1,721,042 research outputs found
Composite Collagen/Poly(ethylene glycol)-based Hydrogels for the Creation of Complex Scaffolds through Stereolitography
No full textRapid Prototyping (RP) techniques have been recently investigated for the production of bioactive and bioresorbable scaffolds for tissue engineering. The possibility to design and create customized scaffolds with complex shape is the main advantage displayed by RP techniques. In this work, we evaluated the suitability of composite collagen/poly(ethylene glycol)-based hydrogels (Coll/PEG) to be processed by means of stereolitography, an RP technique which builds three-dimensional objects, starting from a CAD model, following exposure of a photosensitive solution to an ultraviolet laser beam. Coll/PEG-based hydrogels, with different weight ratios between the two components (i.e., Type I collagen and poly(ethylene glycol) diacrylate) were synthesized in a two-step process, which involved the physical entrapment of collagen in a PEG network, followed by the crosslinking of collagen and PEG. The hydrogels were then characterized in terms of swelling capability, dynamic-mechanical properties, morphology, collagen content and degradation rate. The production of hydrogels possessing a complex shape (e.g., meniscus-like) was finally investigated by means of stereolitography. The results demonstrated that the developed hydrogels might be useful platforms for the creation of novel scaffolds for several tissue engineering applications, provided that the photopolymerization-based production is optimized in terms of biocompatibility of the starting materials (e.g., the photoinitiator and the crosslinking agent used). Interestingly, through a proper design of the stereolitographic process, it might be possible to produce Coll/PEG-based patient-specific scaffolds
Experimental investigation and theoretical modelling of the nonlinear acoustical behaviour of a liver tissue and comparison with a tissue mimicking hydrogel
No full textNative harmonics generated by nonlinear distortion of ultrasound during propagation in a medium may cause misinterpretations in spectral analysis when studying contrast agents. The aim of this paper is to quantitatively evaluate nonlinear propagation effects of diagnostic ultrasound pulses in biological tissues and to assess whether a cellulose-based hydrogel can be a suitable material for tissue mimicking purposes. Hydrogel and pig liver tissue samples of various thicknesses were insonified in a through-transmission set-up, employing 2.25-MHz pulses with different mechanical index (MI) values (range 0.06-0.60). Second harmonic and first harmonic amplitudes were extracted from spectra of received signals and their ratio was then used to compare hydrogel and liver behaviours. Resulting trends are very similar for sample thicknesses up to 8 cm and highlight a significant increase in nonlinearity for MI > 0.3, for both liver and hydrogel. A numerical procedure was also employed to calculate pressure distribution along the beam axis: these theoretical results showed a very good agreement with experimental data in the low pressure range, though failed in predicting the MI threshold. In conclusion, the hydrogel resulted to be a suitable material for manufacturing tissue mimicking phantoms, in particular to study contrast agent behaviour with a "low power approach
Correction of MHS Viscosimetric Constants upon Numerical Simulation of Temperature Induced Degradation Kinetic of Chitosan Solutions
Full text linkThe Mark–Houwink–Sakurada (MHS) equation allows for estimation of rheological properties, if the molecular weight is known along with good understanding of the polymer conformation. The intrinsic viscosity of a polymer solution is related to the polymer molecular weight according to the MHS equation, where the value of the constants is related to the specific solvent and its concentration. However, MHS constants do not account for other characteristics of the polymeric solutions, i.e., Deacetilation Degree (DD) when the solute is chitosan. In this paper, the degradation of chitosan in different acidic environments by thermal treatment is addressed. In particular, two different solutions are investigated (used as solvent acetic or hydrochloric acid) with different concentrations used for the preparation of chitosan solutions. The samples were treated at different temperatures (4, 30, and 80 °C) and time points (3, 6 and 24 h). Rheological, Gel Permeation Chromatography (GPC), Fourier Transform Infrared Spectroscopy (FT-IR), Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analyses (TGA) were performed in order to assess the degradation rate of the polymer backbones. Measured values of molecular weight have been integrated in the simulation of the batch degradation of chitosan solutions for evaluating MHS coefficients to be compared with their corresponding experimental values. Evaluating the relationship between the different parameters used in the preparation of chitosan solutions (e.g., temperature, time, acid type and concentration), and their contribution to the degradation of chitosan backbone, it is important to have a mathematical frame that could account for phenomena involved in polymer degradation that go beyond the solvent-solute combination. Therefore, the goal of the present work is to propose an integration of MHS coefficients for chitosan solutions that contemplate a deacetylation degree for chitosan systems or a more general substitution degree for polymers in which viscosity depends not only on molecular weight and solvent combinations
Biodegradable cellulose-based hydrogels: design and applications
Full text linkHydrogels are macromolecular networks able to absorb and release water solutions in a reversible manner, in response to specific environmental stimuli. Such stimuli-sensitive behaviour makes hydrogels appealing for the design of ‘smart’ devices, applicable in a variety of technological fields. In particular, in cases where either ecological or biocompatibility issues are concerned, the biodegradability of the hydrogel network, together with the control of the degradation rate, may provide additional value to the developed device. This review surveys the design and the applications of cellulose-based hydrogels, which are extensively investigated due to the large availability of cellulose in nature, the intrinsic degradability of cellulose and the smart behaviour displayed by some cellulose derivatives
Editorial on the Special Issue “Advances in Cellulose-Based Hydrogels”
Full text linkCellulose is one of the most ubiquitous and naturally abundant biopolymers found on Earth and is primarily obtained from plants and other biomass sources [...
Polymeric hydrogels for burn wound care: Advanced skin wound dressings and regenerative templates
Full text linkWound closure represents a primary goal in the treatment of very deep and/or large wounds, for which the mortality rate is particularly high. However, the spontaneous healing of adult skin eventually results in the formation of epithelialized scar and scar contracture (repair), which might distort the tissues and cause lifelong deformities and disabilities. This clinical evidence suggests that wound closure attained by means of skin regeneration, instead of repair, should be the true goal of burn wound management. The traditional concept of temporary wound dressings, able to stimulate skin healing by repair, is thus being increasingly replaced by the idea of temporary scaffolds, or regenerative templates, able to promote healing by regeneration. As wound dressings, polymeric hydrogels provide an ideal moisture environment for healing while protecting the wound, with the additional advantage of being comfortable to the patient, due to their cooling effect and non-adhesiveness to the wound tissue. More importantly, recent advances in regenerative medicine demonstrate that bioactive hydrogels can be properly designed to induce at least partial skin regeneration in vivo. The aim of this review is to provide a concise insight on the key properties of hydrogels for skin healing and regeneration, particularly highlighting the emerging role of hydrogels as next generation skin substitutes for the treatment of full-thickness burns
Fast synthesis of poly(ethylene glycol) diacrylate cryogels via UV irradiation
No full textPoly(ethylene glycol) diacrylate (PEGDA) cryogels, particularly useful for biotechnological applications, are currently fabricated exploiting crosslinking systems that require long freezing/crosslinking times (20 h or longer). The aim of this work was to assess whether fast UV irradiation (up to 60 s) of frozen PEGDA solutions could be an advantageous alternative for cryogel production. By using different polymer concentrations and UV times, cryogels with highly interconnected macropores (about 50–90 μm) were produced. A gelation yield in the range 60–80% was recorded, with higher values obtained for low PEGDA concentrations (5 and 10% w/v). Interestingly, while decreasing the swelling and increasing the stiffness of the cryogels, a higher polymer concentration was also found to reduce the pore size. Furthermore, increasing the UV time resulted in significantly higher swelling and larger pores for 10% PEGDA samples, while having negligible effect on other cryogel types and/or features. Although deserving further exploration, fast UV irradiation is an effective method to produce PEGDA cryogels with tunable properties
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