Molecular engineering of glycosaminoglycan chemistry for biomolecule delivery

Modulating the release of bioactive molecules of human mesenchymal stromal cell secretome: Heparinization of hyaluronic acid-based hydrogels

An amine derivative of hyaluronic acid (HA) was crosslinked to obtain a 3D dried sponge. The sponge was subsequently rehydrated using secretome from human mesenchymal stromal cells (MSCs), resulting in the formation of a hydrogel. The release kinetics analysis demonstrated that the hydrogel effectively sustained secretome release, with 70% of the initially loaded wound-healing-associated cytokines being released over a 12-day period. Tuning the hydrogel properties through heparin crosslinking resulted in a biomaterial with a distinct mechanism of action. Specifically, the presence of heparin enhanced water uptake capacity of the hydrogel and increased its sensitivity to enzymatic degradation. Notably, the heparin crosslinking also led to a significant retention of cytokines within the hydrogel matrix. Overall, the secretome-rehydrated HA hydrogel holds promise as a versatile device for regenerative medicine applications: the non-heparinized hydrogel may function as a biomaterial with low reabsorption rates, sustaining the release of bioactive molecules contained in MSC secretome. In contrast, the heparinized hydrogel may serve as a depot of bioactive molecules with faster reabsorption rates. Given its patch-like characteristic, the HA-based hydrogel appears suitable as topical treatment for external organs, such as the skin.

Sweet but Challenging: Tackling the Complexity of GAGs with Engineered Tailor-Made Biomaterials

Glycosaminoglycans (GAGs) play a crucial role in tissue homeostasis by regulating the activity and diffusion of bioactive molecules. Incorporating GAGs into biomaterials has emerged as a widely adopted strategy in medical applications, owing to their biocompatibility and ability to control the release of bioactive molecules. Nevertheless, immobilized GAGs on biomaterials can elicit distinct cellular responses compared to their soluble forms, underscoring the need to understand the interactions between GAG and bioactive molecules within engineered functional biomaterials. By controlling critical parameters such as GAG type, density, and sulfation, it becomes possible to precisely delineate GAG functions within a biomaterial context and to better mimic specific tissue properties, enabling tailored design of GAG-based biomaterials for specific medical applications. However, this requires access to pure and well-characterized GAG compounds, which remains challenging. This review focuses on different strategies for producing well-defined GAGs and explores high-throughput approaches employed to investigate GAG-growth factor interactions and to quantify cellular responses on GAG-based biomaterials. These automated methods hold considerable promise for improving the understanding of the diverse functions of GAGs. In perspective, the scientific community is encouraged to adopt a rational approach in designing GAG-based biomaterials, taking into account the in vivo properties of the targeted tissue for medical applications.

Extending the enzymatic toolbox for heparosan polymerization, depolymerization, and detection

Heparosan is an acidic polysaccharide expressed as a capsule polymer by pathogenic and commensal bacteria, e.g. by E. coli K5. As a precursor in the biosynthesis of heparan sulfate and heparin, heparosan has a high biocompatibility and is thus of interest for pharmaceutical applications. However, due to its low immunogenicity, developing antibodies against heparosan and detecting the polymer in biological samples has been challenging. In this study, we exploited the enzyme repertoire of E. coli K5 and the E. coli K5-specific bacteriophage ΦK5B for the controlled synthesis and depolymerization of heparosan. A fluorescently labeled heparosan nonamer was used as a priming acceptor to study the elongation mechanism of the E. coli K5 heparosan polymerases KfiA and KfiC. We could demonstrate that the enzymes act in a distributive manner, producing labeled heparosan of low dispersity. The enzymatically synthesized heparosan was a useful tool to identify the tailspike protein KflB of ΦK5B as heparosan lyase and to characterize its endolytic depolymerization mechanism. Most importantly, using site-directed mutagenesis and rational construct design, we generated an inactive version of KflB for the detection of heparosan in ELISA-based assays, on blots, and on bacterial and mammalian cells.

A review of glycosaminoglycan-modified electrically conductive polymers for biomedical applications

The application areas of electrically conductive polymers have been steadily growing since their discovery in the late 1970s. Recently, electrically conductive polymers have found their way into biomedicine, allowing the realization of many relevant applications ranging from bioelectronics to scaffolds for tissue engineering. Extracellular matrix components, such as glycosaminoglycans, build an important class of biomaterials that are heavily researched for biomedical applications due to their favorable properties. Due to their highly anionic character and the presence of sulfate groups in glycosaminoglycans, these biomolecules can be employed to functionalize conductive polymers, which enables the tailorability and improvement of cell-material interactions of conductive polymers. This review paper gives an overview of recent research on glycosaminoglycan-modified conductive polymers intended for biomedical applications and discusses the effect of different biological dopants on material characteristics, such as surface roughness, stiffness, and electrochemical properties. Moreover, the key findings of the biological characterization in vitro and in vivo are summarized, and remaining challenges in the field, particularly related to the modification of electrically conductive polymers with glycosaminoglycans to achieve improved functional and biological outcomes, are discussed. STATEMENT OF SIGNIFICANCE: The development of functional biomaterials based on electrically conductive polymers (CPs) for various biomedical applications, such as neural regeneration, drug delivery, or bioelectronics, has been increasingly investigated over the last decades. Recent literature has shown that changes in the synthesis procedure or the chosen dopant could adjust the resulting material characteristics. Hence, an interesting approach lies in using natural biomolecules as dopants for CPs to tailor the biological outcome. This review comprehensively summarizes the state of the art in the field of glycosaminoglycan-modified electrically conductive polymers for the first time, particularly highlighting the effect of the chosen dopant on material characteristics, such as surface morphology or stiffness, electrochemical properties, and consequently, cell-material interactions.

Scaffolds containing GAG-mimetic cellulose sulfate promote TGF-β interaction and MSC Chondrogenesis over native GAGs

Cartilage tissue engineering strategies seek to repair damaged tissue using approaches that include scaffolds containing components of the native extracellular matrix (ECM). Articular cartilage consists of glycosaminoglycans (GAGs) which are known to sequester growth factors. In order to more closely mimic the native ECM, this study evaluated the chondrogenic differentiation of mesenchymal stem cells (MSCs), a promising cell source for cartilage regeneration, on fibrous scaffolds that contained the GAG-mimetic cellulose sulfate. The degree of sulfation was evaluated, examining partially sulfated cellulose (pSC) and fully sulfated cellulose (NaCS). Comparisons were made with scaffolds containing native GAGs (chondroitin sulfate A, chondroitin sulfate C and heparin). Transforming growth factor-beta3 (TGF-β3) sequestration, as measured by rate of association, was higher for sulfated cellulose-containing scaffolds as compared to native GAGs. In addition, TGF-β3 sequestration and retention over time was highest for NaCS-containing scaffolds. Sulfated cellulose-containing scaffolds loaded with TGF-β3 showed enhanced chondrogenesis as indicated by a higher Collagen Type II:I ratio over native GAGs. NaCS-containing scaffolds loaded with TGF-β3 had the highest expression of chondrogenic markers and a reduction of hypertrophic markers in dynamic loading conditions, which more closely mimic in vivo conditions. Studies also demonstrated that TGF-β3 mediated its effect through the Smad2/3 signaling pathway where the specificity of TGF-β receptor (TGF- βRI)-phosphorylated SMAD2/3 was verified with a receptor inhibitor. Therefore, studies demonstrate that scaffolds containing cellulose sulfate enhance TGF-β3-induced MSC chondrogenic differentiation and show promise for promoting cartilage tissue regeneration.

Biopolymer-Based Nanogel Approach in Drug Delivery: Basic Concept and Current Developments

Due to their increased surface area, extent of swelling and active substance-loading capacity and flexibility, nanogels made from natural and synthetic polymers have gained significant interest in scientific and industrial areas. In particular, the customized design and implementation of nontoxic, biocompatible, and biodegradable micro/nano carriers makes their usage very feasible for a range of biomedical applications, including drug delivery, tissue engineering, and bioimaging. The design and application methodologies of nanogels are outlined in this review. Additionally, the most recent advancements in nanogel biomedical applications are discussed, with particular emphasis on applications for the delivery of drugs and biomolecules.

Marine-Inspired Approaches as a Smart Tool to Face Osteochondral Regeneration

The degeneration of osteochondral tissue represents one of the major causes of disability in modern society and it is expected to fuel the demand for new solutions to repair and regenerate the damaged articular joints. In particular, osteoarthritis (OA) is the most common complication in articular diseases and a leading cause of chronic disability affecting a steady increasing number of people. The regeneration of osteochondral (OC) defects is one of the most challenging tasks in orthopedics since this anatomical region is composed of different tissues, characterized by antithetic features and functionalities, in tight connection to work together as a joint. The altered structural and mechanical joint environment impairs the natural tissue metabolism, thus making OC regeneration even more challenging. In this scenario, marine-derived ingredients elicit ever-increased interest for biomedical applications as a result of their outstanding mechanical and multiple biologic properties. The review highlights the possibility to exploit such unique features using a combination of bio-inspired synthesis process and 3D manufacturing technologies, relevant to generate compositionally and structurally graded hybrid constructs reproducing the smart architecture and biomechanical functions of natural OC regions.

State-of-the-art glycosaminoglycan characterization

Glycosaminoglycans (GAGs) are heterogeneous acidic polysaccharides involved in a range of biological functions. They have a significant influence on the regulation of cellular processes and the development of various diseases and infections. To fully understand the functional roles that GAGs play in mammalian systems, including disease processes, it is essential to understand their structural features. Despite having a linear structure and a repetitive disaccharide backbone, their structural analysis is challenging and requires elaborate preparative and analytical techniques. In particular, the extent to which GAGs are sulfated, as well as variation in sulfate position across the entire oligosaccharide or on individual monosaccharides, represents a major obstacle. Here, we summarize the current state-of-the-art methodologies used for GAG sample preparation and analysis, discussing in detail liquid chromatograpy and mass spectrometry-based approaches, including advanced ion activation methods, ion mobility separations and infrared action spectroscopy of mass-selected species.

Glycoconjugates: Synthesis, Functional Studies, and Therapeutic Developments

Glycoconjugates are major constituents of mammalian cells that are formed via covalent conjugation of carbohydrates to other biomolecules like proteins and lipids and often expressed on the cell surfaces. Among the three major classes of glycoconjugates, proteoglycans and glycoproteins contain glycans linked to the protein backbone via amino acid residues such as Asn for N-linked glycans and Ser/Thr for O-linked glycans. In glycolipids, glycans are linked to a lipid component such as glycerol, polyisoprenyl pyrophosphate, fatty acid ester, or sphingolipid. Recently, glycoconjugates have become better structurally defined and biosynthetically understood, especially those associated with human diseases, and are accessible to new drug, diagnostic, and therapeutic developments. This review describes the status and new advances in the biological study and therapeutic applications of natural and synthetic glycoconjugates, including proteoglycans, glycoproteins, and glycolipids. The scope, limitations, and novel methodologies in the synthesis and clinical development of glycoconjugates including vaccines, glyco-remodeled antibodies, glycan-based adjuvants, glycan-specific receptor-mediated drug delivery platforms, etc., and their future prospectus are discussed.

Tailored Polyelectrolyte Multilayer Systems by Variation of Polyelectrolyte Composition and EDC/NHS Cross-Linking: Controlled Drug Release vs. Drug Reservoir Capabilities and Cellular Response for Improved Osseointegration

Polyelectrolyte multilayers (PEM) are versatile tools used to investigate fundamental interactions between material-related parameters and the resulting performance in stem cell differentiation, respectively, in bone tissue engineering. In the present study, we investigate the suitability of PEMs with a varying collagen content for use as drug carriers for the human bone morphogenetic protein 2 (rhBMP-2). We use three different PEM systems consisting either of the positively charged poly-L-lysine or the glycoprotein collagen type I and the negatively charged glycosaminoglycan heparin. For a specific modification of the loading capacity and the release kinetics, the PEMs were stepwise cross-linked before loading with cytokine. We demonstrate the possibility of immobilizing significant amounts of rhBMP-2 in all multilayer systems and to specifically tune its release via cross-linking. Furthermore, we prove that the drug release of rhBMP-2 plays only a minor role in the differentiation of osteoprogenitor cells. We find a significantly higher influence of the immobilized rhBMP-2 within the collagen-rich coatings that obviously represent an excellent mimicry of the native extracellular matrix. The cytokine immobilized in its bioactive form was able to achieve an increase in orders of magnitude both in the early stages of differentiation and in late calcification compared to the unloaded layers.

Enhancing adoptive T-cell therapy with fucoidan-based IL-2 delivery microcapsules

Adoptive cell therapy (ACT) with antigen-specific T cells is a promising treatment approach for solid cancers. Interleukin-2 (IL-2) has been utilized in boosting the efficacy of ACT. However, the clinical applications of IL-2 in combination with ACT is greatly limited by short exposure and high toxicities. Herein, a complex coacervate was designed to intratumorally deliver IL-2 in a sustained manner and protect against proteolysis. The complex coacervate consisted of fucoidan, a specific IL-2 binding glycosaminoglycan, and poly-l-lysine, a cationic counterpart (FPC²). IL-2-laden FPC² exhibited a preferential bioactivity in ex vivo expansion of CD8⁺T cells over Treg cells. Additionally, FPC² was embedded in pH modulating injectable gel (FPC²-IG) to endure the acidic tumor microenvironment. A single intratumoral administration of FPC²-IG-IL-2 increased expansion of tumor-infiltrating cytotoxic lymphocytes and reduced frequencies of myeloid populations. Notably, the activation and persistency of tumor-reactive T cells were observed only in the tumor site, not in the spleen, confirming a localized effect of FPC²-IG-IL-2. The immune-favorable tumor microenvironment induced by FPC²-IG-IL-2 enabled adoptively transferred TCR-engineered T cells to effectively eradicate tumors. FPC²-IG delivery system is a promising strategy for T-cell-based immunotherapies.

The Rheology and Printability of Cartilage Matrix-Only Biomaterials

The potential chondroinductivity from cartilage matrix makes it promising for cartilage repair; however, cartilage matrix-based hydrogels developed thus far have failed to match the mechanical performance of native cartilage or be bioprinted without adding polymers for reinforcement. There is a need for cartilage matrix-based hydrogels with robust mechanical performance and paste-like precursor rheology for bioprinting/enhanced surgical placement. In the current study, our goals were to increase hydrogel stiffness and develop the paste-like precursor/printability of our methacryl-modified solubilized and devitalized cartilage (MeSDVC) hydrogels. We compared two methacryloylating reagents, methacrylic anhydride (MA) and glycidyl methacrylate (GM), and varied the molar excess (ME) of MA from 2 to 20. The MA-modified MeSDVCs had greater methacryloylation than GM-modified MeSDVC (20 ME). While GM and most of the MA hydrogel precursors exhibited paste-like rheology, the 2 ME MA and GM MeSDVCs had the best printability (i.e., shape fidelity, filament collapse). After crosslinking, the 2 ME MA MeSDVC had the highest stiffness (1.55 ± 0.23 MPa), approaching the modulus of native cartilage, and supported the viability/adhesion of seeded cells for 15 days. Overall, the MA (2 ME) improved methacryloylation, hydrogel stiffness, and printability, resulting in a stand-alone MeSDVC printable biomaterial. The MeSDVC has potential as a future bioink and has future clinical relevance for cartilage repair.

Characteristics of Marine Biomaterials and Their Applications in Biomedicine

Oceans have vast potential to develop high-value bioactive substances and biomaterials. In the past decades, many biomaterials have come from marine organisms, but due to the wide variety of organisms living in the oceans, the great diversity of marine-derived materials remains explored. The marine biomaterials that have been found and studied have excellent biological activity, unique chemical structure, good biocompatibility, low toxicity, and suitable degradation, and can be used as attractive tissue material engineering and regenerative medicine applications. In this review, we give an overview of the extraction and processing methods and chemical and biological characteristics of common marine polysaccharides and proteins. This review also briefly explains their important applications in anticancer, antiviral, drug delivery, tissue engineering, and other fields.

Analysis of the aggregation mechanism of chondroitin sulfate/chitosan particles and fabrication of hydrogel cell scaffolds

In this study, the aggregation mechanism of polyion complex (PIC) particles from chitosan (CHI) and chondroitin sulfate C (CS) in phosphate-buffered saline (PBS) was analyzed, and a novel method for the fabrication of hydrogels via aggregation was developed. The PBS induced a decrease in the ζ-potential of the CS/CHI PIC particles, increase in their diameter, and aggregation in a concentration-dependent manner. The hydrogels prepared by mixing CS/CHI PIC particle dispersion and PBS showed the PIC components, with porous structure, high swelling ratio (161.4 ± 13.3%), and high storage moduli (26.2 ± 1.4 kPa). By mixing PBS with suspended adhesive cells and CS/CHI PIC particle dispersion, hydrogels with high cell-loading efficiency were successfully synthesized. The loaded cells within the hydrogels exhibited high viability, uniform distribution, and formation of cell aggregates. These results indicate that CS/CHI-based hydrogels have a potential application as three-dimensional scaffolds for cell culture in tissue engineering.

Biomedical applications of polysaccharide nanoparticles for chronic inflammatory disorders: Focus on rheumatoid arthritis, diabetes and organ fibrosis

Polysaccharides are biopolymers distinguished by their complex secondary structures executing various roles in microorganisms, plants, and animals. They are made up of long monomers of similar type or as a combination of other monomeric chains. Polysaccharides are considered superior as compared to other polymers due to their diversity in charge and size, biodegradability, abundance, bio-compatibility, and less toxicity. These natural polymers are widely used in designing of nanoparticles (NPs) which possess wide applications in therapeutics, diagnostics, delivery and protection of bioactive compounds or drugs. The side chain reactive groups of polysaccharides are advantageous for functionalization with nanoparticle-based conjugates or therapeutic agents such as small molecules, proteins, peptides and nucleic acids. Polysaccharide NPs show excellent pharmacokinetic and drug delivery properties, facilitate improved oral absorption, control the release of drugs, increases in vivo retention capability, targeted delivery, and exert synergistic effects. This review updates the usage of polysaccharides based NPs particularly cellulose, chitosan, hyaluronic acid, alginate, dextran, starch, cyclodextrins, pullulan, and their combinations with promising applications in diabetes, organ fibrosis and arthritis.

Unmodified and tyrosine-modified polyethylenimines as potential carriers for siRNA: Biophysical characterization and toxicity

Polyethylenimines (PEIs) are being explored as efficient non-viral nanocarriers for nucleic acid delivery in vitro and in vivo. To address limitations regarding PEI efficacy and biocompatibility, modifications of the chemical structure of linear and branched PEIs have been introduced, including grafting with tyrosine. The aim has been to compare linear and branched polyethylenimines of a wider range of different molecular mass with their tyrosine-modified derivatives. To do so, physico-chemical and biological properties of the polymers were investigated. Even in the absence of a negatively charged nucleic acid counterpart, PEIs form particle structures with defined size and surface potential. Tyrosine modification of PEI led to significantly reduced toxicity, while simultaneously increasing interaction with cellular membranes. All the effects were also dependent on the PEI molecular weight and structure (i.e., linear vs. branched). Especially in the case of linear PEIs, the improved membrane interaction also translated into slightly enhanced hemolysis, whereas their genotoxic potential was essentially abolished. Due to the improvement of properties critical for nano-vector efficacy and biocompatibility, our data demonstrate that tyrosine-modified PEIs are very promising and safe nanocarriers for the delivery of small RNAs, like siRNAs and miRNAs.

Cellulose Acetate-g-Polycaprolactone Copolymerization Using Diisocyanate Intermediates and the Effect of Polymer Chain Length on Surface, Thermal, and Antibacterial Properties

The need for biodegradable and biocompatible polymers is growing quickly, particularly in the biomedical and environmental industries. Cellulose acetate, a natural polysaccharide, can be taken from plants and modified with polycaprolactone to improve its characteristics for a number of uses, including biomedical applications and food packaging. Cellulose acetate-g-polycaprolactone was prepared by a three-step reaction: First, polymerization of ε-caprolactone via ring-opening polymerization (ROP) reaction using 2-hydroxyethyl methacrylate (HEMA) and functionalization of polycaprolactone(PCL) by introducing NCO on the hydroxyl end of the HEMA-PCL using hexamethyl lenediisocyanate(HDI) were carried out. Then, the NCO–HEMA-PCL was grafted onto cellulose acetate (using the “grafting to” method). The polycaprolactone grafted cellulose acetate was confirmed by FTIR, the thermal characteristics of the copolymers were investigated by DSC and TGA, and the hydrophobicity was analyzed via water CA measurement. Introducing NCO-PCL to cellulose acetate increased the thermal stability. The contact angle of the unreacted PCL was higher than that of cellulose acetate-g-PCL, and it increased when the chain length increased. The CA-g-PCL50, CA-g-PCL100, and CA-g-PCL200 showed very high inhibition zones for all three bacteria tested (E. coli, S. aureus, and P. aeruginosa).

Growth Factor Immobilization Strategies for Musculoskeletal Disorders

PURPOSE OF REVIEW

Tissue regenerative solutions for musculoskeletal disorders have become increasingly important with a growing aged population. Current growth factor treatments often require high dosages with the potential for off-target effects. Growth factor immobilization strategies offer approaches towards alleviating these concerns. This review summarizes current growth factor immobilization techniques (encapsulation, affinity interactions, and covalent binding) and the effects of immobilization on growth factor loading, release, and bioactivity.

RECENT FINDINGS

The breadth of immobilization techniques based on encapsulation, affinity, and covalent binding offer multiple methods to improve the therapeutic efficacy of growth factors by controlling bioactivity and release. Growth factor immobilization strategies have evolved to more complex systems with the capacity to load and release multiple growth factors with spatiotemporal control. The advancements in immobilization strategies allow for development of new, complex musculoskeletal tissue treatment strategies with improved spatiotemporal control of loading, release, and bioactivity.

Recent Advances in the Treatment of Bone Metastases and Primary Bone Tumors: An Up-to-Date Review

In the last decades, the treatment of primary and secondary bone tumors has faced a slow-down in its development, being mainly based on chemotherapy, radiotherapy, and surgical interventions. However, these conventional therapeutic strategies present a series of disadvantages (e.g., multidrug resistance, tumor recurrence, severe side effects, formation of large bone defects), which limit their application and efficacy. In recent years, these procedures were combined with several adjuvant therapies, with different degrees of success. To overcome the drawbacks of current therapies and improve treatment outcomes, other strategies started being investigated, like carrier-mediated drug delivery, bone substitutes for repairing bone defects, and multifunctional scaffolds with bone tissue regeneration and antitumor properties. Thus, this paper aims to present the types of bone tumors and their current treatment approaches, further focusing on the recent advances in new therapeutic alternatives.

Enhanced Neovascularization Using Injectable and rhVEGF-Releasing Cryogel Microparticles

Cryogels are gel networks or scaffolds with a large porous structure; they can be tailored for injectability and for possessing a shape-memory ability. Herein, a growth factor-releasing cryogel microparticle (CMP) system is fabricated, and the therapeutic efficacy of recombinant human vascular endothelial growth factor (rhVEGF)-loaded CMP (V-CMP) for neovascularization is investigated. To prepare the cryogels, both methacrylated chitosan (Chi-MA) and methacrylated chondroitin sulfate (CS-MA) are used, and crosslinking using a radical crosslinking reaction is established. The physical, mechanical, and biological properties of the cryogels are analyzed by varying the amount of CS-MA used. The cryogels are then pulverized, and microsized CMPs are fabricated. CMPs dispersed in saline demonstrate a shear-thinning property, and can thus be extruded through a 23G needle. Additionally, V-CMP exhibit a sustained release profile of rhVEGF and enhance the in vitro proliferation of endothelial cells. Finally, neovascularization and effective tissue necrosis prevention are observed when V-CMPs are injected into a hindlimb ischemia mouse model. Thus, the injectable V-CMP system developed herein demonstrates a high potential utility in various tissue regeneration applications based on cell or growth factor delivery.

Recent Progress on Cellulose-Based Ionic Compounds for Biomaterials

Glycans play important roles in all major kingdoms of organisms, such as archea, bacteria, fungi, plants, and animals. Cellulose, the most abundant polysaccharide on the Earth, plays a predominant role for mechanical stability in plants, and finds a plethora of applications by humans. Beyond traditional use, biomedical application of cellulose becomes feasible with advances of soluble cellulose derivatives with diverse functional moieties along the backbone and modified nanocellulose with versatile functional groups on the surface due to the native features of cellulose as both cellulose chains and supramolecular ordered domains as extractable nanocellulose. With the focus on ionic cellulose-based compounds involving both these groups primarily for biomedical applications, a brief introduction about glycoscience and especially native biologically active glycosaminoglycans with specific biomedical application areas on humans is given, which inspires further development of bioactive compounds from glycans. Then, both polymeric cellulose derivatives and nanocellulose-based compounds synthesized as versatile biomaterials for a large variety of biomedical applications, such as for wound dressings, controlled release, encapsulation of cells and enzymes, and tissue engineering, are separately described, regarding the diverse routes of synthesis and the established and suggested applications for these highly interesting materials.

Doxycycline preserves chondrocyte viability and function in human and calf articular cartilage ex vivo

Prolonging chondrocyte survival is essential to ensure fresh osteochondral (OC) grafts for treatment of articular cartilage lesions. Doxycycline has been shown to enhance cartilage growth, disrupt terminal differentiation of chondrocytes, and inhibit cartilage matrix degradation. It is unknown whether doxycycline prolongs chondrocyte survival in OC grafts. We hypothesized that doxycycline protects against chondrocyte death and maintains function of articular cartilage. To test this hypothesis, we employed human and calf articular cartilages, and incubated chondrocytes isolated from cartilage or cartilage plugs with doxycycline (0, 1 or 10 μg/ml) at either 37°C or 4°C. Chondrocyte viability, apoptosis, glycosaminoglycan (GAG), collagen, and mechanical test in cartilage plugs were measured. We found that reduced chondrocyte viability, increased chondrocyte apoptosis, reduced GAG contents, and impaired equilibrium modulus in cartilage plugs were observed in a time-dependent manner at both 37°C and 4°C. Chondrocyte viability was further reduced when the plugs were cultured at 4°C as compared to 37°C. Doxycycline prolonged viability and reduced apoptosis of chondrocytes during culture of cartilage plugs. Functionally, doxycycline protected against reduced production of GAG and collagen II as well as impaired mechanical properties in cartilage plugs during culture. Mechanistically, doxycycline increased mitochondrial respiration in cultured chondrocytes. In conclusion, preservation at 37°C is beneficial for maintaining chondrocyte viability in cartilage plugs compared to 4°C. Incubation of doxycycline protects against chondrocyte apoptosis, reduced extracellular matrix, and impaired mechanical properties in cartilage plugs. The findings provide a potential approach using doxycycline at 37°C to preserve chondrocyte viability in fresh OC grafts for treatment of articular cartilage lesions.

Hyalinization as a histomorphological risk predictor in oral pathological lesions

Background

Hyalinization is a process of conversion of stromal connective tissue into a homogeneous, acellular translucent material. Nevertheless, hyalinization could provide insights into the biologic behaviour and prognosis of pathological lesions. Few studies with limited sample size have intended to assess the correlation of hyalinization and biologic behaviour in oral lesions.

Aim

The current review aims to comprehensively appraise the mechanism of hyalinization in pathological oral hyalinizing lesions (OHL) and its clinical implications with emphasis on differential stains employed.

Methods

An electronic search was performed in the PubMed database (from year 2000-2020) using the keywords "special stains in oral hyalinizing lesions", "significance of hyalinization in oral lesions" and "hyalinization and biologic behaviour". Original research articles analyzing the effect of hyalinization on biologic characteristics of the lesion were evaluated in this review. Narrative review articles that provided insights into the mechanism of hyalinization and maturity of collagen fibers were also considered for analysis.

Conclusion

The presence of hyalinization does seem to have a significant effect on the biologic behaviour of pathological lesions. There is substantial scope to further investigate the process of hyalinization on larger samples and its correlation with the aggressive behaviour of OHLs. Special stains and advanced investigations such as immunohistochemistry for stromal markers would define the nature of hyalinized material and validate the correlation.

Clinical significance

The prediction of the biologic behaviour of a lesion established through assessment of hyalinization would prevent unwanted over or under treatment leading to a better prognosis.

Biomaterials for protein delivery for complex tissue healing responses

Tissue repair requires a complex cascade of events mediated by a variety of cells, proteins, and matrix molecules; however, the healing cascade can be easily disrupted by numerous factors, resulting in impaired tissue regeneration. Recent advances in biomaterials for tissue regeneration have increased the ability to tailor the delivery of proteins and other biomolecules to injury sites to restore normal healing cascades and stimulate robust tissue repair. In this review, we discuss the evolution of the field toward creating biomaterials that precisely control protein delivery to stimulate tissue regeneration, with a focus on addressing complex and dynamic injury environments. We highlight biomaterials that leverage different mechanisms to deliver and present proteins involved in healing cascades, tissue targeting and mimicking strategies, materials that can be triggered by environmental cues, and integrated strategies that combine multiple biomaterial properties to improve protein delivery. Improvements in biomaterial design to address complex injury environments will expand our understanding of both normal and aberrant tissue repair processes and ultimately provide a better standard of patient care.

BMP-2 delivery strategy modulates local bone regeneration and systemic immune responses to complex extremity trauma

Bone nonunions arising from large bone defects and composite injuries remain compelling challenges for orthopedic surgeons. Biological changes associated with nonunions, such as systemic immune dysregulation, can contribute to an adverse healing environment. Bone morphogenetic protein 2 (BMP-2), an osteoinductive and potentially immunomodulatory growth factor, is a promising strategy; however, burst release from the clinical standard collagen sponge delivery vehicle can result in adverse side effects such as heterotopic ossification (HO) and irregular bone structure, especially when using supraphysiological BMP-2 doses for complex injuries at high risk for nonunion. To address this challenge, biomaterials that strongly bind BMP-2, such as heparin methacrylamide microparticles (HMPs), may be used to limit exposure and spatially constrain proteins within the injury site. Here, we investigate moderately high dose BMP-2 delivered in HMPs within an injectable hydrogel system in two challenging nonunion models exhibiting characteristics of systemic immune dysregulation. The HMP delivery system increased total bone volume and decreased peak HO compared to collagen sponge delivery of the same BMP-2 dose. Multivariate analyses of systemic immune markers showed the collagen sponge group correlated with markers that are hallmarks of systemic immune dysregulation, including immunosuppressive myeloid-derived suppressor cells, whereas the HMP groups were associated with immune effector cells, including T cells, and cytokines linked to robust bone regeneration. Overall, our results demonstrate that HMP delivery of moderately high doses of BMP-2 promotes repair of complex bone nonunion injuries and that local delivery strategies for potent growth factors like BMP-2 may positively affect the systemic immune response to traumatic injury.

Glycosaminoglycans: Carriers and Targets for Tailored Anti-Cancer Therapy

The tumor microenvironment (TME) is composed of cancerous, non-cancerous, stromal, and immune cells that are surrounded by the components of the extracellular matrix (ECM). Glycosaminoglycans (GAGs), natural biomacromolecules, essential ECM, and cell membrane components are extensively altered in cancer tissues. During disease progression, the GAG fine structure changes in a manner associated with disease evolution. Thus, changes in the GAG sulfation pattern are immediately correlated to malignant transformation. Their molecular weight, distribution, composition, and fine modifications, including sulfation, exhibit distinct alterations during cancer development. GAGs and GAG-based molecules, due to their unique properties, are suggested as promising effectors for anticancer therapy. Considering their participation in tumorigenesis, their utilization in drug development has been the focus of both industry and academic research efforts. These efforts have been developing in two main directions; (i) utilizing GAGs as targets of therapeutic strategies and (ii) employing GAGs specificity and excellent physicochemical properties for targeted delivery of cancer therapeutics. This review will comprehensively discuss recent developments and the broad potential of GAG utilization for cancer therapy.

Application prospect of polysaccharides in the development of anti-novel coronavirus drugs and vaccines

Since the outbreak of the novel coronavirus disease COVID-19, caused by the SARS-CoV-2 virus, it has spread rapidly worldwide and poses a great threat to public health. This is the third serious coronavirus outbreak in <20 years, following SARS in 2002-2003 and MERS in 2012. So far, there are almost no specific clinically effective drugs and vaccines available for COVID-19. Polysaccharides with good safety, immune regulation and antiviral activity have broad application prospects in anti-virus, especially in anti-coronavirus applications. Here, we reviewed the antiviral mechanisms of some polysaccharides, such as glycosaminoglycans, marine polysaccharides, traditional Chinese medicine polysaccharides, and their application progress in anti-coronavirus. In particular, the application prospects of polysaccharide-based vaccine adjuvants, nanomaterials and drug delivery systems in the fight against novel coronavirus were also analyzed and summarized. Additionally, we speculate the possible mechanisms of polysaccharides anti-SARS-CoV-2, and propose the strategy of loading S or N protein from coronavirus onto polysaccharide capped gold nanoparticles vaccine for COVID-19 treatment. This review may provide a new approach for the development of COVID-19 therapeutic agents and vaccines.

A Possible Role for Arylsulfatase G in Dermatan Sulfate Metabolism

Perturbations of glycosaminoglycan metabolism lead to mucopolysaccharidoses (MPS)—lysosomal storage diseases. One type of MPS (type VI) is associated with a deficiency of arylsulfatase B (ARSB), for which we previously established a cellular model using pulmonary artery endothelial cells with a silenced ARSB gene. Here, we explored the effects of silencing the ARSB gene on the growth of human pulmonary artery smooth muscle cells in the presence of different concentrations of dermatan sulfate (DS). The viability of pulmonary artery smooth muscle cells with a silenced ARSB gene was stimulated by the dermatan sulfate. In contrast, the growth of pulmonary artery endothelial cells was not affected. As shown by microarray analysis, the expression of the arylsulfatase G (ARSG) in pulmonary artery smooth muscle cells increased after silencing the arylsulfatase B gene, but the expression of genes encoding other enzymes involved in the degradation of dermatan sulfate did not. The active site of arylsulfatase G closely resembles that of arylsulfatase B, as shown by molecular modeling. Together, these results lead us to propose that arylsulfatase G can take part in DS degradation; therefore, it can affect the functioning of the cells with a silenced arylsulfatase B gene.

Recreating Physiological Environments In Vitro: Design Rules for Microfluidic-Based Vascularized Tissue Constructs

Vascularization of engineered tissue constructs remains one of the greatest unmet challenges to mimicking the native tissue microenvironment in vitro. The main obstacle is recapitulating the complexity of the physiological environment while providing simplicity in operation and manipulation of the model. Microfluidic technology has emerged as a promising tool that enables perfusion of the tissue constructs through engineered vasculatures and precise control of the vascular microenvironment cues in vitro. The tunable microenvironment includes i) biochemical cues such as coculture, supporting matrix, and growth factors and ii) engineering aspects such as vasculature engineering methods, fluid flow, and shear stress. In this systematic review, the design considerations of the microfluidic-based in vitro model are discussed, with an emphasis on microenvironment control to enhance the development of next-generation vascularized engineered tissues.

Dermatan sulfate epimerase 1 expression and mislocalization may interfere with dermatan sulfate synthesis and breast cancer cell growth

Dermatan sulfate (DS) is a glycosaminoglycan (GAG) that is produced through the epimerization of the glucuronic acid on chondroitin sulfate into iduronic acid (IduA) by dermatan sulfate epimerase (DS-epi) 1 and 2. Proteoglycans (PGs) play essential physiological and pathological roles during cellular development, proliferation, differentiation, and cancer metastasis. DS proteoglycans play vital roles during the process of tumorigenesis, due to the increased flexibility of the polysaccharide chain in the presence of IduA residues, which facilitate specific interactions with proteins, such as growth factors, cytokines, and angiogenic factors. Furthermore, DS-epi is highly expressed in many tumors, especially in esophageal squamous cell carcinoma. This study aimed to investigate the expression of DS-epi1 in multiple breast cancer cell lines, including MCF7 (luminal A), MDA-MB-231 (triple-negative) and SKBR3 (human epidermal growth factor receptor 2-positive), and its involvement in cancer progression. A SKBR3 variant, SKBR3m, presented the most erratic cell growth pattern when compared with those for MCF7 and MDA-MB-231. Moreover, SKBR3m cells demonstrated the highest level of DS-epi1 gene expression and higher ³⁵S-DS content. However, at the protein level, MCF7 cells displayed the highest protein level for DS-epi1, whereas MDA-MB-231 cells had the lowest level. DS-epi1 was found in vesicles and in the perinuclear compartment only in SKBR3m cells, suggesting localization in the Golgi apparatus in these cells, in contrast with the cytoplasmic localization observed in MCF7 and MDA-MB-231 cells. The cytoplasm location of DS-epi1 likely compromised the formation of DS chains, but the core protein was detected using a decorin antibody. Golgi-specific labeling confirmed the localization of DS-epi1 in SKBR3m cells at the Golgi apparatus, indicating that the location of the enzyme was a determinant for the synthesis of DS in this cell line, suggesting that DS may play a decisive role in the tumor growth observed in this breast cancer cell line.

Membrane lipids destabilize short interfering ribonucleic acid (siRNA)/polyethylenimine nanoparticles

Cell entry of polymeric nanoparticles (NPs) bearing polynucleotides is an important stage for successful gene delivery. In this work, we addressed the influence of cell membrane lipids on the integrity and configurational changes of NPs composed of short interfering ribonucleic acid (siRNA) and polyethylenimine. We focused on NPs derived from two different PEIs, unmodified low molecular weight PEI and linoleic acid (LA)-substituted PEI, and their interactions with two membrane lipids (zwitterionic 2-oleoyl-1-palmitoyl-sn-glycero-3-phosphocholine (POPC) and anionic 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-l-serine (POPS)). Our experiments showed that POPS liposomes interacted strongly with both types of NPs, which caused partial dissociation of the NPs. POPC liposomes, however, did not induce any dissociation. Consistent with the experiments, steered molecular dynamics simulations showed a stronger interaction between the NPs and the POPS membrane than between the NPs and the POPC membrane. Lipid substitution on the PEIs enhanced the stability of the NPs during membrane crossing; lipid association between PEIs of the LA-bearing NPs as well as parallel orientation of the siRNAs provided protection against their dissociation (unlike NPs from native PEI). Our observations provide valuable insight into the integrity and structural changes of PEI/siRNA NPs during membrane crossing which will help in the design of more effective carriers for nucleic acid delivery.

Hydrogel scaffolds for tissue engineering: the importance of polymer choice

We explore the design and synthesis of hydrogel scaffolds for tissue engineering from the perspective of the underlying polymer chemistry. The key polymers, properties and architectures used, and their effect on tissue growth are discussed.

Cellulose nanocrystals of variable sulfation degrees can sequester specific platelet lysate-derived biomolecules to modulate stem cell response

Cellulose nanocrystals can bind different patterns of platelet lysate-derived protein in a surface sulfation dependent manner. The potential to direct stem cell fate by solid-phase presentation of defined protein coronas is demonstrated.

Heparinoid Complex-Based Heparin-Binding Cytokines and Cell Delivery Carriers

Heparinoid is the generic term that is used for heparin, heparan sulfate (HS), and heparin-like molecules of animal or plant origin and synthetic derivatives of sulfated polysaccharides. Various biological activities of heparin/HS are attributed to their specific interaction and regulation with various heparin-binding cytokines, antithrombin (AT), and extracellular matrix (ECM) biomolecules. Specific domains with distinct saccharide sequences in heparin/HS mediate these interactions are mediated and require different highly sulfated saccharide sequences with different combinations of sulfated groups. Multivalent and cluster effects of the specific sulfated sequences in heparinoids are also important factors that control their interactions and biological activities. This review provides an overview of heparinoid-based biomaterials that offer novel means of engineering of various heparin-binding cytokine-delivery systems for biomedical applications and it focuses on our original studies on non-anticoagulant heparin-carrying polystyrene (NAC-HCPS) and polyelectrolyte complex-nano/microparticles (N/MPs), in addition to heparin-coating devices.

Glycosaminoglycan-based biomaterials for growth factor and cytokine delivery: Making the right choices

Controlled, localized drug delivery is a long-standing goal of medical research, realization of which could reduce the harmful side-effects of drugs and allow more effective treatment of wounds, cancers, organ damage and other diseases. This is particularly the case for protein "drugs" and other therapeutic biological cargoes, which can be challenging to deliver effectively by conventional systemic administration. However, developing biocompatible materials that can sequester large quantities of protein and release them in a sustained and controlled manner has proven challenging. Glycosaminoglycans (GAGs) represent a promising class of bio-derived materials that possess these key properties and can additionally potentially enhance the biological effects of the delivered protein. They are a diverse group of linear polysaccharides with varied functionalities and suitabilities for different cargoes. However, most investigations so far have focused on a relatively small subset of GAGs - particularly heparin, a readily available, promiscuously-binding GAG. There is emerging evidence that for many applications other GAGs are in fact more suitable for regulated and sustained delivery. In this review, we aim to illuminate the beneficial properties of various GAGs with reference to specific protein cargoes, and to provide guidelines for informed choice of GAGs for therapeutic applications.

Emerging roles of ECM remodeling processes in cancer

Extracellular matrix (ECM) plays a central and dynamic role in the creation of tumor microenvironment. Herein we discuss the emerging biophysical and biochemical aspects of ECM buildup and proteolysis in cancer niche formation. Dysregulated ECM remodeling by cancer cells facilitate irreversible proteolysis and crosslinking, which in turn influence cell signaling, micro environmental cues, angiogenesis and tissue biomechanics. Further, we introduce the emerging roles of cancer microbiome in aberrant tumor ECM remodeling and membrane bound nano-sized vesicles called exosomes in creation of distant pre-metastatic niches. A detailed molecular and biophysical understanding of the ECM morphologies and its components such as key enzymes, structural and signaling molecules are critical in identifying the next generation of therapeutic and diagnostic targets in cancer.

New SDC function prediction based on protein-protein interaction using bioinformatics tools

The precise roles for SDC have been complex to specify. Assigning and reanalyzing protein and peptide identification to novel protein functions is one of the most important challenges in postgenomic era. Here, we provide SDC molecular description to support, contextualize and reanalyze the corresponding protein-protein interaction (PPI). From SDC-1 data mining, we discuss the potential of bioinformatics tools to predict new biological rules of SDC. Using these methods, we have assembled new possibilities for SDC biology from PPI data, once, the understanding of biology complexity cannot be capture from one simple question.

Biomaterial-assisted local and systemic delivery of bioactive agents for bone repair

Although bone tissues possess an intrinsic capacity for repair, there are cases where bone healing is either impaired or insufficient, such as fracture non-union, osteoporosis, osteomyelitis, and cancers. In these cases, treatments like surgical interventions are used, either alone or in combination with bioactive agents, to promote tissue repair and manage associated clinical complications. Improving the efficacy of bioactive agents often requires carriers, with biomaterials being a pivotal player. In this review, we discuss the role of biomaterials in realizing the local and systemic delivery of biomolecules to the bone tissue. The versatility of biomaterials enables design of carriers with the desired loading efficiency, release profile, and on-demand delivery. Besides local administration, systemic administration of drugs is necessary to combat diseases like osteoporosis, warranting bone-targeting drug delivery systems. Thus, chemical moieties with the affinity towards bone extracellular matrix components like apatite minerals have been widely utilized to create bone-targeting carriers with better biodistribution, which cannot be achieved by the drugs alone. Bone-targeting carriers combined with the desired drugs or bioactive agents have been extensively investigated to enhance bone healing while minimizing off-target effects. Herein, these advancements in the field have been systematically reviewed. STATEMENT OF SIGNIFICANCE: Drug delivery is imperative when surgical interventions are not sufficient to address various bone diseases/defects. Biomaterial-assisted delivery systems have been designed to provide drugs with the desired loading efficiency, sustained release, and on-demand delivery to enhance bone healing. By surveying recent advances in the field, this review outlines the design of biomaterials as carriers for the local and systemic delivery of bioactive agents to the bone tissue. Particularly, biomaterials that bear chemical moieties with affinity to bone are attractive, as they can present the desired bioactive agents to the bone tissue efficiently and thus enhance the drug efficacy for bone repair.

Glycosaminoglycans: A Link Between Development and Regeneration in the Lung

What can we learn from embryogenesis to increase our understanding of how regeneration of damaged adult lung tissue could be induced in serious lung diseases such as chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), and asthma? The local tissue niche determines events in both embryogenesis and repair of the adult lung. Important constituents of the niche are extracellular matrix (ECM) molecules, including proteoglycans and glycosaminoglycans (GAGs). GAGs, strategically located in the pericellular and extracellular space, bind developmentally active growth factors (GFs) and morphogens such as fibroblast growth factors (FGFs), transforming growth factor-β (TGF-β), and bone morphogenetic proteins (BMPs) aside from cytokines. These interactions affect activities in many cells, including stem cells, important in development and tissue regeneration. Moreover, it is becoming clear that the "inherent code," such as sulfation of disaccharides of GAGs, is a strong determinant of cellular outcome. Sulfation patterns, deacetylations, and epimerizations of GAG chains function as tuning forks in gradient formation of morphogens, growth factors, and cytokines. Learning to tune these fine instruments, that is, interactions between GFs, chemokines, and cytokines with the specific disaccharide code of GAGs in the adult lung, could become the key to unlock inherent regenerative forces to override pathological remodeling. This review aims to provide an overview of the role GAGs play during development and similar events in regenerative efforts in the adult lung.

Exploring Structure⁻Property Relationships of GAGs to Tailor ECM-Mimicking Hydrogels

Glycosaminoglycans (GAGs) are a class of linear polysaccharides that are ubiquitous in the extracellular matrix (ECM) and on cell surfaces. Due to their key role in development, homeostasis, pathogenesis, and regeneration, GAGs are increasingly used in the design of ECM-mimicking hydrogels to stimulate tissue formation and regenerative processes via specifically orchestrated cell-instructive signals. These applications first and foremost build on the ability of GAGs to effectively bind, protect, and release morphogens. The specificity and strength of morphogen-GAG interactions are largely governed by the number and spatial distribution of negatively charged sulfate groups carried by GAGs. Herein, we summarize a mean-field approach to quantify the density of ionizable groups, GAG concentration, and cross-linking degree of GAG-containing hydrogels on the basis of microslit electrokinetic experiments. We further present and discuss a continuum model of mucosa that accounts for charge regulation by glycan-ion pairing in biological contexts and under conditions of macromolecular crowding. Finally, we discuss the modulation of the morphogen binding and transport in GAG hydrogels by selective desulfation of the GAG component.

Extracellular Matrix Influencing HGF/c-MET Signaling Pathway: Impact on Cancer Progression

The extracellular matrix (ECM) is a crucial component of the tumor microenvironment involved in numerous cellular processes that contribute to cancer progression. It is acknowledged that tumor–stromal cell communication is driven by a complex and dynamic network of cytokines, growth factors and proteases. Thus, the ECM works as a reservoir for bioactive molecules that modulate tumor cell behavior. The hepatocyte growth factor (HGF) produced by tumor and stromal cells acts as a multifunctional cytokine and activates the c-MET receptor, which is expressed in different tumor cell types. The HGF/c-MET signaling pathway is associated with several cellular processes, such as proliferation, survival, motility, angiogenesis, invasion and metastasis. Moreover, c-MET activation can be promoted by several ECM components, including proteoglycans and glycoproteins that act as bridging molecules and/or signal co-receptors. In contrast, c-MET activation can be inhibited by proteoglycans, matricellular proteins and/or proteases that bind and sequester HGF away from the cell surface. Therefore, understanding the effects of ECM components on HGF and c-MET may provide opportunities for novel therapeutic strategies. Here, we give a short overview of how certain ECM components regulate the distribution and activation of HGF and c-MET.

Effects of sulodexide on stability of sclerosing foams

BACKGROUND AND OBJECTIVES

Foam sclerotherapy is a clinical procedure for the treatment of unhealthy veins. The aim of this study was to investigate the effect of sulodexide (SUL) on stability of foams prepared using polidocanol (POL) and sodium tetradecyl sulfate (STS) detergents, more specifically with 0.25% aethoxysclerol and 0.2% Fibro-Vein sclerosing solutions.

METHODS

Foams were produced by the Tessari method using three different weight ratios of POL-SUL and STS-SUL (1:0, 1:1, and 1:3).

RESULTS

The half-life of STS foams resulted as follows: 82 ± 1.6 s, 101.8 ± 2.6 s, and 109.7 ± 2.1 s for 1:0, 1:1, and 1:3 STS-SUL weight ratios, respectively. The same ratios were used for POL foams with the following results: 90.6 ± 3 s, 106.8 ± 2.6 s, and 107.6 ± 2.7 s for 1:0, 1:1, and 1:3 POL-SUL weight ratios, respectively.

CONCLUSION

The addition of SUL in sclerosing solutions can prolong the half-life of foams, and it could be potentially used as a foam stabilizer.

Heparin-based hydrogels with tunable sulfation & degradation for anti-inflammatory small molecule delivery

Sustained release of anti-inflammatory agents remains challenging for small molecule drugs due to their low molecular weight and hydrophobicity. Therefore, the goal of this study was to control the release of a small molecule anti-inflammatory agent, crystal violet (CV), from hydrogels fabricated with heparin, a highly sulfated glycosaminoglycan capable of binding positively-charged molecules such as CV. In this system, both electrostatic interactions between heparin and CV and hydrogel degradation were tuned simultaneously by varying the level of heparin sulfation and varying the amount of dithiothreitol within hydrogels, respectively. It was found that heparin sulfation significantly affected CV release, whereby more sulfated heparin hydrogels (Hep and Hep(-N)) released CV with near zero-order release kinetics (R-squared values between 0.96-0.99). Furthermore, CV was released more quickly from fast-degrading hydrogels than slow-degrading hydrogels, providing a method to tune total CV release between 5-15 days while maintaining linear release kinetics. In particular, N-desulfated heparin hydrogels exhibited efficient CV loading (∼90% of originally included CV), near zero-order CV release kinetics, and maintenance of CV bioactivity after release, making this hydrogel formulation a promising CV delivery vehicle for a wide range of inflammatory diseases.

Systems for localized release to mimic paracrine cell communication in vitro

Paracrine cell communication plays a pivotal role for signal exchange between proximal cells in vivo. However, this localized, gradient type release of mediators at very low concentrations (pg/ml), relevant during physiological and pathological processes, is rarely reflected within in vitro approaches. This review gives an overview on state-of-the-art approaches, which transfer the paracrine cell-to-cell communication into in vitro cell culture model setups. The traditional methods like trans-well assays and more advanced microfluidic approaches are included. The review focusses on systems for localized release, mostly based on microparticles, which tightly mimic the paracrine interaction between single cells in 3D microenvironments. Approaches based on single microparticles, with the main focus on affinity-controlled storage and release of cytokines, are reviewed and their importance for understanding paracrine communication is highlighted. Various methods to study the cytokine release and their advantages and disadvantages are discussed. Basic principles of the release characteristics, like diffusion mechanisms, are quantitatively described, including the formation of resulting gradients around the local sources. In vitro cell experiments using such localized microparticle release systems in approaches to increase understanding of stem cell behavior within their niches and regulation of wound healing are highlighted as examples of successful localized release systems for mimicking paracrine cell communication.

Microparticle-mediated sequestration of cell-secreted proteins to modulate chondrocytic differentiation

Protein delivery is often used in tissue engineering applications to control differentiation processes, but is limited by protein instability and cost. An alternative approach is to control the cellular microenvironment through biomaterial-mediated sequestration of cell-secreted proteins important to differentiation. Thus, we utilized heparin-based microparticles to modulate cellular differentiation via protein sequestration in an in vitro model system of endochondral ossification. Heparin and poly(ethylene-glycol) (PEG; a low-binding material control)-based microparticles were incorporated into ATDC5 cell spheroids or incubated with ATDC5 cells in transwell culture. Reduced differentiation was observed in the heparin microparticle group as compared to PEG and no microparticle-containing groups. To determine if observed changes were due to sequestration of cell-secreted protein, the proteins sequestered by heparin microparticles were analyzed using SDS-PAGE and mass spectrometry. It was found that heparin microparticles bound insulin-like growth factor binding proteins (IGFBP)-3 and 5. When incubated with a small-molecule inhibitor of IGFBPs, NBI 31772, a similar delay in differentiation of ATDC5 cells was observed. These results indicate that heparin microparticles modulated chondrocytic differentiation in this system via sequestration of cell-secreted protein, a technique that could be beneficial in the future as a means to control cellular differentiation processes.

STATEMENT OF SIGNIFICANCE

In this work, we present a proof-of-principle set of experiments in which heparin-based microparticles are shown to modulate cellular differentiation through binding of cell-secreted protein. Unlike existing systems that rely on expensive protein with limited half-lives to elicit changes in cellular behavior, this technique focuses on temporal modulation of cell-generated proteins. This technique also provides a biomaterials-based method that can be used to further identify sequestered proteins of interest. Thus, this work indicates that glycosaminoglycan-based biomaterial approaches could be used as substitutes or additions to traditional methods for modulating and identifying the cell-secreted proteins involved in directing cellular behavior.