Biomaterials.info - Resources for Engineers

Record 2101 to 2120

Fracture of fully hydroxyapatite-coated titanium femoral stem of a total hip replacement--a report of 3 cases
Sharma, D. K., S. Brooks, et al. (2004), Acta Orthop Scand 75(6): 768-71.

Fracture toughness testing of biomaterials using a mini-short rod specimen design
Pilliar, R. M., R. Vowles, et al. (1987), J Biomed Mater Res 21(1): 145-54.

Free orbital fat graft to prevent porous polyethylene orbital implant exposure in patients with retinoblastoma
Kim, N. J., H. K. Choung, et al. (2005), Ophthal Plast Reconstr Surg 21(4): 253-8.
Abstract: PURPOSE: To determine if porous polyethylene orbital implant (Medpor) exposure can be prevented in retinoblastoma patients when the implant is placed in combination with a free orbital fat graft over the anterior surface of the implant. METHODS: Free orbital fat grafts were performed after enucleation and Medpor implantation, and results were compared with patients who underwent conventional enucleation and Medpor implantation without an orbital fat graft. RESULTS: Although implant exposure occurred in 13 of 39 eyes (33.3%) that had conventional enucleation and Medpor implantation, exposure did not develop in any of the 38 eyes that had the combined procedure with a free orbital fat graft. CONCLUSIONS: These findings suggest that a free orbital fat graft is a simple, effective way to prevent orbital implant exposure in patients requiring enucleation and Medpor implantation.

Freeze drying of biomaterials for the medical practice
Mladenov, D. A., T. D. Tsvetkov, et al. (1993), Cryobiology 30(3): 335-48.
Abstract: Experimentally determined thermophysical characteristics of the new antifibrinolytic bacteriostatic biomedical preparation CAPROCOL are reported. Experimental and theoretical temperature histories at selected locations in a sample of CAPROCOL undergoing freeze drying are compared. The advance of the moving phase interface is also predicted.

Frequency dependent hysteresis of silicone and latex mock arteries used in stent testing
Rajesh, R., E. R. Strope, et al. (2005), Biomed Sci Instrum 41: 163-8.
Abstract: Mock arteries also called as mock vessels are one of the best alternatives available to researchers in evaluating the mechanical characteristics and durability of intravascular medical products without having to use animal and human clinical studies. The behavior of mock arteries depends on the frequency of loading. This makes it essential to evaluate and analyze the compliance and hysteresis of the mock arteries at different frequencies. Hysteresis, the difference in the pressure-volume curve between the loading cycle and the unloading cycle, plays an important role in determining the mechanical properties of the mock arteries. Six each of silicone and latex mock arteries were tested for this study. Three silicone and three latex mock arteries were tested at room temperature for dynamic internal compliance, and the remaining three each of silicone and latex mock arteries were soaked in distilled water at 37 degrees C for 36 hours and then compliance tested using a dynamic compliance tester. All arteries were tested at four different frequencies: 72, 500, 1000, and 1500 beats per minute.

From a marketing perspective: where are the future market opportunities in biomaterials?
Mattox, K. (1990), Clin Mater 5(2-4): 319-24.
Abstract: Europe is becoming a center for the development of biomaterials, as the industry becomes increasingly 'globalized'. From a materials perspective, it is clear that all the activity in the biomaterials/medical device industry is in polymers, and bioabsorbable polymers represent a significant market opportunity. To make profits in biomedical polymers, a chemical company must participate in the 'value added chain', whereby the supplier of the chemical (polymer) participates in the profits of the sale to the end-user.

From concept to patient--biomaterials solutions to medical problems
Bonfield, W. (2004), Med J Malaysia 59 Suppl B: 1.

From hydrocolloids to high specific surface area porous supports for catalysis
Valentin, R., K. Molvinger, et al. (2005), Biomacromolecules 6(5): 2785-92.
Abstract: Polysaccharide hydrogels are effective supports for heterogeneous catalysts. Their use in solvents different from water has been hampered by their instability upon drying. While the freeze-drying process or air-drying of hydrocolloid gels led to compact solids with a low surface area, drying the gel in CO2 beyond the critical point provided mesoporous materials with a high specific surface area. Their effectiveness as a support for catalysis was exemplified in the reaction of substitution of an allyl carbonate with morpholine catalyzed by the hydrosoluble Pd(TPPTS)3 complex. The influence of water on the catalytic activity and the properties of the support was evidenced.

From past to present and future is today: from inert to multifunctional biomaterials
Ashammakhi, N. and P. Tormala (2004), J Craniofac Surg 15(6): 897.

From self-organizing polymers to nanohybrid and biomaterials
Forster, S. and T. Plantenberg (2002), Angew Chem Int Ed Engl 41(5): 689-714.
Abstract: Block copolymers form a large number of superlattices with characteristic dimensions in the range of a few nanometers up to several micrometers by self-organization. The interplay of supramolecular physics and chemistry opens up new approaches to the production of inorganic, organic, and biological structures and to their integration into functional units. Possible applications in the fields of materials science and molecular biology are being investigated. Block copolymers find numerous applications from the production of inorganic nanoparticles (metals, semiconductors, magnets) and mesoporous materials up to take-up/release systems in chemo- and gene therapy.

From stem cells to insulin-producing cells: towards a bioartificial endocrine pancreas
Roche, E., A. Santana, et al. (2005), Panminerva Med 47(1): 39-51.
Abstract: The total absence or low production of insulin by beta-cells avoids a proper control of glycemia forcing diabetic people to daily insulin injection for survival. Islet transplantation represents a hallmark in the cure of diabetes and has been successfully applied to more than 400 patients, resulting in insulin independency for periods longer than 4 years. However, transplantation trials for diabetes have to face the scarcity of islets from cadaveric donors. Therefore, the finding of renewable sources of cells could circumvent this problem. In this respect, embryonic or adult stem cells are representing an interesting alternative. Stem cells display robust proliferation and the plasticity to differentiate to other cell types, including insulin-containing cells. The current therapeutical use in the future of bioengineered insulin-secreting cells derived from stem cells needs at present to fulfill several criteria. These criteria concern to the type of stem cell to be used as starting biomaterial (embryonic or adult), the in vitro differentiation protocol applied, the functional phenotype reached for the final cell product and the transplantation associated problems (likely immune rejection and tumor formation). This review will try to focus on these different aspects in order to emphasize in the key points to consider for designing unified strategies for diabetes cell therapy.

From the Tissue Engineering and Biomaterials Symposium of the XIe Entretiens du Centre Jacques Cartier held in Lyon in December 1998
Germain, L., O. Damour, et al. (2000), Med Biol Eng Comput 38(2): 204.

From wooden limbs to biomaterial organs: the ethics of organ replacement and artificial organs
Kielstein, R. and H. M. Sass (1995), Artif Organs 19(5): 475-80.
Abstract: This paper discussed issues of ethical assessment and moral concern associated with organ replacement and physical enhancement: research, allocation, organ donation, artificial organs, xenografts, biomaterials, and neuromaterials. While emphasizing the medical and moral benefits over associated risks, it calls for a better integration of moral assessment into technology assessment and for the establishment of a cross-cultural and interdisciplinary International Ethics Committee for Organ Replacement Therapy.

FTIR/ATR for protein adsorption to biomaterial surfaces
Chittur, K. K. (1998), Biomaterials 19(4-5): 357-69.
Abstract: It is now well accepted that the initial rapid adsorption of blood proteins to biomaterial surfaces is important in the long-term performance of the implant. Cells that interact with the implant will be reacting to a layer (single or multiple) of adsorbed protein. The parameters of importance in a study of protein adsorption to surfaces of biomaterial interest include total amounts of different adsorbed proteins and the conformation and orientation of these adsorbed proteins. Researchers have developed a number of techniques with which we can now address all these questions. In this paper, we have discussed how Fourier transform infrared (FTIR) attenuated total internal reflection (ATR) techniques can be used for the study of biomaterial surfaces and events at biomaterial surfaces such as protein adsorption. FTIR spectroscopy offers higher signal-to-noise and speeds than spectrometers that use gratings and hence offers the capability of observing the critical early events when proteins interact with surfaces. Perhaps the biggest advantage of the FTIR technique over dispersive spectrometers is wavelength precision. This allows the subtraction of water, a strong infrared absorber, from the spectra of proteins in aqueous solutions. This review starts with an introduction of how ATR can be used to provide information about proteins on surfaces. Equations to calculate the amount of proteins adsorbed to surfaces from analysis of ATR spectra are presented. A discussion of the kinds of surfaces that can be analyzed by FTIR/ATR and difficulties with the subtraction of H2O is given. The rest of the review deals with how information of interest to biomaterials researchers such as kinetics of protein adsorption, changes in protein secondary structure and orientation upon adsorption to surfaces can be obtained by FTIR/ATR.

Fully degradable hydrophilic polyals for protein modification
Yurkovetskiy, A., S. Choi, et al. (2005), Biomacromolecules 6(5): 2648-58.
Abstract: Modification of proteins with hydrophilic polymers is an effective strategy for regulation of protein pharmacokinetics. However, conjugates of slowly or non-biodegradable materials, such as poly(ethylene glycol), are known to cause long-lasting cell vacuolization, in particular in renal epithelium. Conjugates of more degradable polymers, e.g., polysaccharides, have a significant risk of immunotoxicity. Polymers that combine complete degradability, long circulation in vivo, and low immuno and chemical toxicity would be most beneficial as protein conjugate components. This study explores new fully biodegradable hydrophilic polymers, hydrophilic polyals. They are nontoxic, stable at physiological conditions, and undergo proton-catalyzed hydrolysis at lysosomal pH. The model enzyme-polyal conjugates were prepared with 61-98% yield using conventional and novel conjugation techniques and retained 90-95% of specific activity. The model conjugates showed a significant prolongation of protein circulation in rodents, with a 5-fold reduction in the renal accumulation. The data suggests that hydrophilic polyals may be useful in designing protein conjugates with improved properties.

Fully injectable calcium phosphate cement--a promise to dentistry
Komath, M. and H. K. Varma (2004), Indian J Dent Res 15(3): 89-95.
Abstract: Calcium phosphate cements (CPC) are self setting and biocompatible bone substitute materials with potential applications in dentistry. However, its clinical use has been challenged by poor rheological properties. A novel formulation of CPC has been developed, which gives a fully injectable and cohesive paste. This work investigates the suitability of the new "fully injectable calcium phosphate cement" (FI-CPC) for dental applications. The cementing properties, material characteristics, and the rheological properties were tested using a battery of material characteristics methods. The biocompatibility was also evaluated as per ISO 7405. The setting time (20 min) and compressive strength (>11 Mpa) of FI-CPC satisfy the clinical requirements. It underwent setting without any exothermic reaction, keeping good dimensional stability. The cement paste could be extruded through a 18-gauge needle, easily and fully. It showed excellent cohesion when immersed in water. FI-CPC was seen to set into a micro-porous mass of hydroxyapatite, the mineral part of human dentin. It showed good attachment to dentin walls, when filled in tooth perforations. FI-CPC was found non-toxic, non-allergic, non-pyrogenic, and soft-tissue compatible. The study shows that FI-CPC provides a self setting bio-compatible paste with excellent rheological properties for surgical applications. The set cement provides good and stable sealing. The osteoconductive property is an added advantage. FI-CPC proves to be an ideal material for endodontic sealing/filling and periodontic repair.

Functional activity of insulinoma cells (INS-1E) and pancreatic islets cultured in agarose cryogel sponges
Bloch, K., V. I. Lozinsky, et al. (2005), J Biomed Mater Res A 75(4): 802-9.
Abstract: Here, we describe the preparation, structure, and properties of cryogel sponges, which represent a new type of macroporous biomaterial for tissue engineering. Cryogels were produced through freeze-thawing techniques, either from agarose alone or from agarose with grafted gelatin. The aim of this study was to evaluate agarose cryogel sponges as scaffolds for culturing both isolated pancreatic islets and insulinoma cells (INS-1E). In order to evaluate the effect of cell entrapment in artificial scaffolds, cell function reflected by insulin secretion and content was studied in cells cultivated for a 2-week period either in culture plastic plates or in cryogel sponge disks. Our results show that tumor-derived INS-1E cells grown either on plastic or on cryogels do not differ in their proliferation, morphology, insulin release, and intracellular insulin content. However, isolated pancreatic islets cultivated on cryogels sponge show 15-fold higher basal insulin secretion at 3.0 mM glucose than islets cultivated on plastic plates and fail to respond to stimulation with 16.7 mM glucose. In addition, these islets have about 2-fold lower insulin content compared to those grown in plastic plates. It is possible that the cell dysfunction noted in these in vitro experiments is due to the effect of the limited oxygen supply to the islets cultivated in cryogel sponge. Further in vivo studies are needed to clarify the nature of such an observation since according to previous reports, agarose and gelatin induce new vessel formation supporting enhanced oxygen supply. (c) 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2005.

Functional and anatomic outcome after transvaginal rectocele repair using collagen mesh: a prospective study
Altman, D., J. Zetterstrom, et al. (2005), Dis Colon Rectum 48(6): 1233-41; discussion 1241-2; author reply 1242.
Abstract: PURPOSE: This study was designed to evaluate rectocele repair using collagen mesh. METHODS: 32 female patients underwent surgical repair using collagen mesh. Outcome was assessed in 29 patients and preoperative assessment included standardized questionnaire, clinical examination, and defecography. At the six-month follow-up, patients answered a standardized questionnaire and underwent clinical examination. At the 12-month follow-up, patients answered a standardized questionnaire, underwent clinical examination, and defecography. RESULTS: Preoperatively, 26 patients had a Stage II and 3 patients had a Stage III rectocele. At the 6-month follow-up, five patients had rectocele > or = Stage II (P < 0.001) and at the 12-month follow-up, seven patients had rectocele > or = Stage II (P < 0.001) at clinical examination. At the preoperative defecography, all patients presented a rectocele. At the 12-month defecography, 14 patients had no rectocele (P < 0.001) and 15 had a rectocele. At the six-month follow-up, there was a significant decrease in rectal emptying difficulties, need of digital support of the posterior vaginal wall at defecation, and defecation frequency. At the 12-month follow-up, symptom improvement remained, but was less pronounced. CONCLUSIONS: Rectocele repair using collagen mesh improved anatomic support, but there is a substantial risk for recurrence with unsatisfactory anatomic and functional outcome one year after surgery. Rectocele repair using mesh was not associated with an increased risk of dyspareunia. Rectocele repair using biomaterial mesh reinforcement needs further evaluation before adopted into clinical practice.

Functional bone engineering using ex vivo gene therapy and topology-optimized, biodegradable polymer composite scaffolds
Lin, C. Y., R. M. Schek, et al. (2005), Tissue Eng 11(9-10): 1589-98.
Abstract: Bone tissue engineering could provide an alternative to conventional treatments for fracture nonunion, spinal fusion, joint replacement, and pathological loss of bone. However, this approach will require a biocompatible matrix to allow progenitor cell delivery and support tissue invasion. The construct must also support physiological loads as it degrades to allow the regenerated tissue to bear an increasing load. To meet these complex requirements, we have employed topology-optimized design and solid free-form fabrication to manufacture biodegradable poly(propylene fumarate)/beta-tricalcium phosphate composites. These scaffolds were seeded with primary human fibroblasts transduced with an adenovirus expressing bone morphogenetic protein-7 and implanted subcutaneously in mice. Specimens were evaluated by microcomputed tomography, compressive testing, and histological staining. New bone was localized on the scaffold surface and closely followed its designed contours. Furthermore, the total stiffness of the constructs was retained for up to 12 weeks after implantation, as scaffold degradation and tissue invasion took place.

Functional compressive mechanics of a PVA/PVP nucleus pulposus replacement
Joshi, A., G. Fussell, et al. (2006), Biomaterials 27(2): 176-84.
Abstract: Emerging techniques as an alternative to the current treatments of lower back pain include nucleus replacement by an artificial material, which aims to relieve pain and restore the normal spinal motion. The compressive mechanical behavior of the PVA/PVP hydrogel nucleus implant was assessed in the present study. PVA/PVP hydrogels were made with various PVP concentrations. The hydrogels were loaded statically under unconfined and confined conditions. Hydrogels were tested dynamically up to 10 million cycles for a compression fatigue. Also, hydrogel nucleus implants with a line-to-line fit, were implanted in the human cadaveric intervertebral discs (IVD) to determine the compressional behavior of the implanted discs. Hydrogel samples exhibited typical non-linear response under both unconfined and confined compressions. Properties of the confinement ring dictated the observed response. Hydrogel moduli and polymer content were not different pre- and post-fatigues. Slight geometrical changes (mostly recoverable) were observed post-fatigue. In cadavers, hydrogels restored the compressive stiffness of the denucleated disc when compared with equivalent condition of the IVD. The results of this study demonstrate that PVA/PVP hydrogels may be viable as nucleus pulposus implants. Further studies under complex loading conditions are warranted to better assess its potential as a replacement to the degenerated nucleus pulposus.

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