Deciphering the Role of Sulfonated Unit in Heparin-Mimicking Polymer to Promote Neural Differentiation of Embryonic Stem Cells

Electrospun Composite PLLA-PPSB Nanofiber Nerve Conduits for Peripheral Nerve Defects Repair and Regeneration

Peripheral nerve injury (PNI) is a common clinical problem and regenerating peripheral nerve defects remain a significant challenge. Poly(polyol sebacate) (PPS) polymers are developed as promising materials for biomedical applications due to their biodegradability, biocompatibility, elastomeric properties, and ease of production. However, the application of PPS-based biomaterials in nerve tissue engineering, especially in PNI repair, is limited. In this study, PPS-based composite nanofibers poly(l-lactic acid)-poly(polycaprolactone triol-co-sebacic acid-co-N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid sodium salt) (PLLA-PPSB) are aimed to construct through electrospinning and assess their in vitro biocompatibility with Schwann cells (SCs) and in vivo repair capabilities for peripheral nerve defects. For the first time, the biocompatibility and bioactivity of PPS-based nanomaterial are examined at the molecular, cellular, and animal levels for PNI repair. Electrospun PLLA-PPSB nanofibers display favorable physicochemical properties and biocompatibility, providing an effective interface for the proliferation, glial expression, and adhesion of SCs in vitro. In vivo experiments using a 10-mm rat sciatic nerve defect model show that PLLA-PPSB nanofiber nerve conduits enhance myelin formation, axonal regeneration, angiogenesis, and functional recovery. Transcriptome analysis and biological validation indicate that PLLA-PPSB nanofibers may promote SC proliferation by activating the PI3K/Akt signaling pathway. This suggests the promising potential of PLLA-PPSB nanomaterial for PNI repair.

Artificial Extracellular Matrix Composed of Heparin-Mimicking Polymers for Efficient Anticoagulation and Promotion of Endothelial Cell Proliferation

Heparin-mimicking polymers have emerged as an alternative to heparin to construct effective and safe anticoagulant surfaces. However, the present heparin-mimicking polymers are usually limited to the combinations of glucose and sulfonic acid units, and the structure origin of their anticoagulant properties remains vague. Inspired by the structure of natural heparin, we synthesized a series of novel heparin-mimicking polymers (named GSAs) composed of three units, glucose, sulfonic acid, and carboxylic acid. Then, we constructed artificial extracellular matrices composed of GSAs and two typical cationic polymers, polyethyleneimine and chitosan, to investigate the anticoagulation and endothelialization of GSAs. By changing the ratio of the three units, their functions in the matrices were studied systematically. We found that an increase in the sulfonic acid content enhanced surface anticoagulant activity, an increase in glucose and sulfonic acid content promoted the proliferation of human umbilical vein vascular endothelial cells, and an increase in the carboxylic acid content inhibited the adherence of human umbilical vein vascular smooth muscle cells. This work uncovers the important role of the GSAs structure to the anticoagulation properties, which sheds new light on the design and preparation of heparin-mimicking polymers for practical engineering applications.

Cyclic and dimeric fibroblast growth factor 2 variants with high biomedical potential

Fibroblast growth factor 2 (FGF2) is a pleiotropic protein engaged in the regulation of key cellular processes in a wide spectrum of cells. FGF2 is an important object of basic research as well as a molecule used in regenerative medicine, in vitro cell culture maintenance, and as an anticancer drug carrier. However, the unsatisfactory stability and pleiotropic activities of the wild-type FGF2 largely limit its use as a medical product. To overcome these limitations, we have designed a set of FGF2-based macromolecules via sortase A-mediated cyclization and oligomerization. We obtained heparin-switchable FGF2 variants with enhanced stability and improved ability to stimulate cell proliferation and migration. We have shown that stimulation of glucose uptake by adipocytes is modulated by the architecture of FGF2 oligomers. Moreover, we used hyper-stable FGF2 variants for the construction of highly effective drug carriers for selective killing of FGFR1-overproducing cancer cells. The strategy for FGF2 engineering presented in this work provides novel insights into the design of growth factor variants for regenerative and anti-cancer precise medicine.

Vascular cell behavior on glycocalyx-mimetic surfaces: Simultaneous mimicking of the chemical composition and topographical structure of the vascular endothelial glycocalyx

The endothelial glycocalyx is a carbohydrate-rich layer overlying the outermost surface of endothelial cells. It mediates intercellular interactions by specific chemical compositions (e.g., proteoglycans containing glycosaminoglycan (GAG) side chains) and micro/nanotopography. Inspired by the endothelial glycocalyx, we fabricated a series of glycocalyx-mimetic surfaces with tunable chemical compositions (GAG-like polymers with different functional units) and topographical structures (micro/nanopatterns with pillars different in size). The combination of micro/nanopatterns and GAG-like polymers was flexibly and precisely controlled by replica molding using silicon templates (Si templates) and visible light-initiated polymerization. Human umbilical vein endothelial cells (HUVECs) and human umbilical vein smooth muscle cells (HUVSMCs) were suppressed on surfaces modified with polymers of 2-methacrylamido glucopyranose (MAG) but promoted on surfaces modified with polymers of sodium 4-vinyl-benzenesulfonate (SS) and copolymers of SS and MAG. Surface micro/nanopatterns showed highly complicated effects on surfaces grafted with different GAG-like polymers. Moreover, the spread of HUVSMCs was highly promoted on all flat/patterned surfaces containing sulfonate units, and the elongation effect was stronger on surfaces with smaller pillars. On all the flat/patterned surfaces modified with GAG-like polymers, the adsorption of human vascular endothelial growth factor (VEGF) and human basic fibroblast growth factor (bFGF) was improved, and the amount of VEGF and bFGF absorbed on patterned surfaces containing sulfonate units decreased with pattern dimensions. The decreasing trend of VEGF and bFGF adsorption was in accordance with HUVEC density, suggesting that glycocalyx-mimetic surfaces influence the adsorption of VEGF and bFGF and further influence the growth behavior of vascular cells.

Vascular cell behavior on heparin-like polymers modified silicone surfaces: The prominent role of the lotus leaf-like topography

Vascular cell behavior on material surfaces, such as heparin-like polymers, can be affected by the surface chemical composition and surface topological structure. In this study, the effects of heparin-like polymers and lotus leaf-like topography on surface vascular cell behavior are considered. By combining multicomponent thermo-curing and replica molding, a polydimethylsiloxane surface containing bromine (PDMS-Br) with lotus leaf-like topography is obtained. Heparin-like polymers with different chemical compositions are grafted onto PDMS-Br surfaces using visible-light-induced graft polymerization. Compared with unmodified PDMS-Br, surfaces modified by sulfonate-containing polymers are more friendly to vascular cells, while those modified by a glyco-polymer are much more resistant to vascular cells. The introduction of lotus leaf-like topography results in different degrees of decrease in cell density on different heparin-like polymer-modified surfaces. In addition, the combination of heparin-like polymers and lotus leaf-like topography results in the change in protein adsorption, indicating that the two factors may affect the surface vascular cell behavior by affecting the adsorption of relative proteins. The combination of bionic surface topography and different chemical components of heparin-like polymers on material surfaces suggests a new way of engineering cell-material interactions.

The role of carboxylic groups in heparin-mimicking polymer-functionalized surfaces for blood compatibility: Enhanced vascular cell selectivity

Blood compatibility is an eternal topic of biomedical materials. The effect of heparin-mimicking polymers (HMPs) on blood compatibility has been well studied, especially the synergistic effect of sugar unit and sulfonate/sulfate unit. However, carboxylic groups also play an important role in HMPs. In this work, copolymers of sodium 4-vinyl-benzenesulfonate (SS) and 2-methacrylamido glucopyranose (MAG) (poly(SS-co-MAG)) and poly(acrylate acid) (PAA) were self-assembled on Au surfaces with different feed ratios. When self-assembly of poly(SS-co-MAG) alone, the optimized feed ratio of SS and MAG for vascular cell selectivity was 1:1 (PS1M1); at this ratio the Au-PS1M1 surface showed the highest human umbilical vein endothelial cells (HUVECs) density and the lowest human umbilical vein smooth muscle cells (HUVSMCs) density. When self-assembly of PAA alone (surface designated as Au-PAA), the proliferation of both HUVECs and HUVSMCs was inhibited. Compared with either PS1M1 or PAA alone, the surfaces modified with both PAA and PS1M1 at the feed ratio of 1:1 (material designated as Au-PSM/PAA-2) showed enhanced promoting effect on HUVECs as well as enhanced inhibiting effect on HUVSMCs, indicating stronger vascular cell selectivity of carboxylic groups in the presence of sugar and sulfonate units.

Hyaluronic acid bioinspired polymers for the regulation of cell chondrogenic and osteogenic differentiation

As the simplest glycosaminoglycan (GAG) in extracellular matrix, hyaluronic acid (HA) takes part in several important biological processes, such as regulating cell proliferation, differentiation, and migration. In this work, a series of HA-inspired polymers with different saccharide and carboxylate units (HA-analogue polymers) are synthesized by free radical polymerization, and characterized using Fourier transform infrared spectroscopy (FT-IR), gel permeation chromatography (GPC) and nuclear magnetic resonance spectrometer (NMR), Moreover, cell experiments demonstrate that HA-analogue polymers with a certain proportion of saccharide and carboxylate (PM₁G₁) units shows a positive effect on the proliferation and differentiation of bone marrow mesenchymal stem cells (BMSCs). Furthermore, HA-analogue polymers have prominent cartilage inductive capacity in chondrogenic induction medium (CIM) and brilliant bone inductive capacity in osteogenic induction medium (OIM) toward BMSCs. Therefore, it is confirmed that the HA-analogue polymers can effectively mimic the functions of HA and have broad potential application prospects in the biomedical and clinical fields.

Vascular cell responses to silicone surfaces grafted with heparin-like polymers: surface chemical composition vs. topographic patterning

Heparin-like polymers are promising synthetic materials with biological functionalities, such as anticoagulant ability, growth factor binding to regulate cellular functions, and inflammation mediation, similar to heparin. The biocompatibility of heparin-like polymers with well-defined chemical structures has inspired many researchers to design heparin-like surfaces to explore their biological applications. The concept of the recombination of functional heparin structural units (sulfonate- and glyco-containing units) was proven to be successful in designing heparin-mimicking surfaces. However, besides surface structural units, topographic patterning is also an important contributor to the biological activity of the surfaces modified with heparin-like polymers. In this work, both surface structural units and topographic patterning were taken into account to investigate the vascular cell behaviors on the silicone surfaces. A facile method for the production of patterned bromine-containing polydimethylsiloxane surface (PDMS-Br) was developed from a one-step multicomponent thermocuring procedure and replica molding using a nanohole-arrayed silicon template. Different structural units of heparin-like polymers, i.e. homopolymer of sulfonate-containing sodium 4-vinylbenzenesulfonate (pSS), homopolymer of glyco-containing 2-(methacrylamido)glucopyranose (pMAG), and copolymers of MAG and SS (pSG), were then introduced on the flat and patterned PDMS-Br surface using visible light-induced graft polymerization. For the flat surfaces, compared with the PDMS-Br surface, pSS-grafted and pSG-grafted surfaces significantly increased cell densities of both human umbilical vein endothelial cells (HUVECs) and human umbilical vein smooth muscle cells (HUVSMCs), indicating that they are "vascular cell-friendly". In contrast, the pMAG-grafted surface showed decreased cell attachment of both HUVECs and HUVSMCs, indicating that the pMAG-grafted surface is "vascular cell-resistant". Moreover, surface topographic patterning enhanced the cell responses to the corresponding flat surfaces. That is to say, surface patterning can make the "vascular cell-friendly" surface still friendly, and the "vascular cell-resistant" surface much more resistant. The combination of surface structural units and topographic patterning shows promise in the preparation of new heparin-like surfaces with improved cell compatibility that is suitable for blood-compatible biomaterials.

Sulfonated RAFT Copolymers as Heparin Mimetics: Synthesis, Reactivity Ratios, and Anticoagulant Activity

The glycosaminoglycan heparin is a clinically important anticoagulant drug, primarily used to reduce the risk of blood clots (thrombosis) during surgery. Despite its importance in medicine and its continuous use over many decades, heparin suffers from several limitations associated with its heterogeneity and its extraction from animal tissues. In order to address these limitations, reversible addition-fragmentation chain transfer polymerization is utilized to prepare a library of heparin mimetic copolymers from the sulfonated monomers sodium 4-styrene sulfonate, potassium-3-sulfopropyl acrylate, potassium-3-sulfopropyl methacrylate, and sodium-2-acrylamido-2-methyl-1-propane sulfonate. Copolymers are prepared using combinations of two different monomers in various ratios. Monomer reactivity ratios are also determined for some representative monomer combinations, and all polymers are characterized by ¹ H NMR spectroscopy and gel permeation chromatography. The anticoagulant activities of the copolymers are determined by activated partial thromboplastin time and thrombin clotting time assays and structure-activity relationships are explored.

Dermatan sulfate obtained from the Phallusia nigra marine organism is responsible for antioxidant activity and neuroprotection in the neuroblastoma-2A cell lineage

Neurodegenerative diseases are characterized by progressive loss of neurons in the central nervous system (CNS). Several molecules play a role in mammalian CNS regeneration, including glycosaminoglycans (GAGs). GAGs are found in abundance in many marine invertebrates, such as ascidians that belong to the phylum Chordata, which show a high CNS regeneration capacity even in adulthood. Here, we investigated the roles of dermatan sulfate, a type of GAG that was obtained from the ascidian Phallusia nigra. We investigated the neuroprotective and antioxidant properties of Phallusia nigra dermatan sulfate (PnDS) after neurotoxic damage induced by the pesticide rotenone using the Neuro-2A cell lineage. Neuroprotection was observed through a mitochondrial activity analysis. A morphometric analysis revealed long unbranched neurites after incubation with PnDS and co-incubation with PnDS and rotenone. Furthermore, PnDS showed antioxidant activity that reduced reactive oxygen species (ROS) even in co-incubation with rotenone. The reduced ROS probably occurred because PnDS increased the activity of the antioxidant enzymes superoxide dismutase and catalase and improved total antioxidant capacity, which protected cells from damage, as observed through decreased levels of lipid peroxidation. These data suggest a neuroprotective and antioxidant role of PnDS even under neurodegenerative conditions caused by rotenone.

Unraveling the Structural Landscape of Chitosan-Based Heparan Sulfate Mimics Binding to Growth Factors: Deciphering Structural Determinants for Optimal Activity

Chitosan sulfates have demonstrated the ability to mimic heparan sulfate (HS) function. In this context, it is crucial to understand how the specific structural properties of HS domains determine their functionalities and biological activities. In this study, several HS-mimicking chitosans have been prepared to mimic the structure of HS domains that have proved to be functionally significant in cell processes. The results presented herein are in concordance with the hypothesis that sulfated chitosan-growth factor (GF) interactions are controlled by a combination of two effects: the electrostatic interactions and the conformational adaptation of the polysaccharide. Thus, we found that highly charged O-sulfated S-CS and S-DCS polysaccharides with a low degree of contraction interacted more strongly with GFs than N-sulfated N-DCS, with a higher degree of contraction and a low charge. Finally, the evidence gathered suggests that N-DCS would be able to bind to an allosteric zone and is likely to enhance GF signaling activity. This is because the bound protein remains able to bind to its cognate receptor, promoting an effect on cell proliferation as has been shown for PC12 cells. However, S-CS and S-DCS would sequester the protein, decreasing the GF signaling activity by depleting the protein or locally blocking its active site.

Heparin mimics and fibroblast growth factor-2 fabricated nanogold composite in promoting neural differentiation of mouse embryonic stem cells

The replacement therapy or transplantation using neural cells, which differentiated from stem cells, has emerged as a promising strategy for repairing damaged neural tissues and helping functional recovery in the treatment of neural system diseases. The challenge, however, is how to control embryonic stem cell fate so that neural differentiation can be efficiently directed to enrich a neuron cell population, and meanwhile to maintain their bioactivities. This is a key question and has a very significant impact in regenerative medicine. Here we proposed a new neural-differentiation inductive nanocomposite, containing gold nanoparticles (AuNPs), poly(2-methacrylamido glucopyranose-co-3-sulfopropyl acrylate) (PMS), and basic fibroblast growth factor (FGF2), for the high efficient directional neural-specific differentiation of mouse embryonic stem cells (mESCs). In this AuNP-PMS/FGF2 composite, PMS, playing as the high-active mimic of heparin/heparan sulfate (HS), is covalently anchored to AuNPs and bound with FGF2 on the surface of nanoparticles, forming a HS/FGF2 complex nanomimics to facilitate its binding to FGF receptor (FGFR) and promote high neural-inductive activity of mESCs. The stability, bioactivity and biocompatibility of the composite are investigated in this study. The results showed that the AuNP-PMS/FGF2 composite could maintain a long-term stability at room temperature for at least 8 days, and greatly promote the neural differentiation of mESCs. Compared with the other materials, the AuNP-PMS/FGF2 composite could significantly stimulate the expression of the specific neural differentiation markers (nestin and β3-tubulin), while obviously down-regulate the mRNA production of pluripotency marker Oct-4 in mESCs. Moreover, the promotion effect of the composite on neuronal maturation marker β3-tubulin expression achieved maximally at the low concentration of FGF2 (4 ng/mL), which suggested the high efficiency of AuNP-PMS/FGF2 composite in neural differentiation of mESCs. Meanwhile, both mESCs and L929 cells showed desirable growth during the incubation with AuNP-PMS/FGF2 composite. The AuNP-PMS/FGF2 system presents a new way to achieve HS/FGF2 complex nanomimics efficiently for the neural differentiation of mESCs.

Dual Pathway for Promotion of Stem Cell Neural Differentiation Mediated by Gold Nanocomposites

The neural differentiation of embryonic stem cells (ESCs) is of great value in the treatment of neurodegenerative diseases. On the basis of the two related signaling pathways that direct the neural differentiation of ESCs, we used gold nanoparticles (GNP) as a means of combining chemical and physical cues to trigger the neurogenic differentiation of stem cells. Neural differentiation-related functional units (glyco and sulfonate units on glycosaminoglycans, GAG) were anchored on the GNP surface and were then transferred to the cell membrane surface via GNP-membrane interactions. The functional units were able to activate the GAG-related signaling pathway, in turn promoting differentiation and maturation of stem cells into neuronal lineages. In addition, using the photothermal effect of GNP, the differentiation-inducing factor retinoic acid (RA), could be actively delivered into cells via laser irradiation. The RA-related intracellular signaling pathway was thereby further triggered, resulting in strong promotion of neurogenesis with a 300-fold increase in mature neural marker expression. The gold nanocomposites developed in this work provide the basis for a new strategy directing ESCs differentiation into nerve cells with high efficiency and high purity by acting on two related signaling pathways.

Ketamine promotes the neural differentiation of mouse embryonic stem cells by activating mTOR

Ketamine is a widely used general anesthetic and has been reported to demonstrate neurotoxicity and neuroprotection. Investigation into the regulatory mechanism of ketamine on influencing neural development is of importance for a better and safer way of relieving pain. Reverse transcription‑quantitative polymerase chain reaction and western blotting were used to detect the critical neural associated gene expression, and flow cytometry to detect the neural differentiation effect. Hence, in the present study the underlying mechanism of ketamine (50 nM) on neural differentiation of the mouse embryonic stem cell (mESC) line 46C was investigated. The results demonstrated that a low dose of ketamine (50 nM) promoted the differentiation of mESCs to neural stem cells (NSCs) and activated mammalian target of rapamycin (mTOR) by upregulating the expression levels of phosphorylated (p)‑mTOR. Furthermore, inhibition of the mTOR signaling pathway by rapamycin or knockdown of mTOR suppressed neural differentiation. A rescue experiment further confirmed that downregulation of mTOR inhibited the promotion of neural differentiation induced by ketamine. Taken together, the present study indicated that a low level of ketamine upregulated p‑mTOR expression levels, promoting neural differentiation.

Preparation of sulfatide mimicking oleic acid sulfated chitosan as a potential inhibitor for metastasis

Sulfatide is associated with numerous health problems, affecting different parts of the human body, including the metastasis; however, the underlying mechanisms are yet to be fully elucidated. Sulfatide has been used to potential inhibitor for tumor cell metastasis. In the present study we synthesized oleic acid sulfated chitosan (OlcShCs). It shows structural similarity to sulfatide because of its functional groups (sulfate and fatty acyl chains). Chitosan has smart properties such as biocompatibility, biodegradability and non-toxicity. We have prepared oleic acid sulfated chitosan (OlcShCs) by chitosan modification to mimic sulfatide. Its structure was characterized by FT-IR, H-NMR, and thermogravimetric analysis. After characterization studies its antimicrobial, antifungal and cytotoxic properties were investigated. Oleic acid sulfated chitosan (OlcShCs) was tested for its anti-cancer potential against human cancer cell lines (HeLa (ATCC® CCL-2™)) for 24 h, 48 h and 72 h using the MTT assays. This new material which is soluble at physiological conditions, is a potential candidate for further metastasis inhibition investigations.

Growth and Spatial Control of Murine Neural Stem Cells on Reflectin Films

Stem cells have attracted significant attention due to their regenerative capabilities and their potential for the treatment of disease. Consequently, significant research effort has focused on the development of protein- and polypeptide-based materials as stem cell substrates and scaffolds. Here, we explore the ability of reflectin, a cephalopod structural protein, to support the growth of murine neural stem/progenitor cells (mNSPCs). We observe that the binding, growth, and differentiation of mNSPCs on reflectin films is comparable to that on more established protein-based materials. Moreover, we find that heparin selectively inhibits the adhesion of mNSPCs on reflectin, affording spatial control of cell growth and leading to a >30-fold change in cell density on patterned substrates. The described findings highlight the potential utility of reflectin as a stem cell culture material.

Modular Polymers as a Platform for Cell Surface Engineering: Promoting Neural Differentiation and Enhancing the Immune Response

Regulating cell behavior and cell fate are of great significance for basic biological research and cell therapy. Carbohydrates, as the key biomacromolecules, play a crucial role in regulating cell behavior. Herein, "modular" glycopolymers were synthesized by reversible addition-fragmentation chain transfer polymerization. These glycopolymers contain sugar units (glucose), anchoring units (cholesterol), "guest" units (adamantane) for host-guest interaction, and fluorescent labeling units (fluorescein). It was demonstrated that these glycopolymers can insert into cell membranes with high efficiency and their residence time on the membranes can be regulated by controlling their cholesterol content. Furthermore, the behavior of the engineered cells can be controlled by modifying with different functional β-cyclodextrins (CD-X) via host-guest interactions with the adamantane units. Host-guest interactions with the modular polymers were demonstrated using CD-RBITC (X = a rhodamine B isothiocyanate). The glycopolymers were modified with CD-S (X = seven sulfonate groups) and CD-M (X = seven mannose groups) and were then attached, respectively, to the surfaces of mouse embryonic stem cells for the promotion of neural differentiation and to the surfaces of cancer cells for the enhancement of the immune response. The combination of multiple anchors and host-guest interactions provides a widely applicable cell membrane modification platform for a variety of applications.

Improved neural differentiation of stem cells mediated by magnetic nanoparticle-based biophysical stimulation

Stem cell therapy shows great potential in the treatment of neurodegenerative diseases, in which efficient neural differentiation of stem cells is still challenging.

Sustained release of a synthetic structurally-tailored glycopolymer modulates endothelial cells for enhanced endothelialization of materials

GAG-mimicking polymers were prepared by a novel method allowing close control of structure and can be used as potent synthetic bioactive modifiers to promote endothelialization of materials.

Chemical synthesis of glycosaminoglycan-mimetic polymers

This review describes several general chemical approaches for the preparation of glycosaminoglycan (GAG)-mimetic polymers based on different backbones and sidechains, and highlights the importance of these synthetic GAG-mimetic polymers in controlling key biofunctions.

Silk-Graphene Hybrid Hydrogels with Multiple Cues to Induce Nerve Cell Behavior

Cell behavior is dependent in part on chemical and physical cues from the extracellular matrix. Although the influence of various cues on cell behavior has been studied, challenges remain to incorporate multiple cues to matrix systems to optimize and control cell outcomes. Here, aligned silk fibroin (SF)-graphene hydrogels with preferable stiffness were developed through arranging SF nanofibers and SF-modified graphene sheets under an electric field. Different signals, such as bioactive graphene, nanofibrous structure, aligned topography, and mechanical stiffness, were tailored into the hydrogel system, providing niches for nerve cell responses. The desired adhesion, proliferation, differentiation, extensio,n and growth factor secretion of multiple nerve-related cells was achieved on these hydrogels, suggesting strong synergistic action through the combination of different cues. Based on the fabrication strategy, our present study provides a useful materials engineering platform for revealing cooperative influences of different signals on nerve cell behavior, to help in the understanding of cell-biomaterial interactions, with potential toward studies related to nerve regeneration.

Development of Self-Assembled Nanoribbon Bound Peptide-Polyaniline Composite Scaffolds and Their Interactions with Neural Cortical Cells

Degenerative neurological disorders and traumatic brain injuries cause significant damage to quality of life and often impact survival. As a result, novel treatments are necessary that can allow for the regeneration of neural tissue. In this work, a new biomimetic scaffold was designed with potential for applications in neural tissue regeneration. To develop the scaffold, we first prepared a new bolaamphiphile that was capable of undergoing self-assembly into nanoribbons at pH 7. Those nanoribbons were then utilized as templates for conjugation with specific proteins known to play a critical role in neural tissue growth. The template (Ile-TMG-Ile) was prepared by conjugating tetramethyleneglutaric acid with isoleucine and the ability of the bolaamphiphile to self-assemble was probed at a pH range of 4 through 9. The nanoribbons formed under neutral conditions were then functionalized step-wise with the basement membrane protein laminin, the neurotropic factor artemin and Type IV collagen. The conductive polymer polyaniline (PANI) was then incorporated through electrostatic and π–π stacking interactions to the scaffold to impart electrical properties. Distinct morphology changes were observed upon conjugation with each layer, which was also accompanied by an increase in Young’s Modulus as well as surface roughness. The Young’s Modulus of the dried PANI-bound biocomposite scaffolds was found to be 5.5 GPa, indicating the mechanical strength of the scaffold. Thermal phase changes studied indicated broad endothermic peaks upon incorporation of the proteins which were diminished upon binding with PANI. The scaffolds also exhibited in vitro biodegradable behavior over a period of three weeks. Furthermore, we observed cell proliferation and short neurite outgrowths in the presence of rat neural cortical cells, confirming that the scaffolds may be applicable in neural tissue regeneration. The electrochemical properties of the scaffolds were also studied by generating I-V curves by conducting cyclic voltammetry. Thus, we have developed a new biomimetic composite scaffold that may have potential applications in neural tissue regeneration.

Sulfonate Groups and Saccharides as Essential Structural Elements in Heparin-Mimicking Polymers Used as Surface Modifiers: Optimization of Relative Contents for Antithrombogenic Properties

Blood compatibility is a long sought-after goal in biomaterials research, but remains an elusive one, and in spite of extensive work in this area, there is still no definitive information on the relationship between material properties and blood responses such as coagulation and thrombus formation. Materials modified with heparin-mimicking polymers have shown promise and indeed may be seen as comparable to materials modified with heparin itself. In this work, heparin was conceptualized as consisting of two major structural elements: saccharide- and sulfonate-containing units, and polymers based on this concept were developed. Copolymers of 2-methacrylamido glucopyranose, containing saccharide groups, and sodium 4-vinylbenzenesulfonate, containing sulfonate groups, were graft-polymerized on vinyl-functionalized polyurethane (PU) surfaces by free radical polymerization. This graft polymerization method is simple, and the saccharide and sulfonate contents are tunable by regulating the feed ratio of the monomers. Homopolymer-grafted materials, containing only sulfonate or saccharide groups, showed different effects on cell-surface interactions including platelet adhesion, adhesion and proliferation of vascular endothelial cells, and adhesion and proliferation of smooth muscle cells. The copolymer-grafted materials showed effects due to both sulfonate and saccharide elements with respect to blood responses, and the optimum composition was obtained at a 2:1 ratio of sulfonate to saccharide units (material designated as PU-PS1M1). In cell adhesion experiments, this material showed the lowest platelet and human umbilical vein smooth muscle cell density and the highest human umbilical vein endothelial cell density. Among the materials investigated, PU-PS1M1 also had the longest plasma clotting time. This material was thus shown to be multifunctional with a combination of properties, suggesting thromboresistant behavior in blood contact.