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After traumatic brain injury, the brain extracellular matrix undergoes structural rearrangement due to changes in matrix composition, activation of proteases, and deposition of chondroitin sulfate proteoglycans by reactive astrocytes to produce the glial scar. These changes lead to a softening of the tissue, where the stiffness of the contusion core and peripheral pericontusional regions becomes softer than that of healthy tissue. Pioneering mechanotransduction studies have shown that soft substrates upregulate intermediate filament proteins in reactive astrocytes; however, many other aspects of astrocyte biology remain unclear. Here, we developed a platform for the culture of cortical astrocytes using polyacrylamide (PA) gels of varying stiffness (measured in Pascal; Pa) to mimic injury-related regions in order to investigate the effects of tissue stiffness on astrocyte reactivity and morphology. Our results show that substrate stiffness influences astrocyte phenotype; soft 300 Pa substrates led to increased GFAP immunoreactivity, proliferation, and complexity of processes. Intermediate 800 Pa substrates increased Aggrecan+, Brevican+, and Neurocan+ astrocytes. The stiffest 1 kPa substrates led to astrocytes with basal morphologies, similar to a physiological state. These results advance our understanding of astrocyte mechanotransduction processes and provide evidence of how substrates with engineered stiffness can mimic the injury microenvironment.

Antioxidants help safeguard sperm cells from damage during the freeze–thaw process. Melatonin and its metabolites have an antioxidative effect. The current study aimed to evaluate the impact of melatonin supplementation in tris‐based extenders at various concentrations (0.5, 1.0 and 2 mM) on the freezability of Jamnapari goat spermatozoa. A total of 48 ejaculates were collected twice a week from four Jamnapari bucks (n = 12 × 4) using an artificial vagina during the period of October to November 2023. Selected ejaculates diluted with tris‐citric acid egg yolk extender were divided into four equal aliquots, and melatonin (dissolved in 0.1% dimethyl sulfoxide) was added later at 0.5, 1.0 and 2.0 mM to the control group (C) (extender and 0.1% DMSO) and treatment groups T1, T2 and T3, respectively. Various seminal attributes such as progressive motility, livability, acrosomal integrity, sperm abnormalities, sperm plasma membrane integrity, sperm penetration distance by vanguard spermatozoa in polyacrylamide gel and seminal plasma enzyme leakage (AST, ALT, ACP and AKP) were evaluated at post‐dilution and post‐thawed stages. Our findings revealed that all semen quality parameters were superior in melatonin‐treated groups than the C, and the differences were noticeably higher in the T2 group (1.0 mM) than the other groups. Adding 1.0 mM melatonin proved to be the most effective to safeguard sperm cells from cryopreservation induced cryodamage of Jamnapari buck. [ABSTRACT FROM AUTHOR]

Liesegang patterns that develop as a result of reaction‐diffusion can simultaneously form products with slightly different sizes spatially separated in a single medium. We show here a reaction‐diffusion method using a dormant reagent (citrate) for developing Liesegang patterns of cobalt hexacyanoferrate Prussian Blue analog (PBA) particle libraries. This method slows the precipitation reaction and produces different‐sized particles in a gel medium at different locations. The gel‐embedded particles are still catalytically active. Finally, the applicability of the new method to other PBAs and 2D systems is presented. The method proves promising for obtaining similar inorganic framework libraries with catalytic abilities. [ABSTRACT FROM AUTHOR]

• For this study data from a randomized trial performed in 28 patients with FD were used. • Friedewald, Martin-Hopkins, direct assay and gels to determine LDL-C were compared to UC. • All methods over- or underestimated LDL-C concentrations compared to UC. • UC probably overestimates LDL-C concentrations as well. • Non-HDL-C measured by standard assays performed well compared to non-HDL-C by UC. To compare LDL-C concentrations using the Friedewald formula, the Martin-Hopkins formula, a direct assay and polyacrylamide gradient gel electrophoresis (PGGE) to the reference standard density gradient ultracentrifugation in patients with Familial Dysbetalipoproteinemia (FD) patients. We also compared non-HDL-cholesterol concentrations by two methods. For this study data from 28 patients with genetically confirmed FD from the placebo arm of the EVOLVE-FD trial were used. Four different methods for determining LDL-C were compared with ultracentrifugation. Non-HDL-C was measured with standard assays and compared to ultracentrifugation. Correlation coefficients and Bland-Altman plots were used to compare the methods. Mean age of the 28 FD patients was 62 ± 9 years, 43 % were female and 93 % had an ɛ2ɛ2 genotype. LDL-C determined by Friedewald (R2 = 0.62, p <0.01), Martin-Hopkins (R2 = 0.50, p = 0.01) and the direct assay (R2 = 0.41, p = 0.03) correlated with density gradient ultracentrifugation. However, Bland-Altman plots showed considerable over- or underestimation by the four methods compared to ultracentrifugation. Non-HDL-C showed good correlation and agreement. In patients with FD, all four methods investigated over- or underestimated LDL-C concentrations compared with ultracentrifugation. In contrast, standard non-HDL-C assays performed well, emphasizing the use of non-HDL-C in patients with FD. [ABSTRACT FROM AUTHOR]

Polyacrylamide gel (PAAG) has been used for augmentation mammoplasty in certain countries, such as China or Eastern European countries. However, owing to various complications, its use is currently banned in most countries. Nevertheless, because of the migratory stream of female from these countries, we also encounter patients with PAAG mammoplasty in Korea. Owing to the various imaging features of PAAG mammoplasty, it may interfere with the identification of malignancy or other pathologic conditions. Therefore, it is important to identify the imaging findings related to PAAG mammoplasty. However, there is limited literature on the radiologic findings of complications related to PAAG mammoplasty in Korea. Herein we report four cases of PAAG mammoplasty, the complications faced, and depict various radiologic features through multimodality imaging.

Purpose: We sought to determine whether polyacrylamide hydrogel (PAHG) is noninferior to tension-free vaginal tape (TVT) in the treatment of women with primary stress urinary incontinence (SUI). Materials and Methods: In this noninferiority trial, 223 women eligible for operative SUI treatment were randomized for TVT (110) or PAHG (113). Primary outcome was patient satisfaction and the noninferiority margin for the difference was 20%. Secondary outcomes were effectiveness and complications. Results: At 3 years, 188 (84.3%) women attended the followup. The satisfaction score (visual analogue scale 0-100) median was 98.5 (IQR 90e100) in the TVT group and 90.0 (IQR 70e100) in the PAHG group, whereas a score ≥80 was reached in 87 (94.6%) and 65 (67.7%), respectively (difference 26.9%, 95% CI 16.7% to 36.8%). Thus, PAHG did not meet the noninferiority criteria set in our study. The cough stress test was negative in 88 (95.7%) of TVT patients vs 75 (78.1%) of PAHG patients (difference 17.5%, 95% CI 8.6% to 26.9%). Any peri- or postoperative complication before crossover between the groups was detected in 40 (43.5%) women in the TVT group and 23 (24.0%) women in the PAHG group (difference 19.5%, 95% CI 6.8% to 31.4%). Conclusions: In midterm followup, PAHG did not reach in patient satisfaction the noninferiority set in our study. Furthermore, mid urethral TVT slings show better subjective and objective cure rates than PAHG. However, complications were more often associated with TVT. Since the majority of PAHG treated women were also cured or improved, primary SUI women can be offered PAHG as a safe and durable alternative treatment. [ABSTRACT FROM AUTHOR]

Polyacrylamide hydrogel (PAAG) was developed in the 1980s as an injectable filler for breast augmentation and tissue contour improvement, but its potential risk for oncogenesis and the frequent occurrence of chronic complications after injections led to the prohibition of its further use as an injectable material. Although breast augmentation with PAAG injections was mostly performed in China and Eastern Europe, the migration of patients and long-term complications of the procedure made it a global concern. Herein, we describe the case of a 49-year-old woman who immigrated to Korea after undergoing breast augmentation via PAAG injection in China, and complained of persistent mastodynia and retraction of both breasts. Surgical treatment was undertaken, along with removal of the PAAG and total capsulectomy of the fibrous capsule containing the gel through an inframammary fold incision. We share our experience of diagnosing and treating this case, and present a literature review.

We have developed a simple and inexpensive method that improves sensitivity of protein and antigen detection in standard PAGE procedures. Our technique uses a sample microloader device with a funnel-like structure, filled with a 4% stacking gel. When attach to the top of a polyacrylamide slab gel, the proteins in a sample are concentrated by electrophoresis into a small volume as they emerge from the device's narrow outlet. Our microloader has several advantages over previous devices, including simple assembly, high versatility, and absence of cross-contamination between lanes. Addition of this device to a slab gel results in a fivefold increase in the sensitivity of antigen detection in a Western blot. As a result, less protein is required for loading and signal detection. Our protocol is a straightforward modification of a standard experimental technique, and is especially useful when only limited sample quantities are available.

A simple method for the identification of brush-border membrane α-glucosidases is described. The proteins were first solubilized and separated in a gel under native, non-denaturing, conditions. The gel was then incubated in substrate solutions (maltose or sucrose), and the product (glucose) exposed in situ by the oxidation of o-dianisidine, which yields a brown-orange color. Nano-liquid chromatography coupled to mass spectrometry analyses of proteins (nano LC-MS/MS) present in the colored bands excised from the gels, was used to confirm the presence of the enzymes. The stain is inexpensive and the procedure permits testing several substrates in the same gel. Once enzymes are identified, their abundance, relative to that of other proteins in the brush border, can be semi-quantified using nano LC-MS/MS.

Introduction: Traditionally thought to serve active vs. passive mechanical functions, respectively, a growing body of evidence suggests that actin microfilament and keratin intermediate filament (IF) networks, together with their associated cell-cell and cell-matrix anchoring junctions, may have a large degree of functional interdependence. Therefore, we hypothesized that the loss of keratin IFs in a knockout mouse keratinocyte model would affect the kinematics of colony formation, i.e., the spatiotemporal process by which individual cells join to form colonies and eventually a nascent epithelial sheet.Methods: Time-lapse imaging and deformation tracking microscopy was used to observe colony formation for both wild type (WT) and keratin-deficient knockout (KO) mouse keratinocytes over 24 h. Cells were cultured under high calcium conditions on collagen-coated substrates with nominal stiffnesses of ~ 1.2 kPa (soft) and 24 kPa (stiff). Immunofluorescent staining of actin and selected adhesion proteins was also performed.Results: The absence of keratin IFs markedly affected cell morphology, spread area, and cytoskeleton and adhesion protein organization on both soft and stiff substrates. Strikingly, an absence of keratin IFs also significantly reduced the ability of mouse keratinocytes to mechanically deform the soft substrate. Furthermore, KO cells formed colonies more efficiently on stiff vs. soft substrates, a behavior opposite to that observed for WT keratinocytes.Conclusions: Collectively, these data are strongly supportive of the idea that an interdependence between actin microfilaments and keratin IFs does exist, while further suggesting that keratin IFs may represent an important and under-recognized component of keratinocyte mechanosensation and the force generation apparatus. [ABSTRACT FROM AUTHOR]

Cover Feature: A Dormant Reagent Reaction-Diffusion Method for the Generation of Co-Fe Prussian Blue Analogue Periodic Precipitate Particle Libraries (Chem. Eur. J. 48/2023) Liesegang phenomenon, particle size library, periodic patterns, polyacrylamide gels, Prussian blue analogues Keywords: Liesegang phenomenon; particle size library; periodic patterns; polyacrylamide gels; Prussian blue analogues EN Liesegang phenomenon particle size library periodic patterns polyacrylamide gels Prussian blue analogues 1 1 1 08/29/23 20230825 NES 230825 B A reaction-diffusion system b forms a library of different-size catalytically active Prussian Blue analogue (PBA) particles at each generation of the precipitation pattern. [Extracted from the article]

Iron oxide γ-Fe2O3 magnetic nanoparticles (MNPs) were fabricated by laser target evaporation technique (LTE) and their structure and magnetic properties were studied. Polyacrylamide (PAAm) gels with different cross-linking density of the polymer network and polyacrylamide-based ferrogel with embedded LTE MNPs (0.34 wt.%) were synthesized. Their adhesive and proliferative potential with respect to human dermal fibroblasts were studied. At the same value of Young modulus, the adhesive and proliferative activities of the human dermal fibroblasts on the surface of ferrogel were unexpectedly much higher in comparison with the surface of PAAm gel. Properties of PAAm-100 + γ-Fe2O3 MNPs composites were discussed with focus on creation of a new generation of drug delivery systems combined in multifunctional devices, including magnetic field assisted delivery, positioning, and biosensing. Although exact applications are still under development, the obtained results show a high potential of LTE MNPs to be applied for cellular technologies and tissue engineering. PAAm-100 ferrogel with very low concentration of γ-Fe2O3 MNPs results in significant improvement of the cells’ compatibility to the gel-based scaffold.

Cellulose nanofibers (CNFs) have emerged as a promising nanofiller for effective reinforcement of nanocomposites due to their excellent mechanical properties. In this study, CNFs were fabricated by a simple grinding method and used to strengthen polyacrylamide (PAM) gels through in situ free radical polymerization. The morphology, compression properties, and chemical structure of the prepared gels were investigated. The results showed that large amounts of nanofibers embedded inside the PAM matrix and formed network structure by increasing the CNF content. Significantly, PAM/CNF gel with 5 wt% CNF exhibited highly improved compression strength by 6.8-fold as compared to that of pure PAM gel. The FTIR analysis indicated that hydrogen bondings between CNF and PAM chains mainly contributed to the superior mechanical properties of the hybrid gels. In summary, this study provides a novel alternative approach for preparing tough composite gels by combing rigid CNF and soft polymer and extending the application of biomedical load-bearing gel materials such as artificial cartilage and other soft tissues. [ABSTRACT FROM AUTHOR]

We used atomic force microscopy (AFM) technique to measure the viscoelastic response of cancer and normal thyroid cells on different stiffness polyacrylamide gels. After applying a step in contact we recorded the stress relaxation of cells in order to measure their viscous and elastic properties. With the help of an extended version of the Hertz model, we could quantify for the first time by AFM the elastic modulus and the dynamic viscosity of cells on substrates with different stiffnesses. We have cultured anaplastic carcinoma and normal thyroid cells on three different substrates: polyacrylamide gels with elastic modulus in a range of 3-5 and 30-40 kPa and 'infinitely' stiff Petri dishes. Whereas normal thyroid cells adapted their mechanical properties to different stiffness substrates, cancer cells were less affected by the surrounding stiffness. Normal cells changed the elastic modulus from 1.2 to 1.6 and to 2.6 kPa with increasing substrate stiffness; the dynamic viscosity values varied from 230 to 515 and to 470 Pa·s, accordingly. By contrast, the values for cancer cells were rather constant regardless of substrate stiffness (in average the elastic modulus was 1.3 kPa and the dynamic viscosity was 300 Pa·s). This difference in sensing and reacting to the mechanical properties of the substrate shows that normal and cancer cells interact differently with the neighboring tissue, which may be related to the ability of cancer cells to form metastases. [ABSTRACT FROM AUTHOR]

Gel based silver staining of proteins is thought to occur by selective reduction of silver ions to insoluble metallic silver at specific initiation sites in the vicinity of the protein molecules. Silver stained protein bands generally are dark brown or black with considerable variation in color intensity. The color variation has been attributed to diffractive scattering by silver grains of different sizes. Our experiments, however, demonstrate that color variation is due to the formation of silver chromate deposits that are incorporated into formalin fixed proteins. Understanding the mechanism of silver staining is essential for developing a method for protein quantification. [ABSTRACT FROM AUTHOR]

Excess phosphate in natural water can cause algae grow rapidly, to the extent causing many fish deaths that led to the extinction of certain species. Therefore, an analysis or periodic observations of phosphate levels in the water is needed. The commonly used method is diffusive gradient in thin films (DGT) technique. The DGT technique is based on the ability of analyte to diffuse through a gel, which have a value named diffusion coefficient. This research was conducted in order to study the effect of different storage solution to the phosphate diffusion coefficient through polyacrylamide and agarose gels. Initial research performed with making the polyacrylamide and agarose gels. To observe the effect of different storage solutions, the gels partly stored in distilled water gel while the others are stored in a NaCl solution of 0.01 M. Phosphate diffusion coefficient was determined using Fick's Law after analyze the phosphate concentration using UV-Visible spectrophotometer. The results showed that phosphate diffusion coefficient was highest when polyacrylamide and agarose gels stored in NaCl solution of 0.01 M.

Poroelastography is an elastographic technique used to image the temporal mechanical behavior of tissues. One of the major challenges in determining experimental potentials and limitations of this technique has been the lack of complex and realistic controlled phantoms that could be used to corroborate the limited number of theoretical and simulation studies available in the literature as well as to predict its performance in complex experimental situations and in a variety of conditions. In the study described here, we propose and analyze a new class of phantom materials for temporal elastography imaging. The results indicate that, by using polyacrylamide, we can generate inhomogeneous elastographic phantoms with controlled fluid content and fluid flow properties, while maintaining mechanical and ultrasonic properties similar to those of soft tissues. [ABSTRACT FROM AUTHOR]

A reliable, fast, cheap and sensitive silver staining method to detect nucleic acids in polyacrylamide gels was developed from two standard stain procedures. The main differences between the three methods concerned (i) the preexposure with formaldehyde during silver nitrate impregnation, (ii) the addition of sodium thiosulfate and sodium carbonate instead of sodium hydroxide during development; (iii) the removal of the stop reaction or the inclusion of absolute ethanol with acetic acid in the stop solution and (iv) the duration of the different reaction steps. All methods allowed the detection of similar polymorphisms for single sequence repeats with different cotton genotypes but important differences regarding the contrast, background and conservation duration of the gels were observed. Two methods gave superior sensitivity. The improved method was sensitive, fast (20 min), gave lower backgrounds, produced gels with long-term conservation ability, and allowed a reutilization of all the solutions used in the staining procedure from fi ve to seven times, making it quite cheap.

Cervical cancer microenvironment is involved in the regulation of the behavior, morphology, and mechanical properties of the cervical cancer cells. Integrins expressed on the cell membrane combine with the factors of the microenvironment to determine cervical cancer cells' properties. The mechanical properties of integrin-extracellular matrix (ECM) interactions are important for the mechanotransduction of cervical cancer cells. However, the quantified study on the adhesion force and binding probabilities between collagen and integrins on cervical cancer cells grown on different stiffness substrates have not been reported. Polyacrylamide (PA) gel was used as substrate to mimic the mechanical microenvironment of cancer cells. ImageJ software was used to measure the perimeter and area of the cells. SiHa cells were stained with FITC phalloidine to observe the cytoskeleton. Atomic force microscopy (AFM) was used to measure the cell mechanical properties. The perimeters of SiHa cells grown on different stiffness substrates were 63.4 ± 1.3, 102.8 ± 4.0, and 152.6 ± 4.1 μm, for soft, intermediate, and stiff substrates, respectively. These areas were 277.2 ± 13.3, 428.9 ± 26.0, and 1166.0 ± 63.2 μm2, for soft, intermediate, and stiff substrates, respectively. The Young's modulus of SiHa cells grown on stiff substrates (3.0 ± 0.02 kPa) was higher compared with those on soft substrates (0.6 ± 0.01 kPa) or intermediate substrates (bimodal distribution, 1.36 and 1.67 kPa). The adhesion force between the functionalized probe and SiHa cells grown on glass (55.65 ± 0.78 pN) was significantly greater than that on stiff (47.03 ± 0.85 pN), intermediate (34.07 ± 0.58 pN) and soft (27.94 ± 0.47 pN) substrates. The binding probabilities of the collagen-integrin of the four rigid substrates were significantly differed. The changes in substrate stiffness can obviously regulate SiHa cells' mechanical properties, such as the Young's modulus. The adhesion force and binding probabilities of SiHa cells both increased with increasing substrate strength. • Substrates stiffness affected cell spreading areas significantly. • Stiff substrate strongly increased the deformability of the cells. • Substrates stiffness can affect the cell's Young's modulus through its effect on cell cytoskeleton formation. • Adhesion force between integrins and collagen I was regulated by substrates stiffness. [ABSTRACT FROM AUTHOR]

Proteins can be separated according to their size by gel electrophoresis and further analyzed by Western blotting. The proteins can be transferred to a membrane made of nitrocellulose or polyvinylidene fluoride (PVDF), which results in a replica of the protein's separation patterns. The proteins on the membrane can be detected by specific antibodies followed by visualization either on the membrane itself, on film, or by CCD cameras. Western blotting is a sensitive technique to verify data obtained from fluorescence two-dimensional difference gel electrophoresis (2D-DIGE)-based proteomics., (© 2023. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Epithelia act as a barrier against environmental stress and abrasion and in vivo they are continuously exposed to environments of various mechanical properties. The impact of this environment on epithelial integrity remains elusive. By culturing epithelial cells on 2D hydrogels, we observe a loss of epithelial monolayer integrity through spontaneous hole formation when grown on soft substrates. Substrate stiffness triggers an unanticipated mechanical switch of epithelial monolayers from tensile on soft to compressive on stiff substrates. Through active nematic modelling, we find that spontaneous half-integer defect formation underpinning large isotropic stress fluctuations initiate hole opening events. Our data show that monolayer rupture due to high tensile stress is promoted by the weakening of cell-cell junctions that could be induced by cell division events or local cellular stretching. Our results show that substrate stiffness provides feedback on monolayer mechanical state and that topological defects can trigger stochastic mechanical failure, with potential application towards a mechanistic understanding of compromised epithelial integrity during immune response and morphogenesis.

The nucleus is mechanically coupled to the three cytoskeletal elements in the cell via linkages maintained by the LINC complex (for Linker of Nucleoskeleton to Cytoskeleton). It has been shown that mechanical forces from the extracellular matrix (ECM) can be transmitted through the cytoskeleton to the nuclear surface. Here we quantified nuclear shape in NIH 3T3 fibroblasts on polyacrylamide gels with a controlled degree of cross-linking. On soft substrates with a Young's modulus of 0.4 kPa, the nucleus appeared rounded in its vertical cross-section, while on stiff substrates (308 kPa), the nucleus appears more flattened. Over-expression of dominant negative Klarsicht ANC-1 Syne Homology (KASH) domains, which disrupts the LINC complex, eliminated the sensitivity of nuclear shape to substrate rigidity; myosin inhibition had similar effects. GFP-KASH4 over-expression altered the rigidity dependence of cell motility and cell spreading. Taken together, our results suggest that nuclear shape is modulated by substrate rigidity-induced changes in actomyosin tension, and that a mechanically integrated nucleus-cytoskeleton is required for rigidity sensing. These results are significant because they suggest that substrate rigidity can potentially control nuclear function and hence cell function. [ABSTRACT FROM AUTHOR]

Objective: Short insertion-deletion polymorphisms (indels) are the second most abundant form of genetic variations in humans after SNPs. Since indel alleles differ in size, they can be typed using the same methodological approaches and equipment currently utilized for microsatellite genotyping, which is already operational in forensic laboratories. We have previously shown that a panel of 40 carefully chosen indels has excellent potential for forensic identification, with combined probability of identity (match probability) of 7.09 × 10-17 for Europeans. Methods: We describe the successful development of a multiplex system for genotyping the 40-indel panel in long thin denaturing polyacrylamide gels with silver staining. We also demonstrate that the system can be easily fully automated with a simple large scanner and commercial software. Results and Conclusion: The great advantage of the new system of typing is its very low cost. The total price for laboratory equipment is less than EUR 10,000.-, and genotyping of an individual patient will cost less than EUR 10.- in supplies. Thus, the 40indel panel described here and the newly developed 'low-tech' analysis platform represent useful new tools for forensic identification and kinship analysis in laboratories with limited budgets, especially in developing countries. Copyright © 2012 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Abstract: This study investigates polyacrylamide (PA) gel as a calibration material to measure the nanomechanical compressive modulus of cartilage using nanoindentation. Both nanoindentation and unconfined compression testing were performed on PA gel and porcine rib cartilage. The equilibrium moduli measured by the two methods were discernable. Nanoindentation has the advantage of distinguishing between spatially dependent constituent properties that affect tissue mechanical function in heterogeneous and hierarchically structured tissues such as cartilage. Both sets of measurements exhibited similar positive correlation with increasing gel crosslinker concentration. The compressive modulus measurements from compression in the PA gels ranged from 300 kPa–1.4 MPa, whereas those from nanoindentation ranged from 100 kPa–1.1MPa. Using this data, a method for relating nanoindentation measurements to conventional mechanical property measurements is presented for porcine rib cartilage. It is shown that based on this relationship, the local tissue modulus as measured from nanoindentation (1.1–1.4 MPa) was able to predict the overall global modulus of the same sample of rib cartilage (2.2 MPa), as confirmed by experimental measurements from unconfined compression. This study supports the use of nanoindentation for the local characterization of cartilage tissues and may be applied to other soft tissues and constructs. [Copyright &y& Elsevier]

Abstract: Objective: Surgical repair of Achilles tendon (AT) rupture should immediately be followed by active tendon mobilization. The optimal time as to when the mobilization should begin is important yet controversial. Early kinesitherapy leads to reduced rehabilitation period. However, an insight into the detailed mechanism of this process has not been gained. Proteomic technique can be used to separate and purify the proteins by differential expression profile which is related to the function of different proteins, but research in the area of proteomic analysis of AT 3 days after repair has not been studied so far. Methods: Forty-seven New Zealand white rabbits were randomized into 3 groups. Group A (immobilization group, n=16) received postoperative cast immobilization; Group B (early motion group, n=16) received early active motion treatments immediately following the repair of AT rupture from tenotomy Another 15 rabbits served as control group (Group C). The AT samples were prepared 3 days following the microsurgery. The proteins were separated employing two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). PDQuest software version 8.0 was used to identify differentially expressed proteins, followed by peptide mass fingerprint (PMF) and tandem mass spectrum analysis, using the National Center for Biotechnology Information (NCBI) protein database retrieval and then for bioinformatics analysis. Results: A mean of 446.33, 436.33 and 462.67 protein spots on Achilles tendon samples of 13 rabbits in Group A, 14 rabbits in Group B and 13 rabbits in Group C were successfully detected in the 2D-PAGE. There were 40, 36 and 79 unique proteins in Groups A, B and C respectively. Some differentially expressed proteins were enzyme with the gel, matrix-assisted laser-desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). We successfully identified 9 and 11 different proteins in Groups A and B, such as GAPDH, phosphoglycerate kinase 1, pro-alpha-1 type 1 collagen, peroxiredoxin 1, alpha-1-antiproteinase E a-1 and MAD2L1 binding protein, etc. And some with the molecular chaperone, oxidative stress, energy metabolism, signal transduction, coupled with the tendon cell expression and protein synthesis, proliferate, differentiate and are closely related to the AT healing. The GAPDH protein was further validated through Western blotting. It was indicated that some differentially expressed proteins were involved in various metabolism pathways and may play an important role in initial healing of AT rupture. Conclusion: Differentially expressed proteins in rabbit healing AT model may contribute to 3 days healing of AT rupture through a new mechanobiological mechanism due to the application of postoperative early kinesitherapy. [Copyright &y& Elsevier]

Solutions formulated at 40°C with partly hydrolyzed polyacrylamide (HPAm) and Cr(III) acetate 50% active were monitored for 240 hr using 1H nuclear magnetic resonance (1H NMR). The HPAm concentration was kept constant at 2,500 mg/L (which is slightly below the critical polymer concentration) and the HPAm to Cr(III) acetate weight ratio ranged from 5:1 to 60:1. Changes in the 1H NMR transverse relaxation (T2) of the solutions were dominated by the chemistry of Cr(III) acetate. 1H NMR detected changes immediately after HPAm started reacting with Cr(III) acetate. These changes were undetectable by rheology or bottle testing of the studied solutions. [ABSTRACT FROM AUTHOR]

Abstract: DNA electrophoretic mobilities are highly dependent on the nature of the matrix in which the separation takes place. This review describes the effect of the matrix on DNA separations in agarose gels, polyacrylamide gels and solutions containing entangled linear polymers, correlating the electrophoretic mobilities with information obtained from other types of studies. DNA mobilities in various sieving media are determined by the interplay of three factors: the relative size of the DNA molecule with respect to the effective pore size of the matrix, the effect of the electric field on the matrix, and specific interactions of DNA with the matrix during electrophoresis. [Copyright &y& Elsevier]

Abstract: In vivo, cardiomyocytes interact with surrounding extracellular matrix while performing periodically a contractile behaviour, which is the main determinant of heart performance. As extracellular substrates with easily tunable stiffness properties, polyacrylamide gels (PAGs) provide valuable flexible media for studying in vitro the dynamical behaviour of cardiomyocytes responding to stiffness variations of their surrounding environment. We propose in this paper an original mechano-chemical model of the cardiac cell contraction that sheds light on the adaptive response of cardiomyocytes evidenced recently in the experiments of Qin et al. [2007. Dynamical stress characterization and energy evaluation of single cardiac myocyte actuating on flexible substrate. Biochem. Biophys. Res. Commun. 360, 352–356]. The model links the amplitude of the extracellular PAGs strain fields to the spatio-temporal variation of the intracellular stresses in every part of the cell during the sarcomeres contraction–relaxation. In a continuum mechanics framework, we derived a unified description of the sarcomere-length dependence of intracellular active stress and of its control by anisotropic calcium diffusion and autocatalytic calcium release from the sarcoplasmic reticulum. Taking benefit of our previous work on the characterization of mechanical properties of PAGs with varying stiffness, we were thus able to evaluate the active intracellular stress exerted by the cardiomyocyte on flexible PAGs with different and known Young''s moduli. Interestingly, we were able to explain the intriguing increase of maximal cellular stress observed experimentally when substrate stiffness is increased. By providing an evaluation of the whole-field cell stresses and strains, this integrative approach of cardiomyocyte contraction provides a reliable basis for further analysis of additional cooperativity and mechanotransduction mechanisms involved in cell contractility regulation, notably in physiological and pathological situations where modifications of cardiac performance are linked to varied stiffness of the cardiomyocytes environment. [Copyright &y& Elsevier]

Abstract: Electroosmotic pumping through uncharged hydrogels can be achieved by embedding the polymer network with charged colloidal inclusions. Matos et al. [M.A. Matos, L.R. White, R.D. Tilton, J. Colloid Interface Sci. 300 (2006) 429–436], recently used the concept to enhance the diffusion-limited flux of uncharged molecules across polyacrylamide hydrogel membranes for the purpose of improving the performance of biosensors. This paper seeks to link their reported macroscale diagnostics to physicochemical characteristics of the composite microstructure. The experiments are characterized by a Debye screening length that is much larger than the radius of the silica nanoinclusions and the Brinkman screening length of the polymer skeleton. Accordingly, closed-form expressions for the incremental pore mobility are derived, and these are evaluated by comparison with numerically exact solutions of the full electrokinetic model. A mathematical model for the bulk electroosmotically enhanced tracer flux is proposed, which is combined with the electrokinetic model to ascertain the electroosmotic pumping velocity from measured flux enhancements. Because the experiments are performed with a known current density, but unknown bulk conductivity and electric field strength, theoretical estimates of the bulk electrical conductivity are adopted. These account for nanoparticle polarization, added counterions, and non-specific adsorption. Theoretical predictions of the flux enhancement, achieved without any fitting parameters, are within a factor of two of the experiments. Alternatively, if the Brinkman screening length of the polymer skeleton is treated as a fitting parameter, then the best-fit values are bounded by the range 0.9–1.6 nm, depending on the inclusion size and volume fraction. Independent pressure-driven flow experiments reported in the literature for polyacrylamide gels without inclusions suggest 0.4 or 0.8 nm. The comparison can be improved by allowing for hindered ion migration, while uncertainties regarding the inclusion surface charge are demonstrated to have a negligible influence on the electroosmotic flow. Finally, and perhaps most importantly, anomalous variations in the flux enhancement with particle size and volume fraction can be rationalized at present only by acknowledging that particle–particle and particle–polymer interactions increase the effective permeability of the hydrogel skeleton. This bears similarities to the increase in polymer free volume that accompanies the addition of silica nanoparticles to certain polymeric membranes. [Copyright &y& Elsevier]

Abstract: This is the first published study that investigates the viscoelastic properties of an organically cross-linked polymeric gel used in water shut-off treatments. A copolymer of acrylamide and t-butyl acrylate was cross-linked with polyethylene imine. The effects of various parameters on the rheological properties of the gel were addressed. Experimental results indicated that the storage modulus of the gel decreases with the increase in the salinity of mixing water. Also, higher gel elastic modulus was obtained at higher cross-linker concentrations. A highest elastic modulus of 3.4 kPa was obtained for a gel with a composition of 7 wt.% polymer and 1.2 wt.% cross-linker. However, syneresis was observed in gel samples with 1.2 wt.% cross-linker concentration. The gel lost 53% of its elastic modulus after 1 month of ageing at 150 °C. Based on the trends noted with the elastic modulus, two different mechanisms for gel formation were identified below and above 100 °C. [Copyright &y& Elsevier]

Abstract: Needle-free jet injections constitute an important method of drug delivery, especially for insulin and vaccines. This report addresses the mechanisms of interactions of liquid jets with skin. Liquid jets first puncture the skin to form a hole through which the fluid is deposited into skin. Experimental studies showed that the depth of the hole significantly affects drug delivery by jet injections. At a constant jet exit velocity and nozzle diameter, the hole depth increased with increasing jet volume up to an asymptotic value and decreased with increasing values of skin''s uniaxial Young''s modulus. A theoretical model was developed to predict the hole depth as a function of jet and skin properties. A simplified model was first verified with polyacrylamide gels, a soft material in which the fluid mechanics during hole formation is well understood. Prediction of the hole depth in the skin is a first step in quantitatively predicting drug delivery by jet injection. [Copyright &y& Elsevier]

Serving as an elastic model system for food gels, characteristics of polyacrylamide (PAAm) gels were investigated using small amplitude and large deformation rheological tests. The PAAm gels displayed elastic or viscoelastic behavior depending on network crosslink density. For elastic PAAm gels, the rheological properties obeyed the theory of rubber elasticity; whereas for viscoelastic PAAm gels, shear modulus depended on temperature. The elastic PAAm gel fracture parameters did not change with deformation rate (0.2–5.5 s−1), indicating insignificant viscous flow during deformation. Fracture stress was correlated with gel monomer concentration, whereas the fracture strain remained constant regardless of the monomer concentration. In addition, the stress was linearly proportioned with strain up to fracture, indicating that PAAm gels did not experience finite network chain extensibility during large deformation. Consequently, the fracture of PAAm gels did not result from the extensional limitation of network chains, nor did gel fracture result from the nonlinear force–distance relationship between polymer connections. Purportedly, the fracture of PAAm gels was caused by external force overcoming the gel cohesive forces, and low strength of PAAm gels compared to rubbers caused fracture prior to experiencing nonlinear stress-strain deformation. [ABSTRACT FROM AUTHOR]

Abstract: We have found that polyacrylamide gels cross-linked with bisacrylamide induce a larger macromolecular osmotic pressure than the non cross-linked gels. This means also that in the cross-linked gels hydration water is held more tightly to the polymer, i.e., more work is needed to remove water, than in the non cross-linked gel. Since the chemical nature of the two gels is extremely similar, we propose that the formation of the network alters per se the water activity. [Copyright &y& Elsevier]

Jet injectors employ high-velocity liquid jets that penetrate into human skin and deposit drugs in the dermal or subdermal region. Although jet injectors have been marketed for a number of years, relatively little is known about the interactions of high-speed jets with soft materials such as skin. Using polyacrylamide gels as a model system, the mechanics of jet penetration, including the dependence of jet penetration on mechanical properties, was studied. Jets employed in a typical commercial injector, (orifice diameter: 152 μm, velocity: 170–180 m/s) were used to inject fluid into polyacrylamide gels possessing Young''s moduli in the range of 0.06–0.77 MPa and hardness values in the range of 4–70 HOO. Motion analysis of jet entry into polyacrylamide gels revealed that jet penetration can be divided into three distinct events: erosion, stagnation, and dispersion. During the erosion phase, the jet removed the gel at the impact site and led to the formation of a distinct cylindrical hole. Cessation of erosion induced a period of jet stagnation (∼600 μs) characterized by constant penetration depth. This stage was followed by dispersion of the liquid into the gel. The dispersion took place by crack propagation and was nearly symmetrical with the exception of injections into 10% acrylamide (Young''s modulus of 0.06 MPa). The penetration depth of the jets as well as the rate of erosion decreased with increasing Young''s modulus. The mechanics of jet penetration into polyacrylamide gels provides an important tool for understanding jet injection into skin. [Copyright &y& Elsevier]

Surfaces of polyacrylamide hydrogels synthesized in the presence of surfactants were imaged by atomic force microscopy (AFM), and the surface morphology was studied by numerical scaling analysis. The gels were formed by polymerizing acrylamide plus a cross-linker in the presence of surfactants, which were then removed by soaking in distilled water. Gels formed in the presence of over 20% surfactant (by weight) formed clear, but became opaque upon removal of the surfactants. Other gels formed and remained clear. The surface morphology of the gels was studied by several one- and two-dimensional numerical scaling methods. The surfaces were found to be self-affine on short length scales, with a roughness (Hurst) exponent in the range from 0.85 to 1, crossing over to a constant root-mean-square surface width at long scales. Both the crossover length between these two regimes and the saturation value of the surface width increased significantly with increasing surfactant concentration, coincident with the increase in opacity. We propose that the changes in the surface morphology are due to a percolation transition in the system of voids formed upon removal of the surfactants from the bulk. [Copyright &y& Elsevier]

Compressed and stretched polyacrylamide hydrogels previously have been shown to offer a robust method for aligning proteins. A simple, funnel-like apparatus is described for generating uniformly stretched hydrogels. For prolate-shaped proteins, gels stretched in the direction of the magnetic field yield two-fold larger alignment than gels compressed to the same aspect ratio in this direction. Empirically, protein alignment is found to be proportional to (c-2.3)2 [(do/dN)3-1], where do and dN are the diameters of the cylindrical gels before and after stretching, respectively, and c is the polyacrylamide weight fraction in percent. Low gel densities, in the 4–7% range, are found to have minimal effects on macromolecular rotational correlation times, τc, and no effect of the compression ratio on τc could be discerned over the range studied (do/dNle1.4). Application is demonstrated for a sample containing the first Ig-binding domain of protein G, and for a detergent-solubilized peptide. [ABSTRACT FROM AUTHOR]

Although conventional imprinting involving the use of charged functional monomers has been used by many authors for selective adsorption of small molecules, it has not been very successful with high-molecular-weight substances, for example proteins (“...macromolecules, such as proteins are difficult to apply as templates...”; H. S. Andersson, Doctoral Thesis, Trycki Högskolan Kalmar, 1999, p. 8.). Four years ago we therefore introduced an alternative method based on the polymerization of non-charged monomers (acrylamide and N,N′-methylenebisacrylamide) in the presence of the protein of interest. The selectivity of the gels for proteins was high (for instance, myoglobin from horse was adsorbed by a column designed to be selective for this protein, whereas, myoglobin from whale was not adsorbed) and they can therefore be regarded as ‘artificial antibodies’ (or ‘artificial receptors’). This paper deals with improvements of the chromatographic properties of these gels. For example, by modifying the polymerization conditions the protein (hemoglobin) capacity, as well as the flow rate were increased fouifold. This was achieved by entrapment of the selective soft polyacrylamide gel in the pores of a rigid inert gel by letting the monomers and the protein diffuse into the pores of agarose beads (SepharoseTM) before starting the polymerization. The gel formed was cut into pieces. The agarose beads were freed from the surrounding polyacrylamide gel by stirring. This technique is universal and is recommended also for molecular imprinting studies of small molecules. Another universal method has been introduced for rapid screening of potential monomers and gels for the preparation of selective adsorbents. This very simple method is based on the assumption that the absorption maximum of a protein changes when the protein interacts with the free monomers or the adsorbent synthesized from the monomers (and does not change when the protein does not interact). Preliminary docking experiments indicate that selective adsorption of the protein by the polyacrylamide matrix is based primarily on hydrogen-bonding and dipole-dipole interactions. The strengths of these interactions can be varied by choosing different gel matrices (for removal of a given protein the interactions should be very strong, whereas they should be weaker for chromatographic analysis). [ABSTRACT FROM AUTHOR]