摘要:

AbstractA biodegradable particulate composite bone cement consisting of a crosslinked gelatin matrix and tricalcium phosphate particles was implanted intraosseously in rabbits for up to 12 weeks. Cured cylindrical implants were inserted in holes drilled in the proximal tibial metaphysis. Sequential fluorochrome labeling and radiographs were done, and specimens were processed for decalcified and nondecalcified histology. At 4 weeks, the cross‐sectional diameter of the implant was slightly greater than at implantation. There was considerable dissolution of the matrix and some new bone ingrowth. At 12 weeks, the diameter was reduced to half the original diameter and bone had grown throughout the matrix. In the distal femur, freshly mixed cement was used to stabilize an osteochondral fracture. Mechanical testing of the cement‐stabilized fracture revealed a decrease in compressive strength and modulus at 4 weeks followed by an increase to greater than initial values at 12 weeks. Over time, the osteochondral fragment subsided into the underlying cement, but the subsidence did not correlate with mechanical strength. This osteochondral fracture model permits measurement of the overall material properties of a cement simultaneously weakened by resorption and reinforced by ingrowing b

ISSN:0021-9304    

DOI:10.1002/jbm.820230102

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractBiodegradable beta‐tricalcium phosphate disks (TCP) of two configurations were inserted into 15‐mm‐diameter craniotomy wounds and nontreated control sites were evaluated in 60 rabbits. There were no adverse tissue reactions and no apparent difference in the clinical appearance of the 12‐ and 24‐week implanted disks. By 36 weeks and continuing to 48 weeks, the omnidirectional TCP (OTCP) implants were degrading more rapidly than the unidirectional TCP (UTCP) implants, with degradation progressing centripetally and replacement by woven bone and maturing lamellar bone. Host‐implant interface of both TCP configurations was a bone bond without interposed soft tissue. TCP disks may be clinically useful for cranio

ISSN:0021-9304    

DOI:10.1002/jbm.820230103

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractThe brain tissue reaction to permselective polymer capsules implanted in rats was evaluated for 1 to 54 weeks. The polymer capsules were well tolerated in all animals and no recognizable neurological or behavioral deficits were associated with the implants. Necrosis at the brain/polymer interface, as assessed with Nissl stain, was not observed. Foreign body giant cells were consistently absent. Immunocytochemically identified reactive neuroglial cells showed a remarkably low‐grade tissue response to the synthetic material be yond the first 2 weeks of observation. Immunolabeled cortical neurons revealed conserved columnar arrays around the implants. Transmission electron microscopy showed a minimal degree of collagen deposition compared to implants in peripheral sites, and normal synapses within a few micrometers from the brain/polymer interface, supporting the prospect of biocompatible, immunoisolated xenografts in the central nervous syste

ISSN:0021-9304    

DOI:10.1002/jbm.820230104

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractYttrium‐oxide‐partially‐stabilized zirconia (YPSZ) belongs to a new class of ceramics exhibiting an improved toughness when compared to alumina. The toughening mechanism is related to a martensitic‐like transformation of tetragonal metastable grains into a monoclinic state occurring at the crack tip. Specific tests showed that YPSZ exhibited a high bending strength (900–1200 MPa), a low Young's modulus (200 GPa), and a high toughness (KIC= 9–10 MN/m3/2). Its average grain size of 0.5 m̈m allows a surface roughness as low as 0.008 m̈m. Sterilization or aging in saline solution at room temperature for 100 days did not affect the toughness of this material. Cylindrical YPSZ samples, manufactured by cold isostatic pressing and sintering, were implanted in the paraspinal muscles in the rat up to 12 weeks. The tissue reaction was evaluated with reference to alumina (ISO requirements) by means of quantitative histomorphometry. No significant differences were found between YPSZ and alumina for both the membrane thickness and cell distributions surrounding

ISSN:0021-9304    

DOI:10.1002/jbm.820230105

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractA study of the fracture behavior of poly‐(methyl methacrylate) (PMMA) bone cement reinforced with short ultra‐high‐molecular‐weight polyethylene (Spectra 900) fibers is presented. Linear elastic and nonlinear elastic fracture mechanics results indicate that a significant reinforcing effect is obtained at fiber contents as low as 1% by weight, but beyond that concentration a plateau value is reached and the fracture toughness becomes insensitive to fiber content. The flexural strength and modulus are apparently not improved by the incorporation of polyethylene fibers in the acrylic cement, probably because of the presence of voids, the poor mixing practice and the weakness of the fiber/ matrix interfacial bond. The present polyethylene/PMMA composite presents several advantages as compared to other composite cements, but overall the mechanical performance of this system resembles that of Kevlar 29/PMMA cement, with a few differences. Scanning electron microscopy reveals characteristic micromechanisms of energy absorption in Spectra 900/PMMA bone cement. A scheme for the strength of random fiber‐reinforced composites, which is a simple extension of the Kelly and Tyson model for the strength of unidirectional composites, is presented and discussed. Young's modulus and the fracture toughness results are discussed in the framework of existing theories. More fundamental modeling treatments are needed in terms of fracture micromechanisms to understand and optimize the various mechanical properties with respect to structural parameters and cement preparation

ISSN:0021-9304    

DOI:10.1002/jbm.820230106

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractOne aim of thisin vitroinvestigation was to determine the effect of substituting four phenols and two methacrylates with vinyl functions on the dentin bond strengths of several new experimental dentin bonding agents. Another objective was to determine the effect of postextraction age and dentin level within the tooth on tensile bond strengths of these toluene diisocyanate‐derived adhesives. Extracted third molars were divided into postextraction age groups and sectioned into three slices ∼400 m̈m thick. The four substituted phenols were: eugenol,o‐methoxyphenol,o‐chlorophenol, andp‐cresol. Substituted methacrylates with vinyl ligands were 2‐hydroxyethyl methacrylate (HEMA) and 6‐hydroxyhexyl methacrylate (HHMA). Results showed that adhesives made witho‐chlorophenol,p‐cresol, and methoxyphenol with HEMA were the best, while those made with eugenol and HHMA were the worst. The post extraction age of the tooth and the dentin depth had no consistent effect on most adhesive bond strengths which were generally around 1

ISSN:0021-9304    

DOI:10.1002/jbm.820230107

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractAn implant may release a drug either by diffusion concurrent with dissolution of the polymeric implant material without depolymerization (Type A) or by bioerosion involving depolymerization (Type B). The Type A material may induce immune response, while the erosion of Type B polymer releases fragments which could cause toxicity problems. It is proposed that a combination of the two types of polymers may attenuate the intensity of immune response and toxicity, because the presence of one in an implant of the same weight reduces the amount of the other. However, it is important to determine first, if sustained delivery may be achieved by such an implant. In this study, partially hydrolyzed poly(vinyl acetate) (PVA) and polycaprolactone (PCL) were chosen as the model Type A, and B polymers, respectively, to evaluate this objectivein vitro. Pellet discs were prepared to assess the effects of compression, proportion of PVA to PCL, acetyl content of PVA, PCL hydrolysis catalyst and drug loading, using methylene blue (MB) as a model drug. Results showed that sustained delivery could be effected, but PCL erosion did not occur as planned. Therefore, PCL served only as a passive component of the implant, while PVA was eroded with the release of MB. Consequently, it was inferred that a polymer may not be required as a passive component, which suggested the use of other compounds of known biocompatibility. Tests with insulin in a compressed solid admixture with cholesterol showed that reduction of hyperglycemia in diabetic Wistar rat could be effected reproducibly for at least 2 weeks. Thus, the present study, originally planned to test a proposed concept, indicates that many nonpolymeric materials of known biocompatibility may be suitable for drug delivery implants as well.

ISSN:0021-9304    

DOI:10.1002/jbm.820230108

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractUnderstanding how platelet activation responses are affected by polymers having varied surface physicochemical properties can lead to improved materials for vascular applications. Thein vitroresponses of human platelets were studied upon adherence to four polyurethaneureas with different soft segments, as well as to Biomer, and to Formvar. Platelets were observed by video‐enhanced light microscopy (VLM) as they adhered to polymer films. Platelets were subsequently prepared for high‐voltage transmission electron microscopy (HVEM) to view the cytoskeleton and other ultrastructural features. Scanning electron microscopy (SEM) was then used to characterize cell surface morphology and to survey platelet populations. Shape change and cytoskeletal reorganization differed on the various surfaces. The extent of shape change and cytoskeletal reorganization was related to polyurethane surface energetic properties. While the most extensive shape change was observed on the hydrophilic and polar Formvar surface, the least shape change was observed on a polyethylene oxide soft segment polyurethane with similar surface‐water energetic properties. Therefore properties other than surface‐water energetics must be involved in determining platelet responses to different classes of polymers. HVEM also showed that cytoskeletal reorganization proceeded to completion only on Formvar. Polyurethane adherent platelets, although appearing fully spread by SEM or VLM, never exhibited complete cytoskeletal reorgan

ISSN:0021-9304    

DOI:10.1002/jbm.820230109

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

摘要:

AbstractTissue biocompatibility of cellulose and its derivatives was examined in twoin vivotests, one for absorbance by living tissue and one for foreign body reaction. The samples examined were regenerated celluloses and cellulose derivatives: methylcellulose, ethyl cellulose, aminoethyl cellulose, hydroxyethyl cellulose, and cellulosic polyion complexes. Thein vivoabsorbance by living tissue was found to depend on the degree of crystallinity and the chemical structure of the sample. The foreign body reaction was relatively mild for all the samples examined, showing that cellulose can be converted to biocompatible materials by physical and/or chemical transformation.

ISSN:0021-9304    

DOI:10.1002/jbm.820230110

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY

ISSN:0021-9304    

DOI:10.1002/jbm.820230111

出版商:John Wiley&Sons, Inc.    

年代:1989

数据来源: WILEY