Fibrin glue for wound repair: facts and fancy

Preparation of Chitosan/Clay Composites for Safe and Effective Hemorrhage Control

Uncontrolled hemorrhage from trauma or surgery can lead to death. In this study, chitosan/kaolin (CSK) and chitosan/montmorillonite (CSMMT) composites were prepared from chitosan (CS), kaolin (K), and montmorillonite (MMT) as raw materials to control bleeding. The physiochemical properties and surface morphology of CSK and CSMMT composites were analyzed by Fourier transform infrared spectrometry (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), zeta potentials, and X-ray fluorescence (XRF). The hemostatic mechanism was measured in vitro by activated partial thromboplastin time (APTT), prothrombin time (PT), in vitro clotting time, erythrocyte aggregation, and thromboelastogram (TEG). The hemostasis ability was further verified by using tail amputation and arteriovenous injury models in rats. The biocompatibility of CSK and CSMMT was evaluated by in vitro hemolysis, cytotoxicity assays, as well as acute toxicity test and skin irritation tests. The results show that CSK and CSMMT are promising composite materials with excellent biocompatibility and hemostatic properties that can effectively control bleeding.

The effect of mesenchymal stem cells combined with platelet-rich plasma on skin wound healing

INTRODUCTION

Mesenchymal stem cells (MSCs) are multipotent stem cells that have the potential of proliferation, high self-renewal, and the potential of multilineage differentiation. The differentiation potential of the MSCs in vivo and in vitro has caused these cells to be regarded as potentially appropriate tools for wound healing. After the burn, trauma or removal of the tumor of wide wounds is developed. Although standard treatment for skin wounds is primary healing or skin grafting, they are not always practical mainly because of limited autologous skin grafting.

EVIDENCE ACQUISITIONS

Directory of Open Access Journals (DOAJ), Google Scholar, PubMed (NLM), LISTA (EBSCO), and Web of Science have been searched.

EVIDENCE SYNTHESIS

For clinical use of the MSCs in wound healing, two key issues should be taken into account: First, engineering biocompatible scaffolds clinical use of which leads to the least amount of side effects without any immunologic response and secondly, use of stem cells secretions with the least amount of clinical complications despite their high capability of healing damage.

CONCLUSION

In light of the MSCs' high capability of proliferation and multilineage differentiation as well as their significant role in modulating immunity, these cells can be used in combination with tissue engineering techniques. Moreover, the MSCs' secretions can be used in cell therapy to heal many types of wounds. The combination of MSCs and PRP aids wound healing which could potentially be used to promote wound healing.

Use of platelet concentrates in oral and maxillofacial surgery: an overview

OBJECTIVE

To describe and provide a comprehensive overview on the development, use and efficacy of autologous platelet concentrates in different in vitro and in vivo studies focusing on oral and maxillofacial pathologies.

MATERIALS AND METHODS

Present work employs an extensive critical overview of the literature on the development and application of platelet concentrates.

RESULTS

Platelet concentrates are innovative endogenous therapeutic agents which gained a lot of interest in different medical and dental disciplines due to their potential ability to stimulate and increase regeneration of soft and hard tissues. The effect of platelet-derived products is considered to be a result of the high number of platelets which contain a wide range of growth factors. They are not just therapeutic products but autologous blood concentrates containing active molecules. The quality of platelet concentrates may vary according to the individual physical state of donors making it difficult to to compare the outcomes of their application. Although, there are many studies analyzing the properties of these biomaterials both in vivo and in vitro, a consensus regarding their efficacy still has to be reached.

CONCLUSION

Evidences described in the literature on the efficacy of platelet concentrates in procedures in oral and maxillofacial region are controversial and limited. In order to clarify the real advantages and priorities for the patients, when the blood-derived products are applied, further in vitro and in vivo research about the activity of PRP and PRF on the dental cells biology should be conducted.

Fibrin gel versus papain gel in the healing of chronic venous ulcers: A double-blind randomized controlled trial

Objectives Compare the efficacy and safety of fibrin gel to 8% papain gel for wound dressing of venous ulcers. Method Patients with chronic venous ulcers were randomly assigned to one in three groups: Group 1-fibrin gel; Group 2-8% papain gel; Group 3-carbopol gel (control). Patients were seen every 15 days during 2 months, verifying reduction of the ulcer area, local infection, exudation, and epithelization. All serious or nonserious adverse events were recorded. Results Fifty-five patients (total of 63 ulcers) were randomly distributed in three groups (G1 = 21; G2 = 19; G3 = 23). No patient was excluded or discontinued treatment throughout the study. The areas of the ulcers were similarly reduced in all groups (14.3%, 21.1%, and 30.4% in groups 1, 2, and 3, respectively), and all had significant reduction in exudation and contamination. Conclusion The data demonstrate that neither fibrin gel nor papain gel were able to improve the process of ulcer-healing, as compared to control.

Intraoperative Intrasac Thrombin Injection to Prevent Type II Endoleak after Endovascular Abdominal Aortic Aneurysm Repair

Purpose:

To report a prospective, nonrandomized pilot study to determine whether fibrin glue aneurysm sac embolization at the time of endovascular aneurysm repair (EVAR) is a safe and effective procedure to primarily prevent type II endoleaks.

Methods:

Between June 2003 and December 2005, 84 consecutive patients (79 men; mean age 73.8±7.8 years, range 64–86) with degenerative infrarenal abdominal aortic aneurysm underwent EVAR with bifurcated stent-grafts and fibrin glue injection into the aneurysm sac at the conclusion of the endovascular procedure. A total of 424 imaging studies and 348 visits were recorded during the study period and reviewed.

Results:

Selective catheterization of the aneurysm sac and fibrin glue injection immediately after initial stent-graft deployment was successful in 83 (99%) of 84 cases; there was one failure to access the excluded aneurysm sac due to severe iliac artery calcification. The estimated primary and assisted clinical success rates at 2 years were 91.3% and 98.8%, respectively, but the major findings were the low rate of delayed type II endoleak (2.4%) and the statistically significant decrease in the maximum transverse aneurysm diameter (50.40±6.70 versus 42.03±6.50 mm, p=0.0001) at follow-up. In addition, of 31 patients available for 24-month follow-up, 14 (45.2%) patients showed a reduction in maximum transverse aneurysm diameter by ≥5 mm; 16 (51.6%) patients had no significant changes, whereas only 1 patient showed a >5-mm enlargement.

Conclusion:

This clot engineering approach to aneurysm sac embolization at the time of endografting appears to be safe and may spare the patient a repeated catheter-based intervention or surgical procedure.

The Effect of Bone Marrow-Derived Mesenchymal Stem Cells and Their Conditioned Media Topically Delivered in Fibrin Glue on Chronic Wound Healing in Rats

Bone marrow-derived mesenchymal stem cells (BM-MSCs) represent a modern approach for management of chronic skin injuries. In this work, we describe BM-MSCs application versus their conditioned media (CM) when delivered topically admixed with fibrin glue to enhance the healing of chronic excisional wounds in rats. Fifty-two adult male rats were classified into four groups after induction of large-sized full-thickness skin wound: control group (CG), fibrin only group (FG), fibrin + MSCs group (FG + SCs), and fibrin + CM group (FG + CM). Healing wounds were evaluated functionally and microscopically. Eight days after injury, number of CD68+ macrophages infiltrating granulation tissue was considerably higher in the latter two groups. Although--later--none of the groups depicted a substantially different healing rate, the quality of regenerated skin was significantly boosted by the application of either BM-MSCs or their CM both (1) structurally as demonstrated by the obviously increased mean area percent of collagen fibers in Masson's trichrome-stained skin biopsies and (2) functionally as supported by the interestingly improved epidermal barrier as well as dermal tensile strength. Thus, we conclude that topically applied BM-MSCs and their CM-via fibrin vehicle--could effectively improve the quality of healed skin in chronic excisional wounds in rats, albeit without true acceleration of wound closure.

Vascular extracellular matrix in atherosclerosis

The extracellular matrix (ECM) is an essential component of the human body that is responsible for the proper function of various organs. Changes in the ECM have been implicated in the pathogenesis of several cardiovascular conditions including atherosclerosis, restenosis, and heart failure. Matrix components, such as collagens and noncollagenous proteins, influence the function and activity of vascular cells, particularly vascular smooth muscle cells and macrophages. Matrix proteins have been shown to be implicated in the development of atherosclerotic complications, such as plaque rupture, aneurysm formation, and calcification. ECM proteins control ECM remodeling through feedback signaling to matrix metalloproteinases (MMPs), which are the key players of ECM remodeling in both normal and pathological conditions. The production of MMPs is closely related to the development of an inflammatory response and is subjected to significant changes at different stages of atherosclerosis. Indeed, blood levels of circulating MMPs may be useful for the assessment of the inflammatory activity in atherosclerosis and the prediction of cardiovascular risk. The availability of a wide variety of low-molecular MMP inhibitors that can be conjugated with various labels provides a good perspective for specific targeting of MMPs and implementation of imaging techniques to visualize MMP activity in atherosclerotic plaques and, most interestingly, to monitor responses to antiatheroslerosis therapies. Finally, because of the crucial role of ECM in cardiovascular repair, the regenerative potential of ECM could be successfully used in constructing engineered scaffolds and vessels that mimic properties of the natural ECM and consist of the native ECM components or composite biomaterials. These scaffolds possess a great promise in vascular tissue engineering.

The regenerative potential of fibroblasts in a new diabetes-induced delayed humanised wound healing model

Cutaneous diabetic wounds greatly affect the quality of life of patients, causing a substantial economic impact on the healthcare system. The limited clinical success of conventional treatments is mainly attributed to the lack of knowledge of the pathogenic mechanisms related to chronic ulceration. Therefore, management of diabetic ulcers remains a challenging clinical issue. Within this context, reliable animal models that recapitulate situations of impaired wound healing have become essential. In this study, we established a new in vivo humanised model of delayed wound healing in a diabetic context that reproduces the main features of the human disease. Diabetes was induced by multiple low doses of streptozotocin in bioengineered human-skin-engrafted immunodeficient mice. The significant delay in wound closure exhibited in diabetic wounds was mainly attributed to alterations in the granulation tissue formation and resolution, involving defects in wound bed maturation, vascularisation, inflammatory response and collagen deposition. In the new model, a cell-based wound therapy consisting of the application of plasma-derived fibrin dermal scaffolds containing fibroblasts consistently improved the healing response by triggering granulation tissue maturation and further providing a suitable matrix for migrating keratinocytes during wound re-epithelialisation. The present preclinical wound healing model was able to shed light on the biological processes responsible for the improvement achieved, and these findings can be extended for designing new therapeutic approaches with clinical relevance.

Beaded plasma clot: a potent sustained-release, drug-delivery system

Aim: The aim of the study was to prepare a drug-entrapped, beaded form of blood plasma for possible sustained drug delivery. Method: Blood plasma mixed with various drugs was enriched with CaCl2 and transferred in the form of small droplets on to a glass slide covered with parafilm. Clot formation was induced by incubation at 37°C. Results: Plasma-bead entrapped tetracycline, amphotericin B and daunorubicin were released gradually in vitro. Crosslinking of the beads with glutaraldehyde decreased the release rate of drugs remarkably. The plasma bead-entrapped cefotaxime administered subcutaneously in mice was released in a slow and sustained fashion and remained in circulation for a longer duration than the antibiotic administered in the free form. Conclusion: The plasma beads have potential for the sustained delivery of drugs in vivo, since their preparation does not require additional thrombin or other proteins and can be readily accomplished by using autologous plasma, thereby minimizing the risk of immunological complications.

Leucocyte-platelet haemocomponents for topical use: regenerative potentiality

Wider and wider is the interest in different clinical ambits in the application of haemocomponents produced from peripheral blood for regenerative purposes. These are mainly made up of concentrated platelets capable of releasing locally growth factor (GF) that stimulates tissue regeneration. Our group has devised a method to produce a new leucocyte-platelet haemocomponent enriched in fibrinogen that integrates the GF stimulus with the presence of cells involved in the regenerative processes: monocytes and stem cells. The use of the cell separator to collect these haemocomponents from peripheral blood has allowed us to realize a safe standardized product, with good regenerative potentiality and reasonable costs. This is obtained by modifying some parameters of separation, and without cell manipulation.

Functional stability of endothelial cells on a novel hybrid scaffold for vascular tissue engineering

Porous and pliable conduits made of biodegradable polymeric scaffolds offer great potential for the development of blood vessel substitutes but they generally lack signals for cell proliferation, survival and maintenance of a normal phenotype. In this study we have prepared and evaluated porous poly(ε-caprolactone) (PCL) integrated with fibrin composite (FC) to get a biomimetic hybrid scaffold (FC PCL) with the biological properties of fibrin, fibronectin (FN), gelatin, growth factors and glycosaminoglycans. Reduced platelet adhesion on a human umbilical vein endothelial cell-seeded hybrid scaffold as compared to bare PCL or FC PCL was observed, which suggests the non-thrombogenic nature of the tissue-engineered scaffold. Analysis of real-time polymerase chain reaction (RT-PCR) after 5 days of endothelial cell (EC) culture on a hybrid scaffold indicated that the prothrombotic von Willebrand factor and plasminogen activator inhibitor (PAI) were quiescent and stable. Meanwhile, dynamic expressions of tissue plasminogen activator (tPA) and endothelial nitric oxide synthase indicated the desired cell phenotype on the scaffold. On the hybrid scaffold, shear stress could induce enhanced nitric oxide release, which implicates vaso-responsiveness of EC grown on the tissue-engineered construct. Significant upregulation of mRNA for extracellular matrix (ECM) proteins, collagen IV and elastin, in EC was detected by RT-PCR after growing them on the hybrid scaffold and FC-coated tissue culture polystyrene (FC TCPS) but not on FN-coated TCPS. The results indicate that the FC PCL hybrid scaffold can accomplish a remodeled ECM and non-thrombogenic EC phenotype, and can be further investigated as a scaffold for cardiovascular tissue engineering.

Cell Compatibility of Fibrin Sealants: In Vitro Study with Cells Involved in Soft Tissue Repair

Fibrin sealants can be used to support tissue regeneration or as vehicles for delivery of cells in tissue engineering. Differences in the composition of fibrin sealants, however, could determine the success of such applications. The results presented in this article show clear differences between Fibrin sealant A (FS A) clots and Fibrin sealant B (FS B) clots with respect to their compatibility with primary human cells involved in soft tissue repair. FS A clots, which are characterized by a physiological coarse fibrin structure, promoted attachment, spreading, and proliferation of keratinocytes, fibroblasts, and endothelial cells. In contrast, FS B clots displaying a fine to medium clot structure failed to support spreading of all three cell types. Adhesion of keratinocytes was decreased on FS B clots compared to FS A clots after 3 h incubation, whereas number of attached fibroblasts and endothelial cells was initially comparable between the two fibrin sealants. However, all three cell types proliferated on FS A clots but no sustained proliferation was detected on FS B clots. We further demonstrate that the observed differences between FS A and B clots are partly based upon 1 M sodium chloride extractable constituents, like thrombin, and partly on nonextractable constituents or the fibrin structure. In conclusion, our in vitro results demonstrate that FS A clots serve as a provisional matrix that encourages adhesion and growth of keratinocytes, fibroblasts, and endothelial cells. Therefore, FS A seems to be well suited for applications in tissue engineering.

Biomaterials for vascular tissue engineering

Cardiovascular disease is the leading cause of mortality in the USA. The limited availability of healthy autologous vessels for bypass grafting procedures has led to the fabrication of prosthetic vascular conduits. While synthetic polymers have been extensively studied as substitutes in vascular engineering, they fall short of meeting the biological challenges at the blood-material interface. Various tissue engineering strategies have emerged to address these flaws and increase long-term patency of vascular grafts. Vascular cell seeding of scaffolds and the design of bioactive polymers for in situ arterial regeneration have yielded promising results. This article describes the advances made in biomaterials design to generate suitable materials that not only match the mechanical properties of native vasculature, but also promote cell growth, facilitate extracellular matrix production and inhibit thrombogenicity.

Inkjet printing of bioadhesives

Over the past century, synthetic adhesives have largely displaced their natural counterparts in medical applications. However, rising concerns over the environmental and toxicological effects of the solvents, monomers, and additives used in synthetic adhesives have recently led the scientific community to seek natural substitutes. Marine mussel adhesive protein is a formaldehyde-free natural adhesive that demonstrates excellent adhesion to several classes of materials, including glasses, metals, metal oxides, and polymers. In this study, we have demonstrated computer aided design (CAD) patterning of various biological adhesives using piezoelectric inkjet technology. A MEMS-based piezoelectric actuator was used to control the flow of the mussel adhesive protein solution through the ink jet nozzles. Fourier transform infrared spectroscopy (FTIR), microscopy, and adhesion studies were performed to examine the chemical, structural, and functional properties of these patterns, respectively. FTIR revealed the piezoelectric inkjet technology technique to be nondestructive. Atomic force microscopy was used to determine the extent of chelation caused by Fe(III). The adhesive strength in these materials was correlated with the extent of chelation by Fe(III). Piezoelectric inkjet printing of naturally-derived biological adhesives may overcome several problems associated with conventional tissue bonding materials. This technique may significantly improve wound repair in next generation eye repair, fracture fixation, wound closure, and drug delivery devices.

Polymeric materials for tissue engineering of arterial substitutes

Cardiovascular disease is the leading cause of mortality in the United States. The limited availability of healthy autologous vessels for bypass grafting procedures has led to the fabrication of prosthetic vascular conduits. Synthetic polymeric materials, while providing the appropriate mechanical strength, lack the compliance and biocompatibility that bioresorbable and naturally occurring protein polymers offer. Vascular tissue engineering approaches have emerged in order to meet the challenges of designing a vascular graft with long-term patency. In vitro culture techniques that have been explored with vascular cell seeding of polymeric scaffolds and the use of bioactive polymers for in situ arterial regeneration have yielded promising results. This review describes the development of polymeric materials in various tissue engineering strategies for the improvement in the mechanical and biological performance of an arterial substitute.

Novel cryoprecipitate for wound healing and skin grafts in rats

The authors sought to evaluate the ability of locally administered enhanced cryoprecipitate (eCryo) to improve the wound healing of split thickness skin grafts (STSG) and their donor sites. An STSG (5 x 5 cm) was harvested on the back of 30 rats and divided into four areas that were then treated in one of the following groups: A: 'standard' dressing without STSG; B: eCryo without STSG; C: eCryo with STSG coverage and D: STSG alone. Macroscopic and histological assessments (histomorphometric grading scale and cellular composition) were evaluated at days 7, 14, 21 and 28 for wound healing. All wound beds as well as STSGs healed well without any complications. Eighty per cent of the STSG showed a histological graft take of >75% after 28 days. There were no statistically significant differences of macroscopic or histological results between the groups at any time point. Preparation of eCryo is easy and effective. Its use as an adhesive for STSGs is safe and shows similar results as controls. The theoretical benefits of eCryo did not show significant differences. Possible reasons as well as important findings for future research on wound healing are discussed.

An endogenously deposited fibrin scaffold determines construct size in the surgically created arteriovenous loop chamber model of tissue engineering

BACKGROUND

An arteriovenous loop (AVL) enclosed in a polycarbonate chamber in vivo, produces a fibrin exudate which acts as a provisional matrix for the development of a tissue engineered microcirculatory network.

OBJECTIVES

By administering enoxaparin sodium - an inhibitor of fibrin polymerization, the significance of fibrin scaffold formation on AVL construct size (including the AVL, fibrin scaffold, and new tissue growth into the fibrin), growth, and vascularization were assessed and compared to controls.

METHODS

In Sprague Dawley rats, an AVL was created on femoral vessels and inserted into a polycarbonate chamber in the groin in 3 control groups (Series I) and 3 experimental groups (Series II). Two hours before surgery and 6 hours post-surgery, saline (Series I) or enoxaparin sodium (0.6 mg/kg, Series II) was administered intra-peritoneally. Thereafter, the rats were injected daily with saline (Series I) or enoxaparin sodium (1.5 mg/kg, Series II) until construct retrieval at 3, 10, or 21 days. The retrieved constructs underwent weight and volume measurements, and morphologic/morphometric analysis of new tissue components.

RESULTS

Enoxaparin sodium treatment resulted in the development of smaller AVL constructs at 3, 10, and 21 days. Construct weight and volume were significantly reduced at 10 days (control weight 0.337 +/- 0.016 g [Mean +/- SEM] vs treated 0.228 +/- 0.048, [P < .001]: control volume 0.317 +/- 0.015 mL vs treated 0.184 +/- 0.039 mL [P < .01]) and 21 days (control weight 0.306 +/- 0.053 g vs treated 0.198 +/- 0.043 g [P < .01]: control volume 0.285 +/- 0.047 mL vs treated 0.148 +/- 0.041 mL, [P < .01]). Angiogenesis was delayed in the enoxaparin sodium-treated constructs with the absolute vascular volume significantly decreased at 10 days (control vascular volume 0.029 +/- 0.03 mL vs treated 0.012 +/- 0.002 mL [P < .05]).

CONCLUSION

In this in vivo tissue engineering model, endogenous, extra-vascularly deposited fibrin volume determines construct size and vascular growth in the first 3 weeks and is, therefore, critical to full construct development.

Comparison of the effectiveness of autologous fibrin glue and macroporous biphasic calcium phosphate as carriers in the osteogenesis process with or without mesenchymal stem cells

BACKGROUND

Facial bone reconstruction has been a challenge for oral and maxillofacial surgeons for a long time. Recently, some studies have reported the use of stem cells in facial reconstruction to achieve osteogenesis. However, to ensure that stem cells remain in the recipient site, a biocompatible carrier is needed to transfer the stem cells. Fibrin glue has been shown to promote hemostasis in wound management and accelerate soft tissue healing, but the role of fibrin glue in bone regeneration remains debatable. The purpose of this study was to compare the effectiveness of autologous fibrin glue and macroporous biphasic calcium phosphate (MBCP) as carriers in the osteogenesis process with/without mesenchymal stem cells.

METHODS

Fifteen New Zealand white rabbits were used in this study. Mesenchymal stem cells were harvested from the iliac bone, and autologous fibrin glue was made from peripheral blood. Three cranial defects with a diameter of 6 mm were created over the cranial bone in each rabbit. The 15 animals were separated into 2 groups. The first group contained 12 rabbits. The grafted substances placed over the regions of defect were: (1) stem cells plus autologous fibrin glue; (2) stem cells plus MBCP; (3) defect alone as control. In the second group of 3 rabbits, the cranial defects were grafted with: (1) autologous fibrin glue alone; (2) MBCP alone; (3) defect alone as control. Rabbits were sacrificed at 1, 2 and 3 months post operation. Radiography and histology were used to detect bone formation.

RESULTS

Stem cells plus autologous fibrin glue induced more bone formation 2 months post operation and more mature bone was found 3 months post operation compared with the other groups. MBCP with or without stem cells showed moderate tissue reaction, including giant cell, histiocyte and eosinophil cell accumulation.

CONCLUSION

Using stem cells plus autologous fibrin glue as the carrier may accelerate new bone regeneration.

Elastic plasma protein film blended with platelet releasate accelerates healing of diabetic mouse skin wounds

BACKGROUND AND OBJECTIVES

The growth factors derived from platelets and plasma proteins mediate the wound-healing process that is characterized by the sequential migration and differentiation of several cell populations that give rise to angiogenesis, collagen synthesis, wound contraction, and re-epithelialization. To evaluate the efficacy of the blood-derived factors in wound healing, we examined a novel wound dressing consisting of concentrated human plasma proteins and platelet releasate (CPPP).

MATERIALS AND METHODS

To generate CPPP, plasma proteins and platelets in the peripheral blood (n = 5) were concentrated with the cold ethanol precipitation method. The thrombin obtained from the same blood unit and calcium chloride (CaCl(2)) were mixed to a concentrate. The CPPP has enough strength to dress cutaneous wounds and contains large amounts of cytokines and fibronectin. We applied the CPPP to excisional skin wounds in genetically healing-impaired model mice (n= 5) and the wounds were evaluated 10 days after the operation.

RESULTS

The area of CPPP-treated wounds decreased significantly compared with that of the control wounds (65% vs. 94% of the original size, respectively, P= 0.032). The immunostained section revealed a striking effect of CPPP on vascularization compared with the control wounds (13.2 vs. 2.7 vessels per mm(2) as mean vascular density observed in the sections, respectively, P= 0.013).

CONCLUSIONS

Our results suggest that CPPP is a promising biologically active dressing for full-thickness skin wounds. CPPP can be an entirely autologous biological dressing, suggesting that it is free from the risk of transmission of pathogens through blood products.

A novel poly(ethylene glycol)–fibrinogen hydrogel for tibial segmental defect repair in a rat model

The aim of this study is to investigate regeneration in a segmental bone defect using a novel fibrinogen-based hydrogel material. The use of hydrogels made from poly(ethylene glycol) (PEG) conjugated to fibrinogen for this purpose may be better to conventional fibrin-based materials as it offers an additional degree of control over the structural characteristics and biodegradation of the material. At the same time, it maintains some of the inherent biofunctionality of the fibrinogen molecule. PEGylated fibrinogen hydrogels with various degrees of proteolytic resistance based on PEG and fibrinogen composition were designed for slow, intermediate, and fast biodegradation. The hydrogels were implanted into 7-mm segmental rat tibial defects without additional osteoinductive factors with the rationale that the ingrowth matrix will displace the normal fibrin clot while sustaining a similar healing effect for a longer duration. Histological and X-ray results confirmed that the extent and distribution of newly formed bone in the defect after 5 weeks strongly parallels the biodegradation pattern of the implanted material. When compared to nonunions in animals treated with the fast-degrading implants and untreated control animals, the rats implanted with the intermediate-degrading material exhibited osteoneogenesis. This data supports the hypothesis that the perseverance of the PEGylated fibrinogen material can be synchronized with the optimal healing characteristics of a segmental osseous defect and that the consequent sustained release of fibrinogen fragments facilitates the osteogenic response at the injury site. The PEGylated fibrinogen material may, therefore, be a highly efficacious material for promoting the healing of bone defects and especially nonunion fractures.

Fibrin structure and wound healing

Fibrinogen and fibrin play an important role in blood clotting, fibrinolysis, cellular and matrix interactions, inflammation, wound healing, angiogenesis, and neoplasia. The contribution of fibrin(ogen) to these processes largely depends not only on the characteristics of the fibrin(ogen) itself, but also on interactions between specific-binding sites on fibrin(ogen), pro-enzymes, clotting factors, enzyme inhibitors, and cell receptors. In this review, the molecular and cellular biology of fibrin(ogen) is reviewed in the context of cutaneous wound repair. The outcome of wound healing depends largely on the fibrin structure, such as the thickness of the fibers, the number of branch points, the porosity, and the permeability. The binding of fibrin(ogen) to hemostasis proteins and platelets as well as to several different cells such as endothelial cells, smooth muscle cells, fibroblasts, leukocytes, and keratinocytes is indispensable during the process of wound repair. High-molecular-weight and low-molecular-weight fibrinogen, two naturally occurring variants of fibrin, are important determinants of angiogenesis and differ in their cell growth stimulation, clotting rate, and fibrin polymerization characteristics. Fibrin sealants have been investigated as matrices to promote wound healing. These sealants may also be an ideal delivery vehicle to deliver extra cells for the treatment of chronic wounds.

Small-Diameter Artificial Arteries Engineered In Vitro

Although the need for a functional arterial replacement is clear, the lower blood flow velocities of small-diameter arteries like the coronary artery have led to the failure of synthetic materials that are successful for large-diameter grafts. Although autologous vessels remain the standard for small diameter grafts, many patients do not have a vessel suitable for use because of vascular disease, amputation, or previous harvest. As a result, tissue engineering has emerged as a promising approach to address the shortcomings of current therapies. Investigators have explored the use of arterial tissue cells or differentiated stem cells combined with various types of natural and synthetic scaffolds to make tubular constructs and subject them to chemical and/or mechanical stimulation in an attempt to develop a functional small-diameter arterial replacement graft with varying degrees of success. Here, we review the progress in all these major facets of the field.

Healing of perforating rat corneal incisions closed with photodynamic laser-activated tissue glue

BACKGROUND AND OBJECTIVES

Laser-activated photodynamic biologic tissue glues may be useful for closing incisions in ophthalmology. We report on the use of two such preparations to close perforating corneal incisions in living rats.

STUDY DESIGN/MATERIALS AND METHODS

A previously described preparation containing a covalent albumin-chlorin e6 (ce6) conjugate (bovine serum albumin (BSA)-ce6), and a novel mixture of albumin and Janus Green (BSA/JG), both activated with a 665-nm diode laser were used to glue mouse skin ex vivo. The optimized glues were then used to seal incisions in rat corneas and results were compared to control incisions. Rats were sacrificed at day 1, 7, and 14 and eyes tested for leaking pressure and examined histopathologically.

RESULTS

One day after treatment eyes closed with BSA-ce6 had a leaking pressure (in mmHg) of 357 compared to 193 for control incisions (P<0.01); closure with BSA/JG gave a leaking pressure of 430 (P<0.05 compared to BSA-ce6, and P<0.001 compared to control). Histological examination showed eyes sealed with BSA/JG have less inflammation present than untreated eyes at 7 days.

CONCLUSIONS

These data demonstrate that photodynamic laser activated tissue glues can be used to effectively seal corneal incisions in living animals without thermal damage or undue inflammation.

Fibrin sealants in surgical or traumatic hemorrhage

PURPOSE OF REVIEW

Fibrin sealants have been used to control surgical hemorrhage for three decades, and numerous articles have reported their use in a variety of surgical procedures in both animal models and humans. This article reviews the recent literature on fibrin sealants with the specific aim of highlighting the use of fibrin sealants in planned and simulated trauma to provide background for clinicians who may consider using fibrin sealants in specific cases. An overview of the mechanisms of action of fibrin sealants, their indications, and current commercial formulations is also provided.

RECENT FINDINGS

Recent studies have evaluated the use of fibrin sealants in vascular surgery, including aortic anastomosis in an animal model, gastrointestinal anastomoses, plastic surgery, urologic procedures including heminephrectomy, and other procedures.

SUMMARY

Fibrin sealants continue to be used and evaluated in animal models and surgery. Their use in military settings and in civilian trauma centers, explored for several years, is not reported extensively in the literature. Recent events and the current tempo of military operations dictate that many potential scenarios exist for using fibrin sealants to control traumatic hemorrhage.