|Articles about Biomaterials|
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| Poly(lactide) stereocomplexes: formation, structure, properties, degradation, and applications
Tsuji, H. (2005), Macromol Biosci 5(7): 569-97.
Abstract: Poly(lactide)s [i.e. poly(lactic acid) (PLA)] and lactide copolymers are biodegradable, compostable, producible from renewable resources, and nontoxic to the human body and the environment. They have been used as biomedical materials for tissue regeneration, matrices for drug delivery systems, and alternatives for commercial polymeric materials to reduce the impact on the environment. Since stereocomplexation or stereocomplex formation between enantiomeric PLA, poly(L-lactide) [i.e. poly(L-lactic acid) (PLLA)] and poly(D-lactide) [i.e. poly(D-lactic acid) (PDLA)] was reported in 1987, numerous studies have been carried out with respect to the formation, structure, properties, degradation, and applications of the PLA stereocomplexes. Stereocomplexation enhances the mechanical properties, the thermal-resistance, and the hydrolysis-resistance of PLA-based materials. These improvements arise from a peculiarly strong interaction between L-lactyl unit sequences and D-lactyl unit sequences, and stereocomplexation opens a new way for the preparation of biomaterials such as hydrogels and particles for drug delivery systems. It was revealed that the crucial parameters affecting stereocomplexation are the mixing ratio and the molecular weight of L-lactyl and D-lactyl unit sequences. On the other hand, PDLA was found to form a stereocomplex with L-configured polypeptides in 2001. This kind of stereocomplexation is called "hetero-stereocomplexation" and differentiated from "homo-stereocomplexation" between L-lactyl and D-lactyl unit sequences. This paper reviews the methods for tracing PLA stereocomplexation, the methods for inducing PLA stereocompelxation, the parameters affecting PLA stereocomplexation, and the structure, properties, degradation, and applications of a variety of stereocomplexed PLA materials.
| Poly(lactide) swelling and melting behavior in supercritical carbon dioxide and post-venting porous material
Fujiwara, T., T. Yamaoka, et al. (2005), Biomacromolecules 6(4): 2370-3.
| Poly(N-isopropylacrylamide) (PNIPAM)-grafted gelatin as thermoresponsive three-dimensional artificial extracellular matrix: molecular and formulation parameters vs. cell proliferation potential
Ohya, S. and T. Matsuda (2005), J Biomater Sci Polym Ed 16(7): 809-27.
Abstract: A series of poly(N-isopropylacrylamide)-grafted gelatins (PNIPAM gelatins) of three different graft densities (approx. 11, 22 and 34 graft chains per gelatin molecule) and three different molecular weights of their graft chains (molecular weight approximately 1.2 x 10(4), 5.0 x 10(4) and 1.3 x 10(5) g/mol) were prepared by multiple derivatization of dithiocarbamyl (DC) group in a gelatin molecule and subsequent iniferter (acts as an initiator, transfer-agent and terminator)-based photopolymerization of NIPAM. The weight ratio of PNIPAM graft chains to gelatin (P/G) varied from 1.4 to 49. Aqueous solutions of PNIPAM-gelatins showed thermo-responsiveness, depended on the graft density and the molecular weight of PNIPAM graft chain or P/G. Aqueous solutions (10 or 20%, w/v) of PNIPAM-gelatins with P/G of more than 5.8 were converted to gels at 37 degrees C. Focal plane images of PNIPAM-gelatin gels by confocal laser scanning microscopy revealed that the size of hydrophobically clustered aggregates increased with P/G, whereas the space of microvoids decreased with concentration. Compressive strain-stress measurements revealed that compressive strength of PNIPAM-gelatin increased with P/G. Bovine smooth muscle cells (SMCs)-entrapped gels were produced from PNIPAM-gelatin-containing cell-suspended medium solutions at 37 degrees C. The entrapped cells proliferated in the gel with P/G of more than 12. A higher cell proliferativity was obtained at low concentration (5%, w/v) and higher P/G (>18). Tissue formation composed of proliferative SMCs and cell-secreted extracellular matrices (collagen) was obtained at 14 days incubation. The inter-relationship between the molecular parameters of PNIPAM-gelatin, internal structural features and cell proliferation potential was discussed.
| Poly(vinyl alcohol) as versatile biomaterial for potential biomedical applications
Paradossi, G., F. Cavalieri, et al. (2003), J Mater Sci Mater Med 14(8): 687-91.
Abstract: In this paper, we present some new case examples where the chemical versatility of poly (vinyl alcohol) (PVA) can be used for potential biomedical applications. PVA, the polymeric material used for designing new nanostructured devices, is water soluble, biocompatible and has excellent physical properties. We point out the possibility of obtaining wall-to-wall chemical hydrogels as well as microgels without diminishing the biocompatibility available in the starting PVA material. Injectability is another important factor to take into account in controlled drug delivery for gene therapy. In this respect, in this paper, established and more innovative methods are prospected in order to obtain particles with dimensions suitable for these applications.
| Polyacrylamide gel electrophoresis separation and detection of polyamidoamine dendrimers possessing various cores and terminal groups
Sharma, A., A. Desai, et al. (2005), J Chromatogr A 1081(2): 238-44.
Abstract: Detection and separation of polyamidoamine dendrimers possessing various cores and surface groups was studied by polyacrylamide gel electrophoresis. Although many dyes and staining techniques were able to detect dendrimers on polyacrylamide gels, Coomassie Blue was found to be the most sensitive and convenient. Amine and hydroxyl terminated dendrimers were best separated under acidic conditions, while dendrimers with carboxyl surfaces required alkaline buffers. Some dendrimers were very susceptible to diffusion that could occur during their separation, staining or destaining steps. In the absence of an appropriate fixation step, dendrimers could be resolved by using small pore size gels and low voltage or current. Increasing core lengths did not significantly affect migration of a given dendrimer generation but exhibited improved separation and staining characteristics. Polyacrylamide gel electrophoresis was found to be a rapid, inexpensive, and reliable procedure to characterize many different water-soluble dendritic macromolecules.
| Polyamide/silver antimicrobials: effect of filler types on the silver ion release
Kumar, R., S. Howdle, et al. (2005), J Biomed Mater Res B Appl Biomater 75(2): 311-9.
Abstract: The efficiency of various silver-based antimicrobial fillers (elementary silver and silver substituted materials) in polyamide (PA) toward their silver ion (Ag+) release characteristics in an aqueous medium was investigated and discussed. Anode stripping voltammetry (ASV) was used for the quantitative estimation of Ag+ release from these composites. The biocidal (Ag+) release from the composites was found to be dependent on the time of soaking in water and the nature of the filler. The long-term Ag+ release capability of the elementary silver-based PA/Ag composite is promising compared with the commercial counterparts. The silver ion release potential of polyamide composites where the silver filling was performed by using supercritical carbon dioxide (scCO2) is also discussed. The composites release Ag+ at a concentration level capable of rendering antimicrobial efficacy and proved to be active against the microbes. A good agreement exists between the Ag+ release experiments and antimicrobial test results. The observed results on the influence of the nature of the filler and crystallinity on the biocidal release and the varying long-term release properties could be helpful in the design of industrially relevant biomaterials.
| Polycarbonate-urethane hard segment type influences esterase substrate specificity for human-macrophage-mediated biodegradation
Labow, R. S., D. Sa, et al. (2005), J Biomater Sci Polym Ed 16(9): 1167-77.
Abstract: Previous studies have shown that esterase activity can degrade a variety of polyurethanes (PUs), including polycarbonate-based PUs (PCNUs). When cultured on PCNUs, differing in their chemistries, monocyte-derived macrophages (MDM) synthesized and secreted different amounts of both cholesterol esterase (CE) and monocyte-specific esterase (MSE). MDM were seeded on PCNUs synthesized with hexane diisocyanate (HDI) or 4,4'-methylene-bis-phenyl diisocyanate (MDI), PCN and [14C]butanediol (BD) in the ratio 3:2:1 (referred to as HDI321 or MDI321). The effect of phenylmethylsulfonyl fluoride (PMSF, a serine esterase and proteinase inhibitor), sodium fluoride (NaF, a MSE inhibitor) and sodium taurocholate (NaT, a CE stimulator) was assessed on degradation (measured by radiolabel release (RR)) and esterase activity in MDM lysate. The results were compared to the effect that these reagents had on commercially available CE and carboxyl esterase (CXE), which has a specificity similar to MSE. NaF inhibited CXE- and MDM-mediated RR to the same extent as for both PCNUs. However, the MDM-mediated RR from MDI321 was 1.8-times higher than HDI321 in the presence of NaT (P = 0.005). This study suggests that the difference in diisocyanate chemistry may dictate the relative contribution of each esterase to a specific material's degradation. This may be related to both the substrate specificity of each esterase, as well as by the relative amount of each esterase that the specific biomaterial substrates induce the cells to synthesize and secrete.
| Polycarnitine--a new biomaterial
Kamm, B., M. Kamm, et al. (2005), Appl Microbiol Biotechnol 67(1): 1-7.
Abstract: The natural product L-carnitine is--due to its biotechnological accessibility and specific properties--on the way to becoming an attractive biobased bulk product. L-carnitine is a natural betaine with vitamin properties. Carnitine is an essential part of the fatty acid metabolism of human beings and animals. Carnitine was first isolated in 1905 from meat extract and important recent developments include the biosyntheses of L-carnitine from L-lysine or gamma-butyrobetaine. Our synthesis routes are designed to maintain the primary structure and specific properties of carnitine, such as hydrophilicity and "stiffening" effects for polymeric structures and applications. L-carnitine is converted via lactonization or olefinization into polymerizable basic molecules. The properties and the applications of carnitine polymers are described.
| Polyelectrolyte multilayer films with pegylated polypeptides as a new type of anti-microbial protection for biomaterials
Boulmedais, F., B. Frisch, et al. (2004), Biomaterials 25(11): 2003-11.
Abstract: Adhesion of bacteria at the surface of implanted materials is the first step in microbial infection, leading to post-surgical complications. In order to reduce this adhesion, we show that poly(L-lysine)/poly(L-glutamic acid) (PLL/PGA) multilayers ending by several PLL/PGA-g-PEG bilayers can be used, PGA-g-PEG corresponding to PGA grafted by poly(ethylene glycol). Streaming potential and quartz crystal microbalance-dissipation measurements were used to characterize the buildup of these films. The multilayer films terminated by PGA and PGA-g-PEG were found to adsorb an extremely small amount of serum proteins as compared to a bare silica surface but the PGA ending films do not reduce bacterial adhesion. On the other hand, the adhesion of Escherichia coli bacteria is reduced by 72% on films ending by one (PLL/PGA-g-PEG) bilayer and by 92% for films ending by three (PLL/PGA-g-PEG) bilayers compared to bare substrate. Thus, our results show the ability of PGA-g-PEG to be inserted into multilayer films and to drastically reduce both protein adsorption and bacterial adhesion. This kind of anti-adhesive films represents a new and very simple method to coat any type of biomaterials for protection against bacterial adhesion and therefore limiting its pathological consequences.
| Polyelectrolyte multilayers and degradable polymer layers as multicompartment films
Garza, J. M., N. Jessel, et al. (2005), Langmuir 21(26): 12372-7.
Abstract: Polyelectrolyte multilayers are now a well established concept with numerous potential applications in particular as biomaterial coatings. To timely control the biological activity of cells in contact with a substrate, multicompartment films made of different polyelectrolyte multilayers deposited sequentially on the solid substrate constitute a promising new approach. In a first paper (Langmuir 2004, 20, 7298) we showed that such multicompartment films can be designed by alternating exponentially growing polyelectrolyte multilayers acting as reservoirs and linearly growing ones acting as barriers. In the present study, we first demonstrate however that these barriers composed of synthetic polyelectrolytes are not degraded despite the presence of phagocytic cells. We propose an alternative approach where exponentially growing poly(L-lysine)/hyaluronic acid (PLL/HA) multilayers, used as reservoirs, are alternated with biodegradable polymer layers consisting in poly(lactic-co-glycolic acid) (PLGA) and acting as barriers for PLL chains that diffuse within the PLL/HA reservoirs. We first show that these PLGA layers can be deposited alternatively with PLL/HA multilayers leading to polyelectrolyte multilayer/hydrolyzable polymeric layer films and acting as a reservoirs/barriers system. Bone marrow cells seeded on these films ending by a PLL/HA reservoir rapidly degrade it and internalize the PLL chains confined in this reservoir. Then the cells degraded locally the PLGA barrier and internalize the PLL localized in a lower (PLL/HA) compartment after 5 days of seeding. By changing the thickness of the PLGA layer, we hope to be able to tune the time delay of degradation. Such mixed architectures made of polyelectrolyte multilayers and hydrolyzable polymeric layers could act as coatings allowing us to induce a time scheduled cascade of biological activities. We are currently working on the use of comparable films with compartments filled by proteins or peptides and in which the degradation of the barriers results from a hydrolysis over tunable time scales.
| Polyetheretherketone as a biomaterial for spinal applications
Toth, J. M., M. Wang, et al. (2006), Biomaterials 27(3): 324-34.
Abstract: Threaded lumbar interbody spinal fusion devices (TIBFD) made from titanium have been reported to be 90% effective for single-level lumbar interbody fusion, although radiographic determination of fusion has been intensely debated in the literature. Using blinded radiographic, biomechanic, histologic, and statistical measures, we evaluated a radiolucent polyetheretherketone (PEEK)-threaded interbody fusion device packed with autograft or rhBMP-2 on an absorbable collagen sponge in 13 sheep at 6 months. Radiographic fusion, increased spinal level biomechanical stiffness, and histologic fusion were demonstrated for the PEEK cages filled with autograft or rhBMP-2 on a collagen sponge. No device degradation or wear debris was observed. Only mild chronic inflammation consisting of a few macrophages was observed in peri-implant tissues. Based on these results, the polymeric biomaterial PEEK may be a useful biomaterial for interbody fusion cages due to the polymer's increased radiolucency and decreased stiffness.
| Polyethylene glycol (PEG) modified bovine pericardium as a biomaterial: a comparative study on immunogenicity
Aravind, S., W. Paul, et al. (1998), J Biomater Appl 13(2): 158-65.
Abstract: Bioprosthetic heart valves made from glutaraldehyde (GA)-fixed porcine aortic valves or bovine pericardium (BP) are having some advantages over mechanical valves. However, their durability is low due to the calcification and immunological rejection. Study on immunogenicity is an important part in understanding the biocompatibility of materials. Polyethylene glycol (PEG) on pericardium can control biodegradation and calcification. Also, PEG exhibits low immunogenicity. We have studied the complement activation potential and the contribution of complement factors (biologic factors) on the calcification of PEG grafted pericardium samples and compared with standard (control) glutaraldehyde-treated pericardium samples. PEG-grafted BP activated using GA and carbodiimide (EDC) could be selected for further studies since complement activation and calcification observed on these samples has been relatively low.
| Polyethylene oxide surfaces of variable chain density by chemisorption of PEO-thiol on gold: adsorption of proteins from plasma studied by radiolabelling and immunoblotting
Unsworth, L. D., H. Sheardown, et al. (2005), Biomaterials 26(30): 5927-33.
Abstract: The mechanisms involved in the inhibition of protein adsorption by polyethylene oxide (PEO) are not completely understood, but it is believed that PEO chain length, chain density and chain conformation all play a role. In this work, surfaces formed by chemisorption of PEO-thiol to gold were investigated: the effects of PEO chain density, chain length (600, 750, 2000 and 5000 MW) and end-group (-OH, -OCH3) on protein adsorption from plasma are reported. Similar to previous single protein adsorption studies (L.D. Unsworth et al., Langmuir 2005;21:1036-41) it was found that, of the different surfaces investigated, PEO layers formed from solutions near the cloud point adsorbed the lowest amount of fibrinogen from plasma. Layers of hydroxyl-terminated PEO of MW 600 formed under these low solubility conditions showed almost complete suppression (versus controls) of the Vroman effect, with 20+/-1 ng/cm2 adsorbed fibrinogen at the Vroman peak and 6.7+/-0.6 ng/cm2 at higher plasma concentration. By comparison, Vroman peak adsorption was 70+/-20 and 50+/-3 ng/cm2, respectively, for 750-OCH3 and 2000-OCH3 layers formed under low solubility conditions; adsorption on these surfaces at higher plasma concentration was 16+/-9 and 12+/-3 ng/cm2. Thus in addition to the effect of solution conditions noted previously, the results of this study also suggest a chain end group effect which inhibits fibrinogen adsorption to, and/or facilitates displacement from, hydroxyl terminated PEO layers. Fibrinogen adsorption from plasma was not significantly different for surfaces prepared with PEO of molecular weight 750 and 2000 when the chain density was the same (approximately 0.5 chains/nm2) supporting the conclusion that chain density may be the key property for suppression of protein adsorption. The proteins eluted from the surfaces after contact with plasma were investigated by SDS-PAGE and immunoblotting. A number of proteins were detected on the various surfaces including fibrinogen, albumin, C3 and apolipoprotein A-I. The blot responses were zero or weak for all four proteins of the contact system; some complement activation was observed on all of the surfaces studied.
| Polyethylene wear particle generation in vivo in an alumina medial pivot total knee prosthesis
Minoda, Y., A. Kobayashi, et al. (2005), Biomaterials 26(30): 6034-40.
Abstract: Polyethylene wear particle generation is one of the most important factors affecting mid- to long-term results of total knee arthroplasties. It has been reported that the medial pivot total knee prosthesis (MP) design and alumina ceramic femoral component reduce polyethylene wear. The aim of this study is to evaluate in vivo polyethylene wear particle generation in the newly introduced alumina MP, in comparison with a metal MP. Synovial fluid was obtained from 11 knees with alumina MP and 15 knees with metal MP at nine months after the operation. Polyethylene particles were isolated, and examined using scanning electron microscope and image analyzer. Total number of particles in each knee was 7.10+/-2.86x10(6) in alumina (mean+/-standard error), and 5.70+/-2.82x10(7) in metal MP (p=0.048). Particle size (equivalent circle diameter) was 0.78+/-0.04 microm in alumina, and 0.66+/-0.06 microm in metal MP (p=0.120). Particle shape (aspect ratio) was 1.52+/-0.05 in alumina, and 1.88+/-0.11 in metal MP (p=0.014). Apart from the femoral component, the material and manufacturing method of polyethylene insert differed between the two groups, although the sterilization method was the same. Alumina MP generated fewer and rounder polyethylene wear particles than metal MP in early clinical stage, and could potentially reduce prevalence of osteolysis and aseptic loosening.
| Polyglycolic acid/chitosan glue and apoptosis of endometriotic cells
Wang, Y. C., R. H. Fu, et al. (2005), Fertil Steril 84(1): 75-81.
Abstract: OBJECTIVE: To induce apoptosis of endometriotic cells of patients with endometriosis. DESIGN: To demonstrate that polyglycolic acid/chitosan glue directly inhibits cell proliferation by inducing apoptosis. SETTING: University hospital infertility center. PATIENT(S): Twelve women who visited the center for infertility therapy. INTERVENTION(S): Polyglycolic acid/chitosan glue was applied into primary endometriotic cells; the manipulated cells were collected 1-4 days after polyglycolic acid/chitosan glue treatment. MAIN OUTCOME MEASURE(S): Primary endometriotic cell cultures from eutopic endometriotic tissue were established. The effect of the novel biological glue, polyglycolic acid/chitosan glue A, on endometrial cells in vitro was examined. The different stages of apoptosis were analyzed using flow cytometry with fluorescein isothiocyanate conjugate (FITC)-annexin V and propidium iodide staining. RESULT(S): The growth inhibitory effects of polyglycolic acid/chitosan glue A on endometrial cells were found to be dose-response and time dependent. Less than 15% viability was detected in cultures containing 2,000 microg of polyglycolic acid/chitosan glue A after 4 days of treatment. Induced apoptosis and caspase activity were revealed. The caspase-3 activity increased 2.2-fold with 4 days of culture with 2,000 microg of polyglycolic acid/chitosan glue A. CONCLUSION(S): This is the first study to demonstrate that polyglycolic acid/chitosan glue directly inhibits cell proliferation by inducing apoptosis, thus suggesting that this new biological glue may be useful for endometriosis therapy.
| Polyglycolic acid/poly-L-lactic acid copolymer use in laryngotracheal reconstruction: a rabbit model
Klein, A. M., V. L. Graham, et al. (2005), Laryngoscope 115(4): 583-7.
Abstract: OBJECTIVE: To evaluate the tissue response and resorption of the polyglycolic acid/poly-L-lactic acid (PGA/PLLA) implant in laryngotracheal reconstruction and compare its dynamic stability with autologous cartilage grafts. STUDY DESIGN: An interventional, before-after trial. METHODS: Twenty-one white, female, New Zealand rabbits were divided into four groups. Groups A and B underwent laryngotracheoplasty using the PGA/PLLA implants of 3 and 4 mm widths. Group C received autologous ear cartilage grafts. Group D was the control group and did not undergo surgery. The subjects were sedated at 12 months, and the larynges were evaluated in vivo for stability and area measurements by way of endoscopy during spontaneous respiration. The subjects were then killed, the larynges harvested, and the negative intraluminal pressures applied to the laryngotracheal unit were measured in a closed-system apparatus. The larynges were then evaluated for inflammatory reaction and implant resorption by way of histologic analysis. RESULTS: All implanted subjects survived without complications and grew normally. There was no appreciable subglottic collapse during spontaneous respiration under anesthesia. Ex vivo examination of maximum negative intraluminal pressures (-50 cm H2O) in a closed system demonstrated subglottic collapse of 78%, 72%, 61%, and 3% for groups A, B, C, and D, respectively, revealing the inherent weakness in the surgically manipulated airways regardless of grafting material. Histologically, the PGA/PLLA implants were essentially completely resorbed. CONCLUSIONS: PGA/PLLA appears to be a safe and effective synthetic material for use in laryngotracheal reconstruction in the rabbit model while avoiding donor site morbidity and additional operative time. Reconstructed airways maintained adequate strength and patency under physiologic conditions and are comparable with autologous cartilage grafts.
| Polyimide-polyethylene glycol block copolymers: synthesis, characterization, and initial evaluation as a biomaterial
Pathak, C. P., A. S. Sawhney, et al. (1994), J Biomater Sci Polym Ed 6(4): 313-23.
Abstract: Block copolyimides with varying amounts of polyethylene glycol (PEG) were synthesized and characterized by copolymerization of diaminodiphenyl ether (DDE), amino terminated PEG, and benzophenone tetracarboxylic acid dianhydride (BTDA). Strong materials were obtained, with enhanced flexibility as compared to the parent DDE-BTDA polyimide homopolymer. Incorporation of PEG led to an increase in water absorption by these copolymers, and hydrophilicity was increased as reflected by a decrease in air-water-polymer contact angle. These materials supported less cell adhesion in vitro than the parent polyimide homopolymer. Short term in vivo evaluation of these copolymers showed reduced fibrous encapsulation than was observed in the absence of PEG.
| Polyimides as biomaterials: preliminary biocompatibility testing
Richardson, R. R., Jr., J. A. Miller, et al. (1993), Biomaterials 14(8): 627-35.
Abstract: A number of commercially available polyimide materials were evaluated in vitro using a selected battery of levels I and II testing protocols prescribed by the National Institutes of Health Guidelines for Blood-Material Interactions. These procedures consisted of electron spectroscopy for chemical analysis and contact angle characterization surface studies, and protein adsorption, cell culture cytotoxicity, clotting time and haemolysis biocompatibility testing. The polyimide surfaces were invariant from the bulk composition with 60-80% C, 10-20% O and 2-5% N, producing advancing contact angles in the hydrophobic range (80-100 degrees). Consequently, they adsorbed significant amounts of albumin (2-3 micrograms/cm2) and fibrinogen (0.5-0.8 microgram/cm2). The polyimides also displayed an insignificant level of cytotoxicity and haemolysis, and clotting times ranged from 63 to 98% of normal. These clotting times and haemolytic index values were intermediate between the values observed for Teflon and Silastic controls. These factors, along with the strong adherence of polyimides to metal oxide substrates, indicate that polyimide materials are good candidates for further testing as encapsulants for implantable biosensors.
| Polyketal nanoparticles: a new pH-sensitive biodegradable drug delivery vehicle
Heffernan, M. J. and N. Murthy (2005), Bioconjug Chem 16(6): 1340-2.
Abstract: In this report, we present an acid-sensitive drug delivery vehicle, termed polyketal nanoparticles, which are designed to target therapeutics to the acidic environments of tumors, inflammatory tissues, and phagosomes. The polyketal nanoparticles are formulated from poly(1,4-phenyleneacetone dimethylene ketal) (PPADK), a new hydrophobic polymer which contains ketal linkages in its backbone. The polyketal nanoparticles undergo acid-catalyzed hydrolysis into low molecular weight hydrophilic compounds and should therefore release encapsulated therapeutics at an accelerated rate in acidic environments. Importantly, the polyketal nanoparticles do not generate acidic degradation products after hydrolysis, as with polyester-based biomaterials. Dexamethasone-loaded nanoparticles, 200-600 nm in diameter, were fabricated with PPADK via an emulsion procedure using chloroform and water. The hydrolysis half-life of PPADK was measured to be 102 h at pH 7.4 and 35 h at pH 5.0. PPADK was synthesized by a new polymerization strategy based on the acetal exchange reaction. This new delivery system should find numerous applications in the field of drug delivery because of its ease of synthesis and excellent degradation properties.
| Polylactide-polyglycolide antibiotic implants
Garvin, K. and C. Feschuk (2005), Clin Orthop Relat Res(437): 105-10.
Abstract: Surgeons continually struggle to reduce orthopaedic infections, but no current treatment offers minimum side effects with maximum effectiveness. Antibiotics mixed in plaster of paris have been successful in treating large bony defects in patients with chronic osteomyelitis, and have the advantage of being well tolerated and absorbed by the body. Antibiotics impregnated in polymethylmethacrylate (PMMA) have offered local antibiotic delivery with some success. However, the effect of the antibiotic on the bone cement, the inconsistent elution of the antibiotic, and the need to remove the PMMA implant drives the need for a better system of antibiotic delivery. Polymers or copolymers of antibiotic-impregnated polylactic acid, polyglycolic acid or polyparadioxanone may provide an absorbable system for localized antibiotic delivery. Similar biodegradable systems used to treat small bone fractures have been successful with minimal side effects. In vitro studies have shown promising results of antibiotic elution from bioabsorbable microspheres and beads. Animal in vivo tests have shown that antibiotic impregnated polymers can successfully treat induced osteomyelitis in rabbits and dogs. These studies have provided consistent reproducible results, and now it is time to plan human trials to assess the efficacy of antibiotic microspheres implanted in infected bone and to plan in vivo and in vitro animal testing to investigate the feasibility of antibiotic-polymer-coated components.
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