ABSTRACT
Subcutaneous immunization with SYI, a peptide construct based on Streptococcus mutans glucan binding protein B (GbpB) residues 113-132, significantly reduces experimental dental caries. Since mucosal immunization may be preferred for human vaccine applications, the present objective was to determine what formulation of SYI combined with polylactide-coglycolide microparticles could give rise to significant levels of salivary IgA antibody reactive with the native GbpB protein. A comparison of the SYI construct, loaded into or mixed with polylactide-coglycolide revealed the SYI-loaded microparticles to induce significant and sustainable levels of salivary and nasal wash IgA antibody to the peptide and the native protein. SYI mixed with unloaded microparticles was less effective in mucosal antibody response induction. These studies indicate that mucosal immunization with the SYI construct can induce salivary IgA antibody to a pathogenesis-associated component of S. mutans if delivered within polylactide-coglycolide microparticles, suggesting that this approach could successfully induce protective salivary immunity to dental caries caused by S. mutans.
Subject(s)
Antigens, Bacterial/immunology , Bacterial Proteins/immunology , Bacterial Vaccines/immunology , Glycoproteins/immunology , Saliva/immunology , Streptococcus mutans/immunology , Animals , Dental Caries/prevention & control , Particle Size , Rats , Rats, Sprague-Dawley , Streptococcus mutans/drug effectsABSTRACT
Intranasally administered dental caries vaccines show significant promise for human application. Alternate mucosal routes may be required, however, to induce caries-protective salivary IgA antibody in children with respiratory diseases. Since rectal mucosa contains inductive lymphoid tissue, we hypothesized that the rectal route could be used to induce salivary immunity to mutans streptococcal glucosyltransferase (GTF), resulting in protective immunity to experimental dental caries. We first explored the ability of glucosyltransferase, incorporated into polylactide-co-glycolide (PLGA) microparticles (MP), and administered rectally together with mucosal adjuvant, to induce a salivary IgA antibody response. Groups of Sprague-Dawley rats (6/group) were immunized rectally on days 0, 7, 14 and 21 with a) GTF-MP alone, b) GTF-MP with cholera toxin, c) GTF-MP with detoxified mutant Escherichia coli toxin (dLT), or d) sham immunized with PLGA and cholera toxin. An additional group was immunized intranasally with GTF-MP alone. Saliva and nasal washes of all intranasally immunized rats contained IgA antibody to glucosyltransferase on day 28. Salivary IgA antibody was also detected in 7/12 rats rectally immunized with GTF-MP and cholera toxin or dLT, although responses were lower than those obtained by intranasal immunization. Most fecal extracts from rectally delivered GTF-MP plus cholera toxin or dLT rats contained IgA antibody to GTF-MP. Low levels of fecal IgA antibody were detected in 3/6 intranasally immunized rats and 2/6 rats rectally immunized with GTF-MP alone. We then examined the extent to which salivary IgA antibody induced by the rectal route could be protective. At 25, 31 and 38 days of age, two groups of female Sprague-Dawley rats (13/group) were rectally immunized with GTF-MP and cholera toxin or with empty microparticles and cholera toxin (sham group). A third group was intranasally immunized with GTF-MP alone. After demonstrating salivary IgA responses to GTF in most GTF-immunized rats, all animals were infected with streptomycin-resistant Streptococcus sobrinus and placed on diet 2000. After 79 days of infection, total caries on molar surfaces were lower in both rectally (7.9 +/- 1.0) and intranasally (7.1 +/- 0.9; P < 0.0.03) immunized groups compared with the sham-immunized group (11.9 +/- 1.6). Smooth surface caries were significantly lower (P < 0.05) in both rectally and intranasally immunized groups. These results support the interconnectedness of the mucosal immune system and indicate that rectal immunization with GTF-MP, together with adjuvant, or intranasal immunization with GTF-MP alone, can induce protective levels of salivary antibody in rats.
Subject(s)
Antibodies, Bacterial/biosynthesis , Dental Caries/prevention & control , Glucosyltransferases/immunology , Saliva/immunology , Streptococcal Vaccines/administration & dosage , Administration, Rectal , Animals , Dental Caries/immunology , Female , Immunity, Mucosal , Immunoglobulin A, Secretory/biosynthesis , Lactic Acid , Polyglycolic Acid , Polylactic Acid-Polyglycolic Acid Copolymer , Polymers , Rats , Rats, Sprague-Dawley , Streptococcus mutans/immunology , Streptococcus sobrinus/enzymologyABSTRACT
In this study a matrix of poly(propylene fumarate) (PPF) was crosslinked with N-vinylpyrrolidone (NVP), 2-hydroxyethylmethacrylate (HEMA), or a mixture of NVP and ethyleneglycol dimethacrylate (EGDMA) in the presence of poly(lactide-co-glycolide) (PLGA) to reinforce and preserve the form of PLGA bone plates. The degree of crosslinkage varied depending on the crosslinker as shown by the rapid and almost complete leaching of NVP upon incubation in phosphate buffered saline at 37 degrees C in 900 h and retention of 92% of HEMA. With the reinforced bone plates extracted for 72 h at room temperature methylene chloride, the extracted PLGA from NVP/PPF, NVP-EGDMA/PPF, and HEMA/PPF were 75.42% (w/w), 59.52% (w/w), and 30.86% (w/w), respectively. The flexural modulus and compressive strength of the crosslinked PPF reinforced bone plates were higher than that of the unreinforced bone plate. Atomic force microscopy showed that NVP/PPF reinforced PLGA bone plates eroded substantially (a mean surface roughness of 19.319 nm) whereas NVP-EGDMA-PPF reinforced bone plate showed a distinct crystalline organization (and a higher roughness, 43.525 nm). In conclusion, we propose the consideration of NVP-EGDMA/PPF reinforced PLGA as a biodegradable orthopedic implant material that has a lower likelihood of warping or failing catastrophically than the currently available materials.
ABSTRACT
Techniques of liver replacement would benefit patients awaiting donor livers and may be a substitute for transplantation in patients whose livers can regenerate. Poly(lactic-co-glycolic acid) (PLGA) copolymers are biodegradable and have been shown to be useful as scaffolds for seeding and culturing various types of cells. In this study, foam disks were prepared from PLGA (lactic-to-glycolic mole ratio of 85:15) by lyophilization of benzene (5% w/v) solutions. These disks were then used as scaffolds for rat hepatocyte culture. Foams were coated with either a type I collagen gel (0.1% w/v), coated with gelatin (5% w/v), or treated with oxygen plasma (25 W, 90 s) to modify their surface chemistry and wettability. The disks were then seeded with rat hepatocytes (10(6)/mL) and cultured for a period of 2 weeks. All surface treatments resulted in increased hydrophilicity, the greatest being obtained by collagen treatment (contact angle < 10 degrees ), and a minimal decrease in void fraction (5%). DNA content after a 2-week culture period increased proportionally with the wettability of the treated foam surface. Urea synthesis in untreated foams averaged 15.3 +/- 2.3 microg/h/microg DNA, which was significantly higher than that for controls, whereas gelatin and collagen treated foams exhibited urea synthetic rates below the control levels at all times. The DNA content decreased significantly by about 50% between days 1 and 12. PLGA foams, treated and untreated, represent a promising scaffold for scaling up hepatocyte cultures.
Subject(s)
Biocompatible Materials , Lactic Acid , Liver/physiology , Polyglycolic Acid , Polymers , Tissue Engineering , Animals , Bioprosthesis , Cell Adhesion/physiology , Cells, Cultured , Liver/cytology , Liver Transplantation , Male , Polylactic Acid-Polyglycolic Acid Copolymer , Rats , Rats, Inbred F344ABSTRACT
Biodegradable materials have various important applications in the biomedical field. There are basically two groups of polyesters which have significant importance in this field. These are polylactides and polyhydroxybutyrates. Both groups degrade via hydrolysis with the rates of degradation depending on medium properties such as pH, temperature, solvent and presence of biocatalysts, as well as on chemical compositions. In order for these biomaterials to be suitable for use in load bearing applications without deformation or warping their strengths and their capability to maintain their form must be improved. To insure dimensional stability during degradation and to match modulus and strength to that of bone, introduction of a reinforcing structure for those applications to plate fixation through the creation of an interpenetrating network might be a feasible approach. In this study, poly(lactide-co-glycolide) (PLGA), was the major structural element to be strengthened by a three-dimensional network or "scaffold" of another biodegradable polymer, poly(propylene fumarate) (PPF). PPF would be crosslinked with a biocompatible vinyl monomer, vinylpyrrolidone (VP). Three different approaches were tested to create dimensionally stable bone plates. First, via in situ crosslinking of PPF in the presence of PLGA. Secondly, by blending of precrosslinked PPF with PLGA. Finally, by simultaneous crosslinking and molding of the PLGA, PPF and VP. These were compared against extruded or compression molded PLGA controls. Results showed that compression molding at room temperature followed by crosslinking under pressure at elevated temperature and subsequently by gamma-irradiation appeared to yield the most favorable product as judged by swelling, hardness and flexural strength data. The composition of the implant material, PLGA(3):PPF(1):VP(0.7), appeared to be suitable and formed the compositional and procedural basis for in vivo biocompatibility studies.
Subject(s)
Absorbable Implants , Fumarates , Lactic Acid , Polyglycolic Acid , Polymers , Polypropylenes , Pyrrolidinones , Absorption , Animals , Biocompatible Materials , Biodegradation, Environmental , Biopolymers , Bone Plates , Hardness Tests , Male , Polylactic Acid-Polyglycolic Acid Copolymer , Rats , Rats, Sprague-DawleyABSTRACT
Biodegradable bone plates were prepared as semi-interpenetrating networks (SIPN) of crosslinked polypropylene fumarate (PPF) within a host matrix of either poly(lactide-co-glycolide)-85:15 (PLGA) or poly(1-lactide-co-d,l-lactide)-70:30 (PLA) using N-vinylpyrrolidone (NVP), ethylene glycol dimethacrylate (EGDMA), 2-hydroxyethyl methacrylate (HEMA), and methyl methacrylate (MMA) as crosslinking agents. Hydroxyapatite (HAP), an inorganic filler material, was used to further augment mechanical strength. The control crosslinking agent (NVP) was replaced partially and totally with other crosslinking agents. The amount of crosslinking agent lost, the characterization change in the mechanical properties and the dimensional stability of the bone plates after in vitro treatment was calculated. The optimum crosslinking agent was selected on the basis of low in vitro release of NVP from SIPN matrix. Bone plates were then prepared using this crosslinking agent at 5 MPa pressure and at temperatures between 100-140 degrees C to determine if there was any augmentation of mechanical properties in the presence of the crosslinked network. In vitro analysis showed that 90% of the crosslinking agent was lost on plates using NVP as a crosslinking agent. This loss was reduced to 50% when NVP was partially replaced with EGDMA or MMA. EGDMA was determined to be superior because (1) its low release as a crosslinking agent, (2) flexural plate strength of 50-67 MPa, (3) flexural modulus of 7-13 GPa, and (4) manufacturability stiffness of 300-600 N/m. HAP-loading resulted in an additional increase in values of mechanical parameters. Substituting PLGA with PLA in the PPF-SIPN did not show any additional improvement of mechanical properties.
Subject(s)
Absorbable Implants , Biocompatible Materials/chemistry , Bone Plates , Cross-Linking Reagents/chemistry , Durapatite/chemistry , Elasticity , Equipment Design , Fumarates/chemistry , Hot Temperature , Humans , Lactic Acid/chemistry , Methacrylates/chemistry , Methylmethacrylate/chemistry , Pliability , Polyesters/chemistry , Polyglycolic Acid/chemistry , Polylactic Acid-Polyglycolic Acid Copolymer , Polymers/chemistry , Polypropylenes/chemistry , Pressure , Pyrrolidinones/chemistry , Stress, MechanicalABSTRACT
Using an established rat peripheral nerve regeneration model, we investigated the role of glial growth factor (GGF) in nerve regeneration in combination with a novel bioresorbable poly(lactic-co-glycolic) acid (PLGA) guide in vivo. Schwann cells, established from a 1-cm segment of excised rat sciatic nerve, were isolated and seeded onto nerve guides with or without GGF (n = 24/group). Living nerve guides were re-established in these animals, and nerve regeneration was assessed over a period of 12 weeks. Histological studies revealed a reduction in the total axon count and the number of myelinated axons in the presence of exogenously added Schwann cells compared to saline controls. In contrast, the addition of GGF alone enhanced the total number of axons and significantly increased the number of blood vessels. Although combining GGF with Schwann cells negated the enhanced numbers of axons and blood vessels seen with GGF alone, this combination resulted in the highest myelination index and the fastest conduction velocities recorded. The PLGA guide material did not trigger any histologically detectable host response and was permissive for nerve regeneration in this animal model. The results from this study demonstrate the potential utility of this guide in vivo and establish a promotional role for GGF in nerve regeneration.
Subject(s)
Nerve Regeneration/drug effects , Neuregulin-1/pharmacology , Peripheral Nerves/drug effects , Schwann Cells/drug effects , Animals , Axons/drug effects , Axons/ultrastructure , Biocompatible Materials , Biomedical Engineering , Electrophysiology , Female , Lactic Acid , Myelin Sheath/drug effects , Myelin Sheath/physiology , Neovascularization, Physiologic/drug effects , Nerve Regeneration/physiology , Peripheral Nerves/cytology , Peripheral Nerves/physiology , Polyglycolic Acid , Polylactic Acid-Polyglycolic Acid Copolymer , Polymers , Rats , Rats, Sprague-Dawley , Schwann Cells/cytology , Schwann Cells/physiologyABSTRACT
Clinical outcomes of bone allograft procedures may be improved by modifying the surface of the graft with an osteoconductive biopolymeric coating. In this comparative in vitro study, we evaluated the dimensional stability, mechanical strength, hydrophilicity, and water uptake of biodegradable foams of poly(propylene fumarate) (PPF) and poly(d,l-lactic-co glycolic acid) (PLGA) when applied as surface coatings to cortical bone. Cortical bone samples were divided into four groups: Type I, untreated bone; Type II, laser-perforated bone; Type III, partially demineralized bone; and Type IV, laser-perforated and partially demineralized bone. Results show that PPF wets easily, achieving 12.5% wt/wt in 30 min. Compressive tests on the PPF foam material showed that the compressive strength was 6.8 MPa prior to in vitro incubation but then gradually reduced to 1.9 MPa at 8 weeks. Push-out and pulloff strength tests showed that initially both PPF and PLGA foam coatings had comparable adherence strengths to the cortical bone samples (100-150 N). When additional geometrical surface alteration by perforation and demineralization of the bony substrate was employed, in vitro adherence of the PPF foam coating was further increased to 120 N, demonstrating a statistically significant improvement of push-out strength throughout the entire 8-week observation period (p<0.0002 for all four data points). The pore geometry of PPF-foam coatings changed little over the 2-month evaluation period. In comparison, PLGA foam coating around the cortical bone samples rapidly lost structure with a decrease of 67% in strength seen after 1-week in vitro incubation. These new types of bone allografts may be particularly useful where the use of other replacement materials is not feasible or practical.
Subject(s)
Bone Remodeling , Bone Substitutes , Bone Transplantation , Fumarates , Lactic Acid , Polyglycolic Acid , Polymers , Polypropylenes , Tibia , Polylactic Acid-Polyglycolic Acid Copolymer , Transplantation, HomologousABSTRACT
Plates for internal fixation fabricated from biodegradable polymers degrade via an autocatalytic route. When they are used in bone implants of significant size and thickness, hollowing of the implant may occur while the overall dimensions appear unchanged. We hypothesized that incorporation of a cross-linked polypropylene fumarate matrix into polylactide-co-glycolide bone plates may provide an internal molecular network which prevents implant collapse. Cross-linking reagents of varying hydrophilicity including N-vinylpyrrolidone (VP), hydroxyethylmethacrylate (HEMA), and ethyleneglycol dimethacrylate (EGDMA) were employed. With the objective of determining the most biocompatible and structurally sound composition for molecular reinforcement, we investigated tissue responses in both subcutaneous and orthotopic rodent implantation models in relation to maintenance of implant integrity by histologic, histomorphometric, and stereomicroscopic analysis. Results showed that tissue responses were correlated with dimensional stability of the implants. The most favorable results were seen with the hydrophobic cross-linker EGDMA; this may have been related to the initial reduction of the water uptake by the implant. Cross-linking of polypropylene fumarate with EGDMA within a polylactide-co-glycolide bone plate may offer a means to maintain excellent biocompatibility while improving dimensional stability of biodegradable bone plates.
Subject(s)
Biocompatible Materials/chemistry , Prostheses and Implants , Animals , Biocompatible Materials/pharmacology , Bone and Bones/chemistry , Bone and Bones/metabolism , Cross-Linking Reagents/pharmacology , Lactic Acid/chemistry , Male , Methacrylates/chemistry , Polyglycolic Acid/chemistry , Polylactic Acid-Polyglycolic Acid Copolymer , Polymers/chemistry , Pyrrolidinones/pharmacology , Rats , Rats, Long-Evans , Tibia/chemistryABSTRACT
We have investigated an injectable form of a resorbable bone cement based on in situ crosslinking of the unsaturated polyester, poly(propylene glycol-co-fumaric acid) (PPF). This material, filled with calcium gluconate/hydroxyapatite (CG/HA), cures to a hard cement degradable by hydrolysis. The purpose of this study was to evaluate the osteoconductive properties of this injectable cement. The cement was used as an adjunct to fixation with an intramedullary rod in the rat femoral osteotomy model. Ingrowth of new bone into the cement was examined in vivo. Negative and positive controls with rigid and loose internal fixation were included for comparison. Animals were evaluated histologically and histomorphometrically at 4 weeks postoperatively. Results of this study showed osteoblastic activity and new bone formation at the interface between the femoral bone and the cement in the experimental group. However, there was little bone remodeling at the endosteal surface in positive and negative controls. Histologic evaluation of the cement revealed the formation of cavitations, which likely resulted from leaching of the highly soluble calcium gluconate portion of the filler from the cement. These cavitations were sites of ingrowth of vascular and bony tissues. Intimate contact between the bone cement and the endosteal surface of the cortex was found. Quantitative histomorphometric analysis corroborated these observations. Findings of this study demonstrated the osteoconductivity of this type of injectable PPF-based bone cement.
Subject(s)
Bone Cements , Bone Remodeling , Fumarates , Polypropylenes , Animals , Male , Rats , Rats, Sprague-DawleyABSTRACT
The effect of mucosal delivery of Streptococcus sobrinus glucosyltransferase (GTF) in bioadhesive poly (D,L-lactide-co-glycolide) (PLGA) microparticles on induction of salivary IgA and serum IgG antibody responses was measured in Sprague-Dawley rats. Preparations of GTF/PLGA/gelatin microparticles, or PLGA/gelatin microparticles or GTF in alum, were administered four times at weekly intervals by intranasal or intragastric routes. Two subcutaneous injections of GTF in PLGA/gelatin microparticles or in alum were given to separate groups of rats. Significant elevations in salivary IgA antibody levels to S. sobrinus GTF were observed only in the groups immunized intranasally 28 days after immunizations were begun. Five of six rats given the GTF microparticles intranasally had positive salivary IgA antibody responses to GTF, and the mean salivary IgA antibody level of this group was 30-fold higher than any other mucosally or systemically immunized group. Salivary IgA responses in the GTF-microparticle group remained significantly higher than all other mucosally immunized groups for at least 10 weeks after the primary immunization. All rats in this group demonstrated aspects of anamnesis following a more limited secondary course of intranasal administration. Intranasal administration of GTF in microparticles also induced a serum IgG response to GTF in some rats. After secondary intranasal GTF microparticle administration, several rats had sustained serum IgG antibody levels that were within the range of sera from rats subcutaneously injected with GTF in microparticles or in alum. Thus intranasal delivery of GTF-containing bioadhesive microparticles induced the highest and longest lasting salivary immune response of any mucosal or systemic route or vehicle tested and could be expected to be a useful method for induction of mucosal immunity.
Subject(s)
Antibodies, Bacterial/analysis , Glucosyltransferases/immunology , Lactic Acid/immunology , Saliva/immunology , Streptococcus sobrinus/immunology , Administration, Intranasal , Alum Compounds , Animals , Antibodies, Bacterial/blood , Gelatin/immunology , Glucosyltransferases/administration & dosage , Immunity, Mucosal , Immunization, Secondary , Immunoglobulin A/analysis , Immunoglobulin G/blood , Polyglycolic Acid , Polylactic Acid-Polyglycolic Acid Copolymer , Polymers , Rats , Rats, Sprague-Dawley , Time Factors , VaccinationABSTRACT
Bioresorbable bone graft substitutes could eliminate disadvantages associated with the use of autografts, allografts and other synthetic materials. We investigated a bioresorbable bone graft substitute made from the unsaturated polyester poly(propylene fumarate) which is crosslinked in the presence of soluble and insoluble calcium filler salts. This compact bone graft substitute material develops porosity in vivo by leaching of the soluble filler salts. In attempt to develop materials whose in vivo porosity can be designed such that implant degradation would occur at a rate that remains supportive of the overall structural integrity of the repairing defect site, we studied the early tissue response upon implantation in a bony defect. Three grout formulations of varying solubilities using slightly soluble hydroxyapatite (HA) and soluble calcium acetate (CA) were evaluated in 3 mm holes made in the anteromedial tibial metaphysis of 200 g Sprague Dawley rats (n = 16 per formulation for a total of 48 animals). Grout formulations cured in situ. Animals from each formulation were sacrificed in groups of 8 at 4 days and 3 weeks postoperatively. Histologic analysis of the healing process revealed improved in vivo osteointegration of bone graft substitutes when a higher loading of calcium acetate was employed. All formulations maintained implant integrity and did not provoke sustained inflammatory responses. This study suggested that the presence of a soluble salt permits in vivo development of porosity of a poly(propylene fumarate) based bone graft substitute material.
Subject(s)
Bone Transplantation/methods , Bone and Bones/physiology , Polymers/pharmacology , Propylene Glycols/pharmacology , Acetates/chemistry , Acetates/pharmacology , Animals , Bone Development/physiology , Bone and Bones/chemistry , Calcium/chemistry , Calcium Compounds , Durapatite/chemistry , Kinetics , Male , Prostheses and Implants , Rats , Rats, Sprague-Dawley , Tibia/chemistry , Tibia/pathology , Time FactorsABSTRACT
Regeneration of skeletal tissues has been recognized as a new means for reconstruction of skeletal defects. We investigated the feasibility of an injectable and expandable porous implant system for in situ regeneration of bone. Therefore, a composite biodegradable foaming cement based on poly(propylene fumarate) was injected into a critical size defect made in the rat tibia. Animals were divided into two groups comparing the foam in the experimental group against sham-operated animals having a drill hole but no implant in the control group. Eight animals were included in each group. Animals were sacrificed at 1, 3, and 7 weeks postoperatively. Implantation sites were then evaluated with histologic and histomorphometric methods. Results of this study showed that defects did not heal in sham-operated animals. In the experimental group, metaphyseal and cortical defects healed within the first postoperative week by formation of immature woven bone. At the site of the cortical drill hole defect, healing was noted to progress to complete closure by formation of mature bone. Histomorphometry corroborated these findings and showed that metaphyseal bone remodeling peaked at 1 week postoperatively and then decreased as healing of the cortical defect progressed. This suggests that near-complete restoration of the original state of the tibial bone occurred in this animal model supporting the concept of in situ bone regeneration by application of engineered biodegradable porous scaffolds. () ()
Subject(s)
Bone Cements , Fumarates , Polypropylenes , Tibia/injuries , Wound Healing , Animals , Biodegradation, Environmental , Bone Cements/pharmacokinetics , Fumarates/chemistry , Fumarates/pharmacokinetics , Male , Microscopy, Electron, Scanning , Polypropylenes/chemistry , Polypropylenes/pharmacokinetics , Rats , Rats, Sprague-Dawley , Tibia/surgeryABSTRACT
Alteration of the geometrical surface configuration of cortical bone allografts may improve incorporation into host bone. A porous biodegradable coating that would maintain immediate structural recovery and subsequently allow normal graft healing and remodeling by promoting bony ingrowth could provide an osteoconductive surface scaffold. We investigated the feasibility of augmenting cortical bone grafts with osteoconductive biodegradable polymeric scaffold coatings. Three types of bone grafts were prepared: Type I--cortical bone without coating (control), Type II--cortical bone coated with PLGA-foam, Type III--cortical bone coated with PPF-foam. The grafts were implanted into the rat tibial metaphysis (16 animals for each type of bone graft). Post-operatively the animals were sacrificed at 2 weeks and 4 weeks (8 animals for each type of bone graft at each time point). Histologic and histomorphometric analysis of grafts showed that the amount of new bone forming around the foam-coated grafts was significantly higher than in the control group (uncoated; p < 0.02). Although both foam formulations were initially equally osteoconductive, PLGA-based foam coatings appeared to have degraded at two weeks postoperatively, whereas PPF-based foam coatings were still present at 4 weeks postoperatively. While significant resorption was present in control allografts with little accompanying reactive new bone formation, PLGA-coated bone grafts showed evidence of bone resorption and subsequent bony ingrowth earlier than those coated with PPF-based foams suggesting that PPF-coated cortical bone grafts were longer protected against host reactions resulting in bone resorption.
Subject(s)
Absorbable Implants , Bone Transplantation/physiology , Coated Materials, Biocompatible/chemistry , Osteogenesis/physiology , Polymers/chemistry , Animals , Bone Cements/chemistry , Bone Regeneration/physiology , Bone Remodeling , Bone Resorption/pathology , Bone Transplantation/pathology , Bone and Bones/anatomy & histology , Decalcification Technique , Feasibility Studies , Follow-Up Studies , Fumarates/chemistry , Graft Survival , Humans , Lactic Acid/chemistry , Male , Polyglycolic Acid/chemistry , Polylactic Acid-Polyglycolic Acid Copolymer , Polypropylenes/chemistry , Porosity , Protective Agents/chemistry , Rats , Rats, Sprague-Dawley , Surface Properties , Tibia/surgery , Tissue Preservation , Transplantation, HeterologousABSTRACT
We investigated the feasibility of enhancing the regeneration of skeletal tissues by augmenting bone grafts with a composite biodegradable bone graft extender material based on the polymer poly(propylene fumarate), PPF. The material was mixed with autograft and allograft and placed directly into a cylindrical metaphyseal defect made in the rat tibia. These formulations were compared to defects without any graft material, autografts, allografts and PPF alone. Nine animals were included in each group. Animals were sacrificed at 1 and 4 weeks postoperatively. Implantation sites were then evaluated using histologic and histomorphometric methods. Results of this study showed that defects did not heal in sham operated animals. In the experimental groups, there was early new woven bone formation in the autograft group with near complete healing of the defect at four weeks. When PPF was used alone, gradual ingrowth of new bone was seen. Mixing of the PPF bone graft extender with either allograft or autograft material resulted in enhancement of new bone formation with both allo- and autograft. However, significantly more new bone formation than in the autograft group was only seen when the PPF bone graft extender was mixed with fresh autograft. Histomorphometry corroborated these findings. Results of this study suggest that a PPF-based material may be used to increase the volume of smaller amounts of bone grafts supporting the concept of "bone graft extenders" by application of engineered biodegradable porous scaffolds.
Subject(s)
Absorbable Implants , Bone Cements/chemistry , Bone Regeneration/physiology , Bone Transplantation/pathology , Coated Materials, Biocompatible/chemistry , Fumarates/chemistry , Polypropylenes/chemistry , Analysis of Variance , Animals , Bone Transplantation/physiology , Feasibility Studies , Follow-Up Studies , Granulation Tissue/pathology , Male , Osteogenesis/physiology , Porosity , Rats , Rats, Sprague-Dawley , Surface Properties , Tibia/pathology , Tibia/surgery , Transplantation, Autologous , Transplantation, Homologous , Wound HealingABSTRACT
The purpose of this study was to compare the effect of polymer foam morphology and density prior to compaction on the kinetics of isoniazid (INH) release from the final high-density extruded matrices. The feasibility of preparing low density foams of several biopolymers, including poly(L-lactide) (PLLA), poly(glycolide) (PGA), poly(DL-lactide-co-glycolide) (PLGA), poly(gamma-benzyl-L-glutamate) (PBLG), and poly(propylene fumarate) (PPF), via a lyophilization technique was investigated. Low-density foams of PLGA, PBLG, and a mixture of PLGA and PPF were successfully fabricated by lyophilization of the frozen polymer solutions either in glacial acetic acid or in benzene. The morphology of these foams depends on the polymer as well as the solvent used in the fabrication process. Thus, PLGA produces a capillary structure when lyophilized from benzene solution and a leaflet structure from glacial acetic acid, but PBLG yields a leaflet structure from benzene. Matrices were prepared by impregnating these foams with aqueous solutions of INH, removing the water by a second lyophilization, and then compressing the low-density INH containing foams by compaction and high-pressure extrusion. The resulting nonporous matrices had densities of approximately 1.30 g/cm3. In vitro kinetics were in accord with the Roseman-Higuchi diffusion model and demonstrate that release rates depend on the initial foam density, while foam structure has little influence on the release kinetics.
Subject(s)
Antitubercular Agents/administration & dosage , Biocompatible Materials , Isoniazid/administration & dosage , Lactic Acid , Polyglycolic Acid , Polymers , Antitubercular Agents/pharmacokinetics , Biocompatible Materials/chemistry , Delayed-Action Preparations , Drug Delivery Systems , Fumarates/chemistry , In Vitro Techniques , Isoniazid/pharmacokinetics , Materials Testing , Microscopy, Electron, Scanning , Polyglutamic Acid/analogs & derivatives , Polyglutamic Acid/chemistry , Polylactic Acid-Polyglycolic Acid Copolymer , Polymers/chemistry , Polypropylenes/chemistry , SolubilityABSTRACT
The release mechanisms of a small molecular drug from biodegradable poly(d,l-lactide-co-glycolide) (PLGA) cylindrical matrices were investigated. Isoniazid (INH), one of the most effective drugs against tuberculosis (TB), was selected as the model drug. Controlled-release matrices consisting of the drug and polymer were fabricated by two methods. The first of these, the dry-mixing method, involved the extrusion of a mixture of micronized drug and polymer particles as rods. In the second technique, the low density polymeric foam method, drug particles were enclosed in the cells of porous polymeric foams prior to extrusion. In vitro, the dry-mixed matrices released INH more rapidly than the polymeric foam matrices. The Roseman-Higuchi diffusion model, which had previously been found to be effective in analyzing the release kinetics of INH from the dry-mixed matrices, also fit the kinetics of INH released from matrices prepared from polymeric foams. This indicated that the release was still diffusion-controlled rather than degradation-controlled. The release mechanisms were further investigated, and two diffusion mechanisms, pore diffusion and lattice diffusion, were proposed for the INH controlled-release matrices according to the way in which they were prepared. Matrices prepared by the dry-mixing method appear to segregate drug particles along polymer grain boundaries and thus have a pore diffusion mechanism, while matrices prepared by the foam method entrap drug within the porous structure of foams and thus display a lattice diffusion mechanism. Theoretically, these two diffusion mechanisms can be identified by their activation energies for diffusion. With varying in vitro temperature, the activation energies were calculated from plots of ln (DIT) vs T-1 and in D vs T-1, where D is the diffusivity and T is the in vitro temperature in K. According to the results, we concluded that the INH from the dry-mixed matrices diffused through the drug channels filled with the medium, while the INH from the foam matrices diffused through the polymer lattice.
Subject(s)
Antitubercular Agents/administration & dosage , Isoniazid/administration & dosage , Lactic Acid , Polyglycolic Acid , Polymers/chemistry , Diffusion , Drug Carriers , Microscopy, Electron, Scanning , Models, Chemical , Polylactic Acid-Polyglycolic Acid Copolymer , Temperature , ThermodynamicsABSTRACT
A resorbable bone cement was formulated from N-vinyl-2-pyrrolidinone (VP), the unsaturated polyester poly(propylene fumarate) (PPF), and the inorganic filler tribasic calcium phosphate (hydroxy apatite). Cure, initiated by benzoyl peroxide and accelerated by N,N-dimethyl-p-toluidine, resulted in the formation of VP crosslinks between polyester chains. During cure the cement hardened from a viscous moldable putty to a rigid structure with a shore D hardness of 50-60. The purpose of this study was to determine the fractions of PPF and VP incorporated into the crosslinked structure. Dissolution of the cured cement in water followed by extraction of the residue in tetrahydrofuran indicated that over 90% of the PPF was crosslinked over the range of PPF/VP ratios explored, but that the fraction of VP used in formation of crosslinks depended linearly on the PPF/VP ratio. Kinetic analysis of these data suggests that k'pp/kpf (the reactivity ratio) was approximately 2.0 where k'pp is the rate constant for the addition of VP radical to VP monomer leading to formation of poly(vinyl pyrrolidone), and kpf is for the addition of VP radical to PPF unsaturation.
Subject(s)
Biocompatible Materials , Bone Cements/chemistry , Fumarates/chemistry , Polypropylenes/chemistry , Pyrrolidinones , Cross-Linking Reagents , Hardness , Kinetics , SolubilityABSTRACT
The studies reported here were directed towards the development of an implantable microcapsule which "pulses" release of follicle stimulating hormone, FSH, for application to superovulating cows. Final dose forms were administered using membrane-coated cylinders. The "pulse" of the FSH is achieved by membrane encapsulation of an effervescent/swelling core containing citric acid, sodium bicarbonate, glucose and FSH. Entry of water results in sufficient pressure increase (by gas generation) to rupture ("burst") the membrane. Time to rupture is dependent upon several factors, such as membrane permeability and thickness, and core composition and loading. The final dose forms were implanted by means of a trochar. This system was tested in sheep to substantiate in vivo "burst" times and then tested in cows to determine efficacy. In vivo burst times in sheep varied from 8 to 96 hr, based upon maximal FSH values in blood serum, and generally paralled the planned times resulting from in vitro tests. Multiple capsules designed to release FSH as a pulse or steady state were tested on a limited number of cows plus a control (n = 10). Four of the combinations resulted in 11, 11, 14 and 16 ovulations, indicating that further development has promise of providing a one-injection system using FSH for superovulating cattle.
ABSTRACT
The gas phase continuous production of acetaldehyde was studied with particular emphasis on the development of biocatalyst (alcohol oxidase on solid phase support materials) for a fixed bed reactor. Based on the experimental results in a batch bioreactor, the biocatalysts were prepared by immobilization of alcohol oxidase on Amberlite IRA-400, packed into a column, and the continuous acetaldehyde production in the gas phase by alcohol oxidase was performed. The effects of the reaction temperature, flow rates of gaseous stream, and ethanol vapor concentration on the performance of the continuous bioreactor were investigated.