Plastination Technique Research Articles

Efficacy of different plastination techniques in lungs of goat: A comparative morphometric study

Efficacy of different plastination techniques in lungs of goat: A comparative morphometric study

Examination of upper respiratory tracts of Siirt-coloured mohair goats by scanning electron microscopy before and after plastination.

Present study was conducted to determine the changes in the surface structure of the upper respiratory tract of Siirt-coloured mohair goats by the silicone plastination method. Accordingly, the heads of 10 Siirt-coloured mohair goats procured from slaughterhouses were divided into two halves. Half of each head was plastinated. After macro-comparisons were made, the deformations of silicone plastination on the surface were examined by comparing the scanning electron microscope (SEM) findings of both upper respiratory tract tissue samples collected from plastinates and fresh material. When the data from scanning electron microscopy were analysed, cilia, cobblestone patterns, goblet cells and gland ducts on the epithelial surface were identified in areas on the upper respiratory tract. The SEM images of the plastinated tissues showed that the surface structures were degenerated due to the deformation of the surface epithelium. The plastination technique damaged the structures on the surface epithelium. Since the plastination technique and scanning electron microscopy have been studied together for the first time, we believe this would contribute to the scientific literature.

Morphometric and histopathological evaluation of modified Elnady's plastinated tissue compared to non-plastinated tissue: Highlighting its relevance for teaching and research.

The present study aims to evaluate the morphometric and histopathological properties of Modified Elnady's plastinated tissue after a period compared to non-plastinated tissue. The plastination technique is utilized in research and teaching due to the potential health risks associated with prolonged exposure to formalin. The tissues and organs are permanently dried during plastination and can be used for further anatomical, histopathological and surgical educational purposes. This method involves drying tissue and allowing synthetic materials like glycerin to permeate it. The study compared non-plastinated and plastinated tissue post-plastination to determine if structural alterations differed from those linked to plastination. The study examined the histopathological examination of dogs' skin, muscles, liver, lung, and intestine using formalin-fixed organs for paraffin embedding and previously plastinated organs for a plastinated group. The study examined non-plastinated and plastinated tissues, their histological composition and biometric parameters revealing typical structures in the non-plastinated group. Plasmodiumted tissues exhibited a compacted appearance, volume changes, nuclear clarity, and cytoplasmic hypereosinophilia, with statistical differences between the two groups. The study reveals that plastinated tissues, after 5 years of plastination, maintain their histological architecture well, with some exceptions. Plastinated tissues can be utilized in future microscopic and immunological studies and will be beneficial for teaching and research.

Qualitative Evaluation of Modified Polyvinyl Alcohol Gel Used as A Preservative Medium Compared to Traditional Modified Kaiserling Iii Solution in Pathology Museum

Pathology and anatomy museums preserve body tissues and organs traditionally in modified Kaiserling III solution and display in transparent glass jars, which serve as valuable teaching materials for students. Other techniques tried in preserving specimens are embedding in molten wax, embedding in epoxy resin, and plastination techniques. Modified Carbopol-940 gel has been tried recently as a preservative mounting medium in pathology museum. However, the use of modified Polyvinyl alcohol (PVA) gel as a preservative medium is not mentioned in the literature. Gel preservative medium can prevent leakage, toxic vapors, and irritation of eyes and skin. Aims: Qualitative evaluation of modified Polyvinyl alcohol gel as a preservative medium for specimens in pathology museums compared to modified Kaiserling III solution over one year. Objectives: 1) To qualitatively evaluate physical integrity of mounted tissue specimens stored in modified Kaiserling III solution and modified Polyvinyl alcohol gel for one year. 2) To qualitatively evaluate physical, chemical and microbiological parameters of modified Kaiserling III solution and modified Polyvinyl alcohol gel for one year. Materials and methods: In this qualitative cross-sectional study, six different organs, two sets each, were preserved in jars containing modified Kaiserling III solution and modified Polyvinyl alcohol gel. The media were evaluated for stability by physical tests, chemical test, and microbiological test, before and after the study. The specimens were assessed for physical disintegration by observing for tissue shredding, and evaluated for histopathological appearances, before and after the study. Results showed mild variability in stability of the preservative media but good tissue integrity of the specimens over a period of one year. 

Qualitative Evaluation of Carbopol-940 Gel Used as a Preservative Medium Compared to Traditional Modified Kaiserling III Solution in Pathology Museum

Introduction: Body organs and tissue specimens have been preserved in human and veterinary anatomy, pathology museums for years in traditional modified Kaiserling III solution. Wax embedding, epoxy-resin embedding and Plastination techniques have also been tried. However, the use of Carbopol-940 gel as a preservative medium is not mentioned in the literature. Gel preservative medium can prevent leakage, toxic vapors, and irritation of eyes and skin. Aims: Qualitative evaluation of carbopol-940 gel as a preservative medium for specimens in pathology museums compared to modified Kaiserling III solution over one year. Objectives: 1) To qualitatively evaluate physical integrity of mounted tissue specimens stored in Kaiserling III solution and carbopol-940 gel for one year. 2) To qualitatively evaluate physical, chemical and microbiological parameters of Kaiserling III solution and carbopol-940 gel for one year. Materials and methods: In this qualitative cross-sectional study, different organs were mounted in jars containing modified Kaiserling III solution and carbopol-940 gel. The media were monitored for stability by physical tests, chemical test, and microbiological test, before and after the study. The organs were monitored for physical disintegration by observing for tissue shredding. Specimens were histologically assessed before and after the study for tissue integrity. Results showed good stability of the preservative media and good tissue integrity of the specimens over a period of one year.

Anatomical evaluation and preparation procedure of a cross-sectioned kidney plastination of a thoroughbred horse with local polyester resin

This study aimed to develop a protocol for the thin section plastination of the kidney with local polyester resin and examine the anatomical details of this specimen. The sample was fixed with 10% formalin fixation solution and then sectioned into 3 mm slices. The four stages of the polyester plastination technique were used. Firstly, the samples were kept in 99.5% acetone baths at -25ºC for the dehydration. After this process, the sections were placed in polyester resin and the impregnation process was started at room temperature (20ºC) under vacuum. Following the forced impregnation, the curing chambers were constructed and the curing process was continued under ultraviolet light. The data of each applied stage were recorded carefully and the protocol for polyester plastination of kidney sections was successfully established. The specimens were observed from a different point of view with a thin cross-sectional appearance. The anatomical morphology and the structures of the sections of the kidney such as renal parenchyma and circulatory components were preserved well. The final products could be used as educational samples for cross-sectional anatomical training of kidneys.

Pituitary adenoma with oculomotor cistern extension: membranous anatomy and clinical application.

The anatomical basis of pituitary adenomas (PAs) with oculomotor cistern (OC) extension as a growth corridor is overlooked in the literature. In this paper, the authors use the technique of epoxy sheet plastination to study the membranous structure of the OC and validate the results by retrospective analysis of patients with OC extension. Eighteen specimens were used to study the membranous anatomy surrounding the OC using the epoxy sheet plastination technique. Thirty-four patients with OC extension were retrospectively reviewed. The OC consisted of two thin membranous layers. The inner layer was extended by the arachnoid layer from the posterior fossa, and the lateral layer consisted of the dura mater sinking from the roof of the cavernous sinus. The oculomotor nerve is more likely to displace with a superolateral trajectory due to the weakness of the posterior dura and the relatively large space in the medial and posterior trajectories, which is consistent with the intraoperative observations. Among the anatomical factors that affect the PA by OC extension, we found that the relative position of the internal carotid artery (ICA) and posterior clinoid process may lead to the narrowing of the OC. Of 34 cases, 28 patients achieved total resection. Among 24 preoperative patients with oculomotor nerve palsy, 16 cases were relieved to varying degrees postoperatively. There was no ICA injury or severe intracranial infection found in any of the patients. Extension into the OC is influenced by two anatomical factors: a weak point in the dura in the posterior OC and a potential space beyond this region of the dura. Meticulous knowledge of the membranous anatomy in endoscopic endonasal surgery is required to safely and effectively resect PA with OC extension.

Through the fingers: Use of plastinated anatomical specimens for visually impaired students.

The plastination technique produces non-toxic human tissues, ensuring their safe handling in educational settings. This investigation aimed to understand if visually impaired students profit from the use of plastinated anatomical specimens in learning the anatomy of the nervous system. For this purpose, their learning performance was compared to sighted and blindfolded students recruited from three primary schools in Fortaleza city, in the state of Ceará. Initially, a questionnaire was applied before carrying out the pedagogical practice, followed by an anatomy lecture with practical components with the use of plastinated anatomical specimens and synthetic anatomical models of the nervous system. After these steps, the students answered the questionnaire previously applied. Our results showed that the tactile perception of the visually impaired participants was significantly more developed compared to sighted (p < 0.001) and the blindfolded (p < 0.0001) students. The average of correct answers in the reapplied questionnaire was higher in the groups that used plastinated specimens (p < 0.05). In conclusion, the use of plastinated specimens has proven to be an effective tool in promoting a better understanding of anatomical structures, mainly for students with or without visual impairments, making it a valuable asset in anatomy teaching.

Macroscopic brain gray matter staining: historical protocol overview and neuroanatomy learning applications in second-year medical students.

Macroscopic staining in anatomical samples of the central nervous system is a technique that has been used for decades to achieve better differentiation of multiple gray matter structures, such as the cortex, basal ganglia, and cerebellar nuclei. Staining methods are based on using the different components of the brain, mainly the lipids present in the white matter. These techniques have been progressively forgotten while computer renderings are increasing; however, as a primary exposure to surgical anatomy, stained brain specimens are considered a helpful tool. We aim to summarize different staining techniques, their principles, and their current applications for neuroanatomy learning purposes. In total, four gray matter staining protocol descriptions (Mulligan's, Roberts's, Alston's, and Prussian Blue) were performed, as well as Likert scale surveys of second-year medical students about their perceptions of the stained sections. The results showed that the different macroscopic stains for brain tissue are based on lipid and reactant interactions, intending to increase the white matter (WM) and gray matter (GM) contrast. The search also showed that most staining protocols would take 2 days to develop. Efficient preservation options include submerging the sections in formaldehyde solutions, formaldehyde-free solutions, ethanol, or applying plastination techniques. Based on the student's perspective, the stained slices seem to be a valuable alternative to facilitate the study and identification of the basal ganglia and their relationships with the white matter (from 51.2 to 72% based on the Likert scale) compared with the non-stained sections. In conclusion, macroscopic staining of brain tissue continues to be a valuable tool for comprehensively studying the brain. Further research is needed to determine the efficacy of stained specimens as teaching tools.

Three-Dimensional Anatomy of the Hypoglossal Canal: A Plastinated Histologic Study

To provide a precise description of the morphology and morphometry of the hypoglossal canal (HC) and its relationship with surrounding structures by using the epoxy sheet plastination technique. Thirty human cadaveric heads were plastinated into 5 sets of gross transparent plastination slices and 43 sets of ultrathin plastination sections. The HC were examined at both macro- and micro levels in these plastination sections and the reconstructed 3-dimensional visualization model. The HC was an upward arched bony canal with a dumbbell-shaped lumen. According to the arched trajectory of its bottom wall, the HC could be divided into a medial ascending segment and a lateral descending segment. The thickness of the compact bone in the middle part of the HC was thinner than that at the intracranial and extracranial orifices. In 14 of 43 sides (32.6%), the posterior wall or the roof of the HC were disturbed by passing venous channels which communicated the posterior condylar emissary vein and the inferior petroclival vein. The trajectory of hypoglossal nerve in HC is mainly from anterosuperior to posteroinferior. The meningeal dura and the arachnoid extended into the HC along the hypoglossal nerve to form the dural and arachnoid sleeves and then fused with the nerve near the extracranial orifice of the HC. Knowledge of the detailed anatomy of the HC can be helpful in avoiding surgical complications when performing surgery for lesions and the occipital condylar screw placement in this complex area.

Plastination: A Novel Way of Preservation of Cadaveric Specimens for Teaching and Learning Human Anatomy

Plastination is a preservation method of anatomical specimens, which can be used for long-term educational purposes both in basic and clinical sciences. Dr. Gunther von Hagens first developed this technique in 1977 in Heidelberg, Germany. There are several plastination methods that are currently used in different countries. Room-temperature silicone plastination using ‘North Carolina technique’ is assumed as the best suited for our institutions considering our country’s climate and feasibility in terms of limited resources. In general, plastination methods involve four stages: i) fixation and specimen preparation; ii) dehydration and defatting; iii) plastic permeation or force impregnation by plastic material; and iv) hardening or curing. Fixation involves addition of formalin to the specimen for preventing decay and bacterial growth. Then dehydration is done by submerging the specimen in acetone baths. Thereafter, the specimen is kept in a vacuum chamber, where plastic permeation or forced impregnation occurs. Polymers penetrate the tissues of the specimen while removing acetone. After leaving the specimen in an airtight chamber maintaining a specific temperature, hardening or curing process follows. Plastination technique has several advantages like making cadaveric specimens easy to handle, easy storage of viscera, prolonged preservation, odourless, dry, non-irritant, nontoxic presentation and ability to present more anatomical details than ever before. Some important drawbacks are that the process is very costly, time consuming, limited size of the impregnation chamber, health and environmental hazards of the chemicals used. Plastination seems to have a great future in all fields of teaching, training and research not only in anatomy education but also in other disciplines in medical, biomedical, veterinary and health science institutions across the globe. Plastinates have opened several new windows to the world of anatomical sciences. Mediscope 2023;10(1): 31-37

Applying a Unified Model of Fiber Dissection, Tractography, Microscopic Anatomy and Plastination Techniques for Basic Neuroanatomy Education: Hacettepe University Experience

Anatomy education has gathered together a great many of many new modalities and was modified from classical lecture-based and laboratory practice system to the blended modules. In the scope of the present study, we develop a new, practical, cost- effective and efficient three dimensional (3D) educational model, which aimed to be helpful for the detection and better understanding of basic neuroanatomy education. Tractographic imaging, fiber dissection, microscopic anatomy and plastination techniques were applied to the white matter regions of the two brains. After the photographs that were taken were converted to 3D images, the specimens were plastinated. By way of establishing an educational model as a whole, we applied it to 202 second-year medical students. The students were separated into two groups when they attended to the theoretical lecture. Group 1 took the classical laboratory education; on the other hand, Group 2 received the newly designed educational model. Pre and post-tests were introduced to each group before and after laboratory sessions, respectively. The success scores were put to comparison. The average achievement scores of each group showed increase significantly (p<0.05) after the laboratory sessions, besides the increase in the post-test results of Group 2 was more statistically significant (p<0.05). Consequently, this new educational model enriched by newly designed unified methods could be regarded as useful for grasping and improving the basic neuroanatomy knowledge.

Bony Structures at the Attachment Areas of the Cruciate Ligaments in Human Knee Joints and Their Clinical Significance-Studied Using the P45 Plastination Technique

For treating cruciate ligament injuries, especially for characterizing the mechanics of the tunnel in cruciate ligament reconstruction, correctly understanding the bony information of the attachment area of the cruciate ligaments is significant. We studied 31 knee joints of middle-aged Chinese adults using the P45 sheet plastination technique, focusing on the attachment areas of the cruciate ligaments, especially the bony structures. The trabeculae at the attachment area were distributed radially and extended deep into the medial wall of the lateral condyle of the femur. However, in the anterior part of the intercondylar eminence, the trabeculae of the anterior group were parallelly arranged along the tendinous fibers of the anterior cruciate ligament, while the trabeculae of the posterior group were parallelly arranged along the perpendicular direction of the anterior cruciate ligament fibers. Similarly, at the attachment area of the lateral wall of the medial condyle of the posterior cruciate ligament, the trabeculae extended radially toward the deep medial condyle. Deep in the posterior part of the intercondylar eminence, the trabeculae were arranged longitudinally. In the anterior part of the intercondylar eminence, the trabeculae were parallelly arranged along the perpendicular directions of ligament fibers. The distribution patterns of the trabecular at the attachment areas of the cruciate ligaments at the ends of the femur and tibia were different. This difference should be considered when orthopedic surgeons reconstruct anterior cruciate ligaments.

The medial wall and medial compartment of the cavernous sinus: an anatomic study using plastinated histological sections

The medial wall of the cavernous sinus (CS) has a significant role in evaluation and treatment of pituitary adenomas. This study was conducted to clarify the fine architecture of the medial wall and medial compartment of the CS at both macro- and micro-levels in twenty-one human cadaveric heads by using the epoxy sheet plastination technique. The sellar part medial wall is an intact dural layer that separates the CS from the pituitary gland. This dural wall adhered to the diaphragma sellae and the periosteum of the sella turcica to form fibrous triangles. Eight micro-protrusions of the pituitary gland were found at both sides of that wall. The thickness of the sellar part medial wall at its central portion was significantly thinner than that at the other surrounding portions. From the superior view, tortuous intracavernous carotid arteries can be divided into outward bending type and inward bending type. The inward bending intracavernous carotid was apt to bent towards the central part of the sellar part medial wall, where there were usually wide and short fibrous bands with more densely stained connective tissues between them. The micro-protrusion of the pituitary gland in the medial wall of the CS could provide an anatomical basis for the occult tumor invasion and the recurrence of residual tumor. Different bending facing states of tortuous intracavernous carotid arteries in the lateral direction may be a factor of the determination of the direction of growth of pituitary tumors.

A new concept of the fiber composition of cervical spinal dura mater: an investigation utilizing the P45 sheet plastination technique

PurposeFew reports have been published regarding the microanatomy of the dura mater located at the craniovertebral junction (CVJ). In clinic, the precise microanatomy of the CVJ dura mater would be taken into account, for reducing surgical complications and ineffective surgical outcomes. The main objective of the present investigation was to further elucidate the fiber composition and sources of the cervical spinal dura mater.MethodsThe formalin-fixed adult head and neck specimens (n = 21) were obtained and P45 plastinated section method was utilized for the present study. The fibers of the upper cervical spinal dura mater (SDM) were examined in the P45 sagittal sections in the CVJ area. All photographic documentation was performed via a Canon EOS 7D Mark camera.ResultsThe posterior wall of the SDM sac at CVJ was found to be composed of stratified fibers, which are derived from three sources: the cerebral dura mater, the occipital periosteum, and the myodural bridge (MDB). The proper layer of the cerebral dura mater passes over the brim of the foramen magnum and enters the vertebral canal to form the inner layer of the SDM, and the fibers originating from the periosteum of the brim of the foramen magnum form the middle layer. The fibers of the MDB are inserted into the SDM and form its outer layer. It was found that the total number of fibers from each origin varied in humans.ConclusionAt the CVJ, the posterior wall of the SDM is a multi-layered structure composed of three different originated fibers. The cerebral dura mater, the periosteum located at the brim of the foramen magnum, and MDB contribute to the formation of the SDM. The present study would be beneficial to the choice of surgical approach at the CVJ and the protection of the SDB.

Congenital Atlanto-Occipital Fusion and its Effect on the Myodural Bridge: A Case Report Utilizing the P45 Plastination Technique

The atlanto-occipital joint is composed of the superior fossa of the lateral masses of the atlas (C1) and the occipital condyles. Congenital Atlanto-occipital fusion (AOF) involves the osseous union of the base of the occiput (C0) and the atlas (C1). AOF or atlas occipitalization/assimilation represents a craniovertebral junction malformation (CVJM) which can be accompanied by other cranial or spinal malformations. AOF may be asymptomatic or patients may experience symptoms from neural compression as well as limited neck movement. The myodural bridge (MDB) complex is a dense fibrous structure that connects the suboccipital muscular and its related facia to the cervical spinal dura mater, passing through both the posterior atlanto-occipital and atlanto-axial interspaces. It is not known if atlas occipitilization can induce structural changes in the MDB complex and its associated suboccipital musculature. The suboccipital region of a cadaveric head and neck specimen from an 87-year-old Chinese male having a congenital AOF malformation with resultant changes to the MDB complex was observed. After being treated with the P45 plastination method, multiple slices obtained from the cadaveric head and neck specimen were examined with special attention paid to the suboccipital region and the CVJM. Congenital atlanto-occipital fusion malformations are defined as partial or complete fusion of the base of the occiput (C0) with the atlas (C1). In the present case of CVJM, unilateral fusion of the left occipital condyle with the left lateral mass of C1 was observed, as well as posterior central fusion of the posterior margin of the foramen magnum with the posterior arch of C1. Also noted was a unilateral variation of the course of the vertebral artery due to the narrowed posterior atlanto-occipital interspace. Surprisingly, complete agenesis of the rectus capitis posterior minor (RCPmi) and the obliques capitis superior (OCS) muscles was also observed in the plastinated slices. Interestingly, the MDB, which normally originates in part from the RCPmi muscle, was observed to originate from a superior bifurcation within an aspect of the nuchal ligament. Therefore, the observed changes involving the MDB complex appear to be an effective compensation to the suboccipital malformations.

Using the silicon (luminal cast plastination technique) for the lower respiratory tract in sheep as an alternative to cement

Using the silicon (luminal cast plastination technique) for the lower respiratory tract in sheep as an alternative to cement

Using the silicon (luminal cast plastination technique) for the lower respiratory tract in sheep as an alternative to cement

The lower respiratory tract of sheep was studied to determine the torsion and branching of the bronchial tree. The respiratory system of ruminants and all living organisms is one of the most important organs in the body that controls the amount of gas exchange between the heart and lungs through the airways, it is clear that in sheep it consists of a narrow bronchial tube that reaches the extent of lung tissue repercussions. He used silicon, water, acid, and at room temperature, and the substance was injected with an injection gun through the trachea and was pushed gently to spread and distribute in all parts of the lungs with moderate manual pressure. The results showed that the mold shape in the lung and the bronchial branches of the bronchi is solid and anti-erosion with a very clear and three-dimensional appearance, easy to handle, store and carry for study and presentation purposes in scientific museums, and in scientific presentations as an anatomical method for large-scale teaching.

A new technique for preparing cadavers using PMMA: Rat and mouse example

BackgroundPolymethyl methacrylate is a member of the acrylic polymer family with superior optical properties. It is used in dentistry, hospital incubators, lenses, and various surgical fields, especially orthopedics. In this preliminary study, we aimed to prepare cadavers using the industrial form of polymethyl methacrylate. MethodsThe new technique consists of fixation, washing, purification, impregnation, and polymerization. For the study, two whole rat bodies, two rat front legs and two rat hind legs, one half rat body, two whole mouse bodies, and all internal organs were used. Wistar albino rats and BALB/c mice were used. After the cadaver samples were fixed and washed, they were passed through an alcohol series starting from 50%, completing the purification process. In the next step, a solution was prepared by mixing 100 ml of Thinner into 1000 ml of a mixture containing styrene, methyl methacrylate, and Co(II)2-ethyl hexanoate. The samples were immersed in the solution under negative pressure (from 10 mmHg to 400 mmHg), allowing the samples to absorb the solution thoroughly. They were then treated with methyl ethyl ketone peroxide and the polymerization step was terminated. ResultsThe cadaver samples obtained using polymer were hard, they maintained the given shape, and showed a relatively transparent quality. The production of these materials took 35 days, excluding fixation. The tissue samples were odorless in the process after polymerization. Also, there was no decay in the samples after the production stage and they could be stored under room conditions. ConclusionThis study determined that cadavers could be prepared using polymethyl methacrylate and methyl ethyl ketone peroxide. The polymer used here cost about $5. The cadavers can be safely exhibited in room conditions for five years without requiring special conditions like pools or cold storage. Further research should compare this technique with the plastination technique in terms of texture, color, weight, application time, and cost.

A validated instrument measuring students' perceptions on plastinated and three-dimensional printed anatomy tools.

Due to the modernization of the medical curriculum and technological advancements, anatomy education has evolved beyond cadaveric dissection alone. Plastination techniques, three-dimensional (3D) modeling, and 3D printing technologies have progressively gained importance. However, there are limited valid and reliable surveys to evaluate students' perceptions of these new anatomy tools. Hence, this study aimed to develop a validated instrument to measure students' learning satisfaction, self-efficacy, humanistic values, and perceived limitations of plastinated and 3D printed models. A 41-item survey (five-point Likert scale, 1 = strongly disagree to 5 = strongly agree) was administered to Year 1 undergraduate medical students following a randomized controlled crossover study that evaluated plastinated and 3D printed cardiac and neck models. Ninety-six responses were received, and a factor analysis was performed with the Kaiser-Meyer-Olkin sampling adequacy of 0.878. The confirmatory factor analysis yielded a 4-factor, 19 items model that had a good fit with the latent constructs of 2 (147) = 211.568, P < 0.001, root mean square error of approximation = 0.068, root mean square residual = 0.064, comparative fit index = 0.946, and Tucker Lewis index = 0.937. The Cronbach's alpha for the individual factors ranged from 0.74 to 0.95, indicating good internal consistency. This demonstrated a psychometrically valid and reliable instrument to measure students' perceptions toward plastinated and 3D printed models.