Collagen sponge as vaginal contraceptive barrier: critical summary of seven years of research

Biomedical applications of collagen

Collagen is regarded as one of the most useful biomaterials. The excellent biocompatibility and safety due to its biological characteristics, such as biodegradability and weak antigenecity, made collagen the primary resource in medical applications. The main applications of collagen as drug delivery systems are collagen shields in ophthalmology, sponges for burns/wounds, mini-pellets and tablets for protein delivery, gel formulation in combination with liposomes for sustained drug delivery, as controlling material for transdermal delivery, and nanoparticles for gene delivery and basic matrices for cell culture systems. It was also used for tissue engineering including skin replacement, bone substitutes, and artificial blood vessels and valves. This article reviews biomedical applications of collagen including the collagen film, which we have developed as a matrix system for evaluation of tissue calcification and for the embedding of a single cell suspension for tumorigenic study. The advantages and disadvantages of each system are also discussed.

Actions of spermicidal and virucidal agents on electrogenic ion transfer across human vaginal epithelium in vitro

Human ectocervical tissue was removed at operation over the menstrual cycle mounted as a sheet in vitro in an Ussing-style chamber and incubated in bicarbonate saline. The net electrogenic ion transport was measured as the short-circuit current (Isc in muamps/cm2) and was characterised as mainly (60-86%) an amiloride-sensitive electrogenic Na+ transport (lumen to serosa). Serosal application of amiloride had no effect. Serosal application of ouabain, a selective Na(+)-pump inhibitor, reduced the Isc to near zero but neither theophylline (10 mM) nor furosemide (1 mM) had any action. The data are compatible with a model ectocervical vaginal cell having an amiloride-sensitive Na+ entry mechanism at the lumenal membrane and a Na(+)-pump at the basolateral membrane removing the ion from the cell. The effects of the putative virucides, chlorhexidine and benzalkonium chloride, were tested on the preparation. Mucosally added chlorhexidine (2 mg/ml) had no effect on the Isc or tissue resistance but benzalkonium chloride, at concentrations between 0.06-1.2%, caused a rapid fall in the Isc. At the highest concentration this was only partly reversible even after two washes with fresh buffer. At the lowest concentration (0.03%) benzalkonium chloride sometimes caused an initial increase in the Isc which then fell to zero. In all the tissues even after the Isc was reduced to near zero, nigrosin left in contact with the tissue for 5 min. did not enter and stain the cells, indicating the detergent had a selective membrane action rather than causing a non-specific increase in permeability. The preparation allows objective measurements to be made of the initial acute membrane actions of putative spermicides and virucides on human vaginal ectocervical epithelial cells and offers a new approach of assessing their pharmacological/toxicological actions.

Porous collagen sponge for esophageal replacement

A new artificial esophagus with a bilayered structure made of porous collagen sponge and silicone was studied. The concept of this study was not to replace an esophageal defect permanently with prosthesis but to promote tissue regeneration by collagen. Five centimeters of cervical esophagus were replaced by this artificial esophagus in 19 adult mongrel dogs. Two weeks after implantation, the collagen sponge was replaced by autologous tissue and regeneration of the "neoesophagus" was observed in all animals. The inner surface of the neoesophagus was covered with mature mucosal epithelium similar to the intact esophagus 4-5 weeks after implantation. The replacement site was not complicated by infection, anastomotic leakage, or exuberant granulation tissue development on the luminal surface. In a long-term survival study, animals showed moderate-grade stenosis but could take normal feed orally and with no clinical problems observed.

The attachment and growth of an established cell line on collagen, chemically modified collagen, and collagen composite surfaces

The attachment and growth of an established cell line derived from mouse fibroblasts on collagen, chemically modified collagen, and collagen composite surfaces were compared. Tissue culture polystyrene dishes provided a suitable control. The substrates included native bovine dermal collagen, succinylated, acetylated and methylated collagen, and a series of composite materials formed from collagen and the glycosaminoglycans hyaluronic acid, chondroitin 4-sulphate and chondroitin 6-sulphate and the glycoprotein fibronectin. Attachment and growth of cells on each of these substrates were assessed by visual inspection under optical microscopy, by detachment of the cells using trypsinization and subsequent counting in a Coulter counter; and by 3H-thymidine incorporation studies. A very good correlation between the results was obtained by the three methods employed which showed that collagen, in comparison to polystyrene, is a relatively poor substrate for cellular attachment, growth and proliferation, but it may be improved by chemical modification and by incorporation of either fibronectin, chondroitin sulphate (5 and 10%), or low levels (less than 5%) of hyaluronic acid into the collagen matrix. Concentrations in excess of 5% hyaluronic acid into the collagen matrix, however, appeared to inhibit cellular attachment and growth and such materials provided a poorer substrate than native collagen.

Cellular invasion and breakdown of three different collagen films in the lumbar muscle of the rat

Collagen films were prepared by three different methods involving acid homogenization at pH 3.0 of a collagen suspension for 1.5 min (film A) and 15 min (film B) and alkaline homogenization at pH 10 for 15 min (film C), after which the resulting slurries were degassed and dried over sterile air. Subsequent examination by scanning electron microscope (SEM) revealed that all samples showed a distinctly layered structure which was much finer in the acid films. Implantation into the lumbar muscle of rats followed by histology and SEM studies revealed that film B was completely resorbed at 14 d whereas remnants of film A could still be seen at this period. The slowest rate of resorption was observed with film C, traces of which could still be found at 70 d. Invading inflammatory cells moved into the collagen films between the layers from the edges only causing the whole structure to 'ribbon out'. The surfaces of all three films appeared to be impenetrable to cells. Incubation of the three films with bacterial collagenase revealed similar relative rates of degradation to those observed in vivo.

Parity and use-effectiveness with the contraceptive sponge

The results of a randomized United States study indicated that the Today contraceptive sponge was less effective than the diaphragm (1-year cumulative life-table rate of 17.4 versus 12.9 pregnancies per 100 women, p = 0.01). However, this overall comparison is misleading. Using univariate and multivariate analyses to account for the effects of user characteristics we found parity to be the most important single determinant of effectiveness for users of the sponge, but parity was unimportant as a risk factor for pregnancy among diaphragm users. For nulliparous women the sponge was as effective as a physician-prescribed barrier method (13.9 for sponge, 12.8 for diaphragm, p = 0.45); however, parous women using the sponge were twice as likely to become pregnant (28.3 for sponge, 13.4 for diaphragm, p = 0.001). The effect of parity among sponge users is consistent with the results of international studies of the contraceptive sponge.