STUDIES OF VEGETATIVE COMPATIBILITY-INCOMPATIBILITY IN HIGHER PLANTS. IV. THE DEVELOPMENT OF TENSILE STRENGTH IN A COMPATIBLE AND AN INCOMPATIBLE GRAFT

Three phases of adhesion between the stock and scion are observable during the formation of a compatible autograft in Sedum telephoides and an incompatible heterograft between Sedum telephoides and Solanum pennellii. The first phase of adhesion is similar in both systems in that it 1) lasts 2 to 3 days, and 2) is characterized by an average increase in tensile strength of 1 g breaking weight (BW)/mm² graft area (GA)/day. In the compatible Sedum autograft, the second phase of adhesion lasts from Days 3 to 11 after grafting and is correlated with a 28-fold increase in the tensile strength of the graft union to approximately 56 g BW/mm² GA by 11 days after grafting. The third phase of adhesion in the compatible autograft is characterized by a leveling off of the tensile strength of the graft union at approximately 56 g BW/mm² GA, roughly equal to that of an ungrafted internode. Graft formation is now complete. These results suggest that the ratio of the tensile strength of the graft union : tensile strength of a comparable ungrafted internode provides an estimate of the percent development of compatible autografts. In the incompatible heterograft between Sedum and Solanum, Phase II adhesion 1) lasts from Days 2 to 5 after grafting, and 2) peaks at 12 g BW/mm² GA at 5 days after grafting. Phase III adhesion in the incompatible heterograft occurs subsequent to Day 5 after grafting and is characterized by an average decrease in the tensile strength of the graft union of 0.3 g BW/mm² GA/day. The results of this study are discussed relative to the quantitative contributions of various structural events to the tensile strength of a graft union.     

Graft Formation in Kalanchoe blossfeldiana

Three phases of cohesion between the stock and scion are observableduring the formation of compatible autografts in Kalanchoe blossfeldiana.The first phase of cohesion: (a) lasts four to five days, (b)is correlated with an accumulation of dictyosomes along thegraft interface and with callus proliferation in the stock andscion, and (c) is characterized by a tensile strength of approximately5 g breaking weight (BW) mm^–2 graft area (GA) by 5 d aftergrafting. The second phase of cohesion lasts from days 5–20after grafting and is correlated with (a) an interdigitationof callus cells at the graft interface, (b) the differentiationof vascular tissue across the graft interface, and (c) a 20-foldincrease in the tensile strength of the graft union to approximately100 g BW mm^–2 GA by 20 d after grafting. This cohesivestrength is comparable to that of an intact, non-grafted stem.The third phase of cohesion is characterized by a levellingoff of the increase in tensile strength of the graft union withtime at approximately 125 g BW mm^–2 GA. The results ofthis study are discussed relative to other structural studiesof and proposed mechanisms for graft development.     

Manipulation of remodeling pathways to enhance the mechanical properties of a tissue engineered blood vessel

There is a current need for a small diameter vascular graft due to the limited supply of autogenous grafts and the failure of synthetic grafts due to thrombosis and/or intimal hyperplasia. The use of living cells and tissues to fabricate a small diameter graft (i.e., tissue engineered blood vessel, TEBV) could be useful given the endothelialization potential and biocompatibility benefits of such a graft. However, while sufficient strength has been attained in a TEBV, coordinate compliance has yet to be fine-tuned. In this study we investigate the effects of biological response modifiers, retinoic acid (RA) and ascorbic acid (AA) on TEBV biomechanics as a function of time and subsequently correlate observed RA/AA induced changes in TEBV mechanics with alterations in smooth muscle cell (SMC) biochemistry. TEBVs were constructed using a fibrillar type I collagen network populated by human aortic smooth muscle cells (AoSMC). Following construction this TEBV was treated with 0.3 mM AA and 0.1 mM RA (concentrations found to induce changes in VSMC phenotype). Ultimate tensile stress (UTS), rate of relaxation (RR) and elastic efficiency (EE) of RA/AA treated and untreated TEBVs were measured following 1, 7, 15, 30, 45, and 60 days of treatment. At corresponding time points, the effect of these treatments on collagen and elastin protein synthesis and mRNA expression was examined. RA/AA treated TEBV strength increased and stiffness decreased compared to controls as a function of time. Relative collagen synthesis in treated TEBVs exceeded control levels by nearly two-fold at 15 and 30 days of incubation. RA/AA treated collagen gene expression followed a similar trend. Relative elastin synthesis was also greater in treated TEBVs as compared to untreated TEBVs at 15 and 30 days of incubation and correspondingly elastin mRNA expression was significantly elevated at 15 days of incubation. These data provide evidence that RA/AA treated TEBVs exhibit mechanical properties which more closely mimic those of a native vessel than their untreated counterparts and that changes in extracellular matrix composition and matrix gene expression in the presence of RA/AA treatment may play an important role in the development of said mechanical properties.     

Graft formation in Solanum pennellii (Solanaceae)

Three phases of cohesion were observable during the development of compatible autografts in Solanum pennellii. Phase I cohesion 1) lasted 4–5 d after grafting, 2) was characterized by an average increase in tensile strength of 4 g breaking weight (BW) mm^–2 graft area (GA) d^–1, and 3) correlated positively with cellular interdigitation at the graft interface. The fresh weight of the scion increased by approximately 5% d^–1 during the first 2 d after grafting. Phase II cohesion occurred 5–15 d after grafting, during which time 1) the tensile strength of the graft union increased by 14 g BW mm^–2 GA d^–1, 2) vascular differentiation across the graft interface was completed, and 3) the fresh weight of the scion increased by 9% d^–1. Phase III cohesion occurred subsequent to 15 d after grafting, during which time 1) the tensile strength of the graft union leveled off at a value similar to that of an ungrafted internode, and 2) the fresh weight of the scion increased by 14% d^–1. These results are discussed relative to mechanisms underlying the formation of compatible grafts.     

Graft-union development: a delicate process that involves cell-cell communication between scion and stock for local auxin accumulation

Grafting is an ancient cloning method that has been used widely for thousands of years in agricultural practices. Graft-union development is also an intricate process that involves substantial changes such as organ regeneration and genetic material exchange. However, the molecular mechanisms for graft-union development are still largely unknown. Here, a micrografting method that has been used widely in Arabidopsis was improved to adapt it a smooth procedure to facilitate sample analysis and to allow it to easily be applied to various dicotyledonous plants. The developmental stage of the graft union was characterized based on this method. Histological analysis suggested that the transport activities of vasculature were recovered at 3 days after grafting (dag) and that auxin modulated the vascular reconnection at 2 dag. Microarray data revealed a signal-exchange process between cells of the scion and stock at 1 dag, which re-established the communication network in the graft union. This process was concomitant with the clearing of cell debris, and both processes were initiated by a wound-induced programme. The results demonstrate the feasibility and potential power of investigating various plant developmental processes by this method, and represent a primary and significant step in interpretation of the molecular mechanisms underlying graft-union development.     

Root Formation in Pea Cuttings

Auxin was applied to the upper part of the cuttings, which were both decapitated and disbudded on the same day. The applied auxin was removed by redecapitating the cuttings at different time intervals. In a second experiment, auxin was applied either to the upper or lower part of the decapitated and disbudded cuttings at different time intervals. In cuttings, which were redecapitated after 1 and 2 days, the root formation was reduced considerably. The redecapitation after 3 days had no adverse effect on the root formation. Cuttings treated with auxin at different time intervals showed a weaker root promotion on days 0 and 1 than on the subsequent days. The results emphasize the fact that auxin is active only during the first part of the root initiation phase. A continuous flow of auxin for a period of the first 3 days during the root initiation is of overriding importance. There appears to be at least two different stages of the root initiation phase, (ia) auxin active stage, and (ib) auxin inactive stage. The results also seem to indicate that some other factors, in addition to auxin, are active during the first stage of the root initiation phase.     

Mechanical recruitment of N- and C-crosslinks in collagen type I

Collagen type I is an extracellular matrix protein found in connective tissues such as tendon, ligament, bone, skin, and the cornea of the eyes, where it functions to provide tensile strength; it also serves as a scaffold for cells and other extracellular matrix components. A single collagen type I molecule is composed of three amino acid chains that form a triple helix for most of the molecule's length; non-triple-helical extensions called N- and C-telopeptides are located at the amino/N-terminal and carboxy/C-terminal ends of the molecule, respectively. In two of the three chains, the C-telopeptide has been reported to possess a hair-pin/hook conformation, while the three N-telopeptides display a more extended structure. These telopeptides are crucial for the formation of enzymatic covalent crosslinks that form in collagens near their N- and C-ends. Such crosslinks provide structural integrity, strength, and stiffness to collagenous tissues. However, deformation mechanisms of N- and C-crosslinks and functional roles for the N- and C-telopeptide conformations are not yet well known. By performing molecular dynamics simulations, we demonstrated that two dehydro-hydroxylysino-norleucine crosslinks, positioned at the N- and C-crosslinking sites, exhibited a two-stage response to the mechanical deformation of their parent molecules. We observed that the N-crosslink served as the first responder to mechanical deformation, followed by the C-crosslink. The results of our simulations suggest a mechanical recruitment mechanism for N- and C-crosslinks. Understanding this mechanism will be crucial for the development of larger-scale predictive models of the mechanical behavior of native collagenous tissues, engineered tissues, and collagen-based materials.     

Development of the embryonic chick wing bud from stage 24 to stage 32

If a graft is placed in an early chick wing bud, the location of the graft after several days of further development cannot be predicted solely from the rate of proximal-distal outgrowth. The movement of the graft depends on the rate of outgrowth of the wing but also on morphogenetic tissue movements intrinsic to the wing and on accommodation to the growth and morphogenetic movements of the body of the embryo. Numerous experiments have been reported in which tissue grafted into ectopic sites in the wing causes abnormal wing development. These experiments have been discussed in terms of pattern formation or positional information. However, until the movement of wing tissue during normal development is understood, it cannot be known in what way the development of grafts placed in ectopic sites is abnormal. Previous experiments have demonstrated that carbon particles placed in the wing move in the same manner as grafts of wing mesenchyme, but the carbon particles do not affect normal wing development. Carbon particles were placed in the wing, dorsal to the base of the wing, and cranial and caudal to the wing, to plot the expected movement of a graft and to discover how this movement can be predicted from the tissue movements at the base of the wing. It is concluded that three tissue movements are responsible for the movement of a graft. These are outgrowth at a rate determined by the rate of cell division, formation of the shoulder through caudal movement of the tissues cranial to the wing, and ventral movement of prospective flank ventral to somite 19. These three tissue movements and their influence on normal wing development are discussed.     

Responses to amputation of denervated ambystoma limbs containing aneurogenic limb grafts

The developing neural tubes and associated neural crest cells were removed from stage 30 Ambystoma maculatum embryos to obtain larvae with aneurogenic forelimbs. Forelimbs were allowed to develop to late 3 digit or early 4 digit stages. Limbs amputated through the mid radius-ulna regenerated typically in the aneurogenic condition. Experiments were designed to test whether grafts of aneurogenic limb tissues would rescue denervated host limb stumps into a regeneration response. In Experiment 1, aneurogenic limbs were removed at the body wall and grafted under the dorsal skin of the distal end of amputated forelimbs of control, normally innervated limbs of locally collected Ambystoma maculatum or axolotl (Ambystoma mexicanum) larvae. In Experiment 1, at the time of grafting or 1, 2, 3, 4, 5, 7, or 8 days after grafting, aneurogenic limbs were amputated level with the original host stump. At 7 and 8 days, this amputation included removing the host blastema adjacent to the graft. The host limb was denervated either one day after grafting or on the day of graft amputation. These chimeric limbs only infrequently exhibited delayed blastema formation. Thus, not only did the graft not rescue the host, denervated limb, but the aneurogenic limb tissues themselves could not mount a regeneration response. In Experiment 2, the grafted aneurogenic limb was amputated through its mid-stylopodium at 3, 4, 5, 7, or 8 days after grafting. By 7 and 8 days after grafting, the host limb stump exhibited blastema formation even with the graft extending out from under the dorsal skin. The host limb was denervated at the time of graft amputation. When graft limbs of Experiment 2 were amputated and host limbs were denervated on days 3, 4, or 5, host regeneration did not progress and graft regeneration did not occur. But, when graft limbs were amputated on days 7 or 8 with concomitant denervation of the host limb, regeneration of the host continued and graft regeneration occurred. Thus, regeneration of the graft was correlated with acquisition of nerve-independence by the host limb blastema. In Experiment 3, aneurogenic limbs were grafted with minimal injury to the dorsal skin of neurogenic hosts. When neurogenic host limbs were denervated and the aneurogenic limbs were amputated through the radius/ulna, regeneration of the aneurogenic limb occurred if the neurogenic limb host was not amputated, but did not occur if the neurogenic limb host was amputated. Results of Experiment 3 indicate that the inhibition of aneurogenic graft limb regeneration on a denervated host limb is correlated with substantial injury to the host limb. In Experiment 4, aneurogenic forelimbs were amputated through the mid-radius ulna and pieces of either peripheral nerve, muscle, blood vessel, or cartilage were grafted into the distal limb stump or under the body skin immediately adjacent to the limb at the body wall. In most cases, peripheral nerve inhibited regeneration, blood vessel tissue sometimes inhibited, but other tissues had no effect on regeneration. Taken together, the results suggest: (1) Aneurogenic limb tissues do not produce the neurotrophic factor and do not need it for regeneration, and (2) there is a regeneration-inhibiting factor produced by the nerve-dependent limb stump/blastema after denervation that prevents regeneration of aneurogenic limbs.     

Direct Lentiviral-Cyclooxygenase 2 Application to the Tendon-Bone Interface Promotes Osteointegration and Enhances Return of the Pull-Out Tensile Strength of the Tendon Graft in a Rat Model of Biceps Tenodesis

This study sought to determine if direct application of the lentiviral (LV)-cyclooxygenase 2 (COX2) vector to the tendon-bone interface would promote osteointegration of the tendon graft in a rat model of biceps tenodesis. The LV-COX2 gene transfer strategy was chosen for investigation because a similar COX2 gene transfer strategy promoted bony bridging of the fracture gap during bone repair, which involves similar histologic transitions that occur in osteointegration. Briefly, a 1.14-mm diameter tunnel was drilled in the mid-groove of the humerus of adult Fischer 344 rats. The LV-COX2 or βgal control vector was applied directly into the bone tunnel and onto the end of the tendon graft, which was then pulled into the bone tunnel. A poly-L-lactide pin was press-fitted into the tunnel as interference fixation. Animals were sacrificed at 3, 5, or 8 weeks for histology analysis of osteointegration. The LV-COX2 gene transfer strategy enhanced neo-chondrogenesis at the tendon-bone interface but with only marginal effect on de novo bone formation. The tendon-bone interface of the LV-COX2-treated tenodesis showed the well-defined tendon-to-fibrocartilage-to-bone histologic transitions that are indicative of osteointegration of the tendon graft. The LV-COX2 in vivo gene transfer strategy also significantly enhanced angiogenesis at the tendon-bone interface. To determine if the increased osteointegration was translated into an improved pull-out mechanical strength property, the pull-out tensile strength of the LV-COX2-treated tendon grafts was determined with a pull-out mechanical testing assay. The LV-COX2 strategy yielded a significant improvement in the return of the pull-out strength of the tendon graft after 8 weeks. In conclusion, the COX2-based in vivo gene transfer strategy enhanced angiogenesis, osteointegration and improved return of the pull-out strength of the tendon graft. Thus, this strategy has great potential to be developed into an effective therapy to promote tendon-to-bone healing after tenodesis or related surgeries.     

Alterations in the biorheological features of some soft tissues after limb lengthening.

The aim of this study was to investigate the effects of a surgical limb lengthening procedure on the biorheological features of some lengthened soft tissues. In this procedure external fixators were applied to goats' right radius to stretch the tissues. The right forelegs of goats were lengthened by 2, 4 cm, respectively. After lengthening ceased, the goats were examined after different periods of time. The lengthened median nerves, arteries and veins were harvested and used to study their biorheological features. Tensile strength of lengthened and control specimens were measured and their stress relaxation features and stress-strain relationships were studied. Results showed that at the beginning of recovery, the stress-strain curves, relaxation curves and tensile strengths of the lengthened specimens began to deviate from those of their controls. However, with increasing recovery time, the curves and tensile strength of the lengthened specimens reverted to those of their controls. All the tissues studied exhibited the same behavior.     

Prevention of mechanical stretch-induced endothelial and smooth muscle cell injury in experimental vein grafts

Vein grafts are subject to increased tensile stress due to exposure to arterial blood pressure, which has been hypothesized to induce endothelial cell (EC) and smooth muscle cell (SMC) injury. This study was designed to verify this hypothesis and to develop a tissue engineering approach that can be used to prevent these pathological events. Two experimental models were created in rats to achieve these goals: (1) a nonengineered vein graft with increased tensile stress, which was created by grafting a jugular vein into the abdominal aorta using a conventional end-to-end anastomotic technique; and (2) an engineered vein graft with reduced tensile stress, which was created by restricting a vein graft into a cylindrical sheath constructed using a polytetrafluoroethylene membrane. The integrity of ECs in these models was examined by using a silver nitrate staining method, and the integrity of SMCs was assessed by using a fluorescein phalloidin-labeling technique. It was found that nonengineered vein grafts were associated with early EC denudation with a change in EC coverage from 100 percent in normal jugular veins to 36 +/- 10, 28 +/- 12, 18 +/- 9, 44 +/- 15, 80 +/- 13, and 97 +/- 6 percent at 1 and 6 hours and 1, 5, 10, and 30 days, respectively. Similarly, rapid SMC actin filament degradation was found during the early period with a change in SMC coverage from approximately 94 percent in normal jugular veins to 80 +/- 10, 41 +/- 17, 25 +/- 9, 51 +/- 15, 79 +/- 15, 98 +/- 2 percent at 1 and 6 hours and 1, 5, 10, and 30 days, respectively, in nonengineered vein grafts. In engineered vein grafts with reduced tensile stress, EC denudation and SMC actin filament degradation were prevented significantly. These results suggested that mechanical stretch due to increased tensile stress contributed to EC and SMC injury in experimental vein grafts, and these pathological events could be partially prevented when tensile stress was reduced by using a biomechanical engineering approach.     

Synthesis and properties of carrageenan grafted copolymer with poly(vinyl alcohol)

The aim of this work was to prepare a carrageenan-g-poly(vinyl alcohol) (CG-g-PVA) polymer using potassium persulphate as an initiator. The effect of different ratios of the polymer blends on the parameters of the grafted polymer was investigated. The grafting ratio decreased with an increase of the CG content in the graft copolymer. The resulting CG-g-PVA was characterized by ATR-FTIR, tensile strength, elongation at break, swelling ratio, contact angle and biodegradation in soil. From the ATR-FTIR the 3,6-anhydride-galactose of the CG showed a peak at 927 cm⁻¹ that was absent in the CG-g-PVA and the ether linkage of PVA-g-CG between the hydroxyl group of PVA and the 3,6-anhydride-galactose of CG showed a peak at 1089 cm⁻¹ in the graft copolymer. The tensile strength and elongation at break decreased with an increase of the CG due to its phase separation. The highest tensile strength was observed at 2:8 CG/PVA. In addition, the swelling ratio decreased and the contact angle increased as a function of the increase of the CG in the grafted copolymer. The best ratio of CG-g-PVA was 2:8 CG/PVA. This graft copolymer was easily biodegraded in natural soil.     

An investigation on skin wound healing in mice with a taurine-chitosan gel formulation

Summary. The process of wound healing begins immediately following surface lesions or just after exposure to radiation, chemical agents or extreme temperatures. Taurine (2-aminoethane sulfonic acid), an amino acid containing sulfur, is found in almost all tissues in mammals, playing various important physio-logical roles in each organ. Taurine exhibits an antioxidant effect and is also known to have effects on cell proliferation, inflammation and collagenogenesis. Many antioxidants have been used to eliminate the negative effects of oxygen free radicals on wound healing. The objective of the present study was to examine the wound healing effect in mice of taurine-chitosan gel, which releases taurine slowly over a long time period. Fifty mM of taurine in 1.5% chitosan polymer (TAU-GEL) and 1.5% chitosan polymer (CHI-GEL) were applied to full thickness skin wounds of mice once a day for seven days. After seven days of treatment, lipid peroxide formation-malondialdehyde (MDA) and hydroxyproline (HPX) levels and the tensile strength of wound tissues were measured. All results were compared with those of the untreated control group (CONT). The structural alterations in the skin layers were also histologically investigated. It was found that locally administered TAU-GEL form significantly increased wound tensile strength by decreasing the MDA and increasing HPX levels. These results were supported by histological findings. All observations suggest that taurine gel may be effective in wound healing. Received January 15, 2001 Accepted June 4, 2001     

Equibiaxial cyclic stretch stimulates fibroblasts to rapidly remodel fibrin

Understanding the effects of the mechanical environment on wound healing is critical for developing more effective treatments to reduce scar formation and contracture. The aim of this study was to investigate the effects of dynamic mechanical stretch on cell-mediated early wound remodeling independent of matrix alignment which obscures more subtle remodeling mechanisms. Cyclic equibiaxial stretch (16% stretch at 0.2 Hz) was applied to fibroblast-populated fibrin gel in vitro wound models for eight days. Compaction, density, tensile strength, and collagen content were quantified as functional measures of remodeling. Stretched samples were approximately ten times stronger, eight-fold more dense, and eight times thinner than statically cultured samples. These changes were accompanied by a 15% increase in net collagen but no significant differences in cell number or viability. When collagen crosslinking was inhibited in stretched samples, the extensibility increased and the strength decreased. The apparent weakening was due to a reduction in compaction rather than a decrease in ability of the tissue to withstand tensile forces. Interestingly, inhibiting collagen crosslinking had no measurable effects on the statically cultured samples. These results indicate that amplified cell-mediated compaction and even a slight addition in collagen content play substantial roles in mechanically induced wound strengthening. These findings increase our understanding of how mechanical forces guide the healing response in skin, and the methods employed in this study may also prove valuable tools for investigating stretch-induced remodeling of other planar connective tissues and for creating mechanically robust engineered tissues.     

Cryopreservation of fetal rat brain tissue later used for intracerebral transplantation

Intracerebral grafting of immature brain tissue is now widely used as a tool to study neuronal development and regeneration in the brain and spinal cord. This has stimulated the interest in methods for storage of such tissue before transplantation. In this study a method for cryopreservation of immature rat central nervous tissue is presented and discussed in relation to current cryobiological principles. The method was applied to brain tissue from 16- and 17-day-old fetal rats, including the neocortex, habenula, septum and basal forebrain, cerebellum, and retina. After storage in liquid nitrogen from 6 to 52 days the tissue was grafted into the brain of adult rats. The recipients survived for 23 to 673 days before their brains were processed by current neuroanatomical, histological methods. The presence of graft tissues was recorded and their cellular and connective organization was examined, including their exchange of nerve connections with the host brain. The results obtained were comparable with results from other studies where the same tissues were grafted immediately after removal from the donor, and a study of cryopreservation of developing hippocampal tissue. We conclude that cryopreservation is a reliable method for storage of immature neural tissue later to be used for intracerebral grafting.     

A novel application of the principles of linear elastic fracture mechanics (LEFM) to the fatigue behavior of tendon tissue

BACKGROUND: Experiments on the fatigue of tendons have shown that cyclic loading induces failure at stresses lower than the ultimate tensile strength (UTS) of the tendons. The number of cycles to failure (Nf) has been shown to be dependent upon the magnitude of the applied cyclic stress. METHOD OF APPROACH: Utilizing data collected by Schechtman (1995), we demonstrate that the principles of Linear Elastic Fracture Mechanics (LEFM) can be used to predict the fatigue behavior of tendons under cyclic loading for maximum stress levels that are higher than 10% of the ultimate tensile strength (UTS) of the tendon (the experimental results at 10% UTS did not fit with our equations). CONCLUSIONS: LEFM and other FM approaches may prove to be very valuable in advancing our understanding of damage accumulation in soft connective tissues.     

Development of an Efficient Protocol of RNA Isolation from Recalcitrant Tree Tissues

Isolation of RNA from recalcitrant tree tissues has been problematic due to large amounts of secondary metabolites and interfering compounds in their cells. We have developed an efficient RNA extraction method, which yielded high-quality RNA preparations from tissues of the lychee tree. The method reported here utilized EDTA, LSS, and CTAB to successfully inhibit RNase activities. It was found that a high ionic strength brought about by 2 M NaCl was necessary. In addition, secondary metabolites and other interfering compounds were effectively removed using sodium borate and PVPP under a deoxidized condition. The quality of purified RNA was tested by both RACE and Northern blotting analysis, ensuring that the RNA could be used for subsequent gene expression analysis. This method has been successfully applied to purify RNA from 15 other plant species. In conclusion, the protocol reported here is expected to have excellent applications for RNA isolation from recalcitrant plant tissues.     

Chemical modification of wheat-protein-based natural polymers: formation of polymer networks with alkoxysilanes to modify molecular motions and enhance the material performance

The mechanical performance of plasticized wheat gluten (WG) materials was significantly modified through the formation of different chemical and network structures with alkoxysilanes. The epoxy-functionalized alkoxysilanes were grafted to segments of WG, and then the condensation reactions between alkoxysilane segments occurred during thermal processing to form WG-siloxane networks. The mechanical properties and molecular motions of the networks were dependent on the amount and type of alkoxysilanes applied. A lower amount of alkoxysilanes caused the alkoxysilane molecules to predominately graft onto WG chains without forming linkages between WG segments, which produced an additional plasticizing effect on the WG systems with a longer elongation value and weaker tensile strength at relative humidity (RH) = 50% as compared to the WG system. However, such grafting improved the hydrostability of the materials and generated an improvement in tensile strength at RH = 85%. Increasing the amount of alkoxysilanes in the systems led to the formation of cross-linked WG-siloxane networks via linkages between alkoxysilane segments. Remarkable strength improvement was obtained for the networks with elongation values still higher than the original plasticized WG due to the flexible nature of the siloxane components. A more significant strength improvement was obtained for the WG-SiA systems at both RH = 50% and 85%, where SiA could form three-dimensional networks from siloxane condensation and generate highly cross-linked network structures with relatively low mobility. For WG-SiB systems, SiB could only form linear linkages, and the higher mobility of the SiB phase caused the systems to display a lower strength improvement with a longer elongation value.     

Changes of the dermal-fascial autograft after transplantation on the vascular-nervous connections using a microsurgical technique

In 56 dogs 86 microsurgical operations on transplantation of free dermal-facial autografts from the internal knee surface have been performed on the hidden vascular-nervous bundle. The animals have been observed for 1 day up to 1 year. The implanted grafts (63) have been studied, using a complex of anatomical, histological and roentgenological methods. During early time (up to 7 days) after the operation in the flap signs of edema, dystrophy and inflammatory infiltration of tissues predominate. The graft gets blood at the expense of the restored main artery and has no vascular connections with the surrounding tissues. Its nervous conductors are fragmented. During 2 weeks--1 month epidermis completely regenerates along the line of the dermal suture. In the flap bed mature granulations result in vascular connections with its surrounding tissues. These connections become stable by the end of the first month, this means that the graft has implanted. Its nervous fibers are also restored. Long-term observations demonstrate that the adaptive changes of the flap and its vascular bed are near to completion. By the end of the 1st year restoration of the main innervational connections of the graft takes place. According to the data obtained, the nervous conductors grow into it along the sewed hidden nerve and along the course of paravasal nerve plexuses. Across the scar from the surrounding tissues the dermal-fascial autograft does not reinnervate.