Scientific Abstract Presentations: Research & Technology Session 8 Saturday, September 28 Sat, Sep 28 5:00-6:00 p.m. PDT

Objectives: Many plastic surgery procedures create large surgical dead spaces, which are prone to fluid accumulation leading to hematomas and seromas. Drains are used to prevent these complications, but they often cause patient discomfort and have potential for infection. Our objective is to develop a biodegradable tissue adhesive with strong adhesion and biocompatibility to obliterate surgical dead space without the drawbacks associated with traditional drainage methods.

Methods: We synthesized a hydrogel-based tissue adhesive with a polyester backbone brush polymers featuring carboxyl and N-hydroxysuccinimide (NHS) ester functional groups. The adhesive strength was evaluated using a universal testing machine. Peel and shear tests were conducted on rat subcutaneous tissue adhered to fat and fascia (n=3). We evaluated the heat release of our tissue adhesive when applied to rat rectus abdominus fascia (n=3), using a FLIR one thermal camera for measurement. For comparison, cyanoacrylate was used as a control due to its strong adhesion properties and known exothermic reaction. Cytocompatibility of our adhesives was tested at various concentrations (0, 7, 14, and 21 mg/mL) on human umbilical vein endothelial cells (HUVECs), using LIVE/DEAD staining and the alamarBlue assay to assess cell viability. Finally, to test tunable biodegradability, we varied the percentage of double bonds in our adhesive (100%, 40%, and 25%). Each was placed in PBS for four weeks and was weighed weekly.

Results: The peel tests demonstrated similar interfacial toughness between our tissue adhesive and cyanoacrylate when bonding subcutaneous tissue to fat (294.2 vs. 340.9 J/m2, p=0.69) and subcutaneous tissue to fascia (394.7 vs. 276.4 J/m2, p=0.65). In shear tests, our tissue adhesive demonstrated comparable shear strength to cyanoacrylate for subcutaneous tissue to fat (27.9 vs. 26.0 kPa, p=0.58) and subcutaneous tissue to fascia (28.7 vs. 25.0 kPa, p=0.76). Thermal analysis demonstrated that cyanoacrylate led to a peak tissue temperature of 29 ºC, compared to 24.8 ºC for our tissue adhesive. After 24 hours, there was no significant decrease in cell viability at any concentration of our tissue adhesive. Lastly, after four weeks, the 100% double bond adhesive retained nearly its original weight, the 40% double bond adhesive was about 60% of its original weight, and the 25% double bond adhesive was about 15% of its original weight.

Conclusion: Our novel tissue adhesive, with its polyester backbone, has demonstrated strong adhesion, tunable biodegradability, and biocompatibility. The adhesion strength tests, comparing our adhesive with cyanoacrylate, demonstrated similar strength in both peel and shear tests on tissues relevant to abdominoplasty. A notable advantage of our tissue adhesive is its minimal exothermic reaction, ensuring higher cell viability, which stands in contrast to cyanoacrylate. Furthermore, we demonstrated tunable biodegradability of our adhesive, which can be optimized for different surgical uses. We are currently optimizing our tissue adhesive to best suit abdominoplasty usage in a small animal model. Our adhesive's subcutaneous use has potential to provide a comfort and safety advantage compared to subcutaneous drains for many operations.

Background The subjective nature of outcomes analysis in facial paralysis makes it challenging to disseminate data accurately and universally about these injuries. Due to the paucity of reliable and quantitative tools to accurately analyze pre- and post-operative facial function, providers resort to subjective surveys, photograph comparisons, and gross physical examination. Prior methods utilizing Emotrics and eFACE software lack automatic point registration and depth-field characterization. The authors in this study describe the creation and implementation of an open-source, electronic, quantitative facial function tool, numeriFACE, that provides clinicians with patient tailored numerical data and interactive facial mapping that allows tracking postoperative outcomes, assessing interventions efficacy, and utilizing objective data universally. Methods numeriFACE can be use both prospectively through three-dimensional (3D) patient images or live video as well as retrospectively using two-dimensional images. numeriFACE was applied retrospectively to 10 patients' facial photographs while performing facial expressions both pre- and post-operatively with varying facial features. 732 points of interest were extracted, and 3D comparison maps were created. Point by point analysis was performed to create 3D deformation maps visualizing and quantifying the changes in: commissure excursion, lower lip depression and upper lip deviation.

Results numeriFACE novelly illustrated depth of change in facial expression as well as registered global changes seen in cases of synkinesis. Focusing on perioral data, postoperatively patients left and commissure excursion (CE) improved 9.9% and 7.9% respectively, while upper and lower lip symmetry improved by 51% and 58%.

Conclusion numeriFACE is a novel, reliable, standardized, and patient-specific clinical tool to quantify, monitor and assess facial function and recovery in facial paralysis patients.

Introduction: We recently showed that inhibiting mechanotransduction (Yes-associated protein [YAP]) in mouse wounds yields regeneration without scarring. However, rodents are loose-skinned and fail to recapitulate key aspects of human wound repair. We sought to elucidate the effects of YAP inhibition in red Duroc pig wounds, the most human-like model of scarring. Methods: Full-thickness excisional wounds (2x5cm hexagons) were produced on the dorsum of adult pigs. Wounds received intradermal verteporfin (YAP inhibitor; 2mg/mL) or vehicle control (PBS) followed by primary repair with 3-0 Vicryl deep dermal and 3-0 Monocryl running subcuticular sutures. Cutometer measurements were obtained to assess tissue stiffness every two weeks. Wounds and unwounded skin were harvested after 2, 4, 8, and 16 weeks for histologic (hematoxylin and eosin staining), mechanical (Instron strength testing), scRNA-seq (10X Chromium) analyses and CODEX protein spatial analysis. Results: Grossly and histologically, verteporfin treatment significantly reduced scarring and promoted skin regeneration, including recovery of hair follicles/glands (Figure 1A-B). Verteporfin-treated wounds were both significantly less stiff (Figure 1C) and stronger (Figure 1D) than PBS-treated wounds, with mechanical properties similar to those of unwounded skin. scRNA-seq identified two novel fibroblast subpopulations, one enriched in regenerating (verteporfin) wounds and unwounded skin, the other enriched in scarring (PBS) wounds (Figure 1E-F; clusters 1 and 4, respectively). Pseudotime trajectory constructs demonstrated putative state transitions between these two populations, which were supported by prospective FACS isolation and force manipulation in a 3D culture system. CODEX protein spatial analysis further supported the fibroblast dynamics among treatment groups as that observed by scRNAseq. CODEX spatial protein expression analysis confirmed that fibrotic and regenerative fibroblast subtype markers identified by scRNA-seq at the protein level, with differential distribution and cell-cell interactions in PBS-versus YAPi-treated wounds. Conclusion: One-time local administration of verteporfin following injury significantly reduces scarring and induces regenerative healing in a large animal model. Collectively, our findings provide critical support for the future translation of local mechanotransduction inhibitors to prevent human skin scarring.

Purpose: Medical device companies rely on the input of plastic surgeons to develop safe and effective products for our patients, often recruiting experienced surgeons as paid consultants. In response to prior controversies related to inappropriate prescribing patterns and financial relationships between physicians and private industry, the Open Payments database was created to reduce bias and promote transparency (1). It is not well understood how educational background, clinical training, and research experience influence consulting payments made to academic plastic surgeons.

Methods: Open payment data for all surgeons affiliated with independent and integrated plastic surgery programs were collected for 2022. Additional data, including each surgeon's educational background, years of clinical experience, and the number of peer-reviewed publications were collected from program websites, LinkedIn, and PubMed.

Results: A total of 969 academic plastic surgeons within 94 institutions were included. A total of $2.15M in consulting payments were made to 107 (11%) surgeons across 54 institutions (57.5%), which represents 16% of the total $12.94M in general payments made to all academic plastic surgeons. Among surgeons who received consulting payments, 21 (19.4%) held additional graduate degrees, 77 (71.3%) completed fellowship training after residency, the average number of peer-reviewed publications per surgeon was 80 (std dev = 74) and the average length of time in practice was 16 years (std dev = 9.2 yrs). Consulting payments ranged from $25 to $59,5158 with an average of $19,920, standard deviation of $6,1716, and median of $6950. The top 20% of surgeons received 76.2% of all consulting payments, and the top 3% received 43% of all payments. Surgeons received consulting payments from an average of 4.42 companies. Additional graduate degrees (p=0.8), fellowship training (p=0.9), number of publications (p=0.85), and years of experience (p=0.5) did not have a significant influence on total consulting payments made to individual academic surgeons. Among the 54 programs with consulting payments, there was an average 9.7% of faculty members per institution engaged in consulting work. Food/beverage payments were the only payment type of payment for 680 (70.1%) of surgeons, and no payments of any kind were reported for 81 (8.4%) of surgeons.

Conclusion: Consulting with the medical device industry is relatively uncommon among academic plastic surgeons, with high variability in payments made between plastic surgeons. Surprisingly, the total consulting payments made to academic surgeons do not appear to be significantly influenced by additional graduate or fellowship training, years of clinical experience, or the number of peer-reviewed publications. This variability may be partially explained by differing levels of availability, personal interest, connections to industry partners, and institutional policies that limit certain relationships with private industry. Further studies are needed to understand attitudes towards consulting among academic plastic surgeons and institutional safeguards to further promote ethical and transparent relationships.

Citations: 1. Ahmed, Rizwan, et al. "The Dawn of Transparency". Annals of Plastic Surgery, vol. 78, no. 3, March 2017, pp. 315-323. doi: 10.1097/SAP.0000000000000874.

Background: The plastic surgery residency match is one of the most competitive in the field of medicine (1). Applicants typically are among the most qualified in terms of research productivity, honor society status, and standardized board scores, yet this field has the lowest match rates amongst all specialties (2,3). Understanding the extent to which each application component plays a role in successfully matching is critical to guiding applicants, especially with USMLE Step 1 transitioning to a pass/fail evaluation (4). The purpose of this study was to evaluate several applicant characteristics associated with a successful outcome in recent years for the integrated plastic surgery residency match.

Method: A retrospective evaluation of the 2017-2023 Texas STAR (Seeking Transparency in Application to Residency) database was conducted. Characteristics and predictors were compared based on applicants' match status. Group differences were assessed using unpaired t-tests, chi-square, and Fisher's exact tests. Logistic regression models were conducted to identify significant predictors associated with matching. A Cochrane-Armitage test was performed to evaluate significance of trends on applicant connections with programs over time.

Results: A total of 381 applicants for integrated plastic surgery residency were included. Of those, 295 (77.4%) matched and 86 (22.6%) did not match. Matched applicants had a significantly higher mean USMLE Step 2 CK score (256 vs 253; p=0.006) and mean honored clerkships (4.4 vs 3.6; p=0.009) compared to unmatched applicants. Additionally, significantly higher rates of AOA (45.1% vs. 29.1%; p=0.009) and MD applicants (100% vs. 97.7%; p=0.009) were observed in the matched group compared to unmatched applicants. Matched applicants applied to significantly more programs (72 vs. 63; p=0.002) and attended more interviews (14 vs. 10; p<0.001). There were no significant differences in mean number of research experiences (p=0.199), abstracts, presentations, and posters (p=0.072), peer-reviewed publications (p=0.318), volunteer experiences (p=0.965) or leadership positions (p=0.432) among groups. Receiving honors in 4 or more clerkships was identified as a significant predictor of a successful match (OR 1.51, 95% CI 1.025-2.227; p=0.037). Most applicants (75.9%) matched at a program where they either did an away rotation, had a personal geographic connection, or attended medical school in the same geographic region. A significant increase in trends was observed in an applicant having a personal geographic connection over time (p=0.005).

Conclusions: Our findings suggest that excelling on clinical rotations and USMLE Step 2 CK appears to be a strong predictor of successfully matching into integrated plastic surgery residency. Increased trends of applicant connections with programs over time underscore the growing relevance of these aspects among successful applicants.

References: 1. Borsting EA. An Updated View of the Integrated Plastic Surgery Match. Ann Plast Surg. 2015 Nov;75(5):556-9. doi: 10.1097/SAP.0000000000000627. 2. NRMP. 2020 Main Residency Match. 2020. Available at:https://mk0nrmp3oyqui6wqfm.kinstacdn.com/wp-content/uploads/2020/03/Advance-Data-Tables-2020.pdf. 3. Asserson DB. A 5-Year Analysis of the Integrated Plastic Surgery Residency Match: The Most Competitive Specialty? J Surg Res. 2022Sep;277:303-309. doi: 10.1016/j.jss.2022.04.023. 4. Whelan AJ. The Change to Pass/Fail Scoring for Step 1 in the Context of COVID-19: Implications for the Transition to Residency Process. Acad Med. 2020 Sep;95(9):1305-1307. doi: 10.1097/ACM.0000000000003449.

Background: Bone morphogenic proteins (BMPs) have numerous applications in craniomaxillofacial surgery and play a central role in the development of regenerative therapies for bone reconstruction. The broad applications of BMPs are limited by its side effect profile, such as severe edema and local inflammation. Nanoscale peptide amphiphiles (PAs) are a novel biomaterial that self-assemble into nanofibers. These PA gels have demonstrated the ability to function as a sustained-release carrier of biological molecules and support tissue regeneration. In this study, we examined the effect of PA gels on in vitro osteogenic differentiation of bone marrow stromal cells (BMSCs) and in vivo bone repair and its associated inflammatory response in craniomaxillofacial bone defect models.

Methods: BMP2 release from PA gels was examined. Human BMSCs were cultured and treated either with growth medium or media with BMP-2 and PAs. Quantitative RT-PCR of genes specifically related to osteogenesis was used to assess for osteogenic differentiation in vitro. Craniomaxillofacial bone defects were created in rabbit calvaria and rat maxilla according to the established method. The defect was treated with collagen material containing BMP2 with or without PA gels. A control group with only collagen material was also designed. After 8 or 12 weeks, the bone tissue including defect was harvested for radiographic analysis with micro-computed tomography and for histology to assess bone repair. Moreover, soft tissue around the defect was harvested and expression of inflammation-related genes were evaluated. The specimens were also subjected to immunohistochemical (IHC) staining to observe the inflammatory response between groups.

Results: BMP2 was released from PA gels in a sustained-release manner. Osteogenic activity on BMSCs under the PA gel incorporating BMP2 was significantly increased compared with control. In the craniofacial bone defect model, collagen with low-dose BMP2 incorporating PA gel showed robust bone regeneration on radiographic and histologic analyses comparable with the collagen with high dose BMP2. The expression of IL6, TNF-alfa, and Cox2 was increased in the defect with the high dose BMP2 group and normalized in the collagen with high or low dose BMP2 incorporating PAs similar to the collagen with PAs group. IHC staining was consistent with this gene expression result.

Conclusions: This study may represent the use of PAs with low dose BMP2 as a viable alternative to current uses of clinical BMP2 in craniofacial surgery. Sustained-release of BMP-2 from PA gels can reduce the inflammatory response to BMP2 without impairing bone regeneration in the craniomaxillofacial area.

Background: Publicly accessible large language model (LLM) chatbots (ChatGPT and Google Gemini) have evolved significantly, including recent adaptations for clinical settings, called medAPIs (medical application programming interfaces) (1). Patients and health care professionals who previously used traditional plastic surgery expert opinion platforms (ie. RealSelf.com) may now utilize these chatbots due to ease of access, instant responses, and privacy. However, given the novelty, little is known on the accuracy and satisfaction of these chatbots versus plastic surgeon expert opinions, and consequent utility in practice integration. Doximity, an online networking service for medical professionals, has recently launched their medAPI, DoximityGPT. As 80% of US physicians are registered on Doximity and have access to DoximityGPT, it is important to study how healthcare specific chatbots compare to traditional ones. This study characterized and compared the accuracy, comprehensiveness, and readability of traditional chatbot- and medAPI-generated responses for common plastic surgery questions, compared to plastic surgery expert opinion (RealSelf).

Methods: The most popular reconstructive and aesthetic procedures on RealSelf.com were identified, including the corresponding top two questions and top two expert provided answers; questions with photographs were excluded. These questions were then queried to healthcare chatbots (DoximityGPT, DrGupta.AI) and traditional chatbots (ChatGPT, Gemini). Three expert evaluators blindly evaluated all chatbot and RealSelf answers on a previously published and validated scale on accuracy (1-6), comprehensiveness (1-3), and recommendation based on answer. Readability scores of answers were calculated (Flesch-Kincaid Grade Level, Gunning Fog Index, Coleman-Liau Index, Simple Measure of Gobbledygook [SMOG] Index, and Automated Readability Index). All readability scores estimate the U.S. academic grade level to comprehend written content. Statistical analysis was conducted with Dunnett's, chi-squared, and ANOVA, with a p-value < 0.05 used for statistical significance.

Results: Evaluators were least likely to recommend an answer from a plastic surgeon on RealSelf (50.95%), and most likely to recommend a response from DoximityGPT or ChatGPT (77.01%, 72.41%, p<0.001). Significant differences were observed in the accuracy rates across all responses. RealSelf had the lowest accuracy score (4.09, SD 1.05) compared to DoximityGPT (4.61, SD 1.08, p<0.001). Similarly, RealSelf had significantly lower scores on how complete the response was (1.63, SD 0.66) across all groups, with DoximityGPT showing the highest score (2.30, SD 0.70, p<0.001). Readability score was significantly higher for all chatbots compared to surgeon answers (10.99, SD 2.72, p<0.001); traditional chatbot reading levels were lower than healthcare chatbots (p<0.001).

Conclusions: Healthcare chatbots provided the most accurate and comprehensive responses to common patient questions, followed by traditional chatbots and RealSelf surgeon answers. However, reading level scores of chatbots were higher, and should be adjusted in the future for all patient reading levels. Future directions will account for empathy level of responses, different languages, safety of responses, and chatbot generated referrals to a board-certified plastic surgeon or other specialties.

References: Thirunavukarasu AJ, et al. Trialing a Large Language Model (ChatGPT) in General Practice With the Applied Knowledge Test: Observational Study Demonstrating Opportunities and Limitations in Primary Care. JMIR Med Educ. 2023;9:e46599.

Introduction: Burn-injured patients develop altered metabolic processes that place them at increased risk of developing venous thromboembolism (VTE) (1). A protocol for enoxaparin titration in the trauma patient has previously been established (2). However, the benefit and safety of enoxaparin titration for prevention of VTE in burn-injured patients has yet to be thoroughly explored. We hypothesized that titration of enoxaparin for VTE prevention in burn patients would be feasible and safe. Methods: We performed a single center retrospective study of burn injured patients admitted to our American Burn Association verified burn center from January 2021 to June 2023. In May 2022, our burn center adopted the American Association for Surgeons in Trauma protocol for enoxaparin dosing. This includes twice daily administration of enoxaparin, followed by measurement of anti-Xa levels prior to administration of the fourth dose. We had previously been administering a standard dose of 30mg twice daily. Anti-Xa levels were used to guide enoxaparin dose adjustments to remain within prophylactic range. Demographic information, burn characteristics, and hospital data were collected and univariate and multivariable analyses were performed. Patients hospitalized for under 48 hours, with chronic kidney disease, and with multiple missed enoxaparin doses were excluded. Results: 239 patients were included. When focusing on VTE, there were five incidences recorded of which four occurred in the non-titrated group (p= 0.40). The presence of VTE was associated with increased mortality (p <0.0001), yet did not correlate with burn TBSA% (p = 0.50) or length of hospitalization (p = 0.96). Of note, mean burn TBSA % did not significantly differ between titrated and non-titrated groups (p= 0.20). When focusing on bleeding, fourteen patients required post-operative intervention for hemostasis. Half occurred in each group, and this was not associated with enoxaparin titration (p = 0.21), TBSA % (p = 0.22), inhalation injury (p = 0.61), length of hospitalization (p = 0.60), or change in mortality (p = 0.72). Conclusion: Enoxaparin titration is a safe and feasible practice for the prevention of VTE in burn-injured patients. Larger studies are needed to determine its effect on VTE prevention.

Citations: 1. Rae L, Fidler P, Gibran N. The Physiologic Basis of Burn Shock and the Need for Aggressive Fluid Resuscitation. Crit Care Clin. 2016 Oct;32(4):491-505. doi: 10.1016/j.ccc.2016.06.001. Epub 2016 Aug 2. PMID: 27600122. 2. Ley EJ, Brown CVR, Moore EE, Sava JA, Peck K, Ciesla DJ, Sperry JL, Rizzo AG, Rosen NG, Brasel KJ, Kozar R, Inaba K, Martin MJ. Updated guidelines to reduce venous thromboembolism in trauma patients: A Western Trauma Association critical decisions algorithm. J Trauma Acute Care Surg. 2020 Nov;89(5):971-981. doi: 10.1097/TA.0000000000002830. PMID: 32590563; PMCID: PMC7587238.

Purpose: This study aimed to identify transcriptomes predictive of clinical outcomes during ex vivo normothermic limb perfusion (EVNLP) and reperfusion. We hypothesized that minimal muscle injury observed following (associated with <5% weight gain) 24 hours EVNLP limbs would be associated with a transcriptomic profile indicative of clinical condition.

Methods: Bilateral porcine forelimbs were procured and randomly allocated to 24h EVNLP (n=4) or SCS (n=4) followed by 3h reperfusion. The perfusate consisted of porcine blood. Limb weight, contractility, hemodynamic parameters, perfusate electrolytes, metabolites, and gases were recorded. Skeletal muscle specimens were collected before limb procurement, every 6h for 24h, then every 30m of reperfusion.

For gene expression analysis, reads were aligned to the sus scrofa genome build using salmon 0.14.1 to quantify transcript abundance in transcripts per million (TPM) values. Transcripts were summarized as gene-level TPM abundances via tximport. A gene with TPM > 1 was considered expressed. Differential expression analysis was then performed using DESEQ2. Pathway analysis was performed using Panther Classification System. Significant genes were called based on p-adj and fold change values.

Results: The median weight change throughout EVLP was -4.55% [-5.5- -0.86%] and for -0.4 [-7.2- -0.2%] for SCS limbs p=0.72. Throughout 2h reperfusion, there was significant weight gain associated with compartmental edema in the SCS group 22.4% [20.6-20.42%] compared to EVNLP 0.7% [0.45-2.85%] (p=0.009).

Along with weight gain after 2h reperfusion, SCS limbs exhibited significantly higher compartment pressures than those of EVNLP limbs: anterior 143±8mmHg vs. 51±7mmHg (p=0.0001); posterior 85±11.3mmHg vs. 29±1mmHg (p=0.001).

Between EVNLP and SCS, a total of 3,940 genes were differentially expressed (p<0.05). The top five differentially expressed pathways were upregulated in EVNLP: intracellular protein transport, cytokine signaling, regulation of cellular response to stress, protein modification, and growth regulation.

Major upregulation was detected as early as 6h: 2,697 differentially expressed genes (DEGs) in EVNLP versus 42 in SCS (p<0.05). By 12h there were 3,414 DEGs (p<0.05); fold change 1.13. At 18h, the most genes (3,379) were significantly differentially expressed (p<0.05); fold change 1.22. By 24h perfusion end, 3,246 were differentially expressed (p<0.05) compared to baseline; fold change 1.19.

During reperfusion, EVNLP limbs had 1,855 DEGs (p<0.05); fold change 1.15 from baseline. However, there were 182 significantly differently expressed genes for SCS limbs during reperfusion compared to baseline (p<0.05); fold change 0.68. When directly comparing expression during reperfusion between the two groups, there were only 41 DEGs (p<0.05); fold change 0.637.

Conclusions: EVNLP significantly upregulates immune and cellular stress pathways compared to baseline and SCS limbs as early as 6h. Interestingly, we found that reperfusion after 24 hours of cold storage does not induce the same level of gene expression as immediate perfusion. Cold storage was associated with halted transcription that does not return with reperfusion, suggesting that limbs stored on ice cannot benefit from reperfusion after a certain timepoint. The clinical weight gain exhibited during reperfusion and evidence of compartment syndrome was not reflected transcriptionally in SCS limbs, presumably due to diminished metabolic activity.

Background: Silicone nasal implants have long been widely utilized in primary rhinoplasty for many years. However, persistent complications such as contracture and calcification have been consistently reported, suggesting associations with excessive mechanical or chemical stress on the tissue, such as friction force and chronic inflammatory responses. Furthermore, it is believed that silicone materials with higher hardness may contribute to complications like continuous stimulation on the nasal envelope, leading to calcification and contracture. Currently, there is a lack of research investigating whether the hardness of nasal implants correlates with the reduction of fibrosis and inflammation. Therefore, this study aims to prospectively explore the relationship between the hardness of silicone implants and fibrosis and inflammation through animal experiments.

Methods: Three types of nasal silicone implants with identical sizes but varying hardness levels were employed. The hardness of the silicone implants was measured on the Shore A scale and designated as 23, 41, and 45, respectively. Subsequently, implants were placed bilateral on the back and head of 15 ten-week-old female Wistar rats, specifically beneath the panniculus carnosus layer, which closely resembles the human SMAS (Figure 1). The size of the silicone implants matched those commonly used in human procedures. After a lapse of 10 weeks post-implantation, clinical aspects such as differences in immune reactions and the formation of peri-implant capsules are analyzed within the host's body. The host's intra-tissue response was assessed through RT-PCR, utilizing 11 markers. Furthermore, specific markers were investigated through Immunohistochemistry staining. Histological analysis of capsule samples was performed by a pathologist to investigate vascular congestion, acute and chronic inflammation, and fibrosis in the tissues surrounding the implant material [1]. Quantification and statistical analysis of these parameters were conducted to derive scores for inter-group comparisons.

Results: Using three different implants, a total of 45 peri-implant capsules were obtained. Histological analysis of the peri-implant capsules revealed lower levels of vascular congestion, fibrosis, acute, or chronic inflammation in the group with lower hardness. The histological analysis indicated lower scores in the group with lower hardness (p-value < 0.05). Significant differences were observed in four RT-PCR markers (IL-4, tumor necrosis factor-α, α-smooth muscle actin, and TGFβ2). Masson trichrome staining for collagen fiber within the capsule showed that the group with lower hardness exhibited fewer collagen layers. These data suggest that lower hardness values, indicating softer silicone material, demonstrate superior anti-inflammatory properties and form thinner and weaker tissue capsules.

Conclusions: In summary, when silicone implants are stably positioned within the host, lower hardness silicone implants result in fewer side effects related to inflammation induction or spherical capsule formation. These findings contribute to our understanding of how alloplastic materials behave in the nasal dorsum and their impact on the skin and soft tissue envelope.

References [1] Cingi C et al. Two new polymers as candidates for rhinoplasty allografts: an experimental study in a rabbit model. Ann Otol Rhinol Laryngol. 2013 Jul;122(7):474-9.