Schiff Base-Based Hydrogel Embedded with In Situ Generated Silver Nanoparticles Capped by a Hyaluronic Acid-Diethylenetriamine Derivative for Wound Healing Application

In this study, hydrogels were produced using a Schiff base reaction between two hyaluronic acid derivatives: one containing aldehyde groups (HA-Ald) and the other holding a diethylenetriamine with terminal amino groups (HA-DETA). The DETA portion promotes the in situ growth, complexation, and stabilization of silver nanoparticles (AgNPs), eliminating the need for external reducing agents. The reaction between HA-DETA and HA-Ald leads to the formation of imine bonds, which results in dynamically pH-responsive cross-linking. While the DETA capping ability helped in embedding the AgNPs, the on/off pH environmental responsivity of the hydrogel allows for a controlled and on-demand release of the drug, mainly when bacterial infections cause pH variation of the wound bed. The injectable hydrogels resulted in being highly compatible in contact with blood red cells, fibroblasts, and keratinocytes and capable of having a proliferative effect on an in vitro wound scratch model. The pH-responsive hydrogels showed proper antibacterial activity againstPseudomonas aeruginosaandStaphylococcus aureus, common bacterial strains presented in wound infections. Finally, in vivo wound model studies demonstrated an overall speeding up in the wound healing rate and advanced wound conditions in the experimental group treated with the hydrogels compared to control samples.

An asymmetric electrospun membrane for the controlled release of ciprofloxacin and FGF-2: Evaluation of antimicrobial and chemoattractant properties

Here, an asymmetric double-layer membrane has been designed and fabricated by electrospinning as a tool for a potential wound healing application. A hydrophobic layer has been produced by using a polyurethane-polycaprolactone (PU-PCL) copolymer and loaded with the antibacterial ciprofloxacin whereas an ion responsive hydrophilic layer has been produced by using an octyl derivative of gellan gum (GG-C₈) and polyvinyl alcohol (PVA) and loaded with the growth factor FGF-2. This study investigated how the properties of this asymmetric membrane loaded with actives, were influenced by the ionotropic crosslinking of the hydrophilic layer. In particular, the treatment in DPBS and the crosslinking in CaCl₂ 0.1 or 1 M of the hydrophilic layer affected the release profile of the bioactive molecules allowing to modulate both the antimicrobial effect, as assayed by logarithmic reduction of the Staphylococcus aureus viable count, and the chemoattractant properties on NIH 3 T3 cell line, as assayed by scratch test and cell chemoattraction assay.

Blend scaffolds with polyaspartamide/polyester structure fabricated via TIPS and their RGDC functionalization to promote osteoblast adhesion and proliferation

Target of this work was to prepare a RGDC functionalized hybrid biomaterial via TIPS technique to achieve a more efficient control of osteoblast adhesion and diffusion on the three-dimensional (3D) scaffolds. Starting from a crystalline poly(l-lactic acid) (PLLA) and an amorphous α,β-poly(N-2-hydroxyethyl) (2-aminoethylcarbamate)-d,l-aspartamide-graft-polylactic acid (PHEA-EDA-g-PLA) copolymer, blend scaffolds were characterized by an appropriate porosity and pore interconnection. The PHEA-EDA-PLA interpenetration with PLLA improved hydrolytic susceptibility of hybrid scaffolds. The presence of free amino groups on scaffolds allowed to tether the cyclic RGD peptide (RGDC) via Michael addition using the maleimide chemistry. Cell culture test carried out on preosteoblastic cells MC3T3-E1 incubated with scaffolds, has evidenced cell adhesion and proliferation. Furthermore, the presence of distributed bone matrix on all scaffolds was evaluated after 70 days compared to PLLA only samples.

Production of a Double-Layer Scaffold for the "On-Demand" Release of Fibroblast-like Limbal Stem Cells

The production and characterization of a double-layer scaffold, to be used as a system for the "on-demand" release of corneal limbal stem cells, are reported here. The devices used in the clinics and proposed so far in the scientific literature, for the release of corneal stem cells in the treatment of limbal stem cell deficiency, cannot control the in vivo space-time release of cells as the biomaterial of which they are composed is devoid of the stimuli-responsive feature. Our approach was to produce a scaffold composed of two different polymeric layers that give the device the appropriate mechanical properties to be placed on the ocular surface and the possibility of releasing the stem cells following a noninvasive and cell-friendly treatment. This device consists of an electrospun microfibrillar scaffold of poly-l-lactic acid coated by a polymeric film based on an amphiphilic derivative of hyaluronic acid sensitive to the ionic strength of the external medium and to the presence of a complexing agent. The latter represents the "sacrificial" cell containing layer of the scaffold that can be dissolved "on demand" by the treatment with a solution of cyclodextrins. The rapid removal of the external polymeric film from the device is exploited to control the space-time release of the cells. In vitro and ex vivo experiments showed that fibroblast-like limbal stem cells cultured on the scaffold without the use of the feeder layer maintained their characteristics of stem cells and can be released "on demand" on the culture well coated with Matrigel or on the decellularized bovine cornea, respectively.

Double-Network-Structured Graphene Oxide-Containing Nanogels as Photothermal Agents for the Treatment of Colorectal Cancer

Here, we reported the production of hyaluronic acid/polyaspartamide-based double-network nanogels for the potential treatment of colorectal carcinoma. Graphene oxide, thanks to the huge aromatic surface area, allows to easily load high amount of irinotecan (33.0% w/w) and confers to the system hyperthermic properties when irradiated with a near-infrared (NIR) laser beam. We demonstrate that the release of antitumor drug is influenced both by the pH of the external medium and the NIR irradiation process. In vitro biological studies, conducted on human colon cancer cells (HCT 116), revealed that nanogels are uptaken by the cancer cells and, in the presence of the antitumor drug, can produce a synergistic hyperthermic/cytotoxic effect. Finally, 3D experiments demonstrate that it is possible to conduct thermal ablation of solid tumors after the intratumoral administration of nanogels.

Synthesis, mechanical and thermal rheological properties of new gellan gum derivatives

New derivatives of gellan gum (GG) were prepared by covalent attachment of octadecylamine (C₁₈-NH₂) to polysaccharide backbone via amide linkage by using bis(4-nitrophenyl) carbonate (4-NPBC) as a coupling agent. The effect of the alkyl chain grafted onto hydrophilic backbone of high molecular weight GG was investigated in terms of physicochemical properties and ability of new derivatives to form hydrogels. A series of hydrogels was obtained in solutions with different kind and concentration of ions and their stability and mechanical properties were evaluated. The obtained derivatives resulted soluble at temperature lower than starting GG and physicochemical properties of obtained hydrogels suggested their potential use in biomedical field.

Dexamethasone dipropionate loaded nanoparticles of α-elastin-g-PLGA for potential treatment of restenosis

A graft copolymer of α-elastin with poly(lactic-co-glycolic) acid (PLGA) has been synthesized and successfully employed to produce nanoparticles. Exploiting the known biological activity of α-elastin to promote the maintenance of smooth muscle cells (SMCs) contractile phenotype and the antiproliferative effect of glucocorticoids, the aim of this research was to produce drug-loaded nanoparticles suitable for potential treatment of restenosis. In particular, nanoparticles of α-elastin-g-PLGA with a mean size of 200 nm have been produced and loaded with dexamethasone dipropionate (10% w/w), chosen as a model drug that inhibits proliferation of vascular SMCs. These nanoparticles are able to prolong the drug release and show a pronounced sensibility to elastase. Drug unloaded nanoparticles stimulate the differentiation of human umbilical artery smooth muscle cells (HUASMCs) toward the contractile phenotype as demonstrated by immunofluorescence, flow cytofluorimetric, and western blotting analyses. Finally, drug-loaded nanoparticles efficiently reduce viability of HUASMCs as evidenced by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2- (4-sulfophenyl)-2H-tetrazolium, inner salt (MTS) assay.

Scaffolds based on hyaluronan crosslinked with a polyaminoacid: Novel candidates for tissue engineering application

New porous scaffolds, with a suitable hydrolytic and enzymatic degradation, useful for tissue engineering applications have been obtained by a carbodiimide mediated reaction between hyaluronan (HA) and a synthetic polymer with a polyaminoacid structure such as alpha,beta-polyaspartylhydrazide (PAHy). Scaffolds with a different molar ratio between PAHy repeating units and HA repeating units have been prepared and characterized from a chemical and physicochemical point of view. Tests of indirect and direct cytotoxicity, cell adhesion, and spreading on these biomaterials have been performed by using murine L929 fibroblasts. The new biomaterials showed a good cell compatibility and ability to allow cell migration into the scaffolds as well as spreading on their surface.

Novel Cationic Copolymers of a Polyasparthylhydrazide: Synthesis and Characterization

Alpha,beta-poly(asparthylhydrazide) (PAHy), a water soluble synthetic polymer, was functionalized by using EDCI chemistry with 3-(carboxypropyl)trimethyl-ammonium chloride (CPTACl) obtaining carboxypropyltrimethyl ammonium copolymers (PAHy-CPTA). Three PAHy-CPTA copolymers at increasing derivatization degrees (38%, 48%, 58%) were chosen for subsequent investigations. The capability of these copolymers to bind, neutralize, and protect DNA against degradation by DNase II was evalued by gel retardation assay and DNA degradation test at pH 5.5. Zeta potential measurements show that all studied polymers are able to neutralize the anionic charge of DNA at polymer/DNA weight ratio in the range of 0.8/1-5/1. Polyplex dimensional distribution analyses in bistilled water, saline solution NaCl 0.9%, and HEPES pH 7 show that polyplex size is strongly affected by both presence and type of electrolyte and with time incubation.

Crosslinked hyaluronan with a protein-like polymer: novel bioresorbable films for biomedical applications

In this work, novel hydrogel films based on hyaluronan (HA) chemically crosslinked with the alpha,beta-poly(N-2-hydroxyethyl) (2-aminoethylcarbamate)-D,L-aspartamide (PHEA-EDA) were produced by solution casting method. The goal was to exploit both the biological key role of HA in tissue repair and regeneration, and the versatility of a synthetic protein-like polymer as the PHEA-EDA, in order to obtain biomaterials with physicochemical and biological properties suitable for a clinical use. By varying the molar ratio between the PHEA-EDA amino groups and HA carboxyl groups, three different films were obtained and characterized. Particularly FTIR, swelling, hydrolysis, and enzymatic degradation studies were performed. In addition, the cytocompatibility of HA/PHEA-EDA hydrogel films was evaluated using human derm fibroblasts, by means of MTT and trypan blue exclusion assays. The high swelling capability, the long-term hydrolysis resistance, and the resistance to hyaluronidase greater than that of only HA, together with the cell compatibility, have suggested the potential application of these novel HA-based hydrogel films in the biomedical field of tissue engineering.

Composite nanoparticles based on hyaluronic acid chemically cross-linked with alpha,beta-polyaspartylhydrazide

In this paper, new composite nanoparticles based on hyaluronic acid (HA) chemically cross-linked with alpha,beta-polyaspartylhydrazide (PAHy) were prepared by the use of a reversed-phase microemulsion technique. HA-PAHy nanoparticles were characterized by FT-IR spectroscopy, confirming the occurrence of the chemical cross-linking, dimensional analysis, and transmission electron micrography, showing a sub-micrometer size and spherical shape. Zeta potential measurements demonstrated the presence of HA on the nanoparticle surface. A remarkable affinity of the obtained nanoparticles toward aqueous media that simulate some biological fluids was found. Stability studies showed the absence of chemical degradation in various media, while in the presence of hyaluronidase, a partial degradation occurred. Cell compatibility was evaluated by performing in vitro assays on human chronic myelogenous leukaemia cells (K-562) chosen as a model cell line and a haemolytic test. HA-PAHy nanoparticles were also able to entrap 5-fluorouracil, chosen as a model drug, and release it in a simulated physiological fluid and in human plasma with a mechanism essentially controlled by a Fickian diffusion.

A new biodegradable and biocompatible hydrogel with polyaminoacid structure

The preparation and physicochemical and biological characterization of a novel polyaminoacid hydrogel have been reported. The alpha,beta-poly(N-2-hydroxyethyl)-dl-aspartamide (PHEA) has been used as a starting polymer for a derivatization reaction with methacrylic anhydride (MA) to give rise to the methacrylate derivative named PHM. Photocrosslinking of PHM has been performed in aqueous solution at 313 nm and in the absence of toxic initiators. PHM-based hydrogel has been characterized by scanning electron microscopy, X-ray diffractometry, swelling measurements in aqueous media; the degradation of PHM-based hydrogel has been evaluated as a function of time in the absence or in the presence of esterase. Besides, the biocompatibility of this hydrogel and of its degradation products has been evaluated by performing in vitro assays on human chronic myelogenous leukaemia cells (K-562), chosen as a model cell line. Finally, ATR-FTIR measurements have showed that interaction between PHM-based hydrogel and each of four plasma proteins (albumin, gamma-globulin, transferrin and fibrinogen) does not cause change in protein conformation thus supporting its potential use as a material to prepare parenteral drug delivery systems.

Photo-cross-linked hydrogels with polysaccharide-poly(amino acid) structure: new biomaterials for pharmaceutical applications

The aim of this work has been the preparation and characterization of novel hydrogels with polysaccharide-poly(amino acid) structure having suitable physicochemical properties for pharmaceutical applications. In the first step, hyaluronic acid (HA) and alpha,beta-poly(N-2-hydroxyethyl)-DL-aspartamide (PHEA) have been derivatized with methacrylic anhydride (AMA), thus obtaining HA-AMA and PHM derivatives, respectively. In the second step, aqueous solutions of both these derivatives have been irradiated at 313 nm to obtain chemical hydrogels. The hydrogel obtained by irradiating for 15 min an aqueous solution containing 4% w/v of HA-AMA and 4% w/v of PHM resulted in the highest yield. Its swelling ability was dependent on the pH and nature of the external medium. Besides, this hydrogel undergoes a partial hydrolysis, especially in the presence of enzymes, such as esterase or hyaluronidase, but the entity of this degradation is lower than that observed for a hydrogel based on HA-AMA alone. The ability of this hydrogel to entrap drug molecules has been evaluated by using thrombin as a model drug. In vitro release studies and a platelet aggregation test demonstrated that the HA-AMA/PHM hydrogel is able to release thrombin in the active form, thus suggesting its suitability for the treatment of hemorrhages.

Attachment and spreading of fibroblasts on an RGD peptide-modified injectable hyaluronan hydrogel

Hyaluronan (HA) hydrogels resist attachment and spreading of fibroblasts and most other mammalian cell types. A thiol-modified HA (3,3'-dithiobis(propanoic dihydrazide) [HA-DTPH]) was modified with peptides containing the Arg-Gly-Asp (RGD) sequence and then crosslinked with polyethylene glycol (PEG) diacrylate (PEGDA) to create a biomaterial that supported cell attachment, spreading, and proliferation. The hydrogels were evaluated in vitro and in vivo in three assay systems. First, the behavior of human and murine fibroblasts on the surface of the hydrogels was evaluated. The concentration and structure of the RGD peptides and the length of the PEG spacer influenced cell attachment and spreading. Second, murine fibroblasts were seeded into HA-DTPH solutions and encapsulated via in situ crosslinking with or without bound RGD peptides. Cells remained viable and proliferated within the hydrogel for 15 days in vitro. Although the RGD peptides significantly enhanced cell proliferation on the hydrogel surface, the cell proliferation inside the hydrogel in vitro was increased only modestly. Third, HA-DTPH/PEGDA/peptide hydrogels were evaluated as injectable tissue engineering materials in vivo. A suspension of murine fibroblasts in HA-DTPH was crosslinked using PEGDA plus PEGDA peptide, and the viscous, gelling mixture was injected subcutaneously into the flanks of nude mice; gels formed in vivo following injection. After 4 weeks, growth of new fibrous tissue had been accelerated by the sense RGD peptides. Thus, attachment, spreading, and proliferation of cells is dramatically enhanced on RGD-modified surfaces but only modestly accelerated in vivo tissue formation.

In situ crosslinkable hyaluronan hydrogels for tissue engineering

We describe the development of an injectable, cell-containing hydrogel that supports cell proliferation and growth to permit in vivo engineering of new tissues. Two thiolated hyaluronan (HA) derivatives were coupled to four alpha,beta-unsaturated ester and amide derivatives of poly(ethylene glycol) (PEG) 3400. The relative chemical reactivity with cysteine decreased in the order PEG-diacrylate (PEGDA)>>PEG-dimethacrylate>PEG-diacrylamide>PEG-dimethacrylamide. The 3-thiopropanoyl hydrazide derivative (HA-DTPH) was more reactive than the 4-thiobutanoyl hydrazide, HA-DTBH. The crosslinking of HA-DTPH with PEGDA in a molar ratio of 2:1 occurred in approximately 9 min, suitable for an in situ crosslinking applications. The in vitro cytocompatibility and in vivo biocompatibility were evaluated using T31 human tracheal scar fibroblasts, which were suspended in medium in HA-DTPH prior to addition of the PEGDA solution. The majority of cells survived crosslinking and the cell density increased tenfold during the 4-week culture period in vitro. Cell-loaded hydrogels were also implanted subcutaneously in the flanks of nude mice, and after immunohistochemistry showed that the encapsulated cells retained the fibroblast phenotype and secreted extracellular matrix in vivo. These results confirm the potential utility of the HA-DTPH-PEGDA hydrogel as an in situ crosslinkable, injectable material for tissue engineering.

pH-Sensitive Hydrogel Based On A Novel Photocross-Linkable Copolymer

A pH sensitive hydrogel has been prepared by a UV irradiation technique. Starting polymer was the PHM (poly hydroxyethylaspartamide methacrylated) obtained from polyaspartamide (PHEA) partially derivatized with methacrylic anhydride (MA). This new copolymer has been further derivatized with succinic anhydride (SA) to obtain PHM-SA that has been cross-linked by UV irradiation to form a pH sensitive hydrogel. The network, recovered after washing as a powder, has been been characterized by FT-IR spectrophotometry and particle size distribution analysis. Moreover, to have information about water affinity of the prepared sample, swelling measurements have been carried out in aqueous media mimicking biological fluids. The possibility to employ the prepared hydrogel as a pH-sensitive drug delivery system (DDS) has been investigated. In particular, ibuprofen ((S)(+)4-isobutyl-alpha-methylphenyl-acetic acid), chosen as a model drug, has been entrapped into the PHM-SA hydrogel, and in vitro release studies have showed that its release rate depends on different swelling of the network as a function of the environmental pH.

Biodegradable hydrogels obtained by photocrosslinking of dextran and polyaspartamide derivatives

The functionalization of dextran with glycidyl methacrylate (GMA) leads to the formation of a derivative that generates hydrogels for irradiation at 365nm. The effects of various polymer concentrations and irradiation times on the yield and the properties of the obtained hydrogels are reported. The networks have been characterized by FT-IR spectra, dimensional analysis and swelling measurements carried out at different pH values. In vitro studies suggest that all samples undergo a partial chemical hydrolysis, whereas the incubation with dextranases causes a total degradation whose rate depends on the degree of crosslinking. In addition, aqueous solutions of functionalized dextran have been irradiated in the presence of PHG (PHEA-GMA), i.e. the copolymer obtained by the reaction of alpha,beta-poly(N-2-hydroxyethyl)-DL-aspartamide (PHEA) with GMA. The crosslinking reaction leads to the formation of new networks containing both polymers whose properties have been investigated. To evaluate the processes which occur during UV irradiation, the sol fractions have been purified and characterized by FT-IR and 1H-NMR analyses. Finally, the suitability of hydrogels deriving from functionalized dextran, crosslinked alone or in the presence of PHG, for drug delivery systems has been investigated choosing theophylline as a model drug.