A comparative study of tissue factor and kaolin on blood coagulation assays using rotational thromboelastometry and thromboelastography.

Rotational thromboelastometry (ROTEM) and thromboelastography (TEG) have been increasingly used to diagnose acute coagulopathy and guide blood transfusion. The tests are routinely performed using different triggering activators such as tissue factor and kaolin, which activate different pathways yielding different results. To optimize the global blood coagulation assays using ROTEM and TEG, we conducted a comparative study on the activation methods employing tissue factor and kaolin at different concentrations as well as standard reagents as recommended by the manufacturer of each device. Key parameter values were obtained at various assay conditions to evaluate and compare coagulation and fibrinolysis profiles of citrated whole blood collected from healthy volunteers. It was found that tissue factor reduced ROTEM clotting time and TEG R, and increased ROTEM clot formation time and TEG K in a concentration-dependent manner. In addition, tissue factor affected ROTEM alpha angle, and maximum clot firmness, especially in the absence of kaolin activation, whereas both ROTEM and TEG clot lysis (LI30, CL30, and LY30) remained unaffected. Moreover, kaolin reduced ROTEM clotting time and TEG R and K, but to a lesser extent than tissue factor, in-tem and ex-tem. Correlations in all corresponding parameters between ROTEM and TEG were observed, when the same activators were used in the assays compared with lesser correlations between standard kaolin TEG and ROTEM (INTEM/EXTEM). The two types of viscoelastic point-of-care devices provide different results, depending on the triggering reagent used to perform the assay. Optimal assay condition was obtained to reduce assay time and improve assay accuracy.

Theta, mental flexibility, and post-traumatic stress disorder: connecting in the parietal cortex.

Post-traumatic stress disorder (PTSD) is a mental health injury characterised by re-experiencing, avoidance, numbing and hyperarousal. Whilst the aetiology of the disorder is relatively well understood, there is debate about the prevalence of cognitive sequelae that manifest in PTSD. In particular, there are conflicting reports about deficits in executive function and mental flexibility. Even less is known about the neural changes that underlie such deficits. Here, we used magnetoencephalography to study differences in functional connectivity during a mental flexibility task in combat-related PTSD (all males, mean age = 37.4, n = 18) versus a military control (all males, mean age = 33.05, n = 19) group. We observed large-scale increases in theta connectivity in the PTSD group compared to controls. The PTSD group performance was compromised in the more attentionally-demanding task and this was characterised by 'late-stage' theta hyperconnectivity, concentrated in network connections involving right parietal cortex. Furthermore, we observed significant correlations with the connectivity strength in this region with a number of cognitive-behavioural outcomes, including measures of attention, depression and anxiety. These findings suggest atypical coordination of neural synchronisation in large scale networks contributes to deficits in mental flexibility for PTSD populations in timed, attentionally-demanding tasks, and this propensity toward network hyperconnectivity may play a more general role in the cognitive sequelae evident in this disorder.

Delayed and disorganised brain activation detected with magnetoencephalography after mild traumatic brain injury.

BACKGROUND: Awareness to neurocognitive issues after mild traumatic brain injury (mTBI) is increasing, but currently no imaging markers are available for mTBI. Advanced structural imaging recently showed microstructural tissue changes and axonal injury, mild but likely sufficient to lead to functional deficits. Magnetoencephalography (MEG) has high temporal and spatial resolution, combining structural and electrophysiological information, and can be used to examine brain activation patterns of regions involved with specific tasks. METHODS: 16 adults with mTBI and 16 matched controls were submitted to neuropsychological testing (Wechsler Abbreviated Scale of Intelligence (WASI); Conners; Alcohol Use Disorders Identification Test (AUDIT); Generalised Anxiety Disorder Seven-item Scale (GAD-7); Patient Health Questionnaire (PHQ-9); Symptom Checklist and Symptom Severity Score (SCAT2)) and MEG while tested for mental flexibility (Intra-Extra Dimensional set-shifting tasks). Three-dimensional maps were generated using synthetic aperture magnetometry beamforming analyses to identify differences in regional activation and activation times. Reaction times and accuracy between groups were compared using 2×2 mixed analysis of variance. FINDINGS: While accuracy was similar, patients with mTBI reaction time was delayed and sequence of activation of brain regions disorganised, with involvement of extra regions such as the occipital lobes, not used by controls. Examination of activation time showed significant delays in the right insula and left posterior parietal cortex in patients with mTBI. CONCLUSIONS: Patients with mTBI showed significant delays in the activation of important areas involved in executive function. Also, more regions of the brain are involved in an apparent compensatory effort. Our study suggests that MEG can detect subtle neural changes associated with cognitive dysfunction and thus, may eventually be useful for capturing and tracking the onset and course of cognitive symptoms associated with mTBI.

Temporal-spatial neural activation patterns linked to perceptual encoding of emotional salience.

It is well known that we continuously filter incoming sensory information, selectively allocating attention to what is important while suppressing distracting or irrelevant information. Yet questions remain about spatiotemporal patterns of neural processes underlying attentional biases toward emotionally significant aspects of the world. One index of affectively biased attention is an emotional variant of an attentional blink (AB) paradigm, which reveals enhanced perceptual encoding for emotionally salient over neutral stimuli under conditions of limited executive attention. The present study took advantage of the high spatial and temporal resolution of magnetoencephalography (MEG) to investigate neural activation related to emotional and neutral targets in an AB task. MEG data were collected while participants performed a rapid stimulus visual presentation task in which two target stimuli were embedded in a stream of distractor words. The first target (T1) was a number and the second (T2) either an emotionally salient or neutral word. Behavioural results replicated previous findings of greater accuracy for emotionally salient than neutral T2 words. MEG source analyses showed that activation in orbitofrontal cortex, characterized by greater power in the theta and alpha bands, and dorsolateral prefrontal activation were associated with successful perceptual encoding of emotionally salient relative to neutral words. These effects were observed between 250 and 550 ms, latencies associated with discrimination of perceived from unperceived stimuli. These data suggest that important nodes of both emotional salience and frontoparietal executive systems are associated with the emotional modulation of the attentional blink.

Prehospital hypertonic saline resuscitation attenuates the activation and promotes apoptosis of neutrophils in patients with severe traumatic brain injury.

BACKGROUND: Activation of polymorphonuclear neutrophils (PMNs) is thought to contribute to traumatic brain injury (TBI). Since hypertonic fluids can inhibit PMN activation, we studied whether hypertonic fluid resuscitation can reduce excessive PMN activation in TBI patients. METHODS: Trauma patients with severe TBI were resuscitated with 250 mL of either 7.5% hypertonic saline (HS; n = 22), HS + 6% dextran-70 (HSD; n = 22), or 0.9% normal saline (NS; n = 39), and blood samples were collected on hospital admission and 12 and 24 h after resuscitation. Polymorphonuclear neutrophil activation (CD11b, CD62L, CD64) and degranulation (CD63, CD66b, CD35) markers and oxidative-burst activity, as well as spontaneous PMN apoptosis were measured by flow cytometry. RESULTS: Relative to healthy controls, TBI patients showed increased PMN activation and decreased apoptosis of PMNs. In the HS group, but not in the HSD group, markers of PMN adhesion (CD11b, CD64) and degranulation (CD35, CD66b) were significantly lower than those in the NS group. These effects were particularly pronounced 12 h after resuscitation. Treatment with HS and HSD inhibited PMN oxidative burst responses compared with NS-treated patients. Hypertonic saline alone partially restored delayed PMN apoptosis. Despite these differences, the groups did not differ in clinical outcome parameters such as mortality and Extended Glasgow Outcome Scale. CONCLUSIONS: This study demonstrates that prehospital resuscitation with HS can partially restore normal PMN activity and the apoptotic behavior of PMNs, whereas resuscitation with HSD was largely ineffective. Although the results are intriguing, additional research will be required to translate these effects of HS into treatment strategies that improve clinical outcome in TBI patients.

Resuscitation of traumatic hemorrhagic shock patients with hypertonic saline-without dextran-inhibits neutrophil and endothelial cell activation.

Posttraumatic inflammation and excessive neutrophil activation cause multiple organ dysfunction syndrome (MODS), a major cause of death among hemorrhagic shock patients. Traditional resuscitation strategies may exacerbate inflammation; thus, novel fluid treatments are needed to reduce such posttraumatic complications. Hypertonic resuscitation fluids inhibit inflammation and reduce MODS in animal models. Here we studied the anti-inflammatory efficacy of hypertonic fluids in a controlled clinical trial. Trauma patients in hypovolemic shock were resuscitated in a prehospital setting with 250 mL of either 7.5% hypertonic saline (HS; n = 9), 7.5% hypertonic saline + 6% dextran 70 (HSD; n = 8), or 0.9% normal saline (NS; n = 17). Blood samples were collected on hospital admission and 12 and 24 h after resuscitation. Multicolor flow cytometry was used to quantify neutrophil expression of cell-surface activation/adhesion (CD11b, CD62L, CD64) and degranulation (CD63, CD66b, CD35) markers as well as oxidative burst activity. Circulating concentrations of soluble intercellular adhesion molecule-1 (sICAM-1), vascular cell adhesion molecule-1 (sVACM-1), P- and E-selectins, myeloperoxidase (MPO), and matrix metalloproteinase 9 (MMP-9) were assessed by immunoassay. Multiple organ dysfunction syndrome, leukocytosis, and mortality were lower in the HS and HSD groups than in the NS group. However, these differences were not statistically significant. Hypertonic saline prevented priming and activation and neutrophil oxidative burst and CD11b and CD66b expression. Hypertonic saline also reduced circulating markers of neutrophil degranulation (MPO and MMP-9) and endothelial cell activation (sICAM-1, sVCAM-1, soluble E-selectin, and soluble P-selectin). Hypertonic saline + 6% dextran 70 was less capable than HS of suppressing the upregulation of most of these activation markers. This study demonstrates that initial resuscitation with HS, but neither NS nor HSD, can attenuate posttraumatic neutrophil and endothelial cell activation in hemorrhagic shock patients. These data suggest that hypertonic resuscitation without dextran may inhibit posttraumatic inflammation. However, despite this effect, neither HS nor HSD reduced MODS in trauma patients with hemorrhagic shock.

Surface-attached amphipathic peptides reduce hemorrhage in vivo.

BACKGROUND: The leading causes of death for trauma patients in civilian and combat settings are traumatic brain injury and uncontrolled hemorrhage, respectively. This study examines the hemostatic activity of an ideal amphipathic peptide (IAP) attached to a biocompatible surface. METHODS: Procoagulant properties of IAP attached to a surface were first tested, in vitro, using factor Xa and thrombin generation assays and thromboelastography. Rabbits and swine were used for in vivo studies. Injuries were performed using scalpel blade 11, and free bleeding was allowed for five seconds. While bleeding, IAP coupled to a hydrogel or QuikClot were applied to the wound and the time was recorded until bleeding stopped. RESULTS: Results show that when IAP is attached to a surface, both factor IXa and factor Xa activities are promoted. Thromboelastography shows that surface-attached IAP results in earlier onset and stronger clot formation. In rabbits, the incorporation of IAP onto a biocompatible hydrogel reduces bleeding times by 40% (p < 0.03). In pigs, bleeding times are reduced 30% to 50% (p < 0.02) by surface-coupled IAP. Finally, using a rabbit liver laceration model, the properties of surface-coupled IAP are less damaging when compared with QuikClot, a currently used material in external hemorrhagic injuries. CONCLUSIONS: This study provides a relevant proof of concept for the development of IAP coupled to a biocompatible surface as a hemostatic agent, that is potentially safer than the commercially available QuikClot.

Characterization of in vitro hemostatic peptide effects by thromboelastography.

In this study, we validated a thromboelastography (TEG) method to evaluate the hemostatic effects of 3 peptides. The first peptide is an ideal amphipathic peptide composed of 22 leucine and lysine in a ratio of 2:1. At a very low concentration, the peptide had a procoagulant effect shown by decreases in reaction time (R) and coagulation time (K) but was impaired by a decrease in maximum amplitude (MA). At higher concentrations, the peptide had an anticoagulant effect. The α angle was minimally affected by the peptide. The second peptide is melittin derived from bee venom. Melittin showed procoagulant effects reflected by a decrease in clotting time but led to lower MA. The third peptide derived from fibrinogen γ chain promoted hemostasis only at an optimal concentration and became anticoagulant at a higher concentration. The hemostatic mechanisms of each peptide were discussed. Our study would facilitate further development of peptides for either hemorrhage control or thrombosis treatment.

A model of low-level primary blast brain trauma results in cytoskeletal proteolysis and chronic functional impairment in the absence of lung barotrauma.

Shock-wave exposure from improvised explosive devices (IEDs) has been implicated as a possible contributing factor to neurological impairment reported in combat veterans. However, evidence-based substantiation of this implication, particularly for low-level exposure in the absence of external signs of trauma, remain elusive. Accordingly, we constructed an open-ended shock tube producing a short-duration, low-amplitude shockwave. Low-level (11.5 kPa static overpressure) complex shock-wave exposure in rats resulted in no histological evidence of lung injury. By contrast, delayed cytoskeletal proteolysis of αII-spectrin was detected in the cortex and hippocampus by 12 h post-injury. Cell death was minimal and localized predominantly in the corpus callosum and periventricular regions. These regions, with presumably different density interfaces, exhibit biological responses to shockwaves consistent with interface turbulence described by Richtmyer-Meshkov instability. Evoked compound action potential (CAP) recordings from the corpus callosum showed a significant increase in the duration of CAP responses at 14 and 30 days post-injury, and a gradual depression in the unmyelinated fiber amplitude. Shielding the head attenuated αII-spectrin cytoskeletal breakdown, thus directly implicating low-level shock-wave exposure as a cause of brain injury in the rat. Despite anatomical and scaling differences in rats compared to humans, the results suggest the potential for undiagnosed traumatic brain pathologies occurring in combat veterans following shock-wave exposure.

Novel wound sealants: biomaterials and applications.

Wound sealants provide an excellent alternative for closing surgical and non-surgical wounds, as well as stopping external bleeding for prehospital trauma injuries. Numerous biomaterials have been investigated to address specific requirements for their use as suitable wound sealants. This article focuses on the development of new wound sealant biomaterials and recent advances in the surgical applications of wound sealants. In the past 5 years, many new sealant materials had been reported, including keratin, mussel-adhesive proteins, dendrimers and in situ-forming hydrogels. Fibrin sealants remain the most clinically studied for a variety of surgical procedures, while clinical experience with wound sealants for orthopedic surgery is limited. Both liquid and solid wound sealants have been developed and found effective by possessing strong adhesive properties. Biocompatible and biodegradable wound sealants hold much promise in eventually replacing sutures in most surgical procedures.

Prehospital resuscitation with hypertonic saline-dextran modulates inflammatory, coagulation and endothelial activation marker profiles in severe traumatic brain injured patients.

BACKGROUND: Traumatic brain injury (TBI) initiates interrelated inflammatory and coagulation cascades characterized by wide-spread cellular activation, induction of leukocyte and endothelial cell adhesion molecules and release of soluble pro/antiinflammatory cytokines and thrombotic mediators. Resuscitative care is focused on optimizing cerebral perfusion and reducing secondary injury processes. Hypertonic saline is an effective osmotherapeutic agent for the treatment of intracranial hypertension and has immunomodulatory properties that may confer neuroprotection. This study examined the impact of hypertonic fluids on inflammatory/coagulation cascades in isolated head injury. METHODS: Using a prospective, randomized controlled trial we investigated the impact of prehospital resuscitation of severe TBI (GCS < 8) patients using 7.5% hypertonic saline in combination with 6% dextran-70 (HSD) vs 0.9% normal saline (NS), on selected cellular and soluble inflammatory/coagulation markers. Serial blood samples were drawn from 65 patients (30 HSD, 35 NS) at the time of hospital admission and at 12, 24, and 48-h post-resuscitation. Flow cytometry was used to analyze leukocyte cell-surface adhesion (CD62L, CD11b) and degranulation (CD63, CD66b) molecules. Circulating concentrations of soluble (s)L- and sE-selectins (sL-, sE-selectins), vascular and intercellular adhesion molecules (sVCAM-1, sICAM-1), pro/antiinflammatory cytokines [tumor necrosis factor (TNF)-alpha and interleukin (IL-10)], tissue factor (sTF), thrombomodulin (sTM) and D-dimers (D-D) were assessed by enzyme immunoassay. Twenty-five healthy subjects were studied as a control group. RESULTS: TBI provoked marked alterations in a majority of the inflammatory/coagulation markers assessed in all patients. Relative to control, NS patients showed up to a 2-fold higher surface expression of CD62L, CD11b and CD66b on polymorphonuclear neutrophils (PMNs) and monocytes that persisted for 48-h. HSD blunted the expression of these cell-surface activation/adhesion molecules at all time-points to levels approaching control values. Admission concentrations of endothelial-derived sVCAM-1 and sE-selectin were generally reduced in HSD patients. Circulating sL-selectin levels were significantly elevated at 12 and 48, but not 24 h post-resuscitation with HSD. TNF-alpha and IL-10 levels were elevated above control throughout the study period in all patients, but were reduced in HSD patients. Plasma sTF and D-D levels were also significantly lower in HSD patients, whereas sTM levels remained at control levels. CONCLUSIONS: These findings support an important modulatory role of HSD resuscitation in attenuating the upregulation of leukocyte/endothelial cell proinflammatory/prothrombotic mediators, which may help ameliorate secondary brain injury after TBI. TRIAL REGISTRATION: NCT00878631.

Abnormal coagulation tests are associated with progression of traumatic intracranial hemorrhage.

BACKGROUND: Intracranial hemorrhage (ICH) is common in traumatic brain injury (TBI) and a major determinant of death and disability. ICH commonly increases in size and coagulopathy has been implicated in such progression. We investigated the association between coagulopathy diagnosed by routine laboratory tests and ICH progression. METHODS: Subgroup post hoc analysis from a randomized controlled trial including adult patients with blunt severe TBI (Glasgow Coma Scale score or=1.3, activated partial thromboplastin time >or=35, or platelet count (PLT)

Resuscitation with hypertonic saline-dextran reduces serum biomarker levels and correlates with outcome in severe traumatic brain injury patients.

In the treatment of severe traumatic brain injury (TBI), the choice of fluid and osmotherapy is important. There are practical and theoretical advantages to the use of hypertonic saline. S100B, neuron-specific enolase (NSE), and myelin-basic protein (MBP) are commonly assessed biomarkers of brain injury with potential utility as diagnostic and prognostic indicators of outcome after TBI, but they have not previously been studied in the context of fluid resuscitation. This randomized controlled trial compared serum concentrations of S100B, NSE, and MBP in adult severe TBI patients resuscitated with 250 mL of 7.5% hypertonic saline plus 6% dextran70 (HSD; n = 31) versus 0.9% normal saline (NS; n = 33), and examined their relationship with neurological outcome at discharge. Blood samples drawn on admission (

Development of in situ-forming hydrogels for hemorrhage control.

We report the preparation of in situ-forming hydrogels, composed of oxidized dextran (Odex) and amine-containing polymers, for their potential use as a wound dressing to promote blood clotting. Dextran was oxidized by sodium periodate to introduce aldehyde groups to form hydrogels, upon mixing in solution with different polymers containing primary amine groups, including polyallylamine (PAA), oligochitosan and glycol chitosan. A series of experiments were conducted to identify the optimum gelation condition for the Odex-PAA system. The polymer concentration appeared to have a major effect on gelation time and the polymer weight ratio affected the resulting gel content and swelling. Other influencing factors included pH of the buffer used to dissolve each polymer, PAA molecular weight, and the type of individual material. The latter also contributed significantly to gel content and swelling. Thromboelastography was used to examine the effects of the in situ gelation on blood coagulation in vitro, where the Odex-PAA combination was found to be most pro-hemostatic, as indicated by a decrease in clotting time and an increase in clot strength. The results of this study demonstrated that in situ-forming hydrogels could promote clotting in vitro; however, further studies are required to determine if the same hydrogel formulations are effective in controlling hemorrhage in vivo.

Synthesis and characterization of a novel in situ forming gel based on hydrogel dispersions.

This report describes the synthesis and characterization of hydrogel dispersions for the potential use as an in situ gel-forming wound sealant. A series of polyacrylamide (PAAm) particles (solid content 5-10 wt %) were prepared by dispersion polymerization of acrylamide (AAm) in a solvent mixture of ethanol/water (90/10 w/w). These particles are characterized by the presence of a "core" [ethylene glycol dimethacrylate (EGDMA) crosslinked PAAm] surrounded by a "shell" [acetoacetoxyethyl methacrylate (AAEMA) or 2-aminoethylmethacrylate-containing PAAm, named as AAEMA-xPAAm and NH(2)-xPAAm, respectively; x represents "crosslinked"]. Two "2-in-1" working systems were prepared: (1) AAEMA-xPAAm mixed with NH(2)-xPAAm and (2) AAEMA-xPAAm mixed with 1,6-diaminohexane [AAEMA:NH(2) (1:1 mol/mol in (1) and (2)]. These systems appeared to possess essential characteristics for their potential use as wound sealants. For example, at 37 degrees C (and/or room temperature), both systems (1) and (2) formed transparent films, within 2 min upon applying them to a substrate; a rapid, concomitant crosslinking reaction occurred between AAEMA and -NH(2) on their outer "shells," knitting the EGDMA-crosslinked PAAm micro-"gel" together into a macro one. In contrast to other reported wound sealants, which are in either solution form or powder form, the advantages of hydrogel dispersion-based sealant may include ease of application (sprayable due to its low viscosity), species encapsulation and protection, and so forth. To our best knowledge, this is the first report on designing a wound sealant based on micro-particle dispersions.

Experimental optimization of an in situ forming hydrogel for hemorrhage control.

The fabrication of a novel in situ forming hydrogel composed of a multifunctional poly(ethylene glycol) (PEG) N-hydroxysuccinimide ester (NHS) and poly(allylamine hydrochloride) (PAA) was investigated. FTIR confirmed that PAA formed the hydrogel matrix (i.e., the formation of a PAA-like hydrogel). A factorial experiment was conducted to identify the key parameters that controlled gelation time, gel content, and swelling properties. The type of PEG (e.g., 4- and 6-arm) appeared to play a major role in determining all three performance parameters, with the greatest effect on gelation time. Other influencing factors include (a) the PEG concentration, which contributes to the gelation time and gel content; (b) pH of the buffer used for dissolving each polymer, which can affect the gelation time; and (c) PAA molecular weights, which contribute to the gel content and swelling. The concentration of PAA solution had no significant effects on hydrogel formation and properties within the investigated range, presumably due to negligible changes in the crosslinking density of the hydrogels. The PAA buffer pH influenced the gel content as well. Finally, thromboelastography was used to examine the effects of each polymer and their in situ gelation on blood coagulation in vitro. All individual polymers tested reduced clot strength, while the gelation of the polymers enhanced overall procoagulant effects. These results suggest that the biomaterial can be optimized to provide a combination of rapid gelation and swelling properties suitable for hemorrhage control and thus warrant further studies in animal bleeding models.

Characterization of an ideal amphipathic peptide as a procoagulant agent.

On the basis of previous evidence that amphipathic helical peptides accelerate Factor IXa activation of Factor X [Blostein, Rigby, Furie, Furie and Gilbert (2000) Biochemistry 39, 12000-12006], the present study was designed to assess the procoagulant activity of an IAP (ideal amphipathic peptide) of Lys(7)Leu(15) composition. The results show that IAP accelerates Factor X activation by Factor IXa in a concentration-dependent manner and accelerates thrombin generation by Factor Xa with a comparable peptide- and substrate-concentration-dependence. A scrambled helical peptide with the same amino acid composition as IAP, but with its amphipathicity abolished, eliminated most of the aforementioned effects. The Gla (gamma-carboxyglutamic acid)-rich domain of Factor X is required for IAP activity, suggesting that this peptide behaves as a phospholipid membrane. This hypothesis was confirmed, using fluorescence spectroscopy, by demonstrating direct binding between IAP and the Gla-rich domain of Factor X. In addition, the catalytic efficiencies of the tenase and prothrombinase enzymatic complexes, containing cofactors Factor VIIIa and Factor Va respectively, are enhanced by IAP. Finally, we show that IAP delays clot lysis in vitro. In summary, these observations demonstrate that IAP not only enhances essential procoagulant reactions required for fibrin generation, but also inhibits fibrinolysis, suggesting a potential role for IAP as a haemostatic agent.

Hydrogel-elastomer composite biomaterials: 3. Effects of gelatin molecular weight and type on the preparation and physical properties of interpenetrating polymer networks.

To optimize the preparation of a gelatin-HydroThane Interpenetrating Polymer Network (IPN) and obtain optimum physical properties for its use as a wound dressing, we studied IPN films prepared with two types of gelatin having different molecular weights. The effects of the gelatin molecular weight and type on the IPN film's structure, morphology, swelling and mechanical properties were determined. While FTIR did not reveal any noticeable differences between the IPNs prepared using different gelatin, light microscopy showed a lesser phase separation of the film prepared with a high-molecular-weight type A gelatin. Furthermore, these films displayed slightly less swelling, higher strength and lower strain, compared to the IPNs prepared with either low-molecular-weight type A or type B gelatin. The IPN prepared with type B gelatin showed higher swelling in serum-containing medium than those prepared with type A gelatin, because of its ionic charges under the condition. Increases in viscosity were observed with increasing molecular weight, type A being more viscous than type B gelatin despite having a lower bloom number. The viscosity of the high-molecular-weight gelatin was in the same magnitude as that of HydroThane, which might lead to less phase separation. A better understanding of the effects of alterations in the gelatin molecular weight and type on the formation and properties of the gelatin-HydroThane IPN should facilitate the development of promising composite biomaterials for wound dressing applications.

Hydrogel-elastomer composite biomaterials: 1. Preparation of interpenetrating polymer networks and in vitro characterization of swelling stability and mechanical properties.

We prepared interpenetrating polymer networks (IPNs) composed of a gelatin hydrogel and a HydroThane elastomer to combine the advantages of both polymers into one biomaterial. Fourier transform Infrared (FTIR) spectroscopy and Differential Scanning Calorimetry (DSC) confirmed the co-existence of the two polymers in the IPNs. Optical light microscopy confirmed hydrogel domains were interspaced into an elastomer network. Hydration and stability studies in aqueous solution showed that, although the IPN biomaterials exhibited stable swelling for more than 30 days, approximately 10% and 50% loss of the hydrogel component were confirmed at room temperature and 37 degrees C, respectively, using gel permeation chromatography (GPC). The swelling study in the serum-containing medium indicated the biomaterials maintained their swelling stability for different periods, depending on the extent of gelatin methacrylation, photoinitiator concentration and incubation temperature. Lastly, the biomaterials exhibited higher failure stress and lower failure strain in a dry state than in a swollen state, and showed limited changes in both stress and strain at room temperature and at 37 degrees C, in contrast with a decrease at 50 degrees C. No significant effects of gelatin methacrylation on mechanical properties were noticed. The preparation and characterization methods were well established and formed the basis of further developing the biomaterials.

Hydrogel-elastomer composite biomaterials: 2. Effects of aging methacrylated gelatin solutions on the preparation and physical properties of interpenetrating polymer networks.

This study was conducted to understand the effects of aging methacrylated gelatin solutions on the properties of gelatin-HydroThane Interpenetrating Polymer Network (IPN) films. The latter were prepared from methacrylated gelatin solutions that were either freshly made or stored at different concentrations and temperatures for various periods. The morphology, swelling stability and mechanical properties of the IPNs were then accordingly characterized. The IPNs prepared with aged solutions showed a reduced phase separation; changed from a network-like structure to a continuous phase structure; and demonstrated higher swelling stabilities and higher elasticity under optimal aging conditions, compared to the IPN prepared with a fresh methacrylated gelatin solution. An increase in viscosity and a change in phase transition of aged methacrylated gelatin solutions were also observed, presumably due to the physical structuring of methacrylated gelatin chains (e.g., by the formation of a helix structure), thus altering the resulting IPN characteristics. A better understanding of the effects of aging methacrylated gelatin solution on the formation and properties of gelatin-HydroThane IPNs should enable us to further develop our composite biomaterials for different dressing applications.