Browsing by Author "Shah, Sarita R."
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Item A rapid, flexible method for incorporating controlled antibiotic release into porous polymethylmethacrylate space maintainers for craniofacial reconstruction(Royal Society of Chemistry, 2016) Mountziaris, Paschalia M.; Shah, Sarita R.; Lam, Johnny; Bennett, George N.; Mikos, Antonios G.Severe injuries in the craniofacial complex, resulting from trauma or pathology, present several challenges to functional and aesthetic reconstruction. The anatomy and position of the craniofacial region make it vulnerable to injury and subsequent local infection due to external bacteria as well as those from neighbouring structures like the sinuses, nasal passages, and mouth. Porous polymethylmethacrylate (PMMA) “space maintainers” have proven useful in staged craniofacial reconstruction by promoting healing of overlying soft tissue prior to reconstruction of craniofacial bones. We describe herein a method by which the porosity of a prefabricated porous PMMA space maintainer, generated by porogen leaching, can be loaded with a thermogelling copolymer-based drug delivery system. Porogen leaching, space maintainer prewetting, and thermogel loading all significantly affected the loading of a model antibiotic, colistin. Weeks-long release of antibiotic at clinically relevant levels was achieved with several formulations. In vitro assays confirmed that the released colistin maintained its antibiotic activity against several bacterial targets. Our results suggest that this method is a valuable tool in the development of novel therapeutic approaches for the treatment of severe complex, infected craniofacial injuries.Item Antibiotic-releasing Porous Poly(methyl methacrylate) for Space Maintenance and Infection Prevention in Large Bone Defects(2016-07-29) Shah, Sarita R.; Mikos, Antonios G.Large tissue defects in the mandible or long bones resulting from trauma or pathology present many challenges to tissue engineers attempting to regenerate lost tissue. These defects present anatomical challenges to regeneration as well as complicating factors, primarily infection. Because infection is a common and debilitating complication, we sought to develop an antibiotic-releasing porous space maintainer as part of a two-stage reconstructive approach that can support the preservation and optimization of large bone defects to facilitate later reconstruction. These porous space maintainers comprise a bulk phase of non-degradable poly(methyl methacrylate) (PMMA) made porous with an aqueous gel porogen. High local concentrations of antibiotic can be achieved by incorporation of drug into the space maintainer and release kinetics can be modified by utilizing different materials for release. In this thesis, we first present the development of poly(lactic-co-glycolic acid) (PLGA) microparticles as a platform for the controlled release of multiple types of antibiotic. We demonstrate in this specific aim that antibiotic physicochemical properties can be used to infer general loading efficiency and release kinetics, providing guidance for efficient decision-making regarding antibiotics suitable for delivery via PLGA microparticles. The second objective of this work was to evaluate antibiotic-loaded porous space maintainers in vivo with regards to the effect of antibiotic dose and release kinetics on bacterial clearance and tissue healing in the craniofacial region using an infected rabbit mandibular defect model. The results from in vitro evaluation demonstrate that the release of antibiotics from porous space maintainers can be controlled by incorporating PLGA microparticles. Furthermore, in vivo evaluation shows that antibiotic dose and release kinetics have significant effects on local tissues and and that these effects may be unique to each antibiotic type, highlighting the importance of evaluating tissue response to antibiotic-releasing constructs in addition to antimicrobial efficacy. In the third specific aim, we evaluated the effects of bacterial contamination and local clindamycin delivery on bacterial clearance and the regenerative potential of an induced in an infected rat femoral defect model. The results from this specific aim demonstrated that local antibiotic delivery influences the gene expression profile of local regenerating tissues and therefore can be leveraged for its effects on host tissues as well as its antimicrobial properties. Finally, we anticipated the future use of space maintainers for one-stage reconstruction. The degradable polymer poly(propylene fumarate) (PPF) was evaluated as a candidate for a degradable antibiotic-releasing porous space maintainer. The results from this study demonstrated that fabrication parameters such as polymer-to-crosslinker ratio and the percent incorporation of PLGA microparticles can be modified to tune the properties of antibiotic-releasing degradable space maintainers suitable for one-stage reconstruction. The overall goal of this work was to develop antibiotic-releasing porous space maintainers as a strategy to support the reconstruction of contaminated bone defects at risk of infection. Through this thesis, we have demonstrated that local antibiotic delivery is a promising strategy for preventing the progression of contamination to infection and that antibiotic dose and release kinetics can be further leveraged to alter local tissue response.Item Biodegradable, phosphate-containing, dual-gelling macromers for cellular delivery in bone tissue engineering(Elsevier, 2015) Watson, Brendan M.; Vo, Tiffany N.; Tatara, Alexander M.; Shah, Sarita R.; Scott, David W.; Engel, Paul S.; Mikos, Antonios G.Injectable, biodegradable, dual-gelling macromer solutions were used to encapsulate mesenchymal stem cells (MSCs) within stable hydrogels when elevated to physiologic temperature. Pendant phosphate groups were incorporated in the N-isopropyl acrylamide-based macromers to improve biointegration and facilitate hydrogel degradation. The MSCs were shown to survive the encapsulation process, and live cells were detected within the hydrogels for up to 28 days inᅠvitro. Cell-laden hydrogels were shown to undergo significant mineralization in osteogenic medium. Cell-laden and acellular hydrogels were implanted into a critical-size rat cranial defect for 4 and 12 weeks. Both cell-laden and acellular hydrogels were shown to degrade inᅠvivo and help to facilitate bone growth into the defect. Improved bone bridging of the defect was seen with the incorporation of cells, as well as with higher phosphate content of the macromer. Furthermore, direct bone-to-hydrogel contact was observed in the majority of implants, which is not commonly seen in this model. The ability of these macromers to deliver stem cells while forming in situ and subsequently degrade while facilitating bone ingrowth into the defect makes this class of macromers a promising material for craniofacial bone tissue engineering.Item Effects of Antibiotic Physicochemical Properties on Their Release Kinetics from Biodegradable Polymer Microparticles(Springer, 2014) Shah, Sarita R.; Henslee, Allan M.; Spicer, Patrick P.; Yokota, Shun; Petrichenko, Sophia; Allahabadi, Sachin; Bennett, George N.; Wong, Mark E.; Kasper, F. Kurtis; Mikos, Antonios G.Purpose: This study investigated the effects of the physicochemical properties of antibiotics on the morphology, loading efficiency, size, release kinetics, and antibiotic efficacy of loaded poly(DL-lactic-co-glycolic acid) (PLGA) microparticles (MPs) at different loading percentages. Methods: Cefazolin, ciprofloxacin, clindamycin, colistin, doxycycline, and vancomycin were loaded at 10 and 20 wt% into PLGA MPs using a water-in-oil-in water double emulsion fabrication protocol. Microparticle morphology, size, loading efficiency, release kinetics, and antibiotic efficacy were assessed. Results: The results from this study demonstrate that the chemical nature of loaded antibiotics, especially charge and molecular weight, influence the incorporation into and release of antibiotics from PLGA MPs. Drugs with molecular weights less than 600 Da displayed biphasic release while those with molecular weights greater than 1,000 Da displayed triphasic release kinetics. Large molecular weight drugs also had a longer delay before release than smaller molecular weight drugs. The negatively charged antibiotic cefazolin had lower loading efficiency than positively charged antibiotics. Microparticle size appeared to be mainly controlled by fabrication parameters, and partition and solubility coefficients did not appear to have an obvious effect on loading efficiency or release. Released antibiotics maintained their efficacy against susceptible strains over the duration of release. Duration of release varied between 17 and 49 days based on the type of antibiotic loaded. Conclusions: The data from this study indicate that the chemical nature of antibiotics affects properties of antibiotic-loaded PLGA MPs and allows for general prediction of loading and release kinetics.Item Evaluation of antibiotic releasing porous polymethylmethacrylate space maintainers in an infected composite tissue defect model(Elsevier, 2013-11) Spicer, Patrick P.; Shah, Sarita R.; Henslee, Allan M.; Watson, Brendan M.; Kinard, Lucas A.; Kretlow, James D.; Bevil, Kristin; Kattchee, Lauren; Bennett, George N.; Demian, Nagi M.; Mende, Katrin; Murray, Clinton K.; Jansen, John A.; Wong, Mark E.; Mikos, Antonios G.; Kasper, F.KurtisThis study evaluated the in vitro and in vivo performance of antibiotic-releasing porous polymethylmethacrylate (PMMA)-based space maintainers comprising a gelatin hydrogel porogen and a poly(DL-lactic-co-glycolic acid) (PLGA) particulate carrier for antibiotic delivery. Colistin was released in vitro from either gelatin or PLGA microparticle loaded PMMA constructs, with gelatin-loaded constructs releasing colistin over approximately 7 days and PLGA microparticle-loaded constructs releasing colistin up to 8 weeks. Three formulations with either a burst release or extended release in different doses were tested in a rabbit mandibular defect inoculated with Acinetobacter baumannii (2 × 107 colony forming units/mL). In addition, one material control that released antibiotic but was not inoculated with A. baumannii was tested. A. baumannii was not detectable in any animal after 12 weeks by culture of the defect, saliva, or blood. Defects with high-dose, extended-release implants had greater soft tissue healing compared to defects with burst release implants, with 8 out of 10 animals showing healed mucosae compared to 2 out of 10 with healed mucosae, respectively. Extended release of locally delivered colistin via a PLGA microparticle carrier improved soft tissue healing over the implants compared to burst release of colistin from a gelatin carrier.Item Novel applications of statins for bone regeneration(Oxford University Press, 2015) Shah, Sarita R.; Werlang, Caroline A.; Kasper, F. Kurtis; Mikos, Antonios G.The use of statins for bone regeneration is a promising and growing area of research. Statins, originally developed to treat high cholesterol, are inhibitors of the enzyme 3-hydroxy-3-methylglutaryl, the rate-limiting enzyme of the mevalonate pathway. Because the mevalonate pathway is responsible for the synthesis of a wide variety of important biochemical molecules, including cholesterol and other isoprenoids, the effects of statins are pleiotropic. In particular, statins can greatly affect the process of bone turnover and regeneration via effects on important cell types, including mesenchymal stem cells, osteoblasts, endothelial cells, and osteoclasts. Statins have also been shown to have anti-inflammatory and antimicrobial properties that may be useful since infection can derail normal bone healing. This review will explore the pleiotropic effects of statins, discuss the current use of statins for bone regeneration, particularly with regard to biomaterials-based controlled delivery, and offer perspectives on the challenges and future directions of this emerging area of bone tissue engineering.Item Osteochondral tissue regeneration through polymeric delivery of DNA encoding for the SOX trio and RUNX2(Elsevier, 2014) Needham, Clark J.; Shah, Sarita R.; Dahlin, Rebecca L.; Kinard, Lucas A.; Lam, Johnny; Watson, Brendan M.; Lu, Steven; Kasper, F. Kurtis; Mikos, Antonios G.Native osteochondral repair is often inadequate owing to the inherent properties of the tissue, and current clinical repair strategies can result in healing with a limited lifespan and donor site morbidity. This work investigates the use of polymeric gene therapy to address this problem by delivering DNA encoding for transcription factors complexed with the branched poly(ethylenimine)–hyaluronic acid (bPEI–HA) delivery vector via a porous oligo[poly(ethylene glycol) fumarate] hydrogel scaffold. To evaluate the potential of this approach, a bilayered scaffold mimicking native osteochondral tissue organization was loaded with DNA/bPEI–HA complexes. Next, bilayered implants either unloaded or loaded in a spatial fashion with bPEI–HA and DNA encoding for either Runt-related transcription factor 2 (RUNX2) or SRY (sex determining region Y)-box 5, 6, and 9 (the SOX trio), to generate bone and cartilage tissues respectively, were fabricated and implanted in a rat osteochondral defect. At 6 weeks post-implantation, micro-computed tomography analysis and histological scoring were performed on the explants to evaluate the quality and quantity of tissue repair in each group. The incorporation of DNA encoding for RUNX2 in the bone layer of these scaffolds significantly increased bone growth. Additionally, a spatially loaded combination of RUNX2 and SOX trio DNA loading significantly improved healing relative to empty hydrogels or either factor alone. Finally, the results of this study suggest that subchondral bone formation is necessary for correct cartilage healing.