having high potential for translational clinical applications.

Recent Advances in Bioengineered Scaffolds for Cutaneous Wound Healing

Wound healing is an evolved dynamic biological process. Though many research and clinical approaches have been explored to restore damaged or diseased skin, the current treatment for deep cutaneous injuries is far from being perfect, and the ideal regenerative therapy remains a significant challenge. Of all treatments, bioengineered scaffolds play a key role and represent great progress in wound repair and skin regeneration. In this review, we focus on the latest advancement in biomaterial scaffolds for wound healing. We discuss the emerging philosophy of designing biomaterial scaffolds, followed by precursor development. We pay particular attention to the therapeutic interventions of bioengineered scaffolds for cutaneous wound healing, and their dual effects while conjugating with bioactive molecules, stem cells, and even immunomodulation. As we review the advancement and the challenges of the current strategies, we also discuss the prospects of scaffold development for wound healing.

Micromechanical Compatibility between Cells and Scaffolds Directs the Phenotypic Transition of Stem Cells

This study experimentally substantiates that the micromechanical compatibility between cell and substrate is essential for cells to achieve energetically favorable mechanotransduction that directs phenotypic transitions. The argument for this compatibility is based on a thermodynamic model that suggests that the response of cells to their substrate mechanical environment is a consequence of the interchange between forms of energy governing the cell-substrate interaction. Experimental validation for the model has been carried out by investigating the osteogenic differentiation of dental follicle stem cells (DFSCs) seeded on electrospun fibrous scaffolds. Electrospinning of blends containing polycaprolactone (PCL) and silk fibroin (SF) with varying composition of cellulose nanocrystals (CNCs) resulted in three-dimensional (3D) fibrous scaffolds with bimodal distribution of fiber diameter, which provides both macroscopically stiff and microscopically compliant scaffolds for cells without affecting the surface chemical functionality of scaffolds. Atomic force microscopy (AFM) with a colloidal probe and single-cell force spectroscopy were used to characterize cell stiffness and scaffold stiffness on the cellular level, as well as cell-scaffold adhesive interaction (chemical functionality). This study has successfully varied scaffold mechanical properties without affecting their surface chemistry. In vitro tests indicate that the micromechanical compatibility between cells and scaffolds has been significantly correlated with mechanosensitive gene expression markers and osteogenic differentiation markers of DFSCs. The agreement between experimental observations and the thermodynamic model affirms that the cellular response to the mechanical environment, though biological in nature, follows the laws of the energy interchange to achieve its self-regulating behavior. More importantly, this study provides systematic evidence, through extensive and rigorous experimental studies, for the first time that rationalizes that micromechanical compatibility is indeed important to the efficacy of regenerative medicine.

Hyaluronic acid regulates heart valve interstitial cell contraction in fibrin-based scaffolds

Heart valve disease is associated with high morbidity and mortality worldwide resulting in hundreds of thousands of heart valve replacements each year. Tissue engineered heart valves (TEHVs) have the potential to overcome the major limitations of traditional replacement valves; however, leaflet retraction has led to the failure of TEHVs in preclinical studies. As native unmodified hyaluronic acid (HA) is known to promote healthy tissue development in native heart valves, we hypothesize that adding unmodified HA to fibrin-based scaffolds common to tissue engineering will reduce retraction by increasing cell-scaffold interactions and density of the scaffolds. Using a custom high-throughput culture system, we found that incorporating HA into millimeter-scale fibrin-based cell-populated scaffolds increases initial fiber diameter and cell-scaffold interactions, causing a cascade of mechanical, morphological, and cellular responses. These changes lead to higher levels of scaffold compaction and stiffness, increased cell alignment, and less bundling of fibrin fibers by the cells during culture. These effects significantly reduce scaffold retraction and total contractile force each by around 25%. These findings increase our understanding of how HA alters tissue remodeling and could inform the design of the next generation of tissue engineered heart valves to help reduce retraction. STATEMENT OF SIGNIFICANCE: Tissue engineered heart valves (TEHVs) have the potential to overcome the major limitations of traditional replacement valves; however, leaflet retraction induced by excessive myofibroblast activation has led to failure in preclinical studies. Developing valves are rich in hyaluronic acid (HA), which helps maintain a physiological environment for tissue remodeling without retraction. We hypothesized that adding unmodified HA to TEHVs would reduce retraction by increasing cell-scaffold interactions and density of the scaffolds. Using a high-throughput tissue culture platform, we demonstrate that HA incorporation into a fibrin-based scaffold can significantly reduce tissue retraction and total contractile force by increasing fiber bundling and altering cell-mediated matrix remodeling, therefore increasing gel density and stiffness. These finding increase our knowledge of native HA's effects within the extracellular matrix, and provide a new tool for TEHV design.

MSC-derived immunomodulatory extracellular matrix functionalized electrospun fibers for mitigating foreign-body reaction and tendon adhesion

Adhesion formation during tendon healing remains a severe problem in clinical practice. Multiple factors contribute to postoperative adhesion formation, and macrophage-driven inflammation is thought to be greatly involved in this process. We hypothesize that reducing macrophage-mediated inflammation in the injured tendon by regulating M1 to M2 macrophage polarization may effectively inhibit adhesion formation. Here, we developed an acellular immunomodulatory biomaterial consisting of an electrospun polycaprolactone/silk fibroin (PCL/SF) composite fibrous scaffold functionalized with mesenchymal stem cell (MSC)-derived extracellular matrix (ECM). To enhance the immunoregulatory potential of MSCs, we performed inflammatory licensing with IFN-γ to obtain immunomodulatory ECM (iECM). Proteomic analyses of MSCs and their secreted ECM components from different culture conditions revealed the MSC-ECM molecular signatures and the potential mechanism of ECM immunoregulation. Then, the immunoregulatory potential of the iECM-modified scaffold was evaluated in vitro and in vivo. Relative to the PCL/SF fibrous scaffold, the iECM-functionalized scaffold facilitated M2 macrophage polarization and inhibited the expression of multiple cytokines (IL-1β, IL-6, CXCL11, IL-10, IL-1R2, and TGF-β1) in vitro, strongly suggesting the immunosuppressive ability of iECM derived from inflammatory licensed MSCs. Consistent with the in vitro findings, the results of rat subcutaneous implantation indicated that a markedly lower foreign-body reaction (FBR) was obtained in the PCL/SF-iECM group than in the other groups, as evidenced by thinner fibrotic capsule formation, less type I collagen production and more M2-type macrophage polarization. In the rat Achilles tendon injury model, the PCL/SF-iECM scaffold greatly mitigated tendon adhesion with clear sheath space formation between the tendon and the scaffold. These data highlight the immunomodulatory potential of iECM-functionalized fibrous scaffolds to attenuate FBR by modulating M2 macrophage polarization, thereby preventing tendon adhesion. STATEMENT OF SIGNIFICANCE: Electrospun PCL/SF fibrous scaffolds functionalized with ECM secreted by MSCs stimulated by inflammatory factor IFN-γ was developed that combined physical barrier and immunomodulatory functions to prevent tendon adhesion formation. PCL/SF micro-nanoscale bimodal fibrous scaffolds prepared by emulsion electrospinning possess high porosity and a large pore size beneficial for nutrient transport to promote intrinsic healing; moreover, surface modification with immunomodulatory ECM (iECM) mitigates the FBR of fibrous scaffolds to prevent tendon adhesion. The iECM-functionalized electrospun scaffolds exhibit powerful immunomodulatory potency in vitro and in vivo. Moreover, the iECM-modified scaffolds, as an anti-adhesion physical barrier with immunomodulatory ability, have an excellent performance in a rat Achilles tendon adhesion model. MSC secretome-based therapeutics, as an acellular regenerative medicine strategy, are expected to be applied to other inflammatory diseases due to its strong immunoregulatory potential.

Angiogenic potential of airbrushed fucoidan/polycaprolactone nanofibrous meshes

Implantation of biomaterials and hybrid constructs in tissue engineering approaches presents major limitations such as inflammatory reaction and the lack of vasculature integration. Therefore, new strategies are needed to enhance implant function, immune protection, and revascularization. In this work, we developed fibrous meshes composed of fucoidan (Fu), a sulfated polysaccharide extracted from brown algae, and polycaprolactone (PCL), a synthetic biodegradable polymer, using the airbrush technique. The chemical characterization by FTIR, EDS, and XPS confirmed the presence of the two polymers in the structure of airbrushed nanofibrous meshes (ANFM). Moreover, these nanofibrous exhibited good wettability and mechanical properties envisaging their application as templates for biomaterials and cell culture. The developed ANFM were directly cultured with human pulmonary microvascular endothelial (HPMEC-ST1.6R) cells for up to 7 days. Biological results demonstrated that ANFM comprising Fu promoted cellular attachment, spreading, and proliferation of human endothelial cells. The angiogenic potential of ANFM was further evaluated by onplantation of PCL and PCL/Fu ANFM in chick chorioallantoic membrane (CAM). In ovo and ex ovo results showed that the incorporation of Fu increased the pro-angiogenic potential of ANFM. Altogether, the results suggest that airbrush biocomposite meshes could be used as a biomaterial substrate to promote vascularization.

Surface modification of electrospun fibers with mechano-growth factor for mitigating the foreign-body reaction

The implantation of synthetic polymeric scaffolds induced foreign-body reaction (FBR) seriously influence the wound healing and impair functionality recovery. A novel short peptide, mechano-growth factor (MGF), was introduced in this study to modify an electrospun polycaprolactone (PCL) fibrous scaffold to direct the macrophage phenotype transition and mitigate the FBR. In vitro studies discovered the cell signal transduction mechanism of MGF regulates the macrophage polarization via the expression of related genes and proteins. We found that macrophages response the MGF stimuli via endocytosis, then MGF promotes the histone acetylation and upregulates the STAT6 expression to direct an anti-inflammatory phenotype transition. Subsequently, an immunoregulatory electrospun PCL fibrous scaffold was modified by silk fibroin (SF) single-component layer-by-layer assembly, and the SF was decorated with MGF via click chemistry. Macrophages seeded on scaffold to identify the function of MGF modified scaffold in directing macrophage polarization in vitro. Parallelly, rat subcutaneous implantation model and rat tendon adhesion model were performed to detect the immunomodulatory ability of the MGF-modified scaffold in vivo. The results demonstrate that MGF-modified scaffold is beneficial to the transformation of macrophages to M2 phenotype in vitro. More importantly, MGF-functionalized scaffold can inhibit the FBR at the subcutaneous tissue and prevent tissue adhesion.

Tailoring Materials for Modulation of Macrophage Fate

Human immune system acts as a pivotal role in the tissue homeostasis and disease progression. Immunomodulatory biomaterials that can manipulate innate immunity and adaptive immunity hold great promise for a broad range of prophylactic and therapeutic purposes. This review is focused on the design strategies and principles of immunomodulatory biomaterials from the standpoint of materials science to regulate macrophage fate, such as activation, polarization, adhesion, migration, proliferation, and secretion. It offers a comprehensive survey and discussion on the tunability of material designs regarding physical, chemical, biological, and dynamic cues for modulating macrophage immune response. The range of such tailorable cues encompasses surface properties, surface topography, materials mechanics, materials composition, and materials dynamics. The representative immunoengineering applications selected herein demonstrate how macrophage-immunomodulating biomaterials are being exploited for cancer immunotherapy, infection immunotherapy, tissue regeneration, inflammation resolution, and vaccination. A perspective on the future research directions of immunoregulatory biomaterials is also provided.

Hyaluronic acid electrospinning: Challenges, applications in wound dressings and new perspectives

Hyaluronic acid (HA) has already been consolidated in the literature as an extremely efficient biopolymer for biomedical applications. In addition to its biodegradability, HA also has excellent biological properties. In the nanofiber form, this polymer can mimic biological tissues, mainly the layers of the skin, and therefore has great potential as structures for the construction of wound dressings. Despite the numerous efforts from the scientific community proposing new dressings, this is an area in constant evolution. A dressing that brings together all the properties of an ideal dressing has not been developed yet. Electrospinning is a simple and versatile technique that correctly aligned with the functional properties of HA can produce multifunctional nanofiber structures capable of promoting skin recover quickly. This review discusses (i) key strategies for successful electrospinning of HA, (ii) main challenges and advances found in the electrospinning process, (iii) the bioactive properties of this polymer in the treatment of wounds, as well as (iv) the results obtained in the last decade by the in vitro and in vivo evaluation of the healing properties of these nanosystems.

Recent Advances in Three-Dimensional Multicellular Spheroid Culture and Future Development

Three-dimensional multicellular spheroids (MCSs) have received extensive attention in the field of biomedicine due to their ability to simulate the structure and function of tissues in vivo more accurately than traditional in vitro two-dimensional models and to simulate cell-cell and cell extracellular matrix (ECM) interactions. It has become an important in vitro three-dimensional model for tumor research, high-throughput drug screening, tissue engineering, and basic biology research. In the review, we first summarize methods for MCSs generation and their respective advantages and disadvantages and highlight the advances of hydrogel and microfluidic systems in the generation of spheroids. Then, we look at the application of MCSs in cancer research and other aspects. Finally, we discuss the development direction and prospects of MCSs.

Co-electrospun nano-/microfibrous composite scaffolds with structural and chemical gradients for bone tissue engineering

Recent trends in scaffold design for tissue engineering have focused on providing structural, mechanical and chemical cues for guiding cell behaviors. In this study, we presented a structural/compositional gradient nano-/microfibrous mesh by co-electrospinning, using silk fibroin-poly(ε-caprolactone) (SF-PCL) nanofibers and PCL microfibers. The pore size, porosity, and physical property of the gradient meshes were qualified. Cell proliferation of mouse osteoblast-like MC3T3-E1 cells was carried out to estimate the effect of structural and compositional gradients on biocompatibility. Furthermore, the 2-D mesh was rolled up and the compressive property of 3-D cylinder was investigated. The results suggested that the rolled-up gradient cylinder scaffold exhibited higher osteogenic differentiation compared to the pristine nanofibrous cylinder sample. By incorporating Chinese medicine ginsenoside Rg1, sustained release was achieved in composite meshes. Rg1-containing nanofibrous meshes and Rg1 gradient cylinders enhanced the cell proliferation of human umbilical vein endothelial cells (HUVECs). The developed fibrous scaffold may provide structural, compositional, and chemical gradients for bone regeneration. BRIEFS: Structural and chemical gradient fibrous scaffold fabricated by co-electrospinning.

Stem Cell-Friendly Scaffold Biomaterials: Applications for Bone Tissue Engineering and Regenerative Medicine

Bone is a dynamic organ with high regenerative potential and provides essential biological functions in the body, such as providing body mobility and protection of internal organs, regulating hematopoietic cell homeostasis, and serving as important mineral reservoir. Bone defects, which can be caused by trauma, cancer and bone disorders, pose formidable public health burdens. Even though autologous bone grafts, allografts, or xenografts have been used clinically, repairing large bone defects remains as a significant clinical challenge. Bone tissue engineering (BTE) emerged as a promising solution to overcome the limitations of autografts and allografts. Ideal bone tissue engineering is to induce bone regeneration through the synergistic integration of biomaterial scaffolds, bone progenitor cells, and bone-forming factors. Successful stem cell-based BTE requires a combination of abundant mesenchymal progenitors with osteogenic potential, suitable biofactors to drive osteogenic differentiation, and cell-friendly scaffold biomaterials. Thus, the crux of BTE lies within the use of cell-friendly biomaterials as scaffolds to overcome extensive bone defects. In this review, we focus on the biocompatibility and cell-friendly features of commonly used scaffold materials, including inorganic compound-based ceramics, natural polymers, synthetic polymers, decellularized extracellular matrix, and in many cases, composite scaffolds using the above existing biomaterials. It is conceivable that combinations of bioactive materials, progenitor cells, growth factors, functionalization techniques, and biomimetic scaffold designs, along with 3D bioprinting technology, will unleash a new era of complex BTE scaffolds tailored to patient-specific applications.

α-Lactalbumin-Based Nanofiber Dressings Improve Burn Wound Healing and Reduce Scarring

Skin wound especially burn injury is a major threat for public health. One of the pursuits in the current wound healing research is to identify new promising biological materials, which can not only promote tissue repair but also reduce scar formation. In this current study, the potentials of α-lactalbumin (ALA), a tryptophan-rich dietary protein acting as a precursor of neurotransmitter serotonin, to promote the burn wound healing and reduce the scar formation were investigated. The ALA was initially electrospun with polycaprolactone (PCL) to accomplish electrospun nanofibrous mats (ENMs), subsequently assessed for their physicochemical attributes and wound healing efficiency on a burn rat model, and then their healing mechanisms at cellular and molecular levels were explored. The results showed that ALA and PCL were physicochemically compatible in ENMs. The average diameter of various nanofibers was within 183-344 nm. Their wettability and mechanical properties could be readily modulated by adjusting the mass ratios of ALA and PCL from 1/9 to 1/2. The selected ENMs exhibited negligible cytotoxicity and satisfactory adhesion to fibroblasts and promoting the proliferation of the fibroblasts. As compared to pristine PCL based ENMs, the composite scaffolds could accelerate the wound healing process and exhibit effects comparable to a marketed wound dressing over 16 days. Moreover, the ALA/PCL based ENMs could increase the synthesis of type I collagen and decrease the expression of α-smooth muscle actin, conferring that the novel wound dressings could reduce the formation of scars. Collectively, this study demonstrates that the ALA is a promising biological material and could promote the regeneration of burn skins with reduced scar formation, when being loaded on ultrafine fibrous scaffolds, mimicking the structure of the natural extra cellular matrix.

Gradient Biomineralized Silk Fibroin Nanofibrous Scaffold with Osteochondral Inductivity for Integration of Tendon to Bone

Enthesis injury repair remains a huge challenge because of the unique biomolecular composition, microstructure, and mechanics in the interfacial region. Surgical reconstruction often creates new bone-scaffold interfaces with mismatched properties, resulting in poor osseointegration. To mimic the natural interface tissue structures and properties, we fabricated a nanofibrous scaffold with gradient mineral coating based on 10 × simulated body fluid (SBF) and silk fibroin (SF). We then characterized the physicochemical properties of the scaffold and evaluated its biological functions both in vitro and in vivo. The results showed that different areas of SF nanofibrous scaffold had varying levels of mineralization with disparate mechanical properties and had different effects on bone marrow mesenchymal stem cell growth and differentiation. Furthermore, the gradient scaffolds exhibited an enhancement of integration in the tendon-to-bone interface with a higher ultimate load and more fibrocartilage-like tissue formation. These findings demonstrate that the silk-based nanofibrous scaffold with gradient mineral coating can regulate the formation of interfacial tissue and has the potential to be applied in interface tissue engineering.

Hyaluronic acid-Based wound dressings: A review

Hyaluronic acid (HA), a non-sulfated glycosaminoglycan (GAG), is a major component of skin extracellular matrix (ECM) and it is involved in the inflammatory response, angiogenesis, and tissue regeneration process. Due to the intrinsic properties of HA (such as biocompatibility, biodegradability and hydrophilic character), it has been used to produce different wound dressings, namely sponges, films, hydrogels, and electrospun membranes. Herein, an overview of the different HA-based wound dressings that have been produced so far is provided as well as the future directions regarding the strategies aimed to improve the mechanical stability of HA-based wound dressings, along with the incorporation of biomolecules intended to ameliorate their biological performance during the healing process.

Development of calcium phosphate/calcium sulfate biphasic biomedical material with hyaluronic acid containing collagenase and simvastatin for vital pulp therapy

OBJECTIVE

In vital pulp therapy (VPT), a barrier is created with appropriate capping to protect the remaining pulp and thus maintain pulp vitality. Here, we evaluated the feasibility of a biphasic calcium phosphate cement (CPC)-calcium sulfate hemihydrate (CSH) biomaterial containing simvastatin (Sim) and collagenase (Col) for VPT.

METHODS

Combinations of varying CPC and CSH concentrations were analyzed for their handling properties and setting times, with their structures observed through scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS). Drug release patterns of simvastatin and collagenase combined with CPC-CSH (CPC-CSH-Sim-Col) were also analyzed, followed by biocompatibility and bioactivity tests on human dental pulp stem cells (hDPSCs) and in vivo animal study in canine models; the in vivo results were obtained through microcomputed tomography and histological analysis.

RESULTS

The results revealed that 70 wt% CPC (CPC7) with 30 wt% CSH (CSH3) exhibited optimal setting time and porous structure for clinical use. The cell viability and cytotoxicity analysis demonstrated that CPC7-CSH3 with or without simvastatin or collagenase did not injure hDPSCs. In vivo, the CPC7-CSH3-Sim-Col induced dentin bridge formation.

SIGNIFICANCE

CPC7-CSH3-Sim-Col in this study has great potential as a VPT biomaterial to enhance the dentin bridge formation.

Polycaprolactone as biomaterial for bone scaffolds: Review of literature

Bone tissue engineering using polymer based scaffolds have been studied a lot in last decades. Considering the qualities of all the polymers desired to be used as scaffolds, Polycaprolactone (PCL) polyester apart from being biocompatible and biodegradable qualifies to an appreciable level due its easy availability, cost efficacy and suitability for modification. Its adjustable physio-chemical state, biological properties and mechanical strength renders it to withstand physical, chemical and mechanical, insults without significant loss of its properties. This review aims to critically analyse the efficacy of PCL as a biomaterial for bone scaffolds.

Enhanced osteogenesis and angiogenesis by PCL/chitosan/Sr-doped calcium phosphate electrospun nanocomposite membrane for guided bone regeneration

Membranes play pivotal role in guided bone regeneration (GBR) technique for reconstruction alveolar bone. GBR membrane that is able to stimulate both osteogenic and angiogenic differentiation of cells may be more effective in clinic practice. Herein, we fabricated the Sr-doped calcium phosphate/polycaprolactone/chitosan (Sr-CaP/PCL/CS) nanohybrid fibrous membrane by incorporating 20 wt% bioactive Sr-CaP nanoparticles into PCL/CS matrix via one-step electrospinning method, in order to endow the membrane with stimulation of osteogenesis and angiogenesis. The physicochemical properties, mechanical properties, Sr²⁺ release behavior, and the membrane stimulate bone mesenchymal stem cell (BMSCs) differentiation were evaluated in comparison with PCL/CS and CaP/PCL/CS membranes. The SEM images revealed that the nanocomposite membrane mimicked the extracellular matrix structure. The release curve presented a 28-day long continuous release of Sr²⁺ and concentration which was certified in an optimal range for positive biological effects at each timepoint. The in vitro cell culture experiments certified that the Sr-CaP/PCL/CS membrane enjoyed excellent biocompatibility and remarkably promoted rat bone mesenchymal stem cell (BMSCs) adhesion and proliferation. In terms of osteogenic differentiation, BMSCs seeded on the Sr-CaP/PCL/CS membrane showed a higher ALP activity level and a better matrix mineralization. What's more, the synergism of the Sr²⁺ and CaP from the Sr-CaP/PCL/CS membrane enhanced BMSCs angiogenic differentiation, herein resulting in the largest VEGF secretion amount. Consequently, the Sr-CaP/PCL/CS nanohybrid electrospun membrane has promising applications in GBR.

Efficient Wound Healing Using a Synthetic Nanofibrous Bilayer Skin Substitute in Murine Model

Treatment of full-thickness skin wounds with minimal scarring and complete restoration of native tissue properties still exists as a clinical challenge. A bilayer skin substitute was fabricated by coating human amniotic membrane (AM) with electrospun silk fibroin nanofibers, and its in vivo biological behavior was studied using murine full-thickness skin wound model. Donut-shaped silicon splints were utilized to prevent wound contraction in mouse skin and simulate re-epithelialization, which is the normal path of human wound healing. Skin regeneration using the bilayer scaffold was compared with AM and untreated defect after 30 d. Tissue samples were taken from healed wound areas and investigated through histopathological and immunohistochemical staining to visualize involucrin (IVL), P63, collagen I, CD31, and vascular endothelial growth factor. In addition, mRNA expression of IVL, P63, interleukin-6, and cyclooxygenase-2 was studied. The application of bilayer scaffold resulted in the best epidermal and dermal regeneration, demonstrated by histopathological examination and molecular analysis. In regenerated wounds of the bilayer scaffold group, the mRNA expression levels of inflammatory markers (interleukin-6 and cyclooxygenase-2) were downregulated, and the expression pattern of keratinocyte markers (IVL and P63) at both mRNA and protein levels was more similar to native tissue in comparison with AM and no-treatment groups. There was no significant difference in the expression level of collagen I, CD31, and vascular endothelial growth factor among different groups. Conclusively, these promising results serve as a supporting evidence for proceeding to clinical phase to examine the capacity of this bilayer scaffold for human skin regeneration.

Tuning the biomimetic behavior of scaffolds for regenerative medicine through surface modifications

Tissue engineering and regenerative medicine rely extensively on biomaterial scaffolds to support cell adhesion, proliferation, and differentiation physically and chemically in vitro and in vivo. Changes to the surface characteristics of the scaffolds have the greatest impact on cell response. Here, we discuss five dominant surface modification approaches used to biomimetically improve the most common scaffolds for tissue engineering, those based on aliphatic polyesters. Scaffolds of aliphatic polyesters such as poly(l-lactic acid), poly(l-lactic-co-glycolic acid), and poly(ε-caprolactone) are often used in tissue engineering because they provide desirable, tunable properties such as ease of manufacturing, good mechanical properties, and nontoxic degradation products. However, cell-surface interactions necessary for tissue engineering are limited on these materials by their smooth postfabrication surfaces, hydrophobicity, and lack of recognizable biochemical binding sites. The surface modification techniques that have been developed for synthetic polymer scaffolds reduce initial barriers to cell adhesion, proliferation, and differentiation. Topographical modification, protein adsorption, mineral coating, functional group incorporation, and biomacromolecule immobilization each contribute through varying mechanisms to improving cell interactions with aliphatic polyester scaffolds. Furthermore, rational combination of methods from these categories can provide nuanced, specific environments for targeted tissue development.

Hyaluronic acid and chitosan-based nanosystems: a new dressing generation for wound care

INTRODUCTION

The main goal in the management of chronic wounds is the development of multifunctional dressings able to promote a rapid recovery of skin structure and function, improving patient compliance.

AREAS COVERED

This review discusses the use of nanosystems, based on hyaluronic acid and chitosan or their derivatives for the local treatment of chronic wounds. The bioactive properties of both polysaccharides will be described, as well as the results obtained in the last decade by the in vitro and in vivo evaluation of the wound healing properties of nanosystems based on such polymers.

EXPERT OPINION

In the last decades, there has been a progressive change in the local treatments of chronic wounds: traditional inert dressings have been replaced by more effective bioactive ones, based on biopolymers taking part in wound healing and able to release the loaded active agents in a controlled way. With the advance of nanotechnologies, the scenario has further changed: nanosystems, characterized by a large area-to-volume ratio, show an improved interaction with the biological substrates, amplifying the activity of the constituent biopolymers. In the coming years, a deeper insight into wound healing mechanisms and the development of new techniques for nanosystem manufacturing will results in the design of new scaffolds with improved performance.

MSOT/CT/MR imaging-guided and hypoxia-maneuvered oxygen self-supply radiotherapy based on one-pot MnO2-mSiO2@Au nanoparticles

Radiotherapy (RT) is one of the most widely applied treatments for cancer therapy in clinics. Herein, we constructed innovative multifunctional nanotheranostic MnO2-mSiO2@Au-HA nanoparticles (MAHNPs) based on one-pot MnO2-mSiO2 nanohybrids (MNHs) and gold nanoparticles (AuNPs) for multispectral optoacoustic tomography (MSOT)/computed tomography (CT) and magnetic resonance (MR) imaging-guided hypoxia-maneuvered radiotherapy. The MNHs were prepared via a facile one-pot approach, which avoided the leakage of MnO2 nanoparticles and increased the synthetic efficiency. The Mn2+ ions triggered the breakdown of endogenous H2O2 to generate O2 to convert the hypoxic tumor micro-environment (TME), thus enhancing radiotherapy by self-supply oxygen. In addition, hyaluronic acid (HA) was employed to modify the surface of the MnO2-mSiO2@Au nanoparticles to improve their biocompatibility and cellular uptake. The well-designed nanoparticles could perform remarkable photothermal therapy (PTT) and hypoxia-maneuvered radiotherapy (RT) simultaneously and MSOT/CT/MR imaging. The in vivo studies showed that the MAHNPs achieved almost total suppression of tumor growth without observable recurrence, which raises new possibilities for clinical nanotheranostics with multimodal diagnostic and therapeutic coalescent design.

Hyaluronan/collagen hydrogels containing sulfated hyaluronan improve wound healing by sustained release of heparin-binding EGF-like growth factor

Functional biomaterials that are able to bind, stabilize and release bioactive proteins in a defined manner are required for the controlled delivery of such to the desired place of action, stimulating wound healing in health-compromised patients. Glycosaminoglycans (GAG) represent a very promising group of components since they may be functionally engineered and are well tolerated by the recipient tissues due to their relative immunological inertness. Ligands of the Epidermal Growth Factor (EGF) receptor (EGFR) activate keratinocytes and dermal fibroblasts and, thus, contribute to skin wound healing. Heparin-binding EGF-like growth factor (HB-EGF) bound to GAG in biomaterials (e.g. hydrogels) might serve as a reservoir that induces prolonged activation of the EGF receptor and to recover disturbed wound healing. Based on previous findings, the capacity of hyaluronan (HA) and its sulfated derivatives (sHA) to bind and release HB-EGF from HA/collagen-based hydrogels was investigated. Docking and molecular dynamics analysis of a molecular model of HB-EGF led to the identification of residues in the heparin-binding domain of the protein being essential for the recognition of GAG derivatives. Furthermore, molecular modeling and surface plasmon resonance (SPR) analyses demonstrated that sulfation of HA increases binding strength to HB-EGF thus providing a rationale for the development of sHA-containing hydrogels. In line with computational observations and in agreement with SPR results, gels containing sHA displayed a retarded HB-EGF release in vitro compared to pure HA/collagen gels. Hydrogels containing HA and collagen or a mixture with sHA were shown to bind and release bioactive HB-EGF over at least 72 h, which induced keratinocyte migration, EGFR-signaling and HGF expression in dermal fibroblasts. Importantly, hydrogels containing sHA strongly increased the effectivity of HB-EGF in inducing epithelial tip growth in epithelial wounds shown in a porcine skin organ culture model. These findings suggest that hydrogels containing HA and sHA can be engineered for smart and effective wound dressings. STATEMENT OF SIGNIFICANCE: Immobilization and sustained release of recombinant proteins from functional biomaterials might overcome the limited success of direct application of non-protected solute growth factors during the treatment of impaired wound healing. We developed HA/collagen-based hydrogels supplemented with acrylated sulfated HA for binding and release of HB-EGF. We analyzed the molecular basis of HB-EGF interaction with HA and its chemical derivatives by in silico modeling and surface plasmon resonance. These hydrogels bind HB-EGF reversibly. Using different in vitro assays and organ culture we demonstrate that the introduction of sulfated HA into the hydrogels significantly increases the effectivity of HB-EGF action on target cells. Therefore, sulfated HA-containing hydrogels are promising functional biomaterials for the development of mediator releasing wound dressings.

Microfibrous scaffolds from poly(l-lactide-co-ε-caprolactone) blended with xeno-free collagen/hyaluronic acid for improvement of vascularization in tissue engineering applications

Success of 3D tissue substitutes in clinical applications depends on the presence of vascular networks in their structure. Accordingly, research in tissue engineering is focused on the stimulation of angiogenesis or generation of a vascular network in the scaffolds prior to implantation. A novel, xeno-free, collagen/hyaluronic acid-based poly(l-lactide-co-ε-caprolactone) (PLC/COL/HA) (20/9.5/0.5 w/w/w) microfibrous scaffold was produced by electrospinning. Collagen types I and III, and hyaluronic acid were isolated from human umbilical cords and blended with the GMP grade PLC. When compared with PLC scaffolds the PLC/COL/HA had higher water uptake capacity (103% vs 66%) which may have contributed to the decrease in its Young's Modulus (from 1.31 to 0.89 MPa). The PLC/COL/HA better supported adipose tissue-derived mesenchymal stem cell (AT MSC) adhesion; within 24 h the cell number on the PLC/COL/HA scaffolds was 3 fold higher. Co-culture of human umbilical vein endothelial cells and AT MSCs induced capillary formation on both scaffold types, but the PLC/COL/HA led to formation of interconnected vessels whose total length was 1.6 fold of the total vessel length on PLC. Clinical use of this scaffold would eliminate the immune response triggered by xenogeneic collagen and transmission of animal-borne diseases while promoting a better vascular network formation.

Electrospun polymeric nanofibres as wound dressings: A review

Skin wounds have significant morbidity and mortality rates associated. This is explained by the limited effectiveness of the currently available treatments, which in some cases do not allow the reestablishment of the structure and functions of the damaged skin, leading to wound infection and dehydration. These drawbacks may have an impact on the healing process and ultimately prompt patients' death. For this reason, researchers are currently developing new wound dressings that enhance skin regeneration. Among them, electrospun polymeric nanofibres have been regarded as promising tools for improving skin regeneration due to their structural similarity with the extracellular matrix of normal skin, capacity to promote cell growth and proliferation and bactericidal activity as well as suitability to deliver bioactive molecules to the wound site. In this review, an overview of the recent studies concerning the production and evaluation of electrospun polymeric nanofibrous membranes for skin regenerative purposes is provided. Moreover, the current challenges and future perspectives of electrospun nanofibrous membranes suitable for this biomedical application are highlighted.

Biomaterials for Skin Substitutes

Patients with extensive burns rely on the use of tissue engineered skin due to a lack of sufficient donor tissue, but it is a challenge to identify reliable and economical scaffold materials and donor cell sources for the generation of a functional skin substitute. The current review attempts to evaluate the performance of the wide range of biomaterials available for generating skin substitutes, including both natural biopolymers and synthetic polymers, in terms of tissue response and potential for use in the operating room. Natural biopolymers display an improved cell response, while synthetic polymers provide better control over chemical composition and mechanical properties. It is suggested that not one material meets all the requirements for a skin substitute. Rather, a composite scaffold fabricated from both natural and synthetic biomaterials may allow for the generation of skin substitutes that meet all clinical requirements including a tailored wound size and type, the degree of burn, the patient age, and the available preparation technique. This review aims to be a valuable directory for researchers in the field to find the optimal material or combination of materials based on their specific application.