Biomedical subjects

D Palanker

Publications and source records attributed to D Palanker.

13 recordsLinked to original sources

PubMed2003

Transient optical elements: application to near-field microscopy.

We report methods of near-field infrared microscopy with transient optically induced probes. The first technique - a transient aperture (TA) - uses photoinduced reflectivity in semiconductors to generate a relatively large transient mirror (TM) with a small aperture at its centre. We report the optical properties of the TM and TA and experiments performed on near-field imaging with the TA. The second technique is based on solid immersion microscopy, in which high resolution is achieved when light is focused inside a solid with a high refractive index. By creating a transient Fresnel lens on the surface of a semiconductor wafer via photoinduction, we were able to form a solid immersion lens (SIL) for use as a near-field probe. The use of transient probes eliminates the need for mechanical scanning of the lens or sample, and thus provides a much faster scanning rate and the possibility to work with soft and liquid objects.

Journal Article↗

PubMed1999

Near-field scanning optical microscopy in cell biology.

Near-field optics has produced the highest optical resolution that has ever been achieved. The methods involved lie at the interface of far-field optical microscopy and scanned probe microscopy. This article describes the principles behind near-field scanning optical microscopy (NSOM) and highlights its potential in cell biology.

Humans↗

PubMed1998

Early nonsurgical removal of chemically injured tissue enhances wound healing in partial thickness burns.

Chemical burns are slow healing injuries and their depth is difficult to assess. Tissue destruction continues as long as active material is present in the wound site. The routine therapy for treatment of full thickness chemical burns is early excision; it shortens hospitalization and reduces morbidity. However, presently there is no specific treatment for chemical burns of partial thickness. This study examined several treatment modalities for partial thickness chemical burns: surgical excision; laser ablation and chemical debridement with Debridase or trypsin-linked to gauze. Chemical burns were inflicted with nitrogen mustard (NM -- a nitrogen analog to sulfur mustard -- mustard gas) in an experimental guinea pig model. Debridase was most effective and reduced significantly lesion area of burns after 'humid' exposure to 2 mg NM. The healing action of Debridase was also evident in the significantly higher histopathological score of biopsies from local tissue obtained on day 5. Laser ablation was most effective and accelerated healing of burn lesions after 'dry' exposure to 5 mg NM. The histopathology score of the laser treated burns was higher on day 4 compared to untreated controls. It is concluded that for partial thickness chemical burns early nonsurgical removal of the damaged tissues accelerates wound healing.

Administration, Topical↗

PubMed1997

Dynamics of ArF excimer laser-induced cavitation bubbles in gel surrounded by a liquid medium.

BACKGROUND AND OBJECTIVE: Cavitation bubbles have been shown to be the driving force of tissue cutting in 193 nm ArF excimer laser-based vitreoretinal microsurgery. In the present work we investigate the dynamics of cavitation bubbles inside a gelatin gel in a saline environment using fast flash microphotography. STUDY DESIGN/MATERIALS AND METHODS: The screening influence of the saline medium was found to restrict the maximal distance between the tip and the tissue at which cavitation bubbles are created to < 100 microns at an energy fluence up to 0.3 J/cm2/pulse (the maximal energy fluence applied in vitreoretinal surgery). RESULTS AND CONCLUSION: Single laser pulses did not cause disruption of gelatin at an energy fluence of up to 0.4 J/cm2/pulse. During the application of repetitive pulses small insoluble gas-containing bubbles were produced and often trapped between the tip and the tissue. They completely changed the shape of the subsequent cavitation bubbles and caused deep crater formation in the gel.

Biomechanical Phenomena↗

PubMed1997

Vitreoretinal surgery assisted by the 193-nm excimer laser.

PURPOSE: Ablating and cutting vitreoretinal membranes using a 193-nm excimer laser-based microsurgical system. METHODS: A 193-nm microsurgical system enables delivery of the beam into a fluid medium to cut preretinal and subretinal membranes. Two patients with proliferative diabetic retinopathy and one patient with proliferative vitreoretinopathy were treated with this new device. RESULTS: Gentle ablation and cutting of the preretinal and subretinal membranes without exerting any traction on or apparent damage to the neighboring tissue was achieved. CONCLUSIONS: The technology is applicable to a variety of intraocular vitreoretinal surgical procedures.

Aged↗

PubMed1994

ArF excimer laser-induced bubble formation during irradiation of NaCl solutions.

During application of the 193 nm excimer laser to vitreoretinal surgery, very deep cutting of the retina of about 100 microm/pulse was detected at the energy fluence in the range of 0.25-0.35 J/cm2/pulse. At the surface of the ablating tip insoluble bubbles were observed during the irradiation. In this paper we study production of these bubbles in aqueous solutions of sodium chloride. The yield of gaseous photoproducts was measured as a function of NaCl concentration and energy fluence. At concentrations of 100 g/L powerful water vapor bubbles and shock waves were observed. A mechanism of soft tissue cutting by the 193 nm laser in highly absorbing liquid media is suggested that explains the features of vitreoretinal ablation with this system: (1) the high cutting depth when the tip touches the tissue and (2) the absence of cutting when the tip is not in contact with tissue. The advantages of the ArF laser for microsurgery of internal organs are discussed.

Lasers↗

PubMed1994

Vitreoretinal ablation with the 193-nm excimer laser in fluid media.

PURPOSE: To ablate retina and vitreous membranes using the 193-nm argon fluoride excimer laser in a fluid medium. METHODS: A special delivery system for the 193-nm excimer laser was developed that enabled the delivery of the laser into high-absorption liquid environments. The system was tested on the retina in an in vitro cup preparation of cow's eyes, and also in vivo on retina and vitreous membranes of rabbit eyes. The depth of cut as a function of laser energy was determined for an ablating needle with a 0.25-mm exit diameter. RESULTS: Gentle cutting of retinal tissue and of vitreous membranes was obtained in an energy range of 0.075 to 0.25 mJ/pulse. At the energy level of 0.075 mJ/pulse, four pulses were required for full-depth cut formation in rabbit retina, whereas at energy levels greater than 0.17 mJ/pulse, one pulse was sufficient for full-depth cut formation. The maximal rate of cutting achieved for the bovine retina was 2 mm/sec at a 20-Hz repetition rate of the laser. Ablation occurred only when the tip was held in contact with the tissue. CONCLUSIONS: The technology described herein appears to be advantageous and applicable to a variety of vitreoretinal surgical procedures.

Animals↗

PubMed1993

The efficacy and safety of zona pellucida drilling by a 193-nm excimer laser.

OBJECTIVE: To examine the efficiency of argon fluoride excimer laser drilling of the zona pellucida of mouse oocytes in improving in vitro fertilization (IVF) at low sperm concentrations and to assess its safety. DESIGN: Oocytes obtained from (Balb/c x C57BL6)CB6F1 female mice were drilled by laser and divided into two groups: group I (89 oocytes) were inseminated with 10(5) sperm cells/mL, and group II (94 oocytes) were inseminated with 10(6) sperm cells/mL. Both groups' fertilization rate and development in vitro was compared with control oocytes that underwent the same preparation steps but no drilling (94 and 88 oocytes for group I and group II, respectively). MAIN OUTCOME MEASURES: The fertilization rate and the development in vitro of the laser-drilled groups is compared with that of the control. In addition, in vivo development of embryos generated from laser-drilled oocytes after transfer to pseudopregnant recipients is assessed. RESULTS: For both sperm concentrations, laser drilling significantly enhanced fertilization over control (67% versus 31% at 10(5) sperm cells/mL and 90% versus 54% at 10(6) sperm cells/mL). The development into the blastocyst stage after 96 hours of incubation was similar for both the laser-drilled and control groups at any sperm cell concentration. However, complete hatching at this point was significantly enhanced by the drilling procedure. Normal litters were obtained from the transfer of embryos developed from zona-drilled oocytes into pseudopregnant recipients. CONCLUSIONS: Excimer laser drilling enhanced IVF at low sperm cell concentration. The procedure is safe and did not interfere with embryo development in vitro or in vivo.

Animals↗

PubMed1993

Interaction between human sperm cells and hamster oocytes after argon fluoride excimer laser drilling of the zona pellucida.

OBJECTIVES: To provide conclusive evidence that sperm cells gain access to the perivitelline space exclusively through a laser-drilled opening. To assess the optimal size of the hole and to evaluate the efficacy of laser drilling in comparison with that of mechanical zona dissection. DESIGN: An interspecies model of human sperm cell that interacts with a laser-drilled or partially zona-dissected hamster oocytes. MAIN OUTCOME MEASURES: Penetration rate into the perivitelline space as related to the size of the opening (group A [5 microns], group B [10 microns], and group C [15 microns]) and to the sperm cell concentrations (1 x 10(6), 5 x 10(6), and 10 x 10(6) cells/mL) used for insemination. RESULTS: For each sperm cell concentration, the penetration rate into the perivitelline space was lowest for group A followed by group C and highest for group B. When penetration was compared for each hole size, it was found that sperm concentration had no effect on the rate of penetration in groups A and C but significantly affected this rate in group B. The highest penetration rate of 73% was observed with a concentration of 10 x 10(6) cell/mL and declined to 58% and 23% at 5 x 10(6) cell/mL and 1 x 10(6) cell/mL, respectively. Oocytes drilled by laser (10-microns hole) demonstrated a significantly higher penetration rate when compared with those treated by partial zona dissection (73% versus 20% and 58% versus 21% for sperm densities of 10 x 10(6) cells/mL and 5 x 10(6) cells/mL, respectively). CONCLUSION: Human sperm cells gain access into the perivitelline space of hamster oocytes exclusively through a hole drilled by an argon fluoride excimer laser. An opening of 10 microns was found to yield optimal results. Laser drilling of the zona pellucida seems to be superior to that of mechanical slitting in terms of sperm oolema interaction.

Animals↗

PubMed1993

Permeabilizing millions of cells with single pulses of an excimer laser.

Poration of millions of cells with single laser pulses of an argon fluoride excimer laser is developed and demonstrated on plant cells. The essence of the technique is to use the large beam size (10 x 25 mm) of the excimer laser and to split it using an appropriate mask into millions of micron- or submicron-sized beams of 193-nm radiation with enough energy to perforate cell membranes and walls. The extremely small depth of penetration of the 193-nm radiation in biological tissue (< 1 microns) is used to great advantage in this technique to provide for a gentle method that does not lead to cell death. This is the first laser-based method that has enough throughput to make it viable for biotechnological applications. Of considerable significance is that the method is applicable not only in the case of the single cells in suspension, but also for cells growing on the leaves of living plants.

Allium↗

PubMed1992

Effect of the ArF excimer laser on human enamel.

Human enamel surface was irradiated with ArF excimer laser and examined under light microscopy and scanning electron microscopy (SEM). Enamel surface was irradiated at three different areas with different energy fluences. It is demonstrated that the ArF excimer laser causes ablation of the calcified hard enamel tissue. Ablation curves were measured. There was no significant difference found in the etch depth between the three different areas of enamel surface. The morphology of the irradiated areas seen under the SEM was found to be dependent on energy fluence. It changed with increase in energy fluence from being etched to forming a smooth, fused, glaze-like surface and then at very high energy fluences producing a rough surface. The influence of the laser irradiation was confined to the irradiated area only, with no visible heat damage to the surroundings. These results suggest that excimer laser could be applied in a controlled and defined manner for tooth enamel treatments in dentistry.

Dental Enamel↗

PubMed1992

Microsurgery of the retina with a needle-guided 193-nm excimer laser.

This article presents a method used to guide the beam from an argon fluoride excimer laser to make it suitable for microsurgical purposes and confine it to areas that can be varied in dimension from 1 micron to tens or hundreds of microns. This approach guides the excimer laser beam with an articulated mechanical arm and confines it with variable-diameter tapered tubes, possibly allowing the use of this laser in in vitro retinal surgery with endolaser techniques. Currently, because of the lack of a delivery and focusing system for the 193-nm argon fluoride beam and its absorption by biologic liquids, this laser is used exclusively in ophthalmology for topical applications, such as corneal sculpting. This new method resolves these problems in a unique way with impressive results. Specifically, it was shown that, with this needle-guided excimer laser, it is possible to remove retinal tissue accurately without detectable damage to surrounding cells. Applications of this new technique in retinal surgery are discussed.

Animals↗

PubMed1991

Technique for cellular microsurgery using the 193-nm excimer laser.

A new cell surgery technique has been developed to produce well-defined alterations in cells and tissue without detectable heating and/or other structural damage in the surroundings. The technique involves the use of an argon fluoride excimer laser, in the deep ultraviolet (UV) region of the spectrum at 193 nm, which is guided through a glass pipette filled with a positive air pressure. To demonstrate the method, holes were drilled in the zona pellucida of mouse oocytes. The diameter of the drilled hole was determined by the pipette tip size, and its depth by an energy emitted per pulse and number of pulses. Scanning electron microscopy of the drilled mouse oocytes showed uniform, round, well-circumscribed holes with sharp edges. Oocytes that had their zona pellucida drilled with this new method fertilized in vitro and developed to the blastocyst stage in a rate similar to that of control group. These results demonstrate the nonperturbing nature of this cold laser microsurgical procedure. In addition to the extension of our results for clinical in vitro fertilization purposes, such as enhancement of fertilization and embryo biopsy, there are wide-ranging possible uses of our method in fundamental and applied investigations that require submicron accuracy in cellular alteration.

Animals↗