PubMed Health⌕ Search

Biomedical subjects

Dennis P Orgill

Publications and source records attributed to Dennis P Orgill.

At least 19 recordsLinked to original sources
PubMed2007

Optimization of UV cross-linking density for durable and nontoxic collagen GAG dermal substitute.

Artificial dermal constructs, based upon collagen-glycosaminoglycan matrices (CGMs), provide new options in treating skin defects. However, their clinical effectiveness may be limited by cytotoxicity related to residual aldehydes left over from the manufacturing process. Although both chemical and dehydrothermal (DHT) cross-linking are used to produce CGMs, we hypothesize that optimized nonchemical cross-linking, using ultra-violet (UV) and DHT treatment combinations, may limit cytotoxicity without sacrificing mechanical strength. Porous CGMs were physically cross-linked using a combination of DHT and varying intensities of UV light. These were compared to glutaraldehyde cross-linked controls. Human keratinocytes were seeded in each matrix, and cellular proliferation measured using a microculture tetrazolium dye assay. A scoring system (based on the in vitro contraction rate, stiffness, and cellular growth of a small cylindrical specimen) was developed to assess the best overall physical cross-linking method. More cellular growth was observed in the 90-120 min UV cross-linked group than in the glutaraldehyde-treated group (p < 0.05). Stiffness was maximized after 0-30 min of UV cross-linking. On the basis of our scoring system, DHT combined with 45 min of UV cross-linking produced the best overall matrix in terms of cellular growth and physical durability. UV cross-linked collagen-based biomaterials could be a viable alternative for use in biological applications to eliminate glutaraldehyde-associated cytotoxicity.

Cell Proliferation↗
PubMed2006

Lower extremity trauma: trends in the management of soft-tissue reconstruction of open tibia-fibula fractures.

BACKGROUND: Open lower leg fractures with exposed bone or tendon continue to be challenging for plastic surgeons. Microvascular free-tissue transfer increases the ability to close wounds, transfer vascularized bone, and prevent amputation, yet remains a complex, invasive procedure with significant complication rates, donor-site morbidity, and failure rates. This review documents the changing treatment protocol in the authors' institution for these injuries. METHODS: Two hundred ninety consecutive open tibia-fibula fractures over a 12-year period (1992 to 2003) were retrospectively reviewed and methods and outcomes were compared by grouping the fractures into 4-year intervals. RESULTS: The number of open lower extremity fractures increased, whereas the distribution of Gustilo grade I to III fractures remained unchanged. Overall, free-tissue transfer was performed less frequently and constituted 20 percent of reconstructions in period 1 (1992 to 1995), 11 percent in period 2 (1996 to 1999), and 5 percent in period 3 (2000 to 2003). For the most severe fractures, Gustilo grade III, free-flap reconstruction has decreased significantly, constituting 42 percent, 26 percent, and 11 percent of procedures in periods 1, 2, and 3, respectively. Local flaps for grade III fractures have remained relatively constant throughout the study. In contrast, local wound care for grade III fractures, including skin grafts, delayed primary closures, and secondary intention closures has significantly increased from 22 percent to 49 percent of reconstructions from periods 1 through 3. In 1997, the authors began to use the vacuum-assisted closure device and now use it in nearly half of all open fractures. Despite this trend, there has been no change in infection, amputation, or malunion/nonunion rates and a decrease in reoperation rate with at least 1-year follow-up. CONCLUSIONS: These results demonstrate a change in practice, with a trend down the reconstructive ladder, currently using fewer free flaps and more delayed closures and skin grafts with frequent use of the vacuum-assisted closure sponge. Possible reasons for this change are a better understanding of lower leg vascular anatomy and better use of improved wound care technology.

Adult↗
PubMed2006

Microdeformational wound therapy: effects on angiogenesis and matrix metalloproteinases in chronic wounds of 3 debilitated patients.

The vacuum-assisted closure (VAC) device causes microdeformations of the wound surface in contact with the foam. Because angiogenesis and matrix metalloproteinase (MMP) activity are altered in chronic wounds, we hypothesized that microdeformations stimulate capillary formation and affect MMP activity. A VAC device was used to deliver microdeformational wound therapy (MDWT) to the chronic wounds of 3 debilitated patients. Debrided tissue was obtained from wound areas with and without foam contact. Microvessel density and MMP activity were determined by immunohistochemistry and zymography, respectively. Microvessel density of MDWT-treated wounds was 4.5% (+/-0.8) compared with areas not covered by foam [1.6% (+/-0.1)] (P = 0.05) during the first week of treatment and 2.7% (+/-0.3) compared with untreated tissue [1.3% (+/-0.1)] (P = 0.03) during the second treatment week. Wounds subjected to MDWT had greater microvessel density compared with the same wound prior to treatment [1.5% (+/-0.3)] (P = 0.02). MMP-9/NGAL (neutrophil gelatinase-associated lipocalin), MMP-9, latent MMP-2, and active MMP-2 were reduced by 15%-76% in MDWT-treated wounds. MDWT provides a favorable wound-healing environment by increasing angiogenesis and decreasing MMP activity in chronic wounds.

Aged↗
PubMed2005

Expired liquid preserved platelet releasates retain proliferative activity.

BACKGROUND: Donated platelets for clinical use currently have a shelf life of 5 days as the result of possible bacterial contamination and loss of hemostatic function. Platelet releasates contain multiple growth factors that have been shown to accelerate wound healing. We sought to demonstrate that although expired platelets can no longer sustain hemostasis, they serve a longer term role as a reservoir of growth factors that could be harnessed in wound healing applications. MATERIALS AND METHODS: Liquid preserved human platelets were activated from 1 to 21 days after collection using zeolite and were then analyzed for their ability to stimulate human fibroblast proliferation, which is an in vitro serogate of growth factor activity and wound healing potential. Total protein content, the concentration of platelet-derived growth factor (PDGF) and transforming growth factor-beta were also measured. RESULTS: Activated liquid preserved platelet releasates significantly stimulated fibroblast proliferation. Twenty-one-day-old platelets were as stimulatory as 2-day-old platelets. Total protein concentration, PDGF, and transforming growth factor-beta concentrations remained constant throughout the 21-day course. Western blot analysis using an antibody against human PDGF revealed minimal protein degradation over time. CONCLUSIONS: These data demonstrate that although the role of platelets as hemostatic agents degrades rapidly with time, platelets' ability to serve as a reservoir for growth factors remains intact for at least 3 weeks. These growth factors could be collected, stored, and used as a topical agent to promote healing of chronic and recalcitrant wounds.

Blood Platelets↗
PubMed2005

Island grafts: a model for studying skin regeneration in isolation from other processes.

This chapter introduces the concept of an island graft, in which large full-thickness skin wounds are created with a small treatment area in the center. The island graft is a simple method for demonstrating the effect of epithelial derivatives on wound regeneration without using sophisticated biologic or genetic markers. In the absence of disease, mammalian wounds of the dermis close by scarring and contraction. The island graft permits observation of the test material within the wound without interference from the periphery for several days until wound contraction and epithelialization of the surrounding skin encroach upon the study area.

Animals↗
PubMed2005

Simultaneous in vivo regeneration of neodermis, epidermis, and basement membrane.

Full-thickness skin loss does not undergo complete spontaneous regeneration in mammals. To restore the normal function of skin, dermal and epidermal components can be supplied by grafting various substrates, concurrently or in stages. A tissue-engineering technique that combines disaggregated autologous keratinocytes and a highly porous, acellular collagen-glycosaminoglycan matrix has been shown in a porcine model to regenerate a dermis and epidermis in vivo. During regeneration, a basement membrane of normal appearance forms at the dermoepidermal junction, and vascularization of the construct occurs. Cell-seeded grafts can be produced with either uncultured or cultured keratinocytes and can be immediately applied in a single grafting procedure. The seeding process itself and the cell culture, when used, markedly expand the donor epithelial surface area, allowing large skin defects to be repaired using grafts created from very little donor tissue. This skin-substitute technology may have useful clinical applications.

Animals↗
PubMed2005

Effects of crowding on the thermal stability of heterogeneous protein solutions.

Crowding can substantially affect the transition of a protein between its native (N) and unfolded (U) states via volume exclusion effects. Also, it influences considerably the aggregation (A) of unfolded proteins. To examine the details, we developed an approach for computing the kinetic rates of the process N <--> U --> A in which the concentration of the protein is explicitly taken into account. We then compute the relative change with temperature of the protein denaturation for various fractional volume occupancies and partition of proteins in solution. The analysis indicates that, in protein solutions in which the average distance between proteins is comparable with the radius of gyration of an unfolded protein, steric effects increase the stability of the proteins which are in compact, native states. In heterogeneous protein solutions containing various types of proteins with different thermal stabilities, the unfolding of the most thermolabile proteins will increase the stability of the other proteins. The results shed light on the way proteins change the thermal stability of a cell as they unfold and aggregate. This study may be valuable in questions related to the dynamics of thermal injuries.

Animals↗
PubMed2005

Thermal diffusion probe analysis of perfusion changes in vascular occlusions of rabbit pedicle flaps.

BACKGROUND: The purpose of this study was to show the efficacy of a novel tissue blood flow measuring device in an animal model. Thermal diffusion technology evaluates changes in perfusion in small volumes of tissue. METHODS: The thermal diffusion probe device is a long, 0.9-mm-diameter flexible catheter with two thermistors, which are placed directly into the tissue; it excites an active thermistor to a constant temperature slightly above the tissue baseline and collects data on the power dissipated in the active thermistor. It also continuously monitors the baseline tissue temperature using an additional passive thermistor placed outside the heated field. In this study, rabbit epigastric pedicle flaps were instrumented with two thermal diffusion probes (peripheral and deep) to continuously monitor flap perfusion. RESULTS: Twenty-five vascular occlusion studies were performed in 16 flaps. Blood vessel occlusions (arterial, venous, and arteriovenous) were easily detectable with this system. Waveforms for arterial and arteriovenous occlusions differed from those for venous occlusions. Probes in both peripheral and deep tissue locations were sensitive to changes in tissue perfusion. CONCLUSION: Thermal diffusion probes may provide a useful clinical method for monitoring flap perfusion.

Animals↗
PubMed2005

Early experience using low-frequency ultrasound in chronic wounds.

Periodic wound debridement promotes healing in chronic wounds. Low-frequency ultrasonic debridement (LFUD) is a promising adjunct to wound care, which offers relatively painless debridement and bacterial biofilm destruction. We performed LFUD on 17 patients over 8 months, with a minimum follow-up of 3 months. Nine of the wounds (53%) healed primarily or with the aid of a skin graft. Six additional patients (35%) experienced a wound-size reduction of at least 50%. The remaining 2 patients (12%), one with sickle cell anemia and one with a venous stasis ulcer, had reductions in wound area of 20%-30%. None of the patients required initiation of antibiotic treatment after starting LFUD. LFUD has had an early favorable experience in our institution. Further randomized clinical studies are required to better define the mechanism of action and the patient populations most appropriate for this modality.

Acute Disease↗
PubMed2005

Molecular crowding effects on protein stability.

The volume fraction occupied by the dry matter of the cell can be as large as 40%, of which more than half (approximately 60%) are proteins. Thus, cellular proteins and protein assemblies occupy a large volume that can have a profound effect on their own native-state stabilities and on their unfolding/refolding rates. In addition, macromolecular crowding can change the properties of a significant fraction of the water in the cell. We review features of the molecular crowding effect which are relevant for describing the microscopic mechanism of thermal injuries.

Mathematics↗
PubMed2005

Heat injury to cells in perfused systems.

Tissue injury in response to excessive heat results in a clinical burn. Burns cause a range of physiologic derangements, including denaturation of macromolecular structures, leakage of cell membranes, activation of cytokines, and cessation of blood flow, all leading to tissue death. The purpose of this paper is to examine the mechanisms and consequences of burn injury and to discuss potential therapies based on these mechanisms. Knowledge of the thermal properties of tissues can predict the time-temperature relationship necessary to cause a specified thermal insult. Changes in cell membrane biochemistry and the stabilization of proteins through the heat-shock response can enable biomacromolecules to withstand supraphysiological temperatures. Mechanisms of cellular repair allow recovery of cellular function after thermal insult. An understanding of the response of proteins, cellular organelles, and cells to heat provides the foundation for understanding the pathophysiology and treatment of burn injury. The physics, biochemistry, and cellular biology behind the host response to thermal injury in perfused systems are reviewed.

Burns↗
PubMed2004

Continuous and real-time blood perfusion monitoring in prefabricated flaps.

The Thermal Diffusion Probe (TDP) System allows continuous real-time measurement of tissue perfusion in flaps. The authors used a TDP with two thermistors, one active, the other passive, embedded in a 0.9-mm diameter catheter to measure continuous tissue perfusion in rabbit epigastric flaps. The distal thermistor is heated to 2 degrees C above the tissue baseline temperature. The power required to maintain this temperature difference is mathematically related to the tissue perfusion in the volume surrounding the probe tip. Central and peripheral TDPs were placed. The TDP effectiveness in detecting and measuring daily tissue perfusion in buried epigastric flaps was tested. Contralateral epigastric pedicles were transposed into the flaps prior to ligation of the original pedicle. Flaps with transposed pedicles showed a progressive and significant increase in tissue perfusion during the initial 3 weeks of the experiment, compared to flaps without the pedicle transfer. The TDP System is a useful experimental method for the continuous and real-time quantification of flap perfusion and may be helpful in making clinical decisions about prefabricated flap transfer.

Animals↗
PubMed2004

Occult breast carcinoma in reduction mammaplasty specimens: 14-year experience.

Reduction mammaplasty is commonly performed for bilateral macromastia, congenital asymmetry, or as a contralateral symmetry procedure in breast reconstruction following mastectomy for cancer. Occult carcinoma has been detected in 0.06 percent to 0.4 percent of breast reduction specimens. The purpose of this study was to examine the incidence of breast cancer in breast reductions performed in one institution over a 14-year period. The authors reviewed their experience with 800 reduction mammaplasties performed between 1988 and 2001. Six cancers were detected (0.8 percent). Of these cancers, three were invasive (0.4 percent) and three were ductal carcinoma in situ (0.4 percent). Stratified by indication for surgery, there was a trend toward higher detection rates in the reconstruction group (1.2 percent) compared with the macromastia (0.7 percent) or congenital asymmetry (0 percent) groups. Mammography was performed preoperatively in these patients and all results were negative for masses or suspicious microcalcification. Pathological diagnosis was guided by gross specimen evaluation in two patients and specimen radiography in one patient. Reduction mammaplasty has a small but definite risk of finding cancer in the resection specimen.

Adult↗
PubMed2004

Two-photon confocal microscopy: a nondestructive method for studying wound healing.

Two-photon confocal microscopy is a new technology useful in nondestructive analysis of tissue. The pattern generated from laser-excited autofluorescence and second harmonic signals can be analyzed to construct a three-dimensional, microanatomical, structural image. The healing of full-thickness guinea pig skin wounds was studied over a period of 28 days using two-photon confocal microscopy. Three-dimensional data were rendered from two-dimensional images and compared with conventional, en face, histologic sections. Two-photon confocal microscopy images show resolution of muscle, fascia fibers, collagen fibers, inflammatory cells, blood vessels, and hair. Although these images do not currently have the resolution of standard histology, the ability to noninvasively acquire three-dimensional images of skin promises to be an important tool in wound-healing studies.

Animals↗
PubMed2004

Vacuum-assisted closure: microdeformations of wounds and cell proliferation.

The mechanism of action of the Vacuum Assisted Closure Therapy (VAC; KCI, San Antonio, Texas), a recent novel innovation in the care of wounds, remains unknown. In vitro studies have revealed that cells allowed to stretch tend to divide and proliferate in the presence of soluble mitogens, whereas retracted cells remain quiescent. The authors hypothesize that application of micromechanical forces to wounds in vivo can promote wound healing through this cell shape-dependent, mechanical control mechanism. The authors created a computer model (finite element) of a wound and simulated VAC application. Finite element modeling is commonly used to engineer complex systems by breaking them down into simple discrete elements. In this model, the authors altered the pressure, pore diameter, and pore volume fraction to study the effects of vacuum-induced material deformations. The authors compared the morphology of deformation of this wound model with histologic sections of wounds treated with the VAC. The finite element model showed that most elements stretched by VAC application experienced deformations of 5 to 20 percent strain, which are similar to in vitro strain levels shown to promote cellular proliferation. Importantly, the deformation predicted by the model also was similar in morphology to the surface undulations observed in histologic cross-sections of the wounds. The authors hypothesize that this tissue deformation stretches individual cells, thereby promoting proliferation in the wound microenvironment. The application of micromechanical forces may be a useful method with which to stimulate wound healing through promotion of cell division, angiogenesis, and local elaboration of growth factors. Finite element modeling of the VAC device is consistent with this mechanism of action.

Cell Proliferation↗
PubMed2004

Management of early groin vascular bypass graft infections with sartorius and rectus femoris flaps.

Groin infections adjacent to vascular bypass grafts continue to be a source of morbidity. The authors reviewed retrospectively 9 consecutive patients with early localized groin infections treated at their institution with sartorius or rectus femoris muscle flaps between 1998 and 2002. All wounds were initially opened and drained. Wounds with necrotic tissue were treated with serial surgical debridements, with a vacuum-assisted closure device, or with wet-to-dry dressing changes. Two bypass grafts were excised and replaced in the presence of marked exposure or pseudoaneurysm. Small wounds were closed with a turnover sartorius flap and larger wounds were closed with either a muscle or musculocutaneous rectus femoris flap. Groin wounds healed in all patients without subsequent graft exposure, rupture, or pseudoaneurysm. Local wound therapy with staged debridement and muscle flaps is effective for most early localized graft infections.

Aged↗