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PubMedDate not supplied

Biomaterials used in injectable implants (liquid embolics) for percutaneous filling of vascular spaces.

The biomaterials currently used in injectable implants (liquid embolics) for minimally invasive image-guided treatment of vascular lesions undergo, once injected in situ, a phase transition based on a variety of physicochemical principles. The mechanisms leading to the formation of a solid implant include polymerization, precipitation and cross-linking through ionic or thermal process. The biomaterial characteristics have to meet the requirements of a variety of treatment conditions. The viscosity of the liquid is adapted to the access instrument, which can range from 0.2 mm to 3 mm in diameter and from a few centimeters up to 200 cm in length. Once such liquid embolics reach the vascular space, they are designed to become occlusive by inducing thrombosis or directly blocking the lesion when hardening of the embolics occurs. The safe delivery of such implants critically depends on their visibility and their hardening mechanism. Once delivered, the safety and effectiveness issues are related to implant functions such as biocompatibility, biodegradability or biomechanical properties. We review here the available and the experimental products with respect to the nature of the polymer, the mechanism of gel cast formation and the key characteristics that govern the choice of effective injectable implants.

Absorbable Implants↗
PubMedDate not supplied

Scleral implants: an historical perspective.

Scleral implants are made of absorbable or nonabsorbable materials. One category of absorbable materials consists of donor tissue, either autogenous (fascia lata, plantaris gracilis tendon) or from cadavers (dura mater, sclera, fascia lata). A second category includes gelatin, reconstituted collagen, absorbable gut, fibrin, blood plasma, air, and sodium hyaluronate; of these, specially prepared gelatin seems to be the most useful. Nonabsorbable implant materials have proven more practical than absorbable implants. Solid silicone rubber is currently the most popular scleral implant material. It is soft, easy to handle, and well tolerated. Expandable implants, either temporary or permanent, are used in the form of a silicone balloon filled with liquid. Silicone sponge, also widely used, has the advantage of great softness. However, hydrogels seem to be the ideal scleral implants. The only one commercially available is Refojo's MAI implant. It is very soft and is not damaged by sutures, has a smooth surface, is molded in several sizes and shapes, and has small pores that microorganisms cannot penetrate. When saturated with a water-soluble antibiotic before implantation, this implant releases the antibiotic postoperatively for a longer time than any other implant material. Finally, surgical adhesives are useful when the sclera is too thin or weak to tolerate sutures. The best adhesive available seems to be isobutyl cyanoacrylate.

Biocompatible Materials↗
PubMed2001

Single stage surgery combining transmucosal implant placement with guided bone regeneration and bioresorbable materials.

The aim of the present clinical study was to test whether peri-implant bone defects can successfully be filled with bone by applying bioresorbable materials for guided bone regeneration (GBR) procedures in conjunction with implants in the transmucosal healing position. Three women and 7 men ranging in age from 32 to 68 years (median 54.5) needed tooth replacement with dental implants. Eight to 14 weeks following careful tooth extraction, implants of the ITI Dental Implant System were placed at the extraction sites. At this time, all implants presented dehiscence defects of the alveolar bone partly exposing the rough titanium plasma sprayed (TPS) surfaces. GBR procedures were performed using deproteinized bovine bone mineral (Bio-Oss) as a membrane-supporting material and a bioresorbable collagen membrane (Bio-Gide) as a barrier. The membranes and the flaps were adjusted to fit around the necks of the implants, thus leaving the implants extending transmucosally into the oral cavity. Clinical measurements were taken at 6 sites around each implant (mesio-buccal, buccal, disto-buccal, disto-lingual, lingual, mesio-lingual) using a calibrated periodontal probe. These included: i) defect depth measured from the shoulder of the implant to the first bone-to-implant contact, ii) infrabony defect component measured from the bone crest to the first bone-to-implant contact, iii) defect width measured from the crest to the implant body in a direction perpendicular to the long axis of the implant. The Wilcoxon Matched Pairs Signed Rank Test was applied to detect differences over time. At baseline, the mean defect depth per patient amounted to 3.6 mm (Standard Deviation 1.6 mm, range 1.8-6.8 mm). The deepest extensions of the defects were located at the buccal aspects (mean 7.8 mm, SD 1.9 mm). At re-entry, the mean defect had decreased to 2.5 mm (SD 0.6 mm). This difference was statistically significant (P < 0.01). Initially, in 62% of sites the depth ranged from 0-3 mm, in 23% it ranged from 2-4 mm, and in 15% it amounted to more than 6 mm. Six to 7 months later, at re-entry, 95% of sites were 3 mm and less in depth and 5% ranged from 4-6 mm. Defect resolution, as assessed by the amount of coverage of the initially exposed rough implant surface, reached a mean value of 86% (SD 33%). One hundred percent resolution was accomplished at 8 out of 10 implants, 60% at one and 0% at another implant. The tissue at the latter implant showed signs of infection and inflammation during the healing phase. It is concluded that bioresorbable materials in GBR procedures at transmucosal implants can lead to successful bone regeneration into peri-implant defects.

Absorbable Implants↗
PubMed2002

Craniofacial reconstruction with computer-generated HTR patient-matched implants: use in primary bony tumor excision.

The aim of this clinical series is to report the effectiveness and safety of using computer-generated alloplastic hard tissue replacement (HTR) implants for the reconstruction of large defects of the cranio-orbital region when combined with simultaneous bone tumor excision. Seven patients who had large nonmalignant bony lesions of the anterior cranial vault and orbit underwent simultaneous bony excision and reconstruction with preoperatively fabricated custom alloplastic implants. Preoperatively, a 3D computed tomography (CT) scan was obtained from which an anatomical model was fabricated. On the anatomical model, the predicted amount of bone excision was performed. The defect in the model was then used to create an alloplastic (HTR polymer) implant for reconstruction and surgical placement. At the time of surgery, the implant was secured into position with either metal or resorbable plates and screws. In cases where the frontal sinus was in proximity to the implant, it was either cranialized and covered with a pericranial flap or obliterated with hydroxyapatite cement. All computer-generated implants required some modification intraoperatively due to a larger amount of bony excision than was preoperatively planned. This was accomplished by modifying the sterile back-up of the implant as an addition to the original implant or completing reconstruction of the bony defect with hydroxyapatite cement. All patients have healed uneventfully with a minimum of 1 year follow-up (average, 2.6 years). In all cases, excellent contours have been maintained and all patients have remained infection-free. In the management of large benign bony tumors of the cranio-orbital region, simultaneous reconstruction with custom implants fabricated from porous, hydrophilic HTR polymer can be preoperatively fabricated based on an estimate of the subsequent bony defect. The successful use of this approach depends on a favorable tissue quality of the recipient site, a generous preoperative estimate of the amount of bone that will be resected so that the implant is adequate, intraoperative techniques of expanding the implant reconstruction, and intraoperative methods to assure a partitioning of the implant from the frontal sinus.

Absorbable Implants↗
PubMed2006

Biodegradable materials in arthroscopy.

The use of biodegradable materials as implants has revolutionized the way medicine is practiced today. This review provides a general description of salient biodegradable polymeric materials currently used in arthroscopy. These materials include polyglycolic acid, self-reinforced polyglycolic acid, poly-L-lactic acid, self-reinforced polylactic-L-acid, poly-D-L-lactic acid, copolymer of poly-D-L-lactic acid polyglycolic acid, and polyglyconate. The mechanical strength, degradation properties, and widespread use of these materials, especially in the knee and shoulder, are discussed individually. Also discussed are the relatively few complications that are related to these materials' arthroscopic use. Future directions in biodegradable materials, including smart polymers, are also considered. In the future, novel techniques to identify the ideal polymer for a particular application will need to be developed to minimize the risk for implant complications.

Absorbable Implants↗
PubMed2007

First-in-human implantation of a fully bioabsorbable drug-eluting stent: the BVS poly-L-lactic acid everolimus-eluting coronary stent.

The first-in-human fully bioabsorbable drug-eluting stent (BVS poly-L-lactic acid everolimus-eluting coronary stent) implantation was performed at Auckland City Hospital, New Zealand as part of the ABSORB trial. There were no adverse events in-hospital or by 1 month. A stent that supports the vessel when needed, delivers an antiproliferative drug then disappears has theoretical advantages with regard to CT and MRI compatibility, restored vessel vasomotion, and facilitated future percutaneous intervention or surgical grafting to the treated site.

Absorbable Implants↗
PubMed2005

Biocompatibility and stability of disulfide-crosslinked hyaluronan films.

Hyaluronan (HA) can be chemically modified to engineer robust materials with pre-selected mechanical properties and resorption rates that can be dictated by the intended clinical use. Disulfide-crosslinked HA films were prepared by air oxidation of thiol-modified HA, followed by treatment with 0.3% hydrogen peroxide. The degradation of the disulfide-crosslinked films in vitro was very slow (<10% in 7 days) in buffer alone and shorter (t1/2=3-5 days) in the presence of hyaluronidase (HAse). The cytocompatibility of the disulfide-crosslinked HA films was determined using two separate conditions: (i) in vitro culture of mouse fibroblasts in indirect contract with the films, and (ii) in vitro culture of fibroblasts directly on films coated with poly d-lysine. Excellent cytocompatibility was observed in murine fibroblasts that were cultured in indirect contact with thiolated HA films. Although cells were unable to attach and spread on thiolated HA films, pre-coating the thiolated HA films with poly D-lysine resulted in attachment and spreading equivalent to that observed on polystyrene. Rates of resorption in vivo were obtained by subcutaneous implantation of disulfide-crosslinked HA films into the backs of Wistar rats. Biocompatibility in vivo was determined in both subcutaneous flank and peritoneal cavity implantation of the films in Wistar rats. The disulfide-crosslinked HA films were less than 30% resorbed after 42 days in vivo, and histochemical and cytochemical analysis indicated that the films were well-tolerated with mild inflammatory response at both sites of implantation.

Absorbable Implants↗
PubMed2003

Imaging of periimplant bone levels of implants with buccal bone defects.

The aim of the present study was to use four different methods to evaluate three radiographic techniques for their accuracy in assessing the marginal periimplant bone levels at implants with buccal bone defects in an experimental setting. Twenty-four implants were placed in the mandibles of six adult beagle dogs with substantial buccal bone defects, which were augmented by bone particles with and without resorbable membranes. After healing for 5 months, (1) periapical radiographs, (2, 3) reformatted images in (2) sagittal and (3) coronal planes from axial computer tomography (CT) scans and (4) direct magnification images (DIMA) were made and compared with histometric analysis of bone levels. Two values were used for comparison: (i) the lingual bone level and (ii) the true bone level calculated as a mean value from the lingual and the buccal bone levels of all histologic sections of each implant. Metric evaluation of periapical radiographs, sagittal reformation of CT scans and DIMA showed that the results were close to the histometrically assessed lingual bone level, while the true bone level was significantly lower and not reflected by any of the imaging modalities. Coronal reformation showed that there was significant overestimation of the lingual and underestimation of the buccal bone level when compared with histometric values. It is concluded that assessment of bone level and bone regeneration in implants with buccal bone defects remains problematic, and data from periapical radiograms tend considerably to overestimate the bone anchorage of these implants.

Absorbable Implants↗
PubMed2003

Effects of sealing the perforated sinus membrane with a resorbable collagen membrane: a pilot study in humans.

The effects of repairing the perforated sinus membrane with collagen membrane are unknown. The purpose of this pilot study was to clinically, histologically, and histomorphometrically evaluate the results of repairing the perforated sinus membrane with resorbable collagen membrane. A split-mouth design was followed in the current study. Five subjects requiring bilateral sinus grafting were included in the study, where one site was accidentally perforated during sinus augmentation procedures and the other site was not perforated. The perforated sites were repaired with a resorbable collagen membrane. Dental implants were placed at a second stage and biopsies were harvested from both sinuses. New bone formation was measured for all sites. Implant survival was recorded at second-stage surgery. Nonperforated sites demonstrated significantly more bone formation (34.40%) than perforated sites (12.80%) (P = .016). Implant survival at second-stage surgery was significantly inferior in perforated sites (54.5%) when compared with nonperforated sites (100%) (P = .0146). The study demonstrated that perforation and repair of the Schneiderian membrane can compromise new bone formation and implant survival rate.

Absorbable Implants↗
PubMed2001

The preliminary evaluation of HAP + TCP composite material biodegradation after implantation in muscular tissue of rats.

Ceramic biomaterials based on calcium phosphates have a special position among modern implantation material in osteosurgery. Non-reabsorbable hydroxyapatite (HAP) and reabsorbable tricalcium phosphate are the most popular calcium phosphate ceramics. The appropriate ratio of these two compounds should result in forming the gradually reabsorbable implants, overgrowing with the bone tissue which mechanical strength should not be negatively affected. The aim of this work was to evaluate a local tissue reaction and the HAP + TCP composite resorption rate as compared with HAP, after implantation in a muscle tissue of rats. On the basis of carried macroscopic and microscopic evaluations, it can be stated that the new HAP + TCP composite had high biocompatibility and were gradually reabsorbed. This enables faster overgrowing the implant with tissue.

Absorbable Implants↗
PubMed1993

[Resorbable implant materials in retinal detachment surgery. Initial animal experiment studies].

In detachment surgery after a mechanically stabile chorioretinal scar is at present full scleral indentation no longer mandatory. Following these considerations absorbable scleral implants have been developed and tested in an animal model. Cylindrical pieces of absorbable composite-material with a diameter of 5 mm were sutured as radial scleral explants in 18 rabbits. The composite material consisted of a polyglactin-polydioxanon ratio 7:1. The absorption time for polyglactin is 60 days, for polydioxanon 180 days. The explants produced initially in ultrasonographically measured buckle height between 3.2 and 4.0 mm. The clinical and ultrasonographical follow up study demonstrated a continuous decrease of buckle height. Two weeks after implantation there was a medium height of 2.0 mm after five weeks a medium elevation of 0.5 mm was found. Histopathological examinations showed incidence of a slight resorptive inflammation in the area of the buckle which was not evident after 12 weeks. No scleral infiltration or scleral thinning was found. The promising results have justified controlled clinical trials with the absorbable material which might allow to combine the advantages of silicone sponge explants (precise localization) with those of scleral buckles by inflatible balloons (reversibility).

Absorption↗
PubMed2000

Clinical biocompatibility of biodegradable orthopaedic implants for internal fixation: a review.

When the polymeric material reaches the final stages of its degradation process, biodegradable orthopaedic fixation devices elicit a local foreign-body reaction. In most cases, the symptoms of this tissue response are subclinical and pass unnoticed, but in some patients a clinically manifest inflammatory foreign-body reaction ensues. Mild clinical reactions consist of a painful erythematous papule, those of medium severity show a sinus discharging polymeric debris for up to 6 months, and in the patients affected by a severe reaction, extensive osteolytic lesions may develop at the implant tracks. The histopathologic picture is that of a non-specific foreign-body reaction. For implants made of polyglycolide, the average incidence of the manifest reactions is 5%. When slow-degrading polymers are used, the incidence is lower. The tissue responses to polyglycolide manifest themselves 11 weeks after surgery, on an average, whereas foreign-body reactions to devices made of poly-L-lactide can emerge as late as 4 or 5 yr after the original fracture fixation operation. A poorly vascularized bone section, use of a quinone dye as an additive in the polymer, and an implant geometry with large surface area each seems to be associated with an increased risk of the occurrence of a foreign-body reaction. Yet in majority of the patients affected, no known individual marker of high risk is present. Some recent laboratory experiments indicate that it may be possible to diminish the risk of an adverse tissue response by incorporating alkaline salts or antibodies to inflammatory mediators in the implants. The results of in vitro and animal experiments, however, cannot always be directly extrapolated to humans. Only large-scale long-term clinical research will ultimately show which physico-chemical characteristics of a biodegradable orthopaedic implant provide the optimal clinical biocompatibility.

Absorbable Implants↗