Transabdominal Intrapericardial Approach in Liver Transplantation for Unresectable Primary Hepatic Functioning Paraganglioma With Invasion Into Hepatic Veins and Suprahepatic Vena Cava: A Surgical and Anesthesia Management Challenge.

Primary hepatic functional paraganglioma is a rare form of extra-adrenal catecholamine-secreting tumor. Definitive treatment of functioning paraganglioma is challenging because of the critical location of the tumor frequently in close proximity to vital structures and risk of excessive catecholamine release during operative manipulation. We report the multidisciplinary management approach for a case of unresectable primary hepatic functional paraganglioma with invasion into the hepatic veins and suprahepatic vena cava. To our knowledge, this is the first report showing that orthotopic liver transplantation is curative for patients with unresectable primary hepatic paraganglioma. For locally advanced unresectable hepatic paraganglioma that involves the intrapericardial vena cava, a meticulous pre- and intraoperative medical management and transabdominal intrapericardial vascular control of the suprahepatic vena cava during orthotopic liver transplantation allows for complete extirpation of the tumor and achieves optimal outcome.

Determination of the in vivo degradation mechanism of PEGDA hydrogels.

Poly(ethylene glycol) (PEG) hydrogels are one of the most extensively utilized biomaterials systems due to their established biocompatibility and highly tunable properties. It is widely acknowledged that traditional acrylate-derivatized PEG (PEGDA) hydrogels are susceptible to slow degradation in vivo and are therefore unsuitable for long-term implantable applications. However, there is speculation whether the observed degradation is due to hydrolysis of endgroup acrylate esters or oxidation of the ether backbone, both of which are possible in the foreign body response to implanted devices. PEG diacrylamide (PEGDAA) is a polyether-based hydrogel system with similar properties to PEGDA but with amide linkages in place of the acrylate esters. This provides a hydrolytically-stable control that can be used to isolate the relative contributions of hydrolysis and oxidation to the in vivo degradation of PEGDA. Here we show that PEGDAA hydrogels remained stable over 12 weeks of subcutaneous implantation in a rat model while PEGDA hydrogels underwent significant degradation as indicated by both increased swelling ratio and decreased modulus. As PEGDA and PEGDAA have similar susceptibility to oxidation, these results demonstrate for the first time that the primary in vivo degradation mechanism of PEGDA is hydrolysis of the endgroup acrylate esters. Additionally, the maintenance of PEGDAA hydrogel properties in vivo indicates their suitability for long-term implants. These studies serve to elucidate key information about a widely used biomaterial system to allow for better implantable device design and to provide a biostable replacement option for PEGDA in applications that require long-term stability.

Drying and storage effects on poly(ethylene glycol) hydrogel mechanical properties and bioactivity.

Hydrogels based on poly(ethylene glycol) (PEG) are increasingly used in biomedical applications because of their ability to control cell-material interactions by tuning hydrogel physical and biological properties. Evaluation of stability after drying and storage are critical in creating an off-the-shelf biomaterial that functions in vivo according to original specifications. However, there has not been a study that systematically investigates the effects of different drying conditions on hydrogel compositional variables. In the first part of this study, PEG-diacrylate hydrogels underwent common processing procedures (vacuum-drying, lyophilizing, hydrating then vacuum-drying), and the effect of this processing on the mechanical properties and swelling ratios was measured. Significant changes in compressive modulus, tensile modulus, and swelling ratio only occurred for select processed hydrogels. No consistent trends were observed after processing for any of the formulations tested. The effect of storage conditions on cell adhesion and spreading on collagen- and streptococcal collagen-like protein (Scl2-2)-PEG-diacrylamide hydrogels was then evaluated to characterize bioactivity retention after storage. Dry storage conditions preserved bioactivity after 6 weeks of storage; whereas, storage in PBS significantly reduced bioactivity. This loss of bioactivity was attributed to ester hydrolysis of the protein linker, acrylate-PEG-N-hydroxysuccinimide. These studies demonstrate that these processing methods and dry storage conditions may be used to prepare bioactive PEG hydrogel scaffolds with recoverable functionality after storage.

Multilayer vascular grafts based on collagen-mimetic proteins.

A major roadblock in the development of an off-the-shelf, small-caliber vascular graft is achieving rapid endothelialization of the conduit while minimizing the risk of thrombosis, intimal hyperplasia, and mechanical failure. To address this need, a collagen-mimetic protein derived from group A Streptococcus, Scl2.28 (Scl2), was conjugated into a poly(ethylene glycol) (PEG) hydrogel to generate bioactive hydrogels that bind to endothelial cells (ECs) and resist platelet adhesion. The PEG-Scl2 hydrogel was then reinforced with an electrospun polyurethane mesh to achieve suitable biomechanical properties. In the current study, initial evaluation of this multilayer design as a potential off-the-shelf graft was conducted. First, electrospinning parameters were varied to achieve composite burst pressure, compliance, and suture retention strength that matched reported values of saphenous vein autografts. Composite stability following drying, sterilization, and physiological conditioning under pulsatile flow was then demonstrated. Scl2 bioactivity was also maintained after drying and sterilization as indicated by EC adhesion and spreading. Evaluation of platelet adhesion, aggregation, and activation indicated that PEG-Scl2 hydrogels had minimal platelet interactions and thus appear to provide a thromboresistant blood contacting layer. Finally, evaluation of EC migration speed demonstrated that PEG-Scl2 hydrogels promoted higher migration speeds than PEG-collagen analogs and that migration speed was readily tuned by altering protein concentration. Collectively, these results indicate that this multilayer design warrants further investigation and may have the potential to improve on current synthetic options.

Compositional control of poly(ethylene glycol) hydrogel modulus independent of mesh size.

Poly(ethylene glycol) (PEG) hydrogels are of great interest in tissue engineering because of their established biocompatibility, high permeability, and tunable material properties. However, rational design of PEG hydrogel scaffold properties has been inhibited by the interdependence of key material properties such as modulus and mesh size. This study examined the effect of an acrylated 4-arm PEG cross-linker on gel modulus and mesh size as a means of inducing local increases in cross-link density to decouple these two parameters. It was determined that adding the 4-arm PEG cross-linker to PEG hydrogels resulted in statistically significant increases in both tensile and compressive modulus while having minimal effects on overall gel mesh size. The incorporation of the 4-arm PEG cross-linker also broadened the range of achievable mechanical properties. This study provides the methodology to independently tune PEG hydrogel modulus and mesh size, which may be utilized in future investigations of the individual and combined effects of PEG hydrogel modulus and mesh size on cell behavior and viability. It also presents a more finely tunable hydrogel scaffold with utility in a broad range of tissue engineering applications.

Bioactive hydrogels based on Designer Collagens.

Designer Collagens are based on streptococcal collagen-like (Scl) proteins that form a triple helix similar to mammalian collagens but that are non-platelet aggregating. In contrast to the numerous cell-binding sites on collagen, Scl2 from Streptococcus pyogenes serotype M28 does not contain any known cell-binding sites and thus provides a blank slate in terms of cellular interactions. In the current study, Scl2 protein was modified to include receptor binding motifs that interact with alpha1 and/or alpha2 integrin subunits. The modfied Scl2 proteins have been demonstrated to mediate differential endothelial cell (EC) and smooth muscle cell (SMC) adhesion via these integrins and to retain the non-platelet aggregating properties of the "parent" Scl2. Thromboresistant scaffolds which selectively bind ECs vs. SMCs would be desirable for vascular repair or replacement. Despite the potential of these Scl proteins in vascular applications, the utility of this recombinant protein family is currently limited to coatings due to the inability of Scl proteins to assemble into stable three-dimensional networks. To address this limitation, the Scl2 proteins were functionalized with photocrosslinking sites to enable incorporation into a hydrogel matrix. Characterization studies confirmed that the functionalization of the Scl2 proteins did not disrupt triple helix conformation, integrin binding or cell adhesion. Bioactive hydrogels were fabricated by combining the functionalized Scl2 proteins with poly(ethylene glycol) diacrylate (PEGDA) and photocrosslinking. EC and SMC adhesion studies confirmed cell-specific adhesion due to selective integrin binding to the two receptor binding motifs investigated. These results serve to highlight the potential of this novel biomaterial platform in the development of improved tissue engineered vascular grafts.

Rapamycin enriches for CD4(+) CD25(+) CD27(+) Foxp3(+) regulatory T cells in ex vivo-expanded CD25-enriched products from healthy donors and patients with multiple sclerosis.

BACKGROUND: CD4(+) CD25(bright+) regulatory T cells (Treg) can be expanded to clinical doses using CD3/CD28 Ab-coated beads plus IL-2. However, this method requires high purity of the starting population to prevent overgrowth by non-regulatory T cells. Rapamycin, an agent that inhibits T-cell proliferation but selectively spares Treg, may be a means to expand Treg from less pure CD25-enriched cells. METHODS: CD25-enriched cells were prepared by a single-step immunomagnetic-selection using anti-CD25 microbeads. The cells were activated with a single addition of anti-CD3/CD28 beads and expanded in ex vivo 15-5% HS and autologous CD4(+) CD25(-) feeder cells,+/-rapamycin (0.01-20 ng/mL). IL-2 was added on day 3. Cells were rested for 2 days in ex vivo 15-5% HS and tested for phenotype, intracellular Foxp3 protein and suppressor activity. RESULTS: In the absence of rapamycin, CD25-enriched fractions expanded >17 000-fold by 21 days. Although suppressor activity was detected to day 14, it declined significantly by 21 days as non-regulatory cells expanded. The addition of rapamycin inhibited expansion of non-regulatory T cells at doses > or =1 ng/mL while increasing suppressor activity and the percentage of CD4(+) CD25(+) CD27(+) Foxp3(+) cells. Rapamycin did not enrich for Foxp3(+) cells in expanded cultures of CD4(+) CD25(-) cells. Treg were also readily expanded in cultures of CD25-enriched cells obtained from patients with multiple sclerosis in the presence of rapamycin. DISCUSSION: The addition of 1-20 ng/mL rapamycin to CD25-enriched cultures increased the purity of cells with the phenotype and function of Treg. This approach may alleviate the need for rigorous enrichment of Treg prior to activation and expansion for potential clinical use.