Effects of immobilizing sites of RGD peptides in amphiphilic block copolymers on efficacy of cell adhesion

Collagen-Like Peptide Bioconjugates

Collagen-like peptides (CLPs), also known as collagen-mimetic peptides (CMPs), are short synthetic peptides that mimic the triple helical conformation of native collagens. Traditionally, CLPs have been widely used in deciphering the chemical basis for collagen triple helix stabilization, mimicking collagen fibril formation and fabricating other higher-order supramolecular self-assemblies. While CLPs have been used extensively for elucidation of the assembly of native collagens, less work has been reported on the use of CLP-polymer and CLP-peptide conjugates in the production of responsive assemblies. CLP triple helices have been used as physical cross-links in CLP-polymer hydrogels with predesigned thermoresponsiveness. The more recently reported ability of CLP to target native collagens via triple helix hybridization has further inspired the production of CLP-polymer and CLP-peptide bioconjugates and the employment of these conjugates in generating well-defined nanostructures for targeting collagen substrates. This review summarizes the current progress and potential of using CLPs in biomedical arenas and is intended to serve as a general guide for designing CLP-containing biomaterials.

Poly(lactic acid) based hydrogels

Polylactide (PLA) and its copolymers are hydrophobic polyesters used for biomedical applications. Hydrogel medicinal implants have been used as drug delivery vehicles and scaffolds for tissue engineering, tissue augmentation and more. Since lactides are non-functional, they are copolymerized with hydrophilic monomers or conjugated to a hydrophilic moiety to form hydrogels. Copolymers of lactic and glycolic acids with poly(ethylene glycol) (PEG) provide thermo-responsive hydrogels. Physical crosslinking mechanisms of PEG-PLA or PLA-polysaccharides include: lactic acid segment hydrophobic interactions, stereocomplexation of D and L-lactic acid segments, ionic interactions, and chemical bond formation by radical or photo crosslinking. These hydrogels may also be tailored as stimulus responsive (pH, photo, or redox). PLA and its copolymers have also been polymerized to include urethane bonds to fabricate shape memory hydrogels. This review focuses on the synthesis, characterization, and applications of PLA containing hydrogels.

Biodegradable Injectable Polymer Systems Exhibiting Temperature-Responsive Irreversible Sol-to-Gel Transition by Covalent Bond Formation

Biodegradable injectable polymer (IP) systems exhibiting temperature-responsive sol-to-gel transitions between room temperature and body temperature have the potential for use in biomedical applications. However, gelation of such IP systems is a reversible process through physical cross-linking, and the hydrogels thus formed are likely to revert to the sol state under highly wet conditions after injection. In this study, a biodegradable IP system exhibiting temperature-responsive irreversible sol-to-gel transition by covalent bond formation was developed by simple mixing of polymers. A triblock copolymer of poly(caprolactone-co-glycolic acid) and poly(ethylene glycol) (tri-PCG) and tri-PCG with attached succinimide ester groups at both termini (tri-PCG-SA-OSu) were prepared and mixed together with a water-soluble polyamine (typically poly-l-lysine). The obtained IP formulation was in the sol state after mixing, but exhibited a rapid sol-to-gel transition within 30 s upon increasing the temperature to 37 °C. Once formed, the hydrogel did not revert to the sol state, even after cooling to 4 °C, because of the formation of covalent bonds upon transition. The obtained hydrogel soaked in phosphate buffered saline (PBS) exhibited a significantly longer duration time of the gel state. This IP system exhibiting a rapid and irreversible sol-to-gel transition is convenient for medical professionals and possesses great potential for use in biomedical devices for clinical applications such as drug delivery systems and antiadhesive materials.

A Review of Injectable Polymeric Hydrogel Systems for Application in Bone Tissue Engineering

Biodegradable, stimuli-responsive polymers are essential platforms in the field of drug delivery and injectable biomaterials for application of bone tissue engineering. Various thermo-responsive hydrogels display water-based homogenous properties to encapsulate, manipulate and transfer its contents to the surrounding tissue, in the least invasive manner. The success of bioengineered injectable tissue modified delivery systems depends significantly on their chemical, physical and biological properties. Irrespective of shape and defect geometry, injectable therapy has an unparalleled advantage in which intricate therapy sites can be effortlessly targeted with minimally invasive procedures. Using material testing, it was found that properties of stimuli-responsive hydrogel systems enhance cellular responses and cell distribution at any site prior to the transitional phase leading to gelation. The substantially hydrated nature allows significant simulation of the extracellular matrix (ECM), due to its similar structural properties. Significant current research strategies have been identified and reported to date by various institutions, with particular attention to thermo-responsive hydrogel delivery systems, and their pertinent focus for bone tissue engineering. Research on future perspective studies which have been proposed for evaluation, have also been reported in this review, directing considerable attention to the modification of delivering natural and synthetic polymers, to improve their biocompatibility and mechanical properties.

Biodegradation and Osteosarcoma Cell Cultivation on Poly(aspartic acid) Based Hydrogels

Development of novel biodegradable and biocompatible scaffold materials with optimal characteristics is important for both preclinical and clinical applications. The aim of the present study was to analyze the biodegradability of poly(aspartic acid)-based hydrogels, and to test their usability as scaffolds for MG-63 osteoblast-like cells. Poly(aspartic acid) was fabricated from poly(succinimide) and hydrogels were prepared using natural amines as cross-linkers (diaminobutane and cystamine). Disulfide bridges were cleaved to thiol groups and the polymer backbone was further modified with RGD sequence. Biodegradability of the hydrogels was evaluated by experiments on the base of enzymes and cell culture medium. Poly(aspartic acid) hydrogels possessing only disulfide bridges as cross-links proved to be degradable by collagenase I. The MG-63 cells showed healthy, fibroblast-like morphology on the double cross-linked and RGD modified hydrogels. Thiolated poly(aspartic acid) based hydrogels provide ideal conditions for adhesion, survival, proliferation, and migration of osteoblast-like cells. The highest viability was found on the thiolated PASP gels while the RGD motif had influence on compacted cluster formation of the cells. These biodegradable and biocompatible poly(aspartic acid)-based hydrogels are promising scaffolds for cell cultivation.

Interplay of Matrix Stiffness and Cell-Cell Contact in Regulating Differentiation of Stem Cells

Stem cells are capable of sensing and responding to the mechanical properties of extracellular matrixes (ECMs). It is well-known that, while osteogenesis is promoted on the stiff matrixes, adipogenesis is enhanced on the soft ones. Herein, we report an "abnormal" tendency of matrix-stiffness-directed stem cell differentiation. Well-defined nanoarrays of cell-adhesive arginine-glycine-aspartate (RGD) peptides were modified onto the surfaces of persistently nonfouling poly(ethylene glycol) (PEG) hydrogels to achieve controlled specific cell adhesion and simultaneously eliminate nonspecific protein adsorption. Mesenchymal stem cells were cultivated on the RGD-nanopatterned PEG hydrogels with the same RGD nanospacing but different hydrogel stiffnesses and incubated in the induction medium to examine the effect of matrix stiffness on osteogenic and adipogenic differentiation extents. When stem cells were kept at a low density during the induction period, the differentiation tendency was consistent with the previous reports in the literature; however, both lineage commitments were favored on the stiff matrices at a high cell density. We interpreted such a complicated stiffness effect at a high cell density in two-dimensional culture as the interplay of matrix stiffness and cell-cell contact. As a result, this study strengthens the essence of the stiffness effect and highlights the combinatory effects of ECM cues and cell cues on stem cell differentiation.

Biomaterials for 4D stem cell culture

Stem cells reside in complex three-dimensional (3D) environments within the body that change with time, promoting various cellular functions and processes such as migration and differentiation. These complex changes in the surrounding environment dictate cell fate yet, until recently, have been challenging to mimic within cell culture systems. Hydrogel-based biomaterials are well suited to mimic aspects of these in vivo environments, owing to their high water content, soft tissue-like elasticity, and often-tunable biochemical content. Further, hydrogels can be engineered to achieve changes in matrix properties over time to better mimic dynamic native microenvironments for probing and directing stem cell function and fate. This review will focus on techniques to form hydrogel-based biomaterials and modify their properties in time during cell culture using select addition reactions, cleavage reactions, or non-covalent interactions. Recent applications of these techniques for the culture of stem cells in four dimensions (i.e., in three dimensions with changes over time) also will be discussed for studying essential stem cell processes.

Promoting endothelialization on decellularized porcine aortic valve by immobilizing branched polyethylene glycolmodified with cyclic-RGD peptide: an in vitro study

We functionally modify a decellularized porcine aortic valve using a novel complex biologically active cyclic- (c)-RGD modified with branched polyethylene glycol (PEG), namely, c-RDG-PEG. Human umbilical vein endothelial cell (HUVEC) adhesion and proliferation were detected for up to 8 d after seeding on the scaffold. (1)H nuclear magnetic resonance (D2O) showed signal peaks at 7.27 and 7.38 ppm associated with protons of the phenyl group in c-RGD-PEG. Attenuated total reflectance Fourier transform infrared spectroscopy showed characteristic peaks for PEG at 1100 and 1342 cm(-1). These represented vibration peaks of C-O and -CH2 bonds, suggesting successful grafting of c-RGD-PEG to a decellularized porcine aortic valve (DPAV). The tensile strengths were significantly increased in the c-RGD-PEG-DPAV group compared to the native valve and DPAV groups (P < 0.05), while the elastic modulus was sigficantly decreased in the c-RGD-PEG-DPAV group compared to the native valve and DPAV groups (P < 0.05). HUVEC proliferation was significantly higher in the c-RGD-PEG-DPAV group than in the PEG-DPAV and DPAV groups (P < 0.01). Maximum adhesion occurred at 4 h, and on the 8th day, a confluent and compact monolayer formed on the valve surface. The modified DPAV resulted in good adhesion and proliferation of endothelial cells and is an appropriate approach to modify tissue engineered heart valves for promoting endothelialization.

Effects of Nanoscale Spatial Arrangement of Arginine-Glycine-Aspartate Peptides on Dedifferentiation of Chondrocytes

Cell dedifferentiation is of much importance in many cases such as the classic problem of dedifferentiation of chondrocytes during in vitro culture in cartilage tissue engineering. While cell differentiation has been much investigated, studies of cell dedifferentiation are limited, and the nanocues of cell dedifferentiation have little been reported. Herein, we prepared nanopatterns and micro/nanopatterns of cell-adhesive arginine-glycine-aspartate (RGD) peptides on nonfouling poly(ethylene glycol) (PEG) hydrogels to examine the effects of RGD nanospacing on adhesion and dedifferentiation of chondrocytes. The relatively larger RGD nanospacing above 70 nm was found to enhance the maintainence of the chondrocyte phenotype in two-dimensional culture, albeit not beneficial for adhesion of chondrocytes. A unique micro/nanopattern was employed to decouple cell spreading, cell shape, and cell-cell contact from RGD nanospacing. Under given spreading size and shape of single cells, the large RGD nanospacing was still in favor of preserving the normal phenotype of chondrocytes. Hence, the nanoscale spatial arrangement of cell-adhesive ligands affords a new independent regulator of cell dedifferentiation, which should be taken into consideration in biomaterial design for regenerative medicine.

Biotin-Avidin Based Universal Cell-Matrix Interaction for Promoting Three-Dimensional Cell Adhesion

To promote cell adhesion in three-dimensional (3D) extracellular matrix (ECM) is crucial for avoiding cell anoikis, which is one of the most important issues for fundamental cell biology. Herein, a biotin-avidin based universal cell-matrix interaction for different types of cells is developed in order to achieve the promoted adhesion in 3D ECM. For the purpose, biotinylated nanofibrous hydrogels are constructed by coassembling 1,4-benzyldicarboxamide (C2) based non-biotinylated and biotinylated supramolecular gelators. The used cells are modified by avidin (AV-cells) through biotinylating cells and then interacting with avidin. After in situ encapsulating AV-cells in the hydrogels, the adhered amount can be increased by tens of percent even with adding several percentages of the biotinylated C2 gelators in the coassembly due to the specific biotin-avidin interaction. Reverse transcription polymerase chain reaction (RT-PCR) confirms that AV-cells can proliferate without varying gene expression and denaturation. Compared with the interaction between RGD and cells, this avidin-biotin interaction should be much more universal and it is feasible to be employed to promote cell adhesion for most types of cells in 3D matrix.

Nanoparticles complexed with gene vectors to promote proliferation of human vascular endothelial cells

Amphiphilic block copolymers containing biodegradable hydrophobic segments of depsipeptide based copolymers have been synthesized and explored as gene carriers for enhancing proliferation of endothelial cells in vitro. These polymers form nanoparticles (NPs) with positive charges on their surface, which could condense recombinant plasmids of enhanced green fluorescent protein plasmid and ZNF580 gene (pEGFP-ZNF580) and protect them against DNase I. ZNF580 gene is efficiently transported into EA.hy926 cells to promote their proliferation, whereby the transfection efficiency of NPs/pEGFP-ZNF580 is approximately similar to that of Lipofectamine 2000. These results indicate that the NPs might have potential as a carrier for pEGFP-ZNF580, which could support endothelialization of cardiovascular implants.

Self-Assembly of a Designed Alternating Arginine/Phenylalanine Oligopeptide

A model octapeptide peptide consisting of an alternating sequence of arginine (Arg) and phenylalanine (Phe) residues, namely, [Arg-Phe]4, was prepared, and its self-assembly in solution studied. The simple alternating [Arg-Phe]4 peptide sequence allows for unique insights into the aggregation process and the structure of the self-assembled motifs. Fluorescence and UV-vis assays were used to determine critical aggregation concentrations, corresponding to the formation of oligomeric species and β-sheet rich structures organized into both spheroidal aggregates and highly ordered fibrils. Electron and atomic force microscopy images show globular aggregates and long unbranched fibers with diameters ranging from ∼4 nm up to ∼40 nm. Infrared and circular dichroism spectroscopy show the formation of β-sheet structures. X-ray diffraction on oriented stalks show that the peptide fibers have an internal lamellar structure, with an orthorhombic unit cell with parameters a ∼ 27.6 Å, b ∼ 9.7 Å, and c ∼ 9.6 Å. In situ small-angle X-ray scattering (SAXS) shows the presence of low molecular weight oligomers in equilibrium with mature fibers which are likely made up from 5 or 6 intertwined protofilaments. Finally, weak gel solutions are probed under gentle shear, suggesting the ability of these arginine-rich fibers to form networks.

Fabrication of RGD micro/nanopattern and corresponding study of stem cell differentiation

Micropatterns of gold (Au) nanoarrays on inorganic and polymeric substrates were fabricated by combining block copolymer micelle nanolithography to obtain gold nanoarrays on glass, photolithography plus hydrofluoric acid (HF) etching to generate microislands, and transfer lithography to shift the gold micro/nanopatterns from glass to a bioinert poly(ethylene glycol) (PEG) hydrogel surface. Further the modification of the gold nanodots via cell-adhesive arginine-glycine-aspartate (RGD) ligands was carried out to achieve peptide micro/nanopatterns. Whereas the micro/nanopatterns of noble metals could be useful in various applications, the peptide micro/nanopatterns especially enable persistent cell localization on adhesive micropatterns of RGD nanoarrays on the background of potently nonfouling PEG hydrogels, and thus offer a powerful tool to investigate cell-material interactions on both molecular and cellular levels. As a demonstration, we cultured human mesenchymal stem cells (hMSCs) on micro/nanopatterns with RGD nanoarrays of nanospacings 46 and 95 nm, and with micropans of side lengths 35 and 65 μm (four groups in total). The osteogenic and adipogenic differentiation of hMSCs was conducted, and the potential effect of RGD nanospacing and the effect of cell spreading size on cell differentiation were decoupled for the first time. The results reveal that RGD nanospacing, independent of cell spreading size, acts as a strong regulator of cell tension and stem cell differentiation, which cannot be concluded unambiguously based on either merely micropatterns or nanopatterns.

Ligand engagement on material surfaces is discriminated by cell mechanosensoring

Peptide or protein ligands can be used for molecular decoration to enhance the functionality of synthetic materials. However, some skepticism has arisen about the efficacy of such strategy in practical contexts since serum proteins largely adsorb. To address this issue, it is crucial to ascertain whether a chemically conjugated integrin-binding peptide is fully recognized by a cell even if partially covered by a physisorbed layer of serum protein; in more general terms, if competitive protein fragments physisorbed onto the surface are distinguishable from those chemically anchored to it. Here, we engraft an RGD peptide on poly-ε-caprolactone (PCL) surfaces and follow the dynamics of focal adhesion (FA) and cytoskeleton assembly at different times and culture conditions using a variety of analytical tools. Although the presence of serum protein covers the bioconjugated RGD significantly, after the first adhesion phase cells dig into the physisorbed layer and reach the submerged signal to establish a more stable adhesion structure (mature FAs). Although the spreading area index is not substantially affected by the presence of the RGD peptide, cells attached to chemically bound signals develop a stronger adhesive interaction with the materials and assemble a mechanically stable cytoskeleton. This demonstrates that cells are able to discriminate, via mechanosensoring, between adhesive motives belonging to physisorbed proteins and those firmly anchored on the material surface.

Choline phosphate functionalized surface: protein-resistant but cell-adhesive zwitterionic surface potential for tissue engineering

A choline phosphate (CP) modified zwitterionic surface is prepared with both protein-resistant and cell-adhesive properties, exhibiting great potential for biomedical applications such as tissue engineering.

Surface modification and endothelialization of biomaterials as potential scaffolds for vascular tissue engineering applications

This review highlights the recent developments of surface modification and endothelialization of biomaterials in vascular tissue engineering applications.

A zwitterionic surface with general cell-adhesive and protein-resistant properties

A choline phosphate functionalized surface is proved to have general cell-adhesive and protein-resistant properties, which give it potential for biomaterials.

RGD-peptides modifying dexamethasone: to enhance the anti-inflammatory efficacy and limit the risk of osteoporosis

RGD-peptides modifying dexamethasone can enhance the anti-inflammatory efficacy and limit the risk of osteoporosis.

Surface modulation of complex stiffness via layer-by-layer assembly as a facile strategy for selective cell adhesion

A facile approach to achieve selective cell adhesion by modulating surface complex stiffness based on layer-by-layer assembly is reported.

Thermoresponsive self-assembly of nanostructures from a collagen-like peptide-containing diblock copolymer

Temperature-triggered formation of nanostructures with distinct biological activity offers opportunities in selective modification of matrices and in drug delivery. Toward these ends, diblock polymers comprising poly(diethylene glycol methyl ether methacrylate) (PDEGMEMA) conjugated to a triple helix-forming collagen-like peptide were produced. Triggered by the collapse of the thermoresponsive domain above its LCST, the conjugate undergoes a reversible transition in aqueous solution to form well-defined nanovesicles with diameters of approximately 100 nm, with a transition temperature of 37 °C. The incorporation of CLP domains in these nanostructures may offer opportunities for the selective targeting of collagen-containing matrices.

Modulation of the stemness and osteogenic differentiation of human mesenchymal stem cells by controlling RGD concentrations of poly(carboxybetaine) hydrogel

In vitro modulation of the differentiation status of mesenchymal stem cells (MSCs) is important for their application to regenerative medicine. We suggested that the morphology and differentiation states of MSCs could be modulated by controlling the cell affinity of a substrate. The objective of this study was to investigate the effects of surface bio-adhesive signals on self-renewal and osteogenic differentiation of MSCs using a low-fouling platform. Cell-resistant poly(carboxybetaine) hydrogel was conjugated with 5 μM or 5 mM of cell-adhesive arginine-glycine-aspartic acid (RGD) peptides in order to control the cells' affinity to the substrate. Human mesenchymal stem cells (hMSCs) were cultured on the RGD-modified poly(carboxybetaine) hydrogel and then the cells' states of stemness and osteogenic differentiation were evaluated using reverse-transcriptase polymerase chain reaction. The hMSCs formed three-dimensional spheroids on the 5 μM RGD substrate, while cells on the 5 mM RGD substrate exhibited spreading morphology. Furthermore, cells on the 5 μM RGD hydrogel maintained a better stemness phenotype, while the hMSCs on the 5 mM RGD hydrogel proliferated faster and underwent osteogenic differentiation. In conclusion, the stemness of hMSCs was best maintained on a low RGD surface, while osteogenic differentiation of hMSCs was enhanced on a high RGD surface.

Effect of the distribution of adsorbed proteins on cellular adhesion behaviors using surfaces of nanoscale phase-reversed amphiphilic block copolymers

In order to create suitable biocompatible materials for various tissue engineering applications, it is important to be able to understand protein adsorption and cell adhesion behaviors on the material's surfaces. It is known that the nanoscale distribution of adsorbed proteins affects cell adhesion behaviors. However, how nanoscale structures affect cell adhesion behaviors is still unclear. Therefore, in this study, we investigate the effect of the distribution of adsorbed proteins by the phase reversal of amphiphilic block copolymers composed of protein-non-adsorptive poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and protein-adsorptive poly(3-methacryloyloxy propyltris(trimethylsilyloxy) silane) (PMPTSSi) on cell adhesion behaviors. The nanodomain structures of phase-separated block copolymers were successfully confirmed using transmission electron microscopy and atomic force microscopy. Surfaces that had PMPC dot-like domains (23 ± 4 nm) and ones that had PMPTSSi dot-like domains (25 ± 6 nm) were made. From protein adsorption and L929 cell adhesion measurements, it was found that even on surfaces with equal quantities of protein adsorption, the number of cells on surfaces with PMPC dot-like domains was larger than those with PMPTSSi dot-like domains. This suggests that the simple phase-reversal of the distribution of adsorbed proteins can be used to affect cell adhesion behaviors for designing biomaterial surfaces for tissue engineering applications.

Real-time and non-invasive fluorescence tracking of in vivo degradation of the thermosensitive PEGlyated polyester hydrogel

The real-time monitoring of materials degradation is crucial to determine the in vivo retention time and the design or screening of degradable biomaterials. However, in vivo performance cannot always be predicted through the traditional determination of in vitro erosion and current standard methods sacrifice samples or animals, preventing the sequential measurement of the same specimen. Herein, a non-invasive fluorescence imaging method was developed to sequentially follow in vivo loss of fluorescence signal to simultaneously characterize the hydrolytic and enzymatic degradation of PEGlyated polyester hydrogel. Rhodamine B was conjugated to thermosensitive amphiphilic triblock copolymer based on cyclic ether modified PCL and PEG (abbreviated as PECT) and no obvious influence on gelation time or gel strength was observed with the conjugation content under 0.121% (w/w). Both in vitro and in vivo degradation profiles followed linear fittings while in vivo and in vitro hydrogel degradation rates correlated in an exponential mathematical model, enabling the general prediction of in vivo erosion trends of new biomaterial formulations from in vitro data. This methodology possibly enabled rational design and rapid in vitro screening of degradable materials, and might be potentially extended to simultaneously determine the material erosion and speculate the drug release from a drug-incorporated scaffold, or the cell growth profile in tissue-engineering formulations.

Three-dimensional printed trileaflet valve conduits using biological hydrogels and human valve interstitial cells

Tissue engineering has great potential to provide a functional de novo living valve replacement, capable of integration with host tissue and growth. Among various valve conduit fabrication techniques, three-dimensional (3-D) bioprinting enables deposition of cells and hydrogels into 3-D constructs with anatomical geometry and heterogeneous mechanical properties. Successful translation of this approach, however, is constrained by the dearth of printable and biocompatible hydrogel materials. Furthermore, it is not known how human valve cells respond to these printed environments. In this study, 3-D printable formulations of hybrid hydrogels are developed, based on methacrylated hyaluronic acid (Me-HA) and methacrylated gelatin (Me-Gel), and used to bioprint heart valve conduits containing encapsulated human aortic valvular interstitial cells (HAVIC). Increasing Me-Gel concentration resulted in lower stiffness and higher viscosity, facilitated cell spreading, and better maintained HAVIC fibroblastic phenotype. Bioprinting accuracy was dependent upon the relative concentrations of Me-Gel and Me-HA, but when optimized enabled the fabrication of a trileaflet valve shape accurate to the original design. HAVIC encapsulated within bioprinted heart valves maintained high viability, and remodeled the initial matrix by depositing collagen and glyosaminoglycans. These findings represent the first rational design of bioprinted trileaflet valve hydrogels that regulate encapsulated human VIC behavior. The use of anatomically accurate living valve scaffolds through bioprinting may accelerate understanding of physiological valve cell interactions and progress towards de novo living valve replacements.

Transfection in the third dimension

An understanding of parameters that modulate gene transfer in 3-D will assist in the formation of gene delivery systems and scaffolds, which can mediate efficient non-viral delivery for guiding in vivo tissue regeneration and therapy. We have previously demonstrated the cell area and length, integrin expression, and RhoGTPase mediated signalling to be pivotal parameters that guide gene transfer to mouse mesenchymal stem cells (mMSCs) cultured in 2-D and are modulated by ECM proteins. In this study, we were interested in determining if cationic polymer mediated gene transfer to cells seeded in 3-D would occur through different mechanisms as compared to those seeded in 2-D. In particular, we examined the endocytosis pathways used to internalize polyplexes, and the role of cytoskeletal dynamics and RhoGTPases in non-viral gene transfer for cells seeded in 2-D and 3-D. Inhibition of clathrin- and caveolae-mediated endocytosis resulted in a more drastic decrease in overall transgene expression for cells seeded in 3-D than for those in 2-D. In addition, polyplex internalization was only significantly decreased in 3-D when clathrin-mediated endocytosis was inhibited, while caveolae-mediated endocytosis inhibition for cells seeded in 2-D resulted in the strongest polyplex internalization inhibition. Actin and microtubule polymerization affected 2-D and 3-D transfection differently. Microtubule depolymerization enhanced transgene expression in 2-D, but inhibited transgene expression in 3-D. Lastly, inhibition of RhoGTPases also affected 2-D and 3-D transfection differently. The inhibition of ROCK effectors resulted in a decrease of transgene expression and internalization for cells seeded in 3-D, but not in 2-D, and the inhibition of the effector PAK1 resulted in an increase of transgene expression for both 2-D and 3-D. Overall, our study suggests that the process of gene transfer occurs through different mechanisms for cells seeded in 2-D compared to those seeded in 3-D.

Click chemistry plays a dual role in biodegradable polymer design

Click chemistry plays a dual role in the design of new citrate-based biodegradable elastomers (CABEs) with greatly improved mechanical strength and easily clickable surfaces for biofunctionalization. This novel chemistry modification strategy is applicable to a number of different types of polymers for improved mechanical properties and biofunctionality.

Poly(amido-amine)-based hydrogels with tailored mechanical properties and degradation rates for tissue engineering

Poly(amido-amine) (PAA) hydrogels containing the 2,2-bisacrylamidoacetic acid-4-amminobutyl guanidine monomeric unit have a known ability to enhance cellular adhesion by interacting with the arginin-glycin-aspartic acid (RGD)-binding αVβ3 integrin, expressed by a wide number of cell types. Scientific interest in this class of materials has traditionally been hampered by their poor mechanical properties and restricted range of degradation rate. Here we present the design of novel biocompatible, RGD-mimic PAA-based hydrogels with wide and tunable degradation rates as well as improved mechanical and biological properties for biomedical applications. This is achieved by radical polymerization of acrylamide-terminated PAA oligomers in both the presence and absence of 2-hydroxyethylmethacrylate. The degradation rate is found to be precisely tunable by adjusting the PAA oligomer molecular weight and acrylic co-monomer concentration in the starting reaction mixture. Cell adhesion and proliferation tests on Madin-Darby canine kidney epithelial cells show that PAA-based hydrogels have the capacity to promote cell adhesion up to 200% compared to the control. Mechanical tests show higher compressive strength of acrylic chain containing hydrogels compared to traditional PAA hydrogels.

Poly(lactic acid-co-glycolic acid)-poly(ethylene glycol)-poly(lactic acid-co-glycolic acid) thermogel as a novel submucosal cushion for endoscopic submucosal dissection

Endoscopic submucosal dissection (ESD) is a clinical therapy for early stage neoplastic lesions in the gastrointestinal tract. It is, however, faced with a crucial problem: the high occurrence of perforation. The formation of a submucosal fluid cushion (SFC) via a fluid injection is the best way to avoid perforation, and thus an appropriate biomaterial is vital for this minimally invasive endoscopic technique. In this study, we introduced an injectable thermogel as a novel submucosal injection substance in ESD. The hydrogel synthesized by us was composed of poly(lactic acid-co-glycolic acid)-poly(ethylene glycol)-poly(lactic acid-co-glycolic acid) (PLGA-PEG-PLGA) triblock copolymers. The polymer/water system was a low-viscosity fluid at room temperature and thus easily injected, and turned into a non-flowing gel at body temperature after injection. The submucosal injection of the thermogel to create SFCs was performed in both resected porcine stomachs and living minipigs. High mucosal elevation with a clear margin was maintained for a long duration. Accurate en bloc resection was achieved with the assistance of the thermogel. The mean procedure time was strikingly reduced. Meanwhile, no obvious bleeding, perforation and tissue damage were observed. The application of the thermogel not only facilitated the ESD procedure, but also increased the efficacy and safety of ESD. Therefore, the PLGA-PEG-PLGA thermogel provides an excellent submucosal injection system, and has great potential to improve the ESD technique significantly.

Effects of l-lactide and d,l-lactide in poly(lactide-co-glycolide)-poly(ethylene glycol)-poly(lactide-co-glycolide) on the bulk states of triblock copolymers, and their thermogellation and biodegradation in water

In this study, the effects of l-lactide and d,l-lactide on the thermogelling and biodegradation behaviors of PLGA-PEG-PLGA copolymers were revealed.

Comparative studies of thermogels in preventing post-operative adhesions and corresponding mechanisms

Thermogelling PLGA–PEG–PLGA, PCGA–PEG–PCGA, and PCL–PEG–PCL triblock copolymers and their efficacies of prevention of post-surgical peritoneal adhesions in rabbits were investigated and compared.

A review of polypeptide-based polymersomes

Self-assembled systems from biodegradable amphiphilic polymers at the nanometer scale, such as nanotubes, nanoparticles, polymer micelles, nanogels, and polymersomes, have attracted much attention especially in biomedical fields. Among these nano-aggregates, polymersomes have attracted tremendous interests as versatile carriers due to their colloidal stability, tunable membrane properties and ability of encapsulating or integrating a broad range of drugs and molecules. Biodegradable block polymers, especially aliphatic polyesters such as polylactide, polyglycolide and poly (ε-caprolactone) have been widely used as biomedical materials for a long time to well fit the requirement of biomedical drug carriers. To have a precise control of the aggregation behavior of nano-aggregates, the more ordered polypeptide has been used to self-assemble into the drug carriers. In this review we focus on the study of polymersomes which also named pepsomes formed by polypeptide-based copolymers and attempt to clarify the polypeptide-based polymersomes from following aspects: synthesis and characterization of the polypeptide-based copolymers, preparation, multifunction and application of polypeptide-based polymersomes.

Functionalization of biomaterials with small osteoinductive moieties

Human mesenchymal stem cells (MSCs) are currently recognized as a powerful cell source for regenerative medicine, notably for their capacity to differentiate into multiple cell types. The combination of MSCs with biomaterials functionalized with instructive cues can be used as a strategy to direct specific lineage commitment, and can thus improve the therapeutic efficacy of these cells. In terms of biomaterial design, one common approach is the functionalization of materials with ligands capable of directly binding to cell receptors and trigger specific differentiation signaling pathways. Other strategies focus on the use of moieties that have an indirect effect, acting, for example, as sequesters of bioactive ligands present in the extracellular milieu that, in turn, will interact with cells. Compared with complex biomolecules, the use of simple compounds, such as chemical moieties and peptides, and other small molecules can be advantageous by leading to less expensive and easily tunable biomaterial formulations. This review describes different strategies that have been used to promote substrate-mediated guidance of osteogenic differentiation of immature osteoblasts, osteoprogenitors and MSCs, through chemically conjugated small moieties, both in two- and three-dimensional set-ups. In each case, the selected moiety, the coupling strategy and the main findings of the study were highlighted. The latest advances and future perspectives in the field are also discussed.

Control of olfactory ensheathing cell behaviors by electrospun silk fibroin fibers

Olfactory ensheathing cells (OECs), the only glial cell type that normally penetrates the transition zone between the peripheral and central nervous systems, are one of the most promising candidates for cell transplantation in repairing spinal cord injury (SCI). However, we must manipulate and regulate OECs' behavior to make these cells effective in cell transplantation. In the present study, we assessed the response of rat OECs to different variants of nanofibrous silk fibroin mats with regard to cell morphology, adhesion, proliferation, and migration and the related gene and protein expression. Results showed that OECs adhere and spread more easily on Tussah silk fibroin (TSF) fibers than Bombyx mori silk fibroin fibers, resulting in a higher rate of cell proliferation and gene and protein expression, examined by RT-PCR and ELISA. In addition, the morphology of OECs on microfibers is mainly polygonal with short protrusions, whereas the OECs on nanofibers exhibit a bipolar shape with long protrusions that align along the fibers, especially when aligned fibers are employed. Moreover, OECs on silk fibroin nanofibers migrate more efficiently than those on poly-L-lysine (PLL). Based on the experimental results, the morphology, adhesion, spread, gene and protein expression, and migration of OECs could be modulated and regulated by adjusting the contents and structure of silk fibroin nanofibers, shedding light on the control of OECs' behavior in nerve tissue engineering and thus the future therapeutic intervention for nerve repair after injury. This manuscript is published as part of the International Association of Neurorestoratology (IANR) supplement issue of Cell Transplantation.

Cell-material interactions revealed via material techniques of surface patterning

Cell-material interactions constitute a key fundamental topic in biomaterials study. Various cell cues and matrix cues as well as soluble factors regulate cell behaviors on materials. These factors are coupled with each other as usual, and thus it is very difficult to unambiguously elucidate the role of each regulator. The recently developed material techniques of surface patterning afford unique ways to reveal the underlying science. This paper reviews the pertinent material techniques to fabricate patterns of microscale and nanoscale resolutions, and corresponding cell studies. Some issues are emphasized, such as cell localization on patterned surfaces of chemical contrast, and effects of cell shape, cell size, cell-cell contact, and seeding density on differentiation of stem cells. Material cues to regulate cell adhesion, cell differentiation and other cell events are further summed up. Effects of some physical properties, such as surface topography and matrix stiffness, on cell behaviors are also discussed; nanoscaled features of substrate surfaces to regulate cell fate are summarized as well. The pertinent work sheds new insight into the cell-material interactions, and is stimulating for biomaterial design in regenerative medicine, tissue engineering, and high-throughput detection, diagnosis, and drug screening.

Nanosized aspirin-Arg-Gly-Asp-Val: delivery of aspirin to thrombus by the target carrier Arg-Gly-Asp-Val tetrapeptide

Resistance and nonresponse to aspirin dramatically decreases its therapeutic efficacy. To overcome this issue, a small-molecule thrombus-targeting drug delivery system, aspirin-Arg-Gly-Asp-Val (A-RGDV), is developed by covalently linking Arg-Gly-Asp-Val tetrapeptide with aspirin. The 2D ROESY NMR and ESI-MS spectra support a molecular model of an A-RGDV tetramer. Transmission electron microscopy images suggest that the tetramer spontaneously assembles to nanoparticles (ranging from 5 to 50 nm in diameter) in water. Scanning electron microscopy images and atomic force microscopy images indicate that the smaller nanoparticles of A-RGDV further assemble to bigger particles that are stable in rat blood. The delivery investigation implies that in rat blood A-RGDV is able to keep its molecular integrity, while in a thrombus it releases aspirin. The in vitro antiplatelet aggregation assay suggests that A-RGDV selectively inhibits arachidonic acid induced platelet aggregation. The mechanisms of action probably include releasing aspirin, modifying cyclic oxidase, and decreasing the expression of GPIIb/IIIa. The in vivo assay demonstrates that the effective antithrombotic dose of A-RGDV is 16700-fold lower than the nonresponsive dose of aspirin.