Showing papers in "Journal of Biomedical Materials Research in 1991"
TL;DR: The extent of bone-implant interface is positively correlated with an increasing roughness of the implant surface, and hydroxylapatite (HA)-coated implants with 60-70% showed signs of resorption.
Abstract: The purpose of the present study was to evaluate the influence of different surface characteristics on bone integration of titanium implants. Hollow-cylinder implants with six different surfaces were placed in the metaphyses of the tibia and femur in six miniature pigs. After 3 and 6 weeks, the implants with surrounding bone were removed and analyzed in undecalcified transverse sections. The histologic examination revealed direct bone-implant contact for all implants. However, the morphometric analyses demonstrated significant differences in the percentage of bone-implant contact, when measured in cancellous bone. Electropolished as well as the sandblasted and acid pickled (medium grit; HF/HNO3) implant surfaces had the lowest percentage of bone contact with mean values ranging between 20 and 25%. Sandblasted implants with a large grit and titanium plasma-sprayed implants demonstrated 30-40% mean bone contact. The highest extent of bone-implant interface was observed in sandblasted and acid attacked surfaces (large grit; HCl/H2SO4) with mean values of 50-60%, and hydroxylapatite (HA)-coated implants with 60-70%. However, the HA coating consistently revealed signs of resorption. It can be concluded that the extent of bone-implant interface is positively correlated with an increasing roughness of the implant surface.
1,683 citations
TL;DR: The trends in protein adsorption together with the water contact angle results and the gravimetric analysis suggest that a kind of "cooperative" water structuring around the larger PEO molecules may create an "excluded volume" of the hydrated polymer coils.
Abstract: Surfaces containing poly(ethylene oxide) (PEO) are interesting biomaterials because they exhibit low degrees of protein adsorption and cell adhesion. In this study different molecular weight PEO molecules were covalently attached to poly(ethylene terephthalate) (PET) films using cyanuric chloride chemistry. Prior to the PEO immobilization, amino groups were introduced onto the PET films by exposing them to an allylamine plasma glow discharge. The amino groups on the PET film were next activated with cyanuric chloride and then reacted with bis-amino PEO. The samples were characterized by scanning electron microscopy, water contact angle measurements, gravimetric analysis, and electron spectroscopy for chemical analysis (ESCA). The adsorption of 125I-labeled baboon fibrinogen and bovine serum albumin was studied from buffer solutions. Gravimetric analysis indicated that the films grafted with the low-molecular-weight PEO contained many more PEO molecules than the surfaces grafted with higher-molecular-weight PEO. The high-molecular-weight PEO surfaces, however, exhibited greater wettability (lower water contact angles) and less protein adsorption than the low-molecular-weight PEO surfaces. Adsorption of albumin and fibrinogen to the PEO surfaces decreased with increasing PEO molecular weight up to 3500. A further increase in molecular weight resulted in only slight decreases in protein adsorption. Protein adsorption studies as a function of buffer ionic strength suggest that there may be an ionic interaction between the protein and the allylamine surface. The trends in protein adsorption together with the water contact angle results and the gravimetric analysis suggest that a kind of "cooperative" water structuring around the larger PEO molecules may create an "excluded volume" of the hydrated polymer coils. This may be an important factor contributing to the observed low protein adsorption behavior.
621 citations
TL;DR: It is concluded that the reduction of protein adsorption at the blood contacting surface of phospholipid polymers may result in the inhibition of thrombus formation.
Abstract: Protein adsorption from human plasma was investigated on phospholipid polymers, poly (2-methacryloyloxyethyl phos-phorylcholine (MPC)-co-n-butyl methacrylate (BMA)) or glass by radioim-munoassay and immunogold labeling techniques. In the present studies the focus was to determine the composition and distribution of proteins at the surface of these materials after contact with human blood plasma. On all materials, protein adsorption was detected and included identification of albumin, IgG, fibrinogen, fibronectin, Hageman factor (factor XII), factor VIII/von Willebrand factor, high-molecular-weight kininogen (HMWK) and the complement protein C5. The amount of protein adsorbed decreased with an increase in MPC composition and appeared to adsorb to the surfaces in a uniform and evenly distributed manner. Therefore, we suggest that MPC moieties play an important role in suppression of protein adsorption. From these findings, it is concluded that the reduction of protein adsorption at the blood contacting surface of phospholipid polymers may result in the inhibition of thrombus formation.
439 citations
TL;DR: Responses of neonatal rat calvarial osteoblasts to a variety of orthopedic implant materials were examined in vitro and cell adhesion and growth were similar on nonapatitic materials.
Abstract: Responses of neonatal rat calvarial osteoblasts to a variety of orthopedic implant materials were examined in vitro. Attachment, proliferation, and collagen synthesis of a well-characterized line of osteoblasts with 316L stainless steel, Ti-6Al-4V, Co-Cr-Mo, PMMA, hydroxyapatite, borosilicate glass, and tissue culture polystyrene were studied. Cell adhesion and growth were similar on nonapatitic materials. In contrast, attachment and growth of osteoblasts were significantly lower and slower, respectively, on hydroxyapatite. Collagen synthesis per cell and relative collagen synthesis, however, were comparable on all the materials tested.
338 citations
TL;DR: Although PET and PTFE-OH supported adhesion when incubated in serum-supplemented medium, neither of these materials support adhesion with only albumin present, indicating that cell adhesion is mediated by adsorbed CAM proteins.
Abstract: The attachment, spreading, spreading rate, focal contact formation, and cytoskeletal organization of human umbilical vein endothelial cells (HUVECs) were investigated on substrates that had been covalently grafted with the cell adhesion peptides Arg-Gly-Asp (RGD) and Tyr-Ile-Gly-Ser-Arg (YIGSR). This approach was used to provide substrates that were adhesive to cells even in the absence of serum proteins and with no prior pretreatment of the surface with proteins of the cell adhesion molecule (CAM) family. This approach was used to dramatically enhance the cell-adhesiveness of substrates that were otherwise cell-nonadhesive and to improve control of cellular interactions with cell-adhesive materials by providing stably bound adhesion ligands. Glycophase glass was examined as a model cell-nonadhesive substrate prior to modification, and polyethylene terephthalate (PET) and polytetrafluoroethylene (PTFE) were examined as representative materials for biomedical applications. The peptides were surface-coupled by their N-terminal amine to surface hydroxyl moieties using tresyl chloride chemistry. Prior to peptide grafting, the PET and PTFE were surface hydroxylated to yield PET-OH and PTFE-OH. The PET-OH was less cell-adhesive and the PTFE-OH was much more cell-adhesive than the native polymers. Radioiodination of a C-terminal tyrosine residue was used to quantify the amount of peptide coupled to the surface, and these amounts were 12.1 pmol/cm2 on glycophase glass, 139 fmol/cm2 on PET-OH, and 31 fmol/cm2 on PTFE-OH. Although the glycophase glass did not support adhesion or spreading even in the presence of serum, the RGD- and YIGSR-grafted glycophase glass did support adhesion and spreading, even when the only serum protein that was included was albumin. Although PET and PTFE-OH supported adhesion when incubated in serum-supplemented medium, neither of these materials supported adhesion with only albumin present, indicating that cell adhesion is mediated by adsorbed CAM proteins. When these materials were peptide-grafted, however, extensive adhesion and spreading did occur even when only albumin was present. Since the peptide grafting is quite easily controlled and is temporally stable, while protein adsorption is quite difficult to precisely control and is temporally dynamic, peptide grafting may be advantageous over other approaches employed to improve long-term cell adhesion to biomaterials.
317 citations
301 citations
TL;DR: It was concluded that PEO of molecular weights neighboring 18,500 and higher was effective in reducing protein adsorption and cellular interactions on these surfaces.
Abstract: Polyethylene oxide (PEO) of molecular weights 5,000, 10,000, 18,500, and 100,000 g/mol was covalently grafted to surfaces of otherwise cell adhesive polyethylene terephthalate (PET) films. Analysis of these surfaces by measurement of contact angles and ESCA verified the presence of the grafted PEO. Protein adsorption assays of radiolabeled albumin and fibrinogen showed a marked reduction in adsorbed protein for the 18,500 and 100,000 molecular weight PEO coupled surfaces. Cell growth assays using human foreskin fibroblasts in culture showed that the higher-molecular-weight PEO surfaces supported cell growth to a much lower extent than the two lower-molecular-weight PEOs. Flow of whole blood over these surfaces and visualization of platelet adherence using epifluorescence video-microscopy showed very low platelet adherence only on the two higher-molecular-weight PEO coupled surfaces. Scanning electron microscopy corroborated these results. It was concluded that PEO of molecular weights neighboring 18,500 and higher was effective in reducing protein adsorption and cellular interactions on these surfaces. [on SciFinder (R)]
255 citations
TL;DR: Histological examinations revealed that hydroxylapatite and tetracalciumphosphate give rise to an excellent bone formation, while alpha-TCP and blanco titanium evoked remodeling and less bone contact.
Abstract: In order to study the interaction of calcium phosphate coatings with bone tissue, coated titanium cylinders with a standard size were implanted in dog femora. Coatings were made by plasma spraying powders of hydroxylapatite, beta-whitlockite, and tetracalciumphosphate particles. The plasma spraying process turns beta-whitlockite into alpha-TCP. Bone bonding and bone formation were evaluated by mechanical push-out tests and histological observations. Hydroxylapatite and tetracalciumphosphate coatings show an interface strength after 3 months of implantation of 34.3 +/- 6.5 MPa and 26.8 +/- 3.9 MPa, respectively, while alpha-TCP and blanco titanium lead to an interface strength of 10.0 +/- 3.5 MPa and 9.7 +/- 1.3 MPa, respectively. Histological examinations revealed that hydroxylapatite and tetracalciumphosphate give rise to an excellent bone formation, while alpha-TCP and blanco titanium evoked remodeling and less bone contact.
251 citations
TL;DR: Findings indicated that Ceravital-type glass-ceramics also form the bonelike apatite layer on its surface in the body and bond to living bone through the apatites layer.
Abstract: Previous studies on surface structural changes in vitro as well as in vivo of bioactive A-W-type glass-ceramics and Bio-glass-type glasses showed that the essential condition for glasses and glass-ceramics to bond to living bone is formation of a bonelike apatite layer on their surfaces in the body. Gross et al., however, had explained the bone-bonding mechanism of Ceravital-type apatite-containing glass-ceramic without mentioning formation of the surface apatite layer. In the present study, apatite formation on the surface of one of Ceravital-type glass-ceramics was investigated in vitro as well as in vivo. An apatite-containing glass-ceramic of the composition Na2O 5, CaO 33, SiO2 46, Ca(PO3)2 16 wt%, which was named KGS by Gross et al., was soaked in an acellular simulated body fluid which had ion concentrations almost equal to those of the human blood plasma. The same kind of glass-ceramic was implanted into a rabbit tibia. Thin-film x-ray diffraction, Fourier transform infrared reflection spectroscopy, and scanning electron microscopic observation of the surfaces of the specimens soaked in the simulated body fluid showed that Ceravital-type glass-ceramic also forms a layer of carbonate-containing hydroxyapatite of small crystallites and/or a defective structure on its surface in the fluid. Electron probe x-ray microanalysis of the interface between the glass-ceramic and the surrounding bone showed that a thin layer rich in Ca and P is present at the interface. These findings indicated that Ceravital-type glass-ceramics also form the bonelike apatite layer on its surface in the body and bond to living bone through the apatite layer.
248 citations
TL;DR: The benefits of, and the need for, a multilevel approach to evaluate and improve these plasma-sprayed ceramic-metal substrate interfaces are illustrated.
Abstract: The successful use of plasma-sprayed hydroxyapatite (HA) coatings on Ti-alloy implants for implant-to-bone fixation requires strong adherence of the ceramic coating to the underlying metal substrate. In this study, the metal-ceramic interface was evaluated using mechanical, chemical, and structural characterization methods. Evaluations of an HA-coated Ti-6A1-4V implant system using a modified short bar technique for interfacial fracture toughness determination revealed relatively low fracture toughness values. Additionally, conventional tensile bond strength testing indicated much lower values than previously reported. Using high resolution electron spectroscopic imaging, evidence of chemical bonding was revealed at the plasmasprayed HA/Ti-6AI-4V interface, though bonding was primarily due to mechanical interlock at the interface. This study illustrates the benefits of, and the need for, a multilevel approach to evaluate and improve these plasma-sprayed ceramicme tai subst rate interfaces.
242 citations
TL;DR: In this article, the calcium phosphate formation at the surface of bioactive glass was studied in vitro by means of scanning electron microscopy and energy dispersive x-ray analysis, where glass rods and grains were immersed in different aqueous solutions.
Abstract: The calcium phosphate formation at the surface of bioactive glass was studied in vitro. Glass rods and grains were immersed in different aqueous solutions and studied by means of scanning electron microscopy and energy dispersive x-ray analysis. Surface morphological changes and weight loss of corroded grains were monitored. In-depth compositional profiles were determined for rods immersed in the different solutions. The solutions used were tris-buffer (tris-hydroxymethylaminomethane + HCl), tris-buffer prepared using citric acid (tris-hydroxymethylaminomethane + C6H8O7.H2O), and a simulated body fluid, SBF, containing inorganic ions close in concentration to those in human blood plasma. It was found that the calcium phosphate formation at the surface of bioactive glass in vitro proceeds in two stages. When immersing the glass in tris or in SBF a Ca,P-rich surface layer forms. This accumulation takes place within the silica structure. Later, apatite crystals forming spherulites appear on the surface. The Ca/P-ratio of initially formed calcium phosphate was found to be about unity. It is proposed that this is due to bonding of phosphate to a silica gel. The surface is stabilized, i.e., leaching is retarded, by the rapid Ca,P-accumulation within the silica structure before apatite crystals are observed on the surface. It is proposed that the initially formed calcium phosphate is initiated within the silica gel. The crystallizing surface provides nucleation sites for extensive apatite formation on the glass surface. In the presence of citrate no Ca,P-accumulation occur at the glass surface, but soluble Ca-citrate complexes form. By comparing the weight loss during corrosion in tris with that in the calcium and phosphate containing SBF, it is possible to establish whether the glass can induce apatite formation at its surface or not.
TL;DR: Although there were no marked differences in bony reaction at the cortical level to the different implant materials, HA-coating appeared to induce more bone formation in the medullary cavity, 3 months after insertion loss of coating thickness had occurred.
Abstract: The aim of this study was to obtain more information about the bone reaction to titanium and hydroxyapatite (HA)-coated titanium implants during the first 3 months after implantation. Therefore, uncoated and coated implants were inserted into the tibia of rabbits for various implantation periods. The histological results demonstrated that although there were no marked differences in bony reaction at the cortical level to the different implant materials, HA-coating appeared to induce more bone formation in the medullary cavity. It was also noted, that 3 months after insertion loss of coating thickness had occurred.
TL;DR: The ultra-high-strength SR-PGA rods were concluded to be suitable for fixation of cancellous bone fractures, osteotomies, and epiphyseal plate fractures where the fixation is not exposed to excessive mechanical stresses and where the loads are predominantly of a shear nature.
Abstract: The ultra-high-strength, self-reinforced (SR) absorbable polymeric composites, consisting of reinforcement elements, like fibers, and of matrix polymer which have the same chemical element composition as reinforcement, were defined. A method to manufacture self-reinforced, absorbable polyglycolide (SR-PGA) rods of polyglycolide sutures (Dexon) by sintering them partially together at elevated temperature and pressure was presented. The rods with nominal diameters of 1.5 mm, 2.0 mm, 3.2 mm, and 4.5 mm showed initial bending modulus and strength values of 8-15 GPa and 220-405 MPa, respectively. Their initial shear strengths were 165-255 MPa. The smallest rods (diam. 1.5 mm) lost their mechanical strength after implantation in the subcutis of rabbits in 4-5 weeks while the thickest rods retained their strength over 8 weeks. The ultra-high-strength SR-PGA rods were concluded to be suitable for fixation of cancellous bone fractures, osteotomies, and epiphyseal plate fractures where the fixation is not exposed to excessive mechanical stresses and where the loads are predominantly of a shear nature.
TL;DR: Results suggest that β-TCP bonds to bone through microanchoring between bone and rough surface of resorbed β- TCP, an essential condition for chemical bonding between ceramics and bone tissue.
Abstract: It has been proposed that the formation of a surface apatite layer in vivo on surface active ceramics is an essential condition for chemical bonding between ceramics and bone tissue. To clarify the difference in bone-bonding mechanisms between surface active ceramics and bioresorbable ceramics, two experiments were performed using plates of dense β-tricalcium phosphate (β-TCP). First, plates of β-TCP were implanted subcutaneously in rats for 8 weeks. Surface change due to bioresorption was observed with scanning electron microscopy. Formation of the apatite layer on the surface was investigated using thin-film x-ray diffraction and Fourier transform infrared reflection spectroscopy. Second, plates of β-TCP were implanted in tibiae of rabbits for 8 and 25 weeks and subjected to the detaching test to measure bone-bonding strength. β-TCP bonded strongly to bone. Undecalcified sections of the interface of bone and β-TCP were examined with SEM-EPMA. However, by physicochemical methods, no formation of surface apatite layer was observed. These results suggest that β-TCP bonds to bone through microanchoring between bone and rough surface of resorbed β-TCP.
TL;DR: If glasses and glass-ceramics release at least Ca2+ and HSiO3- ions, this would be sufficient for them to form the Ca,P-rich layer on their surfaces in vivo, enabling them to bond directly with bone.
Abstract: An apatite- and wollastonite-containing glass-ceramic (A.W-GC) has been reported to form a tight bond with living bone through an apatite layer formed on its surface. This layer is considered to be formed by dissolution of Ca2+ and HSiO3- ions from the glass-ceramic into the surrounding body fluids. In order to confirm this proposed mechanism for the surface reaction of A.W-GC, three kinds of glass in the systems CaO-SiO2, CaO-SiO2-CaF2, and CaO-SiO2-P2O5 were implanted into the tibiae of rabbits for 3 or 8 weeks. Contact microradiography and SEM-EPMA showed that all three kinds of glass formed a Ca,P-rich layer in combination with a Si-rich layer on their surfaces within 3 weeks and formed a direct bond with bone via these layers. The detaching test, performed 8 weeks after implantation, showed that the loads required to detach the implants from the bone were almost equal for the phosphorus-free and the phosphorus-containing glasses. It was concluded that even P2O5-free CaO.SiO2 glass formed a Ca,P-rich layer on its surface and bonded tightly with living bone. If glasses and glass-ceramics release at least Ca2+ and HSiO3- ions, this would be sufficient for them to form the Ca,P-rich layer on their surfaces in vivo, enabling them to bond directly with bone.
TL;DR: Partially stabilized zirconia ceramic is being recognized among ceramics for its high strength and toughness and is possible to manufacture a 22-mm-size femoral head for low friction arthroplasty of the hip joint in association with an ultra-high-molecular-weight polyethylene socket.
Abstract: Partially stabilized zirconia ceramic is being recognized among ceramics for its high strength and toughness. With this ceramic, is possible to manufacture a 22-mm-size femoral head for low friction arthroplasty of the hip joint in association with an ultra-high-molecular-weight polyethylene socket. Wear-resistant properties of zirconia ceramic were screened on two principally different wear devices. Sterile calf bovine serum, physiological saline, and distilled water were chosen as the lubricant fluid media. Depending on the lubricant medium, the wear factor of polyethylene against zirconia ceramic counterfaces was 40 to 60% less than that against alumina ceramic counterfaces, and 5 to 10 times lower than with the SUS316L metal counterfaces. Polyethylene wear against metal was more susceptible in saline in which it had 2 to 3 times higher wear rate than with serum. On the other hand, different fluid media had little effect on polyethylene wear against ceramic counterfaces. In each set of tests, the wear factor obtained on an unidirectional wear device showed 10 to 15 times higher values, in comparison to the wear factor estimated on a reciprocating wear device.
TL;DR: SEM-investigation of the interfaces revealed that FA did not degrade while both MW and HA showed extensive degradation at 12 and 25 weeks, and the interface after push-out testing showed for the MW, HA, and Ti alloy implants to be fractured at the implant-tissue interface and for the FA to be fractures at the coating-titanium interface.
Abstract: Ceramic coatings of fluorapatite (FA), magnesiumwhitlockite (MW), and hydroxylapatite (HA), and noncoated Ti-6Al-4V alloy (Ti) implants were evaluated before and after implantation in an animal study. Cylindrical plugs were coated by plasma-spraying with FA, MW, and HA. X-ray-diffraction patterns showed for FA and HA a crystalline and for MW, an amorphous-crystalline coating structure. The plugs were implanted into the right femora and left humeri of 16 adult goats. Follow-up periods were 12 and 25 weeks. The in vivo results were evaluated using push-out tests and scanning electron microscopy. There were significant differences in push-out strengths between femur and humerus. The FA and HA implants showed significantly higher push-out strengths than the MW and Ti alloy implants, especially for the 12 week follow-up period. Furthermore, at 12 week follow-up period. Furthermore, at 12 weeks, MW showed significantly lower push-out strengths than Ti alloy. SEM-investigation of the interfaces revealed that FA did not degrade while both MW and HA showed extensive degradation at 12 and 25 weeks. In addition, the interface after push-out testing showed for the MW, HA, and Ti alloy implants to be fractured at the implant-tissue interface and for the FA to be fractured at the coating-titanium interface.
TL;DR: Bone remodeling around three different endosseous dental implant designs placed in dog mandibles was studied using radiography during lengthy periods of function and by histology after animal sacrifice, indicating that some crestal bone loss occurred for both the threaded and partially porous-coated implants.
Abstract: Bone remodeling around three different endossesous dental implant designs placed in dog mandibles was studied using radiography during lengthy periods of function and by histology after animal sacrifice. The three designs investigated were (a) threaded (c.p. titanium), (b) fully porous-coated (titanium alloy), and (c) partially porous-coated (titanium alloy). The implants were kept in function for either 32 weeks (fully porous-coated) or 73 to 77 weeks (partially porous-coated and threaded). The studies indicated that some crestal bone loss occurred for both the threaded and partially porous-coated implants while no significant bone loss was seen with fully porous-coated implants in the absence of plaque-associated infection. It is suggested that these observed differences are a result of the different stress states that develop in bone surrounding the three designs underlying the importance of implant design on bone remodeling.
TL;DR: Materials to enhance cell adhesion were synthesized by surface integration of peptide, Arg-Gly-Asp-Ser(RGDS), which is an active-site sequence of cell-adhesive proteins, which was more stable against heat treatment and pH variation than the FN-immobilized film.
Abstract: Materials to enhance cell adhesion were synthesized by surface integration of peptide, Arg-Gly-Asp-Ser(RGDS), which is an active-site sequence of cell-adhesive proteins. Polystyrene film was glow-discharged and graft-copolymerized with acrylic acid. Then the peptide was immobilized to the poly(acrylic acid) grafts by using water-soluble carbodiimide. The cell-adhesive activity of the RGDS-immobilized film increased with increasing amount of immobilized peptide, and approached the activity of fibronectin(FN)-immobilized film. The RGDS-immobilized film was more stable against heat treatment and pH variation than the FN-immobilized film. In addition, the RGDS-immobilized film enhanced cell growth more strongly than the FN-immobilized film.
TL;DR: Different commercial materials, such as polyurethane (PU), plasticized PVC (PVC), glass, Gore-tex, and Dacron, were coated with a well-characterized biomaterial (PUPA) based on polyurehane and poly(amido-amine) components and all the stable coatings showed the ability to bind as much heparin as PUPA material by itself.
Abstract: Different commercial materials, such as polyurethane (PU), plasticized PVC (PVC), glass, Gore-tex, and Dacron, were coated with a well-characterized biomaterial (PUPA) based on polyurethane and poly(amido-amine) components. Two different classes of coating were obtained due to the different characteristics of the substrates. In the case of PVC and polyurethane which are soluble in the solvent of the PUPA-coating solution, there was penetration and blending of the coating and underlying materials. In the case of glass, Gore-tex, and Dacron, which are insoluble in the solvent of the coating solution, only a superficial layer of PUPA could be obtained. The coating stability was investigated and the interaction between coating and underlying material studied by FT-IR. All the stable coatings showed the ability to bind as much heparin as PUPA material by itself.
TL;DR: A consistent repair of the articular defects was achieved with and without periosteal grafts resulting in a tissue that closely resembled hyaline articular cartilage.
Abstract: In order to find a material that would improve cartilage repair, we investigated the use of porous polylactic acid matrix (PLA) with and without periosteal grafts in large articular defects in the medial femoral condyles of 18 New Zealand white rabbit knees. The right knee defect was filled with PLA, the left defect was filled with PLA and a periosteal graft. All animals were killed at 12 weeks. PLA allowed for the de novo growth of neocartilage at the articular surface in all specimens and appeared to serve as a scaffolding for cell migration and matrix formation. Histologically, small amounts of PLA remained under the neocartilage with the majority being replaced by bone. PLA was a suitable carrier for periosteal grafts with a high graft survival rate (89%) and proliferation of a neocartilage which was thicker and more closely resembled articular cartilage than PLA alone knees. Biochemically, there was more type II collagen in the grafted knees (83%) than in the PLA alone knees (65%). Biomechanical tests of the neocartilage included equilibrium displacement, aggregate modulus, and apparent permeability. These tests were not statistically different between PLA alone and grafted knees. Comparison to normal cartilage indicated that the neocartilage was less stiff but had similar permeability. A consistent repair of the articular defects was achieved with and without periosteal grafts resulting in a tissue that closely resembled hyaline articular cartilage.
TL;DR: The in vitro cytotoxicity of nine metal cations common in dental casting alloys was evaluated using Balb/c 3T3 fibroblasts and four toxicity parameters: total protein production,3H-leucine incorporation, 3H-thymidine incorporation, and MTT-formazan production.
Abstract: The in vitro cytotoxicity of nine metal cations common in dental casting alloys was evaluated using Balb/c 3T3 fibroblasts and four toxicity parameters: total protein production, 3H-leucine incorporation, 3H-thymidine incorporation, and MTT-formazan production. Concentrations causing 50% toxicity compared to controls (TC50's) and reversibility of these effects were determined. The range of potency of the metal cations was 2-3 orders of magnitude, with Cd2+ showing the greatest potency and In3+ showing the least. Potency did not correlate with atomic weight for these metals. For each metal cation, the TC50's of the various toxicity parameters were similar in most cases. However, several cations (Cu2+, Ga3+) showed greater potency with 3H-thymidine incorporation. Reversibility of the toxic effects was observed for all cations; the effects generally became irreversible at concentrations in the range of the TC50 value for each cation. Several stimulatory effects were seen. Small but statistically significant stimulations were observed after 24 h of metal exposure for Ag1+, Au4+, Cu2+, Ga3+, and Ni2+. Residual stimulations 24 h after removal of the metal cations were observed for Au4+, Cd2+, Ni2+, and Zn2+. Stimulations always occurred at concentrations below the TC50 concentrations. This study should be useful in evaluating the potential cytotoxic effects of metal cations released from dental alloys.
TL;DR: The oxidative resistance of SPUs containing aliphatic hydrocarbon soft segments was significantly improved over the poly(tetramethylene oxide) (PTMO) based polyurethane.
Abstract: A series of segmented polyurethanes (SPUs) containing various polyol soft segments was prepared and their resistance to oxidative degradation was investigated after aging in AgNO3 solution. The SPU with the polyether soft segment showed a large reduction in mechanical strength after exposure to the oxidative environment. Surface cracking was often observed for these specimens. XPS measurements revealed that scission of the ether linkage occurs upon oxidation. The oxidative resistance of SPUs containing aliphatic hydrocarbon soft segments was significantly improved over the poly(tetramethylene oxide) (PTMO) based polyurethane.
TL;DR: Measurements made on samples prepared from cyclically stressed and unstressed cups, and on samples following oxidations in nitric acid and intralipid solutions provided sufficient data to gain more knowledge about the combined chemical and mechanical effects on PE free radicals during implantation.
Abstract: An electron spin resonance (ESR) technique is employed to determine the free radical distribution in the articulating surfaces of retrieved acetabular cups and knee-joint plateaus (retrieved after more than 6 years of implantation). Similar measurements made on samples prepared from cyclically stressed and unstressed cups, and on samples following oxidations in nitric acid and intralipid solutions provided sufficient data to gain more knowledge about the combined chemical and mechanical effects on PE free radicals during implantation. In UHMWPE free radicals are primarily initiated by gamma-ray sterilization; however, during implantation, peroxy (scission type) free radicals are formed and reach a maximum concentration level (equilibrium state) due to oxidation by chemical (hemoglobin and/or synovial fluids) environment of the joints. Subsequently, due to frictional heating and stress in the loading zones, free radical reaction is accelerated and their number is reduced only in those areas. This is consistent with the observations of a temperature rise in acetabular cups during in vitro frictional wear stress tests and in vivo telemetry observations, as reported by others. Compared with the previously reported SEM micrographs the low-free-radical regions are correlated with high-wear areas and the high-free-radical regions with the low-wear areas.
TL;DR: Cell culture techniques were used to determine the source of cytotoxic agents in a commercial BIS-GMA composite and the removal of leachable components caused a 90% decrease in toxicity compared to the nonextracted BIS -GMA samples.
Abstract: Cell culture techniques were used to determine the source of cytotoxic agents in a commercial BIS-GMA composite. The material was polymerized according to the manufacturer's directions and leachable components were removed by room temperature extraction in ethanol, chloroform, or toluene. The leachable components in the extracts were identified using infrared spectrographic analysis. Thin layer chromatographic analysis was used to determine the number of constituents. These constituents were separated by gas chromatography and then identified by mass spectrographic analysis. Succinic dehydrogenase activity and radioactive labeling with tritiated leucine were used to evaluate cell metabolism and protein synthesis, respectively. The infrared analysis of the extracts showed that the primary component was unreacted BIS-GMA. Trace amounts of 2-hydroxy-4-methoxy-benzophenone, a light stabilizer, as well as a phenyl ester of benzoic acid which was probably degraded from BIS-GMA, were detected by the mass spectrographic method. The removal of leachable components caused a 90% decrease in toxicity compared to the nonextracted BIS-GMA samples. The extracted BIS-GMA samples showed no cellular response compared to the Teflon negative control.
TL;DR: The results of this study suggest that a reconstituted type I collagen film crosslinked with cyanamide acts as a temporary barrier preventing loss of fluid and adhesion formation and is replaced after approximately 2 months with host collagen with limited inflammatory and fibrotic complications.
Abstract: Cadaver grafts, laminated metallic materials, and synthetic fabrics have been evaluated as dural substitutes. Use of cadaver tissues is limited by fear of transmission of infectious disease while use of synthetic materials is associated with implant encapsulation and foreign body reactions. The purpose of this study is to evaluate the use of collagen film as a dural substitute. Collagen films prepared from bovine skin were used to replace the dura of rabbits and histological observations were made at 16, 28, 42, and 56 days postimplantation. Controls consisted of dura that was removed and then reattached. Control dura showed no signs of inflammation or adhesion to underlying tissue at 16 and 28 days postimplantation. By 56 days postimplantation, extensive connective tissue deposition was observed in close proximity to adjacent bone as well as pia arachnoid adhesions. Implanted collagen film behaved in a similar manner to control dura showing minimal inflammatory response at all time periods. At 56 days postimplantation collagen film appeared strongly infiltrated by connective tissue cells that deposited new collagen. The results of this study suggest that a reconstituted type I collagen film crosslinked with cyanamide acts as a temporary barrier preventing loss of fluid and adhesion formation. It is replaced after approximately 2 months with host collagen with limited inflammatory and fibrotic complications. Further studies are needed to completely characterize the new connective tissue formed as well as long-term biocompatibility and functioning of a reconstituted collagen dural substitute.
TL;DR: Experimental results indicate that fibroblast seeding and bFGF coating in conjunction with a type I collagen sponge matrix facilitate early dermal and epidermal wound healing.
Abstract: Healing of large open dermal wounds is associated with decreased values of the tensile strength even up to 6 months post-wounding. Results of previous studies have shown that healing is facilitated in the presence of a type I collagen sponge by promoting deposition of newly synthesized large-diameter collagen fibers parallel to the fibers of the sponge. In this study healing is evaluated in dermal wounds treated with a collagen sponge seeded with fibroblasts or coated with basic fibroblast growth factor (bFGF). Experimental results indicate that the presence of a collagen sponge results in increased wound tensile strength and increased collagen fiber diameters in the upper dermis 15 days post-wounding in an excisional guinea pig dermal wound model. In comparison, dermal wounds treated with collagen sponges seeded with fibroblasts or coated with bFGF showed increased tensile strengths 15 days postimplantation and increased degree of reepithelialization. These results indicate that fibroblast seeding and bFGF coating in conjunction with a type I collagen sponge matrix facilitate early dermal and epidermal wound healing.
TL;DR: As oblique orientation of F has been associated with the inhibition of epithelial downgrowth, micromachined grooved surfaces of appropriate dimensions have the potential to improve the performance of percutaneous devices.
Abstract: Previous studies using light microscopy have demonstrated that micromachined grooved surfaces inhibit epithelial (E) downgrowth and affect cell orientation at the tissue/implant interface. This study investigates the ultrastructure of the epithelial and connective-tissue attachment to titanium-coated micromachined grooved, as well as smooth control, implant surfaces. V-shaped grooves, 3, 10, or 22 microns deep, were produced in silicon wafers by micromachining, replicated in epoxy resin, and coated with 50-nm titanium. These grooved, as well as smooth, titanium-coated surfaces were implanted percutaneously in the parietal area of rats and after 7 days processed for electron microscopy. The tissue preparation technique used in this study enabled us to obtain ultrathin sections with few artifacts from the area of epithelial and connective-tissue attachment. The histological observations demonstrated that E cells closely attached to, and interdigitated with, the 3-microns and 10-microns grooves. In contrast, E cells were not found inside the 22-microns-deep grooves and made contact only with the flat ridges between the grooves. As a general rule, fibroblasts (F) were oriented parallel to the long axis of the implants and produced a connective tissue capsule with 3-microns and 10-microns-deep grooved surfaces as well as smooth surfaces. On the 22-microns-deep grooved surfaces, however, F inserted obliquely into the implant. The attachment of F to the titanium surface was mediated by two zones; a thin (approximately 20 nm), amorphous, electron dense zone immediately contacting the titanium surface, and a fine fibrillar zone extending from the amorphous zone to the cell membrane. As oblique orientation of F has been associated with the inhibition of epithelial downgrowth, micromachined grooved surfaces of appropriate dimensions have the potential to improve the performance of percutaneous devices.
TL;DR: The NIR absorptivity, e, of water absorbed in a polymeric medium was found to be inversely related to the degree of hydrophilicity and hydrogen bonding capability of the polymer.
Abstract: A near infrared (NIR) method using the 5200 cm(-1) absorption of water has been employed to examine water absorbed in photopolymerized dental resins and composites in the form of 0.01-cm- to 0.15-cm-thick specimens. The concentration, c [mol L(-1)], of absorbed water in specimens of thickness t [cm] was calculated by means of Beer's law, A = e ct. A is the NIR absorbance and e is the absorptivity of absorbed water. e depends on the environment of the water molecule and it is necessary to estimate e for water in each material. Water sorption was determined gravimetrically and correlated to the absorbance in the NIR spectrum. Once the relationship between e and water content was known for a material, water sorption was determined rapidly on very thin specimens for faster equilibration. Where dissolution of the specimen occurred, the solubility behavior of the specimen was evaluated from a comparison of NIR and gravimetric measurements. The NIR absorptivity, e, of water absorbed in a polymeric medium was found to be inversely related to the degree of hydrophilicity and hydrogen bonding capability of the polymer. The presence of water clusters in a polyethylene oxide methacrylate polymer was inferred from convex-up curvature in the plot of e vs. water content.
TL;DR: Calcite is a biodegradable material that bonds to bone without a surface apatite layer and the mechanical bonding provided by the anchoring effect of the newly formed bone into the surface roughness of calcite is considered to be a major factor in calcite-bone bonding.
Abstract: Plates of calcite (CaCO3) were implanted in rabbit tibiae, and their biocompatibility and bonding ability to bone were studied. The plates were also implanted subfascially in rabbit muscle for 8 weeks, and changes on their surfaces in the body were examined. Contact microradiography and Giemsa surface stain demostrated direct bonding between calcite and bone without interpositions. The average failure load of the interface between calcite and bone was 4.11 kg, indicating an adequate strength of bonding. However, a Ca-P-rich layer, which formed on the surfaces of other bioactive ceramics in vivo, was not detected by a scanning electron microscope-electron probe x-ray microanalyzer. Scanning electron micrographs of the surface of calcite implanted subfascially for 8 weeks showed marked degradation and a rough surface. However, the surface apatite layer was not detected by thin-film x-ray diffraction analysis and Fourier transform infrared reflection spectroscopy. Calcite is a biodegradable material that bonds to bone without a surface apatite layer. The mechanical bonding provided by the anchoring effect of the newly formed bone into the surface roughness of calcite is considered to be a major factor in calcite-bone bonding.