Radiation quality dependence of DNA damage induction.

Analysis of DNA fragmentation and repair in relation to radiation quality may give important information about the role of break complexity and correlated double strand breaks (DSBs). DNA fragment analysis was performed by pulsed-field gel electrophoresis after exposure to different radiation qualities. Normal human fibroblasts were irradiated with boron ions (40, 80 and 160 keV.micron-1), nitrogen ions (80, 125, 175 and 225 keV.micron-1) and neon ions (225 and 300 keV.micron-1). The amount of DNA less than 1.1 Mbp decreased with increasing linear energy transfer (LET) for all three ions. When theoretical random distributions were subtracted from the experimental data for 225 keV.micron-1 nitrogen ions in all size intervals (5-5700 kbp), there was a significant non-random distribution of DSBs for sizes up to 1-3 Mbp. This non-random distribution of breaks, probably produced by intra-track correlated DSBs, may constitute a substantial portion of the high-LET induced DSBs.

Pore diameter of more than 100 microm is not requisite for bone ingrowth in rabbits.

The optimal pore size for bone ingrowth is claimed to be 100-400 microm. With the use of a highly standardized experimental model, the present study reevaluated whether a pore size of 100 microm is the threshold value for bone ingrowth into porous structures under non-load-bearing conditions. Titanium triangle-shaped plates 250 or 500 microm thick were perforated with the use of a laser in order to create standard-sized holes ( 50, 75, 100, and 125 microm) in multiple rows. The amount of bone ingrowth through the implant holes was studied in the cancellous bone of the distal rabbit femur. Twelve weeks after implantation, detailed analysis of bone ingrowth was performed with computerized image analysis of backscattered electron imaging techniques of scanning electron microscopy. The results showed that the amount of ingrown new bone was independent of the pore size and implant thickness. The median value for bone ingrowth varied between 64 and 78%. A striking feature was the formation of secondary osteonal structures even in the smallest holes. Based on these results, there is no threshold value for new bone ingrowth in pore sizes ranging from 50 to 125 microm under non-load-bearing conditions.

Bone implants--a challenge to materials science.

The review paper discusses the conditions for obtaining in vivo a composite from a synthetic, inorganic material and collagen fibres. Bone itself is a composite containing collagen fibres and hydroxoapatite crystals. The crystal size is, however, far smaller than can be made using conventional methods of ceramics technology. The paper discusses therefore the possibilities to synthesize the apatite in a gel. The requirements of initial load bearing can be met by forming the gel on the surface of glass particle, sintered to a porous body. In the pores calcium ions react with the gel to form (= SiO)Ca+ complexes. When the phosphate concentration in the pore is high enough to exceed the solubility product of apatite, the calcium-gel complexes release the calcium and highly dispersed apatite crystallites are precipitated in the gel. These give the gel the osteoconductive properties observed for bioactive glasses. Glass compositions, which give a gel surface enough hydrated to form calcium complexes, are discussed.

Porous bioactive glass matrix in reconstruction of articular osteochondral defects.

BACKGROUND AND AIMS: This study was carried out to investigate the use of porous bioactive glass implants in promotion of articular cartilage and subchondral bone repair in large osteochondral joint defects. MATERIAL AND METHODS: Two conical osteochondral defects (top diameter 3.0-3.2 mm) were drilled into the patellar grooves of the distal femurs in the rabbit. The defects, extending (approximately 6-7 mm) from the surface of the articular cartilage to the subchondral marrow space, were reconstructed with size-matched porous conical implants made of sintered bioactive glass microspheres (microsphere diameter 250-300 microm, structural implant compression strength 20-25 MPa) using press-fit technique. The implant surface was smoothened to the level of the surrounding articular cartilage. One of the two defects in each femur was left empty to heal naturally and to serve as the control. At 8 weeks, the defect healing was analyzed with use of a semiquantitative histological grading system, histomorphometry of subchondral bone repair, back-scattered electron imaging of scanning electron microscopy (BEI-SEM), and a microindentation test for characterization for the stiffness properties of the cartilage repair tissue. RESULTS: The porous structure of the bioactive glass implants, extending from the articular defect of the patellar groove into the posterior cortex of the femur, was extensively filled by new bone. Cartilage repair varied from near-complete healing by hyaline cartilage to incomplete healing predominantly by fibrocartilage or fibrous tissue. There were, however, no statistical differences in the histological scores of repair between the glass-filled and control defects, although the sum of the averages of each category was lowest for the bioactive glass filled defects. The indentation stiffness values of all the defects were also significantly lower than that of normal cartilage on the patellar groove. CONCLUSIONS: Porous textures made by sintering bioactive glass microspheres may expand the opportunities in reconstruction of deep osteochondral defects of weight-bearing joints. The implants act mechanically as a supporting scaffold and facilitate the penetration of stromal bone marrow cells and their chondrogenic and osteogenic differentiation. Ionic properties of the bioactive glasses make the substances highly potential even as delivery systems for adjunct growth factor therapy.

A philosophy of care for a neonatal intensive care unit. Operationalization of a nursing model.

Crisis reactions, a stressful environment, infant care practices, and nurse behavior may cause difficulties in entering the natural parental role for parents of infants who are admitted to a neonatal intensive care unit (NICU). In connection with discussions in the Uppsala NICU on what constitutes good care, a philosophy of care, based on Callista Roy's adaptation model, was formulated for the purpose of providing developmentally supportive, family-centered care, and for defining good care and the professional nurse role. The philosophy describes the infant's needs and environment. Caring activities focus on support of the infant's and his parent's roles and self-concept in their progress towards independence from professional assistance. The philosophy is an essential component in the introductory program which integrates newly recruited personnel from different disciplines into the unit. It is presented as a suggestion of how a model-based philosophy of care can be formulated by operationalization of the theoretical concepts of a nursing model.

Effect of glass bioactivity on new bone development induced by demineralized bone matrix in a rat extraskeletal site.

The effects of two kinds of bioactive glass and two kinds of phosphate-free glass on new bone development induced by demineralized bone matrix (DBM) were studied in the rat abdominal muscle pouch model. After 8 weeks' implantation histomorphometric analysis revealed that the amount of new bone in DBM combined with bioactive glass was comparable to DBM without bioactive glass. DBM grafts combined with phosphate-free glass showed significantly less new bone formation. Scanning electron microscopic examination confirmed that new bone bonded to the surface of bioactive glass. The release of ions from the glass seemed to slow down after new bone had bonded to it. Exclusion of phosphate from a bioactive glass resulted in loss of ability to develop the Ca,P-rich surface layer needed for bone bonding.

Dissolution, leaching, and Al2O3 enrichment at the surface of bioactive glasses studied by solution analysis.

Five glass compositions in or near the bioactive region in the system SiO2-Na2O-CaO-P2O5-Al2O3-B2O3 were studied in vitro by immersion in Tris buffer. The Si concentration can be taken as a measure of the amount of dissolved glass, whereas the Na concentration can be used to estimate the thickness of the Si-rich (Si gel) layer. Upon immersing a bioactive glass into Tris buffer, a surface layer of a few micrometer thickness is dissolved during the first 8 h. During the first few hours of immersion, the rate of dissolution of the glass network is equal to or exceeds that of the growth of the Si-rich layer. If the glass contains Al2O3, most of the aluminum that would be released due to dissolution of the silica network is enriched in the Si-rich surface layer that forms due to leaching. Al2O3 is not only bonded by the Si gel but also interferes with formation of calcium phosphate.

Induction of new bone by allogeneic demineralized bone matrix combined to bioactive glass composite in the rat.

Allogeneic diaphyseal demineralized bone matrix (DBM) cylinders containing bioactive glass rods were implanted for 4 and 8 weeks in the abdominal muscle wall of rats. DBM without glass served as control. The results suggest that new bone induction by DBM was accelerated by the presence of bioactive glass implants. However, the bone formation induced by DBM on the glass surface was relatively small. The biocompatibility of the glass was verified by the absence of adverse cellular reactions in the interface region between glass and bone. The method used provides a simple and fast means of exploring the characteristics of potential bone substitutes.

Effect of bovine bone morphogenetic protein and bioactive glass on demineralized bone matrix grafts in the rat muscular pouch.

New bone formation induced by allogeneic demineralized bone matrix (DBM) and bone morphogenetic protein (BMP) combined with bioactive glass (BG) was studied in a rat abdominal muscle pouch model. At four weeks the amount of new bone was not influenced by DBM combined with BMP and/or bioactive glass. The mean proportional areas of new bone varied among different DBM test groups from 8.6% to 13.4%. New bone was induced in inactivated DBM samples containing BG, while no bone formation was seen in DBM samples without BG. The results indicate that bioactive glass favours bone induction in inactivated allogeneic bone matrix.

Chemical characterization of a potassium hydroxyapatite prepared by soaking in potassium chloride and carbonate solutions.

A potassium-doped synthetic apatite was prepared by soaking hydroxyapatite in potassium carbonate and potassium chloride solutions. The hydroxyapatite was prepared by firing slip cast ceramic bodies in vacuum at 1100 degrees C. The conical ceramic samples and a crushed material of this were soaked in carbonate and chloride solutions for 2, 4, 6, and 8 weeks. Potassium, calcium, and phosphate were determined by direct current plasma emission spectroscopy. The carbonate content was determined by thermogravimetric analysis and chloride titrimetrically. After 2 weeks, one potassium ion substituted one calcium ion when soaked in a carbonate solution. When soaked in the chloride solution substitution occurred to the same extent. At phosphate sites the substitution of phosphate for carbonate occurred at one sixth of the sites after 2 weeks. Chloride incorporated one half of the OH-sites after 2 weeks. After 4 weeks about one chloride ion was found in the apatite, and after 6 weeks one and a half of the OH-sites were occupied by chloride ions.