Obtaining new composite biomaterials by means of mineralization of methacrylate hydrogels using the reaction–diffusion method

Hydrogels with dual sensitivity to temperature and pH in physiologically relevant ranges as supports for versatile controlled cell detachment

Thermosensitive hydrogels based on the N-vinyl caprolactam (VCL), capable of allowing for cell adhesion and proliferation, as well as non-aggressive detachment by controlled temperature drop, were functionalized with 23 % or lower molar percentages of the cationizable hydrophobic unit 2-(diisopropylamino) ethyl methacrylate (DPAEMA), to obtain networks with dual sensitivity to temperature and pH. The swelling analysis of the systems has shown a transition pK (pKb) close to physiological values, dependent on the temperature of the medium (pKb of 6.6 and 6.9 when the temperature of the medium is above and below the transition temperature VPTT, respectively) and little dependence on the degree of functionalization of DPAEMA. In addition, at temperatures below the transition temperature (VPTT), the systems have shown large swelling variations as a function of the pH (i.e. below and above the pKb), exhibiting greater absorption capacity at pHs below pKb, where the DPAEMA units are cationized. Cytocompatibility and transplant capacity have been evaluated using the C166-GFP endothelial cell line. None of the thermosensitive hydrogels with variable DPAEMA content showed a delay with respect to the control without DPAEMA neither in terms of adhesion nor in proliferation. However, by increasing the percentage of DPAEMA functionalization -and decreasing thermosensitivity-, a correlative decrease in mitochondrial activity was obtained in the transplant, with significant differences for the hydrogels with DPAEMA molar percentage of 3 % or higher. Taking advantage of the proximity of the pKb to the physiological value, we have evaluated the cellular response and the capacity for transplantation after lowering the pH to 6.5, below pKb. A direct relationship of the DPAEMA functionalization degree on the detachment efficiency was observed, since the hydrogels with the highest molar load of DPAEMA showed higher mitochondrial metabolic activity after cell detachment.

Poly(ethylene Glycol) Methyl Ether Methacrylate-Based Injectable Hydrogels: Swelling, Rheological, and In Vitro Biocompatibility Properties with ATDC5 Chondrogenic Lineage

Here, we present the synthesis of a series of chemical homopolymeric and copolymeric injectable hydrogels based on polyethylene glycol methyl ether methacrylate (PEGMEM) alone or with 2-dimethylamino ethyl methacrylate (DMAEM). The objective of this study was to investigate how the modification of hydrogel components influences the swelling, rheological attributes, and in vitro biocompatibility of the hydrogels. The hydrogels' networks were formed via free radical polymerization, as assured by 1H nuclear magnetic resonance spectroscopy (1H NMR). The swelling of the hydrogels directly correlated with the monomer and the catalyst amounts, in addition to the molecular weight of the monomer. Rheological analysis revealed that most of the synthesized hydrogels had viscoelastic and shear-thinning properties. The storage modulus and the viscosity increased by increasing the monomer and the crosslinker fraction but decreased by increasing the catalyst. MTT analysis showed no potential toxicity of the homopolymeric hydrogels, whereas the copolymeric hydrogels were toxic only at high DMEAM concentrations. The crosslinker polyethylene glycol dimethacrylate (PEGDMA) induced inflammation in ATDC5 cells, as detected by the significant increase in nitric oxide synthase type II activity. The results suggest a range of highly tunable homopolymeric and copolymeric hydrogels as candidates for cartilage regeneration.

Fabrication of 3D cylindrical thermosensitive hydrogels as supports for cell culture and detachment of tubular cell sheets

Pseudo interpenetrating vinyl-caprolactam (VCL) based thermosensitive tubular hydrogels with a volume phase transition temperature, VPTT, around 35 °C, have been prepared by combining two different crosslinkers, a di-methacrylate (C1) and a di-vinyl urea (C2). The molar ratio between the two crosslinkers (for a global crosslinker molar percentage of 1.9) has shown to play a key role on the properties of the hydrogel. Increasing the amount of di-vinyl urea, leads to transparent but rather fragile materials and to a lower extent of thermosensitivity, that is, to a lower variation in the hydrogel swelling upon temperature change. However, tubes prepared with a selected crosslinker molar ratio C1/C2 of 65/35 provided a compromise between transparency, thermosensitivity and maneuverability and were, thus, evaluated as supports for cell culture using premyoblastic cells. These hydrogels, used as supports, allow for surface adhesion and cell proliferation until confluence, and eventually an efficient monolayer detachment (and transplant to a 3D-printed polylactic acid (PLA) support) through a controlled drop in temperature. As a result, this method permits to obtain tubular tissue constructs with potential applications in tissue engineering such as in the elaboration of vascular grafts.

PEGDA/HA mineralized hydrogel loaded with Exendin4 promotes bone regeneration in rat models with bone defects by inducing osteogenesis

Scaffolds with osteogenic differentiation function play an important role in the healing process of bone defects. Here, we designed a high strength Poly(ethyleneglycol) diacrylate/Hydroxyapatite (PEGDA/HA) mineralized hydrogel loaded with Exendin4 for inducing osteogenic differentiation. In this study, PEGDA hydrogel was prepared by photo initiating method. PEGDA/HA mineralized hydrogel was prepared by in-situ precipitation method, and Exendin4 was loaded by gel adsorption. The effects of different calcium and phosphorus concentrations on the strength and Exendin4 release of PEGDA/HA hydrogels were investigated. Rat models of bone defect were made and randomly divided into 5 groups. The experimental group was implanted with PEGDA hydrogel, Exendin4-PEGDA hydrogel, PEGDA/HA mineralized hydrogel, Exendin4-PEGDA/HA mineralized hydrogel, and no materials were implanted in the blank control group. Computed tomography (CT) and histology were observed 4 and 8 weeks after operation. Our results revealed that the PEGDA/HA mineralized hydrogel had porous structure, high mechanical strength and good biocompatibility. In vitro release test showed that the mineralized hydrogel exhibited good sustained release profile within 20 d. The animal experiments showed that the mineralized hydrogel accelerated the formation of new bone after 4 and 8 weeks, and formed a seamless union on the defected bone area after 8 weeks. In conclusions, The Exendin4-PEGDA/HA mineralized hydrogel can effectively repair bone defects in rats, and it is expected to be used as a biomaterial for human bone tissue repair.

Shape memory histocompatible and biodegradable sponges for subcutaneous defect filling and repair: greatly reducing surgical incision

Reducing surgical incision for large area subcutaneous defect filling and repair is a great challenge in the biomedical field, especially for plastic surgery. In this study, a novel hydroxyethyl cellulose/soy protein isolate (HEC/SPI) composite sponge (EHSS) with a fluid responsive shape memory property was constructed, whose thickness could be controlled by hot-pressing conditions to reduce the required surgical incision greatly. Effects of the main factors such as pressure, temperature and hot-pressing cycles on the recovery degree of EHSS were investigated systematically. The structure and physical properties of the sponges were characterized by FTIR spectroscopy, XRD, SEM etc. The results showed that EHSS could be pressed into thin disks with much smaller thickness, and the thickness retention ratio and recovery ratio were affected by hot-pressing conditions such as pressure and temperature. Especially, EHSS could be hot-pressed into a dense thin disk (EHSS-PT-130) at 130 °C with the pressure of 30 MPa, which could quickly recover its original shape by soaking in hydrophilic fluids. EHSS-PT-130 also exhibited good hydrophilicity, cytocompatibility, histocompatibility and in vivo biodegradability. Compared with the original EHSS, in vivo shape memory EHSS-PT-130 required much smaller surgical incision to reach the same repair effect and no need of extra sterilization, showing potential application for subcutaneous defect filling and repair.

Entrapment of chitosan, pectin or κ-carrageenan within methacrylate based hydrogels: Effect on swelling and mechanical properties

Composite hydrogels were obtained by the entrapment of chitosan, pectin or κ-carrageenan within methacrylate-based hydrogels to improve their swelling and the mechanical properties. The results indicated that the water uptake (WU) of κ-carrageenan and chitosan hydrogels were until 3.5 and 2.2 times higher than the WU of the synthetic hydrogel, respectively. The surface morphologies of the hydrogels showed that the pectin and κ-carrageenan favors the formation of larger and more defined pores. The mechanical properties indicated that the pectin increased slightly the mechanical properties and the κ-carrageenan improves the mechanical properties of the synthetic hydrogel reaching up 400 N of compression load. Therefore, the entrapment of κ-carrageenan within synthetic hydrogels improved both the swelling and the mechanical properties. The biocompatibility of the hydrogels was evaluated with in vitro cytotoxicity assays and the results indicated that they could be considered as candidates for biomedical use.

Free-standing supramolecular hydrogel objects by reaction-diffusion

Self-assembly provides access to a variety of molecular materials, yet spatial control over structure formation remains difficult to achieve. Here we show how reaction-diffusion (RD) can be coupled to a molecular self-assembly process to generate macroscopic free-standing objects with control over shape, size, and functionality. In RD, two or more reactants diffuse from different positions to give rise to spatially defined structures on reaction. We demonstrate that RD can be used to locally control formation and self-assembly of hydrazone molecular gelators from their non-assembling precursors, leading to soft, free-standing hydrogel objects with sizes ranging from several hundred micrometres up to centimeters. Different chemical functionalities and gradients can easily be integrated in the hydrogel objects by using different reactants. Our methodology, together with the vast range of organic reactions and self-assembling building blocks, provides a general approach towards the programmed fabrication of soft microscale objects with controlled functionality and shape.

An Injectable Hydrogel as Bone Graft Material with Added Antimicrobial Properties

Currently, the technique which provides the best chances for a successful bone graft, is the use of bone tissue from the same patient receiving it (autograft); the main limitations are the limited availability and the risks involved in removing living bone tissue, for example, explant site pain and morbidity. Allografts and xenografts may overcome these limitations; however, they increase the risk of rejection. For all these reasons the development of an artificial bone graft material is particularly important and hydrogels are a promising alternative for bone regeneration. Gels were prepared using 1,4-butanediol diacrylate as crosslinker and alpha tricalciumphosphate; ZnCl₂ and SrCl₂ were added to the aqueous phase. MTT results demonstrated that the addition of strontium had a beneficial effect on the osteoblast cells density on hydrogels, and zinc instead did not increase osteoblast proliferation. The amount of calcium produced by the osteoblast cells quantified through the Alizarin Red protocol revealed that both strontium and zinc positively influenced the formation of calcium; furthermore, their effect was synergistic. Rheology properties were used to mechanically characterize the hydrogels and especially the influence of crosslinker's concentration on them, showing the hydrogels presented had extremely good mechanical properties. Furthermore, the antimicrobial activity of strontium and zinc in the hydrogels against methicillin-resistant Staphylococcus aureus and Staphylococcus epidermidis was determined.

Silver nanoparticle based antibacterial methacrylate hydrogels potential for bone graft applications

Infections are frequent and very undesired occurrences after orthopedic procedures; furthermore, the growing concern caused by the rise in antibiotic resistance is progressively dwindling the efficacy of such drugs. Artificial bone graft materials could solve some of the problems associated with the gold standard use of natural bone graft such as limited bone material, pain at the donor site and rejections if donor tissue is used. We have previously described new acrylate base nanocomposite hydrogels as bone graft materials. In the present paper, we describe the integration of silver nanoparticles in the polymeric mineralized biomaterial to provide non-antibiotic antibacterial activity against Staphylococcus epidermidis and Methicillin-resistant Staphylococcus aureus. Two different crosslinking degrees were tested and the silver nanoparticles were integrated into the composite matrix by means of three different methods: entrapment in the polymeric hydrogel before the mineralization; diffusion during the process of calcium phosphate crystallization and adsorption post-mineralization. The latter being generally the most effective method of encapsulation; however, the adsorption of silver nanoparticles inside the pores of the biomaterial led to a decreasing antibacterial activity for adsorption time longer than 2 days.

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Acrylate based hydrogels were prepared.

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Hydrogels were mineralized through reaction diffusion.

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Silver nanoparticles were encapsulated in different ways.

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Nanoparticle adsorption after mineralization was the most effective antibacterial method.