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Viscoelasticity of porcine skin and its material substitute, modelled by variously concentrated bovine gelatin, was determined in static (creep test) and dynamic (oscillatory test) mode by the means of rotational rheometry to obtain creep compliance and complex shear modulus. Mechanical properties characterization was also supple-mented with large deformation compression test in order to determine and correlate shear and compression moduli of gelatin with its concentration dependence. Obtained data was fitted with fractional viscoelastic models (Poynting-Thomson, Maxwell) in order to quantify in detail gelatin's transition from viscous-like behavior to-wards solid-like state with increasing gelatin concentration and hence crosslinking density. Potential of gelatin as biomaterial for skin surrogate was identified as well as a concentration region in which gelatin exhibits closest viscoelastic behavior to native porcine skin used.

Nonlinear differential equations are considered to be an important tool for describing a number of phenomena in engineering and the natural sciences, and their study is thus subject to contemporary research. The purpose of the paper is to show applications of the differential transform to second-order half-linear Euler equations with and without delay. The case of proportional delay is considered. Finding a numerical solution to an initial value problem is reduced to solving recurrence relations. The outputs of the recurrence relations are coefficients of the Taylor series of the solution. Validity of the presented algorithm is demonstrated on concrete examples of initial value problems. Numerical results are compared with solutions produced by Matlab function "ddesd".