Bio-Medical Materials and Engineering

Alteration of the geometrical surface configuration of cortical bone allografts may improve incorporation into host bone. A porous biodegradable coating that would maintain immediate structural recovery and subsequently allow normal graft healing and remodeling by promoting bony ingrowth could provide an osteoconductive surface scaffold. We investigated the feasibility of augmenting cortical bone grafts with osteoconductive biodegradable polymeric scaffold coatings. Three types of bone grafts were prepared: Type I – cortical bone without coating (control), Type II – cortical bone coated with PLGA‐foam, Type III – cortical bone coated with PPF‐foam. The grafts were implanted into the rat tibial metaphysis (16 animals for each type of bone graft). Post‐operatively the animals were sacrificed at 2 weeks and 4 weeks (8 animals for each type of bone graft at each time point). Histologic and histomorphometric analysis of grafts showed that the amount of new bone forming around the foam‐coated grafts was significantly higher than in the control group (uncoated; $p<{}$ 0.02). Although both foam formulations were initially equally osteoconductive, PLGA‐based foam coatings appeared to have degraded at two weeks postoperatively, whereas PPF‐based foam coatings were still present at 4 weeks postoperatively. While significant resorption was present in control allografts with little accompanying reactive new bone formation, PLGA‐coated bone grafts showed evidence of bone resorption and subsequent bony ingrowth earlier than those coated with PPF‐based foams suggesting that PPF‐coated cortical bone grafts were longer protected against host reactions resulting in bone resorption.

Dual‐phase stainless steels have been developed in order to reduce the nickel content, which is potentially responsible to an allergic reaction when these steels are used as medical or dental applications. In this study, two different dual‐phase stainless steels (2205 and Z100) were electrochemically tested to evaluate their corrosion resistance in three corrosive solutions (i.e., synthetic saliva, 0.9% NaCl solution, and Ringer solution). Particularly, an attempt was made to correlate the corrosion resistance to a metallographic parameter, which is, in this study, the alpha/gamma phase ratio. It was concluded that (1) type 2205 stainless steel exhibited excellent corrosion resistance in all three corrosion media; however 2205 stainless steel decreases its corrosion resistance by increasing chloride concentration in tested electrolytes from synthetic saliva through 0.9% NaCl solution to Ringer solution. (2) X‐ray diffraction analysis indicated that the α/γ phase ratio of 2205 (1.735) was higher than that of Z100 (0.905). As a result, it is suggested that by increasing the α/γ phase ratio the material shows more corrosion‐prone behavior when being subjected to a hostile environment containing higher chloride ion concentration.

A new training system was designed and realised by the engineer G. Scuderi: a centrifugal track for runners. The principal advantage of this track is to increase the forces on athlete during the run with an effect very similar to that of an “artificial gravity”, so the athlete can develop more muscle power. A multibody numerical model of a runner was developed to analyse the behaviour of the athlete on the centrifugal track. The multibody model was calibrated by experimental analysis; in fact, the joint angles were measured by a digital image processing system and introduced as input in the numerical simulation. The numerical results obtained are the values of many kinematic and dynamic variables, in particular the ground reaction force and the moments in the hip, knee, and ankle joints. A comparison between the normal running and that on the centrifugal track was carried out, demonstrating the validity of training on the latter. The results of the numerical simulation confirm that the power developed during running on the track, and the corresponding work performed by the joints, is considerably greater than that found during normal running.

The sandwiched osmotic tablet core, which is composed of a middle push layer and two attached drug layers, has been prepared and systematically studied with the purpose of delivering water‐insoluble nifedipine. The advantage of the sandwiched osmotic tablet system over the commercialized push‐pull osmotic tablet system is its simplicity of preparation, as the surface identification was avoided. It was observed that polyethylene oxides (PEO) with molecular weight (MW) of 300,000 and 8,000,000 g/mole were suitable for the thickening agent of drug layer and the expandable hydrogel of push layer, respectively. The weight ratio of 190/190 for drug layer/push layer was also found to be suitable. It has been observed that PEO amount of the push layer and the KCl amount of the drug layer had profoundly positive influence on nifedipine release. A push layer/drug layer co‐controlled osmotic delivery mechanism has been proposed and the optimal tablet formulation has been obtained. It was also found that PEO and nifedipine were miscible, which may support the application of PEO in nifedipine dosage forms. Meanwhile, the PEO/nifedipine binary phase diagram has been constructed. The sandwiched osmotic tablet system can deliver nifedipine in an approximate zero‐order rate up to 24 hours. It may be potentially used for the delivery of water‐insoluble drugs.

The opening angles of 16 rings excised from human coronary arteries with different degrees of atherosclerosis were determined 10 hours after death. Atherosclerosis, as a chronic inflammatory response of arterial endothelium and intima, is defined by three degrees of its development. The opening angle decreases more or less linearly with the distance from the right coronary artery orifice. This is in accordance with the functional requirements posed on blood transport into the coronary arteries. A decrease of the opening angle with age is affected by hardening of the arterial wall, among other factors. This is in accordance with a stochastic model of age related changes in the initial modulus of elasticity of the coronary artery. A part of the free energy of smooth muscle cells, fibroblasts, collagen and elastic fibres is used not for creating residual strain but for remodeling the arterial wall structure. The opening angle is also considerably affected by the degree of atheroclerosis. The dependence on age of the external diameter and the thickness of the intact left and right coronary arteries in the vicinity of the aortic sinus was also analyzed in two female and two male subjects. To ensure the objectivity of the results it is necessary to carry out additional experiments and studies in vivo.

Many investigators have advocated that hydroxyapatite ceramics may be extremely prospective bone substitute material mainly through evidence with its given biocompatibility towards bone and demonstrated continuity between living bone and hydroxyapatite. Its mechanical brittleness and strength, however, have been the most serious considerations. In this paper, a study has been performed using animal experiments, massive hydroxyapatite ceramics are implanted into rectangular bone defect created by operation at the load‐bearing area in close contact with tibia plateau. The changes of surface strain at the hydroxyapatite implantation of retrieved tibiae are measured at any week after implantation when the compressive stress were applied in the direction of long axis in order to clarify the mechanical behaviors of hydroxyapatite living bone complex. The compression strength of hydroxyapatite implant crash was also determined at each week after implantation. Results revealed that the hydroxyapatite living bone complex has been proven to have sufficient flexibility such that it shows no hysteresis in stress versus strain relationship up to 200 kg of applied load. The strain pattern on the surface of hydroxyapatite implant develops quite similar to that of natural cortical bone. The material crash of hydroxyapatite implant tolerates up to 500 kg of load at 52 weeks after implantation. These characteristics suggest that it achieves normal skeletal function in the points of biomechanical properties in vivo.

We investigated the feasibility of enhancing the regeneration of skeletal tissues by augmenting bone grafts with a composite biodegradable bone graft extender material based on the polymer poly(propylene fumarate), PPF. The material was mixed with autograft and allograft and placed directly into a cylindrical metaphyseal defect made in the rat tibia. These formulations were compared to defects without any graft material, autografts, allografts and PPF alone. Nine animals were included in each group. Animals were sacrificed at 1 and 4 weeks postoperatively. Implantation sites were then evaluated using histologic and histomorphometric methods. Results of this study showed that defects did not heal in sham operated animals. In the experimental groups, there was early new woven bone formation in the autograft group with near complete healing of the defect at four weeks. When PPF was used alone, gradual ingrowth of new bone was seen. Mixing of the PPF bone graft extender with either allograft or autograft material resulted in enhancement of new bone formation with both allo‐ and autograft. However, significantly more new bone formation than in the autograft group was only seen when the PPF bone graft extender was mixed with fresh autograft. Histomorphometry corroborated these findings. Results of this study suggest that a PPF‐based material may be used to increase the volume of smaller amounts of bone grafts supporting the concept of “bone graft extenders” by application of engineered biodegradable porous scaffolds.

Procedures for studying the dynamic response of the occupant within a rear‐end impacted vehicle are presented. Most of the researches in the impact analysis were performed by experimental approach and this costs a lot of time and money. Especially, the repeatability is very hard to produce in a destructive condition. Most of all, the analytic parameters can be investigated are limited by the experimental approach. By using numerical techniques, this research employs Kane’s equation and Huston’s method to develop a simulated system with visual graphic output to observe the rear‐end impact response. According to the simulated results, at a constant seatback angle the maximum acceleration values of head and chest increased with the increasing of impact velocity. Furthermore, at a constant impact velocity the relative rotation angle of a passenger’s head to chest decreased with the increasing of initial seatback angle.

PVA‐hydrogel has excellent biocompatibility as well as preferable tribological characteristics as an artificial articular cartilage. One of the most difficult problems is the attachment of PVA‐hydrogel to the underlying bone (or metal substrate). In the present study, the micro‐mechanical attachment between the PVA‐hydrogel and metal fibre mesh was at first accomplished to obtain a composite artificial cartilage device (CACD), then the surface of fibre mesh is chemically bonded to the metal substrate (or underlying bone) by adhesive (PMMA). This method can be used to accomplish mechanical‐chemical attachment between composite artificial cartilage device and underlying bone (or metal substrate). Microstructure analysis and mechanical tests indicate that the CACD can be firmly bonded to the metal substrate (or underlying bone).