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Allograft and Alloplastic Bone Substitutes: A Review of Science and Technology For the Craniomaxillofacial Surgeon
Eppley, B. L., W. S. Pietrzak, et al. (2005), J Craniofac Surg 16(6): 981-989.
Abstract: Bone healing is a complex and multifactorial process. As such, there are numerous steps in the process to which intervention can be directed. This has given rise to many bone graft technologies that have been used to regenerate bone, creating, perhaps, a bewildering array of options. The options that surgeons have the most familiarity with are the ones that have been available the longest (i.e., autograft and allograft). Although useful for the widest spectrum of clinical applications, limitations of these grafts has prompted the development of new materials. Demineralized bone matrix formulations and synthetic ceramic materials are now being used with greater frequency. These biomaterials have demonstrated their usefulness in facial plastic and reconstructive surgery with their ability to augment and replace portions of the craniofacial skeleton. The purpose of this article is to describe and discuss the allograft and alloplastic bone grafting technologies so that the reader can consider each in the context of the others and gain a better appreciation for how each fits into the universe of existing and emerging treatments for bone regeneration.

Alloplastic reconstruction of large cranio-orbital defects: a comparative evaluation
Greenberg, B. M. and S. J. Schneider (2005), Ann Plast Surg 55(1): 43-51; discussion 51.
Abstract: Norian CRS, Bone Cement (Synthes CMF), and Mimix (Lorenz) have been used to reconstruct large cranio-orbital defects in 85 patients. Resorbable mesh (Macropore), used in combination in selected patients, obviates dura pulsations that have been postulated to cause fragmentation of alloplastic material. Norian is composed of monocalcium phosphate, monohydrate, alpha-tricalcium phosphate, and calcium carbonate. Admixture with NaPO4 creates dahllite, which has a higher carbonate content (4%--6%) than hydroxyapatite (0%). CRS is soluble at low pH, facilitating its resorption and replacement by bone. In contradistinction, Mimix is converted to aqueous solution at 37 degrees C, supports fibrovascular ingrowth and bony interdigitation at the implant-material surface. Forty-five adults (mean age=42 years) and 40 children (mean age=8 years) were evaluated with respect to etiology of defect, size, location, gram usage of alloplast material, type of alloplast, postoperative clinical course, and complications. A minimum of 3-year follow-up is available; 22 adult patients additionally underwent resorbable mesh reconstruction. There were 7 (8%) complications, including infection, extrusion, a sterile loculated fluid collection and fragmentation. No difference in complication rate was noted between biomaterials. Two additional patients exhibited resorption (Norian), necessitating reaugmentation. Alloplastic replacement of cranio-orbital defects has recently advanced dramatically. Bivalved cranial bone grafting with its attached morbidity and sequelae can be avoided. Resorbable mesh allows for the placement of alloplast material in larger defects while avoiding dura pulsation causing alloplast fragmentation. In avoiding titanium type reconstruction, it obviates any interference with radiologic diagnosis and radiotherapeutic modalities. Long-term results are needed to assess bone growth within alloplast and to study bone growth in alloplastic reconstructed pediatric patients.

All-optical control of microfluidic components using form birefringence
Neale, S. L., M. P. MacDonald, et al. (2005), Nat Mater 4(7): 530-3.
Abstract: The reflection and refraction of light at a dielectric interface gives rise to forces due to changes in the photon momentum. At the microscopic level, these forces are sufficient to trap and rotate microscopic objects. Such forces may have a profound impact in the emergent area of microfluidics, where there is the desire to process minimal amounts of analyte. This places stringent criteria on the ability to pump, move and mix small volumes of fluid, which will require the use of micro-components and their controlled actuation. We demonstrate the modelling, fabrication and rotation of microgears based on the principle of form birefringence. Using a geometric anisotropy (a one-dimensional photonic crystal etched into the microgear), we can fabricate microgears of known birefringence, which may be readily rotated by manipulating the input polarization in a standard optical trap. This methodology offers a new and powerful mechanism for generating a wide range of microfabricated machines, such as micropumps, that may be driven by purely optical control.

Alteration of human neuroblastoma cell morphology and neurite extension with micropatterns
Yang, I. H., C. C. Co, et al. (2005), Biomaterials 26(33): 6599-609.
Abstract: The spatial orientation of nerve cells plays a pivotal role in nerve regeneration. Here we report a new method for regulating neuronal cell morphology and guiding neurite extension on standard tissue culture dishes. Random copolymers of oligoethyleneglycol methacrylate and methacrylic acid [poly(OEGMA-co-MA)], microcontact printed on standard tissue culture dishes, resist cell attachment and remain intact in serum-containing medium for up to 2 weeks. Cell viability assay of SH-SY5Y cells demonstrated that poly(OEGMA-co-MA) on the substrate or in solution has no cytotoxic effect. When retinoic acid was added to SH-SY5Y cells, they extended neurites along the line patterns that are significantly longer than cells cultured on non-patterned culture dishes. The ability to guide neurite extension with micrometer precision is valuable for guiding directional growth of neurites and path finding of regenerating nerves.

Alteration of leukocyte motility on plasma-conditioned prosthetic biomaterial, ePTFE, via a flow-responsive cell adhesion molecule, CD43
Rosenson-Schloss, R. S., C. C. Chang, et al. (2002), J Biomed Mater Res 60(1): 8-19.
Abstract: The physiologic determinants of leukocyte migration on vascular prosthetic biomaterials remain poorly understood, despite their relevance to the control of periprosthetic infection. Using hemodynamic exposure of human polymorphonuclear leukocytes adherent to expanded polytetrafluoroethylene (ePTFE) in vitro, we investigated the role of fluid shear in regulating leukocyte migratory behavior on plasma-adsorbed, prosthetic vascular biomaterial. The presence of flow at a wall shear stress of 25 dyn/cm(2) increased the degree of leukocyte displacement along the flow direction without altering the degree of overall cell attachment. Moreover, plasma-ePTFE elicited a lower overall degree of displacement under flow in comparison with untreated ePTFE. We further probed the molecular level regulation of leukocyte migratory responses under flow through the immunocytochemical quantification of specific leukocyte adhesion molecules and determined that CD43, a cell adhesion molecule, was upregulated via flow exposure for leukocytes adherent to plasma-ePTFE, whereas basal levels of CD43 expression were not significantly altered on untreated ePTFE. When flow-exposed, adherent leukocytes were incubated in the presence of substrate immobilized anti-CD43 immunoglobulin, the degree of cell displacement along flow was found to be significantly enhanced on plasma-ePTFE. Quantification of the cell population redistribution under flow using a modified random motility model, indicated that the incorporation of anti-CD43 on plasma-ePTFE led to a significant increase (243 +/- 60%) in the cell dispersion coefficient, mu(D), whereas only a minimal increase (61 +/- 30%) was detected on non-adsorbed ePTFE. Overall, our results suggest that flow exposure can induce the migration of leukocytes adherent to prosthetic materials in a substrate-dependent manner. An important implication of our study is that, although biomaterials exposed to plasma intrinsically passivate leukocyte migration even under hemodynamic conditions, it may be possible to promote cell motility by targeting a specific, flow-responsive, adhesion molecule.

Altering the mechanics of spider silk through methanol post-spin drawing
Brooks, A. E., M. S. Creager, et al. (2005), Biomed Sci Instrum 41: 1-6.
Abstract: Spiders have evolved to produce up to seven different silks; for each silk the balance between strength and elasticity is optimized according to the silk's specific use. Amino acid motifs have been identified and predicted functions have been assigned to these motifs. In addition to understanding the underlying molecular basis for structure/function relationships, it is also necessary to understand the contribution of the spinning process to the overall mechanical properties for both native and synthetic silk fibers. It is hypothesized that the natural silk fiber is produced through a process that involves dehydration. Current artificial spinning methods attempt to reproduce the natural dehydrating conditions by pulling the newly formed fiber through a methanol (or other dehydrating solvent) bath. However, the consequences of this treatment on the mechanical properties of the artificial fiber in relation to the natural fiber are unknown. To evaluate the effect of methanol on fiber properties, mechanical testing was done on native fibers from Nephila clavipes. Single major ampullate fibers were spun either in 47% ambient humidity or drawn post-spinning through a methanol bath. A comparison of the mechanical properties of the silk fibers revealed that post-spin drawing of a single major ampullate silk fiber through a methanol bath correlates to changes in the mechanical properties of the fiber.

Alternative bearing surfaces in total hip arthroplasty
Tuli, R. and J. Parvizi (2005), Expert Rev Med Devices 2(4): 445-52.
Abstract: Total hip arthroplasty continues to be one of the most effective surgical procedures currently available. The longevity of this otherwise very successful procedure is compromised by the wear of the bearing surface. In recent years, great advances have been made in the design of bearing surfaces that poise to offer extended performance to these artificial joints. The purpose of this review is to discuss the recent technologic advances in bearing surfaces and offer an insight to the potential benefits and concerns with the alternative bearing surfaces.

Alternative management of the aging jawline and neck
Sclafani, A. P. and E. Kwak (2005), Facial Plast Surg 21(1): 47-54.
Abstract: The lower third of the face and neck have distinct changes that occur with aging. These changes can be globally and dramatically addressed with a traditional rhytidectomy. However, as the demographics of facial plastic surgery patients evolve, patients seek increasingly less invasive procedures that will result in faster recovery time and less postoperative morbidity. To accommodate this change, today's facial plastic surgeon must include less invasive procedures in the treatment strategies for the lower face and neck. Correct, patient-specific procedure selection and patient education can yield results similar to those of a traditional facelift. This article discusses options available for treatment of the lower face and neck.

Alumina ceramic as a biomaterial for use in afterloading radiation catheters for hyperthermia
Ferraro, F. T., M. Salcman, et al. (1989), Neurosurgery 25(2): 209-12; discussion 212-3.
Abstract: A major technical challenge to the use of interstitial hyperthermia in malignant brain tumors is the production of a well-defined, uniform hyperthermal field. In theory, A 915-MHz microwave antenna should allow fewer antennas to be used and cause less mechanical brain damage; however, standard radiation afterloading catheters require antennas to be 12 cm long; this is clearly impractical for intracranial use. Since alumina ceramic (Al2O3) catheters permit short microwave antennas (3-5 cm in length) to function properly in neural tissue, it is important to test the biocompatibility of alumina for use in combined interstitial microwave hyperthermia and brachytherapy. A 5-mm length of alumina catheter was implanted into the brains of 15 white rats. The animals were killed at 3, 7, 14, 28, and 56 days. Histological examination revealed only minor mechanical damage and no encapsulation until 1 month; even then, the glial wall was only a few cell layers thick. Five animals received implants and were killed at similar intervals for x-ray microanalysis with the scanning electron microscope. No migration of aluminum into the brain was detected when compared with two control animals that did not receive implants and an alumina blank. Although we measured 50% attenuation of the radiation from iridium-192 sources in alumina catheters as compared with conventional ones, alumina catheters can still be used for interstitial radiation by increasing either the activity of the seeds or the duration of treatment.

Alumina ceramic finger implants: a preliminary biomaterial and clinical evaluation
Doi, K., N. Kuwata, et al. (1984), J Hand Surg [Am] 9(5): 740-9.
Abstract: An alumina ceramic hinge-type finger prosthesis, composed of alumina ceramics and high-density polyethylene, is described. Biomaterial evaluations, including flexion-extension tolerance, stretching, twisting, extraction tests, and histologic examinations of affinity for bone, demonstrated that this implant has characteristics superior to those of previous finger implants. Eighteen proximal interphalangeal joints and 13 metacarpophalangeal joints have been replaced with this alumina ceramic finger implant. Follow-up studies (12 to 31 months) have been most encouraging with satisfactory functional recovery and no fracture or dislocation of the implants.

Alveolar ridge augmentation with a prototype trilayer membrane and various bone grafts: a histomorphometric study in baboons
Busenlechner, D., M. Kantor, et al. (2005), Clin Oral Implants Res 16(2): 220-7.
Abstract: Barrier membranes have become a standard treatment option in alveolar ridge augmentation prior to implant placement. However, non-resorbable membranes require secondary surgery and resorbable membranes show an unfavorable degradation profile. The purpose of this study was to evaluate the potential of a slowly biodegradable/bioresorbable prototype trilayer membrane (PTLM) for supporting bone regeneration in alveolar ridge augmentation. Clinically relevant cavities were made 3 months after the extraction of the first and second molars in each jaw of six baboons. Each animal was treated with four different regimens: (1) autogenous bone block (ABB) alone, (2) ABB+PTLM, (3) deproteinized bovine bone mineral (DBBM)+PTLM and (4) no treatment. After 9 months, the baboons were sacrificed and block sections of the augmented area were subjected to histologic and histomorphometric analyses. Newly formed bone areas were determined at a distance of 1, 3, 7 and 10 mm from crestal. The data showed a well-preserved ridge profile at the membrane-protected sites, whereas non-protected bone blocks and control sites underwent severe resorption resulting in knife-edge ridge profiles. Significant differences were found between ABB+PTLM and ABB (P=0.0137-0.0232). DBBM+PTLM also produced a larger bone area compared with ABB alone (P=0.0396-0.0439). No significant difference in bone area was detectable between ABB+PTLM and DBBM+PTLM (P>0.05). The present study supports the use of the slowly biodegradable/bioresorbable PTLM with autografts and DBBM for lateral ridge augmentation in this type of bone defects.

Alveolar ridge preservation at tooth extraction
Douglass, G. L. (2005), J Calif Dent Assoc 33(3): 223-31.
Abstract: The principles of guided bone regeneration, which are at the core of contemporary periodontal therapy, have evolved into the present generation of barrier membranes, which greatly improve the overall result by not requiring primary closure. The supplemental addition of calcium sulfate to the graft materials appears to accelerate the rate of vital bone formation. In the future, these procedures are likely to become less invasive and more predictable, barrier membranes may not be needed and additional materials will be available that will accelerate the formation of bone.

Ammonium hexafluorosilicate increased acid resistance of bovine enamel and dentine
Kawasaki, A., T. Suge, et al. (2005), J Mater Sci Mater Med 16(5): 461-6.
Abstract: Although diamine silver fluoride (AgF: (NH3)2AgF) stains teeth black, it is known as a very effective agent to prevent the dental caries progress. In order to find another fluoride that has a similar anticariogenic effect without changing tooth color, we prepared ammonium hexafluorosilicate (SiF: (NH4)2SiF6), in which the silver of AgF is replaced with silicon. In this study, the anticariogenic effect of SiF was evaluated using bovine teeth. Fluoride solutions, SiF, AgF, acidulated phosphate fluoride (APF), and sodium fluoride (NaF), were applied to bovine enamel and dentine blocks, and the depth of demineralization was measured after exposure to a demineralizing solution for 24 h. Also, fluoride was applied to a simulated dentine caries specimen to evaluate the caries progress-preventing ability. For the dentine specimens, mineral loss (Delta Z) was also measured with microradiography. We found that SiF treated enamel showed better acid resistance than specimens treated with NaF or APF. AgF treated enamel also showed similar acid resistance, but was stained black. SiF and AgF treated caries-affected dentine showed reduced demineralization when exposed to a demineralization solution for 24 h. Mineral loss (Delta Z) was reduced to 85% and 75%, respectively. Although the acid resistance of the SiF treated teeth was inferior to that of the AgF treated teeth, we consider that SiF has good potential as anticariogenic agent, since it increased acid resistance without changing tooth color.

An 8-year retrospective study: 1,100 patients receiving 1,557 implants using the minimally invasive hydraulic sinus condensing technique
Chen, L. and J. Cha (2005), J Periodontol 76(3): 482-91.
Abstract: BACKGROUND: For many clinicians, inadequate alveolar bone height and anatomical features of the maxillary sinus complicate sinus lift procedures and placement of endosseous implants. We present a new internal crestal approach that addresses these issues. METHODS: Sinus burs and condensers of increasing width are used in conjunction with pliable atraumatic bone grafting mixture and hydraulic pressure from a surgical handpiece. The risk of a membrane perforation is minimized when the surgeon's tactile skill is administered in a two-stage process to first loosen and then graft bone particulate under the Schneiderian membrane. Threaded implants can then be placed in the same visit and secured via primary closure. RESULTS: A retrospective investigation of 1,100 cases showed that eight implants failed and 14 required longer healing periods in patients with alveolar ridge heights varying between <1 to 5 mm. CONCLUSIONS: Our experience suggests that hydraulic sinus condensing is a predictable and minimally invasive alternative for prosthetic rehabilitation of maxillary anterior and posterior regions in the presence of anatomical restrictions to implant placement.

An active intervention on flap vasculature: flap prefabrication by pedicle implantation, delay, pre-expansion, pre-grafting, tissue engineering, biomaterials and perforators surgery
Colonna, M. R., L. Teot, et al. (2002), Ann Ital Chir 73(1): 71-4.
Abstract: The technology of flap prefabrications is a new, powerful tool in plastic and reconstructive surgery. It is based on an old idea, while applying the latest innovations in surgery. It involves any modification of a surgical flap done before its transfer to the final donor site, including surgical delay, pre-expansion, pre-grafting, the use of tissue engineering, biomaterials and perforators surgery, or the creation of a new pedicle by staged transfer of a vascular bundle. The different possibilities are discussed, with special reference to their biologic basis.

An analytical model for the dissolution of different particle size samples of Bioglass in TRIS-buffered solution
Cerruti, M. G., D. Greenspan, et al. (2005), Biomaterials 26(24): 4903-11.
Abstract: We analyzed the early stages of reactivity of three different particle size samples of Bioglass 45S5 and a bulk sample in TRIS-buffered solution at pH 8. Ion release, measured with ion-coupled plasma emission spectroscopy, and pH variations are reported. It was demonstrated that differences in the initial surface area influence the increase in pH, the rate of elemental release, and the rate of calcium phosphate reprecipitation. In particular, a thicker Ca/P layer was obtained on larger particles. The equilibrium value of Si in solution was independent of sample form and amount of sample dissolved, and was always close to the value observed when bulk silica is dissolved at pH 8. An analytical model is proposed for cation release, based on a two-step mechanism. It was found that the early stage of dissolution was nearly diffusion controlled for larger particles and bulk samples. The second stage was similar to a first-order homogeneous dissolution. The influence of sample surface area/solution volume ratio seemed to be more complex than that proposed in the early works presented in the literature. It is suggested that variation of surface area has a significant impact on the course of the dissolution.

An antibacterial surface on dental implants, based on the photocatalytic bactericidal effect
Suketa, N., T. Sawase, et al. (2005), Clin Implant Dent Relat Res 7(2): 105-11.
Abstract: BACKGROUND: It is well known that the moderately roughened surfaces of dental implants enhance direct bone-implant contact. However, rough implant surfaces, as compared to smooth surfaces, are thought to pose a higher risk of bacterial infection when exposed to the oral cavity. PURPOSE: This study was focused on evaluating the photocatalytic bactericidal effects of anatase titanium dioxide (TiO(2)) on gram-negative anaerobic bacteria known to be associated with periimplantitis. MATERIALS AND METHODS: A film of photocatalytic anatase TiO(2) was added onto the surface of commercially pure titanium disks by plasma source ion implantation (PSII) followed by annealing. The photocatalytic properties of the film were confirmed by the degradation of methylene blue. Actinobacillus actinomycetemcomitans and Fusobacterium nucleatum cells were incubated anaerobically and seeded on the disk. The disks were then exposed to ultraviolet A (UVA) illumination from black light in an anaerobic environment. After illumination, the number of viable cells was counted in terms of colony-forming units. RESULTS: The anatase TiO(2) film added by the PSII method and annealing exhibited a strong photocatalytic reaction under UVA illumination. The viability of both types of bacteria on the photocatalytic TiO(2) film was suppressed to less than 1% under UVA illumination within 120 minutes. CONCLUSION: The bactericidal effect of the TiO(2) photocatalyst is of great use for sterilizing the contaminated surface of dental implants.

An approach to the numerical quantitation of acute tissue response to biomaterials
Salthouse, T. N. and B. F. Matlaga (1975), Biomater Med Devices Artif Organs 3(1): 47-56.
Abstract: The hydrolytic enzyme activity associated with the tissue reaction to implanted polyvinyl chloride rods containing graded concentrations of an organotin stabilizer was quantitated by microphotometry of tissue sections. The procedure was more sensitive to the effects of the additive than the usual histologic evaluation. It is considered that this type of approach offers a sensitive and objective index to supplement the more subjective morphologic observations in judging the acute histotoxicity of implants.

An assessment of the effects of shell cross-linked nanoparticle size, core composition, and surface PEGylation on in vivo biodistribution
Sun, X., R. Rossin, et al. (2005), Biomacromolecules 6(5): 2541-54.
Abstract: Amphiphilic core-shell nanoparticles have drawn considerable interest in biomedical applications. The precise control over their physicochemical parameters and the ability to attach various ligands within specific domains suggest shell cross-linked (SCK) nanoparticles may be used as multi-/polyvalent scaffolds for drug delivery. In this study, the biodistribution of four SCKs, differing in size, core composition, and surface PEGylation, was evaluated. To facilitate in-vivo tracking of the SCKs, the positron-emitting radionuclide copper-64 was used. By using biodistribution and microPET imaging approaches, we found that small diameter (18 nm) SCKs possessing a polystyrene core showed the most favorable biological behavior in terms of prolonged blood retention and low liver accumulation. The data demonstrated that both core composition, which influenced the SCK flexibility and shape adaptability, and hydrodynamic diameter of the nanoparticle play important roles in the respective biodistributions. Surface modification with poly(ethylene glycol) (PEG) had no noticeable effects on SCK behavior.

An effective method for quantitative evaluation of proteins adsorbed on biomaterial surfaces
Lu, X. Y., Y. Huang, et al. (2003), J Biomed Mater Res A 66(3): 722-7.
Abstract: An effective method for the quantitative evaluation of proteins adsorbed on biomaterial surfaces has been developed. First, the kinetic behavior of a range of human fibrinogen (Fib) adsorbed onto polystyrene (PS) films was investigated by using a reflectometry interference spectroscopy setup. The specific molecular number of adsorbed proteins, N(p) was then defined. According to the definition, the numbers of Fib molecules adsorbed on PS films were calculated. An atomic force microscope (AFM) was used to scan the lateral distribution of the Fib molecules adsorbed on the PS films. From the AFM images, the practical specific molecular numbers were obtained by direct counting of the molecules. In order that the adsorbed number of Fib molecules on a unit area of the PS films could be counted easily, the solution concentration of proteins was reduced to 5 ag/mL (10(-18)g/mL). There was good consistency between the numbers calculated with the formula defined by us and the numbers counted from AFM images. Therefore, the results of the present study prove the validity of our definition of the specific molecular number of adsorbed proteins and the effectiveness of the reflectometry interference spectroscopy-based method for quantitative evaluation of adsorptive proteins.

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Last Modified: 8 February 2006