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Biomedical subjects

U Ripamonti

Publications and source records attributed to U Ripamonti.

At least 37 records · Page 2Linked to original sources
PubMed1996

Osteoinduction in porous hydroxyapatite implanted in heterotopic sites of different animal models.

Previous studies have demonstrated the induction of bone in coral-derived porous hydroxyapatite when implanted intramuscularly in baboons. This hydroxyapatite-induced bone differentiation model was used to study the effect of different animal species on heterotopic bone formation. Porous hydroxyapatite, obtained after hydrothermal conversion of the calcium carbonate exoskeleton of coral (genus Goniopora), was implanted in the rectus abdominis of adult rabbits, dogs and baboons (Papio ursinus). Specimens were harvested on day 90 after implantation and subjected to histological and histomorphometrical analysis. Minimal amounts of bone formed in hydroxyapatite specimens harvested from rabbits and dogs. Substantial bone differentiation did occur, however, in hydroxyapatite specimens harvested from the rectus abdominis of the baboons. In primates, the porous hydroxyapatite, as used in this study, may act as a solid matrix for adsorption, storage and controlled release of circulating or locally produced bone morphogenetic proteins, which locally initiate bone formation. The results of this study on heterotopic bone formation in porous hydroxyapatite underscore the importance of primate models in biomaterial research, which should be exploited for the formulation of porous substrata with intrinsic osteoinductive activity.

Animals↗
PubMed1996

Geometry of porous hydroxyapatite implants influences osteogenesis in baboons (Papio ursinus).

Coral-derived porous hydroxyapatite disks of two geometric configurations were implanted in 16 calvarial defects, 25 mm in diameter, prepared in eight subadult male baboons (Papio ursinus). To determine whether the orientation of the exoskeletal microstructures (corallites) influences bone ingrowth and osteogenesis, hydroxyapatite disks were prepared by cutting the coral either longitudinally or transversally, to obtain two distinct implant geometries defined by the orientation of the corallites. In the same animals, 16 defects were left untreated to assess the regeneration potential of the subadult baboon calvaria. Disks of both geometric configurations were also implanted in heterotopic intramuscular sites to investigate their osteoinductive potential. Histomorphometric analysis on undecalcified and decalcified sections prepared from specimens harvested on day 90 after surgery showed that greater amounts of bone formed in porous hydroxyapatites cut in the longitudinal plane when compared with hydroxyapatites cut in the transversal plane (p < 0.01). Bone formed in hydroxyapatite specimens harvested from the intramuscular sites, but no difference in bone formation was found between the two geometric configurations. Untreated defects showed limited osteogenesis, comparable with a previous series of untreated defects identically prepared in adult baboon calvariae. This finding suggests that skeletally mature, adult primates may not be a requirement for evaluation of craniofacial bone substitutes. These results in a primate indicate that hydroxyapatite disks are able to induce bone differentiation when implanted in intramuscular sites, and that the geometric configuration of the porous hydroxyapatite influences bone ingrowth and osteogenesis in orthotopic calvarial sites. This should be taken into consideration when designing porous bone substitutes for craniofacial applications.

Age Factors↗
PubMed1996

Complete regeneration of bone in the baboon by recombinant human osteogenic protein-1 (hOP-1, bone morphogenetic protein-7).

We examined the efficacy of a single application of recombinant human osteogenic protein-1 (hOP-1, bone morphogenetic protein-7) for its ability to regenerate large calvarial defects in adult male baboons (Papio ursinus). Recombinant hOP-1, in conjunction with baboon or bovine guanidinium-extracted insoluble collagenous bone matrix (0.1, 0.5 and 2.5 mg per g of collagenous matrix as carrier), was implanted in 46 calvarial defects surgically prepared in 14 baboons, whilst 18 defects were implanted with the carrier matrix without hOP-1. Specimens were harvested on d 15, 30, 90 and 365 and subjected to histomorphometry on serial undecalcified sections cut at 7 microm to study the temporal sequence of tissue morphogenesis after the single application of hOP-1. Histological analysis indicated that the induction of new bone formation proceeded from the periphery to the central core of hOP-1 treated specimens after rapid angiogenesis and mesenchymal cell migration in apposition to the collagenous matrix. Whilst chondrogenesis was limited, newly formed bone has already filled with fully differentiated bone marrow elements as early as d 15, even with the 0.1 mg dose of hOP-1. On d 30 and 90, doses of 0.1 and 0.5 mg of hOP-1 showed greater amounts of bone than controls, and on d 90, they induced complete regeneration of the defects. Doses of 2.5 mg hOP-1 per g of matrix induced extensive osteogenesis initially with heterotopic ossification and displacement of the temporalis muscle above the defects. One year after implantation of hOP-1 there was restoration of the internal and external cortices of the calvaria. These results show that hOP-1 induces complete regeneration of calvarial bone in the adult primate, and suggest that the optimal activity of hOP-1 to achieve regeneration is between 100 and 500 microg of hOP-1 per g of matrix. These results in the primate may form the scientific basis for future clinical applications of hOP-1.

Animals↗
PubMed1994

Tissue segregation enhances calvarial osteogenesis in adult primates.

Calvarial defects of adult mammals have a limited potential for regeneration. Osteogenesis may be impaired by the intrusion within the defect of nonosteogenic tissues during healing, which inhibits centripetal bone deposition from the margins of the defects. Using a primate model, we evaluated bone regeneration in calvarial defects treated with demineralized bone matrix versus defects treated according to the strategy of guided tissue regeneration. Sixty-four defects, 25 mm in diameter, were prepared in 16 adult male baboons (Papio ursinus). In each animal, 2 contralateral defects were covered with a template of porous polymer, 35 mm in diameter. Templates were positioned over the calvarial margins to prevent penetration of the pericranium and the temporalis muscle within the defects, thus maintaining tissue segregation during healing. The third defect was implanted with allogeneic demineralized bone matrix, as positive control. The fourth defect was left untreated and was used as negative control. Undecalcified bone sections (7 microns thick) were prepared from the harvested specimens 3 and 6 months after surgery. Although untreated defects showed limited osteogenesis after fusion of the pericranium with the dura, defects covered with the polymeric template often showed extensive bone deposition extending centripetally from the margins of the craniotomies. Histomorphometry demonstrated that defects treated with demineralized bone matrix and defects covered with the polymeric template had greater amounts of bone and osteoid when compared with untreated defects (p < 0.01). At 6 months, greater amounts of bone formed in demineralized bone matrix-treated defects when compared with defects covered with the polymeric template (p < 0.01). The results of this study show that calvarial membranous bones of adult primates retain the potential to regenerate when segregation between the different tissue components participating in the healing of the wound is maintained. In the same model, however, implantation of allogeneic demineralized bone matrix, used as a positive control provided the most effective treatment for the defects.

Age Factors↗
PubMed1994

Bone differentiation in porous hydroxyapatite in baboons is regulated by the geometry of the substratum: implications for reconstructive craniofacial surgery.

Previous studies have shown the morphogenesis of bone in a porous hydroxyapatite substratum when implanted intramuscularly in baboons. This hydroxyapatite-induced osteogenesis model was used to study the effect of geometry and pore size of the substratum on bone differentiation. Two distinct geometric configurations of porous hydroxyapatite of different pore size were obtained after hydrothermal conversion of the calcium carbonate exoskeleton of corals (genera Porites and Goniopora). Substrata were blocks of hydroxyapatite in rod configuration of 200- and 500-microns pore size and granular hydroxyapatite (400 to 620 microns in diameter) of 200- and 500-microns pore size. A total of 64 granular hydroxyapatite implants and 32 hydroxyapatite rods were implanted intramuscularly in 8 subadult male baboons (Papio ursinus). Specimens were harvested on days 60 and 90 and subjected to histologic and histomorphometric analysis. With the exception of an island of bone that formed in two implants of granular hydroxyapatite of 500-microns pore size, bone differentiation occurred only in blocks of hydroxyapatite in rod configuration of either pore size at both observation periods. The lack of bone formation in the granular hydroxyapatite indicates the critical role of geometry of the substratum in bone differentiation. These results in primates may have implications for the appropriate selection of porous bone substitutes for reconstructive craniofacial surgery in humans.

Animals↗
PubMed1994

Periodontal regeneration: potential role of bone morphogenetic proteins.

Initiation of osteogenesis and cementogenesis is a problem central to periodontal regeneration. A major advance in the understanding of bone formation has been the identification of an entirely new family of protein initiators, the bone morphogenetic proteins, that regulate cartilage and bone differentiation in vivo. The purification, genetic cloning and expression of recombinant human bone morphogenetic proteins (BMPs) have laid the foundation for the cellular and molecular dissection of bone development and regeneration. The striking evolutionary conservation of the BMP genes indicates that they are critical in the normal development and function of animals. In addition to postfetal osteogenesis, the BMPs may play multiple roles in embryonic development and organogenesis, including skeletogenesis and the development of craniofacial and dental tissues. The availability of recombinant human BMPs provides several challenges and opportunities to gain insights into the mechanisms regulating the regeneration of bone and cementum for optimal outcome in the periodontal patient.

Animals↗
PubMed1993

Initiation of heterotopic osteogenesis in primates after chromatographic adsorption of osteogenin, a bone morphogenetic protein, onto porous hydroxyapatite.

The chromatographic adsorption of partially purified osteogenin, a bone morphogenetic protein (BMP), onto porous hydroxyapatites for the construction of an osteogenic delivery system was investigated. Osteogenin fractions, with osteogenic activity in rats, were chromatographically adsorbed onto porous hydroxyapatites and implanted intramuscularly in baboons (Papio ursinus). Histology showed extensive bone differentiation within the porous spaces as early as 30 days after implantation in baboons. The unbound eluate from the porous hydroxyapatites showed lack of osteogenic activity when bioassayed in rats. These findings in primates may help to construct custom made porous ceramic as carriers for BMPs resulting in predictable bone formation for treatment of human bone defects.

Adsorption↗
PubMed1993

Histomorphometry of iliac crest trabecular bone in adult male baboons in captivity.

Data in the literature on bone histomorphometry in the baboon are scant. This study provides data from analysis of trabecular bone of the iliac crest of 16 adult male chacma baboons (Papio ursinus) in captivity. Five animals were young adults judging by the presence of growth cartilage in the iliac crest biopsy. Bone volume resembled that in humans, but trabeculae were thinner and more closely spaced. Bone turnover appeared somewhat lower than in humans. Coupling of resorption and formation was excellent as judged by cellular and kinetic variables; erosion surface was an unreliable indicator of ongoing coupling. The similarities between human and baboon trabecular bone make the baboon suited for the study of microstructure and bone turnover of trabecular bone with relevance to humans.

Animals↗
PubMed1993

Expression of the osteogenic phenotype in porous hydroxyapatite implanted extraskeletally in baboons.

A porous hydroxyapatite was used as a morphogenetic matrix to study early tissue formation preceding the morphogenesis of bone in extraskeletal sites of the baboon (Papio ursinus). Porous hydroxyapatites, obtained by hydrothermal conversion of the calcium carbonate exoskeleton of coral, were implanted extraskeletally in 16 baboons. Specimens were harvested at days 30, 60 and 90, and processed to obtain decalcified sections for histomorphometry, and undecalcified sections for enzyme histochemical demonstration of alkaline phosphatase, immunohistochemical demonstration of laminin and type I collagen, and for comparative histologic analysis. At day 30, the tissue that invaded the porous spaces showed mesenchymal condensations at the hydroxyapatite interface, and prominent vascular penetration. Collagen type I staining was localized within mesenchymal condensations. Bone had not formed in any specimen harvested at day 30. At days 30 and 60, alkaline phosphatase staining was initially localized in the invading vasculature, and subsequently found in cellular condensations prior to their transformation into bone, and in capillaries close to cellular condensations. Laminin staining was localized around invading capillaries adjacent to and within mesenchymal condensations, and in capillaries in direct contact with the hydroxyapatite. Bone had formed by day 60; cartilage, however, was never observed. By day 90, bone formation within the porous spaces was often extensive. Goldner's trichrome stain and fluorescence microscopy of tetracycline-labeled specimens demonstrated nascent mineralization within condensations during initial bone morphogenesis. Coating the hydroxyapatite with collagen type I prepared from baboon bone did not increase the amount of bone formation. In this hydroxyapatite-induced osteogenesis model in primates, vascular invasion and bone differentiation appear to be accompanied by a specific temporal sequence of alkaline phosphatase expression. The differentiation of osteogenic cells in direct apposition to the hydroxyapatite suggests that this substratum may act as a solid state matrix for adsorption and controlled release of endogenously-produced bone morphogenetic proteins. The porous hydroxyapatite, as used in this bioassay in primates, may be an appropriate delivery system for bone morphogenetic proteins for the controlled initiation of therapeutic osteogenesis.

Alkaline Phosphatase↗
PubMed1993

Immediate reconstruction of massive cranio-orbito-facial defects with allogeneic and alloplastic matrices in baboons.

40 cranio-orbito-facial osseous defects were created in 20 adult male baboons (Papio ursinus) to test the effectiveness of an allogeneic and an alloplastic matrix implant for the functional and morphological repair of the disassembled craniofacial complex. In each animal, one defect was reconstructed with a craniofacial bone segment harvested from donor adult baboons, and processed so as to obtain autolysed antigen-extracted allogeneic (AAA) bone matrix, preserving the bone morphogenetic protein (BMP) activity essential for bone induction. The contralateral defect was implanted with spherical macrobeads of polymethylmethacrylate (PMMA) coated with poly-2-hydroxyethylmethacrylate (PHEMA), and sintered into a porous molded implant, replicating the structural anatomy of the avulsed osseous segment. Histological analysis was carried out on undecalcified and decalcified bone sections prepared from specimens harvested at 3, 6 and 12 months after surgery. In AAA bone, the morphogenetic response was characterized by vascular invasion and mesenchymal cell aggregation after partial resorption of the implanted matrix. This was followed by bone deposition at the osteotomy interfaces and within the medullary spaces of the implanted AAA bone. Although bone ingrowth did occur in some PMMA/PHEMA specimens, the majority of implants showed fibrous union at the recipient interfaces. The limited bone ingrowth may be related to narrow interconnections between larger porous spaces after chemical synthesis of the two polymeric components. Osteogenesis in AAA bone appeared consistent with osteoconductive invasion from the viable bone at the recipient interfaces. In addition, the finding of a delicate trabecular-like bone, appositional to the central areas of the implanted matrix, suggests bone formation by induction.

Animals↗
PubMed1993

Reconstruction of the bone--bone marrow organ by osteogenin, a bone morphogenetic protein, and demineralized bone matrix in calvarial defects of adult primates.

Information concerning the efficacy of osteogenin, a bone morphogenetic protein, and demineralized bone matrix in orthotopic sites in nonhuman primates is a prerequisite for potential clinical application in humans. After exposure of the calvaria, 84 cranial defects, 25 mm in diameter, were prepared in 26 adult male baboons (Papio ursinus). Defects were implanted with insoluble collagenous bone matrix (ICBM, the inactive collagenous residue after dissociative extraction of bone matrix with 4 M guanidine hydrochloride) reconstituted with osteogenin fractions isolated from baboon bone matrix by chromatography on heparin-Sepharose and hydroxyapatite-Ultrogel (Og Hep-HA) or osteogenin further purified using Sephacryl S-200 gel filtration chromatography (Og S-200). Baboon osteogenin with the highest biologic activity in a rodent bioassay, as determined by alkaline phosphatase activity, calcium content, and histologic analysis, was used for orthotopic implantation in baboons. Additional defects were implanted with baboon demineralized bone matrix (DBM) or ICBM without osteogenin as control. Defects also were grafted with corticocancellous bone harvested from the iliac crest or left ungrafted to monitor the spontaneous regeneration potential of the adult baboon calvaria. Undecalcified bone sections at 7 microns were prepared from the harvested specimens 30 and 90 days after surgery. Histomorphometry demonstrated that Og S-200 induced copious amounts of bone and osteoid as early as day 30 (P < 0.01 versus ICBM, autogenous grafts and untreated defects). At day 90, in implants of Og S-200, Og Hep-HA, and DBM, bone and marrow formation was extensive, culminating in complete regeneration of the craniotomies. In implants of DBM, bone formed with an intervening phase of cartilage development. This provides the phenotypic evidence of endochondral bone differentiation by induction in defects of membranous calvarial bone in adult primates. These results establish the potential therapeutic application of osteogenin and demineralized bone matrix for the architectural reconstruction of the bone-bone marrow organ in humans.

Animals↗
PubMed1993

Delivery systems for bone morphogenetic proteins. A summary of experimental studies in primate models.

The characterization and molecular cloning of the family of the bone morphogenetic proteins (BMPs) have laid the foundation for the cellular and molecular analysis of bone development and regeneration. A carrier substratum is required, however, to optimize osteogenic activity initiated by BMPs bound to the surface of the carrier. Native and recombinant human (rh) BMPs induce local endochondral bone formation in conjunction with the insoluble collagenous bone matrix, the inactive residue obtained after dissociative extraction of the matrix with chaotropic agents. While the cellular and molecular biology of BMPs and related members is advancing at a furious pace, progress in the formulation and implementation of novel delivery systems has been slow. The creation of inorganic nonimmunogenic carriers with defined geometries capable of delivering BMPs in the absence of the collagenous matrix is a crucial goal for skeletal reconstructionists and molecular biologists alike. Significant advances in skeletal reconstruction may be expected when novel carrier substrata are implemented for delivery of optimal doses of now available recombinant human BMPs.

Animals↗
PubMed1992

Initiation of bone regeneration in adult baboons by osteogenin, a bone morphogenetic protein.

Osteogenin, and related bone morphogenetic proteins, induce endochondral bone differentiation through a cascade of events which include formation of cartilage, hypertrophy and calcification of the cartilage, vascular invasion, differentiation of osteoblasts, and formation of bone. These events have been studied in a postnatal model of bone development in rodents. Information concerning the morphogenetic potential of osteogenin in primates is a prerequisite for potential clinical application in man. The efficacy of allogeneic osteogenin in primates was investigated in both extraskeletal and skeletal sites in 19-Chacma baboons (Papio ursinus). Osteogenin was isolated from demineralized baboon bone matrix and purified by chromatography on heparin-Sepharose, hydroxyapatite, and Sephacryl S-200. Protein fractions with a molecular mass range of 26-42 kDa induced cartilage and bone differentiation in the subcutaneous space of rats. Final purification to homogeneity was obtained by electroendosmotic elution from a preparative sodium dodecyl sulphate (SDS) polyacrylamide gel, resulting in a single band on a SDS-polyacrylamide gel with an apparent molecular mass of 30-34 kDa, with biological activity in rats. The osteoinductive potential of osteogenin in primates was tested first in intramuscular sites in baboons and found to be active. The bone regeneration potential was investigated in nonhealing calvarial defects surgically prepared in adult male baboons. Baboon osteogenin induced complete regeneration of the cranial wound. These findings in adult primates establish a primary role for osteogenin in initiation and promotion of osteogenesis, and imply a potential therapeutic application based on cell biology of extracellular matrix-cell interactions.

Animals↗
PubMed1992

The critical role of geometry of porous hydroxyapatite delivery system in induction of bone by osteogenin, a bone morphogenetic protein.

The collagenous extracellular matrix of bone obtained after dissociative extraction with 4 M guanidine-HCl is an optimal substratum for bone induction by osteogenin, a bone morphogenetic protein. As a proteinaceous substratum, this matrix and other collagen-based materials may be immunogenic. Thus, the search and discovery of a non-immunogenic substratum is a necessary prerequisite for the therapeutic application of the principle of bone induction to skeletal repair. Bovine osteogenin, purified greater than 50,000-fold and with an apparent molecular mass of 28-42 kilodaltons, was delivered into nonresorbable porous hydroxyapatite in granular and disc configuration. A total of 328 preparations were bioassayed for osteogenic activity by subcutaneous implantation into 164 Long-Evans rats. Specimens were harvested at day 7, 11 and 21 after implantation and subjected to alkaline phosphatase activity determination and histologic analysis. Osteogenin combined with discs of porous hydroxyapatite induced in vivo differentiation of the osteogenic phenotype in mesenchymal cells invading the three-dimensional porous space of the inorganic substratum. The geometry of the substratum had a profound influence on bone induction, since the expression of the osteogenic phenotype was solely confined in porous hydroxyapatite with disc configuration. Osteogenin did not induce bone differentiation when combined with granules of porous hydroxyapatite with identical pore dimensions. The finding that the biological activity of osteogenin can be restored and delivered by a substratum with defined geometry other than the insoluble collagenous matrix may form the basis of the potential therapeutic application of bone morphogenetic proteins.

Animals↗
PubMed1992

Calvarial reconstruction in baboons with porous hydroxyapatite.

The growth of bone into porous hydroxyapatite implanted in nonhealing calvarial defects of adult baboons is evaluated. Seventy-two anterior and posterior calvarial defects, 25 mm in diameter, were prepared in 24 adult male baboons (Papio ursinus). In each animal, one defect was implanted with a disc of porous hydroxyapatite obtained after hydrothermal conversion of the calcium carbonate exoskeleton of coral (genus Goniopora); pores averaged 600 microns in diameter, pore interconnections averaged 260 microns in diameter, and the void fraction was 70% (Interpore 500). Another defect was grafted with autogenous corticocancellous bone harvested from the iliac crest. The third defect was left ungrafted and used as a control. Histology and histomorphometry on nondecalcified and decalcified sections prepared from specimens harvested at 3, 6, and 9 months after surgery showed that substantial bone growth had occurred in the hydroxyapatite implants (p < 0.01 vs bone grafts at 3 mos), culminating in complete penetration of bone within the tridimensional porous spaces. Anterior untreated defects showed greater amounts of bone when compared to posterior defects. The extent of bone growth in hydroxyapatite implants, however, appeared to be independent of the site of surgical implantation. This finding suggests that bone deposition within the porous spaces was a function of the implanted matrix rather than the healing potential of specific regions within the calvaria. Of concern was the presence of nonunions at the hydroxyapatite/calvarial interfaces, despite the often extensive bone deposition within the center of the hydroxyapatite implants. Further studies are required to identify the reasons for nonunion and to evaluate the mechanical performance of the bone-porous matrix complex.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗