Epidermal and fibroblast growth factors enhance fibrovascular integration of porous polyethylene implants

Vascularization Strategies for Porous Polyethylene Implants

Porous polyethylene (pPE) is a frequently implanted biomaterial in craniofacial reconstructive surgery. Its rapid vascularization and tissue incorporation are major prerequisites to prevent complications, such as material infection, migration, and extrusion. To achieve this, several sophisticated strategies have been introduced and evaluated during the last 20 years. These include (i) the angiogenic stimulation of the host tissue with epidermal growth factor, basic fibroblast growth factor or macrophage-activating lipopeptide-2, (ii) material modifications, such as increase of surface roughness and incorporation of bioactive glass particles, (iii) surface coatings with growth factors, glycoproteins, acrylic acid, arginine/glycine/aspartic acid peptide as well as components of the plasminogen activation system and autologous clotted blood or serum, and (iv) the seeding with fibroblasts, chondrocytes, stem cells, or adipose-tissue-derived microvascular fragments. The majority of these approaches showed promising results in experimental studies and, thus, may be capable of improving the success rates after pPE implantation in future clinical practice.

Mechanical and Cytocompatibility Evaluation of UHMWPE/PCL/Bioglass® Fibrous Composite for Acetabular Labrum Implant

In this study, a fibrous composite was developed as synthetic graft for labral reconstruction treatment, comprised of ultra-high molecular weight polyethylene (UHMWPE) fabric, ultrafine fibre of polycaprolactone (PCL), and 45S5 Bioglass®. This experiment aimed to examine the mechanical performance and cytocompatibility of the composite. Electrospinning and a slurry dipping technique were applied for composite fabrication. To assess the mechanical performance of UHMWPE, tensile cyclic loading test was carried out. Meanwhile, cytocompatibility of the composite on fibroblastic cells was examined through a viability assay, as well as SEM images to observe cell attachment and proliferation. The mechanical test showed that the UHMWPE fabric had a mean displacement of 1.038 mm after 600 cycles, approximately 4.5 times greater resistance compared to that of natural labrum, based on data obtained from literature. A viability assay demonstrated the predominant occupation of live cells on the material surface, suggesting that the composite was able to provide a viable environment for cell growth. Meanwhile, SEM images exhibited cell adhesion and the formation of cell colonies on the material surface. These results indicated that the UHMWPE/PCL/Bioglass® composite could be a promising material for labrum implants.

Vitronectin promotes the vascularization of porous polyethylene biomaterials

Rapid implant vascularization is a prerequisite for successful biomaterial engraftment. Vitronectin (VN) is a matricellular glycoprotein well known for its capability to interact with growth factors, proteases, and protease inhibitors/receptors. Since such proteins are highly relevant for angiogenic processes, we hypothesized that VN contributes to the tissue integration of biomaterials. Employing different in vivo and ex vivo microscopy techniques, engraftment of porous polyethylene (PPE) implants was analyzed in the dorsal skinfold chamber model in wild-type (WT) and VN^-/- mice. Upon PPE implantation, vascularization of this biomaterial was severely compromised in animals lacking this matricellular protein. Proteome profiling revealed that VN deficiency does not cause major changes in angiogenic protein composition in the implants suggesting that VN promotes PPE vascularization via mechanisms modulating the activity of angiogenic factors rather than by directly enriching them in the implant. Consequently, surface coating with recombinant VN (embedded in Matrigel®) accelerated implant vascularization in WT mice by enhancing the maturation of a vascular network. Thus, VN contributes to the engraftment of PPE implants by promoting the vascularization of this biomaterial. Surface coating with VN might provide a promising strategy to improve the vascularization of PPE implants without affecting the host's integrity. STATEMENT OF SIGNIFICANCE: Porous polyethylene (PPE) is a biomaterial frequently used in reconstructive surgery. The proper vascularization of PPE implants is a fundamental prerequisite for its successful engraftment in host tissue. Although the overall biocompatibility of PPE is good, there are less favorable application sites for its use in tissue reconstruction mostly characterized by low blood supply. Employing advanced in vivo microscopy methods and proteomic analyses in genetically engineered mice, we here describe a previously unrecognized function of vitronectin (VN) that enables this abundantly present glycoprotein to particularly promote the vascularization of PPE biomaterial. These properties of VN specifically facilitate the formation of a dense vessel network within the implant which relies on modulating the activity of angiogenic mediators rather than on the enrichment of these factors in the implant. Consequently, surface coating with this matricellular protein effectively accelerated and intensified implant vascularization which might be beneficial for its implementation at unfavorable sites for implantation without affecting the host's integrity.

Components of the plasminogen activation system promote engraftment of porous polyethylene biomaterial via common and distinct effects

Rapid fibrovascularization is a prerequisite for successful biomaterial engraftment. In addition to their well-known roles in fibrinolysis, urokinase-type plasminogen activator (uPA) and tissue plasminogen activator (tPA) or their inhibitor plasminogen activator inhibitor-1 (PAI-1) have recently been implicated as individual mediators in non-fibrinolytic processes, including cell adhesion, migration, and proliferation. Since these events are critical for fibrovascularization of biomaterial, we hypothesized that the components of the plasminogen activation system contribute to biomaterial engraftment. Employing in vivo and ex vivo microscopy techniques, vessel and collagen network formation within porous polyethylene (PPE) implants engrafted into dorsal skinfold chambers were found to be significantly impaired in uPA-, tPA-, or PAI-1-deficient mice. Consequently, the force required for mechanical disintegration of the implants out of the host tissue was significantly lower in the mutant mice than in wild-type controls. Conversely, surface coating with recombinant uPA, tPA, non-catalytic uPA, or PAI-1, but not with non-catalytic tPA, accelerated implant vascularization in wild-type mice. Thus, uPA, tPA, and PAI-1 contribute to the fibrovascularization of PPE implants through common and distinct effects. As clinical perspective, surface coating with recombinant uPA, tPA, or PAI-1 might provide a novel strategy for accelerating the vascularization of this biomaterial.

Effect of stem cells and fibrin concentration on the vascularization of the Medpor orbital implant

BACKGROUND

To determine the effect of adipose-derived adult stem cells (ADASCs) and optimal concentration of fibrin on fibrovascular ingrowth into porous polyethylene orbital implants (Medpor).

METHODS

Medpor sheet treated with O.25% fibrin only and ADASCs in mixtures containing fibrin (0.25%, 0.5% or 1.25%) were applied to a Medpor sheet and implanted in the back of each of 20 athymic nude mice. After 10 days, implants were removed and observed for fibrovascularization and stability. Haemoglobin, collagen and cellular DNA content were determined in quantitative assays.

RESULTS

Haemoglobin, collagen and cellular DNA levels were significantly higher in ADASC group than in the cell-free implant (0.25% fibrin only) group (P < 0.01). The level of haemoglobin and collagen content was significantly higher in the ADASC + 0.5% fibrin group among the ADASC and fibrin mixtures (P < 0.01).

CONCLUSION

ADASCs significantly improved fibrovascularization on Medpor compared with implants alone. Fibrin, used together with ADASCs to potentiate fibrovascularization, was most effective at concentrations of 0.5%.

Effect of basic fibroblast growth factor (bFGF) on the treatment of exposure of the orbital implants

OBJECTIVE

To evaluate the efficacy and the indication of basic fibroblast growth factor (bFGF) in the treatment of exposure of orbital implants.

DESIGN

Retrospective and observational case series.

METHODS

We reviewed 41 patients (41 eyes) suffering exposure of orbital implants from Jan. 2000 to June 2006. The study group patients with mild exposure received combined treatment with bFGF and antibiotic drops, and while the control group patients with mild exposure were treated with antibiotic drops only. The study group patients with moderate and severe exposure received combined treatment with bFGF and antibiotic drops, and after 2 months they were subjected to amniotic membrane transplantation, while the control group patients with moderate and severe exposure underwent amniotic membrane transplantation after using antibiotic drops. Observation of the growth of conjunctival epithelium and comparison of the healing rate of the two groups.

RESULTS

The healing rates of the mild, moderate and severe exposure study group were 100% and 92.3%. The healing rates of the mild, moderate and severe exposure control group were 55.6% and 66.7% respectively. The difference of the healing rates of the mild exposure study group and the control group was significant (P=0.033). And the difference of the healing rates of the moderate and severe exposure study group and the control group was not significant (P=0.167).

CONCLUSION

bFGF may promote obviously the healing of orbital implant exposure, particularly it can be the first choice for the treatment of mild degree exposure. For the moderate and severe cases, it can be administered before surgical repair to enhance neovascularization and will tend to increase the success rate of surgical repair.

Late porous polyethylene implant exposure after motility coupling post placement

PURPOSE

To report the probable association of motility coupling post placement and late porous polyethylene implant exposure.

DESIGN

Retrospective, observational case series.

METHODS

This was a retrospective analysis of 27 patients who had primary porous polyethylene orbital implantation from February 1999 to November 2000. Data on demographics, previous surgery, ocular diagnosis, type of surgery, size of the implant, and motility coupling post placement were collected. Complications of porous polyethylene implants and implant exposure were documented.

RESULTS

Among the 27 patients, 18 eyes (66.7%) received motility coupling post insertion after primary porous polyethylene implantation. Implant exposure occurred in six (33.3%) of the 18 eyes with motility coupling post insertion. None of the eyes without insertion had implant exposure. The mean interval between porous polyethylene implantation and motility coupling post placement for the implant exposure group (6 of 18) was 6.5 +/- 0.4 months, which was not statistically significant compared with 7.2 +/- 0.6 months in the nonexposure group (12 of 18). For these 6 cases of implant exposure, the mean interval between implantation and implant exposure was 24.2 +/- 11.8 months, and the mean interval between pegging and exposure was 17.6 +/- 11.7 months. Among these 6 patients, 4 underwent removal of exposed porous polyethylene implants and reimplantation of hydroxyapatite implant or dermis fat reconstruction.

CONCLUSIONS

We found a trend (P =.07) of increasing risk of porous polyethylene implant exposure with motility coupling post placement. Although the pegging group did not show a statistically significant higher rate of exposure compared with the nonpegging group, we believe that more care was needed when performing motility coupling post placement. In addition, longer postoperative follow-up is needed after insertion of a motility coupling post.

Growth factors embedded in an agarose matrix enhance the rate of porous polyethylene implant biointegration

PURPOSE

Repeated injections of epidermal and basic fibroblastic growth factors have been shown to enhance the biointegration rate of implanted porous polyethylene. A study was done to determine whether agarose, introduced at the time of implant placement, might serve as an adequate "single dose" delivery system for endogenous and exogenous growth factors.

METHODS

Polyethylene cubes coated with agarose-containing growth factors were implanted into fat and muscle in rabbits. Factors studied included autogenous whole blood, autogenous serum, ascorbic acid, epidermal growth factor, basic fibroblast growth factor, transforming growth factor alpha, and transforming growth factor beta. The rate and character of the fibrovascular ingrowth into implants and surrounding capsule thickness were assessed.

RESULTS

Fibroblast infiltration enhanced two- to sixfold with the use of autogenous or allogenic factors introduced in an agarose matrix at the time of cube implantation.

CONCLUSIONS

Growth factors studied altered the thickness of the capsule surrounding implants as well as both the vascularity and stromal density within implants.