Browsing by Author "Spicer, Patrick P."

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    Autologously Generated Tissue-Engineered Bone Flaps for Reconstruction of Large Mandibular Defects in an Ovine Model
    (Mary Ann Liebert, Inc., 2015) Tatara, Alexander M.; Kretlow, James D.; Spicer, Patrick P.; Lu, Steven; Lam, Johnny; Liu, Wei; Cao, Yilin; Liu, Guangpeng; Jackson, John D.; Yoo, James J.; Atala, Anthony; van den Beucken, Jeroen J.J.P.; Jansen, John A.; Kasper, F. Kurtis; Ho, Tang; Demian, Nagi; Miller, Michael John; Wong, Mark E.; Mikos, Antonios G.
    The reconstruction of large craniofacial defects remains a significant clinical challenge. The complex geometry of facial bone and the lack of suitable donor tissue often hinders successful repair. One strategy to address both of these difficulties is the development of an in vivo bioreactor, where a tissue flap of suitable geometry can be orthotopically grown within the same patient requiring reconstruction. Our group has previously designed such an approach using tissue chambers filled with morcellized bone autograft as a scaffold to autologously generate tissue with a predefined geometry. However, this approach still required donor tissue for filling the tissue chamber. With the recent advances in biodegradable synthetic bone graft materials, it may be possible to minimize this donor tissue by replacing it with synthetic ceramic particles. In addition, these flaps have not previously been transferred to a mandibular defect. In this study, we demonstrate the feasibility of transferring an autologously generated tissue-engineered vascularized bone flap to a mandibular defect in an ovine model, using either morcellized autograft or synthetic bone graft as scaffold material.
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    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.
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    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.Kurtis
    This 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.
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    Evaluation of Bone Regeneration Using the Rat Critical Size Calvarial Defect
    (Nature Publishing Group, 2012-10) Spicer, Patrick P.; Kretlow, James D.; Young, Simon; Jansen, John A.; Kasper, F. Kurtis; Mikos, Antonios G.
    Animal models that are reliably reproducible, appropriate analogues to the clinical condition they are used to investigate, and that offer minimal morbidity and periprocedural mortality to the subject are the keystone to the preclinical development of translational technologies. For bone tissue engineering, a number of small animal models exist. Here we describe the protocol for one such model, the rat calvarial defect. This versatile model allows for evaluation of biomaterials and bone tissue engineering approaches within a reproducible, nonload-bearing orthotopic site. Critical steps to ensure appropriate experimental control and troubleshooting tips learned through extensive experience with this model are provided. The surgical procedure itself takes approximately 30 minutes to complete with approximately 2 hours of perioperative care, and tissue harvest is generally performed 4 to 12 weeks postoperatively. Several analytical techniques are presented, which evaluate the cellular and extracellular matrix components, functionality and mineralization, including histological, mechanical and radiographic methods.
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    In vitroﾠandﾠin vivoﾠevaluation of self-mineralization and biocompatibility of injectable, dual-gelling hydrogels for bone tissue engineering
    (Elsevier, 2015) Vo, Tiffany N.; Ekenseair, Adam K.; Spicer, Patrick P.; Watson, Brendan M.; Tzouanas, Stephanie N.; Roh, Terrence T.; Mikos, Antonios G.
    In this study, we investigated the mineralization capacity and biocompatibility of injectable, dual-gelling hydrogels in a rat cranial defect as a function of hydrogel hydrophobicity from either the copolymerization of a hydrolyzable lactone ring or the hydrogel polymer content. The hydrogel system comprised a poly(N-isopropylacrylamide)-based thermogelling macromer (TGM) and a polyamidoamine crosslinker. The thermogelling macromer was copolymerized with (TGM/DBA) or without (TGM) a dimethyl-γ-butyrolactone acrylate (DBA)-containing lactone ring that modulated the lower critical solution temperature and thus, the hydrogel hydrophobicity, over time. Three hydrogel groups were examined: (1) 15wt.% TGM, (2) 15wt.% TGM/DBA, and (3) 20wt.% TGM/DBA. The hydrogels were implanted within an 8mm critical size rat cranial defect for 4 and 12weeks. Implants were harvested at each timepoint and analyzed for bone formation, hydrogel mineralization and tissue response using microcomputed tomography (microCT). Histology and fibrous capsule scoring showed a light inflammatory response at 4weeks that was mitigated by 12weeks for all groups. MicroCT scoring and bone volume quantification demonstrated a similar bone formation at 4weeks that was significantly increased for the more hydrophobic hydrogel formulations - 15wt.% TGM and 20wt.% TGM/DBA - from 4weeks to 12weeks. A complementary in vitro acellular mineralization study revealed that the hydrogels exhibited calcium binding properties in the presence of serum-containing media, which was modulated by the hydrogel hydrophobicity. The tailored mineralization capacity of these injectable, dual-gelling hydrogels with hydrolysis-dependent hydrophobicity presents an exciting property for their use in bone tissue engineering applications.
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    Osteochondral Tissue Regeneration using a Bilayered Composite Hydrogel with Modulating Dual Growth Factor Release Kinetics in a Rabbit Model
    (Elsevier, 2014) Kima, Kyobum; Lama, Johnny; Lua, Steven; Spicer, Patrick P.; Lueckgena, Aline; Yasuhiko, Tabata; Wong, Mark E.; Jansen, John A.; Mikos, Antonios G.; Kasper, F. Kurtis
    Biodegradable oligo(poly(ethylene glycol) fumarate) (OPF) composite hydrogels have been investigated for the delivery of growth factors (GFs) with the aid of gelatin microparticles (GMPs) and stem cell populations for osteochondral tissue regeneration. In this study, a bilayered OPF composite hydrogel that mimics the distinctive hierarchical structure of native osteochondral tissue was utilized to investigate the effect of transforming growth factor-β3 (TGF-β3) with varying release kinetics and/or insulin-like growth factor-1 (IGF-1) on osteochondral tissue regeneration in a rabbit full-thickness osteochondral defect model. The four groups investigated included (i) a blank control (no GFs), (ii) GMP-loaded IGF-1 alone, (iii) GMP-loaded IGF-1 and gel-loaded TGF-β3, and (iv) GMP-loaded IGF-1 and GMP-loaded TGF-β3 in OPF composite hydrogels. The results of an in vitro release study demonstrated that TGF-β3 release kinetics could be modulated by the GF incorporation method. At 12 weeks post-implantation, the quality of tissue repair in both chondral and subchondral layers was analyzed based on quantitative histological scoring. All groups incorporating GFs resulted in a significant improvement in cartilage morphology compared to the control. Single delivery of IGF-1 showed higher scores in subchondral bone morphology as well as chondrocyte and glycosaminoglycan amount in adjacent cartilage tissue when compared to a dual delivery of IGF-1 and TGF-β3, independent of the TGF-?3 release kinetics. The results suggest that although the dual delivery of TGF-β3 and IGF-1 may not synergistically enhance the quality of engineered tissue, the delivery of IGF-1 alone from bilayered composite hydrogels positively affects osteochondral tissue repair and holds promise for osteochondral tissue engineering applications.