Cellular inflammatory response to porcine collagen membranes

Inflammatory Profile of Different Absorbable Membranes Used for Bone Regeneration: An In Vivo Study

BACKGROUND

Guided bone regeneration (GBR) has become a necessary practice in implantology. Absorbable membranes have shown advantages over non-absorbable membranes, such as blood support of bone tissue. This study aimed to evaluate five collagen membranes in rat calvaria critical-size defects through a histomorphometric analysis of the inflammatory profile during the initial phase of bone repair.

MATERIALS AND METHODS

A total of 72 Albinus Wistar rats were used for the study, divided into six groups, with 12 animals per group, and two experimental periods, 7 and 15 days. The groups were as follows: the CG (clot), BG (Bio-Gide®), JS (Jason®), CS (Collprotect®), GD (GemDerm®), and GDF (GemDerm Flex®).

RESULTS

Data showed that the BG group demonstrated an inflammatory profile with an ideal number of inflammatory cells and blood vessels, indicating a statistically significant difference between the JS and CS groups and the BG group in terms of the number of inflammatory cells and a statistically significant difference between the JS and CS groups and the GD group in terms of angiogenesis (p < 0.05).

CONCLUSIONS

We conclude that different origins and ways of obtaining them, as well as the thickness of the membrane, can interfere with the biological response of the material.

Evaluation of Porcine Collagen Membranes Used with Guided Bone Regeneration for Critical Defects: A Histological, Histomorphometric, Immunohistochemical, and Inflammatory Profile Analysis

OBJECTIVE

 The objective of this study was to compare the effectiveness of two porcine collagen membranes of different origin used for guided bone regeneration procedures.

MATERIALS AND METHODS

 Resorbable collagen membrane from porcine dermis (Bio-Gide, Geistlich Pharma AG, Wolhusen, Switzerland) and resorbable collagen membrane from porcine pericardium (Jason, Institut Straumann AG, Peter Merian-Weg, Switzerland) were evaluated; histological, histometric, immunohistochemical, and inflammatory profile analyses were performed. The study was carried out on critical defects created in the calvaria of 72 rats (Rattus norvegicus albinus, Wistar variety) divided into three groups: coagulum group (Co), porcine pericardium group (JS), and porcine collagen group (BG). The defects were filled with clot, over which the membranes were placed. The animals were euthanized 7, 15, 30, and 60 days after surgery.

STATISTICAL ANALYSIS

 The Shapiro-Wilk test was used to assess data distribution. Analysis of variance (ANOVA) and the Bonferroni multiple comparison test were used to compare the differences across the mean values of the variables. Nonparametric tests, Mann-Whitney and Wilcoxon W, were used for the quantitative analysis of the inflammatory profile. A significance level of 5% (p < 0.05) was adopted with a confidence interval of 95%. SPSS software version 2.0 was used.

RESULTS

 A total of 1,008 analyses were performed on 288 histological slides. It was noted that both types of collagen membranes used in this study were effective for the guided bone regeneration procedure, with a greater proportion and thickness of bone formation among recipients of the BG (735 points, p = 0.021). This membrane also had greater permeability (62.25). The animals in the JS group, which received the porcine pericardial membrane, showed early and accelerated bone formation from early bone tissue, milder osteopontin and osteocalcin levels, and greater inflammatory reaction (86.4).

CONCLUSION

 The collagen membrane from porcine dermis demonstrated a more orderly and physiological repair process, while the porcine pericardial membrane presented a more accelerated repair process that did not remain constant over time.

A comparative in vitro and in vivo study of porcine- and bovine-derived non-cross-linked collagen membranes

The porcine-derived non-cross-linked collagen membrane Bio-gide® (BG) and the bovine-derived non-cross-linked collagen membrane Heal-all® (HA) were compared to better understand their in vitro biophysical characteristics and in vivo degradation patterns as a reference for clinical applications. It was showed that the porosity, specific surface area, pore volume and pore diameter of BG were larger than those of HA (64.5 ± 5.2% vs. 48.6 ± 6.1%; 18.6 ± 2.8 m² /g vs. 2.3 ± 0.6 m² /g; 0.114 ± 0.002 cm³ /g vs. 0.003 ± 0.001 cm³ /g; 24.4 ± 3.5 nm vs. 7.3 ± 1.7 nm, respectively); the average swelling ratio of BG was higher than that of HA (412.6 ± 41.2% vs. 270.0 ± 2.7%); the tensile strength of both dry and wet HA was higher than those of BG (18.26 ± 3.27 MPa vs. 4.02 ± 1.35 MPa; 2.24 ± 0.21 MPa vs. 0.16 ± 0.02 MPa, respectively); 73% of HA remained after 72 h in collagenase solution, whereas only 8.2% of BG remained. A subcutaneous rat implantation model revealed that, at 3, 7, 14, 28, and 56 days postmembrane implantation, there were more total inflammatory cells, especially more M1 and M2 polarized macrophages and higher M2/M1 ratio in BG than in HA; in addition, the fibrous capsule around BG was also thicker than that around HA. Moreover, concentrations of dozens of cytokines including interleukin-2(IL-2), IL-7, IL-10 and so forth. in BG were higher than those in HA. It is suggested that BG and HA might be suitable for different clinical applications according to their different characteristics.

Calvaria Critical Size Defects Regeneration Using Collagen Membranes to Assess the Osteopromotive Principle: An Animal Study

Guided bone regeneration (GBR) is a common practice in implantology, and it is necessary to use membranes in this process. The present study aimed to evaluate the osteopromotive principle of two porcine collagen membranes in critical-size defects at rats calvaria. Ninety-six Albinus Wistar rats were divided into BG (positive control), JS, CS, and CG (negative control) groups and were sacrificed at 7, 15, 30, and 60 days postoperatively. The samples were assessed by histological, histometric, immunohistochemical, and microtomographic analyses. More intense inflammatory profile was seen in the JS and CS groups (p < 0.05). At 60 days, the JS group showed a satisfactory osteopromotive behavior compared to BG (p = 0.193), while CS did not demonstrate the capacity to promote bone formation. At the immunohistochemical analysis, the CS showed mild labeling for osteocalcin (OC) and osteopontin (OP), the JS demonstrated mild to moderate for OC and OP and the BG demonstrated moderate to intense for OC and OP. The tridimensional analysis found the lowest average for the total volume of newly formed bone in the CS (84,901 mm2), compared to the BG (319,834 mm2) (p < 0.05). We conclude that the different thicknesses and treatment techniques of each membrane may interfere with its biological behavior.

Recent update on potential cytotoxicity, biocompatibility and preventive measures of biomaterials used in dentistry

Dental treatment is provided for a wide variety of oral health problems like dental caries, periodontal diseases, periapical infections, replacement of missing teeth and orthodontic problems. Various biomaterials, like composite resins, amalgam, glass ionomer cement, acrylic resins, metal alloys, impression materials, bone grafts, membranes, local anaesthetics, etc., are used for dental applications. The physical and chemical characteristics of these materials influence the outcome of dental treatment. It also impacts on the biological, allergic and toxic potential of biomaterials. With innovations in science and their positive results, there is also a need for awareness about the biological risks of these biomaterials. The aim of dental treatment is to have effective, yet safe, and long-lasting results for the benefit of patients. For this, it is important to have a thorough understanding of biomaterials and their effects on local and systemic health. Materials used in dentistry undergo a series of analyses before their oral applications. To the best of our knowledge, this is the first and original review that discusses the reasons for and studies on the toxicity of commonly used biomaterials for applications in dentistry. It will help clinicians to formulate a methodical approach for the selection of dental biomaterials, thus providing an awareness for forecasting their risk of toxic reactions.

Bioprinted Vascularized Mature Adipose Tissue with Collagen Microfibers for Soft Tissue Regeneration

The development of soft tissue regeneration has recently gained importance due to safety concerns about artificial breast implants. Current autologous fat graft implantations can result in up to 90% of volume loss in long-term outcomes due to their limited revascularization. Adipose tissue has a highly vascularized structure which enables its proper homeostasis as well as its endocrine function. Mature adipocytes surrounded by a dense vascular network are the specific features required for efficient regeneration of the adipose tissue to perform host anastomosis after its implantation. Recently, bioprinting has been introduced as a promising solution to recreate in vitro this architecture in large-scale tissues. However, the in vitro induction of both the angiogenesis and adipogenesis differentiations from stem cells yields limited maturation states for these two pathways. To overcome these issues, we report a novel method for obtaining a fully vascularized adipose tissue reconstruction using supporting bath bioprinting. For the first time, directly isolated mature adipocytes encapsulated in a bioink containing physiological collagen microfibers (CMF) were bioprinted in a gellan gum supporting bath. These multilayered bioprinted tissues retained high viability even after 7 days of culture. Moreover, the functionality was also confirmed by the maintenance of fatty acid uptake from mature adipocytes. Therefore, this method of constructing fully functional adipose tissue regeneration holds promise for future clinical applications.

Recombinant human collagen/chitosan-based soft hydrogels as biomaterials for soft tissue engineering

Animal-derived collagen may contain viruses, and its impurity can cause immunological reactions. Chitosan, always required a neutralization step in fabricating it into the biocompatible tissue engineering scaffolds. To avoid these risks and simplify the production process, a series of recombinant human collagen/carboxylated chitosan (RHC-CHI) based soft hydrogel scaffolds were prepared by crosslinking-induced gelation and then investigated their feasibilities for use as soft tissue engineering scaffolds. The gelation time was optimized by modulating the biopolymer concentration or reaction temperature. The hydrogel swelling, degradation rate, and mechanical properties were also investigated. The results showed that these parameters could be tuned by adjusting either the RHC-to-chitosan ratio or the total polymer concentration. The mechanical properties of the hydrogels were improved by adding chitosan, but excess chitosan reduced the hydrogel mechanical strength and accelerated the degradation speed. Cytotoxicity tests showed that all fabricated soft hydrogels were biocompatible and displayed no cytotoxicity. Cytocompatibility tests and qRT-PCR studies indicated that the hydrogel system promoted the adhesion and proliferation of NIH-3T3 cells, and cellular activities were directly up-regulated by RHC. Finally, our in vivo study proved these hydrogels were able to accelerate the cell infiltration and wound closure. These results show that the soft RHC-CHI hydrogels show promise in soft-tissue engineering.

Decellularization of Skin Tissue

Biomaterials science encompasses elements of medicine, biology, chemistry, materials, and tissue engineering. They are engineered to interact with biological systems to treat, augment, repair, or replace lost tissue function. The choice of biomaterial depends on the procedure being performed, the severity of the patient's condition, and the surgeon's preference. Prostheses made from natural-derived biomaterials are often derived from decellularized extracellular matrix (ECM) of animal (xenograft) or human (allograft) origin. Advantages of using ECM include their resemblance in morphology and three-dimensional structures with that of tissue to be replaced. Due to this, scientists all over are now focusing on naturally derived biomaterials which have been shown to possess several advantages compared to synthetic ones, owing to their biocompatibility, biodegradability, and remodeling properties. Advantages of a naturally derived biomaterial enhance their application for replacement or restoration of damaged organs/tissues. They adequately support cell adhesion, migration, proliferation, and differentiation. Naturally derived biomaterials can induce extracellular matrix formation and tissue repair when implanted into a defect by enhancing attachment and migration of cells from surrounding environment. In the current chapter, we will focus on the natural and synthetic dermal matrix development and all of the progress in this field.

In Vivo Comparative Evaluation of Biocompatibility and Biodegradation of Bovine and Porcine Collagen Membranes

Mechanical barriers prevent the invasion of the surrounding soft tissues within the bone defects. This concept is known as Guided Bone Regeneration (GBR). The knowledge about the local tissue reaction and the time of degradation of absorbable membranes favors the correct clinical indication. This study aimed to evaluate the biocompatibility and biodegradation of a bovine collagen membrane (Lyostypt^®, São Gonçalo, Brazil) and compare it to a porcine collagen membrane (Bio-Gide^®) implanted in the subcutaneous tissue of mice, following ISO 10993-6:2016. Thirty Balb-C mice were randomly divided into three experimental groups, LT (Lyostypt^®), BG (Bio-Gide^®), and Sham (without implantation), and subdivided according to the experimental periods (7, 21, and 63 days). The BG was considered non-irritant at seven days and slight and moderate irritant at 21 and 63 days, respectively. The LT presented a small irritant reaction at seven days, a mild reaction after 21, and a reduction in the inflammatory response at 63 days. The biodegradation of the LT occurred more rapidly compared to the BG after 63 days. This study concluded that both membranes were considered biocompatible since their tissue reactions were compatible with the physiological inflammatory process; however, the Bio-Gide^® was less degraded during the experimental periods, favoring the guided bone regeneration process.

In Vitro Feasibility Analysis of a New Sutureless Wound-Closure System Based on a Temperature-Regulated Laser and a Transparent Collagen Membrane for Laser Tissue Soldering (LTS)

For the post-surgical treatment of oral wounds and mucosal defects beyond a certain size, the gold standard is still an autologous skin or mucosal graft in combination with complex suturing techniques. A variety of techniques and biomaterials has been developed for sutureless wound closure including different tissue glues or collagen patches. However, no wound covering that enables for sutureless fixation has yet been introduced. Thus, a new system was developed that allows for sutureless wound covering including a transparent collagen membrane, which can be attached to the mucosa using a specially modified 2λ laser beam with integrated temperature sensors and serum albumin as bio-adhesive. The sutureless wound closure system was tested for its applicability and its cytocompatibility by an established in vitro model in the present study. The feasibility of the laser system was tested ex vivo on a porcine palate. The in vitro cytocompatibility tests excluded the potential release of toxic substances from the laser-irradiated collagen membrane and the bio-adhesive. The results of the ex vivo feasibility study using a porcine palate revealed satisfactory mean tensile strength of 1.2–1.5 N for the bonding of the membrane to the tissue fixed with laser of 980 nm. The results suggest that our newly developed laser-assisted wound closure system is a feasible approach and could be a first step on the way towards a laser based sutureless clinical application in tissue repair and oral surgery.

Tuning the immune reaction to manipulate the cell-mediated degradation of a collagen barrier membrane

In order to elicit a desired barrier function in guided bone regeneration (GBR) or guided tissue regeneration (GTR), a barrier membrane has to maintain its integrity for a certain period of time to guarantee the regeneration of target tissue. Due to the complexity and variety of clinical conditions, the healing time required for tissue regeneration varies from one case to another, which implies the need for tailoring the barrier membranes to diverse conditions via manipulating their degradation property. As a "non-self" biomaterial, a barrier membrane will inevitably trigger host-membrane immune response after implantation, which entails the activation of phagocytic cells. In the degradation process of a barrier membrane, the cell-mediated degradation may play a more vital role than enzymatic and physicochemical dissolution; however, limited studies have been carried out on this topic. In this context, we investigated the cell-mediated degradation and illustrated the possible key cells and mediators for immunomodulation via in vivo and in vitro studies. We discovered that IL-13, a key cytokine mainly released by T helper 2 cells (Th2), induced the formation of foreign body giant cells (FBGCs), thus resulting in membrane degradation. Neutralizing IL-13 could suppress membrane degradation and formation of FBGC. The contributions of this study are (1) unveiling the immune mechanisms underlying the cell-mediated collagen membrane degradation; (2) allowing the formation of an "immunodegradation" strategy to develop an "immune-smart" barrier membrane to manipulate its degradation; (3) providing the key regulatory immune cells and cytokines for the immunomodulation target in collagen membrane degradation. STATEMENT OF SIGNIFICANCE: The significance of this research includes.

The effect of the chitosan-collagen membrane on wound healing process in rat mandibular defect

Background:

Collagen and chitosan are potential biomaterials for medical applications; chitosan-collagen membranes are used as a barrier membrane in guided tissue regeneration and guided bone regeneration.

Aims:

The purpose of this study was to analyze the effect of the chitosan-collagen membrane on wound healing in rat mandibular defect by counting the number of fibroblasts and new blood vessels.

Materials and Methods:

As much as 24 male Wistar rats were divided into two groups, the treatment and control group. Bone defects were made In the rat mandible with diamond bur with a diameter of 2 mm, then the defect was covered with a chitosan-collagen membrane, and the control group was covered without application of chitosan-collagen membrane. After the 3^rd, 7^th, 14^th, and the 21^st day, the defect site was analyzed histologically. The number of fibroblasts and blood vessels was counted under a light microscope, at five fields with ×1000 and ×400 microscope magnification.

Statistical Analysis Used:

This study was done by using analysis of variance and unpaired t-test.

Results:

The average number of fibroblasts and blood vessels in the treatment group was higher than the control group. There was a significant difference in the number of fibroblasts on the 3^rd and 7^th day (P = 0.001; P = 0.001) and the number of blood vessels on the 3^rd day (P = 0.04).

Conclusion:

The chitosan-collagen membrane was able to increase the number of fibroblasts and new blood vessels in the wound healing process.

Contribution of bone marrow-derived cells to in situ engineered tissue capsules in a rat model of chronic kidney disease

Tissue engineered blood vessels (TEBVs) hold great promise for clinical use in patients with end stage renal disease (ESRD) requiring vascular access for hemodialysis. A promising way to make TEBVs is to exploit foreign body response (FBR) of polymeric rods used as templates. However, since the FBR predominantly involves bone-marrow (BM) derived cells and ESRD coincides with impaired function of BM, it is important to assess the generation of TEBVs in conditions of renal failure. To this end, we implanted polymer rods in the subcutis of rats after BM-transplantation with GFP-labeled BM cells in a model of chronic kidney disease (CKD). At 3 weeks after implantation, rods were encapsulated by tissue capsule (TC) composed of collagen, myofibroblasts and macrophages. On average, 13% of CD68⁺ macrophages were GFP⁺, indicating BM origin. Macrophage-to-myofibroblasts differentiation appeared to play an important role in TC formation as 26% of SMA⁺/GFP⁺ myofibroblasts co-expressed the macrophage marker CD68. Three weeks after rod implantation, the cellular response changed towards tissue repair, characterized by 40% increase in CD68⁺/CD163⁺ repair associated macrophages and 95% increase in TGFβ and IL10 gene expression as compared to TCs harvested at 1 week. These results show that both BM derived and tissue resident cells, contribute to TC formation, whereas macrophages serve as precursors of myofibroblasts in mature TCs. Finally, the presence of CKD did not significantly alter the process of TC formation, which holds the potential to support our approach for future clinical use in ESRD patients.

Counting CD4(+) and CD8(+) T cells in the spleen: a novel in vivo method for assessing biomaterial immunotoxicity

As immunotoxicity assessments of newly developed biomaterials are often restricted to use in assessment of local tissue response at the implantation site, they do not always show an immune response acceptable to qualify them for clinical use. We tested a new method to assess systemic toxicity: counting the CD4⁺ and CD8⁺ cells in the spleen. Three different biomaterials were subcutaneously implanted in three groups of rats for the same time period. After 31 days, their spleens were harvested, and CD4⁺ and CD8⁺ cells were counted. The mean CD4⁺/CD8⁺ cell counts were 24.5 ± 3.6/19.8 ± 4.0 (porous collagen matrix group), 25.5 ± 7.1/21.6 ± 3.8 [synthetic collagen matrix (Duragen®) group] and 28.1 ± 4.1/19.6 ± 3.7 (porcine dermis group). Differences in cell counts were not significant. The immunotoxic response generated against porous collagen matrix was comparable to that produced by a similar biomaterial already used clinically. This is, to the best of our knowledge, the first study on cytotoxic lymphocytes in the spleen to quantify systemic immune response to a biomaterial; however, such studies have been conducted with bacterial and viral antigens, and with vaccines. We believe that the present study provides a viable method for larger studies to confirm our current findings.

Phenotypic characterization of mononuclear inflammatory cells following equine hydroxyapatite/collagen block grafting in rats

To measure the inflammatory changes associated with the implantation of an equine hydroxyapatite and collagen-containing block graft (eHAC block) in a rodent model system, an eHAC block graft was implanted subcutaneously in rats. Control groups included saline, turpentine oil, and human mineralized particulate allograft (hMPA). Animals were sacrificed and tissue samples obtained after three days, as well as after 1, 2, 4 and 8 weeks. A panel of immunologic probes was used to identify circulatory monocytic cells (ED1), resident mononuclear phagocytes (ED2), mononuclear phagocytes of lymphoid origin (ED3), expression of Ia antigen (OX6), T-cells (OX19), and B-cells (OX33). Immunocytochemical localization was performed and mononuclear cells localized with each immunologic probe counted. Rat sera obtained after eight weeks were used for nitrocellulose dot-blotting to assess circulating anti-equine immunoglobulins. Statistical analysis was performed using two-way analysis of variance, in conjunction with the Bonferroni correction to account for multiple comparisons. A transient increase in monocytes at 3 days and 1 week was observed in all groups, but was significantly higher in the turpentine control (P < 0.0001). A significant increase in the numbers of mononuclear cells detected with clones ED2 and ED3 was observed in specimens from the turpentine group, in contrast to the other groups in the 3 day to 4 week interval (P < 0.0001), as well as within all time periods (P < 0.0001). A statistically significant difference in numbers of ED3-positive cells was observed in the hMPA group compared to the saline and the eHAC block groups after one week (P < 0.0001). Significantly more OX6-positive cells were observed in the turpentine group, compared to other groups (3 days to 1 week; P < 0.0001). T-lymphocytes were essentially absent except for rats given turpentine (after 1 week). No B-lymphocyte response was found and none of the rats developed systemic anti-equine antibodies. These data indicate that a cellular immune response is not elicited following implantation with the eHAC block graft, which might serve as an alternative material for regenerative therapy.

Cytotoxicity of bovine and porcine collagen membranes in mononuclear cells

This study compared the cytotoxicity and the release of nitric oxide induced by collagen membranes in human mononuclear cells. Peripheral blood was collected from each patient and the separation of mononuclear cells was performed by Ficoll. Then, 2x10(5) cells were plated in 48-well culture plates under the membranes in triplicate. The polystyrene surface was used as negative control. Cell viability was assessed by measuring mitochondrial activity (MTT) at 4, 12 and 24 h, with dosage levels of nitrite by the Griess method for the same periods. Data had non-normal distribution and were analyzed by the Kruskal-Wallis test (p<0.05). Statistically significant differences (p<0.05) were observed between the membranes and the control in the experimental period, although there was a significant reduction in viability over time (p<0.01). At 4 and 12 h, the porcine membrane induced a higher release of nitrite compared with the control and bovine membrane, respectively (p<0.01), and this difference was maintained at 24 h (p<0.05). This in vitro study showed that the porcine collagen membrane induces an increased production of proinflammatory mediators by mononuclear cells in the first hours of contact, decreasing with time.

Management of ear lobule keloids using 980-nm diode laser

The objective of the study was to evaluate the 980-nm diode laser in conjunction with corticosteroids in the treatment of ear lobule keloids. Several methods have been described for the treatment of keloid scars, but none of them have been 100% successful. Advances in laser techniques have enabled surgeons to define the most appropriate lasers for use in the treatment of different scar types. The diode laser pulses are delivered interstitially in a single repeated mode in non-overlapping sites using a bare optical fiber, followed by intralesional triamcinolone acetonide injection. The number of sessions varies between two to five for the management of more than 75% of keloid size, with a total success rate of 75% and no recurrence in the follow-up of 12 months. The technique used proved to be effective in the treatment of ear lobule keloids.

Human immune responses to porcine xenogeneic matrices and their extracellular matrix constituents in vitro

Several tissue engineering approaches for the treatment of cardiovascular diseases are based on a xenogeneic extracellular matrix. However, the application of engineered heart valves has failed in some patients, causing severe signs of inflammation by so far undetermined processes. Therefore we investigated the immune-mediated responses to porcine valve matrices (native, decellularized and glutaraldehyde-fixed) and to purified xenogeneic extracellular matrix proteins (ECMp). The induction of human immune responses in vitro was evaluated by analyzing the co-stimulatory effects of matrices and ECMp collagen and elastin on the proliferation of immune cell sub-populations via CFSE-based proliferation assays. The pattern of cytokine release was also determined. In porcine matrix punches we demonstrated strong immune responses with the native as well as the decellularized type, in contrast to attenuated effects with glutaraldehyde-fixed matrices. Furthermore, our results indicate that collagen type I (porcine and human) and human elastin were able to elicit proliferation in co-stimulation with anti-CD3 antibody, accompanied by a strong release of Th1 cytokines (IFN-gamma, TNF-alpha). In contrast, porcine elastin did not elicit any response at all. This low immunogenic potential of porcine elastin suggests its suitability for the creation of new tissue engineering heart valve scaffolds in the future.

Ossification of a collagen membrane cross-linked by sugar: a human case series

BACKGROUND

Collagen membranes cross-linked by glycation (GLYM) for guided bone regeneration (GBR) and guided tissue regeneration (GTR) are used extensively with proven safety and efficacy. Complete GLYM ossification, when placed in contact with bone, was described in a canine jaw model, suggesting that GLYM may serve as an ossification substrate. The purpose of this case series was to histologically evaluate GLYM in GBR procedures in humans.

METHODS

We retrospectively selected seven consecutive patients with implant-related bony defects who underwent GBR with GLYM. Six defects had bone grafts, and one had a barrier alone. Selection criteria were primary closure upon post-surgical examination and tissue that was 2- to 3-mm thick over the implant's cover screw. Tissue was removed when the implants were uncovered after 20 to 29 weeks. Decalcified sections were stained and analyzed under light microscopy.

RESULTS

In five of seven specimens, GLYM was identified and preserved its barrier effect. The mean membrane thickness was 0.17 +/- 0.054 mm. In two cases, the bone grafts under the membrane were embedded in new bone, whereas in five cases, they were embedded in fibrous connective tissue. Formation of new dense bone was observed along the side of the membrane facing the original bone, and various degrees of membrane ossification were evident in all five cases.

CONCLUSIONS

GLYM maintained its barrier effect in five of seven cases for 25 weeks and induced dense new bone along its interface with underlying tissues. To the best of our knowledge, this is the first report on GLYM ossification in humans with direct mineral apposition on glycated collagen and suggests a new concept of tissue-integrated active barriers.

Ossification of a novel cross-linked porcine collagen barrier in guided bone regeneration in dogs

BACKGROUND

Collagen membranes for guided bone regeneration (GBR) and guided tissue regeneration (GTR) are used extensively as bioabsorbable barriers. Cross-linking of collagen increases its biodurability and enables the control of its degradation kinetics and barrier function. A novel cross-linking technology was used to produce a porcine type I collagen membrane (GLYM). The purpose of this study was to evaluate the safety, efficacy, and degradation kinetics of GLYM compared to a non-cross-linked bilayer type I and III porcine collagen membrane (BCM) in surgically created defects in dogs.

METHODS

After tooth extraction, two mandibular bilateral critical size defects were created in 12 beagle dogs that were randomly assigned to one of five groups: GLYM + bovine bone mineral (BBM), BCM + BBM, BBM alone, sham-operated, or GLYM alone. Dogs were euthanized after 8, 16, and 24 weeks, and sites were prepared for qualitative, semiquantitative, and quantitative light microscopy analyses.

RESULTS

Membrane-protected sites displayed bone filling between the BBM particles with almost complete restoration of the original ridge morphology that increased with time up to 16 weeks and remained unchanged at 24 weeks. Both membranes showed marked degradation within 16 to 24 weeks, with BCM inconsistency that was undetectable in one of four sites at 8, 16, and 24 weeks. Membrane ossification was observed in all GLYM sites and in only one BCM site, which progressed with time to 24 weeks. Bone increased by approximately 1 mm on the lingual side, where the GLYM membrane was in direct contact with bone.

CONCLUSIONS

Both membranes were safe and effective in supporting bone regeneration in critical size alveolar ridge defects in dogs and completely degraded within 24 weeks with marked BCM inconsistency. In areas of direct contact with bone, all GLYM sites were progressively ossified with time and augmented the original alveolar ridge. To the best of our knowledge, this is the first report of complete ossification of a collagen barrier membrane in GBR procedures.

The Application of Recombinant Human Collagen in Tissue Engineering

Collagen is the main structural protein in vertebrates. It plays an essential role in providing a scaffold for cellular support and thereby affecting cell attachment, migration, proliferation, differentiation, and survival. As such, it also plays an important role in numerous approaches to the engineering of human tissues for medical applications related to tissue, bone, and skin repair and reconstruction. Currently, the collagen used in tissue engineering applications is derived from animal tissues, creating concerns related to the quality, purity, and predictability of its performance. It also carries the risk of transmission of infectious agents and precipitating immunological reactions. The recent development of recombinant sources of human collagen provides a reliable, predictable and chemically defined source of purified human collagens that is free of animal components. The triple-helical collagens made by recombinant technology have the same amino acid sequence as human tissue-derived collagen. Furthermore, by achieving the equivalent extent of proline hydroxylation via coexpression of genes encoding prolyl hydroxylase with the collagen genes, one can produce collagens with a similar degree of stability as naturally occurring material. The recombinant production process of collagen involves the generation of single triple-helical molecules that are then used to construct more complex three-dimensional structures. If one loosely defines tissue engineering as the use of a biocompatible scaffold combined with a biologically active agent (be it a gene or gene construct, growth factor or other biologically active agent) to induce tissue regeneration, then the production of recombinant human collagen enables the engineering of human tissue based on a human matrix or scaffold. Recombinant human collagens are an efficient scaffold for bone repair when combined with a recombinant bone morphogenetic protein in a porous, sponge-like format, and when presented as a membrane, sponge or gel can serve as a basis for the engineering of skin, cartilage and periodontal ligament, depending on the specific requirements of the chosen application.