Bone fracture toughness is an important parameter in resistance of bone to monotonic and fatigue failure. Earlier studies on bone fracture toughness were focused on either cortical or cancellous bone, separately [1, 2]. Reported fracture toughness values indicated that cortical bone is tougher to break as compared to cancellous bone. In order to understand complete fracture of a whole bone, the interface between cortical and cancellous bone (named as corticellous bone) might play a crucial role and is interesting topic of research. The goal of this study was to identify fracture toughness in terms of J integral and fracture mechanism of the corticellous bone. Corticellous bone samples (single edge notch bend specimen or SENB) were prepared from bovine proximal femur according to ASTM E399-90 standard (Fig.1). For corticellous bone, samples were prepared in such way that approximately half of the sample width consist of cortical bone and another half is cancellous bone. Precaution was taken while giving notch and pre-crack to corticellous bone that pre-crack should not enter from cortical to cancellous portion. All specimens were tested using a universal testing machine (Tinius Olsen, ± 100 N) under displacement rate of 100 µm/min until well beyond yield point. The fracture toughness parameter in terms of critical stress intensity (KIC) was calculated according to ASTM E399-90 as given by,
Where, P = applied load in kN, S = loading span in cm, B = specimen thickness in cm, W = specimen width in cm, a = total crack length, f(a/W) = geometric function. After the fracture test the J integral of each specimen was calculated using following equation. [ASTM E1820].
Where, Jel is J integral of the elastic deformation, Jpl is J integral of the plastic deformation, E′=E for plane stress condition and E′= E/(1−ν2) for plane strain condition (E is elastic modulus; ν is Poisson's ratio), bo = W−ao, height of the un-cracked ligament, and Apl is the area of the plastic deformation part in the load–displacement curve.Introduction
Material and Methods
Radiation cross-linked UHMWPE is preferred in total hip replacements due to its wear resistance [1]. In total knees, where stresses are higher, there is concern of fatigue damage [2]. Antioxidant stabilization of radiation cross-linked UHMWPE by blending vitamin E into the polymer powder was recently introduced [3]. Vitamin E greatly hinders radiation cross-linking in UHMWPE [4]. In contrast peroxide cross-linking of UHMWPE is less sensitive to vitamin E concentration [5]. In addition, exposing UHMWPE to around 300°C, increases its toughness by inducing controlled chain scission and enhanced intergranular diffusion of chains, simultaneously [6]. We present a chemically cross-linked UHMWPE with high vitamin E content and improved toughness by high temperature melting. Medical grade GUR1050 UHMWPE was blended with vitamin E and with 2,5-Di(tert-butylperoxy)-2,5-dimethyl-3-hexyne or P130 (0.5% Vitamin-E and 0.9% P130). The mixed powder was consolidated into pucks. The pucks were melted for 5 hours in nitrogen at 300, 310 and 320°C. One set of pucks melted at 310°C was accelerated aged at 70°C at 5 atm. oxygen for 2 weeks. Tensile mechanical properties were determined using ASTM D638. Izod impact toughness was determined using ASTM D256 and F648. Wear rate was determined using a bidirectional pin-on-disc (POD) tester with cylindrical pins of UHMWPE against polished CoCr discs in undiluted, preserved bovine serum.Introduction
Methods and Materials
There remains conflicting evidence regarding cortical bone strength
following bisphosphonate therapy. As part of a study to assess the
effects of bisphosphonate treatment on the healing of rat tibial
fractures, the mechanical properties and radiological density of
the uninjured contralateral tibia was assessed. Skeletally mature aged rats were used. A total of 14 rats received
1µg/kg ibandronate (iban) daily and 17 rats received 1 ml 0.9% sodium
chloride (control) daily. Stress at failure and toughness of the
tibial diaphysis were calculated following four-point bending tests.Objectives
Methods
Introduction. The in vivo evolution of surface material properties is important in determining the longevity of bioceramics. Fracture toughness is particularly relevant because of its role in wear resistance. Some bioceramics, such as zirconia (ZrO2) undergo in vivo phase transformation, resulting in a marked reduction in toughness and commensurate increased wear. Here, we investigated the effect of accelerated aging on the surface toughness of alumina (Al2O3), zirconia-toughened alumina (ZTA), and silicon nitride (Si3N4) femoral heads, in order to identify the optimal ceramic material for in vivo implantation and long-term durability. Materials. A newly developed Raman microprobe-assisted indentation method was applied to evaluate and compare surface fracture toughness mechanisms operative in Si3N4 (Amedica Corporation, Salt Lake City, UT, USA), Al2O3 and ZTA (BIOLOX® forte, and delta, respectively, CeramTec, GmbH, Plochingen, Germany) bioceramics. The Al2O3 and ZTA materials have long established histories in total hip arthroplasty; whereas Si3N4 has been newly developed for this purpose. The improved method proposed here consisted in coupling the “traditional” indentation technique with quantitative assessments of microscopic stress fields by confocal Raman microprobe piezo-spectroscopy. Concurrently, crack opening displacement (COD) profiles were also monitored by Raman spectroscopy.
