Biomaterials.info - Resources for Engineers

Record 2221 to 2240

Histologic changes of nonbiodegradable and biodegradable biomaterials used to repair right ventricular heart defects in rats
Ozawa, T., D. A. Mickle, et al. (2002), J Thorac Cardiovasc Surg 124(6): 1157-64.
Abstract: OBJECTIVES: Nonbiodegradable synthetic materials have been widely used to repair cardiac defects. Material-related failures, however, such as lack of growth, thrombosis, and infection, do occur. Because a biodegradable scaffold can be replaced by the patient's own cells and will be treated as a foreign body for a limited period, we compared four biodegradable materials (gelatin, polyglycolic acid (PGA), and copolymer made of epsilon-caprolactone and l-lactic acid reinforced with a poly-l-lactide knitted [KN-PCLA] or woven fabric [WV-PCLA]) with a nonbiodegradable polytetrafluoroethylene (PTFE) material. An animal heart model was tested that simulates the in vivo clinical condition to which a synthetic material would be used. METHODS: The five patches were used to repair transmural defects surgically created in the right ventricular outflow tracts of adult rat hearts (n = 5, each patch group). The PTFE patch group served as a control group. At 8 weeks after implantation, the biomaterials were excised. Patch size, patch thickness, infiltrated cell number, extracellular matrix composition, and patch degradation were evaluated. RESULTS: The PTFE patch itself did not change in size except for increasing in thickness because of fibroblast and collagen coverage of both its surfaces. Host cells did not migrate into the PTFE biomaterial. In contrast, cells migrated into the biodegrading gelatin, PGA, and KN-PCLA and WV-PCLA scaffolds. Cellular ingrowth per unit patch area was highest in the KN-PCLA patch. The KN-PCLA patch increased modestly in size and thinness. The WV-PCNA patch did not change in size or thickness. Fibroblasts and collagen were the dominant cellular infiltrate and extracellular matrix formed in the biodegrading scaffolds. The in vivo rates of biomaterial degradation, thinning, and expansion were material specific. All the subendocardial patch surfaces were covered with endothelial cells. No thrombi were seen. CONCLUSIONS: The unique, spongy matrix structure of the PCLA patch favored cell colonization relative to the other patches. The strong, durable outer poly-l-lactide fabric layers in these patches offered physical, biocompatible, and bioresorbable advantages relative to the other biodegradable materials studied. Host cells migrated into all the biomaterials. The cells secreted matrix and formed tissue, which was endothelialized on the endocardial surface. The biomaterial degradation rates and the tissue formation rates were material related. The PCLA grafts hold promise to become a suitable patch for surgical repair.

Histologic findings after explantation of a modified expanded polytetrafluoroethylene graft used for clinical systemic-to-pulmonary shunting
Takeda, K., H. Uemura, et al. (2005), J Thorac Cardiovasc Surg 130(3): 934-5.

Histological analysis of a displaced femoral ring allograft spacer filled with a recombinant human bone morphogenetic protein-2-soaked collagen sponge. A case report
Lee, J. Y., S. Zeiller, et al. (2005), J Bone Joint Surg Am 87(10): 2318-22.

Histological evaluation of Permacol as a subcutaneous implant over a 20-week period in the rat model
Macleod, T. M., G. Williams, et al. (2005), Br J Plast Surg 58(4): 518-32.
Abstract: This study assessed the suitability of Permacol (a porcine derived, isocyanate cross linked collagen based biomaterial) as an alternative to autologous tissue in soft tissue reconstruction. The Sprague-Dawley rat was used as a model for subcutaneous implantation over a 20 week period and comparison made with two other porcine biomaterials (small intestinal submucosa and glycerol treated-ethylene oxide sterilised porcine dermis). Implants were scored histometrically on the degree of acute inflammation, chronic inflammation, fibrosis and stromal response. The vascularity and percentage composition of collagen within Permacol were assessed by stereology and seescan image analysis, respectively. In general terms, Permacol was well tolerated as a subcutaneous implant, with only a minor chronic inflammatory response remaining after a 20 week period of implantation. There was evidence of collagen degradation during this period and vascular ingrowth into Permacol was limited. Permacol has the potential for a broad range of applications in plastic surgery, but may benefit from modification to promote a more rapid degree of vascularisation.

Histological findings in titanium implants coated with calcium phosphate ceramics installed in rabbit's tibias
Mitri, F. F., M. Yoshimoto, et al. (2005), Ann Anat 187(1): 93-8.
Abstract: Oral reconstruction using osteointegrated implants are widely indicated nowadays. The implant bone anchorage is very important for its functional stability. Thus, ceramic biomaterials are widely used as coatings of the implant surfaces to accelerate local osteogenesis. The purpose of this study is to assess the biocompatibility and the osteoconduction of two types of calcium phosphate ceramics used as titanium dental implant coatings. These implants were installed in rabbit tibia during an 8-week healing period. The light and fluorescent microscopy observations showed that the materials are biocompatible and that they have osteoconductive activities.

Histological investigation of bone induction by demineralized allogeneic bone matrix: a natural biomaterial for osseous reconstruction
Vandersteenhoven, J. J. and M. Spector (1983), J Biomed Mater Res 17(6): 1003-14.
Abstract: The objective of the study was to delineate the histological sequence of events associated with bone formation induced in extraosseous sites by implants of demineralized allogeneic bone matrix (DABM) in order to provide a more complete basis for the clinical use of the natural biomaterial for osseous reconstruction. The rat was the experimental animal model. Implants were prepared by demineralization of diaphyseal cortical rat bone in 0.6N HCl for 18-24 h. A total of 104 specimens, 4 mm square, were implanted both subcutaneously and intramuscularly in 26 rats for periods of 3 days to 22 weeks. Histological evaluation revealed a sequence of events that at 3 days displayed an inflammatory response to surgical trauma and after 6 weeks exhibited the formation of a mature lamellar ossicle with central marrow which was maintained through 22 weeks. Resorption of the DABM, first evident at 1 week, was accompanied by the appearance of chondroblast in vascular canals and in crevices in the implant. Osteoblastic activity, initially seen at 2 weeks, appeared to be associated with capillary and blood vessel formation around the implant and within enlarged resorptive cavities within the specimens. Calcification occurred in the cartilaginous matrix and osteoid and within the implanted matrix. The osteoinductive process comprises (1) the inflammation/granulation/scar formation processes elicited by implantation of a material, (2) the resorptive response elicited by DABM, and (3) the process of induction of nonosseous mesenchymal cells to differentiate to chondroblasts and osteoblasts. The results of the present study support previous investigations demonstrating the bone-inducing property of DABM and provide further evidence for the potential value of this natural biomaterial for use in osseous reconstruction.

Histological investigation of liposuctioned fat for injection laryngoplasty
Sato, K., H. Umeno, et al. (2005), Am J Otolaryngol 26(4): 219-25.
Abstract: PURPOSE: There are a few injectable biomaterials used in vocal-fold-augmentation surgery. In this study, liposuctioned autologous fat, used as the injection material, was investigated histologically. MATERIALS AND METHODS: Liposuctioned fat, which was harvested from 13 patients during injection laryngoplasty, was examined by light and electron microscopy. RESULTS: The cell membranes of most of the liposuctioned fat had not been damaged during harvesting and microinjection by our method. The harvested liposuctioned fat was a group of unilocular fat cells. Each cell was surrounded by a meshwork of fine reticular fibers. The cells were spherical and about 30 to 130 microm in diameter. The cells size and density were different from individual to individual. The diameters of liposuctioned fat cells were correlated with the body mass index. Dense and small fat cells were able to maintain graft volume. Sparse and large fat cells tended to not be able to maintain graft volume. There was little proliferation of unilocular fat cells, which were not able to maintain graft volume. CONCLUSION: The structure consisting of a unilocular cell, containing a single droplet of lipid, surrounded by a meshwork of delicate reticular fiber is one of the reasons why autologous fat has viscous properties similar to those of human lamina propria. Autologous fat was not damaged by our harvesting and microinjection method. The size, density and proliferation of fat cells, and ground substance around them may be related to resorption and a decrease in surviving graft volume.

Histological preparation of implanted biomaterials for light microscopic evaluation of the implant-tissue interaction
Murice-Lambert, E., A. B. Banford, et al. (1989), Stain Technol 64(1): 19-24.
Abstract: A technique is presented for processing implanted biomaterials with surrounding soft tissue for histological assessment of the implant-tissue interaction. Specimens are removed with the implant-tissue interface intact, fixed in formalin, dehydrated in a graded series of ethanol followed by a graded series of acetone in ethanol, and embedded in Spurr's low viscosity epoxy resin. Sections 0.5-1.0 mm thick are cut from the cured blocks using a metallurigical saw with a diamond wafer blade. After being glued to glass microscope slides, they are ground and polished to approximately 75 microns in thickness. The polished sections are treated with 95% ethanol saturated with sodium hydroxide, stained with Gill's hematoxylin and counterstained in eosin Y-phloxine B. The sodium hydroxide solution degrades the resin, allowing the stain to penetrate the tissue. By limiting the time in sodium hydroxide, the depth of staining is controlled and one is able to simulate a thin paraffin section with high resolution of the implant-soft tissue interface.

Histological studies of monofilament and multifilament polypropylene mesh implants demonstrate equivalent penetration of macrophages between fibrils
Papadimitriou, J. and P. Petros (2005), Hernia 9(1): 75-8.
Abstract: The tissue reaction to implanted monofilamentous and multifilamentous polypropylene mesh was compared in samples removed at operation from the perivaginal area of a 58 year old patient. The fibrils of both were surrounded by collagenous connective tissue, collagen types I and III, and proteoglycans. Smaller, less compacted bundles were seen in the vicinity of the monofilamentous mesh than around the multifilamentous mesh, and in addition, a greater number of inflammatory cells and larger multinucleate giant cells were seen apposed to the monofilamentous mesh.Following this, eight rats were implanted with multifilamentous synthetic polypropylene tape and examined at two, four, six and eight weeks after surgery. Macrophages and multinucleated giant cells were seen in the immediate vicinity of the fibrils, while fibrovascular connective tissue surrounded the implantation site.These observations do not support the prevailing hypotheses that macrophages cannot penetrate between the fibrils of multifilament tape. They do suggest that differences in tensile strength may be present in the artificial neoligaments created by the two tapes.

Histomorphometric Evaluation of Human Sinus Floor Augmentation Healing Responses to Placement of Calcium Phosphate or Ricinus communis Polymer Associated with Autogenous Bone
Boeck-Neto, R. J., M. F. Gabrielli, et al. (2005), Clin Implant Dent Relat Res 7(4): 181-8.
Abstract: Background: Prosthetic rehabilitation of the posterior maxilla with dental implants is often difficult because of proximity to the maxillary sinus and insufficient bone height. Maxillary sinus floor augmentation procedures aim to obtain enough bone with an association between biomaterials and autogenous bone. PURPOSE: The purpose of this study was to evaluate histomorphometricaly two grafting materials (calcium phosphate and Ricinus communis polymer) used in maxillary sinus floor augmentation associated with autogenous bone. Materials and Methods: Biopsies were taken from 10 consecutive subjects (mean age 45 years) 10 months after maxillary sinus floor augmentation. The sinus lift was performed with a mixture of autogenous bone and R. communis polymer or calcium phosphate in a 1:2 proportion. Routine histologic processing and staining with hematoxylin and eosin were performed. Results: The histomorphometric analysis indicated satisfactory regenerative results in both groups for a mean of bone tissue in the grafted area (44.24 +/- 13.79% for the calcium phosphate group and 38.77 +/- 12.85% for the polymer group). Histologic evaluation revealed the presence of an inflammatory infiltrate of mononuclear prevalence that, on average, was nonsignificant. The histologic sections depicted mature bone with compact and cancellous areas in both groups. Conclusion: The results indicated that both graft materials associated with the autogenous bone were biocompatible, although both were still present after 10 months.

History of artificial organs in Japan
Atsumi, K. (2005), J Artif Organs 8(1): 1-12.

Homoserine-derived cyclic sulfamidate as chiral educt for the diversity-oriented synthesis of lactam-bridged dipeptides
Galaud, F. and W. D. Lubell (2005), Biopolymers 80(5): 665-74.
Abstract: Introduction of structural constraint into peptides is an effective way for studying their conformation-activity relationships. Conformationally restrained dipeptidyl lactams, important building blocks for the synthesis of peptidomimetics, have now been synthesized from N-[9-(9-phenylfluorenyl)]-L-aspartic acid alpha-cumyl beta-methyl diester as an inexpensive chiral educt. After selective reduction of the beta-methyl ester with diisobutylaluminum hydride (DIBAL-H), homoserine was treated with thionyl chloride, imidazole, and triethylamine to give sulfamidites. Diastereoisomers were separated by chromatography and oxidation of the major sulfamidite (2R,4S)- with catalytic ruthenium trichloride afforded sulfamidate. A series of gamma-lactam-bridged dipeptides was then obtained by ring opening of sulfamidate cumyl ester with a series of amino esters, selective cumyl ester removal, and lactam formation. The resulting dipeptidyl lactams possessed aliphatic, aromatic, amino, thioether, and carboxylate side chains. A gamma-lactam analog of Pro-Leu-Gly-NH2 (PLG), was synthesized to illustrate the potential for using this approach in the synthesis of biologically active peptide mimics.

Hot compaction of poly(methyl methacrylate) composites based on fiber shrinkage results
Wright-Charlesworth, D. D., E. P. Lautenschlager, et al. (2005), J Mater Sci Mater Med 16(10): 967-75.
Abstract: Uniaxial self-reinforced composite poly(methyl methacrylate) (SRC-PMMA) is being investigated as a pre-coat material for the femoral component of total hip replacements. Hot compaction of self-reinforced composites is largely an empirical process which varies the processing parameters of time, temperature and pressure until the desired properties are obtained. Previous work has shown that PMMA fibers have unique thermal relaxation properties dependent upon the retained molecular orientation in them. This work processed composites at times and temperatures that span the relaxation process for a single fiber. It was found that molecular orientation, as measured by birefringence, was lost in composites processed at times greater than relaxation times for single fibers. Flexural properties were also found to vary with processing conditions, with the highest values of 165 +/- 15 MPa and 168 +/- 3 MPa found at high and low processing times, respectively. These are significantly stronger than unreinforced PMMA which has a flexural strength of 127 +/- 14 MPa. It is hypothesized that diffusion between fibers occurs much more quickly than the loss of molecular orientation and it was seen that SRC-PMMA processing conditions can be predicted from the relaxation times and temperatures from single fibers.

How autocatalysis accelerates drug release from PLGA-based microparticles: a quantitative treatment
Siepmann, J., K. Elkharraz, et al. (2005), Biomacromolecules 6(4): 2312-9.
Abstract: The major aim of this study was to better understand the importance of autocatalysis in poly(lactic-co-glycolic acid) (PLGA)-based microparticles used as controlled drug delivery systems. Upon contact with biological fluids, PLGA is degraded into shorter chain alcohols and acids. An accumulation of the latter can lead to significant drops in micro-pH and subsequent accelerated polymer degradation. The system size, determining the diffusion path lengths, plays a crucial role for the occurrence/absence of autocatalytic effects. Using an oil-in-water solvent-extraction/evaporation process, different-sized drug-free and drug-loaded, PLGA-based microparticles were prepared and physicochemically characterized (SEM, DSC, SEC, optical microscopy, and UV-spectrophotometry) before and upon exposure to simulated biological fluids. Based on these experimental results, an adequate mathematical theory was developed describing the dominating mass transfer processes and chemical reactions. Importantly, a quantitative relationship could be established between the dimension of the device and the resulting drug release patterns, taking the effects of autocatalysis into account.

How do serum cobalt and chromium levels change after metal-on-metal hip resurfacing?
Back, D. L., D. A. Young, et al. (2005), Clin Orthop Relat Res 438: 177-81.
Abstract: We prospectively monitored changes in serum cobalt and chromium levels after a new generation metal-on-metal hip resurfacing and the affect on renal function. Levels were measured using inductively coupled plasma mass spectrometry and atomic absorption spectrometry, preoperatively then sequentially at 3, 6, 9, 12, and 24 months. For serum cobalt, there was an initial increase to a peak level at 6 months, followed by a gradual decline during the next 15 months. A similar trend was observed in serum chromium, although the peak level occurred slightly later, at 9 months. There was no adverse affect on renal function during the 2-year study period. All implants were functioning well, with no radiographic evidence of loosening. These levels will continue to be monitored to establish when minimum metal ion levels are reached.

How to optimize seeding and culturing of human osteoblast-like cells on various biomaterials
Wiedmann-Al-Ahmad, M., R. Gutwald, et al. (2002), Biomaterials 23(16): 3319-28.
Abstract: The optimization of seeding and culturing of human osteoblast-like cells on three collagen-based biomaterials (bovine, equine and calf collagen membrane) was studied by cell proliferation and cell colonization (scanning electron microscopy) analysis. Osteoblasts of five patients were seeded onto the three biomaterials and two different parameters were varied: the time intervals between initial seeding and adding culture medium (2 h 6 h. 12 h, 24 h) and the seeding concentration (1 x 10(5), 1 x 10(6), 2 x 10(6)cells/ml) of cells onto biomaterials. The results of the study demonstrated that the time interval between seeding osteoblasts and adding culture medium as well as the seeding concentration effects the cell proliferation and the cell colonization. The best proliferation rate was achieved by adding the culture medium 2 h after initial seeding and with a seeding density of 1 x 10(5) cells/ml. Moreover, all three biomaterials resulted in different proliferation rates. The best proliferation rate resulted with the bovine collagen membrane. In conclusion, the examined parameters are very important for the development of the tissue engineering techniques and in a larger perspective also for reconstructive surgery.

HPLC analysis of PAMAM dendrimer based multifunctional devices
Islam, M. T., I. J. Majoros, et al. (2005), J Chromatogr B Analyt Technol Biomed Life Sci 822(1-2): 21-6.
Abstract: Comprehensive high-performance liquid chromatography (HPLC) analyses were performed on poly(amidoamine) (PAMAM) dendrimer based multifunctional devices. The nanometer-size devices were synthesized by conjugating partially acetylated (Ac) poly(amidoamine) dendrimers of generation 5 (G5) with fluorescein isothiocyanate (FITC), folic acid (FA) and methotrexate (MTX). The devices are intended for targeted intracellular drug delivery to tumor cells through the folate receptor. Methods were developed for detection and separation of various surface functionalized dendrimer conjugates and small molecules (FITC, FA, MTX) using a common gradient. Results indicate that the HPLC technique can be used as a quality control tool for determining purity of the G5 carrier, its acetylated form, and mono-, bi- and tri-functional nanodevices. More importantly, the chromatograms of these novel nanodevices, reported for the first time, provide information on critical properties such as polydispersity, surface heterogeneity and solubility. The benchmark data can be used to optimize the physicochemical properties of the conjugates to improve drug delivery to cancer cells.

Human endothelial cell interactions with surface-coupled adhesion peptides on a nonadhesive glass substrate and two polymeric biomaterials
Massia, S. P. and J. A. Hubbell (1991), J Biomed Mater Res 25(2): 223-42.
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.

Human growth hormone locally released in bone sites by calcium-phosphate biomaterial stimulates ceramic bone substitution without systemic effects: a rabbit study
Guicheux, J., O. Gauthier, et al. (1998), J Bone Miner Res 13(4): 739-48.
Abstract: Calcium-phosphate bone replacement biomaterial has been used as a drug carrier for therapeutic agents. This study investigated the efficacy of local administration of human growth hormone (hGH) by macroporous biphasic calcium phosphate (MBCP) implants in improving the bone substitution qualities of ceramics. hGH release from MBCP implants loaded with 1 microg of hGH was rapid during the first 48 h and then sustained for a total of 9 days. Immunolocalization of hGH in vitro and in vivo by transmission electron microscopy showed its presence inside the material, indicating that it was able to penetrate within the porosity of the ceramic during the adsorption process. MBCP cylinders (6 x 6 mm) were loaded with 0.1, 1, and 10 microg of hGH and implanted into rabbit femurs (n = 40). The effects of locally released hGH on bone ingrowth and ceramic resorption were evaluated by scanning electron microscopy and image analysis. The results indicated that hGH increased bone ingrowth (+65%) and ceramic resorption (+140%) significantly in comparison with control implants and that the increase was dose dependent. Biochemical parameters monitored in rabbit plasma and urine, as well as the absence of any significant difference between contralateral implants and the control, indicated that hGH did not produce detectable systemic effects. Thus, the use of MBCP appears to be effective for local delivery of hGH, resulting in improved bone substitution.

Human monocyte response to particulate biomaterials generated in vivo and in vitro
Shanbhag, A. S., J. J. Jacobs, et al. (1995), J Orthop Res 13(5): 792-801.
Abstract: We studied the ability of four clinically relevant particle species to stimulate human peripheral blood monocytes to release bone-resorbing agents, including interleukin-1 (both interleukin-1 alpha and interleukin-1 beta), interleukin-6, and prostaglandin E2. The species studied were titanium-6% aluminum-4% vanadium (TiAlV), commercially pure titanium, fabricated ultrahigh molecular weight polyethylene, and polyethylene retrieved from interfacial membranes of failed uncemented total hip arthroplasties. For all species, the mean size was less than 1 micron. Human peripheral blood monocytes were challenged with these particles in a uniform manner on the basis of surface area. Phorbol 12-myristate acetate, zymosan, and nonphagocytosable titanium particles served as controls. Stimulation of human monocytes is a function of the composition and concentration of particles. In this study, TiAlV particles appeared to be the most competent to elicit the synthesis and release of inflammatory mediators. Particles of commercially pure titanium and of fabricated ultrahigh molecular weight polyethylene also could induce the release of various cellular mediators, albeit at a lower level, whereas the particles of polyethylene retrieved from interfacial membranes were less stimulatory in these short-term in vitro experiments.

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