Host Responses to Biomaterials and Anti‐Inflammatory Design—a Brief Review

Host responses toward foreign implants that lead to chronic inflammation and fibrosis may result in failure of the biomedical device. To solve these problems, first a better understanding of the biomaterial‐induced host reactions including protein adsorption, leukocyte activation, inflammatory and fibrotic responses to biomaterials is required; second an improved design of biomaterial surfaces is needed that results in an appropriate host response, causing less inflammatory response, and supporting tissue regeneration. Hence, this review provides a brief overview on the host response to implants, as well as in vitro models to study inflammatory and fibrotic responses to biomaterials to predict the clinical outcome of implantation. Moreover, the review highlights anti‐inflammatory strategies to improve the biocompatibility of implants, which contain the modification of physicochemical surface properties of materials as well as the immobilization of anti‐inflammatory reagents and bioactive molecules on biomaterials.     

Ln3+‐Mediated Self‐Assembly of a Collagen Peptide into Luminescent Banded Helical Nanoropes

Design of biomimetic peptides to achieve the desired properties of natural collagen has much potential to build functional biomaterials. A collagen‐peptide/Ln³⁺ system has been constructed and self‐assembled to form helical nanoropes with a distinct periodic banding pattern characteristic of natural collagen. The fully reversible self‐assembly is specifically mediated by lanthanide ions, but not by other commonly used divalent metal ions. Lanthanide ions not only provide an external biocompatible stimulus of the assembly, but also play as a functional unit to endow the assembled materials with easily tunable photoluminescence. To our knowledge, this is the first report of collagen‐peptide‐based materials with exquisite nanorope structure and excellent photoluminescent features. These novel luminescent nanomaterials may have great potential in cell imaging, medical diagnostics, and luminescent scaffolds for cell cultivation.     

Fabrication and properties of mineralized collagen‐chitosan/hydroxyapatite scaffolds

A hydroxyapatite (HAp)/biopolymer composite scaffold was fabricated by mineralizing a crosslinked collagen/chitosan, which was pre‐mineralized with Ca²⁺ and phosphate salts, in simulated body fluid (SBF) for only 24 hr. A self‐organized structure similar to bone is expected. Microstructures of the crosslinked collagen/chitosan scaffold, the pre‐mineralized collagen–chitosan scaffold (CCS), and the mineralized collagen‐chitosan/HAp scaffolds (MCCHS) were characterized by scanning electron microscopy (SEM), revealing non‐alteration of the porous structure and formation of the HAp particles. X‐ray diffractometer (XRD) confirmed the crystalline structure of the HAp. Thermal gravimetric analysis found that more HAp particles were formed when the CCSs were pre‐mineralized in a higher concentration of Ca²⁺. Water‐uptake ratio of the crosslinked CCS was ～160, decreased to ～120 after incubating in Ca²⁺ solution, and further decreased to ～20 after mineralization. Mechanical strength of the CCS was improved significantly after the in situ mineralization too. The method introduced here may be potentially applied to obtain other biopolymer/HAp composite in a short period. Copyright © 2008 John Wiley & Sons, Ltd.     

Novel biomimetic composite based on collagen and poly(γ‐benzyl L‐glutamate)‐co‐poly(glutamic acid)

Novel biomimetic composite was prepared by the reaction of collagen and poly(γ‐benzyl L ‐glutamate)‐co‐poly(glutamic acid) (PBLG‐co‐PGA), which were crosslinked by non‐toxic crosslinking reagents 1‐ethyl‐(dimethylaminopropyl) carbodiimide (EDC) and N‐hydroxysuccinimide (NHS). The composite was characterized by FTIR and DSC. FTIR results confirmed that the collagen in the composite was successfully crosslinked with PBLG‐co‐PGA. DSC results showed that the composites possessed higher shrinkage temperature and higher thermal stability than the collagen. The water absorption test showed that the water absorbency of the composites increased with the increase in PBLG‐co‐PGA content in the composite. The studies of collagenase degradation and the tensile strength showed that the biostability and the tensile strength of the composites were significantly improved in comparison with that of the collagen. According to the investigations of cell adherent ratio and cell proliferation in vitro, the composite possessed good biocompatibility. Copyright © 2007 John Wiley & Sons, Ltd.     

Characterization of polysuccinate and hydroxyapatite‐based nanocomposites containing poly(ester‐anhydride) microspheres

Repair and regeneration of bone defects with particular shape may be enhanced by in situ forming biomaterials which can be used in minimal invasive surgery. This study is aimed to prepare novel in situ forming biodegradable nanocomposites based on poly(3‐allyloxy‐1,2‐propylene) succinate (PSAGE) and nanosized hydroxyapatite (HA). These nanocomposite materials contain poly(ester‐anhydride) (PEA) microspheres embedded in a polyester matrix prepared by crosslinking PSAGE with oligo(1,2‐propylene maleate) and methacrylic monomers. Methyl methacrylate and one of hydrophilic oligo(ethylene glycol) methacrylates with different functionality and various length of oligooxyethylene chains were used as polymerizable diluents. Incorporation of microspheres which degrade faster than crosslinked polyester matrices enables formation of porous structure in situ. The obtained materials are liquid before curing and harden in several minutes with moderate exothermic effect. The effect of the composition of nanocomposite materials on selected properties, such as water sorption, mechanical strength, porosity and hydrolytic degradation process, was investigated. Rheological behavior and injectability of liquid formulations were studied. Analysis by energy dispersive spectroscopy confirmed the presence of characteristic features of HA in the nanocomposite materials. The morphology of the cured nanocomposites subjected to hydrolytic degradation was evaluated by scanning electron microscopy. The MTS cytotoxicity assay was carried out for extracts from crosslinked materials using hFOB1.19 cells. It was found that the extracts exhibit a dose‐dependent cytotoxic response. Copyright © 2014 John Wiley & Sons, Ltd.     

Exploration and Evaluation of Therapeutic Efficacy of Drug‐Free Macromolecular Therapeutics in Collagen‐Induced Rheumatoid Arthritis Mouse Model

Monoclonal antibodies (mAbs) against B cell antigens are extensively used in the treatment of rheumatoid arthritis (RA). The B cell depletion therapy prevents RA symptoms and/or alleviates existing inflammation. The previously established two‐step drug‐free macromolecular therapeutics (DFMT) is applied in the treatment of collagen‐induced rheumatoid arthritis in a collagen‐induced rheumatoid arthritis mouse model. DFMT is a B cell depletion strategy utilizing Fab′ fragment of anti‐CD20 mAb for biorecognition and receptor crosslinking to induce B cell apoptosis. DFMT is composed from two nanoconjugates: 1) bispecific engager, Fab′‐MORF1 (anti‐CD20 Fab′ fragment conjugated with morpholino oligonucleotide MORF1), and 2) a crosslinking (effector) component P‐(MORF2)_X (N‐(2‐hydroxypropyl)methacrylamide copolymer grafted with multiple copies of complementary morpholino oligonucleotide MORF2). The absence of Fc fragment has the potential to avoid development of resistance and infusion‐related reactions. DFMT produces B cell depletion, keeps the RA score low for more than 100 days, and shows minimal cartilage and bone erosion and inflammatory cell infiltration. Further improvements will be explored to optimize DFMT strategy in autoimmune disease treatment.     

Surface Modification of GTA Crosslinked Collagen‐based Composite Scaffolds with Low Temperature Plasma Technology

In this study for preparing the better performance scaffold materials for peripheral nerve repairing, the collagen‐based composite scaffolds are crosslinked with glutaraldehyde and their structure and performance are investigated. The results of FTIR indicated that the collagen and chitosan are certainly crosslinked through GTA without any significant change in the chemical property. It was observed under a scanning electron microscope (SEM) that the crosslinked collagen‐based composite scaffolds had a porous three‐dimensional cross‐linked structure. The experiments showed that the biostability of the scaffold is greatly enhanced, but the GTA crosslinking induces the potential cytotoxicity and poor hydrophilic nature. To overcome these disadvantages, the low temperature plasma technology is utilized to modify the surface of the cross‐linked collagen‐based composite scaffolds in this study. Measurements of water contact angle showed that hydrophilic nature of surface of the scaffolds was improved after low temperature plasma technology modification. The cell proliferation experiments revealed that the modified collagen‐based composite scaffolds still kept their bioactivity and benefited the proliferation.     

Antibacterial poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) fibrous membranes containing quaternary ammonium salts

In this study, antimicrobial membranes based on biodegradable material poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) [P(3HB‐4HB)] and quaternary ammonium salts (QASs) by two methods have been performed. Three QASs with varied alkyl chain lengths have been synthesized successfully and characterized by ¹H nuclear magnetic resonance and Fourier transform infrared. The synthesized QASs were blended with P(3HB‐4HB) and electrospun into composite fibrous membranes or casted into conventional membranes. Electrospun fibrous membranes with large surface areas are a superior type of antimicrobial biomaterials, and they exhibit preferable properties than solution casting membranes. Specifically, electrospun fibrous membranes are tougher and can inactivate both Gram‐positive Staphylococcus aureus and Gram‐negative Escherichia coli O157:H7 in a contact time of 30 min, whereas the solution casting membranes cannot. The length of alkyl chain in the quaternary ammonium groups on the modified P(3HB‐4HB) membranes is able to influence the antimicrobial activity. This type of antimicrobial material may have potential applications in biomaterial field. Copyright © 2016 John Wiley & Sons, Ltd.     

Hydrogel Membrane Improves Batch‐to‐Batch Reproducibility of an Enzymatic Glucose Biosensor

A permselective membrane is a critical component that defines the linear detection limits, the sensitivity, and thus the ultimate efficacy of an enzymatic biosensor. Although membranes like epoxy‐polyurethane (epoxy‐PU) and Nafion are widely used and provide the desired glucose detection limits of 2 to 30 mM, both the within batch and batch‐to‐batch variability of sensors that use these materials is a concern. The hypothesis for this study was that a crosslinked hydrogel would have a sufficiently uniform porosity and hydrophilicity to address the variability in sensor sensitivity. The hydrogel was prepared by crosslinking di‐hydroxyethyl methacrylate, hydroxyethyl methacrylate and N‐vinyl pyrrolidone with 2.5 mol% ethylene glycol dimethacrylate using water soluble initiators – ammonium persulfate and sodium metabisulfite under a nitrogen atmosphere. The hydrogel was applied to the sensor by dip coating during polymerisation. Electrochemical measurements revealed that the response characteristics of sensors coated with this membrane are highly consistent. Scanning electrochemical microscopy (SECM) was used to spatially resolve glucose diffusion through the membrane by measuring the consequent H₂O₂ release and compared with an epoxy‐PU membrane. Hydrogen peroxide measurements using SECM revealed that the epoxy‐PU membranes had uneven lateral diffusion profiles compared to the uniform profile of the hydrogel membranes. The uneven diffusion profiles of epoxy‐PU membranes are attributed to a fabrication method that results in uneven membrane properties, while the uniform diffusion profiles of the hydrogel membranes are primarily dictated by their uniform pore size.     

PEG‐dialdehyde–the new cross‐linking agent for collagen/elastin hydrogels

Collagen and elastin are the major proteins of an extracellular matrix. They possess attractive, complementary mechanical properties in their native state, but during isolation, its unique structure is destroyed, which affects the parameters of the materials. However, they still have excellent biological properties. The cross‐linking process improves the physicochemical properties of protein materials. The ideal cross‐linking agent should be effective and does not impair the biological properties of the material. Therefore, poly(ethylene) glycol‐dialdehyde was used in the study. The results show that the addition of poly(ethylene) glycol‐dialdehyde in combination with the neutralization of a collagen/elastin solution is a useful method for preparation of protein hydrogels. The gels are transparent and relatively stiff. They exhibit good mechanical properties, surface properties and are attractive for 3 T3 cells. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis of siloxane‐crosslinked polysilylenemethylenes by chlorodephenylation

Thermally stable polysilylenemethylenes (PSMs) with siloxane crosslinking moieties were successfully synthesized by chlorodephenylation of preformed poly(methylphenylsilylenemethylene) (PMPSM) and subsequent in situ alcoholysis/hydrolysis/condensation reactions. The simplified process and mild reaction conditions are quite advantageous. The crosslink density of these materials can be adjusted by the degree of chlorodephenylation, although an alkoxysilyl group remains to some extent. The resulting crosslinked PSMs have well defined structures in which the backbone is composed of MePhSiCH₂ and Me(MeO)SiCH₂ as well as Me(O_1/2)SiCH₂ as a crosslinking moiety. The resulting crosslinked PSMs exhibited glass‐transition temperatures ranging from 15 to 20 °C, whereas that of linear PMPSM was 22 °C. The crosslinked PSMs remained unchanged in weight below 300 °C, suggesting that they are thermally stable up to that temperature. The good solvent resistance caused by crosslinking as well as high thermal stability of these materials allow us to design new PSM‐based polymer blends and preceramic polymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 416–422, 2002     

Biocompatible Fibrous Networks of Cellulose Nanofibres and Collagen Crosslinked Using Genipin: Potential as Artificial Ligament/Tendons

Bio‐based fibrous nanocomposites of cellulose nanofibres and non‐crosslinked/crosslinked collagen were prepared by in situ pH‐induced fibrillation of collagen phase and sterilized using gamma rays at 25 KGy. Collagen phase is crosslinked using genipin, a bio‐based crosslinker that introduces flexible crosslinks. Microscopy studies of the prepared materials showed nanostructured fibrous collagen and cellulose dispersed in collagen matrix. Mechanical performance of the sterilized nanocomposites was close to that of natural ligament and tendon, in simulated body conditions. Cytocompatibility studies indicated that these nanocomposites allowed human ligament cell and human endothelial cell adhesion, growth, and differentiation; which is eminently favourable to ligament tissue engineering.

     

Photo‐induced thiol‐ene polysulfide‐crosslinked materials with tunable thermal and mechanical properties

Photo‐induced thiol‐ene crosslinked polymeric networks have been extensively explored in constructing a variety of new materials with enhanced mechanical properties for optical, biomedical, and sensing applications. Toward the broad applications, however, tunable mechanical properties are greatly desired. Here, an effective approach utilizing high‐molecular‐weight methacrylate copolymers having pendant thiol and vinyl groups (MCPsh and MCPenes) to modulate thermal and mechanical properties of photo‐induced thiol‐ene crosslinked materials is reported. The MCP copolymers are synthesized by an industrially friendly polymerization method, followed by post‐modification including either a facile coupling reaction or reductive cleavage. Upon UV irradiation, thiol‐ene reactive blends of MCPsh and MCPenes yield highly crosslinked materials through the formation of flexible sulfide linkages. These polysulfide‐crosslinked materials based on rigid MCP backbones exhibit enhanced mechanical properties. Further, their thermal and mechanical properties are tuned by modulating monomer compositions of MCPs as well as varying numbers of pendant SH or vinyl groups (i.e., extent of crosslinking densities). This approach is versatile and effective for development of high performance polymeric materials. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3060–3068     

α‐Mannosyl‐Functionalized Cationic Nanohydrogel Particles for Targeted Gene Knockdown in Immunosuppressive Macrophages

Immunosuppressive M2 macrophages govern the immunophathogenic micromilieu in many severe diseases including cancer or fibrosis, thus, their re‐polarization through RNA interference is a promising concept to support combinatorial therapies. For targeted siRNA delivery, however, safe and stable carriers are required that manage cell specific transport to M2 macrophages. Here, siRNA‐loaded cationic nanogels are reported with α‐mannosyl decorated surfaces that target and modify M2 macrophages selectively. Via amphiphilic precursor block copolymers bearing one single α‐mannosyl moiety at their chain end mannosylated cationic nanohydrogel particles (ManNP) were obtained of 20 nm diameter determined by dynamic light scattering and cryogenic electron transmission microscopy. α‐Mannosyl surface modification is confirmed by agglutination with concanavalin A. SiRNA‐loaded ManNP preferentially targets the overexpressed mannose receptor CD206 on M2 macrophages, as shown by in vitro cell uptake studies in M2 polarized primary macrophages. This specificity is confirmed, since ManNP uptake could be reduced by blocking of CD206 with mannan. Effective ManNP‐guided siRNA delivery is confirmed by sequence‐specific gene knockdown of CSF‐1R in M2‐type macrophages exclusively, while the expression levels in M1‐polarized macrophages is not affected. In conclusion, α‐mannosyl‐functionalized ManNPs are promising universal siRNA carriers for targeted immunomodulatory treatment of immunosuppressive macrophages.     

Protein‐ and homo poly(amino acid)‐based hydrogels with super‐swelling properties

The use of super‐swelling polymers is steadily increasing and the applications in industry are continuing to grow. With the authorization of the superabsorbents in food packaging by the Food and Drug Administration recently, demand may soon take off in the market. However, the increase in prices of petroleum products in recent years may be a drawback for these acrylic‐based materials. Thus, there is now a need to develop natural‐based super‐swelling hydrogels which are more economical and environment friendly. In addition, the super‐swelling gels are promising novel functions in the biomedical and pharmaceutical applications. This review is aimed to highlight research and trends in protein‐ and homo poly(amino acid)‐based super‐swelling hydrogels. Thus, the proteinaceous hydrogels, including chemically modified soy‐, fish‐ and collagen‐based proteins, are discussed. The protein‐polysaccharide, protein‐synthetics, and the inorganic composites are also investigated as hybrid materials. Finally, the super‐swelling hydrogels based on homo polypeptides, i.e. poly(aspartic acid), poly(glutamic acid), and poly(ε‐L‐lysine) are reviewed. Copyright © 2009 John Wiley & Sons, Ltd.     

On the Effects of UV‐C and pH on the Mechanical Behavior,Molecular Conformation and Cell Viability of Collagen‐Based Scaffold for Vascular Tissue Engineering

Collagen‐based vascular substitutes represent in VTE a valid alternative for the replacement of diseased small‐calibre blood vessels. In this study, collagen gel‐based scaffolds were crosslinked combining modulation of pH and UV‐C radiation. The effects on the mechanical properties, on the molecular structure and on cell viability and morphology were investigated. The mechanical response increased as a function of pH or UV‐C dose and strongly depended on the test speed. Collagen molecular conformation resulted only slightly modified. While cell adhesion was not significantly altered, cell proliferation partially decreased in function of pH and UV‐C. These findings suggest that UV‐C treated collagen gels can represent an adequate substrate for VTE applications.

     

DABCO‐functionalized polysulfones as anion‐exchange membranes for fuel cell applications: Effect of crosslinking

A series of DABCO‐functionalized polysulfones were synthesized and characterized. The effect that crosslinking has on the membrane properties containing different degrees of functionalization was evaluated. These polymers showed good thermal stability below the fuel cell operation temperature, T < 100 °C, reflected by the T_OD, T_FD, and thermal durability. The water uptake increased as the percentage of DABCO groups increased and the crosslinked membranes showed lower capacity to absorb water than the non‐crosslinked ones favoring thus the dimensional stability of the first ones. Membranes in the chloride form containing low degree of functionalization exhibited the highest tensile strength values. The ionic conductivity of non‐crosslinked membranes varied as a function of the functionalization degree until a value of around 100% achieving a maximum value at 86%. However, the crosslinked ones showed satisfactory ionic conductivities for values higher than 100%. The behavior of these polymeric materials in alkaline solutions revealed a great alkaline stability necessary to be used as solid electrolytes in fuel cells. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1326–1336     

7‐(2‐Oxoalkoxy)coumarins: Synthesis and Anti‐Inflammatory Activity of a Series of Substituted Coumarins

A series of 7‐(2‐oxoalkoxy)coumarins have been synthesized by conjugating substituted 7‐hydroxycoumarins with different chloroketones. The anti‐inflammatory properties of 7‐(2‐oxoalkoxy)coumarins were studied in LPS‐induced inflammatory response in J774 macrophages. Western blot was used to determine the expression of iNOS and COX‐2, NO was determined by measuring its metabolite nitrite by Griess reaction and IL‐6 was measured by ELISA. Seventeen of the studied compounds inhibited NO and IL‐6 production over 50% at 100 μM concentrations. IC₅₀ values of the best inhibitors were 21 μM/24 μM (NO/IL‐6) for compound 12 and 30 μM/10 μM (NO/IL‐6) for compound 20 . The main result was that the substitution with 7‐(2‐oxoalkoxy) group improved the anti‐inflammatory properties of most of the investigated 7‐hydroxycoumarins.     

Drug‐Loaded Elastin‐Like Polypeptide–Collagen Hydrogels with High Modulus for Bone Tissue Engineering

Emphasizing the role of hydrogel stiffness and cellular differentiation, this study develops collagen and elastin‐like polypeptide (ELP)–based bone regenerative hydrogels loaded with recombinant human bone morphogenetic protein‐2 (rhBMP‐2) and doxycycline with mechanical properties suitable for osteogenesis. The drug‐incorporated collagen–ELP hydrogels has significantly higher modulus of 35 ± 5 kPa compared to collagen‐only hydrogels. Doxycycline shows a bi‐phasic release with an initial burst release followed by a gradual release, while rhBMP‐2 exhibits a nearly linear release profile for all hydrogels. The released doxycycline shows anti‐microbial activity against Pseudomonas aeruginosa, Streptococcus sanguinis, and Escherichia coli. Microscopic observation of the hydrogels reveals their interconnected, macroporous, 3D open architecture with pore diameters between 160 and 400 µm. This architecture supports human adipose–derived stem cell attachment and proliferation from initial days of cell seeding, forming a thick cellular sheath by day 21. Interestingly, in collagen and collagen–ELP hydrogels, cell morphology is elongated with stretched slender lamellipodial formation, while cells assemble as spheroidal aggregates in crosslinked as well as drug‐loaded hydrogels. Osteogenic markers, alkaline phosphatase and osteocalcin, are expressed maximally for drug‐loaded hydrogels compared to those without drugs. The drug‐loaded collagen–ELP hydrogels are thus promising for combating bacterial infection and promoting guided bone regeneration.     

In Vitro and In Vivo Characterization of Biodegradable Reactive Isocyanate‐Terminated Three‐Armed‐ and Hyperbranched Block Copolymeric Tissue Adhesives

Tissue adhesives are an attractive class of biomaterials, which can serve as a treatment for meniscus tears. In this study, physicochemical and adhesive properties of novel biodegradable three‐armed‐ and hyperbranched block copolymeric adhesives are evaluated. Additionally, their degradation in vitro and in vivo, and the tissue reaction after subcutaneous injection in rats are assessed. The developed adhesives have sufficient adhesive strength to meniscus tissue after curing (66–88 kPa). Networks based on the three‐armed adhesive have tensile properties that are in the same range as human meniscus. After 26 weeks, networks based on the hyperbranched adhesive show a faster mass loss (25.4%) compared to networks prepared from the three‐armed ones (5.5%). Both adhesives induce an inflammatory reaction, however, no necrosis and only initial toxic effects on peripheral tissues are observed. The proposed materials are suitable candidates for the use as resorbable tissue adhesives for meniscus repair.