Water soluble macromers are modified by addition of free radical polymerizable groups, such as those containing a carbon-carbon double or triple bond, which can be polymerized under mild conditions to encapsulate tissues, cells, or biologically active materials. The polymeric materials are particularly useful as tissue adhesives, coatings for tissue lumens including blood vessels, coatings for cells such as islets of Langerhans, coatings, plugs, supports or substrates for contact with biological materials such as the body, and as drug delivery devices for biologically active molecules.

Gels for encapsulation of biological materials

Hydrogels of polymerized and crosslinked macromers comprising hydrophilic oligomers having biodegradable monomeric or oligomeric extensions, which biodegradable extensions are terminated on free ends with end cap monomers or oligomers capable of polymerization and cross linking are described. The hydrophilic core itself may be degradable, thus combining the core and extension functions. Macromers are polymerized using free radical initiators under the influence of long wavelength ultraviolet light, visible light excitation or thermal energy. Biodegradation occurs at the linkages within the extension oligomers and results in fragments which are non-toxic and easily removed from the body. Preferred applications for the hydrogels include prevention of adhesion formation after surgical procedures, controlled release of drugs and other bioactive species, temporary protection or separation of tissue surfaces, adhering of sealing tissues together, and preventing the attachment of cells to tissue surfaces.

Photopolymerizable biodegradable hydrogels as tissue contacting materials and controlled-release carriers

Adhesion-related hospital readmissions after abdominal and pelvic surgery: a retrospective cohort study

Aim: To summarize the most common etiologic factors and describe the pathophysiology in the formation of peritoneal adhesions, to outline their clinical significance and consequences, and to evaluate the pharmacologic, mechanical, and surgical adjuvant strategies to minimize peritoneal adhesion formation. Methods: We performed an extensive MEDLINE search of the internationally published English literature of all medical and epidemiological journal articles, textbooks, scientific reports, and scientific journals from 1940 to 1997. We also reviewed reference lists in all the articles retrieved in the search as well as those of major texts regarding intraperitoneal postsurgical adhesion formation. All sources identified were reviewed with particular attention to risk factors, pathophysiology, clinical manifestations, various methods, and innovative techniques for effectively and safely reducing the formation of postsurgical adhesions. Results: The formation of postoperative peritoneal adhesions is an important complication following gynecological and general abdominal surgery, leading to clinical and significant economical consequences. Adhesion occur in more than 90% of the patients following major abdominal surgery and in 55–100% of the women undergoing pelvic surgery. Small-bowel obstruction, infertility, chronic abdominal and pelvic pain, and difficult reoperative surgery are the most common consequences of peritoneal adhesions. Despite elaborate efforts to develop effective strategies to reduce or prevent adhesions, their formation remains a frequent occurrence after abdominal surgery. Conclusions: Until additional information and findings from future clinical investigations exist, only a meticulous surgical technique can be advocated in order to reduce unnecessary morbidity and mortality rates from these untoward effects of surgery.

Peritoneal adhesions: etiology, pathophysiology, and clinical significance. Recent advances in prevention and management.

Background
Although minimally invasive surgery has been accepted for a variety of disorders, laparoscopic resection of colorectal cancer is performed by few. Concern about oncological radicality and long term outcome has limited the adoption of laparoscopic surgery for colorectal cancer.

Objectives
To determine long-term outcome after laparoscopically-assisted versus open surgery for non-metastasised colorectal cancer.

Search methods
The Cochrane library, EMBASE, Pub med and Cancer Lit were searched for published and unpublished randomised controlled trials.

Selection criteria
Randomised clinical trials comparing laparoscopically-assisted and open surgery for non-metastasised colorectal cancer were included. Studies that did not report any long-term outcomes were excluded.

Data collection and analysis
Two reviewers independently assessed the studies and extracted data. RevMan 4.2 was used for statistical analysis.

Main results
Thirty-three randomised clinical trials (RCT) comparing laparoscopically-assisted versus open surgery for colorectal cancer were identified. Twelve of these trials, involving 3346 patients, reported long-term outcome and were included in the current analysis. No significant differences in the occurrence of incisional hernia, reoperations for incisional hernia or reoperations for adhesions were found between laparoscopically assisted and open surgery (2 RCT, 474 pts, 7.9% vs 10.9%;P = 0.32 and 2 RCT, 474 pts, 4.0% vs 2.8%; P = 0.42 and 1 RCT, 391 pts, 1.1% vs 2.5%;P = 0.30, respectively). Rates of recurrence at the site of the primary tumor were similar (colon cancer: 4 RCT, 938 pts, 5.2% vs 5.6%; OR (fixed) 0.84 (95% CI 0.47 to 1.52)(P = 0.57); rectal cancer: 4 RCT, 714 pts, 7.2% vs 7.7%; OR (fixed) 0.81 (95% CI 0.45 to 1.43) (P = 0.46). No differences in the occurrence of port-site/wound recurrences were observed (P=0.16). Similar cancer-related mortality was found after laparoscopic surgery compared to open surgery ( colon cancer: 5 RCT, 1575 pts, 14.6% vs 16.4%; OR (fixed) 0.80 (95% CI 0.61 to 1.06) (P=0.15); rectal cancer: 3 RCT, 578 pts, 9.2% vs 10.0%; OR (fixed) 0.66 (95% CI 0.37 to 1.19) (P=0.16). 
Four studies were included in the meta-analyses on hazard ratios for tumour recurrence in laparoscopic colorectal cancer surgery. No significant difference in recurrence rate was observed between laparoscopic and open surgery (hazard ratio for tumour recurrence in the laparoscopic group 0.92; 95% CI 0.76-1.13). No significant difference in tumour recurrence between laparoscopic and open surgery for colon cancer was observed (hazard ratio for tumour recurrence in the laparoscopic group 0.86; 95% CI 0.70-1.08).

Authors' conclusions
Laparoscopic resection of carcinoma of the colon is associated with a long term outcome no different from that of open colectomy. Further studies are required to determine whether the incidence of incisional hernias and adhesions is affected by method of approach. Laparoscopic surgery for cancer of the upper rectum is feasible, but more randomised trials need to be conducted to assess long term outcome.

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Long-term results of laparoscopic colorectal cancer resection.

Apart from one post-mortem study, the incidence of adhesions following laparotomy has not been well documented. 1. In a prospective analysis of 210 patients undergoing a laparotomy, who had previously had one or more abdominal operations, we found that 93% had intra-abdominal adhesions that were a result of their previous surgery. This compared with 115 first-time laparotomies in which 10.4% had adhesions. 2. Over a 25-year period, 261 of 28 297 adult general surgical admissions were for intestinal obstruction from adhesions (0.9%). Of 4502 laparotomies, 148 were for adhesive obstruction (3.3%). 3. Over a 13-year period all laparotomies were followed up for an average of 14.5 months (range 0-91 months). From these 2708 laparotomies, 26 developed intestinal obstruction due to postoperative adhesions within 1 year of surgery (1%). Fourteen did so within 1 month of surgery (0.5%). 4. The majority of the operations producing intestinal obstruction were lower abdominal, principally involving the colon. The volume of general surgical work from adhesions is large and the incidence of early intestinal obstruction is high.

Intestinal obstruction from adhesions--how big is the problem?

PURPOSE: Postoperative adhesions are a significant problem after colorectal surgery. However, the basic epidemiology and clinical burden are unknown. The Surgical and Clinical Adhesions Research Study has investigated the scale of the problem in a population of 5 million. METHODS: Validated data from the Scottish National Health Service Medical Record Linkage Database were used to define a cohort of 12,584 patients undergoing open lower abdominal surgery in 1986. Readmissions for potential adhesion-related disease in the subsequent ten years were analyzed. The methodology was conservative in interpreting adhesion-related disease. RESULTS: In the study cohort 32.6 percent of patients were readmitted a mean of 2.2 times in the subsequent ten years for a potential adhesion-related problem. Although 25.4 percent of readmissions were in the first postoperative year, they continued steadily throughout the study period. After open lower abdominal surgery 7.3 percent (643) of readmissions (8,861) were directly related to adhesions. This varied according to operation site: colon (7.1 percent), rectum (8.8 percent), and small intestine (7.6 percent). The readmission rate was assessed to provide an indicator of relative risk of adhesion-related problems after initial surgery. The overall average rate of readmissions was 70.4 per 100 initial operations, with 5.1 directly related to adhesions. This rose to 116.4 and 116.5, respectively, after colonic or rectal surgery—with 8.2 and 10.3 directly related to adhesions. CONCLUSIONS: There is a high relative risk of adhesion-related problems after open lower abdominal surgery and a correspondingly high workload associated with these readmissions. This is influenced by the initial site of surgery, colon and rectum having both the greatest impact on workload and highest relative risk of directly adhesion-related problems. The study provides sound justification for improved adhesion prevention strategies.

Postoperative adhesions: ten-year follow-up of 12,584 patients undergoing lower abdominal surgery.

The reduction in peritoneal plasminogen activator activity (believed to be the pathogenic mechanism of adhesion formation) and its replacement with recombinant tissue plasminogen activator (rt-PA) have been investigated in the prevention of initial (primary) and recurrent adhesion production. Other, potentially harmful, effects of intra-abdominal rt-PA application have also been examined. This included effects on wound and colonic healing and hemostasis. The prevention of adhesion formation was studied in primary and recurrent adhesion formation using a rabbit model. Primary adhesions formed in one of 14 occasions (7 per cent) with rt-PA compared with 12 of 15 occasions (80 per cent) with placebo (chi-square equals 15.542, p less than 0.001). Recurrent adhesions formed on two of 27 occasions (7 per cent) with rt-PA compared with 22 of 28 occasions with placebo (79 per cent) and 12 of 12 occasions with control rabbits (100 per cent, chi-square equals 40.588, p less than 0.0001). The application of rt-PA to abdominal wounds in the rabbit failed to show any reduction in wound strength at four, seven and ten days. Colonic anastomotic healing was unaltered by rt-PA at three, five and seven days. There was no difference seen in hemorrhagic events between control, placebo or rt-PA rabbits at any stage. The use of rt-PA is an exciting development in the field of adhesion prevention; it is an effective inhibitor of adhesion formation and intra-abdominal administration appears safe in a rabbit model.

The role of plasminogen activator in adhesion prevention.

Small bowel obstruction is a significant surgical problem and is commonly caused by postoperative adhesions. Patients suffering from this condition are often difficult to assess and require careful evaluation and management. Articles regarding the diagnosis, evaluation and management of small bowel obstruction have been identified from the Ovid, Embase and Silver Platter electronic databases and then reviewed by the authors. Particular emphasis has been placed on randomised controlled trials or large prospective series. Anecdotal reports or those containing small numbers have been largely excluded, but where they have been included it has been made clear in the text. The management of small bowel obstruction is predominantly the management of obstruction due to postoperative adhesions. The selective use of radiological techniques, such as water soluble contrast and CT studies, often help to characterise the nature of the obstruction and may even help with its resolution. Techniques involving the use of laparoscopy and barrier membranes may reduce morbidity but there is a need to evaluate these strategies further with prospective clinical trials.

D. Menzies

Papers

Intestinal obstruction from adhesions--how big is the problem?

Adhesion-related hospital readmissions after abdominal and pelvic surgery: a retrospective cohort study

Postoperative adhesions: ten-year follow-up of 12,584 patients undergoing lower abdominal surgery.

The role of plasminogen activator in adhesion prevention.

A review of the management of small bowel obstruction. Members of the Surgical and Clinical Adhesions Research Study (SCAR).