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Response of primary fibroblasts and osteoblasts to plasma treated polyetheretherketone (PEEK) surfaces
Briem, D., S. Strametz, et al. (2005), J Mater Sci Mater Med 16(7): 671-7.
Abstract: Polyetheretherketone (PEEK) is a synthetic polymer with suitable biomechanical and stable chemical properties, which make it attractive for use as an endoprothetic material and for ligamentous replacement. However, chemical surface inertness does not account for a good interfacial biocompatibility, and PEEK requires a surface modification prior to its application in vivo.In the course of this experimental study we analyzed the influence of plasma treatment of PEEK surfaces on the cell proliferation and differentiation of primary fibroblasts and osteoblasts. Further we examined the possibility of inducing microstructured cell growth on a surface with plasma-induced chemical micropatterning.We were able to demonstrate that the surface treatment of PEEK with a low-temperature plasma has significant effects on the proliferation of fibroblasts. Depending on the surface treatment, the proliferation rate can either be stimulated or suppressed. The behavior of the osteoblasts was examined by evaluating differentiation parameters.By detection of alkaline phosphatase, collagen I, and mineralized extracellular matrix as parameters for osteoblastic differentiation, the examined materials showed results comparable to commercially available polymer cell culture materials such as tissue culture polystyrene (TCPS). Further microstructured cell growth was produced successfully on micropatterned PEEK foils, which could be a future tool for bioartificial systems applying the methods of tissue engineering.These results show that chemically inert materials such as PEEK may be modified specifically through the methods of plasma technology in order to improve biocompatibility.

Responses of cultured macrophages to microspheres
Luzardo-Alvarez, A., H. P. Merkle, et al. (2005), J Control Release 101(1-3): 347-9.

Restenosis after carotid endarterectomy in patients with paired vein and Dacron patch reconstruction
Archie, J. P., Jr. (2001), Vasc Surg 35(6): 419-27.
Abstract: This is an analysis of restenosis after bilateral carotid endarterectomy (CEA) with saphenous vein patch reconstruction on one side and Dacron patch reconstruction on the other. The possibility that differences in reconstruction geometry between vein and Dacron patched sides effected restenosis outcomes was evaluated as was the value of serial common carotid wall thickness measurements in predicting restenosis. Between 1990 and 1997, 33 bilateral CEA were performed within one year on 22 men and 11 women using a greater saphenous vein patch on one side and a knitted Dacron patch on the other. Interoperative post-CEA geometry was measured. Follow-up was by duplex scans that included wall thickness measurements in the endarterectomized common carotid bulb. Over a mean follow-up of 43 months 10 (30%) Dacron patched and one (3%) vein patched CEA developed > or = 25% restenosis (p = 0.001), seven (21%) Dacron patched and no vein patched CEA developed > or = 50% restenosis (p = 0.01) and four (12%) Dacron patched and no vein patched CEA developed > or = 70% restenosis (p = 0.11). The Kaplan-Meier cumulative > or = 25% restenosis rates for Dacron and vein patched CEA were 22% and 0% at 2 years and 41% and 5% at 5 years respectively (p = 0.002). The cumulative > or = 50% restenosis rates for Dacron and vein patched CEA were 16% and 0% at 2 years and 34% and 0% at 5 years respectively (p = 0.003). The cumulative > or = 70% restenosis rates for Dacron and vein patched CEA were 8% and 0% at 2 years and 20% and 0% at 5 years respectively (p = 0.02). For both patients with and without recurrent stenosis the mean within patient between sides differences of the diameters of the internal carotid, internal carotid bulb, common carotid bulb, and common carotid arteries and the lengths of the internal carotid and total patch segments were not significantly different and all were less than 5%. Common carotid bulb wall thickness measured at the time of identification of the nine unilateral Dacron patched CEA restenosis was 1.5 +/-0.5 mm compared to 1.4 +/-0.4 mm (m +/-1 SD) for the contralateral vein patched CEA (p = 0.45 by paired t test). Dacron patched CEA have a significantly higher incidence of mild, moderate and severe restenosis than do saphenous vein patched CEA independent of systemic risk factors. The within patient equality of Dacron and vein patched carotid reconstruction geometry in patients with unilateral restenosis indicates that patch material is the major local risk factor, not adverse hemodynamics produced by variance in geometry. Common carotid bulb wall thickness measurements after CEA are not predictors or indicators of recurrent stenosis.

Restenosis and drug-eluting stents
Winslow, R. D., S. K. Sharma, et al. (2005), Mt Sinai J Med 72(2): 81-9.
Abstract: The implantation of intracoronary stents for the treatment of coronary atherosclerotic disease is one of the most common percutaneous procedures. While the procedure brings long-term benefit for a large percentage of patients, a significant number of patients experience in-stent restenosis (ISR). ISR may be caused by a number of biological and procedural factors, including lesion characteristics as well as co-existing disease states like diabetes. Many strategies have been developed to try to reduce the incidence of ISR. The primary methods include systemic pharmacologic treatments, as well as attempts at modifying stents to reduce their role in the development of ISR. Drug-eluting stents are one such modality, and are expected to become a widely used tool in the field of interventional cardiology. This review will focus on the pathophysiology of ISR and possible ways to prevent it, including drug-eluting stents.

Restenosis in gold-coated renal artery stents
Nolan, B. W., M. L. Schermerhorn, et al. (2005), J Vasc Surg 42(1): 40-6.
Abstract: BACKGROUND: Gold coating improves stent visibility under fluoroscopy. This is particularly valuable for precise stent placement during renal artery stenting (RAS). There is conflicting evidence regarding restenosis with gold-coated stents. To evaluate the effect of gold coating on restenosis after renal stenting, we reviewed the results of all patients undergoing RAS in our practice. METHODS: A retrospective cohort study of all patients undergoing RAS between June 2000 and September 2003 was performed. During this time, both gold-coated and stainless steel stents were used. Restenosis (>60% diameter) was determined by serial follow-up duplex exams (peak systolic velocity >180 cm/s and renal-aortic ratio >3.5). Restenosis rates were determined by using the Kaplan-Meier life-table method. Variables potentially affecting restenosis were evaluated with the log-rank test and Cox proportional hazards modeling. RESULTS: RAS was performed in 97 arteries (78 patients). Gold-coated (NIRoyal) stents were placed in 59 arteries (48 patients). Stainless steel stents (Corinthian, Genesis, and Herculink) were placed in 38 arteries (34 patients). Patient demographics, indication for treatment, technical success, and complications did not differ between gold and stainless steel stent groups. Mean follow-up was 15 months for gold-coated stents and 18 months for stainless steel stents (NS). By life-table method, 1-year and 2-year freedom from restenosis rates were 84% and 78% in arteries treated with stainless steel stents versus 69% and 39% in those treated with gold-coated stents (P =.012, log-rank test). By multivariate analysis, only the use of gold-coated stents (P =.018; hazard ratio [HR], 3.3; 95% confidence interval [CI], 1.2 to 8.7) and bilateral disease (P =.046; HR, 2.3; 95% CI, 1.02 to 5.2) predicted restenosis. Stent diameter, patient demographics, and indication for RAS had no effect on restenosis by univariate analysis. According to American Heart Association criteria, 87% of patients in the stainless steel group had improved blood pressure at 1 year, compared with 77% in the gold-coated stent group (Kaplan-Meier; P =.042, log-rank test). There were no significant differences in the effect of RAS on serum creatinine levels between the two groups. CONCLUSION: Gold-coated renal stents had a substantially higher rate of restenosis than stainless steel stents in our series. These findings have led us to abandon the use of gold-coated stents for RAS. Patients who have received gold-coated stents for the treatment of atherosclerotic renal artery stenosis should be followed closely for evidence of restenosis.

Restenosis treatment in the drug-eluting stent era
Presbitero, P. and G. Boccuzzi (2005), Ital Heart J 6(6): 514-21.
Abstract: Despite recent advances, the in-stent restenosis (ISR) remains a challenging problem in interventional cardiology with an estimated overall restenosis rate of 20%, 25-30% in bare metal stents and 12% in drug-eluting stents (DES). In this review, we provide an overview of therapeutic options which include balloon angioplasty, cutting balloon, debulking techniques, brachytherapy and DES. Intracoronary brachytherapy using beta or gamma radiation had been considered the standard of care for some years. However, the use of DES to treat ISR has been shown to be safe, effective and ease-of-use for the prevention of recurrent restenosis. ISR after DES when focal angiographic pattern is present can be often treated with balloon angioplasty whereas if a non-focal pattern is recognized a new DES implantation is indicated. Waiting for a definitive answer regarding the optimal treatment of ISR from ongoing trials, we present our current approach to ISR.

Restoration of enophthalmos in anophthalmic socket by HTR polymer
Huang, Z. L. and L. Ma (2005), Ophthal Plast Reconstr Surg 21(4): 318-21.
Abstract: A 2-year-old girl had undergone preoperative radiotherapy and enucleation without implantation for retinoblastoma in her right eye. She presented with supratarsal depression after secondary hydroxyapatite implantation. Computed tomography revealed insufficient right orbital volume, relative to left orbital volume. Injections of Bioplant hard tissue replacement synthetic bone filled the subperiosteal space of the orbital floor and lateral and medial wall for supratarsal augmentation. This had the desired effect: The filler lasted without sequela at least through 1.5 years of follow-up. Hard tissue replacement was also used to fill the remaining socket void and enhance the facial ridge width.

Restoring the interproximal zone using the proximal adaptation technique--Part 2
Terry, D. A. (2005), Compend Contin Educ Dent 26(1): 11-2, 15-6, 18 passim; quiz 30, 53.
Abstract: In this era of modern adhesive dentistry, clinicians are still faced with challenges from microleakage, recurrent decay, and sensitivity. Many of the challenges are a result of using yesterday's restorative techniques and principles with the new formulations of biomaterials. Procedures such as the proximal adaptation and the oblique layering techniques offer modifications to the nonadhesive principles discussed in Part I (The Compendium, December 2004), while providing the patient and clinician with the 3 primary objectives of restorative dentistry: prevention, preservation, and conservation. Using stratification techniques and thorough adhesive protocol as illustrated in this article allows clinicians to provide restorations that have improved physical characteristics while reducing the effects of polymerization shrinkage. Other benefits of these adhesive procedures include enhanced chromatic integration, ideal anatomical form and function, optimal proximal contact, improved marginal integrity, and longer lasting directly placed composite restorations.

Results from a degradable TMC joint Spacer (Artelon) compared with tendon arthroplasty
Nilsson, A., E. Liljensten, et al. (2005), J Hand Surg [Am] 30(2): 380-9.
Abstract: PURPOSE: A new spacer for the trapeziometacarpal joint (TMC) based on a biological and tissue-preserving concept for the treatment of TMC osteoarthritis (OA) has been evaluated. The purpose was to combine a spacing effect with stabilization of the TMC joint. METHODS: Artelon (Artimplant AB, Sweden) TMC Spacer is synthesized of a degradable polyurethaneurea (Artelon), which has been shown to be biocompatible over time and currently is used in ligament augmentation procedures. Fibers of the polymer were woven into a T-shaped device in which the vertical portion separates the bone edges of the TMC joint and the horizontal portion stabilizes the joint. Fifteen patients with disabling pain and isolated TMC OA were included in the study. Ten patients received the spacer device and the remaining 5 (control group) were treated with a trapezium resection arthroplasty with abductor pollicis longus (APL) stabilization. The median ages of the 2 groups were 60 and 59 years, respectively. Pain, strength, stability, and range of motion were measured before and after surgery. Radiographic examination was performed in all patients before and after surgery. At follow-up evaluation 3 years after surgery an unbiased observer evaluated all patients. Biopsy specimens were obtained from 1 patient 6 months after surgery. RESULTS: All patients were stable clinically without signs of synovitis. In both groups all patients were pain free. The median values for both key pinch and tripod pinch increased compared with before surgery in the spacer group but not in the APL group. The biopsy examinations showed incorporation of the device in the surface of the adjacent bone and the surrounding connective tissue. No signs of foreign-body reaction were seen. CONCLUSIONS: This study showed significantly better pinch strength after Artelon TMC Spacer implantation into the TMC joint compared with APL arthroplasty.

Results of a hydroxyapatite-coated (Furlong) total hip replacement: a 13- to 15-year follow-up
Shetty, A. A., R. Slack, et al. (2005), J Bone Joint Surg Br 87(8): 1050-4.
Abstract: We describe the survival of 134 consecutive JRI Furlong hydroxyapatite-coated uncemented total hip replacements. The mean follow-up was for 14.2 years (13 to 15).Patients were assessed clinically, using the Merle d'Aubigne and Postel score. Radiographs were evaluated using Gruen zones for the stem and DeLee and Charnley zones for the cup. Signs of subsidence, radiolucent lines, endosteal bone formation (spot welds) and pedestal formation were used to assess fixation and stability of the stem according to Engh's criteria. Cup angle, migration and radiolucency were used to assess loosening of the cup. The criteria for failure were revision, or impending revision because of pain or loosening. Survival analysis was performed using a life table and the Kaplan-Meier curve.The mean total Merle d'Aubigne and Postel score was 7.4 pre-operatively and 15.9 at follow-up. During the study period 22 patients died and six were lost to follow-up. None of the cups was revised. One stem was revised for a periprosthetic fracture following a fall but none was revised for loosening, giving a 99% survival at 13 years. Our findings suggest that the long-term results of these hydroxyapatite-coated prostheses are more than satisfactory.

Retaining zonal chondrocyte phenotype by means of novel growth environments
Darling, E. M. and K. A. Athanasiou (2005), Tissue Eng 11(3-4): 395-403.
Abstract: The loss of phenotype in articular chondrocytes expanded in monolayer has been established as a possible contributor to the deficiencies associated with in vitro cartilage engineering and autologous cell transplantation procedures. We cultured zonal articular chondrocytes on tissue culture plastic, collagen II-coated polystyrene, and aggrecan-coated polystyrene in an effort to find a surface that can either prevent or slow the loss of phenotype. In addition, we encapsulated passaged cells in agarose to examine the effect of three-dimensional culture on redifferentiating zonal chondrocytes. We used real-time polymerase chain reaction to measure the relative gene expression levels of collagen I and II, aggrecan, and superficial zone protein over relevant passages (P0-P4). Results showed that tissue culture plastic and the collagen II-coated surface induced rapid loss of phenotype in zonal articular chondrocytes. The aggrecan-coated surface had a less detrimental effect on the chondrocytic phenotype of seeded cells, inducing gene expression characteristics comparable to those of agarose-encapsulated cells. Furthermore, when chondrocytes that had been previously passaged on a collagen II surface were placed on an aggrecan surface, the zonal cells showed a dramatic change in gene expression from fibroblastic to chondrocytic. These results indicate that a culture environment using aggrecan as a substratum or agarose as a scaffold is crucial to the development of phenotypically correct articular cartilage.

Retrieval analyses of implanted biomaterials: light microscopic and scanning electron microscopic analyses of implants retrieved from humans
Corpe, R. S., D. E. Steflik, et al. (1999), J Oral Implantol 25(3): 162-78; discussion 161.
Abstract: We report analyses obtained from 135 implant cases retrieved from humans and submitted to the American Academy of Implant Dentistry Research Foundation--Medical College of Georgia Implant Retrieval Center. The undecalcified samples were embedded in polymethyl-methacrylate and examined with scanning electron microscopy and with routine light via polarized or Nomarski microscopy. Cases included both orthopedic and dental implants as well as entire mandibles obtained at autopsy. Significant numbers of submitted implants had substantial amounts of adhered bone, which permitted evaluation of human bone remodeling to osseointegrated implants. These implants failed because of implant fracture. As has been observed in animal studies, an interdigitating canaliculi network provided communication between interfacial osteocytes and osteocytes deeper within the remodeled osteonal and trabecular bone. Significant numbers of osseointegrated fractured hydroxyapatite-coated dental implants demonstrated the adequate serviceability of these implants prior to biomaterial fracture. In contrast, the hydroxyapatite coating was dissociated from retrieved orthopedic implants, leading to extensive cup loosening and case failure. Caution is advised for the use of hydroxyapatite-coated acetabular implants. This study therefore underscores the need for evaluation of failed human dental and orthopedic implants. Correlations can be drawn between human retrieval and experimental animal studies.

Revascularization of diabetic patients: are drug-eluting stents the solution?
Guagliumi, G. and G. Musumeci (2005), Ital Heart J 6(6): 507-13.
Abstract: Restenosis and need of repeat revascularization as well as major adverse cardiac events (MACE) are all significantly increased after coronary stenting in patients with diabetes compared to non-diabetic patients. The potential clinical benefit of drug-eluting stents (DES) in this cohort is currently under definition. Both Cypher and Taxus stents in randomized clinical trials and real world post-approval registries appear to be effective with a substantial reduction in MACE and target lesion revascularization compared to control patients. However, despite stability of target lesion revascularization obtained with DES, diabetes continues to be associated with a significant increase in MACE at mid- and long-term follow-up. These data emphasize the role of a fully integrated medical, glycemic and device treatment for optimal outcome in diabetes. In order to develop new guidelines for diabetic treatment, prospective and randomized studies comparing DES with surgical revascularization in three-vessel and/or left main disease are ongoing. Despite significant amelioration obtained with DES the diabetic population remains an unmet need, requiring further basic and clinical research.

Reversible colorimetric probes for mercury sensing
Coronado, E., J. R. Galan-Mascaros, et al. (2005), J Am Chem Soc 127(35): 12351-6.
Abstract: The selectivity and sensitivity of two colorimetric sensors based on the ruthenium complexes N719 [bis(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II) bis(tetrabutylammonium) bis(thiocyanate)] and N749 [(2,2':6',2' '-terpyridine-4,4',4' '-tricarboxylate)ruthenium(II) tris(tetrabutylammonium) tris(isothiocyanate)] are described. It was found that mercury ions coordinate reversibly to the sulfur atom of the dyes' NCS groups. This interaction induces a color change in the dyes at submicromolar concentrations of mercury. Furthermore, the color change of these dyes is selective for mercury(II) when compared with other ions such as lead(II), cadmium(II), zinc(II), or iron(II). The detection limit for mercury(II) ions--using UV-vis spectroscopy--in homogeneous aqueous solutions is estimated to be approximately 20 ppb for N719 and approximately 150 ppb for N749. Moreover, the sensor molecules can be adsorbed onto high-surface-area mesoporous metal oxide films, allowing reversible heterogeneous sensing of mercury ions in aqueous solution. The results shown herein have important implications in the development of new reversible colorimetric sensors for the fast, easy, and selective detection and monitoring of mercuric ions in aqueous solutions.

Review paper: surface modification for bioimplants: the role of laser surface engineering
Kurella, A. and N. B. Dahotre (2005), J Biomater Appl 20(1): 5-50.
Abstract: Often hard implants undergo detachment from the host tissue due to inadequate biocompatibility and poor osteointegration. Changing surface chemistry and physical topography of the surface influences biocompatibility. At present, the understanding of biocompatibility of both virgin and modified surfaces of bioimplant materials is limited and a great deal of research is being dedicated to this aspect. In view of this, the current review casts new light on research related to the surface modification of biomaterials, especially materials for prosthetic applications. A brief overview of the major surface modification techniques has been presented, followed by an in-depth discussion on laser surface modifications that have been explored so far along with those that hold tremendous potential for bioimplant applications.

Review: peripheral nerve regeneration using non-tubular alginate gel crosslinked with covalent bonds
Hashimoto, T., Y. Suzuki, et al. (2005), J Mater Sci Mater Med 16(6): 503-9.
Abstract: We have developed a nerve regeneration material consisting of alginate gel crosslinked with covalent bonds. in the first part of this study, we attempted to analyze nerve regeneration through alginate gel in the early stages within 2 weeks. in the second part, we tried to regenerate cat peripheral nerve by using alginate tubular or non-tubular nerve regeneration devices, and compared their efficacies. Four days after surgery, regenerating axons grew without Schwann cell investment through the partially degraded alginate gel, being in direct contact with the alginate without a basal lamina covering. One to 2 weeks after surgery, regenerating axons were surrounded by common Schwann cells, forming small bundles, with some axons at the periphery being partly in direct contact with alginate. At the distal stump, numerous Schwann cells had migrated into the alginate 8-14 days after surgery. Remarkable restorations of the 50-mm gap in cat sciatic nerve were obtained after a long term by using tubular or non-tubular nerve regeneration material consisting mainly of alginate gel. However, there was no significant difference between both groups at electrophysiological and morphological evaluation. Although, nowadays, nerve regeneration materials being marketed mostly have a tubular structure, our results suggest that the tubular structure is not indispensable for peripheral nerve regeneration.

Revision of cemented hip arthroplasty using a hydroxyapatite-ceramic-coated femoral component
Raman, R., R. P. Kamath, et al. (2005), J Bone Joint Surg Br 87(8): 1061-7.
Abstract: We report the clinical and radiological outcome of 86 revisions of cemented hip arthroplasties using JRI-Furlong hydroxyapatite-ceramic-coated acetabular and femoral components. The acetabular component was revised in 62 hips and the femoral component in all hips. The mean follow-up was 12.6 years and no patient was lost to follow-up.The mean age of the patients was 71.2 years. The mean Harris hip and Oxford scores were 82 (59 to 96) and 23.4 (14 to 40), respectively. The mean Charnley modification of the Merle d'Aubigne and Postel score was 5 (3 to 6) for pain, 4.9 (3 to 6) for movement and 4.4 (3 to 6) for mobility. Migration of the acetabular component was seen in two hips and the mean acetabular inclination was 42.6 degrees. The mean linear polyethylene wear was 0.05 mm/year. The mean subsidence of the femoral component was 1.9 mm and stress shielding was seen in 23 (28%) with bony ingrowth in 76 (94%). Heterotopic ossification was seen in 12 hips (15%). There were three re-revisions, two for deep sepsis and one for recurrent dislocation and there were no re-revisions for aseptic loosening. The mean EuroQol EQ-5D description scores and health thermometer scores were 0.69 (0.51 to 0.89) and 79 (54 to 95), respectively. With an end-point of definite or probable loosening, the probability of survival at 12 years was 93.9% and 95.6% for the acetabular and femoral components, respectively. Overall survival at 12 years, with removal or further revision of either component for any reason as the end-point, was 92.3%.Our study supports the continued use of this arthroplasty and documents the durability of hydroxyapatite-ceramic-coated components.

RGD modified polymers: biomaterials for stimulated cell adhesion and beyond
Hersel, U., C. Dahmen, et al. (2003), Biomaterials 24(24): 4385-415.
Abstract: Since RGD peptides (R: arginine; G: glycine; D: aspartic acid) have been found to promote cell adhesion in 1984 (Cell attachment activity of fibronectin can be duplicated by small synthetic fragments of the molecule, Nature 309 (1984) 30), numerous materials have been RGD functionalized for academic studies or medical applications. This review gives an overview of RGD modified polymers, that have been used for cell adhesion, and provides information about technical aspects of RGD immobilization on polymers. The impacts of RGD peptide surface density, spatial arrangement as well as integrin affinity and selectivity on cell responses like adhesion and migration are discussed.

RGD-grafted thermoreversible polymers to facilitate attachment of BMP-2 responsive C2C12 cells
Smith, E., J. Yang, et al. (2005), Biomaterials 26(35): 7329-38.
Abstract: The purpose of this study was to design thermoreversible biomaterials for enhanced adhesion of bone morphogenetic protein-2 (BMP-2)-responsive cells. Peptides containing the arginine-glycine-aspartic acid (RGD) sequence were conjugated to N-isopropylacrylamide (NiPAM) polymers via amine-reactive N-acryloxysuccinimide (NASI) groups. In monolayer cultures, the adhesion of BMP-2-responsive C2C12 cells to RGD-grafted NiPAM/NASI surfaces was significantly higher than adhesion on ungrafted NiPAM/NASI surfaces. Although the morphology of cells adhered to RGD-grafted NiPAM/NASI surfaces was comparable to cells adhered on tissue culture polystyrene (TCPS), long-term cell growth was limited on the NiPAM/NASI surfaces, even for RGD-grafted surfaces. Treatment of C2C12 cells with recombinant BMP-2 induced dose-dependent osteoblastic differentiation as assessed by alkaline phosphatase (ALP) activity. In the absence of BMP-2, cells cultured on NiPAM/NASI polymers (either grafted with RGD peptide or not) expressed significantly higher levels of ALP activity than the cells cultured on TCPS, indicating that the polymer surfaces induced some osteoblastic activity in C2C12 cells without the need for BMP-2. We conclude that NiPAM-based thermoreversible biomaterials, despite their limited ability to support cell growth, allowed an enhanced expression of the chosen osteogenic marker (ALP) by C2C12 cells in vitro.

Rheological and recovery properties of poly(ethylene glycol) diacrylate hydrogels and human adipose tissue
Patel, P. N., C. K. Smith, et al. (2005), J Biomed Mater Res A 73(3): 313-9.
Abstract: The viscosity and elastic and viscous moduli of poly(ethylene glycol) diacrylate (PEGDA) hydrogels and human abdominal adipose tissue are measured as a function of shear rate and frequency. Results indicate that both materials exhibit shear thinning and are viscoelastic in nature. Rheological tests suggest that the hydrogels become firmer as strain and frequency increase. Adipose tissue, however, begins to fail at higher strains and frequencies. This behavior is confirmed by measuring the complex modulus of both materials as a function of strain. Recovery properties are also measured for each material as a function of deformation. Although PEGDA hydrogels are able to recover up to 78% of their original height after 15% deformation, adipose tissue is not able to recover over the range of deformations tested. The frequencies and strains over which the tests are conducted are those physiologically experienced by the human body. The hydrogels are able to withstand this range of forces and, hence, are appropriate for use as a soft tissue filler material. In addition, the hydrogels swell 38.1% +/- 0.9% independent of surface area. The complex modulus of hydrogels of varying polymer concentrations is also measured as a function of strain to determine the effects of changing polymer content. These results indicate that as polymer content increases, the hydrogels become firmer due to the higher number of polymer chains and behave more elastically.

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