Zbyněk Sucharda

Strength, elasticity and failure of composites with pyrolyzed matrices based on polymethylsiloxane resins with optimized ratio of D and T components

Two mixtures of T and D siloxane monomeric components labelled as TxDy (molecular ratio x:y equal 3:1 or 4:1) were chosen as matrix precursors for manufacturing Nextel720 reinforced unidirectional composites which, after pyrolysis at 1000 or 1100°C, revealed good endurance in an oxidizing environment up to 1500°C. Vickers hardness of the heat treated (1000–1500°C) samples of pyrolyzed matrices T3D1 and T4D1 are mutually similar (1100–1400 HV0.2) and reach their maximum between 1200–1300°C. Flexural strength of the pyrolyzed composites is 150–170 MPa and 170–250 MPa for T3D1 and T4D1, respectively. After annealing 3 h in air at 1200–1300°C, the strength slightly decreases but similar treatment at 1500°C yields strengths exceeding those of the pyrolyzed material. Shear modulus of the pyrolyzed T4D1 composite is roughly twice that of the T3D1 one (15 GPa vs. 8 GPa) and both increase sharply to 22–25 GPa after annealing at 1500°C, which manifests substantial improvement of the matrix properties. Fracture toughness of the composites, as measured by chevron notch test at RT, 550°C, and 1100°C, yields 4–5 MPa.m−1/2 for T3D1 and 3–4 MPa.m−1/2 for T4D1. For both composite types, the fracture toughness drops by 1 MPa.m−1/2 when measured at 550°C, which can be attributed to suppression of fibre pull-out due to stress state changes caused by the coefficient of thermal expansion (CTE) mismatch. Fracture surfaces generated during flexural tests of the annealed samples reveal decreasing occurrence of pullout towards the highest annealing temperature.

Support for the initial attachment, growth and differentiation of MG-63 cells: a comparison between nano-size hydroxyapatite and micro-size hydroxyapatite in composites

Hydroxyapatite (HA) is considered to be a bioactive material that favorably influences the adhesion, growth, and osteogenic differentiation of osteoblasts. To optimize the cell response on the hydroxyapatite composite, it is desirable to assess the optimum concentration and also the optimum particle size. The aim of our study was to prepare composite materials made of polydimethylsiloxane, polyamide, and nano-sized (N) or micro-sized (M) HA, with an HA content of 0%, 2%, 5%, 10%, 15%, 20%, 25% (v/v) (referred to as N0–N25 or M0–M25), and to evaluate them in vitro in cultures with human osteoblast-like MG-63 cells. For clinical applications, fast osseointegration of the implant into the bone is essential. We observed the greatest initial cell adhesion on composites M10 and N5. Nano-sized HA supported cell growth, especially during the first 3 days of culture. On composites with micro-size HA (2%–15%), MG-63 cells reached the highest densities on day 7. Samples M20 and M25, however, were toxic for MG-63 cells, although these composites supported the production of osteocalcin in these cells. On N2, a higher concentration of osteopontin was found in MG-63 cells. For biomedical applications, the concentration range of 5%–15% (v/v) nano-size or micro-size HA seems to be optimum.

Effects of thermal ageing on the static and cyclic mechanical properties of carbon fibres/PDMS composites for use in medicine.

composites for use in medicine T. Suchý, R. Sedláček*, Z. Sucharda, K. Balı́k and T. Bouda Department of Mechanics, Biomechanics and Mechatronics, Faculty of Mechanical Engineering, Czech Technical University in Prague, Technická 4, 166 07 Prague 6, Czech Republic; Department of Composite and Carbon Materials, Institute of Rock Structure and Mechanics, Academy of Sciences of the Czech Republic, v.v.i, V Holešovickách 41, Prague 8, Czech Republic

Optimizing and evaluating the biocompatibility of fiber composites with calcium phosphate additives.

SummaryComposite materials based on a polyamide fabric (aramid) and a polydymethylsiloxane (PDMS) matrix were designed for application in bone surgery. In order to increase the bioactivity, 2, 5, 10, 15, 20, and 25 vol.% of nano/micro hydroxyapatite (HA) and tricalcium phosphate (TCP) were added. We studied the effect of the additives on the biocompatibility of the composite. It appears that nano additives have a more favorable effect on mechanical properties than microparticles. 15 vol.% of nano hydroxyapatite additive is an optimum amount for final application of the composites as substitutes for bone tissue: in this case both the mechanical properties and the biological properties are optimized without distinct changes in the inner structure of the composite.

Fracture Properties of Basalt Fibre Composites with Cured or Pyrolysed Matrix

Composite materials based on polysiloxane matrix reinforced by basalt fibres were prepared in laboratories of the IRSM ASCR. The composite samples were pyrolysed at 400 ÷ 750 °C after moulding and curing at 250 °C. Measurement of several mechanical characteristics (flexural strength, fracture toughness, impact strength, and measurement of elasticity) demonstrates a favourable influence of pyrolysis in comparison with the cured-only composite material. Fracture toughness was measured by chevron-notch technique and fracture surfaces were investigated using a scanning electron microscopy.

Characterization of the Interphase in Carbon Fiber Reinforced Polymeric Composite by a Modulus Mapping Test

The effect of sterilization on the structural integrity of the polydimethylsiloxane (PDMS) matrix composite reinforced with carbon fibers (CF) is investigated by nanoindentation test. We present the investigation of the influence of sterilization processes on fiber/matrix interphase properties. The effect of multiple widely-used steam sterilization processes on fibers/matrix interphase region properties was studied by modulus mapping test.

Effect of Sterilization Processes on the Fiber/Matrix Interphase Properties of CF/PDMS Composite to be Used in Orthopaedics

In this study we present the investigation of the influence of multiple sterilization processes on micromechanical properties carried out on a composite based on carbon fibers (CF) and polymer matrix composite polydimethylsiloxane (PDMS). The effect of widely-used steam sterilization process on fibers/matrix interphase region properties was studied by nanoindentation.

The influence of sterilisation processes on the micromechanical properties of polyamide fibre-reinforced PDMS composites for orthopaedic applications

fibre-reinforced PDMS composites for orthopaedic applications R. Sedláček*, T. Suchý, Z. Sucharda, K. Balı́k, M. Sochor, J. Šepitka and J. Lukeš Department of Mechanics, Biomechanics and Mechatronics, Faculty of Mechanical Engineering, Czech Technical University in Prague, Technická 4, 166 07 Prague 6, Czech Republic; Department of Composite and Carbon Materials, Institute of Rock Structure and Mechanics, Academy of Sciences of the Czech Republic, v.v.i, V Holešovickách 41, Prague 8, Czech Republic

Nanoindentation characterisation of poly(dl-lactide)/collagen nanocomposites

T. Suchý*, Š. Rýglová, Z. Sucharda, K. Balı́k, J. Šepitka and J. Lukeš Department of Composite and CarbonMaterials, Institute of Rock Structure and Mechanics, Academy of Sciences of the Czech Republic, v.v.i, V Holešovickách 41, Prague 8, Czech Republic; Department of Mechanics, Biomechanics and Mechatronics, Faculty of Mechanical Engineering, Czech Technical University in Prague, Technická 4, 166 07 Prague 6, Czech Republic