I have seen people ask questions about cutting objects before,If you are a beginner shader, it may not be very clear,Here is a relatively simple idea,Can be used directly if needed.(I haven't found a better method for cutting sutures)

Cutting principle:Directly discard the pixels in the world space whose y value (vertical cutting) is greater than the object's own coordinate y value within a certain range.

c#part:

using system.collections;
using system.collections.generic;
using unityengine;
public class discardtest:monobehaviour {
 private material m;
 private void start ()
 {
 m=getcomponent<meshrenderer>(). material;
 }
 void update () {
 m.setfloat ("_ yfactor", transform.position.y);
 }
}

Shader part:

shader "unlit/3ddiscardtest"
{
 properties
 {
 _maintex ("texture", 2d)="white" {}
 //The range of cutting (depending on the size of the actual object,(Assignment via c#)
 _discardfactor ("discardfactor", range (-0.51,0.55))=0.0
 //The color of the incision light
 _lightcolor ("lightcolor", color)=(1,1,1,1)
 //Width of light
 _lightwidth ("lightwidth", range (0.0,0.1))=0.05
 }
 subshader
 {
 tags {"rendertype"="opaque"}
 //You can't see the inside of the object without culling the back
 cull off
 pass
 {
 cgprogram
 #pragma vertex vert
 #pragma fragment frag
 #include "unitycg.cginc"
 struct v2f
 {
 float2 uv:texcoord0;
 float4 vertex:sv_position;
 float3 worldpos:texcoord1;
 };
 sampler2d _maintex;
 float _yfactor;
 float _discardfactor;
 float4 _lightcolor;
 float _lightwidth;
 v2f vert (appdata_base v)
 {
 v2f o;
 o.vertex=unityobjecttoclippos (v.vertex);
 o.worldpos=mul (unity_objecttoworld, v.vertex) .xyz;
 o.uv=v.texcoord;
 return o;
 }
 fixed4 frag (v2f i):sv_target
 {
 float factor=_yfactor-i.worldpos.y + _discardfactor;
 //_yfactor-i.worldpos.y=0 when the pixel is the center of the object,Pixels larger than 0 are below,Less than 0 pixels above,_discardfactor is smaller, the factor is smaller, the less reserved below
 if (factor<0)
 {
 discard;
 }
 float4 color=tex2d (_maintex, i.uv);
 //The part of factor<0 has been cut,The remaining part is cut with a border to make a stroke
 if (factor<_lightwidth)
 {
 return _lightcolor;
 }
 return color;
 //Optimized the writing of the above if, equivalent, but it looks more around
 //float lerpfactor=saturate (sign (_lightwidth -factor));
 //return color * (1-lerpfactor) + lerpfactor * _lightcolor;
 }
 endcg
 }
 }
}