Quality of life and productivity in nurses reporting migraine

Calcium phosphate bone cements (CPBCs) are osteotransductive, i.e. after implantation in bone they are transformed into new bone tissue. Furthermore, due to the fact that they are mouldable, their osteointegration is immediate. Their chemistry has been established previously. Some CPBCs contain amorphous calcium phosphate (ACP) and set by a sol-gel transition. The others are crystalline and can give as the reaction product dicalcium phosphate dihydrate (DCPD), calcium-deficient hydroxyapatite (CDHA), carbonated apatite (CA) or hydroxyapatite (HA). Mixed-type gypsum-DCPD cements are also described. In vivo rates of osteotransduction vary as follows: gypsum-DCPD > DCPD > CDHA approximately CA > HA. The osteotransduction of CDHA-type cements may be increased by adding dicalcium phosphate anhydrous (DCP) and/or CaCO3 to the cement powder. CPBCs can be used for healing of bone defects, bone augmentation and bone reconstruction. Incorporation of drugs like antibiotics and bone morphogenetic protein is envisaged. Load-bearing applications are allowed for CHDA-type, CA-type and HA-type CPBCs as they have a higher compressive strength than human trabecular bone (10 MPa).     

Histological, chemical, and crystallographic analysis of four calcium phosphate cements in different rabbit osseous sites

Four calcium phosphate cement formulations were implanted in the rabbit distal femoral metaphysis and middiaphysis. Chemical, crystallographic, and histological analyses were made at 2, 4, and 8 weeks after implantation. When implanted into the metaphysis, part of the brushite cement was converted into carbonated apatite by 2 weeks. Some of the brushite cement was removed by mononuclear macrophages prior to its conversion into apatite. Osteoclastlike cell mediated remodeling was predominant at 8 weeks after brushite had converted to apatite. The same histological results were seen for brushite plus calcite aggregate cement, except with calcite aggregates still present at 8 weeks. However, when implanted in the diaphysis, brushite and brushite plus calcite aggregate did not convert to another calcium phosphate phase by 4 weeks. Carbonated apatite cement implanted in the metaphysis did not transform to another calcium phosphate phase. There was no evidence of adverse foreign body reaction. Osteoclastlike cell mediated remodeling was predominant at 8 weeks. The apatite plus calcite aggregate cement implanted in the metaphysis that was not remodeled remained as poorly crystalline apatite. Calcite aggregates were still present at 8 weeks. There was no evidence of foreign body reaction. Osteoclastlike cell remodeling was predominant at 8 weeks. Response to brushite cements prior to conversion to apatite was macrophage dominated, and response to apatite cements was osteoclast dominated. Mineralogy, chemical composition, and osseous implantation site of these calcium phosphates significantly affected their in vivo host response.     

Opposing actions of BMP3 and TGF beta 1 in human bone marrow stromal cell growth and differentiation

BMP3 and TGF beta 1 were found to induce opposite effects on human bone marrow stromal cells both in cell proliferation and cell differentiation and on calcium deposition onto the extracellular matrix. Moreover, BMP3 may exert, in part, the inhibitory effect of TGF beta 1 through decreasing the affinity of TGF-beta for its receptors which are now identified in these human bone cells.     

Effects of AISI 316L corrosion products in in vitro bone formation

Rat bone marrow cells were cultured in experimental conditions that favour the proliferation and differentiation of osteoblastic cells (i.e., 2.52 x 10(-4) mol l(-1) ascorbic acid, 10(-2) mol l(-1) beta-glycerophosphate and 10(-8) mol l(-1) dexamethasone) in the absence and in the presence of stainless-steel corrosion products, for a period of 18 days. An AISI 316L stainless-steel slurry (SS) was obtained by electrochemical means and the concentrations of the major metal ions, determined by atomic absorption spectrometry, were 8.78 x 10(-3) mol l(-1) of Fe, 4.31 x 10(-3) mol l(-1) of Cr and 2.56 x 10(-3) mol l(-1) of Ni. Bone marrow cells were exposed to 0.01, 0.1 and 1% of the SS and at the end of the incubation period, control and treated cultures were evaluated by histochemical assays for the identification of the presence of alkaline phosphatase and also calcium and phosphate deposition. Cultures were further observed by scanning electron microscopy. Levels of total and ionised calcium and phosphorus in the culture media collected from control and metal exposed cell cultures were also quantified. Histochemical staining showed that control cultures presented a strong reaction for the presence of alkaline phosphatase and exhibited formation of calcium and phosphates deposits. The presence of 0.01% SS caused no detectable biological effects in these cultures, 0.1% SS impaired osteoblastic behaviour and, 1% SS resulted in cell death. In the absence of bone cells, levels of total and ionised calcium and phosphorus in the control and metal added culture medium were similar throughout the incubation period. A significant decrease in the levels of ionised calcium and phosphorus were observed in the culture medium of control cultures and also in cultures exposed to 0.01% SS after two weeks of incubation, an event related with the formation of mineral calcium phosphate deposits in these cultures. In cultures grown in the presence of 0.1 and 1% SS corrosion products, levels of calcium and phosphorus were similar to those observed in the absence of cells. Results showed that stainless-steel corrosion products above certain concentrations may disturb the normal behaviour of osteoblast-like rat bone marrow cell cultures.     

Carbonated apatite cement augmentation of pedicle screw fixation in the lumbar spine

STUDY DESIGN: Biomechanical testing with human cadaveric lumbar vertebral bodies was used to determine the utility of an injectable carbonated apatite cancellous bone cement for improving the structural performance of pedicle screws subjected to axial pull-out or transverse cyclic loading. OBJECTIVES: To ascertain whether augmentation with a carbonated apatite cement can enhance pedicle screw fixation in the lumbar spine. SUMMARY OF BACKGROUND DATA: The beneficial effects of polymethylmethacrylate augmentation on pedicle screw pull-out strength have been demonstrated. Cancellous bone cement, however, may provide an attractive alternative in this application, as it is remodelable, biocompatible, and nonexothermic. METHODS: Forty-three cadaveric lumbar vertebral bodies were instrumented with pedicle screws. In 20 of these specimens, axial pull-out strength was compared between the control screws and those augmented with cancellous bone cement. In the remaining 23 specimens, the screws were loaded in the superior-inferior direction with a peak displacement of +/- 1 mm at a frequency of 3 Hz for 5000 cycles. Three parameters were calculated from the force-versus-time data: 1) the energy dissipated, 2) the peak force at the start of the test, and 3) the peak force at the end of 5000 cycles. RESULTS: The pull-out strength of the augmented pedicles averaged 68% greater than that of the control side. In response to cyclic loading, all measures of bio-mechanical performance improved 30-63%. CONCLUSIONS: The data suggest that augmentation with this carbonated apatite cancellous bone cement can enhance immediate screw fixation.     

Stump-socket interface pressure as an aid to socket design in prostheses for trans-femoral amputees--a preliminary study

We describe the effects on cell function of treating porous bioactive glass (BG) such that its surface is a composite of carbonated hydroxyapatite and serum protein. The effects on bone cell function of porous hydroxyapatite (HA) ceramic and porous glass treated to become amorphous calcium phosphate only also were studied subsequent to their having adsorbed a serum protein layer. Substrates treated for different durations were seeded with MC3T3-E1 cells and cultured for 3-17 days. Whereas cells seeded on any substrates, BG and HA produced collagen types I and III, bone sialoprotein, and osteopontin, there were significant differences between HA and BG, and among the various surface conditions created on BG. Covering the glass surface with hydroxyapatite and serum protein enhanced expression of high alkaline phosphatase activity, high rates of cell proliferation, and production of mineralized extracellular matrix. The enhancement may be due to the adsorption of a high quantity of fibronectin from the serum onto the reacted bioactive glass surface.     

Restoration of pedicle screw fixation with an in situ setting calcium phosphate cement

STUDY DESIGN: Pedicle screws were pulled out of human cadaveric vertebrae before and after augmentation with polymethylmethacrylate or in situ-setting calcium phosphate cement. The fixation strength of screws augmented with calcium phosphate cement was compared with that of screws augmented with polymethylmethacrylate. OBJECTIVES: To determine whether a new in situ-setting calcium phosphate cement might be suitable for augmenting the fixation of pedicle screws. The principle objective was to compare the pull-out resistance of screws augmented with calcium phosphate cement with the pull-out behavior of screws augmented with polymethylmethacrylate. Polymethylmethacrylate augmentation was chosen as the standard because of its current clinical use. Five types of screws were tested to determine whether screw design had an effect on the efficacy of augmentation. SUMMARY OF BACKGROUND DATA: Although many factors affect the pull-out resistance of pedicle screws, a key determinant of their performance is the strength of their attachment to the spine. In elderly, osteopenic patients, the screw-bone interface is especially at risk for stripping during insertion or pull-out after surgery. In these patients, polymethylmethacrylate has been used to augment pedicle screw fixation, although its use is not without risk. In situ-setting calcium phosphate cements may provide an alternative to polymethylmethacrylate in this application. Like polymethylmethacrylate, calcium phosphate cements can be injected into the prepared screw hole. They have the added advantage of being resorbed and replaced during healing and normal bone remodeling. METHODS: Thirty human lower lumbar vertebrae (L3-L5) were implanted bilaterally with one of five types of pedicle screws (n = 6 for each screw type). The screws were pulled out 3.0 mm at 0.25 mm/sec with a servohydraulic materials testing machine. The 3.0-mm pull-out distance, which was slightly longer than one thread pitch, was designed to strip the screw-bone interface but to leave the pedicle otherwise intact. After the initial testing, the screws in each vertebrae were removed, and the screw tracks were filled with 2.0 cc of polymethylmethacrylate (one side) or calcium phosphate cement (contralateral side). After augmentation, the screws were reinserted, and the cements were allowed to harden for 24 hours. Postaugmentation testing followed the protocols for preaugmentation testing, and the pull-out resistance of screws augmented with calcium phosphate cement was compared with the pull-out resistance of screws augmented with polymethylmethacrylate. RESULTS: Mechanically, calcium phosphate cement compared favorably with polymethylmethacrylate for augmenting pedicle screws. Both restored the strength of the screw-bone interface: across all screw types, the average increase in pull-out strength was 147% with polymethylmethacrylate augmentation and 102% with calcium phosphate cement. There were no significant differences because of screw type with either type of augmentation. CONCLUSIONS: The in situ-setting calcium phosphate cement investigated in this study compared favorably with polymethylmethacrylate in a single-cycle, pull-out test of augmented pedicle screws in senile trabecular bone. With further evaluation, this cement may offer an alternative to polymethylmethacrylate for the enhancement of pedicle screw fixation clinically.     

Feasibility study of a natural crosslinking reagent for biological tissue fixation

The hardening properties of calcium phosphate cements in the CaHPO4-alpha-Ca3(PO4)2 (DCP-alpha-TCP) system have been investigated with interest focused on the compressive strength and microstructure development. Previous studies have shown that the addition of CaCO3(CC) leads to a modification of the calcium-deficient apatite structure of the reaction product, which results in a material more similar to the apatite in bone mineral. The addition of 10% w/w of CC to the initial DCP-alpha-TCP powder mixture resulted, with time, in a retardation of the development of compressive strength. However, the optimum compressive strength reached values up to 40% higher than CC-free samples. This retarding effect also has been monitored as a function of the calcium to phosphorus (Ca/P) ratio of the DCP and alpha-TCP mixture, showing the importance of the final cement properties of the relative quantities of the reactants in the mixture.     

Formation of hydroxyapatite in new calcium phosphate cements

Tetracalcium phosphate (TTCP) has been shown previously to be an essential component of self-setting calcium phosphate cements that form hydroxyapatite (HA) as the only end-product. We report herein on a new self-setting calcium phosphate cement that does not contain TTCP. These cements consist of dicalcium phosphate anhydrous (DCPA), dicalcium phosphate dihydrate (DCPD), alpha-tricalcium phosphate, or amorphous calcium phosphate and, as an additional source of calcium, calcium hydroxide or calcium carbonate. These cements require the use of a phosphate (0.2 moll(-1) or higher) solution or a high pH solution as the cement liquid. The cements harden in relatively short time (5-30 min) and form HA as the dominant end-product in 24 h. The diametral tensile strengths of the 24-h samples are in the range of 0.2 to 7.5 MPa. Results from X-ray diffraction studies suggest that the cement setting is caused by rapid HA formation induced by the high phosphate concentration of the cement liquid. Because DCPA and DCPD are highly soluble at pH values above 12.7, which is the pK3 of phosphoric acid, high phosphate concentration in the slurry solution was also attainable by using a highly alkaline solution as the cement liquid. The physicochemical properties of these cements are comparable to those of TTCP-containing cements, and the new cements may be expected to have in vivo characteristics similar to those of TTCP-containing cements as well.     

Proliferation and differentiation of human trabecular osteoblastic cells on hydroxyapatite

In order to evaluate whether human osteoblastic cells differentiate normally on hydroxyapatite, we have compared the adhesion, proliferation, and differentiation of human trabecular (HT) osteoblastic cells on synthetic-dense hydroxyapatite and on standard plastic culture. We show here that initial HT cell attachment was 4-fold lower on hydroxyapatite than on plastic after 4 h of culture, and that normal cell attachment on hydroxyapatite was restored after 18 h of culture. HT cell proliferation was similar on the two substrates at 2-8 days of culture, but was lower on hydroxyapatite compared to plastic after 15 and 28 days of culture, as evaluated by DNA synthesis or cell number. HT cells cultured on both substrates produced an abundant extracellular matrix which immunostained for Type I collagen. The levels of carboxyterminal propeptide of Type I procollagen (P1CP) in the medium were lower in HT cell cultures on hydroxyapatite than on plastic. In addition, (3H)-proline incorporation into matrix proteins and the mean thickness of matrix layers were 52% and 26% lower, respectively, on hydroxyapatite compared to plastic after 4 weeks of culture, indicating that the total collagenous matrix synthesized by HT cells was lower on hydroxyapatite. However, (3H)-proline and calcium uptake expressed per cell was higher on hydroxyapatite than on plastic. The results show that human osteoblastic cells attach, proliferate, and differentiate on dense hydroxyapatite with a sequence similar to that of plastic. However, the growth of human osteoblastic cells is lower on hydroxyapatite in long-term culture, which results in a reduced amount of extracellular matrix, although matrix production per cell may be increased.     

Human natural killer cell development from bone marrow progenitors: analysis of phenotype, cytotoxicity and growth

We have developed a culture system allowing for generation of NK cells from human CD34+ bone marrow progenitors. The appearance of NK cells expressing CD56+, CD3- phenotype and large granular lymphocyte morphology was observed after 2-3 weeks of culture with IL-2. The NK cell appearance coincided with development of lytic activity. NK cells generated in bone marrow cultures proliferated actively (expansion index ranged from 2- to 200-fold). The phenotype of NK cells generated from CD34+ bone marrow deviated from peripheral blood NK cells in that a lower percentage of the former cells expressed CD16, CD2, CD7, and CD8 antigens. NK cells were also generated from CD34+ populations depleted of the CD34+, CD33+ subset indicating that myeloid-committed progenitors are not required for NK cell development. The dose of IL-2 was not important for generation of NK cells; however, only high doses of IL-2 supported development of optimal NK cell cytotoxic potential. Addition of TNF-alpha facilitated IL-2-dependent NK cell generation. These data showed that NK cells can develop from early bone marrow progenitors and that this system may be instrumental in studies on NK cell lineage and differentiation.     

Metabolic trafficking through astrocytic gap junctions

BACKGROUND: Protocols that incorporate donor-specific cell infusions using bone marrow, spleen, or blood transfusion continue to enhance allograft survival and often lead to tolerance in experimental models. Clinical benefits from these modalities have not been as striking, leading to ongoing study in this field. We have explored culture techniques for the in vitro selection and development of cellular effectors capable of enhancing allograft survival. METHODS: Rat bone marrow or spleen cells cultured under a variety of conditions were screened for suppressor function. Bone marrow cells, nonadherent to plastic, cultured for 7 days with granulocyte-macrophage colony-stimulating factor, lipopolysaccharide, and with or without splenocytes were found to contain predominantly myeloid lineage cells and had the ability to suppress phytohemagglutinin or mixed lymphocyte reaction-induced splenocyte proliferation. Standard donor-specific peripheral blood transfusion was compared with cultured donor-specific bone marrow cells, splenocytes, or marrow cells cultured with splenocytes (cocultured) administered intravenously at 1 x 10(7) cells/kg the day before an ACI to Lewis heterotopic heart transplant. Cyclosporine was administered at 10 mg/kg on day -1 and 2.5 mg/kg on days 0-6 relative to transplantation. RESULTS: Mean allograft survival in cyclosporine-treated animals was 8.5 days without and 16.6 days with a donor-specific blood transfusion. Cocultured cells extended allograft survival (39.5 days), whereas bone marrow or splenocytes cultured alone did not. With Percoll gradient separation, two predominant culture subfractions, one with potent suppressor function and another with stimulator function, were identified. Flow cytometric analysis showed mixed populations enriched for macrophages but also including dendritic cells in both subfractions. The suppressive fraction extended allograft survival to 20.8 days and the stimulatory fraction was less effective, yet remixing of both fractions regained the full allograft survival advantage. CONCLUSIONS: In this model, the coculture of bone marrow cells and splenocytes with granulocyte-macrophage colony-stimulating factor and lipopolysaccharide produced functionally divergent subpopulations that synergistically enhanced allograft survival. The development of cellular effectors with enhanced ability to prolong allograft survival using in vitro culture techniques is possible, and provides a new therapeutic option in the use of cell infusion-based therapies.     

Norian SRS cement augmentation in hip fracture treatment. Laboratory and initial clinical results

Bone quality, initial fracture displacement, severity of fracture comminution, accuracy of fracture reduction, and the placement of the internal fixation device are important factors that affect fixation stability. New high strength cements that are susceptible to remodeling and replacement for fracture fixation may lead to improved clinical outcome in the treatment of hip fractures. Norian SRS is an injectable, fast setting cement that cures in vivo to form an osteoconductive carbonated apatite of high compressive strength (55 MPa) with chemical and physical characteristics similar to the mineral phase of bone. It can be used as a space filling internal fixation device to facilitate the geometric reconstruction, load transfer, and healing of bone with defects and/or fractures in regions of cancellous bone. Furthermore, this cement can improve the mechanical holding strength of conventional fixation devices. Use of this material potentially could improve fracture stability, retain anatomy during fracture healing and improve hip function, thus achieving better clinical outcomes. In vivo animal studies have shown the material's biocompatibility, and cadaveric studies have shown the biomechanical advantage of its use in hip fractures. Initial clinical experience (in 52 femoral neck fractures and 39 intertrochanteric fractures) showed the potential clinical use of this innovative cement in the treatment of hip fractures.     

Isolation and chondrocytic differentiation of equine bone marrow-derived mesenchymal stem cells

OBJECTIVE: To isolate mesenchymal stem cells from adult horses and determine specific monolayer culture conditions required to enhance biochemically and phenotypically defined chondrocytic differentiation. ANIMALS: 2 adult horse bone marrow donors without skeletal or hematologic abnormalities. PROCEDURE: Bone marrow was aspirated from the sternebra, and mesenchymal stem cells were isolated by centrifugation and cultured in monolayers. Subcultures were established in 24-well plates on day 13. Culture medium was harvested every 2 days, and culture of 12 of the 24 wells was terminated on day 6 and of the remaining wells on day 12. Medium proteoglycan content was determined for all samples, and proteoglycan monomeric size was determined for pooled samples from days 2-6 and 8-12. Total nucleated cell numbers were determined at culture termination on days 6 and 12. Histologic, histochemical, and collagen immunohistochemical analyses of multiwell chamber slides harvested on day 6 or 12 were performed. RESULTS: Mesenchymal cells were an abundant cellular constituent of bone marrow aspirates, and separation of hematopoietic elements was achieved by centrifugation and delayed medium exchange. The remaining mesenchymal stem cells progressed from large, spindyloid, fibroblastic-appearing cells to a rounder shaped cell which formed colony plaques; isolated cells remained more spindyloid. Mesenchymal cell transformation toward a chondrocytic phenotype was verified by a shift in expression from collagen type I to type II, and an increase in quantity and molecular size of proteoglycans synthesized over time. CONCLUSIONS: Mesenchymal stem cells obtained from adult horses have the capacity to undergo chondrogenic differentiation in monolayer cultures and may provide a locally recruitable or transplantable autogenous cell source for articular cartilage repair.     

Acidosis and bone

Acidosis has important effects on the bone mineral which can be investigated utilizing neonatal mouse calvariae in organ culture. When calvariae are cultured for 3 h in physiologically acidic medium produced by a reduction of the bicarbonate concentration, a model of acute metabolic acidosis, there is net calcium efflux from bone in addition to net proton influx into bone which lessens the severity of the acidosis. Utilizing a high resolution scanning ion microprobe to study the bone during acidosis we have found that the protons exchange for sodium and potassium on the bone surface. In acute experiments the calcium efflux is the result of mobilization of carbonated apatite through an alteration in the physicochemical driving forces for bone mineral accretion and dissolution. In the more chronic cultures (greater than 48 h) metabolic acidosis induces calcium efflux by stimulating osteoclastic bone resorption and inhibiting osteoblastic bone formation. When calvariae are cultured for 3 h in acidic medium produced by an increase in the partial pressure of carbon dioxide, a model of respiratory acidosis, there is also calcium efflux; however, at the same decrement in pH the net flux is far less than that observed during metabolic acidosis. During acute respiratory acidosis there is no measurable influx of protons into bone and during chronic studies there is no measurable calcium efflux.     

Sequence-related behaviour of transmembrane domains from class I receptor tyrosine kinases

The purpose of this study was to investigate the effects of 316L stainless steel (SS) corrosion products on the in vitro biomineralization process, because tissue necrosis, bone loss, impaired bone mineralization, and loosening of orthopedic implants are associated with ions and debris resulting from biodegradation. Rat bone marrow cells were cultured in experimental conditions that favored the proliferation and differentiation of osteoblastic cells and were exposed to SS corrosion products obtained by electrochemical means for periods ranging from 1 to 21 days. Quantification of total and ionized Ca and P, as well as Fe, Cr, and Ni, ions in the culture media of control and metal added cultures during the incubation period was performed to study the influence of corrosion products on the Ca and P consumption that occurs during the mineralization process. Control cultures and metal effects on cultures were evaluated concerning DNA content, enzymatic reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), and alkaline phosphatase (ALP) activity. Histochemical detection of ALP, Ca, and phosphate deposition, and examination of the cultures by scanning and transmission electron microscopy (SEM and TEM) were also performed. The presence of SS corrosion products resulted in impairment of the normal behavior of rat bone marrow cultures. Levels of Cr and Ni in the medium of cultures exposed to 316L SS corrosion products decreased throughout the incubation period, suggesting a regular deposition of these species; these results were supported by TEM observation of the cultures. Cultures exposed to the corrosion products presented lower DNA content, MTT reduction, and ALP activity and failed to form mineralized areas. These cultures showed negative staining on histochemical reactions for the identification of calcium and phosphate deposition and SEM and TEM examination did not show mineral globular structures or mineralization foci, respectively, which is characteristic of cultures grown in control conditions. These results suggest that metal ions associated with 316L SS are toxic to osteogenic cells, affecting their proliferation and differentiation.     

Nanobacteria: an alternative mechanism for pathogenic intra- and extracellular calcification and stone formation

Calcium phosphate is deposited in many diseases, but formation mechanisms remain speculative. Nanobacteria are the smallest cell-walled bacteria, only recently discovered in human and cow blood and commercial cell culture serum. In this study, we identified with energy-dispersive x-ray microanalysis and chemical analysis that all growth phases of nanobacteria produce biogenic apatite on their cell envelope. Fourier transform IR spectroscopy revealed the mineral as carbonate apatite. The biomineralization in cell culture media resulted in biofilms and mineral aggregates closely resembling those found in tissue calcification and kidney stones. In nanobacteria-infected fibroblasts, electron microscopy revealed intra- and extracellular acicular crystal deposits, stainable with von Kossa staining and resembling calcospherules found in pathological calcification. Previous models for stone formation have led to an hypothesis that elevated pH due to urease and/or alkaline phosphatase activity is a lithogenic factor. Our results indicate that carbonate apatite can be formed without these factors at pH 7.4, at physiological phosphate and calcium concentrations. Nanobacteria can produce apatite in media mimicking tissue fluids and glomerular filtrate and provide a unique model for in vitro studies on calcification.     

Bone transplantation and bone replacement materials

There is a growing need for immediately available material with appropriate qualities for reconstruction of large bone defects. Autologous spongy bone grafts are optimal as to biocompatibility, but are in short supply. Allogenic and xenogenic bone grafts evoke an immunological reaction after implantation and are not biocompatible. In the last thirty years ceramic implants and composites have been developed for bone substitution. New calcium phosphate bone substitutes undergo processes of resorption and precipitation of carbonate apatite that play a part in formation of new bone. These materials are easy to use because of their pastelike consistence. Resorption properties are influenced by particle size, crystallinity and composition. So far, no serious adverse reactions were reported. More clinical experience is necessary especially with composites and combinations with antibiotics, bone growth factors and collagen, to specify the place of these modern calcium phosphates in bone replacement and bone substitution.     

Are rotors at the heart of all biological motors?

A cell culture system for biocompatibility testing of hip implant materials is described. Human bone marrow cells have been chosen because these cells are in direct contact with the biomaterial after implantation in situ. The sensitivity of this method is evaluated for materials which are already being used as implants in humans and animal, e.g., hydroxyapatite (HA) ceramic, pure titanium, and ultra-high-molecular-weight polyethylene (UHMWPE). As indicative parameters of biocompatibility primary cell adherence, cell number, cell proliferation, production of extracellular matrix, cell vitality, and cell differentiation are described. After 2 weeks in culture, obvious differences between the biomaterials with respect to the indicative parameters could be observed. Cell numbers were greatest on the HA specimens. In the case of titanium alloys, we observed a decreased number of cells. The production of extracellular matrix was high for the HA ceramics but reduced for titanium specimens. The polymers allowed only a few adherent cells and showed no signs of extracellular matrix production. The results can be correlated astonishingly well to animal experiments and clinical experiences. Therefore, we suggest that this cell culture system seems to be a useful tool for biocompatibility testing of bone implantation materials. It also helps reduce animal experiments. With the help of flow cytophotometry, we analyzed the influence of biomaterials on large numbers of cells with respect to differentiation. There were similar populations of T cells and monocytes on all specimens tested. Extended B-cell and granulocyte populations, however, were observed with titanium and UHMWPE. Most osteocalcin-containing cells adhered to the HA ceramics.