Effect of bioabsorbable osseous fixation materials on dura mater and brain tissue

Bioabsorbable materials are frequently used in pediatric cranial surgery, but the effects of these materials on neural tissue are not known. The authors assessed the histologic alterations to dura mater and brain tissue associated with bioabsorbable plates. Fifteen Sprague-Dawley rats were given sham cranial surgery; an additional 30 underwent placement of 8 x 8-mm polylactic acid/poly-glycolic acid plates. The rats were assessed weekly for neurologic or behavioral changes suggesting neural damage. A portion of each group was killed at 3, 6, and 12 months for histologic analysis of cranium, dura mater, and brain tissue by standard hematoxylin and eosin stain. None of the animals showed any behavioral changes or neurologic deficits. The plates were gradually hydrolyzed over the study period, and all had disappeared by 12 months. The histologic examination showed fibrous encapsulation around the plates, accompanied by foreign body giant cell reaction and calcification. Focal gliosis, where evident, was mild and confined primarily to the superficial cortex of the brain beneath the plate. The infiltration of the dura mater and underlying brain parenchyma was negligible. In conclusion, the neurologic and histologic effect of bioabsorbable plates on neural tissue may be considered negligible in the early postoperative period.     

Dura mater-derived FGF-2 mediates mitogenic signaling in calvarial osteoblasts

Although dura mater tissue is believed to have an important role in calvarial reossification in many in vivo studies, few studies have shown the direct effect of dura mater cells on osteoblasts. In addition, no reports have yet identified the potential factor(s) responsible for various biological activities exerted by dura mater on calvarial reossification (e.g., cell proliferation). In this study, we tested the effect of dura mater on calvarial-derived osteoblasts by performing both heterotypic coculture and by culturing osteoblast cells with conditioned media harvested from dura mater cells of juvenile (3-day-old) and adult (30-day-old) mice. The results presented here demonstrate that cellular proliferation of juvenile osteoblast cells was significantly increased by juvenile dura mater either in the coculture system or when dura mater cell-conditioned medium was applied to the osteoblast cells. Moreover, high levels of FGF-2 protein were detected in juvenile dura mater cells and their conditioned medium. In contrast, low levels of FGF-2 protein were detected in adult dura mater cells, whereas FGF-2 protein was not detectable in their conditioned medium. Abrogation of the mitogenic effect induced by juvenile dura mater cell-conditioned medium was achieved by introducing a neutralizing anti-FGF-2 antibody, thus indicating that FGF-2 may be responsible for the mitogenic effect of the juvenile dura mater. Moreover, data obtained by exploring the three major FGF-2 signaling pathways further reinforced the idea that FGF-2 might be an important paracrine signaling factor in vivo supplied by the underlying dura mater to the overlying calvarial osteoblasts.     

Dura mater secretes soluble heparin-binding factors required for cranial suture morphogenesis

Summary Cranial sutures play a critical role in calvarial morphogenesis, serving as bone growth centers during skull enlargement. Defective suture morphogenesis, resulting in premature osseous obliteration of sutures and their failure to function appropriately, causes severe craniofacial anomalies. Previously published data demonstrated osseous obliteration of coronal suturesin vitro in the absence of dura mater and the rescue of sutures from osseous obliteration in rudiments cocultured with dura mater on the opposite sides of 0.45-μm polycarbonate filters. With thisin vitro culture system, experiments were designed to examine the nature of the soluble signal secreted by dura mater, required for maintaining intact sutures. The signal remained active in conditioned medium produced from dura mater, which was capable of rescuing coronal sutures from osseous obliteration in calvaria cultured without dura mater. When conditioned medium was segregated into heparin-binding and non-heparin-binding fractions, the signal capable of maintaining intact coronal sutures cosegregated with the heparin-binding component and remained functional in the absence of the non-heparin-binding component of conditioned medium. Evidence indicates that soluble, heparin-binding factors secreted by the dura mater act as osteoinhibitory signals at the suture site.     

Cellular dynamics and tissue interactions of the dura mater during head development

During development and growth of the neurocranium, the dura mater regulates events in the underlying brain and overlying skull by the release of soluble factors and cellular activity. Morphogenesis of the cranial bones and sutures is dependent on tissue interactions with the dura mater, which control the size and shape of bones as well as sutural patency. Development of the brain also involves interactions with dura mater: secretion of stromal derived factor 1 (SDF-1) is a critical event in directing migration of the external granular layer precursors of the cerebellar cortex and the Cajal-Retzius (CR) cells of the cerebral cortex. The dura mater is also required for growth of the hippocampal dentate gyrus. Wnt1Cre/R26R transgenic reporter mice were used to study the origin and fates of the cells of dura mater during head development. The dura mater of mammals is derived entirely from the cranial neural crest. Beginning around neonatal day 10 (N 10), the dura mater is infiltrated by cells derived from paraxial mesoderm, which later come to predominate. Over the course of infancy, the neural crest-derived cells of the dura mater become sequestered in niche-like distribution characteristic of stem cells. Simultaneously, dura mater cells underlying the sagittal suture migrate upward into the mesodermally-derived mesenchyme separating the parietal bones. Although initially the parietal bones are formed entirely from paraxial mesoderm, the cellular composition gradually becomes chimeric and is populated mainly by neural crest-derived cells by N 30. This occurs as a consequence of osteoblastic differentiation at the dura mater interface and intravasation of neural crest-derived osteoclastic and other hematopoietic precursors. The isolated cells of the dura mater are multipotent in vitro, giving rise to osteoblasts, neuronal cells and other derivatives characteristic of cranial neural crest, possibly reflecting the multipotent nature of dura mater cells in vivo.     

Morphofunctional characteristics of the microcirculatory bed of the human spinal dura mater]

Some morphofunctional peculiarities in microcirculatory pathways of the dura mater of the human spinal cord are described. They are concerned with the structure of arteriolo-venular anastomoses through which a rather large amount of arterial blood is transported into the venous bed. Around the vessels of arterial type running at an angle to the longitudinal axis of the vessel connective tissue fibres of the dura mater, there is a tissue layer intensively impregnated with silver salts and stained PAS-positively. The venous part of the dura mater microcirculatory pathways has a large number of accessory reservoirs in the form of venous "lakes". Functional importance of the peculiarities mentioned above for the dura mater and the perimedullar apparatus is clarified.     

An optofluidic mechanical system for elasticity measurement of thin biological tissues

As dura mater has an anisotropic fibrous structure and exists under wet and dynamic stretching conditions in the brain, its mechanical properties have not yet been properly investigated. Here we developed a fluid-assisted mechanical system integrated with a photonic sensor and a pressure sensor in order to measure the elasticity of the dura mater. Porcine dura mater sample was loaded as a stretched diaphragm into a liquid chamber to mimic the in vivo condition. Increasing the flow rate of saline solution into the chamber swelled and deformed the dura mater. The micron-scale deflection of the dura mater was optically detected by the photonic sensor. Fluid pressure and deflection values were then used to calculate the elastic modulus. The average elastic modulus of the porcine dura mater was 31.14 MPa. We further measured the elasticity of a well-known material to further validate the system. We expect that this optofluidic system developed in this study will be useful to measure the elasticity of a variety of thin biological tissues.     

Mechanical strain affects dura mater biological processes: implications for immature calvarial healing

The human brain grows rapidly during the first 2 years of life. This growth generates tensile strain in the overlying dura mater and neurocranium. Interestingly, it is largely during this 2-year growth period that infants are able to reossify calvarial defects. This clinical observation is important because it suggests that calvarial healing is most robust during the period of active intracranial volume expansion. With a rat model, it was previously demonstrated that immature dura mater proliferates more rapidly and produces more osteogenic cytokines and markers of osteoblast differentiation than does mature dura mater. It was therefore hypothesized that mechanical strain generated by the growing brain induces immature dura mater proliferation and increases osteogenic cytokine expression necessary for growth and healing of the overlying calvaria. Human and rat (n = 40) intracranial volume expansion was calculated as a function of age. These calculations demonstrated that 83 percent of human intracranial volume expansion is complete by 2 years of age and 90 percent of Sprague-Dawley rat intracranial volume expansion is achieved by 2 months of age. Next, the maximal daily circumferential tensile strains that could be generated in immature rat dura mater were calculated, and the corresponding daily biaxial tensile strains in the dura mater during this 2-month period were determined. With the use of a three-parameter monomolecular growth curve, it was calculated that rat dura mater experiences daily equibiaxial strains of at most 9.7 percent and 0.1 percent at birth (day 0) and 60 days of age, respectively. Because it was noted that immature dural cells may experience tensile strains as high as approximately 10 percent, neonatal rat dural cells were subjected to 10 percent equibiaxial strain in vitro, and dural cell proliferation and gene expression profiles were analyzed. When exposed to mechanical strain, immature dural cells rapidly proliferated (5.8-fold increase in proliferating cell nuclear antigen expression at 24 hours). Moreover, mechanical strain induced marked up-regulation of dural cell osteogenic cytokine production; transforming growth factor-beta1 messenger RNA levels increased 3.4-fold at 3 hours and fibroblast growth factor-2 protein levels increased 4.5-fold at 24 hours and 5.6-fold at 48 hours. Finally, mechanical strain increased dural cell expression of markers of osteoblast differentiation (2.8-fold increase in osteopontin levels at 3 hours). These findings suggest that mechanical strain can induce changes in dura mater biological processes and gene expression that may play important roles in coordinating the growth and healing of the neonatal calvaria.     

Organizational features and morphometric characteristics of the hemomicrocirculatory bed of the human brain dura mater

By means of silver nitrate impregnation and hematoxylin -- eosin staining the microcirculatory bed of the human brain dura mater (the second half of the mature age) has been investigated. Owing to the analysis of the morphometrical data of module organization of the hemomicrocirculatory bed, an objective quantitative characteristics of its peculiarities in various layers and areas of the dura mater is presented. In three layers of the dura mater in the fornix and skull basis area, falx cerebri and tentorium cerebelli venular links predominate. Most of all morphometrical parameters of the venular vessels increase in the internal layer of the dura mater in the skull basis area. Conditions of functioning for the human brain dura mater are reflected in its blood bed, its specificity manifesting at the microcirculatory level.     

The osteogenic role of the dura mater in adult rabbits during regeneration of the skull]

It was shown in experiments with adult rabbits that the regeneration of skull vault bones after artificial trauma proceeds, mainly, at the expense of osteogenic activity of dura mater, rather than by means of outgrowth of bone from the defect margins. During regeneration, dura mater connects with the granulation tissue which fills the area of defect. The first bone islets are formed by the surface layer of dura mater near the defect margins and then all over the defect area. During regeneration bone islets merge with each other and with the old bone at the defect margins. In experiments with separation of the defect margins from dura mater by millipore filter, regeneration is insignificant over the filter near the old bone margins (bone trabeculae form which close destructed bone marrow cavities); the bone forms intensively under the filter on dura mater. In experiments with the removal of a piece of skull bone together with the adjacent region of dura mater, no bone regeneration occurs, the defect area is filled by the scar tissue.     

Nasal capsular cartilage is required for rat transpalatal suture morphogenesis

In the cranial vault, suture morphogenesis occurs when the growing cranial bones approximate and overlap or abut one another. Patency of developing sutures is regulated by the underlying dura mater. Once cranial sutures form, bone growth proceeds from the sutures in response to growth signals from the rapidly expanding neurocranium. Facial sutures do not develop in contact with the dura mater. It was therefore hypothesized that facial suture morphogenesis and bone growth from facial sutures are regulated by tissues with an equivalent role to the dura mater. The present study was designed to test this hypothesis by characterizing the morphology and growth factor expression in developing transpalatal (TP) sutures and their surrounding tissues, and then assessing the role of the overlying nasal capsular (NC) cartilages in maintaining suture patency. TP sutures develop as overlapping sutures, similar to cranial coronal sutures, and expression of Tgf-betas in TP sutures was similar to their distribution in cranial coronal sutures. To establish whether NC cartilages play a role in regulating TP suture morphogenesis, fetal rat TP sutures were cultured with associated attached NC cartilages or with NC cartilages removed. Sutures cultured for upward of 5 days with intact NC cartilages remained patent and maintained their cellular and fibrous components. However, in the absence of NC cartilages, the cellular nature of the sutures was not maintained and they became progressively acellular, with bony bridging across the suture. This finding is similar to that for cranial vault sutures cultured in the absence of dura mater, indicating that NC cartilages play an equivalent role to dura mater in maintaining the patency of developing sutures. These studies indicate that tissue interactions likely regulate morphogenesis of all cranial and facial sutures.     

Systematic review and meta-analysis of the biomechanical properties of the human dura mater applicable in computational human head models

Accurate biomechanical properties of the human dura mater are required for computational models and to fabricate artificial substitutes for transplantation and surgical training purposes. Here, a systematic literature review was performed to summarize the biomechanical properties of the human dura mater that are reported in the literature. Furthermore, anthropometric data, information regarding the mechanically tested samples, and specifications with respect to the used mechanical testing setup were extracted. A meta-analysis was performed to obtain the pooled mean estimate for the elastic modulus, ultimate tensile strength, and strain at maximum force. A total of 17 studies were deemed eligible, which focused on human cranial and spinal dura mater in 13 and 4 cases, respectively. Pooled mean estimates for the elastic modulus (n?=?448), the ultimate tensile strength (n?=?448), and the strain at maximum force (n?=?431) of 68.1 MPa, 7.3 MPa and 14.4% were observed for native cranial dura mater. Gaps in the literature related to the extracted data were identified and future directions for mechanical characterizations of human dura mater were formulated. The main conclusion is that the most commonly used elastic modulus value of 31.5 MPa for the simulation of the human cranial dura mater in computational head models is likely an underestimation and an oversimplification given the morphological diversity of the tissue in different brain regions. Based on the here provided meta-analysis, a stiffer linear elastic modulus of 68 MPa was observed instead. However, further experimental data are essential to confirm its validity.

     

Basic fibroblast growth factor and transforming growth factor beta-1 expression in the developing dura mater correlates with calvarial bone formation

Numerous studies have found dura mater-calvarial mesenchyme interactions during calvarial bone induction; however, the exact molecular mechanisms governing these inductive events remain unknown. Recent studies have implicated basic fibroblast growth factor (FGF-2) and transforming growth factor-beta1 (TGF-beta1) in regulating bone formation. The purpose of this study was, therefore, to investigate the expression of FGF-2 and TGF-beta1 during calvarial bone formation in rats. Eight rats were killed on embryonic days 14, 18, and 20 and neonatal day 1 (n = 32). Four animals at each time point were analyzed by in situ hybridization, and the remainder were analyzed by immunohistochemistry. The results indicated that the dura mater underlying the developing calvarial bone strongly expressed FGF-2 and TGF-beta1 mRNA at all time points examined. In contrast, minimal growth factor expression was noted in the overlying calvarial mesenchyme until embryonic day 18, but it increased significantly with increasing age. Importantly, FGF-2 and TGF-beta1 mRNA expression in the dura mater underlying the developing calvarium preceded and was significantly greater than expression in the calvarium mesenchyme (p < 0.05). Interestingly, minimal expression of FGF-2 and TGF-beta1 mRNA was noted for all time points in the dura mater underlying the posterior frontal suture and within the posterior frontal suture connective tissue (p < 0.01 when compared with the dura mater underlying the developing calvarium). Immunohistochemical findings closely paralleled mRNA expression, with intense staining for FGF-2 and TGF-beta1 in the dura mater underlying the developing calvarial mesenchyme. Increasing FGF-2 and TGF-beta1 staining was noted within calvarial osteoblasts with increasing age, particularly in cells located near the endocranial surface (i.e., in contact with the developing dura mater). These findings, together with the known biologic functions of FGF-2 and TGF-beta1, implicate these growth factors in the regulation of calvarial bone growth by the developing dura mater. The possible mechanisms of this interaction are discussed.     

Can Creutzfeldt-Jakob disease unravel the mysteries of Alzheimer?

Recent studies on iatrogenic Creutzfeldt-Jakob disease (CJD) raised concerns that one of the hallmark lesions of Alzheimer disease (AD), amyloid-β (Aβ), may be transmitted from human-to-human. The neuropathology of AD-related lesions is complex. Therefore, many aspects need to be considered in deciding on this issue. Observations of recent studies can be summarized as follows: 1) The frequency of iatrogenic CJD cases with parencyhmal and vascular Aβ deposits is statistically higher than expected; 2) The morphology and distribution of Aβ deposition may show distinct features; 3) The pituitary and the dura mater themselves may serve as potential sources of Aβ seeds; 4) Cadaveric dura mater from 2 examined cases shows Aβ deposition; and 5) There is a lack of evidence that the clinical phenotype of AD appears following the application of cadaveric pituitary hormone or dura mater transplantation. These studies support the notion that neurodegenerative diseases have common features regarding propagation of disease-associated proteins as seeds. However, until further evidence emerges, prions of transmissible spongiform encephalopathies are the only neurodegenerative disease-related proteins proven to propagate clinicopathological phenotypes.     

TGF-beta2 stimulates cranial suture closure through activation of the Erk-MAPK pathway

Cranial sutures are important growth sites of the skull. During suture closure, the dura mater is one of the most important sources of various positive and negative regulatory signals. Previous results indicate that TGF-beta2 from dura mater strongly accelerates suture closure, however, its exact regulatory mechanism is still unclear. In this study, we confirmed that removal of dura mater in calvarial organ culture strongly accelerates sagittal suture closure and that this effect is further enhanced by TGF-beta2 treatment. TGF-beta2 stimulated cell proliferation in the MC3T3-E1 cell line. Similarly, it stimulated the proliferation of cells in the sutural space in calvarial organ culture. Furthermore, TGF-beta2-mediated enhanced cell proliferation and suture closure were almost completely inhibited by an Erk-MAPK blocker, PD98059. These results indicate that TGF-beta2-induced activation of Erk-MAPK is an important signaling component that stimulates cell proliferation to enrich osteoprogenitor cells, thereby promoting their differentiation into osteoblasts to achieve a rapid calvarial bone expansion.     

Ultrastructure of the meninges at the site of penetration of veins through the dura mater,with particular reference to Pacchionian granulations

At the sites where a vein penetrates through the dura mater, two aspects deserve particular attention: (i) The delineation of the perivascular cleft, a space belonging to the interstitial cerebrospinal fluid (CSF) compartment, toward the interior hemal milieu of the dura mater. (ii) The relationship between the perivascular arachnoid layer and the subdural neurothelium at the point of vascular penetration. These problems were investigated in the rat and in two species of New-World monkeys (Cebus apella, Callitrix jacchus). Concerning the first aspect, tight appositions of meningeal cells to the vessel wall, the basal lamina of which is widened and enriched with microfibrils, prevent communication between the interstitial CSF in the perivascular cleft and the hemal milieu in the dura mater. With reference to the second aspect, the perivascular arachnoid cells are transformed into neurothelial cells at the point where they become exposed to the hemal milieu of the dura mater and subsequently continuous with the subdural neurothelium. Leptomeningeal protrusions encompassing outer CSF space can penetrate into the dura mater. These protrusions may expand and branch repeatedly, forming along the wall of the dural sinus Pacchionian granulations. At these sites, however, the structural integrity of the sinus wall and the Pacchionian granulation is not lost. Numerous vesiculations not only in the sinus and vascular walls, but also in the cellular arrays of the Pacchionian granulations or paravascular leptomeningeal protrusions indicate mechanisms of transcellular fluid transport. Moreover, the texture of the leptomeningeal protrusions favors an additional function of these structures as a "volume" buffer.     

Cranial suture obliteration is induced by removal of transforming growth factor (TGF)-beta 3 activity and prevented by removal of TGF-beta 2 activity from fetal rat calvaria in vitro

Cranial suture morphogenesis requires soluble, heparin-binding factors secreted by the dura mater to resist premature osseous obliteration. Elevated levels of transforming growth factor (TGF)-beta 1, TGF-beta 2, and TGF-beta 3 have previously been noted in cranial sutures undergoing normal and premature sutural obliteration. To examine the role of TGF-beta s in regulating cranial suture morphogenesis, an established in vitro, serum-free, calvarial culture system was used. In this system, fetal rat coronal sutures undergo apparently normal suture morphogenesis in the presence of dura mater, but undergo osseous obliteration in the absence of dura mater. Neutralizing polyclonal antibodies to TGF-beta 1, TGF-beta 2, or TGF-beta 3 were added to cultures of fetal day 19 rat calvaria, which were harvested at 3, 4, or 5 days, processed for histology, sectioned, and examined. Coronal sutures from calvaria cultured in the presence of dura mater resisted obliteration, either alone or in the presence of TGF-beta 1 or TGF-beta 2 neutralizing antibodies. However, sutures from calvaria cultured in the presence of TGF-beta 3 neutralizing antibodies became obliterated. Conversely, sutures from calvaria cultured in the absence of dura mater became obliterated by bone, either alone or in the presence of neutralizing antibodies to TGF-beta 1 or TGF-beta 3. However, those sutures cultured in the presence of neutralizing antibodies to TGF-beta 2 were rescued from osseous obliteration.     

Co-culture of osteoblasts with immature dural cells causes an increased rate and degree of osteoblast differentiation

For decades surgeons have exploited the ability of infants to reossify large calvarial defects. To demonstrate the role of dura mater-osteoblast communication during the process of calvarial reossification, the authors used a novel in vitro system that recapitulates the in vivo anatomic relationship of these cell populations. Primary cultures of osteoblast cells from 2-day-old Sprague-Dawley rat pups were grown on six-well plates, and cultures of immature, non-suture-associated dura mater cells from 6-day-old Sprague-Dawley rat pups were grown on Transwell inserts. When the osteoblast and dura mater cell cultures reached confluence, they were combined. This Transwell co-culture system permitted the two cell populations to grow together in the same well, but it prevented direct cell-to-cell contact. Therefore, the authors were able to determine, for the first time, whether paracrine signaling from immature, non-suture-associated dura mater could influence the biologic activity of osteoblasts.Osteoblasts co-cultured with dural cells proliferated significantly faster after 2 days (2.1 x 10(5) +/- 2.4 x 10(4) versus 1.4 x 10(5) +/- 2.2 x 10(4), p < or = 0.05) and 4 days (3.1 x 10(5) +/- 5 x 10(4) versus 2.2 x 10(5) +/- 4.0 x 10(4), p < or = 0.01) than did osteoblasts cultured alone. After 20 days, co-cultured osteoblasts expressed greater amounts of mRNA for several markers of osteoblast differentiation, including collagen I alpha I (4-fold), alkaline phosphatase (2.5-fold), osteopontin (3-fold), and osteocalcin (4-fold), than did osteoblasts cultured alone. After 30 days, co-cultured osteoblasts produced bone nodules that were significantly greater both in number (324 +/- 29 nodules versus 252 +/- 29 nodules per well, p , < or = 0.04) and total area of nodules (65 +/- 11 mm(2) versus 24 +/- 1.6 mm(2), p < or = 0.003) than osteoblasts cultured alone.To begin to understand how dural cells effect changes in osteoblast gene expression, the authors compared the expression of candidate genes, transforming growth factor beta 1 and fibroblast growth factor 2, in dural cells and osteoblasts before and after 5 days of culture. Interestingly, the dura mater produced marked amounts of these osteogenic cytokines compared with osteoblasts.The described co-culture system demonstrated that co-cultured osteoblasts proliferated more rapidly and experienced an increased rate and degree of cellular maturation than did osteoblasts cultured alone. The authors hypothesize that this effect was due to paracrine signaling (e.g., transforming growth factor beta 1 and fibroblast growth factor 2) from the dura mater, and they are investigating those mechanisms in ongoing experiments. Collectively these data verify that immature, non-suture-associated dura mater can influence the biologic activity of osteoblasts. Moreover, the production of cytokines derived from the dura mater (e.g., transforming growth factor beta 1 and fibroblast growth factor 2), and they may begin to explain why immature animals and infants with intact dura mater can reossify large calvarial defects.     

Sinuses of the dura mater in dogs]

Sinuses of the dura mater were studied in 50 preparations of the venous system in mongrel dogs--10 moist, 40 corrosive prepared from plastics AKP-7 and AKP-15. Sinuses of the fornix--superior, sagittal, straight, transversal, occipital sinusal gutter, and sinuses of the basis--cavernous, intracavernous, petrous-basal, occipital and marginal were detected and their connections were described. Emissary and diploid veins and extracranial venous plexus are demonstrated to mediate a close connection between the sinuses of the dura mater. Common features in the sinusal structure of the human dura mater and those of the animals studied are noted; comparative-anatomical differences which should be taken into account when planning the experiment are presented.     

Experimental morphologic findings serving as a basis for use of xenogenic dura mater for plastic surgery of blood vessels]

Heterotransplants of the human dura mater were used to replace circular and lateral defects of the thoracic and abdominal aortas, carotid and iliac arteries in experiment. Operations were performed in 106 dogs. Observations of permeability of the vessels, morphological and histochemical studies were carried out at different periods after operation (from 1 day to 2 years). The xenogenous dura mater has well pronounced plastic properties--it is solid, elastic, characterized by low antigenicity. During transplantation there appear no hard inflammatory--destructive changes in reconstructed vessels and the surrounding tissues. The transplant is gradually substituted by recipients tissues characterized by high specialization. They are rich in elastic and smooth muscle fibres, have good blood supply and innervation. The dura mater is a good material for plastics of vascular wall defects.