The Influence of Sulfation Degree of Glycosaminoglycan-Functionalized 3D Collagen I Networks on Cytokine Profiles of In Vitro Macrophage-Fibroblast Cocultures.

Cell-cell interactions between fibroblasts and immune cells, like macrophages, are influenced by interaction with the surrounding extracellular matrix during wound healing. In vitro hydrogel models that mimic and modulate these interactions, especially of soluble mediators like cytokines, may allow for a more detailed investigation of immunomodulatory processes. In the present study, a biomimetic extracellular matrix model based on fibrillar 3D collagen I networks with a functionalization with heparin or 6-ON-desulfated heparin, as mimics of naturally occurring heparan sulfate, was developed to modulate cytokine binding effects with the hydrogel matrix. The constitution and microstructure of the collagen I network were found to be stable throughout the 7-day culture period. A coculture study of primary human fibroblasts/myofibroblasts and M-CSF-stimulated macrophages was used to show its applicability to simulate processes of progressed wound healing. The quantification of secreted cytokines (IL-8, IL-10, IL-6, FGF-2) in the cell culture supernatant demonstrated the differential impact of glycosaminoglycan functionalization of the collagen I network. Most prominently, IL-6 and FGF-2 were shown to be regulated by the cell culture condition and network constitution, indicating changes in paracrine and autocrine cell-cell communication of the fibroblast-macrophage coculture. From this perspective, we consider our newly established in vitro hydrogel model suitable for mechanistic coculture analyses of primary human cells to unravel the role of extracellular matrix factors in key events of tissue regeneration and beyond.

A Multifunctional Nanostructured Hydrogel as a Platform for Deciphering Niche Interactions of Hematopoietic Stem and Progenitor Cells.

For over half a century, hematopoietic stem cells (HSCs) have been used for transplantation therapy to treat severe hematologic diseases. Successful outcomes depend on collecting sufficient donor HSCs as well as ensuring efficient engraftment. These processes are influenced by dynamic interactions of HSCs with the bone marrow niche, which can be revealed by artificial niche models. Here, a multifunctional nanostructured hydrogel is presented as a 2D platform to investigate how the interdependencies of cytokine binding and nanopatterned adhesive ligands influence the behavior of human hematopoietic stem and progenitor cells (HSPCs). The results indicate that the degree of HSPC polarization and motility, observed when cultured on gels presenting the chemokine SDF-1α and a nanoscale-defined density of a cellular (IDSP) or extracellular matrix (LDV) α4ß1 integrin binding motif, are differently influenced on hydrogels functionalized with the different ligand types. Further, SDF-1α promotes cell polarization but not motility. Strikingly, the degree of differentiation correlates negatively with the nanoparticle spacing, which determines ligand density, but only for the cellular-derived IDSP motif. This mechanism potentially offers a means of predictably regulating early HSC fate decisions. Consequently, the innovative multifunctional hydrogel holds promise for deciphering dynamic HSPC-niche interactions and refining transplantation therapy protocols.

Precision Culture Scaling to Establish High-Throughput Vasculogenesis Models.

Hydrogel-based 3D cell cultures can recapitulate (patho)physiological phenomena ex vivo. However, due to their complex multifactorial regulation, adapting these tissue and disease models for high-throughput screening workflows remains challenging. In this study, a new precision culture scaling (PCS-X) methodology combines statistical techniques (design of experiment and multiple linear regression) with automated, parallelized experiments and analyses to customize hydrogel-based vasculogenesis cultures using human umbilical vein endothelial cells and retinal microvascular endothelial cells. Variations of cell density, growth factor supplementation, and media composition are systematically explored to induce vasculogenesis in endothelial mono- and cocultures with mesenchymal stromal cells or retinal microvascular pericytes in 384-well plate formats. The developed cultures are shown to respond to vasculogenesis inhibitors in a compound- and dose-dependent manner, demonstrating the scope and power of PCS-X in creating parallelized tissue and disease models for drug discovery and individualized therapies.

Sulfation of hyaluronic acid reconfigures the mechanistic pathway of bone morphogenetic protein-2 aggregation.

Bone morphogenetic protein-2 (BMP-2) is a critical growth factor of bone extracellular matrix (ECM), pivotal for osteogenesis. Glycosaminoglycans (GAGs), another vital ECM biomolecules, interact with growth factors, affecting signal transduction. Our study primarily focused on hyaluronic acid (HA), a prevalent GAG, and its sulfated derivative (SHA). We explored their impact on BMP-2's conformation, aggregation, and mechanistic pathways of aggregation using diverse optical and rheological methods. In the presence of HA and SHA, the secondary structure of BMP-2 underwent a structured transformation, characterized by a substantial increase in beta sheet content, and a detrimental alteration, manifesting as a shift towards unstructured content, respectively. Although both HA and SHA induced BMP-2 aggregation, their mechanisms differed. SHA led to rapid amorphous aggregates, while HA promoted amyloid fibrils with a lag phase and sigmoidal kinetics. Aggregate size and shape varied; HA produced larger structures, SHA smaller. Each aggregation type followed distinct pathways influenced by viscosity and excluded volume. Higher viscosity, low diffusivity of protein and higher excluded volume In the presence of HA promotes fibrillation having size in micrometer range. Low viscosity, high diffusivity of protein and lesser excluded volume leads to amorphous aggregate of size in nanometer range.

Nerve growth factor receptor (Ngfr) induces neurogenic plasticity by suppressing reactive astroglial Lcn2/Slc22a17 signaling in Alzheimer's disease.

Neurogenesis, crucial for brain resilience, is reduced in Alzheimer's disease (AD) that induces astroglial reactivity at the expense of the pro-neurogenic potential, and restoring neurogenesis could counteract neurodegenerative pathology. However, the molecular mechanisms promoting pro-neurogenic astroglial fate despite AD pathology are unknown. In this study, we used APP/PS1dE9 mouse model and induced Nerve growth factor receptor (Ngfr) expression in the hippocampus. Ngfr, which promotes neurogenic fate of astroglia during the amyloid pathology-induced neuroregeneration in zebrafish brain, stimulated proliferative and neurogenic outcomes. Histological analyses of the changes in proliferation and neurogenesis, single-cell transcriptomics, spatial proteomics, and functional knockdown studies showed that the induced expression of Ngfr reduced the reactive astrocyte marker Lipocalin-2 (Lcn2), which we found was sufficient to reduce neurogenesis in astroglia. Anti-neurogenic effects of Lcn2 was mediated by Slc22a17, blockage of which recapitulated the pro-neurogenicity by Ngfr. Long-term Ngfr expression reduced amyloid plaques and Tau phosphorylation. Postmortem human AD hippocampi and 3D human astroglial cultures showed elevated LCN2 levels correlate with reactive gliosis and reduced neurogenesis. Comparing transcriptional changes in mouse, zebrafish, and human AD brains for cell intrinsic differential gene expression and weighted gene co-expression networks revealed common altered downstream effectors of NGFR signaling, such as PFKP, which can enhance proliferation and neurogenesis in vitro when blocked. Our study suggests that the reactive non-neurogenic astroglia in AD can be coaxed to a pro-neurogenic fate and AD pathology can be alleviated with Ngfr. We suggest that enhancing pro-neurogenic astroglial fate may have therapeutic ramifications in AD.

Analysis of the Binding of Cytokines to Highly Charged Polymer Networks.

A model describing the binding of biological signaling proteins to highly charged polymer networks is presented. The networks are formed by polyelectrolyte chains for which the distance between two charges at the chain is smaller than the Bjerrum length. Counterion condensation on such highly charged chains immobilizes a part of the counterions. The Donnan-equilibrium between the polymer network and the aqueous solution with salt concentration c s b $c_s^b$ is used to calculate the salt concentration of the co- and counterions c s g $c_s^g$ entering the network. Two factors are decisive: i) The electrostatic interaction between the network and the protein is given by the Donnan-potential of the network and the net charge of the protein. In addition to this leading term, a second term describes the change in the Born-energy of the proteins when entering the network. ii) The interaction of the protein with the highly charged chains within the network is governed by counterion release: Patches of positive charge at the protein become multivalent counterions of the polyelectrolyte chains thus releasing a concomitant number of condensed counterions. The model compares favorably to experimental data obtained on a set of biohybrid polymer networks composed of crosslinked glycosaminoglycan chains that interact with a mixture of key signaling proteins.

Discriminant Principal Component Analysis of ToF-SIMS Spectra for Deciphering Compositional Differences of MSC-Secreted Extracellular Matrices.

Identifying characteristic extracellular matrix (ECM) variants is a key challenge in mechanistic biology, bioengineering, and medical diagnostics. The reported study demonstrates the potential of time-of-flight secondary ion mass spectrometry (ToF-SIMS) to detect subtle differences between human mesenchymal stromal cell (MSC)-secreted ECM types as induced by exogenous stimulation or emerging pathology. ToF-SIMS spectra of decellularized ECM samples are evaluated by discriminant principal component analysis (DPCA), an advanced multivariate analysis technique, to decipher characteristic compositional features. To establish the approach, signatures of major ECM proteins are determined from samples of pre-defined mixtures. Based on that, sets of ECM variants produced by MSCs in vitro are analyzed. Differences in the content of collagen, fibronectin, and laminin in the ECM resulting from the combined supplementation of MSC cultures with polymers that induce macromolecular crowding and with ascorbic acid are detected from the DPCA of ToF-SIMS spectra. The results are verified by immunostaining. Finally, the comparative ToF-SIMS analysis of ECM produced by MSCs of healthy donors and patients suffering from myelodysplastic syndrome display the potential of the novel methodology to reveal disease-associated alterations of the ECM composition.

Sustained Release of Human Adipose Tissue Stem Cell Secretome from Star-Shaped Poly(ethylene glycol) Glycosaminoglycan Hydrogels Promotes Motor Improvements after Complete Transection in Spinal Cord Injury Rat Model.

Adipose tissue-derived stem cells (ASCs) have been shown to assist regenerative processes after spinal cord injury (SCI) through their secretome, which promotes several regenerative mechanisms, such as inducing axonal growth, reducing inflammation, promoting cell survival, and vascular remodeling, thus ultimately leading to functional recovery. However, while systemic delivery (e.g., i.v. [intravenous]) may cause off-target effects in different organs, the local administration has low efficiency due to fast clearance by body fluids. Herein, a delivery system for human ASCs secretome based on a hydrogel formed of star-shaped poly(ethylene glycol) (starPEG) and the glycosaminoglycan heparin (Hep) that is suitable to continuously release pro-regenerative signaling mediators such as interleukin (IL)-4, IL-6, brain-derived neurotrophic factor, glial-cell neurotrophic factor, and beta-nerve growth factor over 10 days, is reported. The released secretome is shown to induce differentiation of human neural progenitor cells and neurite outgrowth in organotypic spinal cord slices. In a complete transection SCI rat model, the secretome-loaded hydrogel significantly improves motor function by reducing the percentage of ameboid microglia and systemically elevates levels of anti-inflammatory cytokines. Delivery of ASC-derived secretome from starPEG-Hep hydrogels may therefore offer unprecedented options for regenerative therapy of SCI.

Three-Dimensional Biohybrid StarPEG-Heparin Hydrogel Cultures for Modeling Human Neuronal Development and Alzheimer's Disease Pathology.

In this chapter, we present the methodology currently used in our laboratory to generate a starPEG-MMP (starPEG)- and heparin maleimide HM06 (heparin)-based 3D cell culture system, in a hydrogel, that can be used to study human neuronal development and Alzheimer's disease (AD) pathology. A 3D cell culture system can mimic the in vivo cellular environment better than a 2D format, in which these cells exhibit neural network formation, electrophysiological activity, tissue-specific extracellular matrix (ECM) deposition, and neurotransmitter responsiveness. When treated with amyloid beta-42 (Aß42) peptides, this system recapitulates many of the pathological effects of AD, including reduced neural stem cell proliferation, impaired neuronal network formation, dystrophic axonal ends, synaptic loss, failure to deposit ECM, elevated tau hyperphosphorylation, and formation of neurofibrillary tangles. Culturing human primary cortical astrocyte (pHA)- or induced pluripotent stem cell (iPSC)-derived human neural stem cells in this biohybrid hydrogel system has led to the discovery of novel regulatory pathways underlying neurodegenerative pathology in different phases of AD.

Colorimetric Biosensors Based on Polymer/Gold Hybrid Nanoparticles: Topological Effects of the Polymer Coating.

Gold nanoparticles decorated with analyte recognition units can form the basis of colorimetric (bio)sensors. The presentation of those recognition units may play a critical role in determining sensor sensitivity. Herein, we use a model system to investigate the effect of the architecture of a polymeric linker that connects gold nanoparticles with the recognition units. Our results show that the number of the latter that can be adsorbed during the assembly of the colorimetric sensors depends on the linker topology. We also show that this may lead to substantial differences in colorimetric sensor performance, particularly in situations in which the interactions with the analyte are comparably weak. Finally, we discuss design principles for efficient colorimetric sensor materials based on our findings.

Poly(2-alkyl-2-oxazoline)-Heparin Hydrogels-Expanding the Physicochemical Parameter Space of Biohybrid Materials.

Poly(ethylene glycol) (PEG)-glycosaminoglycan (GAG) hydrogel networks are established as very versatile biomaterials. Herein, the synthetic gel component of the biohybrid materials is systematically varied by combining different poly(2-alkyl-2-oxazolines) (POx) with heparin applying a Michael-type addition crosslinking scheme: POx of gradated hydrophilicity and temperature-responsiveness provides polymer networks of distinctly different stiffness and swelling. Adjusting the mechanical properties and the GAG concentration of the gels to similar values allows for modulating the release of GAG-binding growth factors (VEGF165 and PDGF-BB) by the choice of the POx and its temperature-dependent conformation. Adsorption of fibronectin, growth of fibroblasts, and bacterial adhesion scale with the hydrophobicity of the gel-incorporated POx. In vitro hemocompatibility tests with freshly drawn human whole blood show advantages of POx-based gels compared to the PEG-based reference materials. Biohybrid POx hydrogels can therefore enable biomedical technologies requiring GAG-based materials with customized and switchable physicochemical characteristics.

Amphiphilic Copolymers for Versatile, Facile, and In Situ Tunable Surface Biofunctionalization.

Precision surface engineering is key to advanced biomaterials. A new platform of PEGylated styrene-maleic acid copolymers for adsorptive surface biofunctionalization is reported. Balanced amphiphilicity renders the copolymers water-soluble but strongly affine for surfaces. Fine-tuning of their molecular architecture provides control over adsorptive anchorage onto specific materials-which is why they are referred to as "anchor polymers" (APs)-and over structural characteristics of the adsorbed layers. Conjugatable with an array of bioactives-including cytokine-complexing glycosaminoglycans, cell-adhesion-mediating peptides and antimicrobials-APs can be applied to customize materials for demanding biotechnologies in uniquely versatile, simple, and robust ways. Moreover, homo- and heterodisplacement of adsorbed APs provide unprecedented means of in situ alteration and renewal of the functionalized surfaces. The related options are exemplified with proof-of-concept experiments of controlled bacterial adhesion, human umbilical vein endothelial cell, and induced pluripotent cell growth on AP-functionalized surfaces.

Tuning the network charge of biohybrid hydrogel matrices to modulate the release of SDF-1.

The delivery of chemotactic signaling molecules via customized biomaterials can effectively guide the migration of cells to improve the regeneration of damaged or diseased tissues. Here, we present a novel biohybrid hydrogel system containing two different sulfated glycosaminoglycans (sGAG)/sGAG derivatives, namely either a mixture of short heparin polymers (Hep-Mal) or structurally defined nona-sulfated tetrahyaluronans (9s-HA4-SH), to precisely control the release of charged signaling molecules. The polymer networks are described in terms of their negative charge, i.e. the anionic sulfate groups on the saccharides, using two parameters, the integral density of negative charge and the local charge distribution (clustering) within the network. The modulation of both parameters was shown to govern the release characteristics of the chemotactic signaling molecule SDF-1 and allows for seamless transitions between burst and sustained release conditions as well as the precise control over the total amount of delivered protein. The obtained hydrogels with well-adjusted release profiles effectively promote MSC migration in vitro and emerge as promising candidates for new treatment modalities in the context of bone repair and wound healing.

Chemokine-Capturing Wound Contact Layer Rescues Dermal Healing.

Excessive inflammation often impedes the healing of chronic wounds. Scavenging of chemokines by multiarmed poly(ethylene glycol)-glycosaminoglycan (starPEG-GAG) hydrogels has recently been shown to support regeneration in a diabetic mouse chronic skin wound model. Herein, a textile-starPEG-GAG composite wound contact layer (WCL) capable of selectively sequestering pro-inflammatory chemokines is reported. Systematic variation of the local and integral charge densities of the starPEG-GAG hydrogel component allows for tailoring its affinity profile for biomolecular signals of the wound milieu. The composite WCL is subsequently tested in a large animal (porcine) model of human wound healing disorders. Dampening excessive inflammatory signals without affecting the levels of pro-regenerative growth factors, the starPEG-GAG hydrogel-based WCL treatment induced healing with increased granulation tissue formation, angiogenesis, and deposition of connective tissue (collagen fibers). Thus, this biomaterials technology expands the scope of a new anti-inflammatory therapy toward clinical use.

Injectable Glycosaminoglycan-Based Cryogels from Well-Defined Microscale Templates for Local Growth Factor Delivery.

Glycosaminoglycan-based hydrogels hold great potential for applications in tissue engineering and regenerative medicine. By mimicking the natural extracellular matrix processes of growth factor binding and release, such hydrogels can be used as a sustained delivery device for growth factors. Since neural networks commonly follow well-defined, high-aspect-ratio paths through the central and peripheral nervous system, we sought to create a fiber-like, elongated growth factor delivery system. Cryogels, with networks formed at subzero temperatures, are well-suited for the creation of high-aspect-ratio biomaterials, because they have a macroporous structure making them mechanically robust (for ease of handling) yet soft and highly compressible (for interfacing with brain tissue). Unlike hydrogels, cryogels can be synthesized in advance of their use, stored with ease, and rehydrated quickly to their original shape. Herein, we use solvent-assisted microcontact molding to form sacrificial templates, in which we produced highly porous cryogel microscale scaffolds with a well-defined elongated shape via the photopolymerization of poly(ethylene glycol) diacrylate and maleimide-functionalized heparin. Dissolution of the template yielded cryogels that could load nerve growth factor (NGF) and release it over a period of 2 weeks, causing neurite outgrowth in PC12 cell cultures. This microscale template-assisted synthesis technique allows tight control over the cryogel scaffold dimensions for high reproducibility and ease of injection through fine gauge needles.

Thermodynamic Analysis of the Interaction of Heparin with Lysozyme.

Glycosaminoglycan (GAG)-protein binding governs critically important signaling events in living matter. Aiming at a quantitative analysis of the involved processes, we herein present a thermodynamic study of the interaction of the model GAG heparin and lysozyme in aqueous solution. Heparin is a highly charged linear polyelectrolyte with a charge parameter of 2.9 (37 °C). The binding constant Kb was determined by ITC as a function of the temperature and ionic strength adjusted through the concentration cs of added salt. The dependence on salt concentration cs was used to determine the net number of released counterions. Moreover, the binding constant at a reference salt concentration of 1 M Kb(1 M) was determined by extrapolation. The dependence on temperature of Kb was used to dissect the binding free energy ΔGb into the respective enthalpies ΔHb and entropies ΔSb together with the specific heat Δcp. A strong enthalpy-entropy cancelation was found similar to the results for many other systems. The binding free energy ΔGb could furthermore be split up into a part ΔGci due to counterion release and a residual part ΔGres. The latter quantity reflects specific contributions as, e.g., salt bridges, van der Waals interactions, or hydrogen bonds. The entire analysis shows that heparin-lysozyme interactions are mainly caused by counterion release; that is, ca. three counterions are being released upon binding one lysozyme molecule. Our reported approach of quantifying interactions between glycosaminoglycans and proteins is generally applicable and suitable to provide new insights in the physical modulation of biomolecular signals.

Author Correction: Defined Geldrop Cultures Maintain Neural Precursor Cells.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Glycosaminoglycan-based hydrogels with programmable host reactions.

Glycosaminoglycan (GAG)-based, biohybrid hydrogels offering far-reaching control over their physical and biomolecular signaling properties have been successfully used in various cell and tissue culture applications. To explore the suitability of the materials for in vivo use, we herein studied the host reaction to in situ-assembling star(PEG)-GAG hydrogel variants upon subcutaneous implantation in immunocompetent C57BL/6J mice for up to 28 days. Specifically, we investigated the immune reaction and the angiogenic response to hydrogels with systematically varied cytokine functionalizations, physical network (and mechanical) properties, cell adhesiveness, and enzymatic degradability. The GAG-based hydrogel elicited only minor foreign body reaction with low immune cell infiltration and collagen deposition compared to similarly implanted medical grade silicone. Adjusting of the physical properties, biofunctionalization, and degradability allowed to program the host response from nearly no degradation and infiltration to fast integration of the gel scaffolds into the tissue within days. The results demonstrate that foreign body reactions and starPEG-GAG hydrogel tissue integration can be effectively controlled by defined adjustments of the hydrogel system, suggesting the in situ-assembling materials as safe and effective for in vivo tissue engineering applications.

Multiphasic microgel-in-gel materials to recapitulate cellular mesoenvironments in vitro.

Multiphasic in vitro models with cross-scale heterogeneity in matrix properties and/or cellular composition can reflect the structural and compositional complexity of living tissues more faithfully, thereby creating new options for pathobiology and drug development studies. Herein, a new class of tunable microgel-in-gel materials is reported that build on a versatile platform of multifunctional poly(ethylene glycol)-heparin gel types and integrates monodisperse, cell-laden microgels within cell-laden bulk hydrogel matrices. A novel microfluidic approach was developed to enable the high-throughput fabrication of microgels of in situ adjustable diameters, stiffness, degradability and biomolecular functionalization. By choosing structure and composition of the microgel and the bulk gel compartments independently, our microgel-in-gel arrangements provide cross-scale control over tissue-mimetic features and pave the way for culture systems with designed mesoenvironmental characteristics. The potentialities of the introduced approach are exemplarily shown by creating a reductionistic in vitro model of vascularized prostate cancer tissue.

Temperature-Induced Mechanomodulation of Interpenetrating Networks of Star Poly(ethylene glycol)-Heparin and Poly(N-isopropylacrylamide).

Thermoresponsive interpenetrating networks (IPNs) were prepared by sequential synthesis of a biohybrid network of star-shaped poly(ethylene glycol) [starPEG] and heparin and a poly(N-isopropylacrylamide)-polymer network. Amide bond formation was used for cross-linking of the starPEG-heparin network and photo-cross-linking with N,N'-methylenebis(acrylamide) was applied for the formation of the second polymer network. Both networks were linked by chain entanglements and hydrogen bonds only. The obtained sequential IPNs (seq-IPNs) showed temperature-dependent network properties as reflected by swelling and elasticity data as well as by the release of glycosaminoglycan-binding growth factors. The elastic modulus of the seq-IPNs was found to be amplified up to 50-fold upon temperature change from 22 to 37 °C compared to the intrinsic elastic moduli of the two combined networks. The heparin concentration (as well as the complexation of growth factors with the hydrogel-contained heparin) was demonstrated to be variably independent from the mechanical properties (elastic moduli) of the hydrogels. Illustrating the usability of the developed seq-IPN platform for cell fate control, the thermo-modulation of the release of vascular endothelial growth factor (VEGF) and bone morphogenetic protein 2 (BMP-2) is shown as well as the osteogenic differentiation of human mesenchymal stem cells exposed to stiff and BMP-2 releasing seq-IPNs.