The Role of Nonmetastatic Lymph Nodes in the Survival of Colorectal Cancer: A Systematic Review

Objective

In this review, we aim to provide an overview of literature on lymph node (LN) histomorphological features and their relationship with the prognosis in colorectal cancer (CRC).

Background

Lymph nodes play a crucial role in the treatment and prognosis of CRC. The presence of LN metastases considerably worsens the prognosis in CRC patients. Literature has shown that the total number of LNs and the number negative LNs (LNnegs) has prognostic value in CRC patients. In esophageal carcinoma, LN size seems to be surrogate of the host antitumor response and a potentially clinically useful new prognostic biomarker for (y)pN0 esophageal carcinoma.

Methods

A comprehensive search was performed in Pubmed, Embase, Medline, CINAHL, and the Cochrane library in March 2021. The PRISMA guidelines were followed. Only studies focusing on histomorphological features and LN size and their relation to overall survival were selected.

Results

A total of 9 unique articles met all inclusion criteria and were therefore included in this systematic review. Six of these studies investigated HMF (eg, paracortical hyperplasia, germinal center predominance, and sinus histiocytosis) and 4 studies LNneg size and their relationship with overall survival. The presence of paracortical hyperplasia and an increased number of large LNnegs is related to a more favorable prognosis in CRC.

Conclusion

The results of this systematic review seem to support the hypothesis that there is a relationship between the host antitumor response reflected in different histomorphological reaction patterns visible in LNnegs and LNneg size related to survival in CRC patients.

The clinical importance of the host anti-tumour reaction patterns in regional tumour draining lymph nodes in patients with locally advanced resectable gastric cancer: a systematic review and meta-analysis

BACKGROUND

The status of regional tumour draining lymph nodes (LN) is crucial for prognostic evaluation in gastric cancer (GaC) patients. Changes in lymph node microarchitecture, such as follicular hyperplasia (FH), sinus histiocytosis (SH), or paracortical hyperplasia (PH), may be triggered by the anti-tumour immune response. However, the prognostic value of these changes in GaC patients is unclear.

METHODS

A systematic search in multiple databases was conducted to identify studies on the prognostic value of microarchitecture changes in regional tumour-negative and tumour-positive LNs measured on histopathological slides. Since the number of GaC publications was very limited, the search was subsequently expanded to include junctional and oesophageal cancer (OeC).

RESULTS

A total of 28 articles (17 gastric cancer, 11 oesophageal cancer) met the inclusion criteria, analyzing 26,503 lymph nodes from 3711 GaC and 1912 OeC patients. The studies described eight different types of lymph node microarchitecture changes, categorized into three patterns: hyperplasia (SH, FH, PH), cell-specific infiltration (dendritic cells, T cells, neutrophils, macrophages), and differential gene expression. Meta-analysis of five GaC studies showed a positive association between SH in tumour-negative lymph nodes and better 5-year overall survival. Pooled risk ratios for all LNs showed increased 5-year overall survival for the presence of SH and PH.

CONCLUSIONS

This systematic review suggests that sinus histiocytosis and paracortical hyperplasia in regional tumour-negative lymph nodes may provide additional prognostic information for gastric and oesophageal cancer patients. Further studies are needed to better understand the lymph node reaction patterns and explore their impact of chemotherapy treatment and immunotherapy efficacy.

Burden of disease experienced by patients following a watch-and-wait policy for locally advanced rectal cancer: A qualitative study

AIM

Patient-reported outcome measures (PROMs) are increasingly being used in routine cancer care to evaluate treatment and monitor symptoms, function and other aspects of quality of life (QoL). There is no suitable PROM for rectal cancer patients following a watch-and-wait (W&W) programme. Insight into patient experiences with this programme is an essential step in the development of a PROM. The aim of this qualitative study was to provide insights into the most important functional outcomes and QoL features experienced by patients during our W&W programme.

METHOD

Patients with locally advanced rectal cancer who are enrolled in the W&W programme in the Netherlands were interviewed by telephone using a semistructured interview guide. All interviews were digitally audio-recorded, transcribed verbatim and coded. A thematic approach was used to analyse the data and identify themes and subthemes of importance to patients.

RESULTS

Eighteen patients were interviewed (78% male, mean age 68 years, range 52-83 years). Physical complaints after treatment were present, most notably gastrointestinal problems, neuropathy and fatigue. Furthermore, patients were anxious about a possible recurrence, had a fear of surgery or a stoma, or were experiencing a general feeling of apprehension in daily life. Many patients had different coping mechanisms, such as acceptance, and there were few limitations in daily life.

CONCLUSION

We identified important functional outcomes, such as gastrointestinal complaints, fatigue and neuropathy, in patients who were enrolled in this W&W programme. Furthermore, an emotional burden and unmet needs were reported by these patients. These findings can be used to improve clinical practice and inform the development of a PROM.

Nuss Procedure for Pectus Excavatum: A Comparison of Complications Between Young and Adult Patients

BACKGROUND

The Nuss procedure is the gold standard surgical treatment for pectus excavatum in young patients. Its use in adults has also been described, although it may be associated with increased postoperative morbidity resulting from higher chest wall rigidity. This study aimed to examine the risk of complications after the Nuss procedure in adult patients compared with young patients with pectus excavatum.

METHODS

This single-center retrospective cohort study evaluated all patients who underwent the Nuss procedure between 2006 and 2018. Patients were stratified by age as young (≤24 years old) and adult (>24 years old). The primary end point was the occurrence of perioperative or postoperative complications, subdivided into major (Clavien-Dindo class III_a or higher) and minor (less severe than Clavien-Dindo class III). Between-group differences were analyzed using the Mann-Whitney U and the χ² test with post hoc analysis.

RESULTS

A total of 327 participants were included, 272 in the young group (median age, 16 years; interquartile range [IQR], 15 to 18 years; range, 11 to 24 years) and 55 in the adult group (median age, 32 years; IQR, 27 to 38 years; range, 25 to 47 years). The median Haller index was similar between groups (young, 3.7; IQR, 3.2 to 4.4 vs adult,3.6; IQR, 3.0 to 4.3; P = .44). The median follow-up was 34 and 36 months, respectively. The incidence of major complications was comparable between young and adult participants (P = .43). Minor complications occurred more often among adults (young, 4% vs adult, 11%; P = .002). Chronic postoperative pain was the only minor complication with a significant difference in incidence (young, 1% vs adult, 7%; P = .008).

CONCLUSIONS

The Nuss procedure is a safe surgical treatment for pectus excavatum in both young and adult patients. The risk of major complications is comparable. However, adults more often have chronic pain.

Meniscal replacement in dogs. Tissue regeneration in two different materials with similar properties

In earlier studies, meniscal replacement with a porous polymer implant led to regeneration of neo-meniscal tissue. To evaluate the influence of the chemical properties on the tissue regeneration in the implant, in the present study, the meniscus in the dog's knee was replaced with either an aromatic 4,4-diphenylmethanediisocyanate based polyesterurethane implant (Estane) (n = 6) or with an aliphatic 1,4-butanediisocyanate based polyesterurethane implant (PCLPU) (n = 6). After 6 months, the knee joints were resected and the tissue behavior in the two different prostheses was evaluated microscopically. In both prostheses, a meniscus-like distribution of the tissue phenotype was found with collagen type I in the peripheral fibrous zones and collagen type II in the central, more cartilaginous zones. The compression-stress behavior of the implant-tissue construct remained in between the stiffness of the polymer material and that of the native meniscus. The PCLPU implant seemed to provoke less synovial tissue reaction. After meniscectomy solely, in 5 out of 6 cases, a meniscus-like regenerate was formed. Furthermore, the articular cartilage degeneration after placing a PCLPU implant did also not exceed the degeneration after the Estane implant or after meniscectomy. The differences between these two implants did not seem to influence the tissue regeneration in the implant. However, PCLPU seemed to evoke less tissue reaction and, therefore, is thought to be less or even nontoxic as compared with the Estane implant. Therefore, for studies in the future, the authors prefer the PCLPU prostheses for replacement of the meniscus.

Design, synthesis and properties of a degradable polyurethane scaffold for meniscus regeneration

Longitudinal lesions in menisci are among the most frequent orthopedic problems of the knee. Repair by simple techniques is only limited to the vascular part of the meniscus. For repair of the avascular part of the meniscus a scaffold, which will assist the body in the formation of new meniscus cell tissue, might be applicable. In this study a biomedical segmented polyurethane with poly(epsilon-caprolactone) as soft segment and 1,4-butanediisocyanate and 1,4-butanediol as uniform hard segments has been synthesised. The material has a micro phase separated morphology and excellent mechanical properties. A porous scaffold was prepared via a combination of liquid-liquid phase separation and salt leaching. The foams prepared combined a very high interconnectivity and porosity with the desired compression modulus. After six months of implantation in the knees of beagles full ingrowth with cells was obtained and it was found that meniscus like tissue had been formed in the scaffold. Moreover, compression behaviour appeared to be comparable to native meniscus tissue.

A porous polymer scaffold for meniscal lesion repair--a study in dogs

Meniscal lesions often occur in the avascular area of the meniscus with little chance of spontaneous repair. An access channel in the meniscal tissue can function as an entrance for ingrowing repair tissue from the vascular periphery of the meniscus to the lesion in the avascular zone which again induced healing of the lesion. Implantation of a porous polymer in a full-thickness access channel induced healing. However, a better integration between meniscal tissue and the implant might be achieved with the combination of the newly developed porous polymers and a modified surgical technique. This might improve meniscal lesion healing and the repair of the access channel with neo-meniscal tissue. Longitudinal lesions were created in the avascular part of 24 canine lateral menisci and a partial-thickness access channel was formed to connect the lesion with the meniscal periphery. In 12 menisci, the access channel was left empty (control group), while in the remaining 12 menisci the polymer implant was sutured into the access channel. Repair of the longitudinal lesions was achieved with and without polymer implantation in the partial-thickness access channel. Polymer implants induced fibrous ingrowth with cartilaginous areas, which resembled neo-meniscal tissue. Implantation did not prevent articular cartilage degeneration.

Presence and mechanism of knee articular cartilage degeneration after meniscal reconstruction in dogs

OBJECTIVE

Partial meniscectomy is the golden standard for treating a bucket-handle tear in the meniscus of the knee, but it inevitably leads to articular cartilage degeneration. Surgical creation of an access channel between the lesion and the vascularized synovial lining is intended to induce ingrowth of repair tissue and thus avoid degeneration of articular cartilage.

DESIGN

The presence and mechanism of cartilage degeneration were evaluated in 24 canine menisci after a longitudinal lesion and access channel had been created in the avascular part of the meniscus. In 12 menisci the channel was implanted with a porous polymer scaffold, while the remaining 12 were left empty. Evaluation was performed using routine histology and antibodies directed against denatured type II collagen (Col2-3/4M).

RESULTS

Articular degeneration was apparent in the polymer implant group and the empty channel group. This consisted of fibrillation, loss of chondrocytes and decreased proteoglycan content. Areas of fibrillated cartilage always showed positive labeling with the collagen degradation antibody Col2-3/4M. Collagen degradation was also visible in non-fibrillated areas. The upper zone of the cartilage showed swelling especially in the implant group, with empty cell lacunae and moderate levels of Col2-3/4M antibody labeling.

DISCUSSION

This reconstruction technique cannot be considered superior to partial meniscectomy. We propose that degradation of the collagen type II network is a result of cartilage fibrillation and vice versa.

Cytotoxicity of poly(96L/4D-lactide): the influence of degradation and sterilization

The cytotoxicity of poly(96L/4D-lactide) (PLA96), and of its accumulated degradation products, was investigated following different sterilization methods and pre-determined heat-accelerated degradation intervals. PLA96 samples sterilized by either steam, ethylene oxide, or gamma irradiation were left untreated (S0 samples), or were degraded for 30 h or 60 h (S30 and S60 samples) at 90 degrees C in water. Extracts of the samples and of the remaining degradation fluids (F30 and F60) were prepared. The toxicity of both unfiltered and filtered extracts was analyzed in a cell growth inhibition (CGI) assay and a lactate dehydrogenase (LDH) leakage assay. Physical analysis of the extracted samples and of the degradation fluids also was performed. The S0 extracts demonstrated no significant CGI. The CGI of the S30 extracts ranged from 37 to 78%, whereas the CGI of the S60 extracts ranged from 6 to 33%. The CGI of the F30 extracts ranged from 19 to 38% and the CGI of the F60 extracts was 98 to 123%. The LDH leakage assay only showed a high response to the unfiltered F60 extracts. Neither sterilization nor filtration appeared to influence the cytotoxicity of the extracts. Particle accumulation, however, might affect cell membrane permeability resulting in LDH leakage. The results of this study suggest that the cytotoxicity of PLA96 is related to the pH and possibly the osmolarity of the tested extracts. The pH and osmolarity, in turn, may depend on variations in the amounts of solubilized lactic acid and oligomers. These variations appear to result from degradation stage-dependent differences in crystallinity, molecular weight and molecular weight distribution of the PLA96 samples.

Solvent-free fabrication of micro-porous polyurethane amide and polyurethane-urea scaffolds for repair and replacement of the knee-joint meniscus

New porous polyurethane urea and polyurethane amide scaffolds for meniscal reconstruction have been developed in a solvent-free process. As soft segments, copolymers of 50/50 L-lactide/epsilon-caprolactone have been used. After terminating the soft segment with diisocyanates, chain extension was performed with adipic acid and water. Reaction between the isocyanate groups and adipic acid or water provides carbon dioxide and results in a porous polymer. Extra hydroxyl-terminated prepolymer was added in order to regulate the amount of carbon dioxide formed in the foaming reaction. Furthermore, salt crystals ranging in size from 150 to 355 microm were added in order to induce macroporosity. The pore size was regulated by addition of surfactant and by the use of ultrasonic waves. The resulting porous polymer scaffolds exhibit good mechanical properties like a high-compression modulus of 150 kPa. Chain extension with adipic acid results in better mechanical properties due to better defined hard segments. This results from the lower nucleophilicity of carboxylic acids compared to water and alcohols. By adjusting the reaction conditions, materials in which macropores are interconnected by micropores can be obtained. On degradation only non-toxic products will be released; importantly, the materials were obtained by a simple, reproducible and solvent-free procedure.

Poly(DL-lactide-epsilon-caprolactone) nerve guides perform better than autologous nerve grafts

The aim of this study was to compare the speed and quality of nerve regeneration after reconstruction using a biodegradable nerve guide or an autologous nerve graft. We evaluated nerve regeneration using light microscopy, transmission electron microscopy and morphometric analysis. Nerve regeneration across a short nerve gap, after reconstruction using a biodegradable nerve guide, is faster and qualitatively better, when compared with nerve reconstruction using an autologous nerve graft. Therefore, we conclude that in the case of a short nerve gap (1 cm), reconstruction should be carried out using a biodegradable nerve guide constructed of a copolymer of DL-lactide and epsilon-caprolactone.

The effects of different steam-sterilization programs on material properties of poly(L-lactide)

As-polymerized poly(L-lactide) test rods were sterilized by seven different specially designed computer-operated autoclaving programs. As a control, common hospital sterilization was performed. In all cases, the molecular weight decreased after sterilization. A short time high-temperature sterilization led to less molecular weight decrease than a low sterilization temperature cycle with a longer sterilization time. Regular hospital sterilization significantly reduced the elongation at break and also resulted in a decrease of 35% in tensile strength. The program causing minimal damage to the material properties was studied in detail. This program, with a sterilization period of 60 s and 129 degrees C, was effective for PLLA sterilization and also looks very promising for sterilization of other thermo- and moisture-labile polymers.

A new biomedical polyurethane with a high modulus based on 1,4-butanediisocyanate and epsilon-caprolactone

A new approach to the synthesis of biomedical polyurethanes based on epsilon-caprolactone and 1,4-butanediisocyanate with a high modulus, has been developed. By chain extending an epsilon-caprolactone prepolymer with a long uniform-size diisocyanate block, a segmented polyurethane with uniform-size hard segments was obtained. It shows excellent mechanical properties; an extremely high modulus of 105 MPa and a tensile strength of 35 MPa. The polymer is soluble at high concentrations in various volatile solvents such as chloroform and 1,4-dioxane. By a combination of salt-leaching and freeze-drying, porous materials have been obtained in which macropores ranging in size from 150-300 microm are highly interconnected by micropores. The material shows a sufficiently high compression modulus of 200 kPa and appears to be suitable for biomedical applications such as meniscal prostheses.

The effect of chromic acid treatment on the mechanical and tribological properties of aramid fibre reinforced ultra-high molecular weight polyethylene composite

Surface oxidation of ultra-high molecular weight polyethylene (UHMWPE) powder has an influence on the mixing procedure of chopped fibres and UHMWPE powder. Due to this oxidation hydrogen bonds can be formed between the fibres and powder particles, leading to a more homogeneous fibre-powder mixture. This treatment improves the fibre-matrix interface and thus the physical properties of the composite. Chromic acid treatment also has an influence on the mechanical and tribological properties of the aramid-UHMWPE composite. Although only a relatively small improvement is observed in the modulus, yield stress and stress at break, of 33, 17 and 9%, respectively, a substantial enhancement in wear resistance of 117% is observed.

A novel method for fabrication of biodegradable scaffolds with high compression moduli

It has been previously shown that, when used for meniscal reconstruction, porous copoly(L-lactide/epsilon-caprolactone) implants enhanced healing of meniscal lesions owing to their excellent adhesive properties. However, it appeared that the materials had an insufficient compression modulus to accomplish 100% fibrocartilage formation. In addition, to be used for meniscal prosthesis, the compression modulus of the porous materials should be larger than 150 kPa in order to protect the articular cartilage. A technique was developed to prepare stiff porous materials of a high molecular weight 50/50 copoly(L-lactide/epsilon-caprolactone) suitable for fibrocartilage regeneration in meniscal implants and meniscal prosthesis. Porous microspheres (50-250 microm) were agglutinated in the presence of NaCl crystals (250-300 microm). The microspheres were mixed with solid solvent in order to obtain a homogeneous distribution of solvent over the spheres. By changing the amount of solvent and crystals, the density and the compression modulus could be varied over a range of 0.07 g ml(-1) to 0.5 g dl(-1) and 40-1100 kPa, respectively.

Long-term evaluation of degradation and foreign-body reaction of subcutaneously implanted poly(DL-lactide-epsilon-caprolactone)

The aim of this study was to evaluate the degradation and foreign-body reaction of poly(DL-lactide-epsilon-caprolactone) (PLA85CL50) bars. This specific biomaterial is used for the construction of nerve guides, which can be used in the reconstruction of short nerve gaps. Subcutaneously implanted PLA85CL50 bars were harvested after implantation periods ranging from 3 to 12 months and evaluated for the rate of degradation and the degree of foreign-body reaction. It was observed that this copolymer degraded completely within 12 months and that no lactide or epsilon-caprolactone crystals were formed. Furthermore, we conclude that the foreign-body reaction of PLA85CL50 is very mild. These properties make the amorphous copolymer of DL-lactide and epsilon-caprolactone (50:50) suitable for the construction of nerve guides.

Evaluation of functional nerve recovery after reconstruction with a new biodegradable poly (DL-lactide-epsilon-caprolactone) nerve guide

The aim of this study was to evaluate functional nerve recovery following reconstruction of a 1 cm gap in the sciatic nerve of a rat, using a new biodegradable p (DLLA-epsilon-CL) nerve guide. To evaluate both motor and sensory nerve recovery, walking track analysis and electrostimulation tests were carried out after implantation periods, ranging from 3 to 15 weeks post-operatively. The first signs of functional nerve recovery were observed after 3 weeks. After 15 weeks, 70% of the motor- and 90% of the sensory nerve function was re-established. Return of nerve function was better, in comparison with results from other studies. This study demonstrated successful functional nerve recovery after the reconstruction of a 1 cm nerve gap with a biodegradable p(DLLA-epsilon-CL) nerve guide.

Meniscal tissue regeneration in porous 50/50 copoly(L-lactide/epsilon-caprolactone) implants

Porous materials of a high-molecular-weight 50/50 copolymer of L-lactide and epsilon-caprolactone with different compression moduli were used for meniscal repair. In contrast to the previously used 4,4'-diphenylmethane and 1,4-trans-cyclohexane diisocyanates containing polyurethanes, degradation products of the copolymer are non-toxic. Two series of porous materials with compression moduli of 40 and 100 kPa respectively were implanted in the knees of dogs using a new, less traumatizing suturing technique. A porous aliphatic polyurethane series with compression modulus of 150 kPa was implanted for comparison. Adhesion of the implant to meniscal tissue was found to be essential for healing of the longitudinal lesion. Copolymer implants showed better adhesion, probably due to the higher degradation rate of the copolymer. Fibrocartilage formation was found to be affected by the compression modulus of the implant. Implants with a modulus of 40 kPa did not show ingrowth of fibrocartilage, whereas implants with compression moduli of 100 and 150 kPa yielded 50-70 and 80-100% fibrocartilage respectively. During degradation the copolymer phase separated into a crystalline phase containing mainly L-lactide and an amorphous phase containing mainly epsilon-caprolactone. The copolymer degraded through bulk degradation.

Meniscal repair by fibrocartilage in the dog: characterization of the repair tissue and the role of vascularity

Lesions in the avascular part of 20 canine menisci were repaired by implantation of a porous polyurethane. Seven menisci were not repaired and served as controls. The repair tissue was characterized by biochemical and immunological analysis. The role of vascularity in healing was studied by perfusion of menisci with Indian ink. Histologically, repair tissue inside the implants initially consisted of fibrous tissue containing type I collagen. After 2 months, fibrocartilaginous tissue developed inside the implants, whereas control defects only showed repair with fibrous tissue. Both type I and type II collagen, the two major collagen types of normal meniscal fibrocartilage, could be detected in this newly formed fibrocartilage. The implant guided vascular tissue from the periphery towards the lesion resulting in healing of the tear. After fibrocartilage had formed, vascularity decreased and was completely absent in mature fibrocartilage. Control defects remained filled with vascular connective tissue. Two-thirds of the longitudinal lesions were found to be healed partially or completely. It is concluded that implantation of a porous polymer does enhance vascularity sufficiently to result in healing of meniscal lesions extending into the avascular part. Healing takes place by repair tissue strongly resembling normal meniscal fibrocartilage.

Meniscal replacement using a porous polymer prosthesis: a preliminary study in the dog

A porous polyurethane prosthesis was used to replace the lateral meniscus in the dog. After an initial ingrowth of fibrous tissue, the prostheses became filled with tissue strongly resembling normal meniscal fibrocartilage. Although less severe than seen after total meniscectomy, cartilage degeneration was frequent, possibly because tissue ingrowth in the prostheses occurred too slowly. Porous polymers can be useful for replacement of the meniscus, provided that chemical and physical properties are optimized.

Light-microscopic and electron-microscopic evaluation of short-term nerve regeneration using a biodegradable poly(DL-lactide-epsilon-caprolacton) nerve guide

The aim of this study was to evaluate short-term peripheral nerve regeneration across a 10-mm. gap, using a biodegradable poly(DL-lactide-epsilon-caprolacton) nerve guide, with an internal diameter of 1.5 mm and a wall thickness of 0.30 mm. To do so, we evaluated regenerating nerves using light microscopy, transmission electron microscopy and morphometric analysis after implantation of 12-mm nerve guides in the sciatic nerve of the rat. Evaluation times ranged from 3-10 weeks. Three weeks after reconstruction, myelinated nerve fibers could be observed in the distal nerve stump. Ten weeks after reconstruction, the regenerating nerves already resembled normal nerves. In conclusion, we show that poly(DL-lactide-epsilon-caprolacton) nerve guides can be successfully applied in the reconstruction of severed nerves in the rat model. Furthermore, we have observed the fastest nerve regeneration described thus far, after reconstruction using a biodegradable nerve guide.

Use of porous polyurethanes for meniscal reconstruction and meniscal prostheses

In the past, porous materials made of an aromatic polyurethane (PU) were successfully used to meniscal reconstruction in dogs. Since aromatic PUs yield very toxic fragments upon degradation, a linear PU was synthesized by curing a poly(epsilon-caprolactone) and 1,4-trans-cyclohexane diisocyanate based prepolymer with cyclohexanedimethanol. Porous materials of this polymer were also implanted for meniscal reconstruction. The results were comparable with the most successful implant series so far. Additionally, a porous meniscal prosthesis was developed to replace a total meniscus. Due to the very high shear stresses to which the prosthesis would be exposed, the stress hysteresis phenomenon linear PUs are known to exhibit could be of great consequence. Therefore an aliphatic PU network, synthesized by cross-linking poly(epsilon-caprolactone) and 1,4-trans-cyclohexane diisocyanate with glycerol, was used. Dislocation caused by tearing out of the sutures was found to be a problem because the tear resistance of the material was relatively low. In this study the tearing problem has been partly circumvented by using a complex suturing technique. Meniscal prostheses turned out to induce fibrocartilage upon implantation, and degeneration of articular cartilage was less severe than after meniscectomy.

High-impact poly(L/D-lactide) for fracture fixation: in vitro degradation and animal pilot study

The impact strength of amorphous lactide copolymers can be significantly improved by blending with biodegradable rubbers. Rubber toughening of amorphous poly(85L/15D -lactide) with the copolymer poly (50/50-trimethylenecarbonate-co-epsilon-caprolactone) results in a high-impact polymer (PDLLA/P(TMC-CL)). In vitro, the PDLLA/P(TMC-CL) blend retained its tensile and impact strength for a long period of time. Up to 45 weeks, the amount of water absorbed by the blend remained very low and no significant mass loss was observed. To test the suitability for fracture fixation, in a dog study mandibular fractures were fixated with PDLLA/P(TMC-CL) bone plates and screws. Bone healing was uneventful without premature failure of the implants. Although long-term degradation studies have to be carried out, PDLLA/P(TMC-CL) seems to be promising for application in fracture fixation.

Biological performance of a degradable poly(lactic acid-epsilon-caprolactone) nerve guide: influence of tube dimensions

One of the ways to reconstruct a nerve defect is to use a biodegradable nerve guide. The aim of this study was to establish a nerve guide constructed of an amorphous copolymer of lactic acid-caprolactone. A pilot study was set up to elucidate the effect of the tube dimensions on nerve regeneration. Four types of nerve guides, with internal diameters ranging from 1.12-1.23 mm and wall thicknesses ranging from 0.34-0.68, were tested for this purpose. We evaluated the biodegradation, foreign body reaction and nerve regeneration by light microscopy, after three different implantation times (1, 2, and 3 months). After 2 months, we observed that all types of nerve guides had changed from a transparent to an opaque and swollen state, and that they had lost their strength. The foreign body reaction was characterized by the presence of giant cells and fibroblasts surrounding the degrading nerve guide. From this pilot study, we conclude that nerve guide type 1, with an internal diameter of 1.23 mm and a wall thickness of 0.34 mm, can ensure nerve regeneration in the case of a 1-cm gap in the sciatic nerve of the rat. Nerve guides types 3 and 4, with relatively small lumens, show nerve compression due to a more pronounced swelling of the degrading tube.

In vivo degradation and biocompatibility study of in vitro pre-degraded as-polymerized polyactide particles

The degradation of high molecular weight as-polymerized poly(L-lactide) (PLLA) is very slow; it takes more than 5.6 yr for total resorption. Moreover, the degradation products of as-polymerized PLLA bone plates, consisting of numerous stable particles of high crystallinity, are related with a subcutaneous swelling in patients 3 yr postoperatively. In order to avoid these complications, polymers were developed that are anticipated to have comparable mechanical properties but a higher degradation rate and do not degrade into highly stable particles that can induce a subcutaneous swelling. On chemical grounds it can be expected that copolymerization of PLLA with 4% D-lactide (PLA96) or by modifying PLLA through cross-linking (CL-PLLA) will lead to less stable particles and a higher degradation rate. To evaluate the long-term suitability of these as-polymerized polymers, the biocompatibility of the degradation products should be studied. Considering the very slow degradation rate of as-polymerized PLLA, in vitro pre-degradation at elevated temperatures was used to shorten the in vivo follow-up periods. In this study, the biocompatibility and degradation of as-polymerized PLLA, PLA96 and CL-PLLA were investigated by implanting pre-degraded particulate materials subcutaneously in rats. Animals were killed after a postoperative period varying from 3 to 80 wk. Light and electron microscopical analysis and quantitative measurements were performed. The histological response of all three pre-degraded materials showed a good similarity with in vivo implanted material. Pre-degraded PLLA induced a mild foreign body reaction and showed a slow degradation rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Biocompatibility study of as-polymerized poly(L-lactide) in rats using a cage implant system

To evaluate the biocompatibility of in vitro predegraded as polymerized poly(L-lactide) (PLLA), a cage implant system was used to investigate white cell and enzyme concentrations with time. The use of a cage permits in a serial fashion a quantitative and qualitative measurement of exudate components formed around an implant. Subcutaneously in rats, caped cages manufactured from stainless-steel mesh were implanted with in vitro predegraded, as-polymerized PLLA, as-polymerized PLLA cylinders, and empty cages serving as controls. In vitro predegradation was used to simulate the degradation products of long-term in vitro degradation. Predegraded PLLA particles were obtained by in vitro hydrolysis at elevated temperatures. The first 7 days of implantation were characterized by an acute inflammatory reaction; the exudate extracted from the cages showed predominantly neutrophils for all types of implants. After day 7, there was a more chronic inflammatory reaction with predominantly macrophages and lymphocytes. There were no significant differences in the total leukocyte concentration or macrophage concentration for any of the cages in the period from 10-21 days. Extracellular enzyme activity also did not show any significant differences among the three types of cages. A possible explanation for the absence of any significant differences could be that the in vitro predegraded particles were sieved before implantation, thus eliminating all small particles (< 70 microns) that are probably mandatory to provoke an increased cellular reaction.

Influence of luminal pore size on the patency rate and endothelialization of polymeric microvenous prostheses

In microvenous prosthetic surgery a continuous search for better patency rates is necessary to enable a clinical application. In this search for better patencies, modifications in the wall structure are being made. Directions found in the literature suggest that pore size plays an important role in achieving better patencies. Thus far, no study has been conducted to evaluate the influence of pore size on the patency rate of polyurethane microvenous prostheses. Since polyurethane is known to yield good patency rates, we conducted this study in which we compared different luminal pore sizes with regard to patency. Pore size varied from 0.6 to 20 microns in microvenous polyurethane-based prostheses (length 5-6 mm, internal diameter 1 mm). The results showed a favorable patency rate in the pore sizes larger than 5.0 microns (patency 75%) when compared to pore sizes smaller than 2.0 microns (patency 50%). This study demonstrates that microvenous polyurethane-based prostheses with a luminal pore size larger than 5.0 microns may yield better patency rates than prostheses with a luminal pore size smaller than 5.0 microns. Further studies are currently being performed to elucidate the very reasons for this effect.

Reinforced poly(L-lactic acid) fibres as suture material

In this study, reinforced poly(L-lactic acid) (PLLA) fibers made by a dry-spinning/hot-drawing process were evaluated for use as a suture. The initial tensile strength of the PLLA fibers was lower than the initial tensile strength of the commercially available sutures: PDS, Vicryl, silk, and Ethilon. However, after 12 weeks immersion in a phosphate saline buffer at 37 degrees C, PDS sutures have lower tensile strength than PLLA sutures and the tensile strength of Vicryl was unmeasurable because of fragmentation. Initially, PLLA fibers disintegrated into fibrils during degradation triggering an inflammatory response comparable to degradable multifilament sutures. However, the intensity of the inflammatory response against the PLLA fibers decreased and after 80 weeks implantation in the muscle layer of the abdominal wall of rats it was comparable to the one against Ethilon. The inflammatory response against Ethilon, which is considered to be nondegradable, increased in the same period, probably due to the change in shape. In practice, the handling characteristics of PLLA sutures are superior to the monofilament sutures like PDS and Ethilon and comparable with the multifilament sutures like Vicryl and silk. The knot security of PLLA sutures are expected to be better than the knot security of the monofilament sutures, but this remains to be investigated. It is concluded that dry-spun/hot-drawn (reinforced) PLLA fibers have the potential for use as long-term degradable suture material.

Autoclavable highly cross-linked polyurethane networks in ophthalmology

Highly cross-linked aliphatic polyurethane networks have been prepared by the bulk step reaction of low molecular weight polyols and hexamethylenediisocyanate (HDI). These polyurethane networks are optically transparent, colourless and autoclavable amorphous glassy thermosets, which are suited for use in ophthalmic applications such as intraocular lenses and keratoprostheses. The properties of these glassy polyurethanes, obtained from the reaction of the low molecular weight polyols triisopropanolamine (TIPA) or tetrakis (2-hydroxypropyl)ethylenediamine (Quadrol) and HDI in stoichiometric proportions, have been investigated in more detail. The glassy Quadrol/HDI-based polyurethane exhibits a reduction in ultimate glass transition temperature from 85 to 48 degrees C by uptake of 1% of water, and good ultimate mechanical properties (tensile strength 80-85 MPa, elongation at break ca 15%, modulus ca 1.5 GPa). IR spectra of these hydrophobic polyurethane networks revealed the absence of an isocyanate absorption, indicating that all isocyanates, apparently, had reacted during the cross-linking reaction. The biocompatibility could be increased by grafting tethered polyacrylamide chains onto the surface during network formation. These transparent cross-linked polyurethanes did not transmit UV light up to 400 nm, by incorporation of a small amount of the UV absorbing chromophore Coumarin 102, and could be sterilized simply by autoclaving. They were implanted in rabbit eyes, either in the form of small circular disks or in the form of a keratoprosthesis (artificial cornea). It was shown that the material was well tolerated by the rabbit eyes. Serious opacification of the cornea, a direct result of an adverse reaction to the implant, was never seen. Even 1 yr after implantation of a polyurethane keratoprosthesis the eye was still 'quiet'.

Long-term evaluation of nerve regeneration in a biodegradable nerve guide

Nerve regeneration using artificial biodegradable conduits is of increasing interest. The aim of this study is to evaluate the regeneration and maturation of a nerve after long-term implantation (2 years) of a biodegradable poly-L-lactide/poly-epsilon-caprolactone (PLLA/PCL) copolymeric nerve guide in the sciatic nerve of the rat. After harvesting, we evaluated both the regenerated nerves and the controls, using light microscopy, transmission electron microscopy, and morphometric techniques. Remnants of biomaterial were still present after 2 years of implantation, but the foreign body reaction was very mild at this stage, due to the rounded shapes of the polymer debris. Morphometric analysis showed significant differences between the regenerated nerve and the normal sciatic nerve: the number of myelinated fibers is higher, and the mean fiber diameter of the myelinated fibers in the regenerated nerve is smaller. In conclusion, the results demonstrate that the new PLLA/PCL nerve guide can provide optimal conditions for regeneration and maturation of damaged nerves.

Porous implants for knee joint meniscus reconstruction: a preliminary study on the role of pore sizes in ingrowth and differentiation of fibrocartilage

Implants with four different macropore sizes were implanted in the meniscus of 29 rabbits for assessment of ingrowth and differentiation of fibrocartilage. Implant macropores were 50-90, 90-150, 150-250 and 250-500 mum, the vol.% macropores was 48-55 and total pore volume 84-86 vol.%. Ingrowth was optimal in the two large pore implants whereas the small pore implants partially remained empty up to 1 year post-operative. Capsule formation and the foreign body reaction was severe for the small pore implants whereas this occurred to a lesser extent in the two large pore implants. Fibrocartilage formation, as assessed by morphology and antibody labelling for type I and type II collagen, was observed in a similar way in all implant types. It is concluded that for optimal ingrowth and incorporation of partial or total meniscal prosthesis, macropore sizes must be in the range of 150-500 mum.

Meniscal repair by fibrocartilage? An experimental study in the dog

Longitudinal lesions in the avascular part of the dog's meniscus were repaired by implantation of a porous polyurethane. Ingrowing repair tissue was characterized by biochemical and immunological analysis. Histologically, repair tissue initially was composed of fibrous tissue containing type I collagen. After 3 months, fibrocartilaginous tissue developed inside the implants, whereas control defects only showed fibrous repair tissue. Both type I and II collagen, the major collagen types of normal meniscal fibrocartilage, could be detected in this newly formed fibrocartilage. It is concluded that fibrocartilage resembling normal meniscal tissue is formed and that longitudinal lesions can be healed after meniscal repair by implantation of a porous polymer.

Design of a polyurethane membrane for the encapsulation of islets of Langerhans

A semipermeable membrane for the encapsulation of the islets of Langerhans, consisting of a microporous polymer network, has been developed. The polyurethane network was formed by cross-linking a mixture of linoleic acid and a linear poly(etherurethane) with dicumyl peroxide. Cross-linking the polyurethane impedes the formation of hard domains. Miocroporosity was introduced by adding salt crystals of different sizes before cross-linking and leaching it out afterwards. To optimize the permeability and immunoprotectivity, membranes were prepared with three different porosities. Membranes of this material were filled with islets of Langerhans and implanted in the peritoneal cavity of rats. Short-term in vivo experiments in rats show that membranes with pores in the range 0.3-0.7 micron and a wall thickness of about 8 microns were permeable for insulin and glucose and protected the islets of Langerhans against the cells of the immunological system.

Porous polymer implants for repair of full-thickness defects of articular cartilage: an experimental study in rabbit and dog

Full-thickness defects of articular cartilage were repaired by implantation of porous polymer implants in rabbits and dogs. The quality of the repair tissue was determined by collagen typing with antibodies. Implants with varying pore sizes and chemical composition were used. The effect of loading and motion was determined by inserting implants higher than, level with and lower than the surrounding cartilage. It appeared that healing took place by formation of fibrocartilaginous repair tissue containing both type I and type II collagen. Hyaline cartilage was observed in a minority of the rabbits used but not in the dog. Fibrocartilage formation in the dog was simulated by implantation of a porous polymer. Chemical composition of the polymer did not alter the results, neither did loading of the implant. It is concluded that the formation of fibrocartilaginous repair cartilage is stimulated by implantation of a porous polymer. This tissue seemed to function adequately in the dog but did show signs of degeneration in the rabbit.

Porous polymer implant for repair of meniscal lesions: a preliminary study in dogs

Artificial meniscal lesions extending into the avascular part of the meniscus, which do not heal by any other means, were repaired by suturing either a porous polymer implant or a synovial flap into the defect. The implant guided the ingrowth of vascular repair tissue into the defect. This fibrous tissue later on transformed into fibrocartilage. Reconstruction with a synovial flap was not successful. It appeared that healing can be achieved by implantation of a porous polymer implant in a large number of cases. Future research will be aiming at improvement of the results of meniscal repair and application of this type of polymer for repair of cartilage defects.

Degradation of and tissue reaction to biodegradable poly(L-lactide) for use as internal fixation of fractures: a study in rats

Samples of high-molecular-weight poly(L-lactide) (PLLA) (Mv = 9.0 x 10(5), a biomaterial developed for plates and screws used in internal fixation of jaw fractures, were implanted subcutaneously in the backs of rats to study tissue reaction to PLLA and to follow the degradation process. The PLLA seemed to follow the degradation pattern typical of biodegradable polyesters. After pure hydrolysis up to about 104 wk, phagocytic activity of macrophages was found at about 143 wk. Full resorption of PLLA was not demonstrated in this study. Except for the early and final parts of the implant period, no acute or chronic inflammatory reaction was observed. No implant was rejected. It is estimated that more than 3 yr will be required for total resorption of PLLA. For bone-healing this long period is of no practical importance. There is no need for removal of PLLA after fracture healing as is the case with metal fixation devices. Thus, PLLA has potential application in internal fixation of fractures and osteotomies in the maxillofacial region and other fractures that are not too heavily loaded in the human body.

Nerve regeneration through a two-ply biodegradable nerve guide in the rat and the influence of ACTH4-9 nerve growth factor

Biodegradable polyurethane-based (PU) nerve guides, instilled with or without ACTH4-9 analog (a melanocortin) were used for bridging an 8 mm gap in the rat sciatic nerve and were evaluated for function and histological appearance after 16 weeks of implantation. Autologous nerve grafts functioned as controls. The guides successfully enabled the sciatic nerve to regenerate across the 8 mm gap, thus effectively reestablishing the contact between the proximal and distal nerve ends. The mean conduction velocity, motor latency, and muscle action potentials of all the nerve guides did not differ significantly from the autografts. The histological quality of the regeneration in the nerve guides was significantly better than in the autografts; in the nerve guides, a well-defined nerve cable of normal architecture had regenerated without extensive endoneural scarring as seen in the autografts. ACTH4-9 instilled in the nerve guides showed a slight, but significant, increase in the number of myelinated axons. It is concluded that biodegradable PU nerve guides result in similar functional recovery when compared with autografts, but their histological quality is significantly better. ACTH4-9 showed only slight, but significant, improved nerve growth promoting activity. Therefore biodegradable PU nerve guides with ACTH4-9 would appear to be promising alternatives to autografts for bridging nerve defects.

Influence of resorbable poly(L-lactide) bone plates and screws on the dose distributions of radiotherapy beams

Metallic bone plates have been shown to affect radiation in vitro. Although no damage has ever been demonstrated in vivo these plates may cause dose enhancements and shielding of the adjacent tissue. Resorbable high molecular weight as-polymerized poly(L-lactide) (PLLA) bone plates have recently been used for reconstruction in the maxillofacial area. To determine their influence on dose distribution, a 4-hole bone plate and screws of PLLA were exposed to electron and photon beams. A tissue-equivalent phantom of perspex was irradiated and measurements were made with LiF thermoluminescent dosimeters. No significant changes in dose deviations could be determined when the dose distribution in the homogeneous phantom was compared with that of the phantom in which the PLLA material was placed. From this study it can be concluded that the PLLA material can be regarded as tissue-equivalent and can, thus, be safely used for fracture fixation of bone fragments when postoperative irradiation is anticipated.

Poly(L-lactide) implants in repair of defects of the orbital floor: an animal study

Because of the life-long presence of alloplastic, nonresorbable orbital floor implants and the complications of their use mentioned in literature, the use of a resorbable material appears to be preferable in the repair of orbital floor defects. A high-molecular-weight, as-polymerized poly(L-lactide) (PLLA) was used for repair of orbital floor defects of the blowout type in goats. An artificial defect was created in the bony floor of both orbits. Reconstruction of the orbital floor was then carried out using a concave PLLA implant of 0.4-mm thickness. At 3, 6, 12, 19, 26, 52, and 78 weeks postoperatively, one goat was killed. Microscopic examination showed full encapsulation of the implant by connective tissue after 3 weeks. After 6 weeks, resorption and remodeling of the bone at the points of support of the implant could be detected. A differentiation between the sinus and orbital sides of the connective tissue capsule was observed. The orbital side showed a significantly more dense capsule than the antral side, which had a loose appearance. At 19 weeks, a bony plate was progressively being formed, and at 78 weeks, new bone had fully covered the plate on the antral and orbital side. No inflammation or rejection of the PLLA implant was seen.

Patency and healing of polymeric microvenous prostheses implanted into the rat femoral vein by means of the sleeve anastomotic technique

The sleeve anastomotic technique was used to enhance the longer term patency and healing of polyurethane-based (PU) microvenous prostheses (ID: 1 mm, length: 5 mm, wall thickness: 0.2 mm; n = 34) in the rat femoral vein. In the control group, PU prostheses (n = 12) were implanted by means of the conventional end-to-end technique, and all were found to be occluded after one day (n = 6) and three weeks (n = 6). In the other experimental groups, the prostheses were evaluated after one day (n = 6), three weeks (n = 10), and six weeks (n = 18) of implantation by means of routine light- and scanning-electron microscopy. The occluded prostheses in the control group demonstrated a firmly attached mural thrombus at the anastomoses at one day and a completely organized thrombus at three weeks after implantation. Thirty-one of the 34 PU prostheses implanted by means of the sleeve technique were patent. At one day, all patent PU prostheses (five out of six) demonstrated minimal thrombus accumulation and a smooth transition at the anastomotic sites. At three and six weeks, all patent PU prostheses (16 out of 18) were covered by a complete endothelial layer. Underneath the endothelial layer, a subendothelial layer, composed of two to four layers of smooth muscle cells, could be observed. The wall of the prostheses were penetrated by fibrohistiocytic tissue. Stenosis was not observed. These results demonstrate that the sleeve anastomotic technique not only improves the short-term patency of PU microvenous conduits, but also the longer-term patency rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Two-ply biodegradable nerve guide: basic aspects of design, construction and biological performance

A synthetic biodegradable nerve guide was constructed of two polymeric layers: an inner microporous layer prepared from a copolymer of L-lactide and epsilon-caprolactone (pore size range 0.5-1 micron) and an outer microporous layer prepared from a polyurethane/poly(L-lactide) mixture (pore size range 30-70 microns). This nerve guide was used to bridge a 7 mm gap in the right sciatic nerve of rats. It enabled the sciatic nerve to regenerate across the gap, forming a new, well-defined nerve that effectively re-established the contact between the proximial and distal nerve end, as effective as an autograft.

Biodegradable lysine diisocyanate-based poly(glycolide-co-epsilon-caprolactone)-urethane network in artificial skin

A biodegradable lysine diisocyanate-based poly(glycolide-co-epsilon-caprolactone)urethane network has been evaluated as a material for the construction of a macroporous bottom layer (dermal analogue) in a two-layer artificial skin. High rates of in vitro degradation were observed; degradation of the porous poly(glycolide-co-epsilon-caprolactone)urethane networks was faster in vivo than in vitro. Subcutaneous implantation in guinea pigs showed that the porous polyurethane networks allowed rapid cell ingrowth, degraded almost completely 4-8 wk after implantation and evoked no adverse tissue reaction.

A new porous polyetherurethane wound covering

A polyetherurethane (PEU) wound covering with non-interconnected micropores up to approximately 5 microns has been prepared by means of a phase inversion process. This highly elastic, very thin (15-20 microns), pliable wound covering showed good, immediate adherence to wet wound surfaces and high water vapor permeability, but was impermeable to bacteria. In guinea pigs epidermal wound healing of partial-thickness wounds under PEU wound coverings was accelerated compared with uncovered controls and an occlusive wound covering, OpSite. Water in liquid form or wound exudate could not leak through the PEU covering, but its high water vapor permeability induced concentration of the wound exudate into a jellylike clot layer, which apparently accelerated reepithelialization. The main conclusion from a clinical study on 20 donor sites was that the use of the PEU covering reduced pain, besides prevention of fluid retention. No differences in epithelialization were seen in comparison to tulle gras-treated wounds.

Bio-absorbable plates and screws for internal fixation of mandibular fractures. A study in six dogs

Bio-absorbable plates and screws were used for internal fixation of artificially created mandibular fractures in 6 dogs. The plates and screws were fabricated from a block of poly(L-lactide) (PLLA), with a high molecular weight. The material is microporous and has excellent mechanical properties. Plates and screws were inserted in accordance with Champy's principles on internal fixation. Clinical and radiographical follow-up and examination of the fracture site under general anesthesia showed that all fractures healed without callus and without complications. The plates or screws did not fail, despite the tensile strength of the PLLA used is less than stainless steel or any other metal. An explanation for their successful application may be the high impact resilience of this material. The proprioceptive mechanisms, however, that keep the dogs from maximal loading of their broken mandibles, may also play a role. Plates and screws of this bio-absorbable PLLA appear to be an attractive alternative for internal fixation of mandibular fractures and certainly for less loaded fractures of the human skeleton. The necessity to remove metallic osteosynthesis can be avoided.

Bone-plates and screws of bioabsorbable poly (L-lactide)--an animal pilot study

Poly (L-lactide), a polymer of lactic acid (PLLA), with an extremely high molecular weight (Mv up to 1 x 10(6] has been synthesised under strictly controlled conditions resulting in a new microporous material with excellent mechanical properties. Bone-plates and screws machined from PLLA were used for fixation of two artificial mandibular fractures in sheep effected by a specially designed bone clamp. Fracture healing was uneventful without visible callus formation. Plates and screws of PLLA gave good stability over a sufficiently long period to enable normal fracture healing. Application in humans seems to be justified.

[Bioabsorbable poly(L-lactide) osteosynthesis plates and screws for the fixation of zygomatic bone fractures]

Ten unstable zygomatic bone fractures were treated with osteosynthesis plates and screws made of bioabsorbable poly(l-lactide) (PLLA). This study has shown that our PLLA plates and screws guarantee stable osteosynthesis of zygomatic bone fractures for an adequate period of time and allow undisturbed healing of the fracture. Bioabsorption takes more or less 18 months. Thus, a second operation for removal of the osteosynthesis material is avoided.

Patency and long-term biological fate of a two-ply biodegradable microarterial prosthesis in the rat

This study was undertaken to determine the long-term performance of a two-ply biodegradable, compliant microarterial prosthesis for its ability to function successfully as a temporary scaffold for the regeneration of a neoartery. Two-ply microarterial prostheses (internal diameter 1.5 mm, length 1 cm), prepared from a polyurethane-based (PU) material, were implanted into the abdominal aorta of rats (n = 22) and were evaluated at 3 months (n = 6), 6 months (n = 6) and one year (n = 10) after implantation, by means of macroscopic inspection, light microscopy and electron microscopy. All implants were patent and all, except two with a very small local dilatation at one year, were normally shaped. Arterial pulsations were reduced but still visible in all implants. In all implants a neoartery had regenerated: (1) a complete neointima composed of endothelial cells, (2) a neomedia composed of smooth muscle cells surrounded with elastin and collagen and of comparable thickness to rat media, and (3) a neoadventitia composed of fibrohistiocytic tissue that had organised the graft wall. In 2 out of the 10 one-year implants, smooth muscle cells were predominantly circularly arranged as in normal arterial tissue; in all other implants smooth muscle cells were predominantly longitudinally arranged. These results demonstrate that two-ply biodegradable PU-based prostheses have a good long-term performance when implanted into rat abdominal aortas.

Prosthetic microvenous grafting into the femoral vein of the rat; considerations concerning the anastomotic technique

The sequential thrombotic events which occur after implantation of microvenous prostheses prepared from a polyurethane-based material (I.D. 1 mm, length 5 mm, n = 36) into the rat femoral vein by means of the conventional end-to-end suture technique were evaluated by direct inspection and by scanning electron microscopy during the first 24 postoperative hours. Thrombus formation started at the anastomotic sites on the exposed collagenous vessel wall tissue and increased with increasing postoperative time intervals, leading to complete occlusion of the prostheses after 30 minutes of implantation. As a result of these findings, 8 more microvenous prosthetic implantations were performed with the sleeve anastomotic technique and evaluated after 24 hours. Six of these prostheses were patent with only minimal exposure of collagenous tissue at the anastomotic sites and subsequently minimal thrombus accumulation. Two prostheses left in situ and evaluated after 3 weeks were then still patent and completely endothelialised. Based upon the present study, we recommend the sleeve anastomotic technique for implanting synthetic microvenous prostheses because this technique prevents extensive exposure of collagenous vessel wall tissue at the anastomoses, thus leading to less thrombus accumulation and subsequently to a higher patency rate.

Poly(ether urethane) wound covering with high water vapour permeability compared with conventional tulle gras on split-skin donor sites

The experimental poly(ether urethane) (PEU) wound covering with a high water vapour permeance was compared with tulle gras treatment on adjacent areas of the same 20 split-skin donor sites. All patients experienced little or no pain from the PEU-covered areas, while 70 per cent of the patients complained of more pain from the tulle gras-covered areas. The PEU covering did not absorb the wound exudate underneath, neither did it retain wound fluid, but turned the wound exudate into a jelly-like clot layer by allowing a high evaporative water loss from the wound. Tulle gras treatment also prevented wound desiccation, but the exudate was absorbed into the overlaying cotton pads, where it became dry at the outer surface. Microscopy revealed that re-epithelialization occurred at a similar rate under the PEU covering as under tulle gras. In conclusion, the high water vapour permeable PEU wound covering prevents fluid retention, induces clotting of the wound exudate and reduces pain in split-skin donor sites. Tulle gras dressed with gauzes and crêpe bandage prevents wound desiccation, but causes more pain.

Experimental fractures of the mandibular body of sheep and dogs. A new technique

In order to create artificial fractures in animals resembling those which occur naturally, a new technique for fracture production was developed. Using a specially designed clamp, artificial fractures were produced in the mandibular body of seven sheep and 12 dogs. Radiographical analysis of the effects of the clamp on the mandibular body showed simple, single vertical fractures in the buccal cortex, inferior border and the alveolar process comparable to those which occur naturally. Using the technique described it was possible, in all cases, to carry out treatment with the use of 4-hole poly(L-lactide) plates and screws.