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PubMed1998

Arterial uptake of biodegradable nanoparticles for intravascular local drug delivery: results with an acute dog model.

Biodegradable nanoparticles (NP) with a spherical diameter ranging from 70 to 160 nm were investigated for potential usefulness for the local intraluminal therapy of restenosis, the disease process responsible for arterial reobstruction following angioplasty. NPs containing a water-insoluble anti-proliferative agent U-86983 (U-86, Pharmacia and Upjohn, Kalamazoo, MI) were formulated from oil-water emulsions using biodegradable polymers such as poly(lactic acid-co-glycolic acid) (PLGA), and specific additives after particle formation, to enhance arterial retention using either heparin, didodecylmethylammonium bromide (DMAB), or fibrinogen, or combinations. Femoral and carotid arteries of male mongrel dogs were isolated in situ, and were then subjected to a balloon angioplasty. A NP suspension of a predetermined concentration was then infused into the artery for various durations. This was followed by a 30 min restoration of blood flow through the vessel. The arterial segments were excised and analyzed for drug levels. From the drug loading the NP and the drug levels in the artery, the quantity of nanoparticles retained was calculated and expressed as microgram per 10 mg dry arteries. In general, repeated short infusions of nanoparticle suspension (15 s x 4) were two-fold more effective in terms of higher arterial U-86 levels than a single prolonged infusion (60 s). A single 15 s infusion was not significantly different than a 60 s compared to non-modified NPs (39.2 +/- 2.5 and 49.1 +/- 2.4 vs. 21.5 +/- 0.6 micrograms/10 mg mean +/- s.e., respectively). A comparably enhanced NP uptake was noted with a combined heparin/DMAB modification. Increasing the concentration of NP in infusate from 5 to 30 mg ml-1 significantly increased arterial NP uptake level (from 22.5 +/- 3.5 to 83.7 +/- 1.4 micrograms/10 mg). Thus, the results support the view that modified nanoparticles along with optimized infusion conditions could enhance arterial wall drug concentrations of agents to treat restenosis.

Angioplasty, Balloon↗

PubMed1999

Antibiotic release from biodegradable PHBV microparticles.

For the treatment of periodontal diseases, design of a controlled release system seemed very appropriate for an effective, long term result. In this study a novel, biodegradable microbial polyester, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV of various valerate contents containing a well established antibiotic, tetracycline, known to be effective against many of the periodontal disease related microorganisms, was used in the construction of a controlled release system. Tetracycline was loaded in the PHBV microspheres and microcapsules both in its acidic (TC) and in neutral form (TCN). Microcapsules of PHBV were prepared under different conditions using w/o/w double emulsion and their properties such as encapsulation efficiency, loading, release characteristics, and morphological properties were investigated. It was found that concentration of emulsifiers polyvinyl alcohol (PVA) and gelatin (varied between 0-4%) influenced the encapsulation efficiency appreciably. In order to increase encapsulation efficiency (from the obtained range of 18.1-30.1%) and slow down the release of the highly soluble tetracycline.HCl, it was neutralized with NaOH. Encapsulation efficiency of neutralized tetracycline was much higher (51.9-65.3%) due to the insoluble form of the drug used during encapsulation. The release behaviour of neither of the drugs was found to be of zero order. Rather the trends fitted reasonably well to Higuchi's approach for release from spherical micropheres. Biodegradability was not an appreciable parameter in the release from microcapsules because release was complete before any signs of degradation were observed.

Bacteria↗

PubMed1999

Biodegradable recombinant human erythropoietin loaded microspheres prepared from linear and star-branched block copolymers: influence of encapsulation technique and polymer composition on particle characteristics.

Recombinant human erythropoietin (EPO) and fluorescein isothiocyanate labeled dextran (FITC-dextran) loaded microspheres were prepared by a modified W/O/W double-emulsion technique. Biodegradable linear ABA block copolymers consisting of poly(L-lactide-co-glycolide) A blocks attached to central poly(ethyleneoxide) (PEO) B blocks and star-branched AB block copolymers containing A blocks of poly(L-lactide) or poly(L-lactide-co-glycolide) and star-branched poly(ethyleneoxide) B blocks were investigated for their potential as sustained release drug delivery systems. Microsphere characteristics were strongly influenced by the polymer composition. In the case of the linear block copolymers, a reduced lactic acid content in a linear block copolymer yielded smaller particles, a lower encapsulation efficiency, and a higher initial drug release both in the case of EPO and FITC-dextran. The investigation of the effects of several manufacturing parameters on microsphere formation showed that the process temperature plays an important role. Microsphere formation in a +1 degrees C environment resulted in higher drug loadings without increasing the amount of residual dichloromethane inside the particles. Other parameters such as the homogenization of the primary W/O emulsion and of the W/O/W double-emulsion have less impact on microsphere characteristics. Branched block copolymers containing star-shaped PEO also showed potential for the preparation of drug loaded microspheres. A certain amount of glycolic acid in the copolymer was necessary for the successful preparation of non-aggregating microspheres at room temperature. Again, the processing temperature strongly affected particle characteristics. Microsphere preparation at +1 degrees C allows the formation of microspheres from a polymer not containing glycolic acid, a result which could not be achieved at room temperature. Moreover, compared to microsphere formation at room temperature, the effective FITC-dextran loading was increased. Concerning the EPO loaded microspheres, the amount of EPO aggregated was comparable to that using the linear ABA polymers. A continuous release of the protein from these star-shaped polymers could not be achieved. In conclusion, apart from microsphere preparation in a +1 degrees C environment the choice of the polymer represents the main factor for a successful entrapment of proteins into biodegradable microspheres.

Biodegradation, Environmental↗

PubMed2000

Biodegradable semi-crystalline comb polyesters influence the microsphere production by means of a supercritical fluid extraction technique (ASES).

The aerosol solvent extraction system (ASES) is a method based on solvent extraction using supercritical carbon dioxide for the preparation of microspheres. The ASES technology seems to be strongly affected by physico-chemical properties of biodegradable polymers, leading to incomplete or unsuccessful microsphere formation. The number of suitable polymers for ASES, such as poly(L-lactide) (L-PLA) and poly(beta-hydroxy-butyric acid) (PHB) is rather limited for unknown reasons. Therefore linear and novel branched polyesters were synthesized and subjected to the ASES process to explore the function property relationship. The properties of these polymers as well as of the ASES products were characterized by NMR spectroscopy, differential scanning calorimetry, light scattering, wide-angle X-ray scattering and scanning electron microscopy. It appears that high degrees of polymer crystallinity are the key factor for successful microsphere formation using the ASES process. Under the conditions investigated two types of polymers were especially suitable: semi-crystalline comb polyesters as well as comb polyesters in which crystallinity could be induced. These novel polymers are of particular interest for the ASES encapsulation technology since they combine beneficial properties both controlling drug release due to their three-dimensional architecture and faster biodegradability with sufficient mechanical stability to allow particle formation using supercritical carbon dioxide.

Biocompatible Materials↗

PubMed2001

Modeling hydrocarbon biodegradation in tidal aquifers with water-saturation and heat inhibition effects.

A model is developed for hydrocarbon biodegradation, which includes saturated and unsaturated flow, multi-species transport, heat transport, and bacterial growth processes. Numerical accuracy of the model was tested against analytical solutions. The model was also verified against laboratory results for a saturated-flow problem and reasonable match was obtained. Expressions are proposed for inhibition due to water content and temperature fluctuations. Bioactivities under cyclic water content variation were studied under no-flow conditions. A quantitative approach was used to reconcile some of the apparent contradictory conclusions regarding the efficiency of biodegradation of soils under wetting and drying conditions. The efficiency depends on the nature of the oxygenation process. For cases involving the presence of dissolved oxygen and the absence of O2 vapor, subjecting the soil to constant water content close to its optimal value for degradation is most efficient. However, wetting and drying can enhance degradation if O2 is only provided through aeration or direct contact between air and the medium. Also presented are the results of a typical field application of the model and a discussion of the effects of tides, saturation inhibition, and heat inhibition. Other inhibition factors, such as pH or salinity, can be easily incorporated in the formulation. The quantitative approach developed here can be used in assessing bioremediation not only in tidal aquifers but also in areas where water-table or temperature effects are of significance. The approach can be useful in the design of remediation strategies under water-flow or no-flow conditions involving water content and temperature fluctuations.

Biodegradation, Environmental↗

PubMed2001

Successive identification of biodegradation rates for multiple sequentially reactive contaminants in groundwater.

At the field scale, the biodegradation rate is usually estimated from analytical solutions to single species transport with first-order reactions, using measured data as input. Because many contaminants, e.g., chlorinated solvents, are degraded in a sequential pattern, with degradation products further reacting to produce new species, it is of great interest to quantify the transformation rate of every reaction. The conventional inverse solutions for identifying the transformation rates are limited to single species problems. In the present study, we propose a successive optimization approach to identify the biodegradation rate for each species by using a previously developed analytical solution to multi-species first-order reactive transport using data obtained at the field scale. By specifying a link between analytical solutions to sequentially reactive transport problems and optimization methods and assuming constant transport parameters (velocity, dispersivities, and retardation factors), the first-order transformation rates are optimized successively from parent species to its daughter species.

Biodegradation, Environmental↗

PubMed2003

Modelling biodegradation of hydrocarbons in aquifers: when is the use of the instantaneous reaction approximation justified?

In-situ bio-remediation is a viable cleanup alternative for aquifers contaminated by hydrocarbons such as BTEX. Transport models of varying complexity and capabilities are used to quantify their degradation. A model that has gained wide acceptance in applications is BIOPLUME II, which assumes that oxygen-limited biodegradation takes place as an instantaneous reaction. In this work we have employed theoretical analysis, using non-dimensional variables, and numerical modelling to establish a quantitative criterion demarcating the range of validity of the instantaneous reaction approximation against biodegradation kinetics. Oxygen was the limiting species and sorption was ignored. This criterion relates (o), the Dahmköhler number at oxygen depletion, to O(o)*, the ratio of initial to input oxygen concentration, (o) > or = 0.7(O(o)*)(2) + 0.1O(o)* + 1.8. The derived (o) reflects the intrinsic characteristics of the physical transport and of the biochemical reaction, including the effect of biomass density. Relative availability of oxygen and hydrocarbons exerts a small influence on results. Theory, verified and refined via numerical simulations, showed that significant deviations of instantaneous reactions from kinetics are to be expected in the space-time region s<L(d), t<T(d) ('near source' and 'initial period'). Under the assumptions considered, numerical simulations also verified the wide applicability of the computationally efficient, stoichiometry-based (algebraic) BIOPLUME concept. Kinetic modelling is required only in active (engineered) bio-remediation cases, with high velocities (e.g., near pumped wells), and for short distances from the source.

Biodegradation, Environmental↗

PubMed1997

Mandibular osteotomy fixed with biodegradable plates and screws: an animal study.

The objective of the study was to evaluate the use of a totally biodegradable fixation device in the fixation of mandibular osteotomy in sheep. Mandibular unilateral body osteotomies were fixed with biodegradable self-reinforced poly-L-lactide (SR-PLLA) multi-layer plates and screws in nine sheep. The unoperated sides acted as control. The follow-up times were 6, 12 and 24 weeks, after which radiological, mechanical and histological studies were carried out. An analysis of the implanted material was also carried out. The results showed that the SR-PLLA plates and screws were strong enough to fix the osteotomy and that the osteotomies healed mainly with callus formation. Therefore we conclude that SR-PLLA multi-layer plates and screws can be used together successfully in the fixation of mandibular osteotomies without maxillomandibular fixation. However, before they can be used in humans, the size of the plate and screws should be decreased.

Animals↗

PubMed2002

Mass transfer studies on the biodegradation of phenols in up-flow packed bed reactors.

A quantitative analysis of the effect of mass transfer coefficients on the operating parameters namely, flow rate, bed height, particle and column diameter, voidage and initial concentration of phenols, etc. is carried out for the biodegradation of phenols in an up-flow packed bed reactor. A mass transfer correlation of the type, j(D)=K (Re')(n-1) is developed to represent the present experimental data obtained using activated carbon-Pseudomonas pictorum-alginate, celite-P. pictorum-alginate and P. pictorum-alginate beads for the continuous biodegradation of phenol. The overall reaction rate was found to be of the first order with the mass transfer as the rate-limiting step. For mass transfer with biochemical reaction, a correlation of experiment with theory is made. A realistic estimate of the effects of external mass transfer coefficients is also made in this present work.

Biodegradation, Environmental↗

PubMed2003

Treatment of brines by combined Fenton's reagent-aerobic biodegradation. II. Process modelling.

Process modelling of the integrated Fenton's reagent-aerobic biodegradation system has been carried out by considering a detailed reaction mechanism for the chemical oxidation step and the generalised Monod equation for the biological treatment. Chemical oxygen demand has been contemplated as a pseudo-component for simulation purposes. The proposed mechanism takes into consideration different features experimentally found. Thus, the inefficient hydrogen peroxide decomposition into oxygen and water, the influence of temperature and other operating variables and the role of oxygen have been considered. The aerobic biodegradation of the effluent after the chemical oxidation has taken place has been well simulated by Monod equation with no inhibitory terms. Dependency on temperature has been correlated by Arrhenius expression.

Bacteria, Aerobic↗

PubMed2002

Biodegradability of inhaled p-aramid respirable fiber-shaped particulates (RFP): mechanisms of RFP shortening and evidence of reversibility of pulmonary lesions.

These studies elucidated mechanisms of inhaled p-aramid respirable fiber-shaped particulates (RFP) biodegradation in the lungs of exposed rats and hamsters. We postulate that lung fluids coat/activate inhaled p-aramid RFP which deposits in the lung and promote enzymatic attack and consequent shortening. p-Aramid or cellulose (biopersistent control) RFP were instilled into the lungs of rats and the lungs digested 24 h later using two different (KOH or enzymatic) digestion techniques. In vivo, the enzyme but not the KOH solution produced shortening of p-aramid but not cellulose RFP recovered from the lungs. For in vitro studies, the two RFP-types were incubated with BAL fluids and underwent simulated digestions; also rat lung epithelial cells, macrophages or co-cultures were incubated with p-aramid and digested at 1, 24, or 168 h postexposure. The results of in vitro acellular studies demonstrated that only p-aramid RFP incubated in BAL fluids and digested by the enzyme method were shortened. In vitro cellular studies demonstrated a shortening of p-aramid RFP in macrophages and co-cultures but not in lung epithelial cells at 24 h and 1 week postexposure. These results demonstrate that lung fluids coat and catalyze the p-aramid RFP as a prelude for shortening and describe a likely mechanism for the biodegradability of inhaled p-aramid RFP in the lungs of exposed animals.

Administration, Inhalation↗

PubMed1999

A method using biodegradable polylactides/polyethylene glycol for drug release with reduced initial burst.

Post-coating of biodegradable polylactides (PLA)/polyethylene glycol (PEG) microspheres with a gelatin film produced by dipping the microspheres into a gelatin solution to reduce the initial drug release burst was investigated. Biodegradable block PLA/PEG microspheres, prepared by w/o emulsion/solvent evaporation, showed that the hydrophilic segment PEG protruded to the sphere surface. However, these microspheres also showed a large burst release in the initial period. Post-coating of the PLA/PEG microspheres with a gelatin film by dipping the microspheres into a dilute gelatin solution effectively inhibited the initial burst release rate in the drug release tests. Post-coating of gelatin reduced 98% of the burst release. With thicker coatings, there were slower releasing rates, and the release rate can be simply related to the coating thickness.

Anti-Arrhythmia Agents↗

PubMed1999

Importance of Xanthobacter autotrophicus in toluene biodegradation within a contaminated stream.

Toluene-degrading strains T101 and T102 were isolated from rock surface biomass in a toluene-contaminated freshwater stream. These organisms were present at a density of 5.5 x 10(6) cells/g of rock surface biomass. Both are aerobic, rod-shaped, Gram-negative, non-motile, catalase-positive, oxidase-positive, with yellow pigments, and can grow on benzene. Phylogenetic analyses show that strains T101 and T102 have 16S rDNA sequences identical to Xanthobacter autotrophicus. Fatty acid analyses indicate that they are different strains of the same species Xanthobacter autotrophicus, and that they have high levels of cis-11-octadecenoic acid and cis-9-hexadecenoic acid; 3-hydroxyhexadecanoic acid is the major hydroxy fatty acid present. Strains T101 and T102 had maximal velocities (Vmax) for toluene biodegradation of 3.8 +/- 0.5 and 28.3 +/- 2.2 mumoles toluene/mgprotein-hr, and half-saturation constants (Ks) of 0.8 +/- 0.5 and 11.5 +/- 2.4 microM, respectively. Strain T102 has a higher capacity than strain T101 to degrade toluene, and kinetic calculations suggest that strain T102 may be a major contributor to toluene biodegradation in the stream.

Biodegradation, Environmental↗

PubMed1997

Pharmacokinetics and pharmacodynamics of a sustained-release biodegradable pellet containing imidapril, a new angiotensin-converting enzyme inhibitor in spontaneously hypertensive rats.

The pharmacokinetics and pharmacodynamics (PK/PD) of a sustained-release biodegradable pellet containing imidapril, a new angiotensin-converting enzyme (ACE) inhibitor, were investigated in comparison with those of an osmotic pump in male spontaneously hypertensive rats (SHRs). A pellet was prepared from copolymer of DL-lactic acid and glycolic acid by the melt-pressing technique. Imidapril was released in vitro from the pellet at an approximately zero-order rate and the release profile was similar to that of the osmotic pump. Imidapril was administered subcutaneously via a pellet or an osmotic pump implanted under the skin in the back of SHRs. Plasma concentrations of imidaprilat as an active metabolite of imidapril, plasma ACE activity and systolic blood pressure (SBP) were determined periodically. The plasma concentration of imidaprilat during the administration of a pellet was maintained for 4 weeks, and the plasma concentration profile was close to that of the osmotic pump. Both groups of pellet and osmotic pump significantly inhibited plasma ACE activity and reduced SBP for 4 weeks, and these action profiles were similar in both groups. In addition, in vivo release profile of the pellet was close to the in vitro release profile, and the in vivo release profiles of the pellet and the osmotic pump were similar to each other. From these results, it was found that the PK/PD of a biodegradable pellet were close to those of the osmotic pump, and it was shown that the pellet may be a useful system to maintain the plasma concentration of imidaprilat for a long time.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1997

All-inside anterior cruciate ligament reconstruction using semitendinosus tendon and soft threaded biodegradable interference screw fixation.

A modification of anterior cruciate ligament (ACL) reconstruction using a minimally invasive and endoscopic all-inside technique is presented. Both the femoral and tibial socket are approached through the joint so that there is no open tibial tunnel, which otherwise often causes significant pain and discomfort during early rehabilitation. The autologous semitendinosus tendon is harvested with a bone plug attached to its tibial insertion. The triple-stranded semitendinosus tendon is looped around the adjacent bone plug and fixed at the original tibial attachment site of the ACL using a soft threaded biodegradable poly-(D,L-lactide) interference screw. The screw is inserted endoscopically in an inside-out direction. In the femoral socket the graft is fixed without a bone plug directly to the tunnel wall using the biodegradable screw. The free part of the graft is thus not longer than the intra-articular distance, which may increase stiffness of the construct.

Absorption↗

PubMed1997

Failure strengths of suture versus biodegradable arrow for meniscal repair: an in vitro study.

Advances in our understanding of meniscal function and consequences of menisectomy have spawned meniscal repair techniques that yield success rates approaching 90% in properly selected patients. Biodegradable implants have been fashioned for meniscal fixation to simplify the technique and minimize neurovascular complications. We performed the current study to determine the in vitro biomechanical behavior of the BIOFIX Meniscal Arrow, a polylactic acid tack developed for meniscal repair. Eight pairs of menisci were harvested from cadaveric knees kept frozen before testing. Peripheral vertical tears were created in the posterior horn of all menisci, and each was subsequently repaired using a vertical loop suture of 2-0 Ethibond and a Meniscal arrow. Ultimate load to failure of each method was determined on a Hounsfield H25KM Universal Testing machine. The mean failure load for the suture group was 58.3 N compared with the Arrow group mean of 29.6 N (P < .001). All sutures failed by rupture at the knot but did not pull through the meniscus. All but one of the arrows failed by pulling out of the meniscus. The Arrows also permitted gapping at the repair site at considerably lesser loads than the sutures subject to strain. The concept of a biodegradable tack is appealing. Vertical loop sutures should be the standard by which their biomechanical performance is judged. We suggest modifications to the Arrow design that could enhance the fixation strength of this implant.

Aged↗

PubMed1998

Orthopaedic applications for PLA-PGA biodegradable polymers.

Biodegradable polymers, especially those belonging to the family of polylactic acid (PLA) and polyglycolic acid (PGA), play an increasingly important role in orthopaedics. These polymers degrade by hydrolysis and enzymatic activity and have a range of mechanical and physical properties that can be engineered appropriately to suit a particular application. Their degradation characteristics depend on several parameters including their molecular structure, crystallinity, and copolymer ratio. These biomaterials are also rapidly gaining recognition in the fledging field of tissue engineering because they can be fashioned into porous scaffolds or carriers of cells, extracellular matrix components, and bioactive agents. Although their future appears to be bright, several questions regarding the biocompatibility of these materials linger and should be addressed before their wide-scale use. In the context of musculoskeletal tissue, this report provides a comprehensive review of properties and applications of biodegradable PLA/PGA polymers and their copolymers. Of special interest are orthopaedic applications, biocompatibility studies, and issues of sterilization and storage of these versatile biomaterials. Also discussed is the fact that terms such as PLA, PGA, or PLA-PGA do not denote one material, but rather a large family of materials that have a wide range of differing bioengineering properties and concomitant biological responses. An analysis of some misconceptions, problems, and potential solutions is also provided.

Absorbable Implants↗

PubMedDate not supplied

Biodegradation of hydroxylated and methoxylated benzoic, phenylacetic and phenylpropenoic acids present in olive mill wastewaters by two bacterial strains.

Two aerobic bacterial strains, a chlorophenol-degrading bacterium characterized in this work as a Ralstonia sp. LD35 on the basis of the sequence of the gene encoding for 16S ribosomal RNA, and Pseudomonas putida DSM 1868, capable of metabolizing 4-methoxybenzoic acid, were tested for their capacity to degrade monocyclic aromatic acids responsible for the toxicity of olive mill wastewaters (OMWs). Both strains possess interesting and complementary degradation capabilities in resting cell conditions: Ralstonia sp. LD35 was found to metabolize 4-hydroxybenzoic, 4-hydroxyphenylacetic, 3,4-dihydroxycinnamic and cinnamic acid, whereas DSM 1868 was capable of metabolizing 4-hydroxy-3-methoxybenzoic, 3,4-dimethoxybenzoic and 4-hydroxy-3,5-dimethoxybenzoic acid, as well as 4-hydroxybenzoic and 4-hydroxyphenylacetic acid. The kinetic parameters describing the growth of the two strains on the same compounds were determined in growing-cell batch conditions, and showed that both strains presented high affinity and high specific growth rates towards all assayed substrates. In addition, the two strains were capable of growing on and extensively biodegrading a mixture of monocyclic aromatic acids commonly found at high concentrations in OMWs, and of growing on a 20% dilution of a natural OMW. All these features make the two strains attractive candidates for the development of a biotechnological process for the biodegradation of aromatic compounds found in OMWs.

Betaproteobacteria↗