Tissue damage force estimation in porcine small intestine from its elasticity.

PURPOSE: Post-surgical complications are correlated to the surgeon's technical skill level. Thus, efforts are being put in finding ways to improve the surgeon's technical skills, such as not causing unwanted damage to tissues during surgery. In this study, we aim to investigate the possibility of estimating biological tissue damage, in view of preventing unwanted damage during surgery. METHODS: A series of tensile tests were performed on porcine small intestinal tissue to determine the elasticity and the tearing force. The tissue was then microscopically observed to investigate the influence of fibrous protein configuration in the tissue's mechanical properties. RESULTS: The results from the tensile test showed that the fracture energy had a positive and linear correlation with the elasticity to the negative 0.5th power (R2 = 0.897), which was also suggested by an existing damage model for polymeric materials (Lake-Thomas model). The results from the microscopic observations also showed a resembling influence of fiber configuration on the elasticity as suggested in polymer mechanics (affine network model). CONCLUSION: We showed that the fracture energy had a correlation with the elasticity in porcine small intestinal tissues, which was also suggested in polymer mechanics, thus being a promising avenue toward the ability to estimate the maximum applicable force onto a biological tissue without causing damage during surgery. Attention should also be pointed, however, towards investigating the extent at which polymer mechanics and biomechanics overlap.

Development of a fluorescent probe library enabling efficient screening of tumour-imaging probes based on discovery of biomarker enzymatic activities.

Fluorescent probes that can selectively detect tumour lesions have great potential for fluorescence imaging-guided surgery. Here, we established a library-based approach for efficient screening of probes for tumour-selective imaging based on discovery of biomarker enzymes. We constructed a combinatorial fluorescent probe library for aminopeptidases and proteases, which is composed of 380 probes with various substrate moieties. Using this probe library, we performed lysate-based in vitro screening and/or direct imaging-based ex vivo screening of freshly resected clinical specimens from lung or gastric cancer patients, and found promising probes for tumour-selective visualization. Further, we identified two target enzymes as novel biomarker enzymes for discriminating between tumour and non-tumour tissues. This library-based approach is expected to be an efficient tool to develop tumour-imaging probes and to discover new biomarker enzyme activities for various tumours and other diseases.

Effect of PEGylation on the Drug Release Performance and Hemocompatibility of Photoresponsive Drug-Loading Platform.

Coronary stenosis has been one of the most common heart diseases that drastically increases the risk of fatal disorders such as heart attack. Angioplasty using drug coated balloons (DCB) has been one of the most safe and promising treatments. To minimize the risk of thrombosis of such DCBs during intervention, a different approach that can secure high hemocompatibility under blood flow is necessary. Here we report a method of improving the photoresponsive platform's hemocompatibility by conjugating polyethylene glycol (PEG), onto the functional groups located at the balloon surface. In this study, latex microbeads were used as models for balloons to enable precise observation of its surface under microscopy. These beads were decorated with PEG polymers of a variety of lengths and grafting densities, along with the Cy5-Photoclevable (PC) linker conjugate to mimic drugs to be loaded onto the platform. Results showed that PEG length and grafting density are both critical factors that alter not only its hemocompatibility, but also the drug load and release efficiency of such platform. Thus, although further investigation is necessary to optimize the tradeoff between hemocompatibility, drug load, and release efficiency, it is safe to conclude that PEGylation of DCB surface is an effective method of enhancing and maintaining high hemocompatibility to minimize the risk of thrombosis during angioplasty.

A novel reaction force-fluorescence measurement system for evaluating pancreatic juice leakage from an excised swine pancreas during distal pancreatectomy.

BACKGROUND: Resection using a stapler is a popular approach to distal pancreatectomy. However, the resulting leakage of pancreatic juice represents a serious problem. We have developed a force-fluorescence measurement as a first step towards the quantitative evaluation of pancreatic leakage due to tissue tearing under compression. METHODS: The system comprises a testing machine with an indenter, similar in size to a stapler, which controls compression speed and measures reaction force, and a fluorescence measurement system to measure pancreatic juice leakage. Pancreatic juice leakage is measured as the maximum value of the increasing rate of fluorescence intensity (max value). Ten excised swine pancreases were compressed at a speed of 500, 100, and 10 mm/min until their thicknesses became 2 mm. RESULTS: A strong positive correlation (0.804) was observed between the increase in max value before and after compression and the amount of reaction force drop due to tissue destruction. No pancreatic juice leakage was observed when compressed slowly (10 mm/min). CONCLUSIONS: We have successfully developed a novel force-fluorescence measurement system that can detect and quantify pancreatic juice leakage caused by tissue tearing. This system can determine the optimal compression conditions for preventing pancreatic juice leakage.

Relationship between Bulk Physicochemical Properties and Surface Wettability of Hydrogels with Homogeneous Network Structure.

Controlling hydrogel surface wettability is of great importance in the viewpoint of engineering biomaterials that are in contact with cells and tissues. However, studies reporting how the hydrogel bulk properties would affect the surface is scarce, and thus it has been difficult to fabricate hydrogels with the desired properties. Also, there has been no effective method to elucidate this, due to the inhomogeneity introduced in the network structure of conventional hydrogels. Here we report our approach in elucidating the relationship between hydrogel physicochemical parameters and surface wettability by using Tetra-PEG gels, which are known to have homogeneous network structure. Specifically, the polymer volume fraction (φ) and the molecular weight (MW) between the cross-links were controlled. The number of anions, cations, and ionic pairs introduced within the hydrogel, were also individually controlled. The surface wettability of the resulting hydrogels was then evaluated. Results showed that surface wettability is largely dependent on the concentration of charged groups that are introduced in the hydrogel bulk, especially those that are not paired and ionically stabilized. Our findings strongly support the fact that with conventional hydrogels, the correlation between surface wettability and its physicochemical properties had not been evaluated appropriately, and thus our insights will contribute significantly to accumulating further knowledge on controlling hydrogel surface wettability.

Co-lyophilized Aspirin with Trehalose Causes Less Injury to Human Gastric Cells and Gastric Mucosa of Rats.

BACKGROUND: Aspirin is one of the most popular NSAIDs worldwide because of its anti-inflammatory and anticoagulant effects, and however, gastrointestinal injury remains a major complication. We previously reported co-lyophilized aspirin/trehalose (Lyo A/T) decreased the aspirin-induced gastric lesions in dogs. AIM: This study investigated the mechanism of gastroprotective effects of trehalose in vitro and in vivo. METHODS: The apoptotic assays were performed in a human gastric carcinoma cell line, which was treated with aspirin, mixed aspirin/trehalose (Mix A/T) or Lyo A/T. Gastric ulcer severity was examined after oral administration of drugs in rats. In addition, the mucosal tissue apoptotic status in drug-treated rats was evaluated. Molecular dynamics simulations and laser Raman spectroscopy were performed in order to examine the molecular properties of Lyo A/T. RESULTS: DNA fragmentation was detected in AGS cells that were treated with aspirin and Mix A/T, but not in the Lyo A/T-treated cells. There were fewer apoptotic cells in the Lyo A/T-treated cells than in the other cells. Gastric injury was reduced in rats that received oral Lyo A/T compared with the others, while PGE2 synthesis was equally decreased in all groups. TUNEL assay and immunohistochemistry of cleaved caspase-3 in the mucosal tissues also revealed that Lyo A/T treatment induced less apoptosis than the others. The Lyo A/T spectrum showed clear differences in several Raman bands compared with that of Mix A/T. CONCLUSIONS: Our data showed that co-lyophilization of aspirin with trehalose reduced gastric injury, potentially through suppression of aspirin-induced mucosal cell apoptosis while retaining its anti-inflammatory effects.

Distribution and evolution of the serine/aspartate racemase family in invertebrates.

Free D-amino acids have been found in various invertebrate phyla, while amino acid racemase genes have been identified in few species. The purpose of this study is to elucidate the distribution, function, and evolution of amino acid racemases in invertebrate animals. We searched the GenBank databases, and found 11 homologous serine racemase genes from eight species in eight different invertebrate phyla. The cloned genes were identified based on their maximum activity as Acropora millepora (Cnidaria) serine racemase (SerR) and aspartate racemase (AspR), Caenorhabditis elegans (Nematoda) SerR, Capitella teleta (Annelida) SerR, Crassostrea gigas (Mollusca) SerR and AspR, Dugesia japonica (Platyhelminthes) SerR, Milnesium tardigradum (Tardigrada) SerR, Penaeus monodon (Arthropoda) SerR and AspR and Strongylocentrotus purpuratus (Echinodermata) AspR. We found that Acropora, Aplysia, Capitella, Crassostrea and Penaeus had two amino acid racemase paralogous genes and these paralogous genes have evolved independently by gene duplication at their recent ancestral species. The transcriptome analyses using available SRA data and enzyme kinetic data suggested that these paralogous genes are expressed in different tissues and have different functions in vivo. Phylogenetic analyses clearly indicated that animal SerR and AspR are not separated by their particular racemase functions and form a serine/aspartate racemase family cluster. Our results revealed that SerR and AspR are more widely distributed among invertebrates than previously known. Moreover, we propose that the triple serine loop motif at amino acid positions 150-152 may be responsible for the large aspartate racemase activity and the AspR evolution from SerR.

Experimental verification of fracture mechanism for polymer gels with controlled network structure.

Recently, polymer gels have drawn much attention as scaffolds for regenerative medicines, soft actuators, and functional membranes. These applications need tough and robust polymer gels as represented by the double network gels. To fully understand this mechanism and develop further advanced polymer gels, we need to fully understand the molecular origin of fracture energy for conventional polymer gels, which is inhibited by the inherent heterogeneity. In this paper, we show the experimental results on the fracture of model polymer gels with controlled network structure, and discuss the mechanism of the fracture of polymer gels.

Autonomous viscosity oscillation via metallo-supramolecular terpyridine chemistry of branched poly(ethylene glycol) driven by the Belousov-Zhabotinsky reaction.

Herein, we report an autonomous viscosity oscillation of polymer solutions coupled with the metal-ligand association/dissociation between Ru and terpyridine (tpy), driven by the Belousov-Zhabotinsky (BZ) reaction. The tpy ligand for the Ru catalyst was attached to the terminals of poly(ethylene glycol) (PEG) with different numbers of branches (linear-, tetra-, and octa-PEG). It is well known that mono-tpy coordination is stable when Ru is oxidized (Ru(tpy)(3+)), whereas bis-tpy coordination is stable when the Ru centre is reduced (Ru(tpy)2(2+)). In the oxidized state, the three different polymers existed as solutions. In contrast, when the Ru centre was reduced, gels were obtained for the tetra- and octa-PEG owing to the formation of a three-dimensional polymer network through Ru-tpy coordination. Rheological measurements confirmed that the sol-gel transition occurred much more quickly in the octa-PEG system than in the tetra-PEG system, because of the requirement of fewer crosslinking points. The polymer solutions exhibited self-oscillation of absorbance and viscosity when BZ substrates were added to the solutions of Ru(2+)-tpy-modified tetra-/octa-PEG. This indicated that the Ru(tpy)2(2+) attached to the polymer ends could work as a metal catalyst for the BZ reaction. By increasing the number of branches from 4 to 8, the amount of crosslinking changed more remarkably during the oscillation, with a maximum value closer to that necessary for gelation. Thus, viscosity oscillation with a larger amplitude in the region of higher viscosity was achieved by using octa-PEG.

"Nonswellable" hydrogel without mechanical hysteresis.

Hydrogels are three-dimensional polymer networks that contain a large amount of water inside. Certain hydrogels can be injected in solution and transformed into the gel state with the required shape. Despite their potential biomedical applications, the use of hydrogels has been severely limited because all the conventional hydrogels inevitably "swell" under physiological conditions, which drastically degrades their mechanical properties. We report the synthesis of injectable "nonswellable" hydrogels from hydrophilic and thermoresponsive polymers, in which two independently occurring effects (swelling and shrinking) oppose each other. The hydrogels can endure a compressive stress up to 60 megapascals and can be stretched more than sevenfold without hysteresis. Our results demonstrate that the suppression of swelling helps retain the mechanical properties of hydrogels under physiological conditions.

Fracture energy of polymer gels with controlled network structures.

We have investigated the fracture behaviors of tetra-arm polyethylene glycol (Tetra-PEG) gels with controlled network structures. Tetra-PEG gels were prepared by AB-type crosslink-coupling of mutually reactive tetra-arm prepolymers with different concentrations and molecular weights. This series of controlled network structures, for the first time, enabled us to quantitatively examine the Lake-Thomas model, which is the most popular model predicting fracture energies of elastomers. The experimental data showed good agreement with the Lake-Thomas model, and indicated a new molecular interpretation for the displacement length (L), the area around a crack tip within which the network strands are fully stretched. L corresponded to the three times of end-to-end distance of network strands, regardless of all parameters examined. We conclude that the Lake-Thomas model can quantitatively predict the fracture energy of polymer network without trapped entanglements, with the enhancement factor being near 3.

Highly Elastic and Deformable Hydrogel Formed from Tetra-arm Polymers.

After decades of efforts by many researchers, we have succeeded in realizing a near-ideal polymer network. This network, the Tetra network, is made by cross-end-coupling of tetra-arm polymer modules. The mechanical energy dissipation was extremely low (tan δ ≈ 10(-4) ). The macroscopic stress-strain relationship of the Tetra network was in good agreement with that of microscopic elastic blobs. The maximum breaking strength was extremely high (≥27 MPa). These results indicate that the Tetra network is closer to an ideal polymer network than any other conventional model networks. Because the Tetra network can be treated as uniformly packed elastic blobs, it should help apply the knowledge of single polymer chains seamlessly to the design of polymer materials and help further develop the theory of rubber elasticity.