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One of the main hurdles to improving scaffolds for regenerative medicine is the development of non-invasive methods to monitor cell proliferation within three-dimensional environments. Recently, an electrical impedance-based approach has been identified as promising for three-dimensional proliferation assays. A low-cost impedance-based solution, easily integrable with multi-well plates, is here presented. Sensors were developed using biocompatible carbon-based ink on foldable polyimide substrates by means of a novel aerosol jet printing technique. The setup was tested to monitor the proliferation of human mesenchymal stromal cells into previously validated gelatin-chitosan hybrid hydrogel scaffolds. Reliability of the methodology was assessed comparing variations of the electrical impedance parameters with the outcomes of enzymatic proliferation assay. Results obtained showed a magnitude increase and a phase angle decrease at 4 kHz (maximum of 2.5 kΩ and -9 degrees) and an exponential increase of the modeled resistance and capacitance components due to the cell proliferation (maximum of 1.5 kΩ and 200 nF). A statistically significant relationship with enzymatic assay outcomes could be detected for both phase angle and electric model parameters. Overall, these findings support the potentiality of this non-invasive approach for continuous monitoring of scaffold-based cultures, being also promising in the perspective of optimizing the scaffold-culture system.

Human mesenchymal stromal cells (hMSCs), whether used alone or together with three-dimensional scaffolds, are the best-studied postnatal stem cells in regenerative medicine. In this study, innovative composite scaffolds consisting of a core–shell architecture were seeded with bone-marrow-derived hMSCs (BM-hMSCs) and tested for their biocompatibility and remarkable capacity to promote and support bone regeneration and mineralization. The scaffolds were prepared by grafting three different amounts of gelatin–chitosan (CH) hydrogel into a 3D-printed polylactic acid (PLA) core (PLA-CH), and the mechanical and degradation properties were analyzed. The BM-hMSCs were cultured in the scaffolds with the presence of growth medium (GM) or osteogenic medium (OM) with differentiation stimuli in combination with fetal bovine serum (FBS) or human platelet lysate (hPL). The primary objective was to determine the viability, proliferation, morphology, and spreading capacity of BM-hMSCs within the scaffolds, thereby confirming their biocompatibility. Secondly, the BM-hMSCs were shown to differentiate into osteoblasts and to facilitate scaffold mineralization. This was evinced by a positive Von Kossa result, the modulation of differentiation markers (osteocalcin and osteopontin), an expression of a marker of extracellular matrix remodeling (bone morphogenetic protein-2), and collagen I. The results of the energy-dispersive X-ray analysis (EDS) clearly demonstrate the presence of calcium and phosphorus in the samples that were incubated in OM, in the presence of FBS and hPL, but not in GM. The chemical distribution maps of calcium and phosphorus indicate that these elements are co-localized in the same areas of the sections, demonstrating the formation of hydroxyapatite. In conclusion, our findings show that the combination of BM-hMSCs and PLA-CH, regardless of the amount of hydrogel content, in the presence of differentiation stimuli, can provide a construct with enhanced osteogenicity for clinically relevant bone regeneration. [ABSTRACT FROM AUTHOR]

Motivated by the enormous potential of hydrogels in regenerative medicine, new biocompatible gelatin-based hybrid hydrogels were developed through a green process using poly(ethylene glycol) diglycidyl ether as a cross-linking agent, adding carrageenan and chitosan polysaccharides to the network to better mimic the hybrid composition of native extracellular matrix. Overall, the hydrogels show suitable structural stability, high porosity and pore interconnectivity, good swellability, and finally, biocompatibility. Their mechanical behavior, investigated by tensile and compression tests, appears to be characterized by nonlinear elasticity with high compliance values, fast stress-relaxation, and good strain reversibility with no sign of mechanical failure for compressive loading–unloading cycles at relatively high deformation levels of 50%. Degradation tests confirm the hydrogel bioresorbability by gradual hydrolysis, during which the structural integrity of both materials is maintained, while their mechanical behavior becomes more and more compliant. Human Umbilical Cord-derived Mesenchymal Stem Cells (hUC-MSCs) were used to test the hydrogels as potential carriers for cell delivery in tissue engineering. hUC-MSCs cultured inside the hydrogels show a homogenous distribution and maintain their growth and viability for at least 21 days of culture, with an increasing proliferation trend. Hence, this study contributes to a further understanding of the potential use of hybrid hydrogels and hUC-MSCs for a wide range of biomedical applications, particularly in soft tissue engineering. [ABSTRACT FROM AUTHOR]

Hydrogels are attracting ample attention for tissue engineering application thanks to their water-loving attribute and closely mimicry to the natural extracellular matrix. However, effectively and efficiently sterilization of hydrogels without compromising their end-use beneficial attributes is a major challenge. The aim of this work is to study the resistance to gamma sterilization of newly developed gelatin-based hybrid hydrogels for tissue engineering. This study reported the investigation of 25 kGy gamma sterilization, a typical sterilization procedure for healthcare products, on the physicomechanical and thermal properties of a three set of gelatin-based novel hydrogels, namely, gelatin-polyethylene glycol (G/PEG), G-PEG-hydroxyethyl cellulose (G/PEG/HEC), and G-PEG-chitosan (G/PEG/CH). Fourier transform infrared and thermogravimetric analysis were done to evaluate the chemical change and variation of thermal behavior, respectively, imposed by the gamma exposure, and the results showed that gamma sterilization did not modify the chemical composition and thermal degradation behavior of the hydrogels. The water uptake, mechanical properties (both in tension and compression), and stress relaxation experiments revealed that parent G/PEG and interpenetrating polymer network (IPN) G/PEG/CH were nearly negligibly sensitive to the gamma sterilization. However, semi-IPN G/PEG/HEC appeared to be slightly vulnerable to the gamma exposure: a decrease in modulus and strength but simultaneous increase in water uptake, percentage dissipation energy, and stress relaxation responses were observed., INTRODUCTION Hydrogels, a water-rich polymeric cross-linked network, have emerged as the most potential scaffolding substrate for three-dimensional (3D) cell culture in tissue engineering. They excel over other scaffolding materials owing [...]

In this work hydroxyethylcellulose (HEC) was employed to prepare macroporous polyacrylamide (PAAm) hydrogels with different porosities and degrees of interconnectivity. The porosity and the equilibrium mass swelling ratio of hydrogels equilibrated in 0.1 M NaCI increased with the amount of HEC employed in the reaction mixture. Tensile and fracture tests were performed to investigate the mechanical behavior of both as prepared hydrogels and of hydrogels equilibrated in 0.1 M NaCI. As prepared hydrogels displayed invariably better mechanical properties than the corresponding equilibrated hydrogels. The mechanical stiffness decreased regularly as the amount of HEC (and porosity) was increased. A more complex trend was observed for the ultimate properties (elongation and stress at break) and for the fracture resistance, which displayed a maximum at intermediate HEC contents., INTRODUCTION According to IUPAC macroporous polymers contain a large number of macropores (50 nm to 1 pm in diameter), while pore diameters are less than 2 nm in microporous polymers [...]

A series of amine-hardened epoxies were prepared by systematically varying the stoichiometric ratio and the relative amounts of diepoxide and monoepoxide resin to chemically control the material composition and macromolecular architecture (chain segments flexibility; crosslink density; amounts of dangling groups). Positron Annihilation Lifetime Spectroscopy was used to investigate the free volume associated to the various epoxy formulations, while dynamic-mechanical analysis was employed to investigate their network density and their primary and secondary mechanical relaxations. The mechanical behavior at small and large strain was studied by means of tensile and compression tests. The results pointed out that deviations from the ideal stoichiometric composition and the addition of monoepoxide resins lead to significant room temperature stiffening, together with a reduction of the crosslink density and glass transition temperature. This behavior, phenomenologically associated to antiplasticization, was interpreted according to the specific macromolecular architecture and ascribed to chain mobility hindrance, as revealed by secondary transitions, whereas no significant contribution from the free volume could be evidenced. Furthermore, it was shown that depending on the strain scale and on the corresponding deformational mechanisms, the mechanical response may be differently influenced either by the presence of dangling groups or by the network density., INTRODUCTION Epoxy resins are a large class of thermosetting polymers that encounter large interest in various technological applications (e.g., adhesives, coatings and high-performance composites) thanks to their thermomechanical and chemical [...]

Bisphenol-A polycarbonate (PC)/poly(methyl methacrylate) (PMMA) blends (PC/PMMA) were prepared by melt mixing with and without a trans-esterification catalyst (tetrabutylammoniun tetraphenylborate), which is able to promote inter-exchange reactions between PC and PMMA. Evidences of the ester-ester exchange reaction taking place were pointed out via Fourier Transform Infra-Red and size exclusion chromatography analyses. A series of enthalpy relaxation measurements were carried out for the pure polymers and for blends thereof. The data were analyzed on the basis of the Tool-Narayanaswamy-Moynihan/Kohlraush-Williams-Watts model. This model characterizes the structural relaxation in the glass transition region by means of four parameters: the apparent activation energy (Δh*), the nonlinearity (x), the nonexponentiality (β), and the pre-exponential factor ([τ.sub.0]). The apparent activation energy can be determined from the cooling rate dependence of the fictive temperature ([T.sub.f]) measured using DSC. Δh* values of homogeneous blend and of the starting polymers were determined in this way, while an estimation of x, β and [τ.sub.0] was proposed. Comparisons were made between a single glass transition temperature PC/PMMA blend and homopolymers data. The experimental values of Δh* suggest that the degree of cooperativity decreases on going from the starting polymers to the blend. POLYM. ENG. SCI., 47:218-224, 2007. © 2007 Society of Plastics Engineers, INTRODUCTION Among a number of studies on poly(methyl methacrylate) (PMMA) blends the mixture PMMA and of bisphenol-A polycarbonate (PC) is one of the most deeply studied polymers pair. This may [...]