Polymers that display a physicochemical response to stimuli are widely explored as potential drug-delivery systems. Stimuli studied to date include chemical substances and changes in temperature, pH and electric field. Homopolymers or copolymers of N-isopropylacrylamide and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (known as poloxamers) are typical examples of thermosensitive polymers, but their use in drug delivery is problematic because they are toxic and non-biodegradable. Biodegradable polymers used for drug delivery to date have mostly been in the form of injectable microspheres or implant systems, which require complicated fabrication processes using organic solvents. Such systems have the disadvantage that the use of organic solvents can cause denaturation when protein drugs are to be encapsulated. Furthermore, the solid form requires surgical insertion, which often results in tissue irritation and damage. Here we report the synthesis of a thermosensitive, biodegradable hydrogel consisting of blocks of poly(ethylene oxide) and poly(L-lactic acid). Aqueous solutions of these copolymers exhibit temperature-dependent reversible gel-sol transitions. The hydrogel can be loaded with bioactive molecules in an aqueous phase at an elevated temperature (around 45 degrees C), where they form a sol. In this form, the polymer is injectable. On subcutaneous injection and subsequent rapid cooling to body temperature, the loaded copolymer forms a gel that can act as a sustained-release matrix for drugs.

Biodegradable block copolymers as injectable drug-delivery systems

Burns are one of the most common and devastating forms of trauma. Patients with serious thermal injury require immediate specialized care in order to minimize morbidity and mortality. Significant thermal injuries induce a state of immunosuppression that predisposes burn patients to infectious complications. A current summary of the classifications of burn wound infections, including their diagnosis, treatment, and prevention, is given. Early excision of the eschar has substantially decreased the incidence of invasive burn wound infection and secondary sepsis, but most deaths in severely burn-injured patients are still due to burn wound sepsis or complications due to inhalation injury. Burn patients are also at risk for developing sepsis secondary to pneumonia, catheter-related infections, and suppurative thrombophlebitis. The introduction of silver-impregnated devices (e.g., central lines and Foley urinary catheters) may reduce the incidence of nosocomial infections due to prolonged placement of these devices. Improved outcomes for severely burned patients have been attributed to medical advances in fluid resuscitation, nutritional support, pulmonary and burn wound care, and infection control practices.

Burn Wound Infections

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International commission on non-ionizing radiation protection.

The medical literature describes numerous in vitro and in vivo wound-healing models. The selection of an animal model depends on a number of factors including availability, cost, ease of handling, investigator familiarity, and anatomical/functional similarity to humans. Small mammals are frequently used for wound healing studies, however, these mammals differ from humans in a number of anatomical and physiological ways. Anatomically and physiologically, pig skin is more similar to human skin. The many similarities between man and pig would lead one to believe that the pig should make an excellent animal model for human wound healing. The purpose of this paper is to review the existing literature for evidence of this supposition and determine how well the various models correlate to human wound healing. Studies of wound dressings, topical antimicrobials, and growth factors are examined. Over 180 articles were utilized for this comparative review. Our conclusion is that the porcine model is an excellent tool for the evaluation of therapeutic agents destined for use in human wounds.

The pig as a model for human wound healing

IEEE C95.1-1991 gives recommendations to prevent harmful effects in human beings exposed to electromagnetic fields in the frequency range from 3 kHz to 300 GHz. The recommendations are intended to apply to exposures in controlled, as well as uncontrolled, environments. They are not intended to apply to the purposeful exposure of patients under the direction of practitioners of the healing arts. The induced and contact current limits of IEEE C95.1-1991 are modified in this edition. In addition, field strengths below which induced and contact currents do not have to be measured are specified, spatial averaging and measurement distance requirements are clarified, and more precise definitions for averaging volume and radiated power are provided.

IEEE standard for safety levels with respect to human exposure to radio frequency electromagnetic fields, 3kHz to 300 GHz

A. R. Moxr, M.D., and F. C. HENRIQuES, JR., Ph.D. (From the Departmen of Legal Medcixe, Harvrd Medical School, Boston, Mass.) Although it is common knowledge that there is an inverse relationship between the intensity of a thermal exposure and the amount of time required to produce a burn, there is remarkably little available information as to the rate at which burning of huiman skin occurs at any given surface temperature or as to the pathogenesis and pathological characteristics of burns in which the duration and degree of rise in intracutaneous temperature was known or could be calculated with any degree of accuracy. Considerable information regarding the time-temperature thresholds at which cutaneous burning occurs in animals is provided by the experiments of Hudack and McMaster1 and of Leach, Peters, and Rossiter.2 In the former, water at temperatures ranging between 420 and 670C. either was applied directly or was passed through a thinwalled glass chamber, the base of which was brought in contact with the skin of mice. In the experiments performed by Leach, Peters, and Rossiter water was pumped through a metal chamber at temperatures ranging between 450 and 8o0C. and the base of the chamber was held in contact with the skin of guinvea-pigs for varying periods of time. Both groups of investigators observed that the time required to produce injury diminished rapidly as the temperature of the water was raised. The former reported that a source temperature of 440C. was critical for the causation of hyperthermic edema. The latter reported that the critical temperature for causing permanent and irreversible injury of guinea-pig skin lies between 500 and SS°C. Neither of the above-cited investigations provided data from which the timetemperature requirements for the production of burns of huiman skin could be estimated. Although Leach, Peters, and Rossiter 2 made a careful study of the pathological characteristics of different kinds of burns of guinea-pig skin, the extent to which these chges are representative of those that occur in cutaneous burning in man was not disclosed.

F C Henriques

Papers

Studies of Thermal Injury: II. The Relative Importance of Time and Surface Temperature in the Causation of Cutaneous Burns*