Hydrogel Graft Research Articles

Combined Intrastromal Implantation of a Semipermeable Hydrogel Membrane in Case of Corneal Graft Failure and Multiple Keratoplasty (Clinical Observation)

Introduction: penetrating keratoplasty (PK) is an effective method for the surgical treatment of corneal failure and its layers and low visual acuity. It is well-known that the graft degrades over time, it is associated with “chronic immune destruction”. Rekeratoplasty is conducted in case of rapid decrease of transplant functions, but even with multiple rekeratoplasty iterations, the result can be unstable.Patient and methods. Patient D., 42 years old, complaints to low vision of left eye — arm movement 10 cm on face. Both eyes have been previously surgically operated for the last 10 years. Two iterations of an artificial iris transplantation in combination with IOL implantation, and Ahmed drainage implantation and five rekeratoplasty on the left eye were conducted. Corneal graft failure with transplant thickness — 802 μm. The patient suffers from Mediterranean fever and polyarthritis. We conducted a course of conservative therapy, which increased visual acuity to 0.05. Then we performed a surgical procedure for hybrid type of keratotransplantation. The following procedures were gradually conducted: mechanical removal of epithelium, femto-laser formation in a recipient’s replaceable corneal disk formation with 500 μm thick and a diameter of 7.0 mm, removal of disk, femto-laser formation of a central penetrating hole with a diameter of 3 mm opposite the artificial pupil, placing of the hydrogel graft 60 μm thick on the bottom of the bed. Hydrogel graft was covered by a donor corneal graft, which was fixed by interrupted sutures and soft contact lens.Results: Visual acuity of the left eye after 1 day after keratoplasty — 0.2; after 1 month — 0.3, the transplant was transparent; after 4 months — 0.4 with complex correction — 0.7, the transplant was transparent, the thickness of the donor disc — 275 μm.Conclusion. After multiple rekeratoplasty iterations the presented method of combined keratotransplantation allows to obtain a non-permanent effective result. At the same time, the polymer metabolism is preserved, since it has a circulation with the front camera. The case requires further observation.

Influence of cross-linkers on the properties of cotton grafted poly (acrylamide-co-acrylic acid) hydrogel composite: swelling and drug release kinetics

Cross-linker plays a crucial role in monitoring water holding and drug release properties of a hydrogel system, an essential requirement for smart wound dressings. Present study is focused on the influence of cross-linkers poly ethylene glycol (PEG) and N,Nʹ-methylene bisacrylamide (MBAAm) on the properties of poly (acrylamide-co-acrylic acid) hydrogel grafted over the cotton fabric to form composite for medicated dressings. Fourier transform infrared spectroscopy (FTIR) confirms the grafting of hydrogel on the cotton fabric. Uniform hydrogel layer on the cotton surface is obtained under scanning electron microscopy (SEM). Swelling of the composite prepared using PEG follow first-order kinetics at acidic and neutral pH whereas second-order kinetic model at pH 8.5 while that prepared using MBAAm follow second-order kinetic equation at all the pHs studied. The swelling kinetics is also governed by Peppas model at all pHs. Release of gentamicin sulphate from both the composites are studied in phosphate buffers having pH 4.5, 7 and 8.5 at 37 ± 0.1 °C and observed that it is fastest in phosphate buffer having pH 7. On fitting drug release data into Peppas model, first and second-order kinetic equations, it is found that drug release is diffusion controlled and follows Fickian diffusion mechanism in case of the composite prepared by using PEG as cross-linker, whereas it is controlled by diffusion as well as chain relaxation in case of the composite prepared by using MBAAm. Mechanical testing using universal testing machine supports a higher mechanical strength of the hydrogel composite as compared to its film.

Injectable hydrogel derived from chitosan with tunable mechanical properties via hybrid-crosslinking system

Thermo-sensitive injectable hydrogels that spontaneously react to physiological temperature have been widely studied to be used in biomedical fields. However, several challenges on their unstable structures with large-sized pores and low mechanical strength under physiological conditions must be addressed to enable their practical applications. We synthesized the hydroxybutyl methacrylated chitosan (HBC-MA) hydrogel that possesses both thermo-sensitive and photo-crosslinkable properties. The HBC-MA showed effective sol-gel transition under physiological temperature as well as a sensitive photo-crosslinkable property with visible light capable of skin penetration. The co-nonsolvency property and thermo-sensitivity of HBC-MA prevented unintended loss of the hydrogel graft after being subcutaneously injected in mice. Subsequently applied visible light on the skin beneath which the hydrogel was injected significantly improved the mechanical strength and stability of the graft. The injectable HBC-MA hydrogel developed in this study can be applicable to a wide range of biomedical fields such as drug delivery system and tissue engineering.

Erratum: Majumder, S. et al. Zinc Oxide Nanoparticles Functionalized on Hydrogel Grafted Silk Fibroin Fabrics as Efficient Composite Dressing. Biomolecules 2020, 10, 710

The authors wish to make the following correction to this paper [...].

Zinc Oxide Nanoparticles Functionalized on Hydrogel Grafted Silk Fibroin Fabrics as Efficient Composite Dressing.

Recent advances in woundcare is targeted towards developing active-dressings, where multiple components are combined to provide a suitable environment for rapid healing. The aim of the present research is to study the preparation of biomimic composite wound dressings by the grafting of hydrogel on silk fibroin fabric. The swelling ability of hydrogel grafted silk fibroin fabric was optimized by changing the initiator concentration. In order to impart antimicrobial properties, these dressing are further coated sono-chemically with zinc oxide nanoparticles. The water vapor transmission rate of the prepared samples was measured. The conformation of silk fibroin proteins after grafting with hydrogel was also confirmed using Fourier Transform Infrared Spectroscopy (FTIR). The morphology of the zinc oxide-coated silk fibroin fabric and hydrogel-coated silk fibroin was studied using Scanning Electron Microscope (SEM). The antimicrobial activity of the zinc oxide-coated samples was studied against E coli. The cytocompatibility of the prepared dressing materials were evaluated using L929 fibroblast cells. MTT assay and phase contrast microscopic studies showed that the adherence, growth, and proliferation of the L929 fibroblast cells that were seeded on zinc oxide nanoparticles on the functionalized hydrogel-coated silk fibroin dressing was significantly higher than that of pure silk fibroin due to the highly porous, bio-mimic structure that allowed ease of passage of nutrients, growth factors, metabolites, and the exchange of gases which is beneficial for successful regeneration of damaged tissues. The expression of TNF-α and IL-2 were not significantly higher than that of control. The proposed composite dressing would be a promising material for wound dressing and regenerative medicine but in order to prove the efficacy of these materials, more in vivo experiments and clinical tests are required to be conducted in future.

Oxytocin-loaded sustained-release hydrogel graft provides accelerated bone formation: An experimental rat study.

Restoration of the lost bone volume is one of the most deliberate issues in dentistry. Sustained-release microspherical oxytocin hormone in a poloxamer hydrogel scaffold combined with a mixture of β-tricalcium phosphate and hydroxyapatite (CP) may serve as a suitable bone graft. The aim of this study was to design and test a novel thermosensitive hydrogel graft incorporating oxytocin-loaded poly(d, l-lactide-co-glycolide) (PLGA) sustained-release microspheres and CP. Thermosensitive poloxamer hydrogel containing CP (HCP graft) was prepared as a base and combined with hollow microspheres (HCPM) and oxytocin-loaded microspheres (HCPOM). Eighty Wistar rats were used for testing the grafts and a control group in 8-mm-diameter critical-sized calvarial defects (CSD); (n = 20). Bone healing at the 4th and 8th weeks was evaluated by histological, histomorphometric, and radiological (micro-computed tomography [µCT]) analyses. The results were analyzed by two-way analysis of variance (P < .05). Oxytocin-loaded PLGA microspheres prepared by the solvent displacement method yielded a high encapsulation efficiency of 89.5% and a slow drug release. Incorporation of the microspheres into the hydrogel graft slowed the release rate down and the release completed within 32 days. HCPOM revealed the highest new bone formation (26.45% ± 6.65% and 30.76% ± 4.37% at the 4th and 8th weeks, respectively; P < .0001) while HCPM and HCP groups revealed a bone formation of around 10% (P > .05). µCT findings of HCPOM group showed the highest mean bone mineral density values (42.21 ± 5.14 and 46.94 ± 3.30 g/cm3 for the 4th and 8th weeks, respectively; P < .0027). The proposed oxytocin-loaded sustained-release PLGA microspheres containing thermosensitive hydrogel graft (HCPOM) provide an accelerated bone regeneration in the rat calvaria.

The effect of oxytocin‐added calcium phosphate hydrogel graft on bone regeneration

The effect of oxytocin‐added calcium phosphate hydrogel graft on bone regeneration

Development and invitro evaluation of infection resistant materials: A novel surface modification process for silicone and Dacron.

Silicone and Dacron are used in a wide spectrum of implantable and indwelling medical products. They elicit a foreign body response, which results in a chronic inflammatory environment and collagenous encapsulation of the medical device that compromises the immune system's ability to effectively fight infections at the biomaterial surface. The objective of this work is to evaluate a novel process to modify silicone and Dacron with a bioactive collagen surface coupled to a gentamicin impregnated hydrogel graft and assess the surface's cytocompatibility and infection resistance properties. Samples of silicone and polyethylene terephthalate (Dacron velour) were modified by plasma deposition and activation followed by a co-polymer acrylic acid (AA)/acrylamide (AAm) hydrogel graft and covalent immobilization of a bioactive collagen surface. The modified surfaces were characterized using FTIR, contact angle, staining, SEM, and XPS. The poly (AA-AAm) hydrogel was impregnated with gentamicin and tested for controlled release characteristics. Each modified surface was evaluated for its ability to resist infection and to promote normal healing as measured by bacterial growth inhibition (Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa) in both broth and agar conditions as well as using fluorescence microscopy to observe adherence of 3T3-NIH fibroblasts. The addition of the poly (AA-AAm) hydrogel with gentamicin inhibited bacterial growth and the subsequent addition of the collagen surface promoted robust fibroblast adhesion on both silicone and Dacron materials. Thorough surface characterization and invitro bacterial and fibroblast evaluation results suggest that this novel surface bioengineering process generated a highly effective surface on silicone and Dacron with the potential to reduce infection and promote healing.

Polyvinyl alcohol/polysaccharide hydrogel graft materials for arsenic and heavy metal removal

Polyvinyl alcohol/polysaccharide hydrogel formation ((A)–(C)) and metallic species adsorption ((D)) for water treatment.

Preparation of starch/poly(N,N-Diethylaminoethyl methacrylate) hydrogel and its use in dye removal from aqueous solutions

Starch/poly(N,N-Diethylaminoethyl methacrylate) graft copolymer was synthesized by graft polymerizing N,N-Diethylaminoethyl methacrylate monomers onto cooked starch using ceric ammonium nitrate/nitric acid mixture as an initiator. After extracting the graft copolymer from the homopolymer and evaluating the graft yield, the graft copolymer was subjected to crosslinking treatment using epichlorohydrin in alkaline medium to convert it to hydrogel. The so prepared hydrogel was evaluated for its swelling ratio which was found to be 100. The hydrogel with its cationic functionality was tried for removing the anionic dye Direct Red 81 from its aqueous solution and all factors affecting the hydrogel adsorption capacity towards the anionic dye, like the hydrogel graft yield, the adsorbate pH, the immersion time and the hydrogel dose were studied. The data obtained from the adsorption results were found to fit well to the Langmuir adsorption model.

Evaluation of an anorganic bovine‐derived mineral with P‐15 hydrogel bone graft: preliminary study in a rabbit cranial bone model

The present investigation aimed to assess the bone-regenerative potential of two formulations of anorganic bovine-derived mineral bound to a P-15 (ABM/P-15) bone graft - the particulate and the hydrogel forms - in a delayed healing rabbit cranial defect model. Ten adult male New Zealand White rabbits were used to create two 8 mm transcortical cranial defects per rabbit and each one received randomly the test material (ABM/P-15 carboxymethyl cellulose (CMC)-hydrogel graft), the standard control material (ABM/P-15 particulate graft) or remained empty as a negative control. The defects were allowed to heal for 2 and 4 weeks. Qualitative and quantitative histological outcomes were assessed on undecalcified sections. In the defects grafted with the test material, at both time points, there was a marked random migration of the bone substitute particles. As a consequence, the space maintenance provision was lost and new bone formation was reduced compared with the control particulate graft material. The histomorphometric analysis showed that the control material attained better results, with an average of 13.8 ± 1.9% and 18.2 ± 4.4% of new bone at 2 and 4 weeks, compared with 8.5 ± 2.4% and 13 ± 2.9% for the test material. These differences were significant at 2 weeks (P ≤ 0.05), but not at 4 weeks (P>0.05). Additionally, there was a significant difference in the total area of mineralized tissue (new bone plus particles), favoring the standard control over the test material: 43.2 ± 14.4% vs. 14.2 ± 5.3% at 2 weeks and 56.9 ± 4.2% vs. 24.2 ± 9.6% at 4 weeks, respectively. The test ABM/P-15 CMC-hydrogel graft material behaved in this animal model by migration of the graft particles, what determined an unpredictable osseoconduction and, consequently, a decreased quality and quantity of bone regeneration as compared with the osseopromotive behavior exhibited by the standard particulate form of the ABM/P-15 control graft. It is therefore suggested to restrain the application of the hydrogel graft form in non-contained anatomical bone defects.

Structure and Properties of Chitosan Containing Polyacrylic Acid Hydrogel Grafted SMS Nonwovens

Hydrogels donate moisture to dehydrated tissue and absorb some moisture and accepted in wound healing. Polypropylene (PP) SMS nonwovens were grafted polyacrylic acid (PAA) hydrogel technique contanining chitosan to enhance hydrophilicity and antibacterial activity. In the first stage, nonwovens were hydroxylated by treatment with aqueous potassium peroxydisulfate solution under a strong flow of nitrogen. In the second stage, the hydroxylated nonwovens were subjected to grafting of acrylic acid using cerric ammonium nitrate as an initiator. Subsequently, chitosan was grafted onto the modified NWs with N,N'-Methylenebisacrylamide. The modified nonwovens were characterized by XPS spectroscopy and SEM, the results showed that acrylic acid was copolymerized and hydrogel grafted onto SMS nonwovens. Hydrogel grafted nonwovens exhibited enhanced wettability and water absorption ability. With introduce of chitosan further, the modified NWs exhibited effectively antibacterial activity against E.coli.

Pore-covered thermoresponsive membranes for repeated on-demand drug release

Reversible on/off-switching of bovine serum albumin (BSA) permeation through a thermoresponsive composite membrane with negligible permeation in the off-state is demonstrated. UV-photografting of poly( N-isopropylacrylamide) onto a poly(ethylene terephthalate) microfiltration membrane results in a hydrogel graft layer on the irradiated side of the membrane only. The amount of hydrogel grafted onto the membrane can be controlled by the amount of crosslinker. Above the lower critical solution temperature (LCST) of the hydrogel (on-state), the shrunken state of the graft layer appears to only partially cover the membrane, allowing BSA permeation through the uncovered pores. Provided the grafting degree is high enough, the swollen hydrogel covers the membrane completely below the LCST (off-state), thus preventing BSA permeation. The on-demand release mechanism proposed here is based on switching the membrane surface coverage rather than previously reported switches based on effective pore size or hydrogel mesh size. The main advantage of our mechanism is that higher fluxes can be achieved in the on-state, since permeation is not limited by pore-narrowing.

Biomechanical and histological evaluation of hydrogel implants in articular cartilage.

We evaluated the mechanical behavior of the repaired surfaces of defective articular cartilage in the intercondylar region of the rat femur after a hydrogel graft implant. The results were compared to those for the adjacent normal articular cartilage and for control surfaces where the defects remained empty. Hydrogel synthesized by blending poly(2-hydroxyethyl methacrylate) and poly(methyl methacrylate-co-acrylic acid) was implanted in male Wistar rats. The animals were divided into five groups with postoperative follow-up periods of 3, 5, 8, 12 and 16 weeks. Indentation tests were performed on the neoformed surfaces in the knee joint (with or without a hydrogel implant) and on adjacent articular cartilage in order to assess the mechanical properties of the newly formed surface. Kruskal-Wallis analysis indicated that the mechanical behavior of the neoformed surfaces was significantly different from that of normal cartilage. Histological analysis of the repaired defects showed that the hydrogel implant filled the defect with no signs of inflammation as it was well anchored to the surrounding tissues, resulting in a newly formed articular surface. In the case of empty control defects, osseous tissue grew inside the defects and fibrous tissue formed on the articular surface of the defects. The repaired surface of the hydrogel implant was more compliant than normal articular cartilage throughout the 16 weeks following the operation, whereas the fibrous tissue that formed postoperatively over the empty defect was stiffer than normal articular cartilage after 5 weeks. This stiffness started to decrease 16 weeks after the operation, probably due to tissue degeneration. Thus, from the biomechanical and histological point of view, the hydrogel implant improved the articular surface repair.

Hydrogel Grafted Surfaces: Protein Interaction and Platelet Adhesion

The blood compatibility of an artificial polymeric implant largely depends on the physicochemical nature of the polymer substrate. In the present study our aim is to develop an understanding of polymer surfaces having similar surface free energy, but different chemical characteristics. We attempted to graft hydrogels onto a silastic polyurethane (Angioflex) material and optimised the surface free energy to about 35.0 ergs/cm2. We compared the protein adsorption and platelet and lymphocyte adhesion on these surfaces. It is observed that there is a relative change in behavior because of the difference in chemical nature.

The kinetic behavior of α-chymotrypsin immobilized inside hydrogel-grafted tubes

Tubular enzyme reactors with α-chymotrypsin (CT) immobilized on the inner wall were prepared and the kinetics of substrate hydrolysis examined. The enzyme was covalently coupled to hydrogel copolymers of 2-hydroxyethyl methacrylate (HEMA) and methacrylic acid (MAAc) radiation grafted onto the inside wan of silicone rubber tubing. An examination of the variation of the rate of hydrolysis of N-acetyl- L-tyrosine ethyl ester (ATEE) with flowrate indicated that the substrate mass-transfer rate in the external solution exerts significant control on the overall reaction rate at low flowrates. However, at sufficiently high flowrates external mass-transfer rate becomes unimportant. A kinetic study of ATEE hydrolysis under the latter conditions showed that substrate diffusion into the hydrogel graft does not occur to any extent before enzyme—substrate reaction occurs. Thus, such an immobilized enzyme preparation may be suitable for applications involving the conversion of large molecular weight substrates. The kinetic parameters of the immobilized CT were evaluated by conventional methods.