Regenerated Cellulose Hydrogels Research Articles

Preparation of pH-responsive oxidized regenerated cellulose hydrogels compounded with nano-ZnO/chitosan/aminocyclodextrin ibuprofen complex for wound dressing

Recently, using oxidized regenerated cellulose (ORC) to build a hydrogel system on promoting healing in wounds has a fast-growing market. However, it remains a challenge to improve the degree of oxidation of regenerated cellulose (RC) and to prepare matrices that are uniquely responsive to the wound environment. Herein, highly oxidized aldehyde-based cellulose from porous RC was prepared by NaBH4-HCl swelling and then NaIO4 oxidation pathway. Chitosan (CS), ethylenediamine-cyclodextrin (EDA-CD) along with ORC have been used to construct hydrogel matrices that are pH-responsive and capable of controlled drug release for use as future wound dressings. And zinc oxide nanoparticles (ZnO NPs) with antimicrobial effect and ibuprofen (IBU) with analgesic effect were piggybacked into the hydrogel system. XRD was used to study the presence of ZnO. SEM was used to observe the surface structure of the prepared hydrogel. TEM was used to observe the particle size of the ZnO NPs. Meanwhile, the oxidation conditions of the ORC were explored. Furthermore, the mechanical, swelling, water retention, cytotoxicity, bacterial inhibition properties and treatment effect, which are closely related to the application of wound dressing, were carefully researched. The unique characteristics of prepared hydrogel, including pH-responsive degradability and sustained release properties of IBU, were also investigated.

One-Step Treatment for Upgrading Bleached Bamboo Pulp to Dissolving Pulp High Solvency in Green Alkali/Urea Aqueous Solution.

Bleached bamboo pulp, as a kind of natural cellulose, has received significant attention in the field of biomass materials due to its advantages of environmental protection and the abundance of raw materials. Low-temperature alkali/urea aqueous system is a green dissolution technology for cellulose, which has promising application prospects in the field of regenerated cellulose materials. However, bleached bamboo pulp, with high viscosity average molecular weight (Mη) and high crystallinity, is difficult to dissolve in an alkaline urea solvent system, restraining its practical application in the textile field. Herein, based on commercial bleached bamboo pulp with high Mη, a series of dissolvable bamboo pulps with suitable Mη was prepared using a method of adjusting the ratio of sodium hydroxide and hydrogen peroxide in the pulping process. Due to the hydroxyl radicals being able to react with hydroxyls of cellulose, molecular chains are cut down. Moreover, several regenerated cellulose hydrogels and films were fabricated in an ethanol coagulation bath or a citric acid coagulation bath, and the relationship between the properties of the regenerated materials and the Mη of the bamboo cellulose was systematically studied. The results showed that hydrogel/film had good mechanical properties, as the Mη is 8.3 × 104 and the tensile strength of a regenerated film and the film have values up to 101 MPa and 3.19 MPa, respectively. In this contribution, a simple method of a one-step oxidation of hydroxyl radicals to prepare bamboo cellulose with diversified Mη is presented, providing an avenue for a preparation of dissolving pulp with different Mη in an alkali/urea dissolution system and expanding the practical applications of bamboo pulp in biomass-based materials, textiles, and biomedical materials.

Surface-enhanced Raman scattering-active AuNR array cellulose films for multi-hazard detection

In this study, we report a surface-enhanced Raman scattering (SERS)-active array film, which is based on regenerated cellulose hydrogels and gold nanorods (AuNRs), by combining a silicon rubber mask with a vacuum filtration method. This strategy enables the direct AuNR array formation on hydrogel surface with a precisely controlled number density. Moreover, the control of interparticle nanogap has been realized by the spatial deformation of hydrogels. A decrease in gaps between AuNRs deposited on hydrogels can result in SERS enhancement because 3D porous hydrogel structures turned into 2D closely packed hydrogel films during drying. In our experiments, SERS sensor arrays show excellent SERS activity to detect rhodamine 6 G and thiram down to 10 pM and 100 fM with competitive enhancement factors of 3.9 × 108 and 9.5 × 109, respectively. Importantly, the resultant SERS-active arrays with nine sensor units can efficiently detect nine different analytes on a single substrates at a time. Moreover, we demonstrate that physical bending has little effect on the SERS activity of flexible AuNR array hydrogel films, which indicates the high reproducibility of SERS measurement. This SERS array film has great potential to simultaneously detect multiple hazards for the practical application of SERS analysis.

Increased solubility of plant core pulp cellulose for regenerated hydrogels through electron beam irradiation

High cellulose solubility is an essential to successful production of regenerated cellulose, from which hydrogels can be produced. Additionally, some pretreatment usually facilitates cellulose solubility. Bleached cellulose pulp from kenaf core (BK), consisting of lignin (0.3%), hemicellulose (5.2%) and ash (0%), was treated with an electron beam irradiation (EBI) at 10, 30, 50 and 70 kGy. The BK and irradiated bleached cellulose pulp (IK) were then dissolved in either sodium hydroxide/urea or lithium hydroxide/urea solvents which subsequently crosslinked with epichlorohydrin (ECH) solution to stabilize the formation of regenerated cellulose hydrogels. The amount of α-cellulose component in IK samples decreased as much as 38% and caused the viscosity average molecular weight (Mv) and degree of polymerization of IK samples to be reduced significantly by 84 and 87%, respectively. This resulted in an increase in cellulose solubility (up to 30%) for the IK samples in both solvent systems. However, this treatment resulted in a reduction in the overall cellulose fibre strength. X-ray diffraction of the hydrogels showed a transformation from cellulose I to amorphous cellulose. These hydrogels exhibited a higher degree of swelling, transparency and porosity compared to hydrogels prepared from non-irradiated pulp.

In situ synthesis of easily separable Au nanoparticles catalysts based on cellulose hydrogels

Cellulose hydrogels are “green” reductants and supports for Au nanoparticles (Au NPs). Herein, we report a facile method for synthesizing Au NPs based on alkali/urea regenerated cellulose hydrogels. By controlling the precursor concentration and the reaction temperature, the size of the Au NPs can be adjusted. We successfully demonstrate that the Au NP/cellulose hydrogels can be used as efficient heterogeneous catalysts in the reduction of 4-nitrophenol (4-NP). Au NPs with smaller sizes have higher catalytic activity. The highest turnover frequency (TOF) of the Au NPs/cellulose hydrogels is 19.4 h−1. The Au NP/cellulose hydrogels can be easily isolated after the catalytic reaction. We report a facile method for synthesizing Au NPs based on alkali/urea regenerated cellulose hydrogels. By controlling the precursor concentration and the reaction temperature, the size of the Au NPs can be adjusted. The Au NP/cellulose hydrogels can be used as efficient heterogeneous catalysts in the reduction of 4-nitrophenol.

Preparation and properties of regenerated cellulose hydrogels

The regenerated cellulose (RCE) hydrogels were successfully prepared via an easy and green environmental method in N-methylmorpholine-N-oxide (NMMO) aqueous solution. The effect of cellulose content on the thermostability properties, swelling behavior and retention rate of hydrogels was investigated. The thermostability of RCE hydrogels was slightly enhanced with the addition of 8 wt% cellulose, the highest decomposition temperature rose from 335 °C to 352 °C, and the least heat loss is about 75.60%. The equilibrium swelling ratio increases from 394.12% for 3% cellulose hydrogels to 619.46% for 8% cellulose hydrogels. The retention ratio increases from 1.13% to 28.46%.

Autohydrolysis processing as an alternative to enhance cellulose solubility and preparation of its regenerated bio-based materials

Kenaf core pulp has been successfully autohydrolysed using an autoclave heated in oil bath at various reaction temperature at 100, 120 and 140 °C. Membranes, hydrogels and aerogels were then prepared from autohydrolysed kenaf in urea/alkaline medium by casting on the glass plate, by using epichlorohydrin (ECH) as cross-linker via stirring and freeze-drying method, respectively. The autohydrolysis process reduced the molecular weight of cellulose and enhanced cellulose solubility and viscosity. Structure and properties of the regenerated products were measured with Field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), Ultraviolet–visible (UV–Vis) spectrophotometer and swelling testing. As the autohydrolysis temperature increased, the porosity of cellulose membranes (as seen from the morphology) increased. The autohydrolysis process improved the swelling porperties and transparency of regenerated cellulose hydrogels. This finding is expected to be useful in reducing molecular weight of cellulose in order to produce regenerated bio-based cellulose materials.

On the subtle tuneability of cellulose hydrogels: implications for binding of biomolecules demonstrated for CBM 1.

Cellulose-based hydrogel materials prepared by regeneration from cellulose solutions in ionic liquids, or ionic liquid containing solvent mixtures (organic electrolyte solutions), are becoming widely used in a range of applications from tissue scaffolds to membrane ionic diodes. In all such applications knowledge of the nature of the hydrogel with regards to porosity (pore size and tortuosity) and material structure and surface properties (crystallinity and hydrophobicity) is critical. Here we report significant changes in hydrogel properties, based on the choice of cellulose raw material (α- or bacterial cellulose - with differing degree of polymerization) and regeneration solvent (methanol or water). Focus is on bioaffinity applications, but the findings have wide ramifications, including in biomedical applications and cellulose saccharification. Specifically, we report that the choice of cellulose and regeneration solvent influences the surface area accessible to a family 1 carbohydrate-binding module (CBM), CBM affinity for the cellulose material, and rate of migration through the hydrogel. By regenerating bacterial cellulose in water, a maximum accessible surface area of 33 m2 g-1 was achieved. However, the highest CBM migration rate, 1.76 μm2 min-1, was attained by regenerating α-cellulose in methanol, which also resulted in the maximum affinity of the biomolecule for the material. Thus, it is clear that if regenerated cellulose hydrogels are to be used as support materials in bioaffinity (or other) applications, a balance between accessible surface area and affinity, or migration rate, must be achieved.

Carboxymethyl cellulose/oxidized regenerated cellulose hydrogels as adhesion barriers: comparative study with different molecular weights and substitution degrees

For hydrogel materials used in surgery to prevent post-operative adhesion formation, the ability to reduce adhesion formation effectively through ease of application is the most outstanding attribute for improving their clinical utility. In this study, hydrogel formulation with carboxymethyl cellulose (CMC) and water soluble sodium oxidized regenerated cellulose (ORC) powder was developed. The formulation was achieved with different molecular weights and degrees of substitution of the CMC to investigate the effects of these two variables on adhesion prevention. In vivo studies showed that hydrogel formulations with medium molecular weight and a higher degree of substitution gave the best anti-adhesion performance. Histological analyses indicated the materials did not damage the tissue at the surgery area. Promising results were obtained for the development of ORC containing hydrogel formulations for post-operative adhesion prevention applications.

Cellulose-Silica Composite Aerogels Prepared with Sodium Silicate by Freeze Drying Method

The cellulose-silica composite aerogels (CAs) were fabricated through a permeation sol-gel process in the regenerated cellulose hydrogels followed by freeze drying. The precursor Na2SiO3 instead of traditional organic precursor was diffused in the cellulose matrix followed by permeating the catalyst into the cellulose nanofibers network gradually to promote the in situ condensation of Na2SiO3 to form a SiO2 gel skeleton from outside to inside. The obtained CAs displayed the interpenetrating network (IPN) structure of the regenerated cellulose nanofibers network and the SiO2 gel skeleton in nanoscale. In the IPN structure, the flexible cellulose nanofibers network was supported by the hard inorganic network effectively to sustain the compression and the silica gel skeleton protect the cellulose nanofibers to avoid the remodeling of their shape in the process of solvent replacement before freeze drying. Due to the synergic effects of the different network, the IPN structure endows the CAs with high compression modulus (as high as 15.48 MPa), high specific surface area (as high as 621 m2 g-1) and low density (less than 0.182 g cm-3).

Evaluation of the biocompatibility of regenerated cellulose hydrogels with high strength and transparency for ocular applications.

Prompt emergency treatment for ocular injury, particularly in a battlefield setting, is essential to preserve vision, reduce pain, and prevent secondary infection. A bandage contact lens that could be applied in the field, at the time of injury, would protect the injured ocular surface until hospital treatment is available. Cellulose, a natural polymer, is widely used in biomedical applications including bandage materials. Hydrogels synthesized from different cellulose sources, such as plants, cotton, and bacteria, can have the optical transparency and mechanical strength of contact lenses, by tailoring synthesis parameters. Thus, we optimized the fabrication of cellulose-based hydrogels and evaluated their invivo biocompatibility and related physical properties. Our data demonstrate that along with tailorable physical properties, our novel cellulose-based hydrogels could be made with contact lens geometry, exhibit no significant signs of material toxicity after 22 days of invivo testing, and show significant promise for use as a corneal bandage immediately following ocular trauma.

In situ synthesis of Ag3PO4/cellulose nanocomposites with photocatalytic activities under sunlight

In this work, we developed a strategy for Ag3PO4/cellulose nanocomposite hydrogels via in situ reduction and oxidation of Ag3PO4 nanoparticles in a cellulose matrix. The results of FT-IR, X-ray diffraction and X-ray photoelectron spectroscopy proved that the Ag3PO4 nanoparticles were successfully synthesized in situ in the cellulose hydrogels. Moreover, scanning electron microscopy and transmission electron microscopy indicated that various Ag3PO4 nanoparticles were synthesized, and they were dispersed uniformly in the regenerated cellulose hydrogels without aggregation with an average diameter of Ag3PO4 particles from 3.1 ± 2.7 to 11 ± 4.5 nm with an increase in Ag ion concentration. The photocatalytic degradation test of Ag3PO4/cellulose nanocomposite hydrogels provided evidence for the excellent photocatalytic degradation activity to rhodamine B under natural sunlight. Moreover, the photocatalytic degradation efficient increased with increasing Ag3PO4 concentration, where the decreasing of the Ag3PO4 nanoparticle size could increase the photocatalytic degradation speed. The porous structure of the cellulose hydrogels supplied not only cavities for the formation of Ag3PO4 nanoparticles, but also a shell to protect their nanostructure. The Ag3PO4/cellulose nanocomposite hydrogels exhibited good mechanical properties and thermal stability. This portable photocatalyst has good potential for application in the field of water pollution treatment. Ag3PO4 nanoparticles at each AgNO3 concentration were synthesized and dispersed uniformly in the regenerated cellulose hydrogels without aggregation and the average diameter of Ag3PO4 particle of SP05, SP10 and SP40 increased gradually from 3.1±2.7 to 11±4.5 nm with increase in AgNO3 concentration. Ag3PO4/cellulose nanocomposite hydrogels posses good degradation efficiency of photocatalytic degradation Rh B. Moreover, Ag3PO4 nanoparticle size is smaller and the degradation efficiency is higher. Ag3PO4/cellulose nanocomposite hydrogels have excellent mechanical property and moderate thermal stability. This material has potential application in field of visible light photocatalytic, water treatment and solar energy conversion.

Synthesis and properties of regenerated cellulose-based hydrogels with high strength and transparency for potential use as an ocular bandage

Cellulose is a biologically derived material with excellent wound-healing properties. The high strength of cellulose fibers and the ability to synthesize gels with high optical transparency make these materials suitable for ocular applications. In this study, cellulose materials derived from wood pulp, cotton, and bacterial sources were dissolved in lithium chloride/N,N-dimethylacetamide to form regenerated cellulose hydrogels. Material properties of the resulting hydrogels, including water content, optical transparency, and tensile and tear strengths, were evaluated. Synthesis parameters, including activation time, dissolution time, relative humidity, and cellulose concentration, were found to impact the material properties of the resulting hydrogels. Overnight activation time improves the optical transparency of the hydrogels from 77% to 97% at 550nm, whereas controlling cellulose concentration improves their tear strength by as much as 200%. On the basis of the measured transmittance and strength values of the regenerated hydrogels prepared via the optimized synthesis parameters, Avicel PH 101, Sigma-Aldrich microcrystalline cellulose 435236, and bacterial cellulose types were prioritized for future biocompatibility testing and potential clinical investigation.

Improvement of mechanical and oxygen barrier properties of cellulose films by controlling drying conditions of regenerated cellulose hydrogels

Mechanical, thermal and oxygen barrier properties of regenerated cellulose films prepared from aqueous cellulose/alkali/urea solutions can be markedly improved by controlling the drying conditions of the films. By pre-pressing followed by vacuum drying under compression, the tensile strength, Young’s modulus, coefficient of thermal expansion and oxygen permeability of the dried films reached 263 MPa, 7.3 GPa, 10.3 ppm K−1 and 0.0007 ml μm m−2 day−1 kPa−1, respectively. Thus, films produced in this way show the highest performance of regenerated cellulose films with no orientation of cellulose chains reported to date. These improved properties are accompanied by a clear increase in cellulose II crystallinity from 50 to 62% during pre-pressing/press-vacuum drying process. At the same time, the film density increased from 1.45 to 1.57 g cm−3, and the moisture content under equilibrium conditions decreased from 14.1 to 9.8%. Hence, the aqueous alkali/urea solvent system has potential applications in producing new and environmentally friendly cellulose films with high performances through control of the drying conditions.

Cellulose phosphates as biomaterials. In vitro biocompatibility studies

Grafting of phosphate groups has been investigated as a means to render biomedical polymers able to induce the formation of an apatite layer. In the present investigation, regenerated cellulose hydrogels were surface modified by phosphorylation using a previously reported method. The in vitro biocompatibility of materials with varying phosphate contents was evaluated in cultured human bone marrow stromal cells (HBMSC), in terms of cytotoxicity, cell attachment, proliferation and immunohistochemistry. Negatively charged cellulose phosphates were neutralized in the form of the calcium salt before contact with cells. Cellulose phosphates were not cytotoxic, independently of the phosphate content. Unmodified regenerated cellulose hydrogels showed good rates of HBMSC attachment and proliferation. On the contrary, negatively charged, highly hydrophilic, phosphorylated surfaces showed poor HBMSC attachment and proliferation, as well as poor alkaline phosphatase-specific activity and expression of osteocalcin and type I collagen. Differences found are discussed in terms of surface chemical functionality, hydrophilicity and charge.

Mineralization of regenerated cellulose hydrogels induced by human bone marrow stromal cells

The proliferation of cultured human bone marrow stromal cells (HBMSC) on regenerated cellulose hydrogels was assessed. Regenerated cellulose hydrogels showed good rates of HBMSC proliferation, the cells exhibiting a flattened morphology, and after 22 days in culture, the cells had homogeneously colonized the surface of the materials. Moreover, since the early days in culture, between the surface of the materials and attached cells a continuous granulated hydroxyapatite layer was formed. It has been previously demonstrated in vitro, but without cells, that these materials did not mineralize. Hence, it seems that HBMSC promoted the mineralization of the surface.

Cellulose phosphates as biomaterials. II. Surface chemical modification of regenerated cellulose hydrogels

Cellulose regenerated by the viscose process was previously investigated as an implantable material in orthopedic surgery. It was envisaged to take advantage not only of its good matching with mechanical properties of bone but also of its hydroexpansivity, therefore allowing a satisfactory fixation to hard tissue. Both the osteoconduction and the lack of osteoinduction of this material were demonstrated. Grafting of phosphate groups was then envisaged as the means to render cellulose more suitable for orthopedic applications by enhancing its bioactivity. In the present work, the previously optimized phosphorylation reaction was successfully adapted to the surface modification of regenerated cellulose. Modified materials were characterized by XPS, FTIR, and 31P MAS NMR spectroscopic studies, and contact angle measurements, revealing the chemical bond between phosphate groups and cellulose, as well as the hydrophilic nature of phosphorylated materials, which increases with increasing phosphate contents. Water swelling and resistance to gamma sterilization were assessed as well, showing that phosphorylated materials swell considerably in water and were not affected when sterilization was carried out under a nitrogen atmosphere. The increase in surface roughness attributed to chemical modification was demonstrated through laser rugosimetry measurements. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3354–3365, 2001

Cellulose phosphates as biomaterials. In vivo biocompatibility studies

Femoral implantation of regenerated cellulose hydrogels revealed their biocompatibility, but a complete osseointegration could not be observed. Phosphorylation was therefore envisaged as the means to enhance cellulose bioactivity. In vitro studies showed that regenerated cellulose hydrogels promote bone cells attachment and proliferation but do not mineralize in acellular simulated physiological conditions. On the contrary, phosphorylated cellulose has shown an opposite behavior, by inducing the formation of a calcium phosphate layer in simulated physiological conditions, but behaving as a poor substrate for bone cells attachment and proliferation. In order to investigate the in vivo behavior of these materials, and assess the influence of mineralization induction ability vs. bone cells compatibility, unmodified and phosphorylated cellulose hydrogels were implanted in rabbits for a maximum period of 6 months and bone regeneration was investigated. Despite the difficulties arising from the retraction of cellulose hydrogels upon dehydration during the preparation of retrieved implants, histological observations showed no inflammatory response after implantation, with bone intra-spongious regeneration of cells and the integration of the unmodified as well as the phosphorylated cellulose implants. After a maximum implantation period of 6 months, histological observations, histomorphometry and the measurement of the amount of 45Ca incorporated in the surrounding tissue indicated a slightly better osseointegration of phosphorylated cellulose, although no significant differences between the two materials were found.

Cellulose phosphates as biomaterials. II. Surface chemical modification of regenerated cellulose hydrogels

AbstractCellulose regenerated by the viscose process was previously investigated as an implantable material in orthopedic surgery. It was envisaged to take advantage not only of its good matching with mechanical properties of bone but also of its hydroexpansivity, therefore allowing a satisfactory fixation to hard tissue. Both the osteoconduction and the lack of osteoinduction of this material were demonstrated. Grafting of phosphate groups was then envisaged as the means to render cellulose more suitable for orthopedic applications by enhancing its bioactivity. In the present work, the previously optimized phosphorylation reaction was successfully adapted to the surface modification of regenerated cellulose. Modified materials were characterized by XPS, FTIR, and 31P MAS NMR spectroscopic studies, and contact angle measurements, revealing the chemical bond between phosphate groups and cellulose, as well as the hydrophilic nature of phosphorylated materials, which increases with increasing phosphate contents. Water swelling and resistance to gamma sterilization were assessed as well, showing that phosphorylated materials swell considerably in water and were not affected when sterilization was carried out under a nitrogen atmosphere. The increase in surface roughness attributed to chemical modification was demonstrated through laser rugosimetry measurements. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3354–3365, 2001

Cellulose phosphates as biomaterials. Mineralization of chemically modified regenerated cellulose hydrogels

Femoral implantation of regenerated cellulose hydrogels revealed their biocompatible and osteoconductive properties, but a complete osseointegration could not be observed. Phosphorylation was therefore envisaged as the means to enhance cellulose bioactivity. Once implanted, phosphorylated cellulose could promote the formation of calcium phosphates, having therefore closer resemblance to bone functionality and assuring a satisfactory bonding at the interface between hard tissue and biomaterial. In the present work, regenerated cellulose hydrogels were surface modified via phosphorylation. Phosphorylated materials, having varying degrees of substitution, were soaked in a Simulated Body Fluid (SBF) solution in order to investigate their ability to induce the formation of a calcium phosphate layer. Mineralization was assessed by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy. It was demonstrated that the calcium salt of cellulose phosphates mineralized at a higher extent than materials only phosphorylated. The degree of phosphorylation influenced the extent of surface mineralization. Moderate degrees of surface phosphorylation promoted the highest extent of mineralization. This was attributed to inadequate functionality of the surface in terms of density of PO4 groups and overall surface charge, in the case of low and high phosphate contents.