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Large mandibular defects are clinically challenging to reconstruct due to the complex anatomy of the jaw and the limited availability of appropriate tissue for repair. We envision leveraging current advances in fabrication and biomaterials to create implantable devices that generate bone within the patients themselves suitable for their own specific anatomical pathology. The in vivo bioreactor strategy facilitates the generation of large autologous vascularized bony tissue of customized geometry without the addition of exogenous growth factors or cells. To translate this technology, we investigated its success in reconstructing a mandibular defect of physiologically relevant size in sheep. We fabricated and implanted 3D-printed in vivo bioreactors against rib periosteum and utilized biomaterial-based space maintenance to preserve the native anatomical mandibular structure in the defect site before reconstruction. Nine weeks after bioreactor implantation, the ovine mandibles were repaired with the autologous bony tissue generated from the in vivo bioreactors. We evaluated tissues generated in bioreactors by radiographic, histological, mechanical, and biomolecular assays and repaired mandibles by radiographic and histological assays. Biomaterial-aided mandibular reconstruction was successful in a large superior marginal defect in five of six (83%) sheep. Given that these studies utilized clinically available biomaterials, such as bone cement and ceramic particles, this strategy is designed for rapid human translation to improve outcomes in patients with large mandibular defects.

This protocol describes the study design, surgical procedure, postoperative care and analysis techniques necessary to produce a preclinical rabbit model of large bone and tooth defects in the mandible, for use in a wide range of areas in craniofacial tissue engineering. Translational biomaterials targeted toward the regeneration of large bone defects in the mandible require a preclinical model that accurately recapitulates the regenerative challenges present in humans. Computational modeling and in vitro assays do not fully replicate the in vivo environment. Consequently, in vivo models can have specific applications such as those of the mandibular angle defect, which is used to investigate bone regeneration in a nonload-bearing area, and the inferior border mandibular defect, which is a model for composite bone and nerve regeneration, with both models avoiding involvement of soft tissue or teeth. In this protocol, we describe a reproducible load-bearing critical-size composite tissue defect comprising loss of soft tissue, bone and tooth in the mandible of a rabbit. We have previously used this procedure to investigate bone regeneration, vascularization and infection prevention in response to new biomaterial formulations for craniofacial tissue engineering applications. This surgical approach can be adapted to investigate models such as that of regeneration in the context of osteoporosis or irradiation. The procedure can be performed by researchers with basic surgical skills such as dissection and suturing. The procedure takes 1.5–2 h, with ∼2 h of immediate postoperative care, and animals should be monitored daily for the remainder of the study. For bone tissue engineering applications, tissue collection typically occurs 12 weeks after surgery. In this protocol, we will present the necessary steps to ensure reproducibility; tips to minimize complications during and after surgery; and analytical techniques for assessing soft tissue, bone and vessel regeneration by gross evaluation, microcomputed tomography (microCT) and histology.

Reconstruction of large bone defects can be complicated by the presence of both infection and local antibiotic administration. This can be addressed through a two-stage reconstructive approach, called the Masquelet technique, that involves the generation of an induced osteogenic membrane over a temporary poly(methyl methacrylate) (PMMA) space maintainer, followed by definitive reconstruction after the induced membrane is formed. Given that infection and antibiotic delivery each have independent effects on local tissue response, the objective of this study is to evaluate the interaction between local clindamycin release and bacterial contamination with regards to infection prevention and the restoration of pro-osteogenic gene expression in the induced membrane. Porous PMMA space maintainers with or without clindamycin were implanted in an 8 mm rat femoral defect model with or without Staphylococcus aureus inoculation for 28 days in a full-factorial study design (four groups, n  = 8/group). Culture results demonstrated that 8/8 animals in the inoculated/no antibiotic group were infected at 4 weeks, which was significantly reduced to 1/8 animals in the inoculated/antibiotic group. Quantitative polymerase chain reaction analysis demonstrated that clindamycin treatment restores inflammatory cytokine and growth factor expression to the same levels as the no inoculation/no antibiotic group, demonstrating that clindamycin can ameliorate the negative effects of bacterial inoculation and does not itself negatively impact the expression of important cytokines. Main effect analysis shows that bacterial inoculation and clindamycin treatment have independent and interacting effects on the gene expression profile of the induced membrane, further highlighting that antibiotics play an important role in the regeneration of infected defects apart from their antimicrobial properties.

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.

ABSTRACT Purpose This work investigates the effects of hyaluronic acid (HA) conjugated onto branched poly(ethylenimine) (bPEI) and varying loading concentrations of these polymers complexed with DNA on their release from poly(DL-lactic-co-glycolic acid) (PLGA) microparticles and the transfection of target cells. Methods To examine the effect of alteration of the gene delivery polymer on the system, we observed the morphology, size, loading efficiency, polymer and DNA release, and the transfection efficiency for the microparticles formed with three internal phase loading concentrations during microparticle formation. Results Addition of HA to this vector allowed for increased loading concentration within these systems and significantly altered release kinetics without changing the morphology of the particles. The incorporation of HA onto the bPEI backbone significantly increased the transfection efficiency of the complexes released from the corresponding microparticle formulation. Conclusions The results show that the modification of bPEI with HA and the concentration of loaded polymer/DNA complexes can significantly alter the entrapment and release profiles from PLGA microparticles. This is significant in that it offers insight into the effects of modification of gene delivery vectors on a controlled release system designed to achieve a sustained therapeutic response.

Regeneration of bone in large segmental bone defects requires regeneration of both cortical bone and trabecular bone. A scaffold design consisting of a hydroxyapatite (HA) ring surrounding a polylactic acid (PLA) core simulates the structure of bone and provides an environment for indirect and direct co-culture conditions. In this experiment, human umbilical vein endothelial cells (EC) and normal human primary osteoblasts (OB) were co-cultured to evaluate cell migration and interactions within this biphasic composite scaffold. Both cell types were able to migrate between the different material phases of the scaffold. It was also observed that OB migration increased when they were co-cultured with ECs, whereas EC migration decreased in co-culture. The results show that co-culture of ECs and OBs in this composite biphasic scaffold allows for migration of cells throughout the scaffold and that pre-seeding a scaffold with ECs can increase OB infiltration into desired areas of the scaffold.

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.

This study from South Africa showed that extensively drug-resistant tuberculosis, an emerging global public health threat, is largely associated with transmission of drug-resistant strains rather than new emergence of drug resistance. Drug-resistant tuberculosis is a major global epidemic, with a half million cases occurring each year. 1 Extensively drug-resistant (XDR) tuberculosis — the most severe form of drug resistance — has been reported worldwide and involves resistance to at least four first-line and second-line drugs for tuberculosis. This high degree of resistance severely limits treatment options, necessitating the use of complex, toxic, and costly regimens. Rates of treatment success are less than 40% in most patient populations, and rates of death are 50 to 80%. 2 – 6 Drug-resistant tuberculosis has traditionally been thought to develop as a result of selection pressure that occurs . . .

Multidrug-resistant (MDR) tuberculosis is a growing clinical and public-health concern. To evaluate existing evidence regarding treatment regimens for MDR tuberculosis, we used a Bayesian random-effects meta-analysis of the available therapeutic studies to assess how the reported proportion of patients treated successfully is influenced by differences in treatment regimen design, study methodology, and patient population. Successful treatment outcome was defined as cure or treatment completion. 34 clinical reports with a mean of 250 patients per report met the inclusion criteria. Our analysis shows that the proportion of patients treated successfully improved when treatment duration was at least 18 months, and if patients received directly observed therapy throughout treatment. Studies that combined both factors had significantly higher pooled success proportions (69%, 95% credible interval [CI] 64–73%) than other studies of treatment outcomes (58%, 95% CI 52–64%). Individualised treatment regimens had higher treatment success (64%, 95% CI 59–68%) than standardised regimens (54%, 95% CI 43–68%), although the difference was not significant. Treatment approaches and study methodologies were heterogeneous across studies. Many important variables, including patients' HIV status, were inconsistently reported between studies. These results underscore the importance of strong patient support and treatment follow-up systems to develop successful MDR tuberculosis treatment programmes.

The metabolic signaling pathways that drive pathologic tissue inflammation and damage in humans with pulmonary tuberculosis (TB) are not well understood. Using combined methods in plasma high-resolution metabolomics, lipidomics and cytokine profiling from a multicohort study of humans with pulmonary TB disease, we discovered that IL-1β-mediated inflammatory signaling was closely associated with TCA cycle remodeling, characterized by accumulation of the proinflammatory metabolite succinate and decreased concentrations of the anti-inflammatory metabolite itaconate. This inflammatory metabolic response was particularly active in persons with multidrug-resistant (MDR)-TB that received at least 2 months of ineffective treatment and was only reversed after 1 year of appropriate anti-TB chemotherapy. Both succinate and IL-1β were significantly associated with proinflammatory lipid signaling, including increases in the products of phospholipase A2, increased arachidonic acid formation, and metabolism of arachidonic acid to proinflammatory eicosanoids. Together, these results indicate that decreased itaconate and accumulation of succinate and other TCA cycle intermediates is associated with IL-1β-mediated proinflammatory eicosanoid signaling in pulmonary TB disease. These findings support host metabolic remodeling as a key driver of pathologic inflammation in human TB disease.