Degradation behaviour of self-reinforced 80L/20G PLGA devices in vitro.

In vitro degradation of self-reinforced PLGA 80L/20G material and bioabsorbable stents was studied in artificial urine and phosphate buffer solution (PBS) to define if the media have an effect on the degradation rate in urological applications. After six weeks, the Mv of the samples immersed in PBS was 40% (16.7 kDa) from the initial value and 57% (24.0 kDa) for the samples immersed in artificial urine. The strength loss of samples that were immersed in PBS was slower when compared with samples in artificial urine. The bending strength of samples immersed 15 weeks in artificial urine was 43% (21.7 MPa) of the bending strength of samples immersed in PBS (50.9 MPa), and the shear strength was 13% (artificial urine 3.7 MPa, PBS 28.8 MPa), respectively. The maximum compression force in PBS was slightly over at the initial level after 2 weeks of immersion. It decreased to half (102.2N) of the initial value (204.1N) in 8 weeks, and after 12 weeks it was 25% (50.8 N) of the initial value. The compression force in artificial urine was 35% (66.8 N) of the initial value (193.9 N) after 8 weeks. In 12 weeks it had lowered to 26 N in artificial urine, which was 14% of the initial value. The degradation rate of self-reinforced L-lactic and glycolic acid stents in vitro tests in artificial urine was coinciding with our clinical test. Based on these results, it is possible to make a sufficiently accurate in vitro model for the degradation rate of bioabsorbable polymers for urological applications.

Viscoelastic memory and self-expansion of self-reinforced bioabsorbable stents.

The possibility to decide the speed and rate of expansion of stents is of great clinical importance by reason of the varying requirements for different indications to use stents. Self-reinforced bioabsorbable stents can be made self-expanding owing to the viscoelastic memory of the material. Stents are stable at room temperature and expansion occurs at body temperature. The level at which the expansion stops depends on the material, crystallinity, initial diameter of spira and annealing temperature. The expansion rate can be estimated by logarithmic equation, if material, draw ratio and diameter of stent wire are constant. This is, however, possible only if processing parameters are constant. Based on the present results annealing temperature and expansion time were seen to be directly proportional to the expansion rate of the stent.

A bioabsorbable self-expandable, self-reinforced poly-L-lactic acid urethral stent for recurrent urethral strictures: long-term results.

BACKGROUND AND PURPOSE: Biodegradable urethral stents have been used clinically for some years mainly in order to prevent postoperative urinary retention after minimally invasive thermotreatment of benign prostatic hyperplasia. We previously reported a 15-month-follow-up pilot study of a bioabsorbable self-expandable, self-reinforced poly-L-lactic acid (SR-PLLA) urethral stent in combination with optical urethrotomy in the treatment of recurrent urethral strictures. The present aim was to evaluate the long-term results of this new treatment modality. PATIENTS AND METHODS: A series of 22 patients with severe urethral strictures (mean number of earlier urethrotomies 2.5) were involved. An SR-PLLA spiral stent with a bioabsorption time of 10 to 12 months was inserted into the urethra at the stricture site immediately after optical urethrotomy. Uroflowmetry, measurement of postvoiding residual urine, urine culture, and urethroscopy were performed preoperatively and at 1 and 3 months and then every 3 months up to 12 months, with subsequent follow-up visits every 6 months. The mean follow-up was 46 months. RESULTS: The treatment was successful in 8 of the 22 patients (36%). Six recurrences were found within the stented area and 15 outside. Patients with failure have since been treated with several urethrotomies and repeat self-dilatations or free skin urethroplasties. CONCLUSIONS: The results of the use of a bioabsorbable SR-PLLA urethral stent for the treatment of recurrent strictures were encouraging. Without this additional therapy, the recurrence rate of strictures might have been much higher. The main problem was sudden collapse of the stent, possibly induced by outer compression. A new generation of bioabsorbable stents is already under development.

Expansion and bioabsorption of the self-reinforced lactic and glycolic acid copolymer prostatic spiral stent.

PURPOSE: Self-reinforced bioabsorbable stents can be made self-expanding due to the viscoelastic memory of the oriented bioabsorbable materials. A new self-expandable self-reinforced copolymer of lactic/glycolic acid, lactic/glycolic molar ratio 80:20 stent was developed to prevent postoperative urinary retention after procedures that induced prostatic edema. In in vitro experiments the expansion rate has been up to 100% during the first few hours at body temperature. We investigated the expansion rate and biodegradation of the self-reinforced lactic and glycolic acid copolymer prostatic spiral stent in vivo in the prostatic urethra. MATERIALS AND METHODS: A total of 39 men, 52 to 84 years old, with lower urinary tract symptoms due to benign prostatic enlargement underwent interstitial laser coagulation of the prostate. A self-reinforced copolymer of lactic/glycolic acid, lactic/glycolic molar ratio 80/20 stent was inserted into the prostatic urethra at the end of the operation. The stent lumen diameter was 4.5 mm. The location and diameter of the lumen and degradation of the stent were studied with transrectal ultrasound at 1, 2, 4 and 6 months postoperatively. At 6 months patients underwent cystoscopy. RESULTS: All except 1 patient voided on postoperative day 1. Mean lumen diameter was 7.4 mm. (range 6.2 to 8.2) at 1 month and 7.2 mm (range 6.2 to 7.5) at 2 months. At 4 months the stent was degraded into small pieces. No pieces of stent were found in the prostatic urethra on ultrasound or cystoscopy at 6 months. However, a portion of the spiral stent was found at the bottom of the bladder in 2 patients. CONCLUSIONS: The speed and expansion rate of the self-reinforced copolymer of lactic/glycolic acid, lactic/glycolic molar ratio 80/20 stent was sufficient to lock the stent in place and ensure voiding in cases of edema induced bladder outlet obstruction. Strength retention greater than 2 months was long enough to avoid later impairments of voiding.

A double-blind, randomized, placebo-controlled pilot study to investigate the effects of finasteride combined with a biodegradable self-reinforced poly L-lactic acid spiral stent in patients with urinary retention caused by bladder outlet obstruction from benign prostatic hyperplasia.

OBJECTIVE: To assess whether patients in acute urinary retention from benign prostatic enlargement can be treated with a combined therapy comprising finasteride and a bioabsorbable self-reinforced poly L-lactic acid (SR-PLLA) urethral stent. PATIENTS AND METHODS: Fifty-five patients in acute urinary retention were treated as outpatients; they had a suprapubic catheter inserted and the SR-PLLA stent placed cystoscopically. After 2 weeks the patients were randomized to receive either finasteride 5 mg daily or placebo. They were assessed at baseline and at 6, 12 and 18 months for maximum urinary flow rate, prostate volume and serum prostate-specific antigen (PSA). RESULTS: Nineteen patients completed the study while 36 discontinued. There was a statistically significant increase in the mean maximum flow rate, and a statistically significant decrease in the prostatic volume and serum PSA in the finasteride group. The same number of patients discontinued in both groups; the major reason for discontinuation was insufficient therapeutic response. CONCLUSIONS: The major problems were discontinuation of treatment because the response to therapy was insufficient, and uncontrolled breakdown of the spiral stent. To solve these problems, new configurations of bioabsorbable stents are needed.

Biodegradation of the copolymeric polylactide stent. Long-term follow-up in a rabbit aorta model.

The behavior of biodegradable polylactide as a stent material has not yet been fully established in small vessels such as arteries with a diameter <3 mm. The aim of this study was to investigate the long-term effect of a copolymeric polylactide (PLA96) stent. Appropriately sized spiral PLA96 stents were implanted into the infrarenal aortas of 20 rabbits. Intraoperative systemic heparinization (150 IU/kg), perioperative subcutaneous enoxaheparin sodium (10 mg), ticlopidine (250 mg/day) for 1 month, and acetosalicylic acid (12.5 mg/day) were continuously administered. Animals were euthanized according to a fixed timetable for up to 34 months for histologic and scanning-electron-microscopic assessment. Endothelialization was complete within 1 month. In 2 of the 3 aortas sampled 3 months after implantation, a mild inflammatory reaction was visible, with no sign of granulomatous or foreign-body reaction in the vessel wall. Instead, in 1 sample examined at the same time point, neointimal chondroid metaplasia was detected. After 6 months, inflammatory reaction declined in the vessel wall. Hydrolyzation of the stent was histologically evident at 12 months, with mild foreign-body reaction detectable in 2 of 5 aortas sampled at this time point. The stent disintegrated without fragmentation by 24 months, as it was gradually replaced by fibrosis. The vessel lumen remained patent at all time points. We conclude that the PLA96 stent degraded with minimal tissue response within 24 months. PLA96 may thus be a promising stent core material for small vessels in the future, although further investigation is needed to establish its final biocompatibility.

Speech perception and functional benefit after cochlear implantation: a multicentre survey in Finland.

This study was done to survey the effect of cochlear implantation on hearing level, speech perception and listening performance in Finnish-speaking adults. The subjects of the study comprise 67 adults. Pure-tone thresholds (0.125-8 kHz), word recognition and listening performance were studied before and after implantation. After switch-on of the implant, the median values of PTA(0.5-4 kHz) in the sound field were fairly stable across the evaluation period. Three months after switch-on of the implant, the mean word recognition score was 54%. There was clear improvement in the mean word recognition scores over a longer period of time, the mean score being 71% 24 months after switch-on. Six months after switch-on, the majority of subjects (40/48) were able to recognize some speech without speechreading, and 26 of these 48 subjects were able to use the telephone with a known speaker, gaining good functional benefit from the implantation.

Biocompatibility of silver nitrate and ofloxacine coated bioabsorbable SR-PLLA rods.

The purpose of this study was to evaluate the biocompatibility of silver nitrate and ofloxacine coatings of bioresorbable self-reinforced poly-L-lactic acid (SR-PLLA) rods. SR-PLLA rods coated with pure poly(caprolactone-co-L-lactide) or blended with silver nitrate (10, 5 or 2 weight-%) or ofloxacine (5 or 2 weight-%) were implanted in the dorsal muscles of 25 male rabbits. Tissue reactions caused by implantation trauma were seen 1 week after implantation. The positive control and 10 w-% silver nitrate coating showed the most marked reactions 1 month after implantation. Only sparse reactions were seen 6 months after implantation. Tissue reactions were scored semi-quantitatively. As a result of this study, we concluded that silver nitrate or ofloxacine coatings up to five w-% did not alter the good biocompatibility of SR-PLLA essentially. The method may lead to the possibility of preventing bacterial adhesion to urological stents during insertion.

On the construction of a Finnish audiometric sentence test.

To respond to the demands of clinical practice and the needs of rehabilitation, a Finnish audiometric sentence test is being developed. The test consists of 10 sets of 10 sentences, each set serving as an independent test. The test is scored by words (50 per set). Homogeneity between the sets was guaranteed by a number of linguistic and phonetic criteria, controlled by using the Virko Sentence Analyzer, a programme especially constructed for the purpose. Recognition tests for the validation of the sentence sets were made with young normally hearing adults (n = 70; age group 18-25 years). Psychometric recognition properties of the test are described. The selection process of the final 10 sentence sets is illustrated.

Speech perception and functional benefit after multichannel cochlear implantation.

This study was done to investigate the effect of a multichannel cochlear implant on speech perception and the functional benefit of cochlear implantation in Finnish-speaking postlingually deafened adults. Fourteen subjects were enrolled. Sentence and word recognition were studied with open-set tests auditorily only. One year after implantation, the listening performance was assessed by case histories and interviews. Before implantation for subjects with a hearing aid, the mean recognition score was 38% for sentences and 17% for words. One year after switching on the implant, the mean recognition score was 84% for sentences and 70% for words. Before implantation, the majority of the subjects were not aware of environmental sounds and only a few were able to recognize some environmental sounds. One year after switching on the implant, the majority of the subjects were able to use the telephone with a familiar speaker. All the subjects were able to recognize speech auditorily only and had thus gained good functional benefit from the implant.

Cochlear implant patients and quality of life.

During the last two decades, cochlear implants have been available for profoundly hearing-impaired patients who do not benefit from conventional hearing aids. The quality of life of these implantees has not been extensively studied, and has not been studied at all in Finland. To assess their quality of life, the Nottingham Health Profile questionnaire was sent to all adult implanted patients in Finland. Implantees tended to have more favourable average pain, emotional reaction and mobility indexes in each age group studied than the average population. Social-isolation seemed to be more common in the youngest and oldest age groups of implantees. Apparently, implantees are physically healthier than the average population. However, a bias caused by the strict selection of implant candidates cannot be excluded.

The effect of a multichannel cochlear implant on phoneme perception.

This study was done to investigate the effects of a multichannel cochlear implant on phoneme perception in Finnish-speaking postlingually deafened adults. Phoneme recognition was studied with 100 prerecorded nonsense syllables (open-set) presented at 70 dB SPL, auditorily only, in a free-field situation. Ten subjects were tested before implantation both with and without a hearing aid (HA), and 3, 6 and 12 months after switching on the implant. Before implantation without a HA, the subjects did not recognize vowels, consonants or syllables. Four of the subjects used a HA before implantation, and the mean recognition scores of these subjects were 34% for vowels, 28% for consonants and 13% for syllables. One year after switching on the implant, the mean recognition scores were 77% for vowels, 66% for consonants and 46% for syllables. According to phonological analysis vowels appear to be easier to perceive than consonants during the first stage after multichannel cochlear implantation.

Cochllear implants and GSM phone.

Use of a telephone and GSM phones, in particular, was assessed by means of a postal interview sent to all adult Finnish implantees. The response rate was very high (87%). Fifty-one of the 61 respondents used a telephone and 27/61 also used a mobile phone, usually a digital phone. Two GSM phone models from Nokia (3110 and 6110) were tested with three different cochlear implant systems used by nine patients. Definite differences between the processors were found. Nucleus Spectra (two implantees) could not be used with any of the GSM phones under any test condition. Nucleus SPrint was incompatible with both GSM phone models in a poor field, while GSM phone model 6110 could be used in a good field. The Med-El Combi 40+ processor was compatible with both GSM models tested under any condition.

Bacterial adherence to silver nitrate coated poly-L-lactic acid urological stents in vitro.

The purpose of this study was to see whether it is possible to prevent bacterial adherence to bioabsorbable self-reinforced L-lactic acid polymer (SR-PLLA) urological stents. The SR-PLLA stents were coated with silver nitrate blended epsilon-caprolactone/L-lactide copolymer. The adherence of five bacterial strains (Pseudomonas aeruginosa, Enterococcus faecalis, Proteus mirabilis and two strains of Escherichia coli) to coated and non-coated SR-PLLA wires were tested. It was found that silver nitrate coating prevented the adherence of bacteria (except E. faecalis) to SR-PLLA stents. The preventive effect correlated with the silver nitrate concentration. It was also found that silver nitrate coating reduced the amount of bacteria in ambient urine. In conclusion, silver nitrate coating may reduce stent-associated bacterial infections by preventing the adherence of bacteria. Further studies are needed to confirm its efficacy and safety in clinical practice.

Bacterial adherence to ofloxacin-blended polylactone-coated self-reinforced L-lactic acid polymer urological stents.

OBJECTIVE: To determine whether ofloxacin coating has any effect on bacterial adherence to bioresorbable self-reinforced L-lactic acid polymer (SR-PLLA) urological stents. MATERIALS AND METHODS: SR-PLLA stents were coated with epsilon-caprolactone/L-lactide copolymer blended with ofloxacin at three different concentrations of ofloxacin (0.5, 2 and 5% w/w). The adherence of five bacterial strains (Pseudomonas aeruginosa, Enterococcus faecalis, Proteus mirabilis and two strains of Escherichia coli) to the coated SR-PLLA stents was analysed. Uncoated stent pieces were used as controls. The effect of ofloxacin coating on bacterial growth in the microenvironment of the stent pieces was also analysed. RESULTS: Ofloxacin coating prevented bacterial adherence to SR-PLLA stent material; this effect correlated significantly with the ofloxacin concentration of the caprolactone coating. Ofloxacin coating reduced the amount of bacteria in the microenvironment of the stent, but because of natural resistance, ofloxacin coating had little effect on E. faecalis. CONCLUSION: Except for E. faecalis, ofloxacin coating may reduce stent-associated infections. However, further studies are needed to confirm its biocompatibility and efficacy in clinical use.

A randomised study to evaluate the efficacy of a biodegradable stent in the prevention of postoperative urinary retention after interstitial laser coagulation of the prostate.

OBJECTIVE: Interstitial laser coagulation (ILC) of the prostate induces necrosis, oedema and increased risk for postoperative urinary retention. The present randomized study was carried out to investigate the feasibility and efficacy of a biodegradable self-reinforced polyglycolic acid (SR-PGA) stent in preventing postoperative urinary retention and the need for prolonged catheterization after ILC treatment. MATERIAL AND METHODS: 35 males with benign prostatic enlargement (BPE) entered the study: 21 in the ILC + stent group and 14 in the ILC group without a stent. A suprapubic catheter was inserted for all patients and ILC was performed. The SR-PGA stent was inserted immediately after laser therapy in the stent group and kept open until the next morning when it was closed and the patient started trying to void. The suprapubic catheter was removed after voiding had started and the urinary bladder emptied adequately. RESULTS: In the ILC + stent group voiding started on the first postoperative day in 17 patients and on the second day in 2 patients. Voiding was delayed in 2 cases: in 1 case due to inadequate length of the stent and in the other as a result of the stent placement being too proximal. There was 1 case of urinary retention due to early degradation of the stent. In the ILC-only group voiding started on average 6.1 days postoperatively. At 1 month follow-up, the mean peak urinary flow rate had increased significantly in the ILC + stent group (p < 0.05) but not in the ILC-only group (p = 0.26). Improvements in symptom scores were significant in both groups (p < 0.005) but in terms of the mean peak urinary flow rates at 6 months follow-up the improvement was significant only in the stent group (p < 0.05). CONCLUSIONS: The use of a SR-PGA stent enabled early voiding and is safe and effective in the treatment of postoperative urinary retention after ILC. The 3-4 week degradation time of the SR-PGA stent was too short for some patients. There is still a need for further development work to improve the stents and larger controlled studies to show the true value of biodegradable stents in the treatment of BPE.

The morphological, in situ effects of a self-reinforced bioabsorbable polylactide (SR-PLA 96) ureteric stent; an experimental study.

PURPOSE: The present study was done to evaluate the biocompatibility of a new biodegradable double helical spiral self-reinforced poly-L, D-lactide copolymer (L/D ratio 96/4, SR-PLA96) ureteric stent. MATERIALS AND METHODS: In sixteen dogs, the right ureter was cut transversally, sutured and stented with a 50 mm. long SR-PLA 96 stent. In eight dogs, left ureter was similarly operated and stented with a double-J pigtail stent (C-Flex, Cook Urological Inc.), while eight remaining ureters served as plain controls. Urine was analyzed for signs of infection. The dogs were terminated at 6, 12 and 24 weeks postoperatively and the ureters dissected to find persistent SR-PLA 96 particles or local ureteric changes. Histologic samples were taken at three levels of dissected ureters in contact with the stent. RESULTS: C-Flex and SR-PLA 96 materials were well tolerated. Both of these induced only minimal ureteral wall edema, epithelial hyperplasia, epithelial destruction and inflammatory cell reaction. In SR-PLA 96 stented ureters the tissue reaction subsided after the degradation of the device. CONCLUSIONS: SR-PLA 96 spiral stent is regarded highly compatible and SR-PLA 96 might be a suitable material for a partial ureteric stent. Biodegradation of a SR-PLA 96 stent makes stent removal unnecessary.

Use of internal bioabsorbable PLGA "finger-type" stents in a rabbit tracheal reconstruction model.

OBJECTIVES: To design and develop a biodegradable tracheal stent that can be used internally to stabilize and support surgically reconstructed airways. DESIGN: In vitro mechanical and degradative properties of 80:20 poly(D,L-lactide-co-glycolide) (PLGA) "finger-like" stents were determined. The stents were then tested in vivo in rabbits that underwent anterior patch tracheoplasties with fascia lata grafts. Comparisons were made between a control group and an internal stent group for stridor development, overall group mortality, reconstructed airway lumen size, and histological findings. SUBJECTS: Twenty-five New Zealand white rabbits. RESULTS: The average dry modulus for the internal stents was 6800 kPa. All of the internal stents cracked by 4 weeks in buffer solution. Significant mass loss was not noted in vitro until after 5 weeks in buffer solution. By 14 weeks, the stents were nearly 100% degraded. The attrition rate for the control group was 23% compared with 17% for the experimental group. The stridor rate for the control group was also higher at 38% compared with 17% for the stented group. The stented rabbits had a significantly smaller average stenosis (23%) across the entire reconstruction site than the control group (34%) (P<.05). CONCLUSION: Biodegradable PLGA stents degrade in a predictable fashion and have a statistically significant effect in augmenting anterior patch tracheoplasties with fascia lata grafts in rabbits.

A new biodegradable stent for the pancreaticojejunal anastomosis after pancreaticoduodenal resection: in vitro examination and pilot experiences in humans.

We sought to develop a biodegradable pancreatic stent that could be easily placed at operation into the human pancreatic duct and the degradation of which could be easily followed up. Spiral-shaped, gamma-sterilized stents were manufactured of 0.4-mm polylactide wire in which there was added 23 weight-% barium sulfate. The biodegradability of the stents was studied in vitro at two different pH values, the first resembling that of pancreatic juice and the other that of bile. The effects of enzymoactivity in the test solution and the composition of the stents (with or without barium addition) also were tested. These kinds of stents have been experimented with in two pilot patients. Degradation of the stents occurred from 24 to 52 weeks of incubation. Alkaline milieu together with the presence of pancreatic enzyme made the stents degrade twice as fast as when either alkaline milieu or enzyme was present. In the milieu resembling pancreatic juice, barium sulfate had no effect on the degradation time. Neither of the pilot patients had any postoperative complications. Biodegradable, x-ray-positive stents degrade faster in pancreatic than in biliary milieu. Their safety and efficacy in human pancreaticojejunal anastomoses need further study.

A pilot study of a bioabsorbable self-reinforced poly L-lactic acid urethral stent combined with finasteride in the treatment of acute urinary retention from benign prostatic enlargement.

OBJECTIVE: To assess whether patients with acute urinary retention from benign prostatic enlargement can be treated with a combined therapy comprising a bioabsorbable self-reinforced poly L-lactic acid (SR-PLLA) urethral stent and finasteride. PATIENTS AND METHODS: Eleven men in acute urinary retention were treated as outpatients; they had a suprapubic catheter inserted and the SR-PLLA stent placed cystoscopically. The patients were allowed to attempt to void spontaneously after 2 days. RESULTS: All patients started to void spontaneously within 2 weeks. There was a steady improvement in urinary flow rates up to 9 months, followed by a slight impairment after the bioabsorption of the stent. During the mean (range) follow-up of 24 (23-26) months only three patients required surgical treatment. CONCLUSION: The bioabsorbable SR-PLLA stent combined with finasteride therapy provides a promising new alternative in the treatment of acute urinary retention, especially in patients unfit for surgical therapy. Larger, placebo-controlled studies are needed to establish the efficacy of this combined therapy.