Trauma to the central and peripheral nervous systems often lead to serious morbidity. Current surgical methods for repairing or replacing such damage have limitations. Tissue engineering offers a potential alternative. Here we show that functionalized α-helical-peptide hydrogels can be used to induce attachment, migration, proliferation and differentiation of murine embryonic neural stem cells (NSCs). Specifically, compared with undecorated gels, those functionalized with Arg-Gly-Asp-Ser (RGDS) peptides increase the proliferative activity of NSCs; promote their directional migration; induce differentiation, with increased expression of microtubule-associated protein-2, and a low expression of glial fibrillary acidic protein; and lead to the formation of larger neurospheres. Electrophysiological measurements from NSCs grown in RGDS-decorated gels indicate developmental progress toward mature neuron-like behavior. Our data indicate that these functional peptide hydrogels may go some way toward overcoming the limitations of current approaches to nerve-tissue repair.

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Surgical limitations require alternative methods of repairing and replacing diseased and damaged tissue. Regenerative medicine is a growing area of research with engineered tissues already being used successfully in patients. However, the demand for such tissues greatly outweighs the supply and a fast and accurate method of production is still required. 3D bioprinting offers precision control as well as the ability to incorporate biological cues and cells directly into the material as it is being fabricated. Having precise control over scaffold morphology and chemistry is a significant step towards controlling cellular behaviour, particularly where undifferentiated cells, i.e., stem cells, are used. This level of control in the early stages of tissue development is crucial in building more complex systems that morphologically and functionally mimic in vivo tissue. Here we review 3D printing hydrogel materials for tissue engineering purposes and the incorporation of cells within them. Hydrogels are ideal materials for cell culture. They are structurally similar to native extracellular matrix, have a high nutrient retention capacity, allow cells to migrate and can be formed under mild conditions. The techniques used to produce these materials, as well as their benefits and limitations, are outlined.

In this paper active screen plasma nitriding (ASPN) is used to chemically modify the surface of UHMWPE. This is an unexplored and new area of research. Active screen plasma nitriding allows the homogeneous treatment of any shape or surface at low temperature, therefore it was thought, that ASPN would be an effective technique to modify organic polymer surfaces. ASPN experiments were carried out at 120 0 C using a DC plasma nitriding unit with a 25% N 2 and 75% H 2 atmosphere at 2.5 mbar of pressure. UHMWPE samples treated for different time periods were characterized by Nanoindentation, FTIR, XPS, Interferometry and SEM. A 3T3 fibroblasts cell line was used for in vitro cell culture experiments. Nano-indentation of UHMWPE showed that hardness and elastic modulus increased with ASPN treatment compared to the untreated material. FTIR spectra did not show significant differences between the untreated and treated samples, however some changes were observed at 30 min of treatment in the range of 1500-1700 cm -1 associated mainly with the presence of N-H groups. XPS studies showed that nitrogen was present on the surface and its amount increased with treatment time. Interferometry showed that no significant changes were observed on the surfaces after the treatment. Finally, cell culture experiments and SEM showed that fibroblasts attached and proliferated in a greater extend on the plasma treated surfaces leading to the conclusion, that ASPN surface treatment can potentially significantly improve the biocompatibility behaviour of polymeric materials.

Bone loss due to accidents or tissue diseases requires replacement of the structure by either autografts, allografts, or artificial materials. Reactive cements, which are based on calcium phosphate chemistry, are commonly used in nonload bearing areas such as the craniofacial region. Some of these materials are resorbed by the host under physiological conditions and replaced by bone. The aim of this study was to test different calcium and magnesium cement composites in vitro for their use as bone substitution material. Phase composition of calcium deficient hydroxyapatite (Ca(9) (PO(4) )(5) HPO(4) OH), brushite (CaHPO(4) ·2H(2) O), and struvite (MgNH(4) PO(4) ·6H(2) O) specimens has been determined by means of X-ray diffraction, and compressive strength was measured. Cell growth and activity of osteoblastic cells (MG 63) on the different surfaces was determined, and the expression of bone marker proteins was analyzed by western blotting. Cell activity normalized to cell number revealed higher activity of the osteoblasts on brushite and struvite when compared to hydroxyapatite and also the expression of osteoblastic marker proteins was highest on brushite scaffolds. While brushite sets under acidic conditions, formation of struvite occurs under physiological pH, similar to hydroxyapatite cements, providing the possibility of additional modifications with proteins or other active components.

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The mechanical testing of thin layers of soft materials is an important but difficult task. Spherical indentation provides a convenient method to ascertain material properties whilst minimising damage to the material by allowing testing to take place in situ. However, measurement of the viscoelastic properties of these soft materials is hindered by the absence of a convenient yet accurate model which takes into account the thickness of the material and the effects of the underlying substrate. To this end, the spherical indentation of a thin layer of viscoelastic solid material is analysed. It is assumed that the transient mechanical properties of the material can be described by the generalised standard linear solid model. This model is incorporated into the theory and then solved for the special case of a stress relaxation experiment taking into account the finite ramp time experienced in real experiments. An expression for the force as a function of the viscoelastic properties, layer thickness and indentation depth is given. The theory is then fitted to experimental data for the spherical indentation of poly(dimethyl)siloxane mixed with its curing agent to the ratios of 5:1, 10:1 and 20:1 in order to ascertain its transient shear moduli and relaxation time constants. It is shown that the theory correctly accounts for the effect of the underlying substrate and allows for the accurate measurement of the viscoelastic properties of thin layers of soft materials.

Active Screen Plasma Nitriding (ASPN) is a well-established technique used for the surface modification of materials, the result of which is often a product with enhanced functional performance. Here we report the modification of the chemical and mechanical properties of ultra-high molecular weight poly(ethylene) (UHMWPE) using 80:20 (v/v) N 2 /H 2 ASPN, followed by growth of 3T3 fibroblasts on the treated and untreated polymer surfaces. ASPN-treated UHMWPE showed extensive fibroblast attachment within three hours of seeding, whereas fibroblasts did not successfully attach to untreated UHMWPE. Fibroblast-coated surfaces were maintained for up to 28 days, monitoring their metabolic activity and morphology throughout. The chemical properties of the ASPN-treated UHMWPE surface were studied using X-ray photoelectron spectroscopy, revealing the presence of C-N, C=N, and C≡N chemical bonds. The elastic modulus, surface topography, and adhesion properties of the ASPN-treated UHMWPE surface were studied over 28 days during sample storage under ambient conditions and during immersion in two commonly used cell culture media. KeywordsActive screen plasma nitriding, atomic force microscopy, fibroblast, interferometry, nanoindentation, X-ray photoelectron spectroscopy 2 1. Introduction Biomaterials that will be used for medical applications are required to have excellent bulk and surface properties to resist mechanical deformation while providing a surface that enables tissue attachment. Designing a material that exhibits good bulk properties together with the appropriate surface characteristics to enable biological integration is often challenging [1][2][3]. Polymeric materials exhibit attractive characteristics for biomedical applications. They are of low density, are easy to process and of relatively low cost. It has also been reported that polymers can be tailored to influence the viability, growth and function of attached cells controlling the cell function by the chemical, morphological and mechanical properties of the polymeric surface [4]. The surface properties of polymers, however, do not often satisfy the requirements for biomedical applications such as scratch resistance, wettability, biocompatibility, gas permeability and friction. They often appear to have low surface energy and poor adhesive properties hence surface modification is required [5][6][7][8].