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Abstract:
This work presents a combined experimental and numerical investigation of local overheating in NiAl during spark plasma sintering (SPS). Experimental studies were conducted on samples sintered under different temperature and pressure conditions to capture both the early and final stages of densification. Both perpendicular and parallel loading directions were analysed for microstructural evidence of local melting. Experimental research comprised post-process analysis using SEM and EBSD, while supplementary XRD analysis was used to assess phase stability and crystallographic characteristics. Microstructural analysis focused on regions most susceptible to overheating (contact areas, small particles trapped between larger ones). Sintered samples showed progressive densification, neck growth and grain coarsening with increasing temperature. EBSD maps of sintered compacts reveal distinct orientations across contacts, with no evidence of epitaxial or equiaxed grain growth. Experimentally, no evidence of melting due to local overheating was detected. The experimental observations were complemented by particle-scale thermo-electric FEM simulations. Geometries of equal-sized particles, arranged in a straight line and in a zig-zag chain, connected by the necks with increased resistance, were considered to analyse the temperature rise in the necks. Geometry consisting of a small particle between two large particles was analysed to assess temperature nonuniformity in heterogeneous microstructures. The results show temperature increase in contacts or in small particles; however, the resulting temperature differences are less than 1 C in all cases studied. Numerical results support the experimental findings that NiAl is not prone to local overheating in SPS under the studied conditions.

Abstract:
The cartilage tissue is neither supplied with blood nor innervated, so it cannot heal by itself. Thus, its reconstruction is highly challenging and requires external support. Cartilage diseases are becoming more common due to the aging population and obesity. Among young people, it is usually a post-traumatic complication. Slight cartilage damage leads to the spontaneous formation of fibrous tissue, not resistant to abrasion and stress, resulting in cartilage degradation and the progression of the disease. For these reasons, cartilage regeneration requires further research, including use of new type of biomaterials for scaffolds. This paper shows cartilage characteristics within its most frequent problems and treatment strategies, including a promising method that combines scaffolds and human cells. Structure and material requirements, manufacturing methods, and commercially available scaffolds were described. Also, the comparison of poly(L-lactide) (PLLA) and polyethersulfone (PES) 3D membranes obtained by a phase inversion method using nonwovens as a pore-forming additives were reported. The scaffolds' structure and the growth ability of human chondrocytes were compared. Scaffolds' structure, cells morphology, and protein presence in the membranes were examined with a scanning electron microscope. The metabolic activity of cells was tested with the MTT assay. The structure of the scaffolds and the growth capacity of human chondrocytes were compared. Obtained results showed higher cell activity and protein content for PES scaffolds than for PLLA. The PES membrane had better mechanical properties (e.g. ripping), greater chondrocytes proliferation, and thus a better secretion of proteins which build up the cartilage structure.

Keywords:
3D-scaffolds, membrane structure, polyethersulfone, poly(L-lactide), chondrocyte culture, cartilage regeneration

Abstract:
An innovative modification of the wet inversion phase method, consisting in the use of a polymer nano‐nonwoven as a nonclassic pore precursor. Mechanical properties of the obtained scaffolds were determined, their hydrophilic properties (serum absorbability) were tested, and the content of residues of materials used in the scaffold preparation was determined. Nontoxicity of the developed scaffolds toward T lymphocyte cells was proved. Cultures of primary chondrocytes were obtained successfully. It was proved that an addition of a polymer nano‐nonwoven changes the properties of the scaffolds favorably in respect of their subsequent application in tissue engineering.

Keywords:
cartilage regeneration, chondrocytes, nano-nonwoven, polyvinylpyrrolidone, T lymphocytes

Abstract:
Results of the preparation of biodegradable porous scaffolds using an original modification of a wet phase inversion method were presented. Influence of gelatin non‐woven as a non‐classic pore precursor and polyvinylpyrrolidone, Pluronic as classic pore precursors on the structure of obtained scaffolds was analyzed. It was shown that the addition of gelatin non‐wovens enables the preparation of scaffolds, which allow for the growth of cells (size, distribution, and shape of pores). Mechanical properties of the obtained cell scaffolds were determined. The influence of pore precursors on mass absorption of scaffolds against isopropanol and plasma was investigated. Interaction of scaffolds with a T‐lymphocyte line (Jurkat) and with fibroblasts (L929) was investigated. Obtained scaffolds are not cytotoxic and can be used as implants, for example, the regeneration of cartilage tissue.

Keywords:
cell cultures, cytotoxic, fibroblasts, imprinted scaffolds

Abstract:
The main goal of tissue engineering (TE) is supporting the regeneration of damaged tissues that are difficult to regenerate. The experimental results of the preparation of semi-permeable membranes for cell cultures are presented. The effect of the PLA molecular weight and addition of pore precursors on the morphology of the membranes was studied. The pore precursor of choice was polyvinylpyrrolidone (PVP). It was found that semi-permeable membranes for application in tissue engineering can be prepared with polylactides of molecular weight more significant than 37,000 g/mol. Moreover, it was observed that the growth of the molecular weight of the polymer, the porosity, the size of the pores, the Young modulus and maximum tensile increased. Additionally, to obtain a better morphology of the membranes, PVP should be added to the polymeric solution. Positive growth of L929 fibroblast cells on the obtained scaffolds was shown.

Keywords:
biodegradable polymers, cell cultures, L929 fibroblasts, polylactide, scaffolds, tissue engineering

Abstract:
Polyester 3D scaffolds were obtained by dry inversion phase method. The influence of a polymer and liquid pore precursor type on the 3D scaffolds morphology, porosity and mechanical properties was tested. Polymers and precursors forming a porous structure were identified. It was found that 3D scaffolds having the most preferable structure for cell cultures were obtained from polylactide with the addition of n‐butanol as the liquid pore precursor.

Keywords:
liquid pore precursors, mechanical properties, dry inversion phase method, 3D scaffolds

Abstract:
Zbadano wpływ dodatku ciekłych prekursorów porów na morfologię, porowatość i właściwości mechaniczne polilaktydowych rusztowań komórkowych. Rusztowania otrzymano metodą mokrej inwersji faz w wariancie freeze extraction. Oceniono cytotoksyczność wybranych rusztowań w stosunku do fibroblastów mysich oraz ich przydatność do hodowli komórkowych. Wykazano, że dodatek prekursora porów dopolilaktydu korzystnie zmienia morfologię wytworzonych rusztowań, jednocześnie pogarszając ich wytrzymałość mechaniczną. Stwierdzono, że polilaktydowe rusztowania komórkowe z powodzeniem mogą być wykorzystywane do hodowli komórkowych.

Keywords:
usztowania komórkowe, polilaktyd, hodowle komórkowe, fibroblasty

Abstract:
Results of the preparation of semi-permeable membranes made of biodegradable polymers membranes were presented. Among known polyesters, polylactide was selected for research. The membranes were obtained using wet phase inversion method. The influence of polyvinylpyrrolidone and polymeric nano-non-wovens as pores precursors on the structure of obtained membranes was analysed. It was shown, that utilisation of polymeric nano-non-wovens enabled preparation of semi-permeable membranes, which could be used as wide-pore 3D-type cellular scaffolds.

Keywords:
Biodegradable polymers membranes, Biodegradable polyesters, Porous three-dimensional scaffolds, Inversion phase method

Abstract:
Three types of membrane structures with wide pores were compared in this study. One of the membranes was obtained from polyethersulfone using cellulose fibers as the macropore precursors. Two of the fibers were obtained from poly(L-lactide). As the macropore precursors olyvinylpyrrolidone (1.2 MDa) and pork gelatin non-woven were used, the influence of non-woven fibers on the structure of membranes was shown. Necessity of specific membrane structure application was explained. The hoice of polymers and co-polymers with a range of biodegradation times can determine the scaffold type suitable for the age of a patient.

Keywords:
Polysulfone membrane, Polyester membranes, Membrane structures, Biodegradable membranes, 3D scaffold