Bio-Medical Materials and Engineering - Volume 18, issue 6

Authors: Choi, Dongkil | Lee, Woojin | Park, Jinwon | Koh, Wongun

Article Type: Research Article

Abstract: In this study, poly(ethylene glycol) (PEG)-based hydrogels having different network structures were synthesized by UV-initiated photopolymerization and used for the enzyme immobilization. PEGs with different molecular weight were acrylated by derivatizing both ends with acryloyl chloride and photopolymerization of PEG-diacrylate (PEG-DA) yielded crosslinked hydrogel network within 5 seconds. Attachment of acrylate groups and gelation were confirmed by ATR/FT-IR and FT-Raman spectroscopy. Network structures of hydrogels could be easily controlled by changing the molecular weight (MW) of PEG-DA and characterized by calculating molecular weight between crosslinks and mesh size from the swelling measurement. Synthesis of hydrogels with higher MW of PEG …produced less crosslinked hydrogels having higher water content, larger value of Mc and mesh size, which resulted in enhanced mass transfer but loss of mechanical properties. For the enzyme immobilization, glucose oxidase (GOX) was immobilized inside PEG hydrogels by means of physical entrapment and covalent immobilization. Encapsulated GOX were covalently bound to PEG backbone using acryloyl-PEG-N-hydroxysuccinimide and maintained their activity over a week period without leakage. Kinetic study indicated that immobilized enzyme inside hydrogel prepared from higher MW of PEG possessed lower apparent Km (Michaelis–Menten constant) and higher activity. Show more

Keywords: Poly(ethylene glycol) hydrogel, network structures, enzyme immobilization

DOI: 10.3233/BME-2008-0551

Citation: Bio-Medical Materials and Engineering, vol. 18, no. 6, pp. 345-356, 2008

Authors: Jaya, S. | Durance, T.D.

Article Type: Research Article

Abstract: Many methods are available for developing three-dimensional porous scaffolds using various polymeric materials for tissue-engineering applications. Each has its own advantages and disadvantages. Some of the available methods and their limitations were discussed briefly. This paper focuses on the scope of novel technology called radiant energy application under vacuum for the fabrication of three-dimensional porous scaffolds for tissue engineering applications. Radiant energy application in the form of microwave under vacuum has been shown to develop and maintain the porous structure in fruits and vegetables after dehydration, which produced the microstructure similar to the freeze dried materials. Same principle of applying …radiant energy under vacuum was used on the biopolymeric gels to create tailor-made, porous scaffolds for biomedical purposes. It has many advantages over the other existing methods of scaffold fabrication. This paper also reviews the scaffolds design recently fabricated by the authors using radiant energy under vacuum. Show more

Keywords: Porous scaffold, tissue engineering, biopolymers, radiant energy, vacuum

DOI: 10.3233/BME-2008-0552

Citation: Bio-Medical Materials and Engineering, vol. 18, no. 6, pp. 357-366, 2008

Authors: Wang, C.X. | Tong, J.

Article Type: Research Article

Abstract: In the present study, nanoclay was introduced to PMMA bone cement to obtain a new formulation of bioactive PMMA cement (PMMA/HA/nanoclay). To evaluate the interfacial property of the new bioactive cement for use as a fixation agent, Brazilian disk specimens were used to study the interfacial strength of synthetic bone–cement interface. The results show that, for tensile loading, the addition of 17.5 wt% HA into PMMA cement produced a notable decrease in the fracture load, while a further addition of 0.5 wt% nanoclay slightly counteracted the decrease due to the addition of HA. The addition of 1.0 wt% nanoclay brought …the fracture load back to the same level as that of pure PMMA cement, although with the further increase of nanoclay (1.5 wt% nanoclay and 2.0 wt% nanoclay), the fracture loads decreased again. The same trend in the calculated strain energy release rates was also observed. For shear loading, however, the same trend was not observed due to the premature fracture and collapsing of the foam. This finding may be useful in the development of novel bioactive bone cements to improve the fixation of joint arthroplasty. Show more

Keywords: Bioactive bone cement, nanoclay, interfacial fracture toughness, strain energy release rate

DOI: 10.3233/BME-2008-0553

Citation: Bio-Medical Materials and Engineering, vol. 18, no. 6, pp. 367-375, 2008

Authors: Shinsako, K. | Okui, Y. | Matsuda, Y. | Kunimasa, J. | Otsuka, M.

Article Type: Research Article

Abstract: Polymethylmethacrylate (PMMA) bone cement loaded with antimicrobial agents is used for the treatment and prevention of infections in orthopaedic surgery. The use of antimicrobial-loaded bone cement allows for high local doses while avoiding systemic toxicity. The release of vancomycin (VCM) from bone cement has been reported. However, the exact mechanism behind the release is unknown. We studied the influence of bead size and polymerization time on elution, and considered the release mechanism for VCM. We used CMW Endurance Bone Cement® . Cements were prepared by mixing 6 g of VCM with 40 g of polymer, and then 10 g of …liquid monomer was added. We kneaded and shaped the preparation into spheres containing 10.7 w/w% VCM. We measured the release of VCM from PMMA beads of three different sizes. Average weights of the beads were 0.96 g (SB) (n=6), 2.86 g (MB) (n=2) and 5.65 g (LB) (n=1). Additionally, we studied beads made with different polymerization times. The polymerization time was taken as the period from the making of the beads until the start of the study, and was 15 min (B15), 20 min (B20), 60 min (B60) or 180 min (B180). The release of VCM showed a bimodal curve with a high initial release followed by a sustained release. Regarding the size of the beads, SB released 7.2%, MB released 4.3% and LB released 3.1%. Regarding polymerization time, B15 released 10.0%, B20 released 6.5%, B60 released 6.3% and B180 released 4.3%, respectively. The release of VCM from PMMA beads was influenced by bead size and polymerization time. Those beads which were smaller and had a shorter polymerization time released more VCM. Total pore volume of beads that polymerization time was 30 min after drug-release test was 1.33 times grater than that of control beads that polymerization time was one week before drug-release test. This suggested that the short polymerization time caused the beads to leak more VCM. We proposed a model with four kinds of the dissolution from bone cement. (A) Dissolution from drug particles on the cement surface. This type shows the burst effect of release curve. (B) Dissolution from micropores near the cement surface. It is responsible the grater part of the curve based on Higuchi's equation. (C) Dissolution from ink-bottle-neck-type micropores. It causes a release based on a non-Higuchi's equation. (D) No dissolution from Encapsulation micropores. It can be concluded that the release of VCM from bone cements is controlled by a combination of surface area and polymerization time. PMMA beads loaded with VCM should be used carefully in orthopaedic surgery, taking into consideration the influence of bead size and polymerization time. Show more

Keywords: Polymethylmethacrylate bone cements, vancomycin, polymerization time, porosity, Higuchi's equation

DOI: 10.3233/BME-2008-0554

Citation: Bio-Medical Materials and Engineering, vol. 18, no. 6, pp. 377-385, 2008

Authors: Zhang, Deyuan | Zhang, Zhiwei | Zi, Zhenjun | Zhang, Yanhong | Zeng, Weijun | Chu, Paul K.

Article Type: Research Article

Abstract: A nano-structured TiN/Ti coating with a total thickness of 0.9 μm was deposited on nitinol cardiac occluders using the filtered multi-arc vacuum ion plating technique at less than 300°C. The coating was composed of laminated TiN/Ti layers with thickness of about 100 nm. The cardiac occluders made of a nitinol mesh with and without a graded nano-structured titanium nitride (TiN) coating were implanted into the hearts of rams. The nickel concentration of the whole blood of the animals were measured one week, one month, three months, and six months after implantation and compared to that before operation. The nickel concentration …in the neo-endocardium covered occluders was also measured using graphite furnace atomic absorption spectrophotometry. After one week, the nickel content in the blood increased by a factor of three compared to the level before operation and decreased afterwards returning to the normal level after six months when endothelialization was complete. Statistical analyses showed that the TiN coating could mitigate nickel release into blood (P<0.01). For example, the nickel concentration released from the control increased from about 2.65±1.20 μg/kg, the normal concentration, to 7.30±1.00 μg/kg but just from 2.56±1.16 μg/kg to 4.68±1.29 μg/kg from the TiN coated occluder after 7 days. The nickel concentration in the neo-endocardium covered and TiN coated occluders reached 17.0±8.05 μg/kg in two months after implantation. In comparison, it was 31.0±5.72 μg/kg for the occluder without the TiN coating. While normal concentration of nickel in endocardium is also 2.6±1.09 μg/kg. Our results demonstrate that the graded TiN coating can significantly reduce nickel release into the endocardium (P<0.01) under in vivo conditions. Show more

Keywords: TiN coating, nickel release, nitinol, occluder

DOI: 10.3233/BME-2008-0555

Citation: Bio-Medical Materials and Engineering, vol. 18, no. 6, pp. 387-393, 2008

Authors: Schofer, Markus D. | Fuchs-Winkelmann, Susanne | Kessler-Thönes, Anja | Rudisile, Markus M. | Wack, Christina | Paletta, Jürgen R.J. | Boudriot, Ulrich

Article Type: Research Article

Abstract: Aseptic loosening is the major factor of failed arthroplasty. Among several theories the particle disease theory is commonly accepted. Different studies examined the complex interactions between wear debris and surrounding cells, especially the monocytic and osteoblastic lineage. This study was designed to elucidate the impact of cobalt–chromium–molybdenum (Co–Cr–Mo) particles on the osteoblastic differentiation and proliferation of human mesenchymal stem cells (hMSC), with respect to the disease pattern of aseptic loosening. The hMSC were incubated in the presence of Co–Cr–Mo particles in different concentrations under growth and osteoinductive conditions. Obtained cultures were analyzed, with respect to cell density and proliferation, using …CASY cell count system and Ki-67 immunostaining. Osteogenic differentiation was analyzed by fluorescence microscopy using antibodies for collagen I, alcaline phosphatase, osteocalcin and osteopontin. Additionally, scanning electron microscopy was used to analyze the localisation of Co–Cr–Mo particles in the culture system. Our findings indicate that these particles were located within the hMSC. Proliferation, as well as cell density, was diminished. The remaining cells showed increased staining of osteocalcin and osteopontin, with visible differences in deposition of these proteins, indicating a deregulation of matrix formation and differentiation respectively. Therefore, it is likely that this influence of Co–Cr–Mo particles on hMSC are involved in the disease pattern of aseptic loosening. Show more

Keywords: Human mesenchymal stem cells, wear debris, Co–Cr–Mo-particles, aseptic loosening, arthroplasty

DOI: 10.3233/BME-2008-0556

Citation: Bio-Medical Materials and Engineering, vol. 18, no. 6, pp. 395-403, 2008

Article Type: Other

Citation: Bio-Medical Materials and Engineering, vol. 18, no. 6, pp. 405-413, 2008

Article Type: Other

Citation: Bio-Medical Materials and Engineering, vol. 18, no. 6, pp. 415-416, 2008