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Glial-cell-line-derived neurotrophic factor (GDNF) is a protein that has therapeutic potential in the treatment of Parkinson's disease and other neurodegenerative diseases. The activity of GDNF is highly dependent on the interaction with sulfated glycans which bind at the N-terminus consisting of 19 residues. Herein, we studied the influence of different glycosaminoglycan (i.e., glycan; GAG) molecules on the conformation of a GDNF-derived peptide (GAG binding motif, sixteen amino acid residues at the N-terminus) using both experimental and theoretical studies. The GAG molecules employed in this study are heparin, heparan sulfate, hyaluronic acid, and sulfated hyaluronic acid. Circular dichroism spectroscopy was employed to detect conformational changes induced by the GAG molecules; molecular dynamics simulation studies were performed to support the experimental results. Our results revealed that the sulfated GAG molecules bind strongly with GDNF peptide and induce alpha-helical structure in the peptide to some extent., (Copyright © 2021. Published by Elsevier B.V.)

Feedback-controlled anticoagulant hydrogels were formed by crosslinking the anticoagulant heparin with star-shaped poly(ethylene glycol) using peptide linkers, which are selectively cleaved by different activated blood coagulation factors acting as proteolytic enzymes. Various cleavable peptide units, differing either in their thrombin turnover rates or in their responsiveness to factors activated earlier in the course of blood coagulation, were used for the formation of the biohybrid materials. Release triggered by the early coagulation factors Xa (FXa) or FXIIa/kallikrein was shown to enhance the efficiency of the released anticoagulant. Furthermore, FXa-cleavable gels enabled a faster release of heparin, which was attributed to the lower affinity of the factor for heparin. Combining early and fast responses, FXa-cleavable gels were shown to provide anticoagulant protection of biomaterial surfaces at low levels of released heparin in human whole-blood incubation experiments. The results demonstrate the potential for employing biomolecular circuits in the design of functional biomaterials to tailor the adaptive delivery of bioactive molecules., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Dialysis or kidney transplantation is the only therapeutic option for end stage renal disease. Accordingly, there is a large unmet clinical need for new causative therapeutic treatments. Obtaining robust models that mimic the complex nature of the human kidney is a critical step in the development of new therapeutic strategies. Here we establish a synthetic in vitro human renal tubulogenesis model based on a tunable glycosaminoglycan-hydrogel platform. In this system, renal tubulogenesis can be modulated by the adjustment of hydrogel mechanics and degradability, growth factor signaling, and the presence of insoluble adhesion cues, potentially providing new insights for regenerative therapy. Different hydrogel properties were systematically investigated for their ability to regulate renal tubulogenesis. Hydrogels based on heparin and matrix metalloproteinase cleavable peptide linker units were found to induce the morphogenesis of single human proximal tubule epithelial cells into physiologically sized tubule structures. The generated tubules display polarization markers, extracellular matrix components, and organic anion transport functions of the in vivo renal proximal tubule and respond to nephrotoxins comparable to the human clinical response. The established hydrogel-based human renal tubulogenesis model is thus considered highly valuable for renal regenerative medicine and personalized nephrotoxicity studies., Statement of Significance: The only cure for end stage kidney disease is kidney transplantation. Hence, there is a huge need for reliable human kidney models to study renal regeneration and establish alternative treatments. Here we show the development and application of an in vitro human renal tubulogenesis model using heparin-based hydrogels. To the best of our knowledge, this is the first system where human renal tubulogenesis can be monitored from single cells to physiologically sized tubule structures in a tunable hydrogel system. To validate the efficacy of our model as a drug toxicity platform, a chemotherapy drug was incubated with the model, resulting in a drug response similar to human clinical pathology. The established model could have wide applications in the field of nephrotoxicity and renal regenerative medicine and offer a reliable alternative to animal models., (Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Polymer hydrogels can be readily modulated with regard to their physical properties and functionalized to recapitulate molecular cues of the extracellular matrix (ECM). However, they remain structurally different from the hierarchical supramolecular assemblies of natural ECM. Accordingly, we herein report a set of hydrogel composite materials made from starPEG-peptide conjugates, maleimide-functionalized heparin and collagen type I that combine semisynthetic and ECM-derived components. Collagen fibrillogenesis was controlled by temperature and collagen concentration to form collagen microstructures which were then homogeneously distributed within the 3D composite matrix during hydrogel formation. The collagen-laden hydrogel materials showed a heterogeneous local variation of the stiffness and adhesion ligand density. Composite gels functionalized with growth factors and cell adhesive peptides (RGDSP) supported the growth of embedded human umbilical cord vein endothelial cells (HUVECs) and induced the alignment of embedded bone marrow-derived human mesenchymal stem cells (MSCs) to the collagen microstructures in vitro. The introduced composite hydrogel material is concluded to faithfully mimic cell-instructive features of the ECM., Statement of Significance: Cell-instructive materials play an important role in the generation of both regenerative therapies and advanced tissue and disease models. For that purpose, biofunctional polymer hydrogels recapitulating molecular cues of the extracellular matrix (ECM) were successfully applied in various different studies. However, hydrogels generally lack the hierarchical supramolecular structure of natural ECM. We have therefore developed a hydrogel composite material made from starPEG-peptide conjugates, maleimide-functionalized heparin and collagen type I fibrils. The collagen-laden scaffolds showed a heterogeneous local variation in the stiffness of the material. The composite gels were successfully tested in culture experiments with human umbilical cord vein endothelial cells and bone marrow-derived human mesenchymal stem cells. It was concluded that the composite scaffold was able to faithfully mimic important cell-instructive features of the ECM., (Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

While vascular endothelial growth factor (VEGF) has been shown to be one of the key players in wound healing by promoting angiogenesis current clinical applications of this growth factor to the wound environment are poorly controlled and not sustainable. Hydrogels made of sulfated glycosaminoglycans (GAG) allow for the sustained release of growth factors since GAGs engage in electrostatic complexation of biomolecules. In here, we explore a set of hydrogels formed of selectively desulfated heparin derivatives and star-shaped poly(ethylene glycol) with respect to VEGF binding and release and anticoagulant activity. As a proof of concept, supportive effects on migration and tube formation of human umbilical vein endothelial cells were studied in vitro and the promotion of wound healing was followed in genetically diabetic (db/db) mice. Our data demonstrate that the release of VEGF from the hydrogels is modulated in dependence on the GAG sulfation pattern. Hydrogels with low sulfate content (11% of initial heparin) were found to be superior in efficacy of VEGF administration, low anticoagulant activity and promotion of angiogenesis.

Angiogenesis, the outgrowth of blood vessels, is crucial in development, disease and regeneration. Studying angiogenesis in vitro remains challenging because the capillary morphogenesis of endothelial cells (ECs) is controlled by multiple exogenous signals. Therefore, a set of in situ-forming starPEG-heparin hydrogels was used to identify matrix parameters and cellular interactions that best support EC morphogenesis. We showed that a particular type of soft, matrix metalloproteinase-degradable hydrogel containing covalently bound integrin ligands and reversibly conjugated pro-angiogenic growth factors could boost the development of highly branched, interconnected, and lumenized endothelial capillary networks. Using these effective matrix conditions, 3D heterocellular interactions of ECs with different mural cells were demonstrated that enabled EC network modulation and maintenance of stable vascular capillaries over periods of about one month in vitro. The approach was also shown to permit in vitro tumor vascularization experiments with unprecedented levels of control over both ECs and tumor cells. In total, the introduced 3D hydrogel co-culture system could offer unique options for dissecting and adjusting biochemical, biophysical, and cell-cell triggers in tissue-related vascularization models.

Poly(ethylene glycol)-peptide- and glycosaminoglycan-peptide conjugates obtained by a regio-selective amino acid protection strategy are converted into cell-instructive hydrogel matrices capable of inducing morphogenesis in embedded human vascular endothelial cells and dorsal root ganglia., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Bio-responsive polymer architectures can empower medical therapies by engaging molecular feedback-response mechanisms resembling the homeostatic adaptation of living tissues to varying environmental constraints. Here we show that a blood coagulation-responsive hydrogel system can deliver heparin in amounts triggered by the environmental levels of thrombin, the key enzyme of the coagulation cascade, which--in turn--becomes inactivated due to released heparin. The bio-responsive hydrogel quantitatively quenches blood coagulation over several hours in the presence of pro-coagulant stimuli and during repeated incubation with fresh, non-anticoagulated blood. These features enable the introduced material to provide sustainable, autoregulated anticoagulation, addressing a key challenge of many medical therapies. Beyond that, the explored concept may facilitate the development of materials that allow the effective and controlled application of drugs and biomolecules.

A new class of biodegradable materials was prepared by combining polyethylene glycol, heparin, and a matrix metalloproteinase-cleavable peptide sequence into a well-defined hydrogel network which mimics native extracellular matrices in its ability to provide mechanical support and chemical signals as well as elicit a dynamic reciprocal response.

Adaptive drug release can combat coagulation and inflammation activation at the blood-material interface with minimized side effects. For that purpose, poly(styrene- alt -maleic-anhydride) copolymers were conjugated to heparin via coagulation-responsive linker peptides and shown to tightly adsorb onto poly(ethersulfone) (PES)-surfaces from aqueous solutions as monolayers. Coagulation-responsive release of unfractionated as well as low molecular weight heparins from the respective coatings was demonstrated to be functionally beneficial in human plasma and whole blood incubation with faster release kinetics resulting in stronger anticoagulant effects. Coated poly(ethersulfone)/poly(vinylpyrrolidone) (PES/PVP) flat membranes proved the technology to offer an easy, effective and robust anticoagulant interfacial functionalization of hemodialysis membranes. In perspective, the modularity of the adaptive release system will be used for inhibiting multiple activation processes. [Display omitted] • conjugates of styrene-maleic anhydrate copolymers and heparin tightly adsorb as monolayers on hemodialysis membranes • conjugates containing thrombin-cleavable peptide linkers enable the adaptive release of heparin • adaptive release from the conjugates enhances the anticoagulant action of unfractionated and low molecular weight heparin [ABSTRACT FROM AUTHOR]

Matrix systems used to study complex three-dimensional (3D) cellular processes like mammary epithelial tissue morphogenesis and tumorigenesis ex vivo often require ill-defined biological components, which lead to poor reproducibility and a lack of control over physical parameters. In this study, a well-defined, tunable synthetic biohybrid hydrogel composed of the glycosaminoglycan heparin, star-shaped poly(ethylene glycol) (starPEG), and matrix metalloproteinase- (MMP-) cleavable crosslinkers was applied to dissect the biophysical and biochemical signals promoting human mammary epithelial cell (MEC) morphogenesis. We show that compliant starPEG-heparin matrices promote the development of polarized MEC acini. Both the presence of heparin and MMP-cleavable crosslinks are essential in facilitating MEC morphogenesis without supplementation of exogenous adhesion ligands. In this system, MECs secrete and organize laminin in basement membrane-like assemblies to promote integrin signaling and drive acinar development. Therefore, starPEG-heparin hydrogels provide a versatile platform to study mammary epithelial tissue morphogenesis in a chemically defined and precisely tunable 3D in vitro microenvironment. The system allows investigation of biophysical and biochemical aspects of mammary gland biology and potentially a variety of other organoid culture studies. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Sulfationpatterns of glycosaminoglycans (GAG) govern the electrostaticcomplexation of biomolecules and thus allow for modulating the releaseprofiles of growth factors from GAG-based hydrogels. To explore optionsrelated to this, selectively desulfated heparin derivatives were prepared,thoroughly characterized, and covalently converted with star-shapedpoly(ethylene glycol) into binary polymer networks. The impact ofthe GAG sulfation pattern on the network characteristics of the obtainedhydrogels was theoretically evaluated by mean field methods and experimentallyanalyzed by rheometry and swelling measurements. Sulfation-dependentdifferences of reactivity and miscibility of the heparin derivativeswere shown to determine network formation. A theory-based design conceptfor customizing growth factor affinity and physical characteristicswas introduced and validated by quantifying the release of fibroblastgrowth factor 2 from a set of biohybrid gels. The resulting new classof cell-instructive polymer matrices with tunable GAG sulfation willbe instrumental for multiple applications in biotechnology and medicine. [ABSTRACT FROM AUTHOR]