Polyester wax: a new embedding medium for the histopathologic study of human temporal bones

Section thickness is identical for the sliding microtome and rotary microtome under the continuous cooling device condition

To date, no report has compared section thickness (ST) between the sliding microtome (SM) and rotary microtome (RM). We used the ice pack (IP) condition, in which the paraffin block was not cooled during slicing, and a continuous cooling device (CCD) for continuous cooling during slicing. The ST was greater for the SM than the RM in the IP condition, but it was identical between the devices under the CCD condition. Thus, we used the CCD condition for subsequent studies. In formalin-fixed, paraffin-embedded (FFPE) fish sausage blocks, the ST of the tissue surface (T-surface) was significantly concaved compared to that of the paraffin surface (P-surface) for both microtomes. On the contrary, in FFPE human kidney blocks, ST did not differ between the T-surface and P-surface. Furthermore, the eosin-positive area of PAM-stained specimens was affected by ST, and the color tone of the thickest sample differed from that of the median or thinnest sample. Our data indicated that we should use CCD conditions to ensure that ST is uniform regardless of the type of microtome. In addition, for quantitative analysis, we should utilize ST measure equipment and specimens with a constant ST.

Structural brain preservation: a potential bridge to future medical technologies

When faced with the prospect of death, some people would prefer a form of long-term preservation that may allow them to be restored to healthy life in the future, if technology ever develops to the point that this is feasible and humane. Some believe that we may have the capacity to perform this type of experimental preservation today-although it has never been proven-using contemporary methods to preserve the structure of the brain. The idea is that the morphomolecular organization of the brain encodes the information required for psychological properties such as personality and long-term memories. If these structures in the brain can be maintained intact over time, this could theoretically provide a bridge to access restorative technologies in the future. To consider this hypothesis, we first describe possible metrics that can be used to assess structural brain preservation quality. We next explore several possible methods to preserve structural information in the brain, including the traditional cryonics method of cryopreservation, as well as aldehyde-stabilized cryopreservation and fluid preservation. We focus in-depth on fluid preservation, which relies on aldehyde fixation to induce chemical gel formation in a wide set of biomolecules and appears to be a cost-effective method. We describe two theoretical recovery technologies, alongside several of the ethical and legal complexities of brain preservation, all of which will require a prudent approach. We believe contemporary structural brain preservation methods have a non-negligible chance of allowing successful restoration in the future and that this deserves serious research efforts by the scientific community.

A fully-flexible and thermally adjustable implantable neural probe with a U-turn polyester microchannel

This work presents a fully flexible implantable neural probe fabricated with Polydimethylsiloxane (PDMS) and including a thermally-tunable stiffness microchannel filled with Polyester. The probe includes an optimized microfluidics mixer for drug delivery. Polyester, which is solid at room temperature and has a low melting point close to body temperature, is used to decrease the stiffness of the probe after insertion, after getting in contact with tissues. We designed a U-turn microchannel inside the PDMS neural probe and filled it up with melted polyester. The microchannel has a cross-section of 30 μm × 5 μm and a length of 14.7 mm. The following probe dimensions were chosen after extensive simulation: thickness = 20 μm, width = 300 μm, and length = 7 mm. These values yield a buckling force above 1 mN, which is sufficient for proper insertion into the brain tissues. Simulation results show that the microfluidics mixer with a cross-section of 90 μm × 5 μm and a length of 7 mm has optimum performance for the desired flow rate and quantity of drug to deliver. The pressure drop inside the microfluidic channel is less than 0.43 kPa, which is appropriate for PDMS-PDMS bonding, whereas the Reynolds number is near 1.91k in the laminar regime. No leakage or bubble occurred during the experimental validation, which suggests an appropriate pressure and a laminar flow in the channel.

A guide to preclinical evaluation of hydrogel-based devices for treatment of cartilage lesions

The drive to develop cartilage implants for the treatment of major defects in the musculoskeletal system has resulted in a major research thrust towards developing biomaterial devices for cartilage repair. Investigational devices for the restoration of articular cartilage are considered as significant risk materials by regulatory bodies and therefore proof of efficacy and safety prior to clinical testing represents a critical phase of the multidisciplinary effort to bridge the gap between bench and bedside. To date, review articles have thoroughly covered different scientific facets of cartilage engineering paradigm, but surprisingly, little attention has been given to the preclinical considerations revolving around the validation of a biomaterial implant. Considering hydrogel-based cartilage products as an example, the present review endeavors to provide a summary of the critical prerequisites that such devices should meet for cartilage repair, for successful implantation and subsequent preclinical validation prior to clinical trials. Considerations pertaining to the choice of appropriate animal model, characterization techniques for the quantitative and qualitative outcome measures, as well as concerns with respect to GLP practices are also extensively discussed. This article is not meant to provide a systematic review, but rather to introduce a device validation-based roadmap to the academic investigator, in anticipation of future healthcare commercialization. STATEMENT OF SIGNIFICANCE: There are significant challenges around translation of in vitro cartilage repair strategies to approved therapies. New biomaterial-based devices must undergo exhaustive investigations to ensure their safety and efficacy prior to clinical trials. These considerations are required to be applied from early developmental stages. Although there are numerous research works on cartilage devices and their in vivo evaluations, little attention has been given into the preclinical pathway and the corresponding approval processes. With a focus on hydrogel devices to concretely illustrate the preclinical path, this review paper intends to highlight the various considerations regarding the preclinical validation of hydrogel devices for cartilage repair, from regulatory considerations, to implantation strategies, device performance aspects and characterizations.

Immunohistochemical techniques for the human inner ear

In this review, we provide a description of the recent methods used for immunohistochemical staining of the human inner ear using formalin-fixed frozen, paraffin and celloidin-embedded sections. We also show the application of these immunohistochemical methods in auditory and vestibular endorgans microdissected from the human temporal bone. We compare the advantages and disadvantages of immunohistochemistry (IHC) in the different types of embedding media. IHC in frozen and paraffin-embedded sections yields a robust immunoreactive signal. Both frozen and paraffin sections would be the best alternative in the case where celloidin-embedding technique is not available. IHC in whole endorgans yields excellent results and can be used when desiring to detect regional variations of protein expression in the sensory epithelia. One advantage of microdissection is that the tissue is processed immediately and IHC can be made within 1 week of temporal bone collection. A second advantage of microdissection is the excellent preservation of both morphology and antigenicity. Using celloidin-embedded inner ear sections, we were able to detect several antigens by IHC and immunofluorescence using antigen retrieval methods. These techniques, previously applied only in animal models, allow for the study of numerous important proteins expressed in the human temporal bone potentially opening up a new field for future human inner ear research.

An Improved Immunostaining and Imaging Methodology to Determine Cell and Protein Distributions within the Bone Environment

Bone is a dynamic tissue that undergoes multiple changes throughout its lifetime. Its maintenance requires a tight regulation between the cells embedded within the bone matrix, and an imbalance among these cells may lead to bone diseases such as osteoporosis. Identifying cell populations and their proteins within bone is necessary for understanding bone biology. Immunolabeling is one approach used to visualize proteins in tissues. Efficient immunolabeling of bone samples often requires decalcification, which may lead to changes in the structural morphology of the bone. Recently, methyl-methacrylate embedding of non-decalcified tissue followed by heat-induced antigen retrieval has been used to process bone sections for immunolabeling. However, this technique is applicable for bone slices below 50-µm thickness while fixed on slides. Additionally, enhancing epitope exposure for immunolabeling is still a challenge. Moreover, imaging bone cells within the bone environment using standard confocal microscopy is difficult. Here we demonstrate for the first time an improved methodology for immunolabeling non-decalcified bone using a testicular hyaluronidase enzyme-based antigen retrieval technique followed by two-photon fluorescence laser microscopy (TPLM) imaging. This procedure allowed us to image key intracellular proteins in bone cells while preserving the structural morphology of the cells and the bone.

Modified paraffin-embedding method for the human cochlea that reveals a fine morphology and excellent immunostaining results

CONCLUSION

A modified paraffin-embedding method could be applied to histopathological and immunohistochemical studies of the human cochlea. The complementary use of molecular and immunohistochemical techniques by means of this method is thus considered to be a valuable tool for the future study of the human inner ear.

OBJECTIVE

To propose a new paraffin-embedding method for the morphological and immunohistochemical study of the human cochlea.

METHODS

Five human temporal bones were harvested at autopsy. The temporal bone specimens were fixed in 20% buffered formalin, decalcified with EDTA, cropped to a cube of approximately 15 mm, embedded in paraffin, and then cut into 6 microm thick sections. The sections were stained with hematoxylin and eosin, and immunostained with anti-prestin and anti-neurofilament antibodies.

RESULTS

Although paraffin-embedded sections cannot show the excellent morphology of the delicate membranous labyrinth obtained with celloidin, this technique successfully preserved the morphology of the cochlea, especially the organ of Corti, thereby enabling us to obtain excellent immunostaining results.

Techniques of celloidin removal from temporal bone sections

OBJECTIVES

We sought to determine whether the technique of celloidin removal influences the results of immunostaining in celloidin-embedded cochleae.

METHODS

We compared four protocols of celloidin removal, including those using clove oil, acetone, ether-alcohol, and methanol saturated with sodium hydroxide. By optimally fixing our tissue (perfused mice), and keeping constant the fixative type (formalin plus acetic acid), fixation time (25 hours), and decalcification time (ethylenediaminetetraacetic acid for 7 days), we determined whether the technique of celloidin removal influenced the immunostaining results. Six antibodies were used with each removal method: prostaglandin D synthase, sodium, potassium adenosine triphosphatase (Na+,K(+)-ATPase), aquaporin 1, connective tissue growth factor, tubulin, and 200 kd neurofilament.

RESULTS

Clove oil, acetone, and ether-alcohol resulted in incomplete removal of the celloidin, thereby negatively affecting the results of immunostaining. The methanol-sodium hydroxide method was effective in completely removing the celloidin; it produced the cleanest and most reproducible immunostaining for all six antibodies.

CONCLUSIONS

Freshly prepared methanol saturated with sodium hydroxide and diluted 1:2 with methanol was the best solvent for removing celloidin from mouse temporal bone sections, resulting in consistent and reproducible immunostaining with the six antibodies tested.

Histopathology of nonsyndromic autosomal dominant midfrequency sensorineural hearing loss

BACKGROUND

Autosomal dominant, nonsyndromic, midfrequency sensorineural hearing loss (SNHL) is a well-known clinical entity. There are no reported histopathologic studies of temporal bones from individuals with such a hearing loss.

OBJECTIVES

To describe the otopathology in 2 affected individuals from 2 different kindreds with nonsyndromic, dominant, midfrequency SNHL.

MATERIAL AND METHODS

Both subjects belonged to multigenerational families with nonsyndromic, autosomal dominant SNHL showing a cookie-bite pattern. Temporal bones were removed at autopsy and studied by light microscopy. Cytocochleograms were constructed for hair cells, stria vascularis, and cochlear neuronal cells.

RESULTS

Subject 1 (a 77-yr-old man) from Kindred A was diagnosed in early childhood with an SNHL that was progressive, reaching profound levels by adulthood. Both cochleae showed complete loss of inner and outer hair cells, moderate to severe diffuse atrophy of the stria vascularis, and severe loss of cochlear neurons, including the peripheral dendrites. The hearing loss in Subject 2 (an 82-yr-old man from Kindred B) began in late childhood, was slowly progressive, and involved the higher frequencies later in life. Histopathology showed loss of outer and inner hair cells in the basal turn of the cochlea, moderate to severe loss of stria vascularis, but relative preservation of peripheral dendrites and cochlear neurons.

CONCLUSION

The main histopathologic abnormalities were loss of hair cells, stria vascularis, and cochlear neurons in 1 case and loss of hair cells and stria vascularis in the second case. Our results are consistent with the hypothesis that dysfunction and loss of hair cells may have been the primary histopathologic correlate for the midfrequency hearing losses in these 2 subjects.

Effects of fixative and embedding medium on morphology and immunostaining of the cochlea

The localization of proteins by immunostaining is a powerful method to investigate otologic disorders. However, the use of fixatives and embedding media (necessary for the preservation of morphology) can obscure antigens, making it difficult to perform immunoassays. We performed a systematic investigation of the effects of fixative and embedding medium on morphology and immunostaining of the mouse cochlea. Three different fixative solutions [4% formaldehyde (F), 4% formaldehyde + 1% acetic acid (FA), and 4% formaldehyde + 1% acetic acid + 0.1% glutaraldehyde (FGA)] and 3 different embedding media (paraffin, polyester wax, and celloidin) were used. Morphology was assessed using light microscopy. Immunostaining was studied using a panel of 6 antibodies (to prostaglandin D synthase, aquaporin 1, connective tissue growth factor, 200-kDa neurofilament, tubulin and Na(+),K(+)-ATPase). Preservation of morphology was suboptimal with paraffin, adequate with polyester wax and superb with celloidin. Immunostaining was successful using all 6 antibodies in all 3 fixatives and all 3 embedding media. While there were differences in strength of signal and localization of antigen between the 3 fixatives, overall, FA and FGA gave the most uniform results. For a given fixative and antibody, there was surprisingly little difference in the quality of immunostaining between celloidin and paraffin, while results in polyester wax were not as good in some cases. These results suggest that celloidin may be the embedding medium of choice for both morphological and pathological studies, including immunostaining when morphology must be optimized.

Quantitative analysis of mRNA in human temporal bones

CONCLUSION

Well-preserved mRNA could be extracted from frozen human inner ears. Therefore, this study demonstrates that analysis of mRNA could be performed to study the molecular mechanisms of inner ear disorders using human specimens.

OBJECTIVES

Analysis of RNA as well DNA is requisite to study the molecular mechanisms of inner ear disorders. Methods of isolating RNA from experimental animals have been established, while isolation of RNA from human inner ears is much more challenging. In the present study, we demonstrate a method by which messenger RNA (mRNA) was extracted from human inner ears and quantitatively analyzed.

MATERIALS AND METHODS

COCH mRNA as well as GAPDH mRNA was extracted from membranous labyrinths dissected from three formalin-fixed and three frozen human temporal bones, removed at autopsy. The length of COCH mRNA and quantity of GAPDH mRNA was compared between the two groups by quantitative RT-PCR.

RESULTS

COCH mRNA could be amplified as much as 976 bp in all three frozen specimens. By contrast, it was amplified to 249 bp in two of the three formalin-fixed specimens, with no amplification observed in the remaining. The quantity of amplifiable GAPDH mRNA in the formalin specimens was only 1% of that of the frozen specimens.