Evaluation of efficacy and biocompatibility of a novel semisynthetic collagen matrix as a dural onlay graft in a large animal model

The Use of Histoacryl Injections to Treat Subgaleal Cerebrospinal Fluid Collection After Cranioplasty

BACKGROUND AND OBJECTIVES

Cranioplasty is an important and basic operation in the neurosurgical field. An emergency craniectomy is performed to control malignant cerebral edema. If the patient survives, cranioplasty is performed to restore the skull defect; however, subgaleal cerebrospinal fluid collection (SCSFC) may occur. The authors aimed to identify risk factors for postoperative SCSFC and effective solutions with the subgaleal Histoacryl injection.

METHODS

From January 2020 to December 2022, 154 craniectomies were performed at our hospital to relieve significant cerebral edema after traumatic brain injury; of these, 67 patients survived and underwent cranioplasty. Ten cases of postcranioplasty SCSFC were identified, among which 6 received subgaleal Histoacryl injection.

RESULTS

Among the 10 SCSFC cases, 3 resolved with compression after cerebrospinal fluid aspiration, and 1 resolved after revision surgery and dural closure. Histoacryl injection was attempted for the other 6 patients. A single injection was sufficient for SCSFC resolution in 3 patients. One patient required 2 injections, and another required 3 injections. The remaining patient underwent epiduroperitoneal shunt surgery because of SCSFC persistence after 3 Histoacryl injections. Five of 6 patients (83.3%) showed an improvement of more than 80% after Histoacryl injection.

CONCLUSION

Subgaleal Histoacryl injection is not considered a fundamental treatment for postoperative SCSFC but can be a successful alternative treatment.

Dural Reconstruction Materials for the Repairing of Spinal Neoplastic Cerebrospinal Fluid Leaks

Spinal tumors often lead to more complex complications than other bone tumors. Nerve injuries, dura mater defect, and subsequent cerebrospinal fluid (CSF) leakage generally appear in spinal tumor surgeries and are followed by serious adverse outcomes such as infections and even death. The use of suitable dura mater replacements to achieve multifunctionality in fluid leakage plugging, preventing adhesions, and dural reconstruction is a promising therapeutic approach. Although there have been innovative endeavors to manage dura mater defects, only a handful of materials have realized the targeted multifunctionality. Here, we review recent advances in dura repair materials and techniques and discuss the relative merits in both preclinical and clinical trials as well as future therapeutic options. With these advances, spinal tumor patients with dura mater defects may be able to benefit from novel treatments.

The Role of Prolonged Bed Rest in Postoperative Cerebrospinal Fluid Leakage After Surgery of Intradural Pathology-A Retrospective Cohort Study

BACKGROUND

Postoperative cerebrospinal fluid leakage (CSFL) is a feared complication after surgery on intradural pathologies and may cause postoperative complications and subsequently higher treatment costs.

OBJECTIVE

To assess whether prolonged bed rest may lower the risk of CSFL.

METHODS

We performed a retrospective cohort study including patients with intradural pathologies who underwent surgery at our department between 2013 and 2021. Cohorts included patients who completed 3 days of postoperative bed rest and patients who were mobilized earlier. The primary end point was the occurrence of clinically proven CSFL.

RESULTS

Four hundred and thirty-three patients were included (female [51.7%], male [48.3%]) with a mean age of 48 years (SD ±20). Bed rest was ordered in 315 cases (72.7%). In 7 cases (N = 7/433, 1.6%), we identified a postoperative CSFL. Four of them (N = 4/118) did not preserve bed rest, showing no significant difference to the bed rest cohort (N = 3/315; P = .091). In univariate analysis, laminectomy (N = 4/61; odds ratio [OR] 8.632, 95% CI 1.883-39.573), expansion duraplasty (N = 6/70; OR 33.938, 95% CI 4.019-286.615), and recurrent surgery (N = 5/66; OR 14.959, 95% CI 2.838-78.838) were significant risk factors for developing CSFL. In multivariate analysis, expansion duraplasty was confirmed as independent risk factor (OR 33.937, 95% CI 4.018-286.615, P = .001). In addition, patients with CSFL had significant higher risk for meningitis (N = 3/7; 42.8%, P = .001).

CONCLUSION

Prolonged bed rest did not protect patients from developing CSFL after surgery on intradural pathologies. Avoiding laminectomy, large voids, and minimal invasive approaches may play a role in preventing CSFL. Furthermore, special caution is indicated if expansion duraplasty was done.

The collagen matrix dural substitute graft prevents postoperative cerebrospinal fluid leakage after ventriculoperitoneal shunt surgery in patients aged <1 year

Background:

Cerebrospinal fluid (CSF) leakage is a common complication of ventriculoperitoneal shunt (VPS) and has the potential to induce shunt infection. Especially in infants and children, these are serious complications. DuraGen is a collagen matrix dural substitute used to reduce the risk of CSF leakage in various neurosurgeries. We report our VPS procedure with DuraGen for preventing postoperative CSF leakage in patients aged <1 year.

Methods:

We used DuraGen to prevent postoperative CSF leakage in six VPS surgeries. Antibiotic-impregnated shunt catheters and programmable valves with anti-siphon devices were also used in all cases. DuraGen was placed inside and atop the burr hole. All cases had an initial shunt pressure of 5 cmH2O. Fibrin glue was not used.

Results:

The patients underwent follow-up for a year after VPS surgery. There was no postoperative subcutaneous CSF collection or leakage after all six VPS surgeries. Furthermore, no postoperative shunt infections or DuraGen-induced adverse events were noted.

Conclusion:

We speculate that DuraGen has a preventive effect on postoperative CSF leakage in VPS cases aged <1 year.

Absorbable Artificial Dura Versus Nonabsorbable Artificial Dura in Decompressive Craniectomy for Severe Traumatic Brain Injury: A Retrospective Cohort Study in Two Centers

Background

Severe traumatic brain injury (TBI) patients usually need decompressive craniectomy (DC) to decrease intracranial pressure. Duraplasty is an important step in DC with various dura substitute choices. This study aims to compare absorbable dura with nonabsorbable dura in duraplasty for severe TBI patients.

Methods

One hundred and three severe TBI patients who underwent DC and dura repair were included in this study. Thirty-nine cases used absorbable artificial dura (DuraMax) and 64 cases used nonabsorbable artificial dura (NormalGEN). Postoperative complications, mortality and Karnofsky Performance Scale (KPS) score in one year were compared in both groups.

Results

Absorbable dura group had higher complication rates in transcalvarial cerebral herniation (TCH) (43.59% in absorbable dura group vs. 17.19% in nonabsorbable dura group, P = 0.003) and CSF leakage (15.38% in absorbable dura group vs. 1.56% in nonabsorbable dura group, P = 0.021). But severity of TCH described with hernial distance and herniation volume demonstrated no difference in both groups. There was no statistically significant difference in rates of postoperative intracranial infection, hematoma progression, secondary operation, hydrocephalus, subdural hygroma and seizure in both groups. KPS score in absorbable dura group (37.95 ± 28.58) was statistically higher than nonabsorbable dura group (49.05 ± 24.85) in one year after operation (P = 0.040), while no difference was found in the rate of functional independence (KPS ≥ 70). Besides, among all patients in this study, TCH patients had a higher mortality rate (P = 0.008), lower KPS scores (P < 0.001) and lower functionally independent rate (P = 0.049) in one year after surgery than patients without TCH.

Conclusions

In terms of artificial biological dura, nonabsorbable dura is superior to absorbable dura in treatment of severe TBI patients with DC. Suturable nonabsorbable dura has fewer complications of TCH and CFS leakage, and manifest lower mortality and better prognosis. Postoperative TCH is an important complication in severe TBI which usually leads to a poor prognosis.

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.

A Multilayered Dural Repair Technique Using Duragen for Early Cranioplasty Following Decompressive Craniotomy

Decompressive craniotomy is a neurosurgical emergency procedure in which a large skull bone is removed and the dura matter is extensively opened. Duraplasty is required to avoid cerebrospinal fluid (CSF) leakage during the decompressive craniotomy. DuraGen® is a safe and effective type I collagen matrix graft, which is frequently used in decompressive craniotomy procedures. Since DuraGen® does not require labor-intensive suturing, the operative time is shortened by DuraGen® closure with sufficient tightness preventing CSF leakage. Recently, early cranioplasty is preferred to achieve efficient rehabilitation after decompressive craniotomy. Although evidence of efficacy and safety of DuraGen® has been increasing in the management of duraplasty, no reports have previously discussed the condition of DuraGen® during the second surgery (cranioplasty) at this early timing. DuraGen®-derived neodura develops a mature dura 1 year post its placement, and the neodura remain fragile at this early time point. A deconstructed fragile neodura may result in postoperative CSF leakage. Here, we illustrated a multilayered dural repair technique with DuraGen® to avoid disruption of the fragile neodura during early cranioplasty.

Effect of a bovine collagen matrix on tendon adhesions during the repair of rat Achilles tendon

Adhesion after a tendon injury is one of the major problems following upper extremity surgery. In the present study, we evaluated a new material that is clinically usable as an adhesion barrier. Twenty-four male Wistar albino rats were used in the study. These rats (48 legs) were divided into three groups: sham, control, and experimental. No surgical intervention was performed in the sham group. After making a full-thickness cut through the right Achilles tendon, the tendon was repaired using the modified Kessler technique in the control group, while bovine collagen matrix was wrapped around the surgically repaired tendon using the modified Kessler technique in the experimental group. Two months after surgery, the operated and non-operated tendons were resected and analyzed through biomechanical, macroscopic, and histopathological examinations. The results of the biomechanical testing did not differ significantly between the control and experimental groups. Macroscopic examination of the adhesions revealed less adhesions in the experimental group but this difference was not statistically significant. Moreover, the results of the histopathological examination, which was performed based on five criteria, did not differ significantly between the two groups. Our study's results indicate that a bovine collagen matrix can be used to prevent tendon adhesion; however, larger studies are needed to verify these findings.

In vivo Evaluation of Fibrous Collagen Dura Substitutes

Dura substitutes are applied in duraplasty to repair lost or damaged dura. Collagen-based dura substitutes are mainstream products in both the US and Chinese markets. In this study, dura substitute devices with potential dura regeneration ability are evaluated. The dura substitutes are composed of fibrous type I collagen that were purified from bovine tendon. Physical and chemical characterization demonstrated that the tested dura substitute has desirable porous scaffolding structures and is composed of highly purified type I collagen. The collagen dura substitutes were further investigated in vivo with a rabbit model for 6 months to evaluate their safety and performance to repair and regenerate dura. No inflammation or infection was observed during the course of in vivo study. The integration of the collagen dura substitutes with surrounding tissue was normal as compared to native tissue. The macroscopic and microscopic histological assessments of the sampled animal tissue showed that the damaged dura were regenerated. The collagen dura substitutes were resorbed between 3 and 6 months along with newly regenerated dura. Both tissue adhesion and dura repair was the worst in blank control group as compared to those in the collagen dura substitutes. Taken together, regenerative collagen dura substitutes demonstrated with suitable physicochemical properties. The in vivo evaluation in a rabbit model further demonstrated the safety and performance of such substitutes for dura repair and regeneration.

Effect of Durotomy versus Myelotomy on Tissue Sparing and Functional Outcome after Spinal Cord Injury

Various surgical strategies have been developed to alleviate elevated intraspinal pressure (ISP) following acute traumatic spinal cord injury (tSCI). Surgical decompression of either the dural (durotomy) or the dural and pial (myelotomy) lining of the spinal cord has been proposed. However, a direct comparison of these two strategies is lacking. Here, we compare the histological and functional effects of durotomy alone and durotomy plus myelotomy in a rodent model of acute thoracic tSCI. Our results indicate that tSCI causes local tissue edema and significantly elevates ISP (7.4 ± 0.3 mmHg) compared with physiological ISP (1.7 ± 0.4 mmHg; p < 0.001). Both durotomy alone and durotomy plus myelotomy effectively mitigate elevated local ISP (p < 0.001). Histological examination at 10 weeks after tSCI revealed that durotomy plus myelotomy promoted spinal tissue sparing by 13.7% compared with durotomy alone, and by 25.9% compared with tSCI-only (p < 0.0001). Both types of decompression surgeries elicited a significant beneficial impact on gray matter sparing (p < 0.01). Impressively, durotomy plus myelotomy surgery increased preservation of motor neurons by 174.3% compared with tSCI-only (p < 0.05). Durotomy plus myelotomy surgery also significantly promoted recovery of hindlimb locomotor function in an open-field test (p < 0.001). Interestingly, only durotomy alone resulted in favorable recovery of bladder and Ladder Walk performance. Combined, our data suggest that durotomy plus myelotomy following acute tSCI facilitates tissue sparing and recovery of locomotor function. In the future, biomarkers identifying spinal cord injuries that can benefit from either durotomy alone or durotomy plus myelotomy need to be developed.

Applications of materials for dural reconstruction in pre-clinical and clinical studies: Advantages and drawbacks, efficacy, and selections

The dura mater provides a barrier to protect the tissue underneath and cerebrospinal fluid. However, dural defects normally cause cerebrospinal fluid leakage and other complications, such as wound infections, meningitis, etc. Therefore, the reconstruction of dura mater has important clinical significance. Current dural reconstruction materials include: homologous, acellular, natural, synthetic, and composite materials. This review comprehensively summarizes the characteristics and efficacy of these dural substitutes, especially in clinical applications, including the advantages and drawbacks of those from different sources, the host tissue response in pre-clinical studies and clinical practice, and the comparison of these materials across different surgical procedures. Furthermore, the selections of materials for different surgical procedures are highlighted. Finally, the challenges and future perspectives in the development of ideal dural repair materials are discussed.

In vivo evaluation of bilayer ORC/PCL composites in a rabbit model for using as a dural substitute

OBJECTIVE

After a neurosurgical procedure, dural closure is commonly needed to prevent cerebrospinal fluids (CSF) leakage and to reduce the risk of complications, including infections and chronic inflammatory reactions. Although several dural substitutes have been developed, their manufacturing processes are complicated and costly and that many of them have been implicated in causing postoperative complications. This study aimed to assess the effectiveness and safety of new bilayer ORC/PCL composites in a rabbit model.

METHODS

Two formulations of bilayer oxidized regenerated cellulose (ORC)/poly ε-caprolactone (PCL) knitted fabric-reinforced composites and an autologous graft (pericranium) were employed for dural closure in forty-five male rabbits. Systemic reaction and the local reaction of the samples were assessed and compared at one-, three- and six-months post-implantation by blood chemistry and gross, and microscopic assessment using hematoxylin-eosin and Masson's trichrome stains.

RESULTS

No signs of CSF leakage or systemic infection were seen for all samples. All samples demonstrated minimal adhesion to adjacent tissues. The degree of host fibrous connective tissue ingrowth into both composites was comparable to that of the autologous group, but bone formation and osteoclast activities were significantly greater. Both composites progressively degraded over times and the residual thickness of the nonporous layer was 50% of the initial thickness at six months post-implantation.

DISCUSSION

Bilayer ORC/PCL composites were successfully employed for dural closure in the rabbit model. They were biocompatible and could support dural regeneration comparable to that of the autologous group, but induced greater osteogenesis.

Performance evaluation of bilayer oxidized regenerated cellulose/poly ε-caprolactone knitted fabric-reinforced composites for dural substitution

Ideally, alloplastic dural substitute should have functional properties resembling human dura mater and retain a watertight closure to prevent cerebrospinal leakage. Therefore, functional properties for successful dural closure application of newly developed bilayer oxidized regenerated cellulose knitted fabric/poly ε-caprolactone knitted fabric-reinforced composites were studied and compared with human cadaveric dura mater and three commercial dural substitutes including two collagen matrices and one synthetic poly-L-lactide patch. It was found that oxidized regenerated cellulose knitted fabric/poly ε-caprolactone knitted fabric-reinforced composites uniquely contained a bilayer structure consisting of micropores distributed within the relatively dense microstructure. Density, tensile properties and stitch tear strength of oxidized regenerated cellulose knitted fabric/poly ε-caprolactone knitted fabric-reinforced composites were found to be closed to human cadaveric dura mater than those of dense-type and porous-type dural substitutes. Water tightness performance in both sutured and non-sutured forms of oxidized regenerated cellulose knitted fabric/poly ε-caprolactone knitted fabric-reinforced composites was slightly inferior to human cadaveric dura mater, but still better than those of commercial dural substitutes. This study revealed that oxidized regenerated cellulose knitted fabric/poly ε-caprolactone knitted fabric-reinforced composite showed better functional properties than typical dural substitutes and was found to be a good candidate for being employed as a dural substitute. The role and relationship of both microstructure and the type of materials on the functional properties and water tightness of the dural substitutes were also elucidated.

EFFECT OF PLATELET-RICH PLASMA, FAT PAD AND DURAL MATRIX IN PREVENTING EPIDURAL FIBROSIS

OBJECTIVE

Epidural fibrosis is one of the main reasons for requiring repeated surgical intervention. Our objective was to compare the effect of Platelet Rich Plasma (PRP) on the development of epidural fibrosis with collagen dural matrix and free autogenous fat graft.

METHODS

Male rats were separated into 3 groups. Laminectomy was implemented on the rats and epidural fat pad was placed in the first group (n = 7); equal size of collagen dural matrix was applied in the second group (n = 7); a single dose of PRP was applied in the third group (n = 7).

RESULTS

Epidural fibrosis was more common in the group that collagen dural matrix was applied when compared the ones that PRP was applied. PRP group presented better values in preventing epidural fibrosis when compared to the fat pad group, however this difference was not statistically significant.

CONCLUSION

PRP is a material that can be easily obtained from the very blood of patients and at an extremely low cost; the main clinical relevance of our study is that the PRP might be an efficient material for better clinical results after laminectomy surgery due to its tissue healing and epidural fibroris preventing potentials. Level of Evidence V, Animal research.

A Stable Large Animal Model for Dural Defect Repair with Biomaterials and Regenerative Medicine

IMPACT STATEMENT

Using biomaterials and regenerative medicine to repair tissue defects has been a very hot research field, during which the development of stable large animal models with appropriate biotechnology is crucial. Recently, more and more researchers are paying attention to dural defect repair. However, the lack of widely recognized stable large animal models has seriously affected the related further research. In this study, a stable large animal dural defect model is developed exactly for the first time. Therefore, the article would attract considerable attention and be highly cited after publication.

Bilayer oxidized regenerated cellulose/poly ε-caprolactone knitted fabric-reinforced composite for use as an artificial dural substitute

A novel bilayer knitted fabric-reinforced composite for potentially being used as a dural substitute was developed by solution infiltration of oxidized regenerated cellulose knitted fabric (ORC) with poly ε-caprolactone (PCL) solution at various concentrations ranging 10-40 g/100 mL. It was found that the density of all formulations did not differ significantly and was lower than that of the human dura. Microstructure of the samples typically comprised a bilayer structure having a nonporous PCL layer on one side and the ORC/PCL composite layer on another side. Tensile modulus and strength of the samples initially decreased with increasing PCL solution concentration for up to 20 g/100 mL and re-increased again with further increasing PCL solution concentration. Strain at break of all formulations were not significantly different. Watertight test revealed that all composites could prevent leakage at the pressure within the normal range of intracranial pressure. In vitro degradation study revealed that the weight loss percentage and change in tensile properties of all samples displayed biphasic profile comprising an initially rapid decrease and followed by a gradual decrease with incubation times afterward. Micro and macro porous channels were observed to be in situ generated in the composite layer by ORC dissolution and PCL resorption during degradation while nonporous layer remained relatively unchanged. The degradation rate was found to decrease with increasing PCL solution concentration. In vitro biocompatibility using alamar blue assay on selected samples showed that fibroblasts could attach and proliferate well at all incubation periods.

Intrathecal decompression versus epidural decompression in the treatment of severe spinal cord injury in rat model: a randomized, controlled preclinical research

Background

In the setting of severe spinal cord injury (SCI), there is no markedly efficacious clinical therapeutic regimen to improve neurological function. After epidural decompression, as is shown in animal models, the swollen cord against non-elastic dura and elevation of intrathecal pressure may be the main causes of aggravated neurologic function. We performed an intrathecal decompression by longitudinal durotomy to evaluate the neuroprotective effect after severe SCI by comparing with epidural decompression.

Methods

Eighty-four adult male Sprague-Dawley rats were assigned to three groups: sham group (group S), epidural decompression (group C), and intrathecal decompression group (group D). A weight-drop model was performed at T9. The Basso-Beattie-Bresnahan (BBB) score was used to evaluate neurological function. Animals were sacrificed at corresponding time points, and we performed pathohistological examinations including HE staining and immunohistochemical staining (IHC) of glial fibrillary acidic protein (GFAP), neurocan, and ED1 at the epicenter of injured cords. Finally, the lesions were quantitatively analyzed by SPSS 22.0.

Results

The mortality rates were, respectively, 5.55 % (2/36) and 13.9 % (5/36) in groups C and D, and there was no significant difference between groups C and D (P = 0.214). Compared with epidural decompression, intrathecal decompression could obviously improve BBB scores after SCI. HE staining indicated that more white matter was spared, and fewer vacuoles and less axon degradation were observed. The expression peak of GFAP, neurocan, and ED1 occurred at an earlier time and was down-regulated in group D compared to group C.

Conclusions

Our findings based on rat SCI model suggest that intrathecal decompression by longitudinal durotomy can prompt recovery of neurological function, and this neuroprotective mechanism may be related to the down-regulation of GFAP, neurocan, and ED1.

A NOVEL FOAMY COLLAGEN AS A DURAL SUBSTITUTE

This study developed an innovative foamy collagen dural substitute. The foamy collagen was prepared by mixing collagen hydrogel and high-pressure oxygen in a stainless steel bottle as a container. A foamy collagen with 101 ± 43 μm in pore size and 50.5 ± 5.1% in porosity formed after release from the container. In the results of the in vitro degradation experiment, foamy collagen degraded slower than the commercially available DuraGen treated with 5 units/mL of collagenase solution. DuraGen degraded completely within three hours and foamy collagen had 39.2% (mean) of its original mass remaining 24 h after immersing in collagenase solution. The oxygen bubble structure was immobilized by the collagen fibrillogenesis and remained intact 3 and 7 days after subcutaneous implantation of the foamy collagen in rats, without any escape or merge of the oxygen bubbles. Fibrous tissue proliferated along the porous structure from the edge of the foamy collagen according to the histology analysis of subcutaneous implantation experiment in rats. The results of in vivo rabbit duraplasty experiment showed that the regenerated dura in foamy collagen group was thicker than that in DuraGen group, and was comparable to the native dura mater, without causing any adverse effects, such as intracranial pressure increase or cerebrospinal fluid leakage.