Experimental evaluation of peritoneum and pericardium as dural substitutes

Tensile properties of human spinal dura mater and pericranium

Autologous pericranium is a promising dural graft material. An optimal graft should exhibit similar mechanical properties to the native dura, but the mechanical properties of human pericranium have not been characterized, and studies of the biomechanical performance of human spinal dura are limited. The primary aim of this study was to measure the tensile structural and material properties of the pericranium, in the longitudinal and circumferential directions, and of the dura in each spinal region (cervical, thoracic and lumbar) and in three directions (longitudinal anterior and posterior, and circumferential). The secondary aim was to determine corresponding constitutive stress-strain equations using a one-term Ogden model. A total of 146 specimens were tested from 7 cadavers. Linear regression models assessed the effect of tissue type, region, and orientation on the structural and material properties. Pericranium was isotropic, while spinal dura was anisotropic with higher stiffness and strength in the longitudinal than the circumferential direction. Pericranium had lower strength and modulus than spinal dura across all regions in the longitudinal direction but was stronger and stiffer than dura in the circumferential direction. Spinal dura and pericranium had similar strain at peak force, toe, and yield, across all regions and directions. Human pericranium exhibits isotropic mechanical behavior that lies between that of the longitudinal and circumferential spinal dura. Further studies are required to determine if pericranium grafts behave like native dura under in vivo loading conditions. The Ogden parameters reported may be used for computational modeling of the central nervous system. Graphical abstract.

A Comparative Study Between Porcine Peritoneum and Pericardium as Cardiovascular Material

Decellularized porcine pericardium has many applications in the cardiovascular field for its excellent properties. The peritoneum is a single-layer bio-dialysis membrane with many similarities and differences in physical characteristics, biochemical composition, and structure to the pericardium. The limited available literature suggests that, similar to the pericardium, the peritoneum has good application potential in the field of cardiovascular substitute materials. This research focused on comparing the differences between decellularized peritoneum and decellularized pericardium in microstructure, biochemical composition, mechanical properties, hemocompatibility, in vitro enzymatic degradation, in vitro calcification, cytocompatibility, and other vital indicators. The peritoneum was consistent with pericardium in terms of fibrous structure, hemocompatibility, in vitro calcification, and cytocompatibility. The peritoneal elastic fiber content (219 μg/mg) was significantly higher than that of the pericardium (66 μg/mg), resulting in two to three times higher maximum load (21.1 N) and burst pressure (1309 mmHg), and better performance than the pericardium in terms of in vitro resistance to enzymatic degradation. In the cardiovascular field, decellularized peritoneum can be used as vascular substitute material. Impact statement There are many similarities between the embryonic origin and morphological structure of the porcine peritoneum and the porcine pericardium, but little research has been done on the use of the porcine peritoneum as a biomaterial. In this compared research, we showed that porcine peritoneum had better resistance to enzymatic degradation, better stretching, and more suitable burst pressure for being used as vascular substitute material. This research is the first to describe the structural composition of porcine peritoneum and its advantageous properties as a cardiovascular material.

A standardized model for in vitro testing of sutures and patches for watertight dural closure

OBJECTIVE

CSF leaks are common complications of spinal and cranial surgeries. Several dural grafts and suture techniques are available to achieve watertight dural closure, but the effectiveness of these techniques remains unclear. The authors developed a standardized in vitro model to test available grafts and suture techniques alone or in combination to find the technique with the most watertight dural closure.

METHODS

A fluid chamber with a dural fixation device, infusion pump, pressure gauge, and porcine pericardium as a dural equivalent was assembled to provide the reusable device for testing. The authors performed dural closure in 4 different fashions, as follows: A) using running versus simple interrupted suture technique and different suture materials to close a 3-cm incision; B) selecting commonly used sealants and dural patches in combination with a running suture; C) performing duraplasty (1.5 × 1.5-cm square defect) with different dural substitutes in a stand-alone fashion; and D) performing duraplasty with different dural substitutes in a double-layer fashion. Each technique was tested 6 times. The hydrostatic burst pressure (BP) was measured and compared using the Kruskal-Wallis test or the Mann-Whitney U-test. Values are reported as mean ± SD.

RESULTS

There was no significant difference between the running and simple interrupted suture technique (p = 0.79). Adding a patch or sealant to a suture resulted in a 1.7- to 14-fold higher BP compared to solitary suture closure (36.2 ± 24.27 cm H2O and 4.58 ± 1.41 cm H2O, respectively; p < 0.001). The highest BP was achieved by adding DuraSeal or TachoSil (82.33 ± 12.72 cm H2O and 74.17 ± 12.64 cm H2O, respectively). For closing a square defect, using a double-layer duraplasty significantly increased BP by a factor of 4-12 compared to a single-layer duraplasty (31.71 ± 12.62 cm H2O vs 4.19 ± 0.88 cm H2O, respectively; p < 0.001). The highest BP was achieved with the combination of Lyomesh and TachoSil (43.67 ± 11.45 cm H2O).

CONCLUSIONS

A standardized in vitro model helps to objectify the watertightness of dural closure. It allows testing of sutures and dural grafts alone or in combination. In the authors' testing, a running 6-0 monofilament polypropylene suture combined with DuraSeal or TachoSil was the technique achieving the highest BP. For the duraplasty of square defects, the double-layer technique showed the highest efficacy.

Mechanical properties of porcine spinal dura mater and pericranium

BACKGROUND

The objective of this study was to characterize and compare the mechanical properties of porcine pericranium and spinal dura mater, to evaluate the mechanical suitability of pericranium as a dural graft.

METHOD

Eighty-eight spinal dura (cervical, thoracic, and lumbar regions, in ventral longitudinal, dorsal longitudinal and circumferential orientations) and eighteen pericranium samples (ventral-dorsal, and lateral orientations) from four pigs, were harvested and subjected to uniaxial loading while hydrated. The stiffness, strain at toe-linear regions transition, strain at linear-yield regions transition and other structural and mechanical properties were measured. Stress-strain curves were fitted to a one-term Ogden model and Ogden parameters were calculated. Linear regression models with cluster-robust standard errors were used to assess the effect of region and orientation on material and structural properties.

RESULTS

Both spinal dura and pericranium exhibited distinct anisotropy and were stiffer in the longitudinal direction. The tissues exhibited structural and mechanical similarities especially in terms of stiffness and strains in the linear region. Stiffness ranged from 1.28 to 5.32 N/mm for spinal dura and 2.42-3.90 N/mm for pericranium. In the circumferential and longitudinal directions, the stiffness of spinal dura specimens was statistically similar to that of pericranium in the same orientation. The strain at the upper bound of the linear region of longitudinal pericranium (28.0%) was statistically similar to that of any spinal dura specimens (24.4-32.9%).

CONCLUSIONS

Autologous pericranium has advantageous physical properties for spinal duraplasty. The present study demonstrated that longitudinally oriented pericranium is mechanically compatible with spinal duraplasty procedures. Autologous pericranium grafts will likely support the mechanical loads transmitted from the spinal dura, but further biomechanical analyses are required to study the effect of the lower yield strain of circumferential pericranium compared to spinal dura. Finally, the Ogden parameters calculated for pericranium, and the spinal dura at each spinal level, will be useful for computational models incorporating these soft tissues.

The collagenic architecture of human dura mater

OBJECT

Human dura mater is the most external meningeal sheet surrounding the CNS. It provides an efficient protection to intracranial structures and represents the most important site for CSF turnover. Its intrinsic architecture is made up of fibrous tissue including collagenic and elastic fibers that guarantee the maintenance of its biophysical features. The recent technical advances in the repair of dural defects have allowed for the creation of many synthetic and biological grafts. However, no detailed studies on the 3D microscopic disposition of collagenic fibers in dura mater are available. The authors report on the collagenic 3D architecture of normal dura mater highlighting the orientation, disposition in 3 dimensions, and shape of the collagen fibers with respect to the observed layer.

METHODS

Thirty-two dura mater specimens were collected during cranial decompressive surgical procedures, fixed in 2.5% Karnovsky solution, and digested in 1 N NaOH solution. After a routine procedure, the specimens were observed using a scanning electron microscope.

RESULTS

The authors distinguished the following 5 layers in the fibrous dura mater of varying thicknesses, orientation, and structures: bone surface, external median, vascular, internal median, and arachnoid layers.

CONCLUSIONS

The description of the ultrastructural 3D organization of the different layers of dura mater will give us more information for the creation of synthetic grafts that are as similar as possible to normal dura mater. This description will be also related to the study of the neoplastic invasion.

Allergic reaction to a bovine dural substitute following spinal cord untethering. Case report

Bovine tissues are now routinely used for dural closure in cranial and spinal surgery. The authors report the case of an 18-year-old woman with a history of myelomeningocele who had symptoms of tethered cord syndrome and presented to a regional hospital. At that hospital she underwent a cord untethering procedure. The spinal dura was closed with Durepair, a dural substitute derived from fetal bovine skin. Her postoperative course was complicated by a cerebrospinal fluid leak that was surgically repaired. Following this, she developed erythroderma, intermittent fevers, eosinophilia, and marked elevation in serum immunoglobulin E. She was then transferred to the authors' institution. A skin antigen test to beef was administered, which revealed a positive reaction. A radioallergosorbent test to beef also yielded positive results. She was taken to the operating room for removal of the bovine graft due to concern for an allergic reaction to the graft. The graft material showed evidence of eosinophilic infiltration. Her clinical symptoms and laboratory values all improved after surgery. To the authors' knowledge this is the first reported case of an allergic reaction to bovine-based dural substitutes.

Experience with management of anterior abdominal wall defects using bovine pericard

During 5 years from 1999 until 2003, our experience with 29 (100%) neonates managed for anterior abdominal wall defects is presented. Twenty-one (72%) neonates presented with gastroschisis and 8 (28%) neonates with giant omphaloceles. The male:female ratio was almost equal in gastroschisis (1:1) while a male predominance was observed in omphaloceles (6:1). A primary closure of the defect was possible in 5 (17%) cases and a single patch along with skin closure was achieved in a further 9 (31%) cases. In 15 (52%) neonates the defect was large and two patches were employed to sufficiently cover the defect. All patients (97%), except one (mortality due to extreme prematurity), were managed successfully. Depending upon the size of the defect and the metabolic condition of the neonate, the defect closure was completed after a mean of 85.7 days. Special protocols were created to manage the bovine pericard patches, which behaved differently to lyophilized dura patches previously used at our center. Integration of the patches was successful in 28 (97%) neonates; however, one neonate with gastroschisis presented significant challenges in the management. Bovine pericard patches are optimal biomaterials for the closure of anterior abdominal wall defects in gastroschisis and omphaloceles.

Suturing technique and the integrity of dural closures: an in vitro study

OBJECTIVE

The watertight closure of the dura mater is fundamental to intracranial procedures in neurosurgery. Nevertheless, for any given operator and type of suture, it is still not certain which suturing technique affords the most watertight dural closure. We have developed a laboratory model that allows us to compare the pressures at which dural closures leak when different suturing techniques are used.

METHODS

Human cadaveric dura was secured to a glass cylinder filled with colored saline. By application of force to a bag of saline attached to the cylinder, the pressure at which sutured dural incisions leak can be recorded. Using this method, we have compared the closure of 2-cm dural incisions with 3-0 silk using the following techniques (10 per group): 1) interrupted simple, 2) running simple, 3) running locked, and 4) interrupted vertical mattress. We have also compared the closure of 1- x 3-cm dural windows with cadaveric dura and 3-0 silk using the same suturing techniques (10 per group).

RESULTS

The pressure at which 2-cm linear dural incisions leaked was significantly higher when they were closed with the interrupted simple suturing technique (P < 0.05). There was no significant difference among the different suturing techniques when they were used to close a 1- x 3-cm dural window with a duraplasty. Overall, the pressures at which sutured linear dural incisions leaked were higher than the pressures at which sutured dural windows closed with duraplasties leaked.

CONCLUSION

In the experimental model described, an interrupted simple suturing technique affords the most watertight dural closure for linear incisions, whereas no suturing technique proved advantageous for the closure of a duraplasty.

Evaluation of a novel propylene oxide—treated collagen material as a dural substitute

Object. The authors evaluated a new non—cross-linked, propylene oxide—treated, acellular collagen matrix for use as a dural substitute in rabbits. They then compared this material to a commonly used dural substitute as well as to native dura mater used during primary closure.

Methods. Forty-six rabbits were randomly assigned to eight groups of five or six rabbits each. These groups differed according to the type of closure material that was used during surgery (native dura, control dural substitute, or experimental dural substitute) and the duration of convalescence. At the end of the experiment, the tightness of the duraplasty was assessed in each live rabbit by continuous infusion of fluid into the cisterna magna until leakage was detected. The animals were killed and each specimen was sectioned and studied histologically. The authors found that the experimental dural substitute was safe in animals for this application, that it held sutures well, and that a watertight closure was usually achieved. There were fewer adhesions between the experimental material and neural tissue was less likely to adhere to the cranium than the control graft. Histological examination showed that the experimental material had slightly more spindle cells and vascularity than the control graft.

Conclusions. The experimental graft material has several features that make it an attractive candidate for use as a dural substitute.

Composition and biomechanical properties of the bladder acellular matrix graft: comparative analysis in rat, pig and human

OBJECTIVE

To compare the composition and mechanical properties of the newly developed bladder acellular matrix graft (BAMG) with the normal urinary bladder in rat, pig and human.

MATERIALS AND METHODS

Rat, pig and human urinary bladders were harvested and divided into control and experimental groups. For the latter, BAMGs were prepared, and light and transmission electron microscopic studies performed. Strips from the normal bladders and the BAMGs (10 in each group) were tested under tension, and the ultimate tensile strength, maximum strain, and elastic modulus were determined from stress/strain curves.

RESULTS

Both types I and III collagen, as well as elastic fibres, were observed as major components of the matrix scaffold. There were more collagen type I fibres in the rat than in the pig and human BAMGs, whereas the pig, and particularly the human, both showed higher levels of type III collagen and elastic fibres. These different matrix scaffold patterns were confirmed by electron microscopy. Results from biomechanical testing showed no significant differences for strength, strain or elastic modulus between BAMG and control bladder strips, except in the rat where the maximum strain values were significantly lower.

CONCLUSION

There are variations in the acellular matrix structure with similar biomechanical properties between the BAMG and the normal urinary bladder in three different species. These results may underscore the potential of the BAMG. Furthermore, this in vitro model provides a suitable method to study the mechanical properties of the urinary bladder and may serve as a diagnostic tool for various investigations.

Duraplasty with freeze-dried cadaveric dura versus occipital pericranium for Chiari type I malformation: comparative study

During the period from October 1, 1989 to October 1, 1995 a total of 26 cases of Chiari type I malformation not associated with syringomyelia were attended in our Hospital. All patients underwent cranio-cervical decompression, with occipital craniectomy and removal of the posterior arch of C1. In 3/26 (11.5%) cases an additional C2 laminectomy had to be performed and in 1/26 (3.8%) case the C3 laminae were also removed. A first group of 13 patients underwent dural repair with freeze-dried cadaveric dura sutured with continuous 4-0 Vicryl running stitches, reinforced with fibrin sealant (Tissucol). A second group of 13 patients underwent duraplasty with autogenous occipital pericranium also sutured with continuous 4-0 Vycril but no fibrin sealant at all was added. In the first group, in which freeze-dried cadaveric dura plus Tissucol was used, there were 2/13 (15.3%) cases of CSF leak, requiring some additional skin stitches to stop the leak. In 5/13 (38.4%) cases there were notorious subcutaneous CSF accumulations that required repeated punctures plus compressive bandage. In 6/13 (46.1%) pseudomeningoceles appeared that took a year to clear completely. In the 13 patients who underwent dural repair with autogenous occipital pericranium watertight closure was achieved with sutures only, no fibrin sealant was added at all. Neither CSF leaks through the wound nor subcutaneous CSF accumulations were noted. We conclude that, in our hands, autologous pericranium taken from the occipital area, gives better results than freeze-dried cadaveric dura mater in duraplasty for surgical repair of Chiari type I malformation.